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Full text of "Modern Fishing Of The World"

MODERN 

FISHING GEAR OF 
THE WORLD 

Edited by 

HIILMAR KR 1ST JONS SON 

Chief, Fishing Gear Section, Fisheries Division, 

Food and Agriculture Organization of the 

United Nations 



THIS volume represents a further important 
stage in the work being done by the Fisheries 
Division, F.A.O. to develop and expand the 
fish production of the world. Just as the Con- 
ferences of 1953 at Paris (France) and Miami 
(U.S.A.) concentrated on the design and operation 
of fishing boats and craft, so the Congress held 
at Hamburg in September 1957, had as its theme 
the comprehensive investigation and survey of 
substantially all advanced and commercially im- 
portant gear and equipment used for catching fish. 

Over 50O representatives from all countries of 
the globe interested in the commercial fisheries 
of both salt and fresh water then attended to 
hear and discuss more than one hundred papers 
contributed by scientists, technologists and manu- 
facturers on the gear and equipment devised for 
the better catching of fish. 

On the foundation of those papers and dis- 
cussions, this volume has been built by the editor 
and technologists of the Fishing Gear Section of 
the Fisheries Division. The papers have been 
collated into some thirteen logical sections, 
amplified where necessary, and supplemented as 
required to round out as full and authoritative a 
presentation as possible on all aspects of modern 
fish catching equipment, from the use of man- 
made fibres in various lines, nets and trawls to 
electronic aids in fish location and detection, and 
to the latest techniques in electric fishing. 

The editorial work necessary to avoid duplica- 
tion and repetition was tremendous and because 
of the need frequently of translation and close 
co-operation with the authors of papers in widely 

Continued on inside back cover 



PRICE 7 5s. Od. 

FISHING NEWS (BOOKS) LTD 

Ludgate House, 1 10 Fleet Street 

London, E.C.4 

England 



MODERN FISHING GEAR OF THE WORLD 



MODERN FISHING GEAR 

OF THE 

WORLD 



Edited by 
HILMAR KRJSTJONSSON 

Chief, Fishing Gear Section, Fisheries Division, Food and Agriculture 
Organization of the United Nations, Rome, Italy 




Published by 

FISHING NEWS (BOOKS) LTD. 
LUDGATE HOUSE, 110 FLEET STREET, LONDON, E.C.4, ENGLAND 

APRIL, 1959 
REPRINTED SI PTfcMBfcR 1968 



COPYRIGHT, 1959 

by 

FOOD AND AGRICULTURE ORGANIZATION 
OF THE UNITED NATIONS 

All rights reserved 



The views expressed in the papers and discussions are those 
of the contributors and not necessarily those of the Food and 
Agriculture Organization of the United Nations 



MADE AND PRINTED IN GREAT BRITAIN 



REPRODUCED BY LITHOGRAPHY AT THF WHITLFRIARS PRESS LTD., LONDON AND TONBRIDCE 



CONTENTS 



General Illustrations 
List of Contributors 
Abbreviations 
Preface 
Introduction 



Page 

No. 

XV 
XVII 
XX11 
XXIII 
XXV 



Section 1. MATERIALS, TERMINOLOGY 
AND NUMBERING SYSTEMS 

Terminology and count of synthetic fibre twines 

for fishing purposes Hans Stutz 1 

Names of fibres ...... 1 

Specific weight and tenacity .... 1 

Numbering systems ..... 3 

Construction and numbering of synthetic net twines 

G. A. Hayhurst and A. Robinson 4 

Yarns 4 

Twines ....... 4 

Terminology and numbering systems used in Japan 

Shigene Takayama 6 

Specifications of fishing materials in Japan . . 6 

Yarn count or numbering systems 

British Standards Institution 8 

Tex system ...... 8 

Direct systems ...... 8 

Indirect systems ...... 8 

Conversion ...... 8 

Discussion on terminology and numbering systems 10 

Yarn size ....... 10 

Twine construction . . . . . 10 

Numbering systems . . . - - 11 

Conversion factors . . . - - 11 

Need for uniformity . . . . . 12 



Section 2. CHARACTERISTICS OF 
FISHING TWINES AND THEIR TESTING 



Man-made fibres R. Arzano 

Properties ..... 

Density ....... 

Strength ...... 

Knot strength ...... 

Loop strength ...... 

Elastic properties ..... 

Toughness ...... 

Stiffness ....... 

Moisture content ..... 

Brief definitions of mechanical properties 



13 
14 
14 
14 
14 
14 
14 
15 
15 
15 
15 



Page 

No. 

Synthetic polymer fibres . . . . . 15 

Polyamides . . . . . . 15 

Polyamide 66 (Nylon) . . . . 16 

Polyamide 6 (Perlon) . . . . . 16 

Polyamide 11 (Rilsan) . . . . 16 

Polyester fibres 17 

Vinyl fibres 17 

Polyvinyl chloride fibres . . . . 17 

Vinylidene chloride fibres . . . . 17 

Polyethylene fibres . . . . . 17 

Polyvinyl alcohol fibres . . . . 18 
Man-made fibres and finishes in protective clothing for 

fishermen . - - . . . 18 

Characteristics of synthetic twines used for fishing 

nets and ropes in Japan Yoshinori Shimozaki 1 9 

How to indicate the structure and size of net twine . 19 

Thickness of netting twines .... 20 

Weight of net twines in the air and in water . . 21 

Sinking speed - . . . . . 21 

Tensile strength of net twine and the knot strength . 22 

Abrasive resistance . . . . . 25 

Other characteristics ..... 28 

Nylon in fishing nets ,/. E. Lonsdale 30 

Specification for ideal fish net fibre ... 30 

Yarn strength . . . . . - 31 

Twine strength . . . . . . 31 

Knot strength . . . . . . 32 

Wetting 33 

In use ....... 33 

The technological characteristics of Perlon for 

fishing equipment Per Ion- Warenzeichen verband 34 

What is Perlon? 34 

Forms of Perlon ...... 34 

Processing into net twines, cordage and ropes . 35 

Properties . . . . . . 37 

Use of Perlon in various types of fishing gear . . 41 

Trawls ....... 42 

Purse seines ...... 42 

Bottom-set gillnets ..... 42 

Stationary fishing gear .... 42 

Whaling ropes and cordage .... 42 

Tarpaulins and protective covers ... 42 

"Terylene" polyester fibre and its relation to the 

fishing industry Imperial Chemical Industries Ltd. 43 

Types of yarn ...... 44 

Physical properties ..... 45 

Knot slippage ...... 46 

Dyeing ....... 47 

Mesh retention ...... 48 

Sunlight exposure ..... 48 



[v] 



MODERN FISHING GEAR OF THE WORLD 



CHARACTERISTICS OF FISHING TWINES 
AND THEIR TESTING "TERYLENE" POLY- 
ESTER FIBRE (continued) 

Durability ....... 

Ease of handling ..... 

Cost 

Construction ...... 

Cords and twines ..... 

Webbing 

Nets 

Gillnets 

Trawl nets ...... 

Purse seines ...... 

Other applications ..... 

Teviron fishing nets The Teikoku Rayon Co. Ltd. 
Characteristics of Teviron .... 

Teviron fishing nets ..... 

Krehalon fishing nets and ropes 

Ktireha Kasei Co. Ltd. 

Some physical properties of manila rope J. Renter 
Influence of the means of manufacture 
Influence of the lay ..... 

The manufacture and testing of synthetic yarns and 
fibres used in Japanese fishing gear 

Japan Chemical Fibres Association 
Production of fishing nets and lines in Japan 1956-57 

(Table) 

Scope and definition of testing methods 
Sampling and preparation .... 

Test items ....... 

Methods of testing ..... 

The physical properties of netting and twines suitable 
for use in commercial fishing gear 

P. J. G. Car rot hers 
Materials tested ...... 

Properties and test procedures 

The physical properties of some common fishing twines 

(Table) 

Definitions and dimensions .... 

Testing methods for net twines and nets, especially 
those manufactured from synthetic materials 

J. K. van Wijngaarden 
Methods of testing yarns and twines . 

Yarn number ...... 

Twist ....... 

Strength and extensibility .... 

Shrinkage ...... 

Stiffness ....... 

Methods of testing knots .... 

Knot strength ...... 

Tip-over resistance ..... 

Knot-slip resistance ..... 

Open-up resistance ..... 
Methods of testing meshes .... 

Testing of materials used in fishing J. Reuter 
Examination of hemp twine .... 
Testing of cotton webbing .... 



Page 
No. 



48 
49 
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49 
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52 
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53 
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57 

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62 

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Testing of silk yarns ..... 

Testing synthetic fibre webbing .... 
Testing of trawl twine ..... 

Lateral strength and knot-firmness of synthetic 
twines for fishing purposes H. Stutz 

Testing methods ..... 

Tensile strength, load-extension .... 

Knot strength ...... 

Knot firmness ...... 

Discussion on properties of twines and testing 

methods 

Methods of testing ..... 

Properties ...... 

Standardization of tests ..... 

Report of the working groups on terminology and 
numbering systems, and testing the properties of 
twines 



Section 3. NET MAKING 

Practical considerations of the use of synthetic 
fibres in twines and nets G. A. Hayhurst and 

A. Robinson 
Impregnation ...... 

Knots ....... 

Shrinkage in water ..... 

Ropes ....... 

Some considerations on net making P. A. Lusyne 
Strains and stresses ..... 

Hanging of webbing ..... 
Joining of webbing ..... 

Tailoring of webbing ..... 

The knotless net The Nippon Seimo Co. Ltd. 
Special advantages ..... 

Mending of knotless nets .... 

Method of manufacture ..... 

Discussion on rational manufacture of fishing gear 

Rationalization and its problems 

Conversion from natural fibres to synthetic fibres 

Standardization of terminology 

Knotless nets ...... 



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No. 
84 
85 
86 

87 
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91 
92 

93 
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97 



98 



100 
100 
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101 

102 
103 
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105 
106 

107 
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109 

110 
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110 
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111 



Section 4. NET PRESERVATION 

Development of fishing net and rope preservation 
in Japan 

Shigene Takayama and Yoshinori Shimozaki 1 1 3 

Preservation by sterilization . . . . 113 

Sunlight disinfection . . . . . 113 

Sunlight disinfection for non-dyed nets . . 113 

Preservation by copper sulphate . . . 114 

Copper naphthcnate preservation . . . 117 

Tannin preservation . . . . .120 

Bichromate treatment of tannin preservation . . 1 20 

Coal-tar dyeing 120 

Preservation by cyanoethylation . . . 121 

Summary 122 



[VI] 



CONTENTS 



Page 
No. 
NET PRESERVATION (continued) 

Rot-resistant fishing nets by the "Arigal" process 

A. Rupert i 123 

Application of acetylated cellulose for fishing 
gear Sandoz Ltd. 125 

History 125 

Properties . . . . . .126 

Tensile strength and cost . . . .126 

Test reports . . . . . 1 26 

Application of partially acetylated cellulose fibres . 127 

Evaluation of rot-retarding net preservatives 

J.Zaucha 128 

"Static" method 129 

"Fishing** method . . . . .129 

Evaluation tests of protection methods . . 131 

Method of testing resistance of net materials to 

micro-organisms A. v. Brandt 133 

Testing methods . . . . . . 133 

Determination of the rotting action of the water . 1 34 

Change of the method with heavy rotting activity . 1 34 

Preparation of samples and number of samples - 135 

Description of experiment . . . . 135 

Evaluation of the results . . . . 135 

Evaluation of the test-figure . - . . 1 36 

Discussion on net preservation . . 137 

Need for preservation treatment . . . 137 

Importance of Cu and tannin content . . . 137 

Testing methods . . . . . . 137 

Chemically modified natural fibres . - . 137 



Section 5. RELATIVE EFFICIENCIES OF 

NETS MADE OF DIFFERENT 

MATERIALS 



The efficiency of synthetic fibres in fishing, 
especially in Germany C. Klust 

Proof against rot ...... 

Types of gear, with regard to the material used 
Evaluation of the most important properties 

Breaking strength in knotted, wet condition - 

Extensibility and elasticity .... 

What significance does this difference in behaviour 
have for fishing gear? .... 

Abrasion resistance ..... 

Resistance to weathering .... 
Choice of synthetic fibres for various fishing gear 

Synthetic fibres in the fishing industry 

E. I. Du Pont de Nemours and Co. 
Fibre properties ...... 

Gillnets ....... 

Purse seines ...... 

Trap nets ....... 

Trawls ....... 

Fish net ropes ...... 

New developments ..... 



139 
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140 
141 
141 
141 

142 
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147 
147 
148 
148 
148 
148 
148 
149 



Page 
No. 
The features and use of "Amilan" fishing nets 

M.Amano 150 

Salmon and trout gillncts in the Northern Pacific . 150 
Sanmai net (trammel net) . . . . 151 
Purse seine net . . . . . 151 
Drag net 151 

Development of synthetic netting and its effect 
on the fishing industry 

Momoi Fishing Net Mfg. Co. Ltd. 152 
Natural fibres . . . . . . 152 

Synthetic fibres . . . . . .152 

Different fibres for different fishing purposes . . 152 

Deep water gill nets and seines . . . .153 

Test with nylon fishing tackle in Swedish inland 

fisheries Goxta Molin 156 

The results of comparative fishing tests . . 157 

The scope of application of nylon nets . . . 157 

F.xperience in the use of nylon nets - . . 157 

Experience with synthetic materials in the 
Norwegian fisheries A'. Mugaas 159 

On the fishing power of nylon gillncts G. Saetersdal \ 6 1 

Specifications of the net . . . . . 161 

Fishing results - . . . . .162 

Discussion on relative efficiencies of nets made 
of different materials - - .164 

Selectivity . . . . . .164 

Comparative fishing . . . . .165 



Section 6. RATIONAL DESIGN: 

ENGINEERING THEORY 
AND MODEL TESTING 

The use of model nets as a method of developing 

trawling gear W. Dickson 166 
Comparison between an eighth scale model and the 

full-sized gear . . . . .167 

Modelling rules 168 

A method of making specification drawings . . 1 70 

Some underwater observations . . . . 171 

Reactions of fish to small nets 173 

Development of mechanical studies of fishing gear 

Tasae Kawakami 1 75 

The hydrodynamic force acting on a twine . . 175 
The equilibrium configuration and tension of a flexible 

twine in a uniform flow - . 1 76 

Estimation of the fishing depth of a towed gear . 1 77 

The resistance of plane netting in a current . . 177 

Equilibrium configuration of webbing in a current - 1 78 

Analytical studies on towed gear . . 1 79 
Practical procedures of model experiments (general 

rules) 180 

Some model tests of fishing gear . . . 1 82 

Full scale tests using underwater measuring instruments 1 82 

Reference literature . . - 183 



[VII] 



MODERN FISHING GEAR OF THE WORLD 



Page 
No. 

RATIONAL DESIGN: ENGINEERING 
THEORY AND MODEL TESTING (continued) 

Increasing the opening height of a trawl net by 

means of a kite 5. Takayama and T. Koyama 185 

Model experiments . . . . . 185 

Construction and specification of the nets - - 1 86 

Comparison of height of net mouth . . 1 87 

Comparison of net shapes . . 1 88 

Conversion of the kite from model to full scale . 189 

Estimation of hydraulic resistance - . 1 89 

The kite 189 

False headline 189 

The connecting legs . . . .190 

Field experiments in Tokyo Bay . . . 191 

Field experiments in the Yellow Sea . . . 193 

The headline, the footrope and their influence on 
the vertical opening of the mouth of the trawl 

S. Okonski and S. Sadowski 196 

The Polish herring trawl net 28/23 for cutters . . 196 

The Polish herring trawl net 22/24/72 ft. for big deep 
sea trawlers . . . . . .198 

The mouth of the trawl Jack Phillips 200 

Raising the headline 200 

The forces involved ..... 200 

Speeds of tow underwater observations . . 202 

Further research tank tests .... 202 

Latest developments ..... 203 

A large-sized experimental tank of twin symmetric 
elliptical circuits 

Yoshikazu Narasako and Masaji Kanamori 205 

Construction of the circulating tank . . . 205 

The general performance of the circulating tank . 206 



Section?. RATIONAL DESIGN: 

USE OF MEASURING INSTRUMENTS 
AND UNDERWATER OBSERVATIONS 



Midwater trawl design by underwater observations 

R. F. Sand 

Underwater television ..... 
Diving sled and camera observations . 
Discussion of results ..... 

Study of the Mediterranean trawl net 

Menachem Ben-Yami 
The trawler ...... 

The gear (other than net) .... 

The net 

Test results ....... 

Further developments ..... 

Factors affecting the efficiency of dredges 

R. H. Baird 
Effect of diving plates ..... 

The effect of teeth 

Absolute efficiency ..... 



209 
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210 
210 



213 
213 
213 
214 
214 
220 



222 
222 
223 
224 



Trawl gear measurements obtained by underwater 
instruments P.A.de Boer 

Description of the instruments .... 

Spread meter ...... 

Clinometer ...... 

Net height meter ..... 

Angle of attack meter .... 

Dynamometer ...... 

Results ....... 

Spread ....... 

Tilt 

Height of the net ..... 

Angle of attack ..... 

Influence of the instruments on the gear . 

Influence of the length of the warps 

Ratio between warp length and depth 

Influence of legs ..... 

Influence of different types of floats on the opening 
height 

Pull on the legs and amount of catch 

Studies on two-boat trawls and otter trawls by 
means of measuring instruments 

Chikamasa Hamuro and Kenji hhii 
The automatic net height meter .... 
The automatic footrope indicator 
Two-boat trawls ...... 

Opening height ...... 

Curvature of the footrope .... 

Otter trawl ...... 

Comparison of both methods 

The use of echo-sounding as a means of observing 
the performance of trawling gear /. Schdrfe 
Depth of the net and opening height 
Position of the lastriches .... 

Position of the otter boards .... 

Slope of the legs 

Position of the net ..... 

Experiments to decrease the towing resistance of 
trawl gear J. Schdrfe 

Results ....... 

The angle of attack ..... 

The size of the net opening 

The opening height ..... 

The angle of attack of the kites 

Towing speed ...... 

The towing resistance ..... 



On the relation 
towing power 



between otter 



trawl gear 

H. Miyamoto 



Engine power and size of otter boards 

Otter boards and nets ..... 

Engine power and size of net . 

Weight of the otter boards .... 

Warp length and water depth .... 

Studies to improve the efficiency of otter doors and 
trawl floats Luigi Catasta 

Otter boards ...... 

Floats ....... 

Lifting device for trawl nets .... 



Page 
No. 

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253 



[vm ] 



CONTENTS 



Page 
No. 



RATIONAL DESIGN: USE OF MEASURING 
INSTRUMENTS AND UNDERWATER 
OBSERVATIONS (continued) 

Simple devices for studying the geometry of 
various gears and for relating some commercial 
fishing operations to the existing water 
movements J. N. Carruthers 

Gillnetting ...... 

Longlining ...... 

Geometry of fishing gear, particularly trawls 

A research on set nets Masaji Kanamori 

Characteristics and possibilities for improvement 
Classification of types ..... 
The effect of direction and speed of current 



254 
254 
255 
255 

256 
256 

257 
258 



Section 8. RATIONAL DESIGN: 
METHODS OF SPECIFYING GEAR 

Specification of fishing gear Albert Percier 260 

Type and size of twine ..... 260 

Webbing 260 

Shape 261 

Assembly of the net . . - . 26 1 

Floats and sinkers ..... 262 

Size of fishing gear ..... 263 

Gillnets 263 

Roundhaul nets ...... 263 

Trawl nets ....... 263 

The size specification of trawl nets in Poland 

M. Szatybelko 264 

Discussion on rational design of fishing gear 266 

Value of engineering theories and methods . . 266 

Model tests 266 

Full scale testing 269 

The opening height of trawl nets . . . 270 

Significance of the weight of net material . . 271 

Specification and standardization of trawl nets . 272 

Performance of floats at speed .... 272 



Section 9. FISHING GEAR AND ITS 
OPERATION 



Classification of fishing gear 

Fishing without gear 

Wounding gear 

Stupefying gear 

Line fishing 

Fish traps . 

Traps for jumping fish 

Bagnets with fixed mouths 

Dragged gear 

Seine nets . 

Surrounding net 

Dip or lift nets 

Falling nets 

Gillnets and tangle nets 



A. von Brandt 



274 
276 
276 
278 
279 
284 
287 
288 
289 
291 
292 
292 
293 
294 



Trawling gear //. N. Binns 

Setting of otter trawl gear .... 

The otter trawl net ..... 

Opening width ...... 

Opening height ...... 

Other gear components ..... 

Herring trawls ...... 

Midwater trawls ...... 

Synthetic net materials ..... 

German cutter trawling gear J. Scharfe 

General ....... 

The vessels ...... 

The trawling gear ..... 
The flatfish and roundfish gear .... 
The herring otter trawling gear 
The herring pair-fishing gear .... 

Shrimp trawling gear as used in the Gulf of Mexico 

John S. Robas 
Try net ....... 

Doors and warps ..... 

Blocks and booms ..... 

Nets 

Production ....... 

Trends in trawling methods and gear on the West 
Coast of the United States Dayton L. Alverson 
Electronic aids ...... 

Depth recorders ...... 

Loran ....... 

Radar 

Fishfinders ....... 

Deep water trawling ..... 

Nets 

Cable meter ...... 

Drum trawlers ...... 



Page 

No. 
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298 
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300 
300 
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311 
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312 
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316 



317 
317 
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318 
319 
319 
320 
320 
320 



Stern trawling versus side trawling C. Birkhoff 321 

Power requirements for deep sea trawling 

G. C. Eddie 325 

Effect of preservation methods on the speed - . 325 

Trawling power ...... 326 

Fleet operation of trawlers with a mothership 

C. Birkhoff 329 

Transfer of the catch 329 

Operation of trawler fleets .... 330 

The Pacific Explorer 330 

Hie Morska Wola 331 

The Russian flotillas . . . .331 

Recent and future developments - - . 332 

Midwater trawls and their operation B. B. Parrish 333 

Factors governing design, operation and efficiency of 

midwater trawls ..... 333 

Regulation of fishing depth .... 333 

Importance of biological factors . - . 335 

General features of design and operation . . 335 



[IX] 



MODERN FISHING GEAR OF THE WORLD 



FISHING GEAR AND ITS OPERATION 

MIDWATER TRAWLS (continued) 

Types of midwatcr trawls .... 

The Larsen two-boat trawl .... 

The net ....... 

The bridles ...... 

Operation ...... 

One-boat midwater trawls .... 

The nets ...... 

Arrangements of rones, bridles and otter boards 

Otter boards ...... 

Danlenos ....... 

Floats, elevators and depressors 

Operational features ..... 

Scandinavian experience with midwater trawling 

Karl- Hugo Larsson 



Midwatcr trawl types in use 
The Thames floating sprat trawl 



Page 
No. 



336 
337 
337 
338 
338 
339 
340 
341 
341 
342 
342 
343 



344 
346 



H. S. Noel 348 



The development of a new herring trawl for use in 
midwater or on the bottom 

W. E. Barraclough and A. W. H. Needier 351 

Design and testing of a midwater trawl, 1954-55 . 351 

The net 352 

Otter boards, floats and depressors . . 353 

Bridles 354 

Operation of the trawl . . . .354 

Fishing tests 354 

Adaptation of the trawl for use close to the bottom . 354 
Modification of the gear . - . .354 

Fishing tests ...... 355 

Commercial use . . . . .355 

Development of a dual-purpose otter board . 355 
Further developments . . . . .356 

Midwater trawl for small vessels - . 356 

Midwater trawls for faster-swimming fish . 356 

On the use of midwater trawls for anchovy in the 

Black Sea Erdogan F. Akyuz 357 

Experimental hauls - 357 

Discussion ...... 358 

Otter boards for Pelagic trawling F. Suberkrtib 359 

Considerations on a new type of midwater trawl 

Y. Grouselle 361 

The Exocet kite 362 

Exocet stabilizers ..... 362 

A practical depth telemeter for midwater trawls 

R. L. McNeely 363 

Description of the electrical depth telemeter . 363 

Sea tests and trials ..... 367 

Advantages and disadvantages - . . 367 



Olympic trawl cable meters Carlyle A. Crecelius 369 



Page 
No. 

Ocean cables and trawlers- the problem of 

compatibility R. A . Goodman and C. S. Law ton 37 1 

Cost of cable interruptions . . . .371 

Theories as to how fouling occurs . . . 372 

Efforts to minimise damage .... 372 

Disregard of regulations .... 373 
Need for closer co-operation . . . -373 

Hopes for ihc future ..... 374 

The use of the Danish seine net W. Dickson 375 

Danish seining versus otter trawling . . . 375 

Anchor seining versus fly dragging . . . 376 

Anchor seining ...... 376 

Fly dragging ...... 376 

The development of Danish seining . . . 376 

Boats 378 

Winches 378 

Gear 380 

General description . . . . . 383 

Anchor seining operation .... 385 

Fly drugging operation .... 386 

Comparison of starboard and port side operation 

for (Danish) seining Ishiro Saito 388 

Fishing with South African pursed lampara 

C G. Du Plessis 391 

Const ruction of gear . . . . .391 

Operation ...... 392 

Menhaden purse seining John S. Robas 394 

Vessels 394 

Operation ...... 395 

Purse boats ...... 396 

Seine net ....... 396 

Fish pumps ...... 398 

Radio-telephone equipment .... 398 

Aircraft spotting ...... 399 

The Puretic power block and its effect on modern 

purse seining Peter G. Schmidt, Jr. 400 

The conception of the power block . . . 400 

Advantages of the power block method . . 401 

Description and application of the power block - 401 

Present models of power block . . . 403 

Selection of proper size and type - - . 404 

Basic systems of hauling with the power block . 405 
Adaptation of the power block to different methods of 

purse seining ...... 406 

Power block principle used for gillnets and drift nets 411 

Effect of power block on purse seining methods . 411 

Effect of the power block on the design of fishing vessels 4 1 2 

The use of fish pumps in the U.S.A. D. W. Burgoon 414 

The boat-to-dock system . . . . . 414 

The ocean-to-boat system . . . . 417 

The development of the Philippine bag net (basnig) 

S. B. Rasalan 418 

The development of the gear . . . . 418 

The modern basnig ..... 420 



[x] 



FISHING GEAR AND ITS OPERATION 

(continued) 

Some improvements in the stick-held dipnet for 
saury fishing Akira Fukuhara 

Present stick-held dip net and its defects 
Particulars of newly devised stick-held dip net . 
Construction and operation .... 

The methods and gear used for mackerel fishing 
in Japan Kaishun Mihara 

Handlining ...... 

Construction of the gear .... 

Operation ...... 

Pole and line fishing ..... 

Construction ...... 

Operation ...... 

A new method of handling longline gear A des- 
cription of POFI "Tub" gear Herbert J. Mann 
Description of the gear ..... 
Operation of the gear ..... 

Drifting lines for large pelagic fish M. Sanchez Roig 
The fishing gear ...... 

General information ..... 

Fishing operation ..... 

Power hauler for longlines Jzuilron Works Co. Ltd. 
Construction ...... 

Operation ...... 

Automatic steering system for ocean-going fishing- 
boats Suiyo-Kai 
Characteristics of the M.C.P. .... 
Installation ...... 

Discussion on choice of fishing gear and some new 
methods 

Factors affecting choice .... 

Difficulties of experimenting during commercial fishing 
Hanging of trawls and seine nets 
Off-the-bottom trawling ..... 
Effect of fish behaviour .... 

Fishing in fresh water ..... 
Trial and error ..... 

Discussion on efficient handling of fishing gear 

Purse seining ...... 

Towing power for trawling .... 

Towing resistance as indication of catch 

Buoylines for traps ..... 

Effect on quality of the catch .... 

Ocean cables ...... 

Decca for small boats ..... 

Safety on trawlers ..... 



CONTENTS 

Page 
No. 



422 
422 
424 
424 



426 
426 
426 
427 
428 
428 
429 



430 
430 
431 

433 
433 
434 
435 

436 
436 

437 

438 
438 
439 

440 
440 
441 
443 
443 
444 
445 
446 

447 
449 
450 
450 
451 
451 
452 
452 
452 



Section 10. THE LOCATION OF FISH 

Locating fish concentrations by thermometric 

methods G. Dietrich. D. Sahrhage, K. Schubert 453 

General basis for fish finding by thermomctric methods 453 

Results in selected hydrographical regions . . 454 

Zones of convergence ..... 454 



Zones of divergence ..... 

Zones of local differences in vertical turbulence . 
Concentration of haddock in relation to bottom 

temperature ...... 

Concentration of herring in relation to temperature 

distribution ...... 

Radio direction finders and radar used by 
Japanese fishing vessels Sw'yo-Kai 

Radio direction finding ..... 
Small marine radars ..... 
Application to fishing operations 

Radio communication apparatus for fishing 
boats in Japan A'. Kodaira 

Radio facilities on board the vessels - 
Frequency bands ...... 

Coast stations ...... 

Equipment ....... 

Radio telegraphy ..... 

MHF Radio telephony .... 

HF Radio telephony .... 

Radio receivers ..... 

Radio buoys ...... 

General tendencies of improvement 

The Decca Navigator system and its application 
to fishing The Decca Navigator Co. Ltd. 

Description of operation ..... 
Coverage and range ..... 

Application to fishing ..... 
The automatic plotter ..... 

Discussion on fish location 

Location, detection definition 
Means of locating fish ..... 
Plankton sampling ..... 

Hydrographic observations .... 

Fishing charts ...... 



Page 
No. 
455 
456 

457 
458 

462 
462 
463 
463 



465 
465 
465 
466 
466 
466 
466 
466 
466 
466 
466 

467 
467 
469 
469 
469 

471 
471 
471 
472 
472 
473 



Section 11. DETECTION OF FISH 

Echo sounding and fish detection R. E. Craig 474 

A dilemma in echo sounding . . . .474 

Fish detection demersal fish - 474 

Fish detection pelagic fish .... 475 

Stabilizing the beam ..... 475 

Assessment of the seabed - 475 

The problem of presentation .... 476 

Sonar ....... 477 

Studies on the behaviour of ultrasound in sea water 

Tomiju Hashimoto and Yoshimutsu Kikuchi 478 

Characteristics of horizontal propagation . 478 

Characteristics of vertical propagation . . 480 

Reflection loss at the sea-bottom . . - 480 

Reflection loss at the fish body . . -481 

Experiments on fish detection with high frequencies 481 

Sounding with 200 kc. . - - .481 

Horizontal ranging with PP1 Sonar . . 482 

Effect of air bubbles on ultrasound of different frequencies 482 

Laboratory experiment .... 482 

Propeller wake ..... 482 



[XI 1 



MODERN FISHING GEAR OF THE WORLD 



DETECTION OF FISH (continued) 

Reliability of bottom topography obtained by 
ultrasonic echo sounding 

T. Hashimoto, M. Nishimwa and Y. Maniwa 
Effect of wide beam ..... 
Method and apparatus ..... 
Results ....... 

On the difference between 24 kc. and 200 kc. 
ultra sound for fish-finding 

T. Hashimoto and Y. Maniwa 
Experimental arrangement .... 

Results ....... 

Recent trends and development in echo fishing 

R. W. Woodgate 

General comparison of paper-recorder and C.R.T. 
display ....... 

The Pye fish-finder ..... 

Depth gauge for midwatcr trawls 

Horizontal ranger ..... 

Fish counter ...... 

Outlook ....... 

The development of echo sounding and echo ranging 

Commander R. G. Haines 
Bottom fish ...... 

Comparison of C.R.T. and paper recording 
White line recording ..... 

Relation between quantity of fish echoes and 
amount of catch ..... 

Horizontal fish detection .... 

Limitations of echo ranging 

Training of operators .... 

Fish-finder for bottom fish 

Tomiju Hashimoto and Yoshinobu Maniwa 
Resolving power of common echo-recording and C.R.T. 

display for bottom fish .... 

Comparison of 200 kc. recorder and 50 kc. recorder 

with suppressor circuit .... 

Improved echo sounding equipment for the detection 

of shoals of bottom fish Hans Kietz 

Significance of length, shape and frequency of the sound 

pulse ....... 

Influence of ship movements .... 

Grey-black recording ..... 

Some electro-technical improvements in echo 
sounders Dr. Fahrentholz 

Improvement of bottom fish representation . 
Cathode ray tube representation 
Simple device for horizontal ranging . 

Fish detection by asdic and echo sounder G Vestnes 
Detection of herring by asdic .... 

Winter season ...... 

Summer season ..... 



Page 

No. 



483 
483 
484 
485 



486 
486 
486 



488 

488 
489 
491 
491 
492 
492 



493 
493 
494 
495 

495 
495 
496 
497 



499 
499 
500 

501 

502 
502 
503 



504 
504 
505 
506 

507 
507 
507 
508 



Experiments with echo sounders 
Improvement of sensitivity 
Identification of bottom fish . 
Bottom blocking 
Fish surveys 

Horizontal echo ranging 

Miniature Lodar . 
Lodar equipment 



Karl Feher 



Correlation of midwater trawl catches with echo 
recordings from the North-Eastern Pacific 

E. A. Schaefers and /). E. Powell 
Gear and equipment used .... 

Fishing results ...... 

Interpretation of "Sea Scanar" traces 

Fish finding on the salmon fishing grounds in the 
North Pacific Ocean 

T. Hashimoto and Y. Maniwa 

The quantitative use of the echo sounder for fish 
surveys D. H. Cushing 

Method 

The relation between catch and signal 
The use of the method on survey 

Locating herring schools on the Icelandic North 
Coast fishing grounds Jakob Jakobsson 

Aerial scouting ...... 

Asdic surveying ...... 

The two methods complement each other 

Discussion on fish detection 

Aerial scouting ...... 

Technical requirements in finders 

Cathode ray lube display .... 

Paper recording ...... 

Representation of bottom fish traces 
Resolving power and quality of sound transmission 
Problems of horizontal ranging 
Echo sounders for small craft .... 

Detection of wrecks ..... 

Incorporating latest improvements in old models 
Echo sounding and efficiency of trawling 



Page 
No. 
509 
509 
510 
510 
510 

512 
513 
514 



517 
518 
519 
520 



523 



525 
525 
526 
526 



528 
529 
530 
531 

532 
532 
532 
532 
533 
533 
533 
533 
535 
536 
536 
537 



Section 12. ATTRACTION OF FISH 

Summary of experiments on the response of tuna 

to stimuli Albert L. Tester 538 

Establishing tuna in captivity .... 538 

Response to visual stimuli .... 539 

Response to auditory stimuli .... 539 

Response to chemical stimuli .... 540 

Response to edible and inedible lures . . 541 
Response to electrical stimuli . . . .541 

Discussion ...... 542 



XII ] 



CONTENTS 



ATTRACTION OF FISH (continued) 

Fundamental studies on the visual sense in fish 

Tamotsu Tamura 
Form perception ...... 

Resolving power of lens and retina - 

Accommodation and visual axis 
Some aspects of the vision of fish 

Diameter of nylon twine that fish can recognize 

Food searching of Lateolabrax japonicus . 

Light fishing ...... 

Optimal intensity of illumination 



On the behaviour of fish schools in relation to 
gillnets Masatsume Nomura 

Depth of net and amount of catch 
Reaction of fish approaching a net 
Influence of light ...... 

Colour of the net . 

Value of echo sounding ..... 



The significance of the quality of light for the 
attraction of fish Nobu Yuki Kawamoto, D.Sc. 
The wave length ..... 
The relation between wave length and radiant energy 
Diurnal rhythm in phototaxis .... 
The significance of light gradient for attraction 
Influence of moonlight ..... 



The use of light attraction for traps and setnets 

Tadayoshi Sasaki 

Effect of a directional fish attraction lamp 
A string of lamps with a setnet 



The basic principles of fishing for the Caspian 
"Kilka" by underwater light /. V. Nikonorov 
The development of the fishery .... 

Theoretical premises of submerged light attraction 
Observations on the behaviour of kilka in an illuminated 
zone ....... 

Investigations of pump-fishing with light attraction 



Fishing jigs in Japan with special reference to an 
artificial bait made of latex sponge rubber 

Takeo Koyama 

Jigs for trolling and angling .... 
Artificial bait for longline fishery 

Discussion on fish attraction 

Fish response to stimuli .... 

Artificial lures ...... 

Reaction to light ..... 

Underwater lamp ..... 

Pump fishing ...... 



Page 
No. 



543 
543 
543 
544 
544 
544 
545 
546 
546 



Attraction of fish by the use of light F. J. Verheyen 548 



550 
550 
551 
551 
551 
552 



553 
553 
554 
555 
555 
555 



556 
556 

557 



559 
559 
560 

561 
562 



567 
567 
568 

571 
571 
572 
572 
573 
574 



Page 
No. 

Section 13. ELECTRICAL FISHING 

The effect of pulsating electric current on fish 

E. Halsband 575 

The effect of variations in the pulse type . - 576 

The effect of variations in the pulse rate - . 576 

The effect of variations in the impulse period . 577 

The influence of the intensity of metabolism . 579 

Electrical fishing in Japan T. Kuroki 581 

Electric screen . . . . . .581 

Fundamental investigations - . . .581 

Trials with electric harpoons, hooks, screens and trawls 582 
Future possibilities ..... 582 

Electro fishing Juergen Dethloff 583 

Possibilities of application .... 583 

Established or successfully tested methods . . 583 

Electric tuna hook ..... 583 

Application to purse seining .... 583 

Narcotising sardines - - . . .584 

The gun-pump method .... 584 

Fencing ....... 584 

Future possibilities ..... 584 

The electro-trawl ..... 584 

Fish magnet ...... 585 

Fencing ....... 585 

Whaling 585 

Technique and construction of pulse devices . 585 
Limitations . . - . . .585 

Electro fishing in Lake Huleh 

O. H. Oren andZ. Fried 586 

Boat and electric equipment .... 587 
Operation . . . . . .587 

Dangers and precautions in the electrical fishery 

A. Hosl 589 

Significance of electrical accidents . . - 589 

Particular dangers of electrical fishing . . 590 

Precautions ...... 590 

Discussion on electrical fishing 592 

Significance of impulse current - . . 592 

Killing effect 593 

Influence on fish quality .... 593 

Frightening effect ...... 593 

Working range of electric gear . . . 594 

Safety requirements ..... 594 

Commercial application in freshwater . . 594 

Developments in Japan ..... 594 



Section 14. CLOSING REMARKS 

Future developments ..... 596 

The economic value of fisheries . . . 597 

The need for research ..... 597 

Spreading the Gospel ..... 597 

International collaboration .... 598 

Detailed Index 601 



[ XHI ] 



NOTICE TO THE READER 

Containing the papers and proceedings of the International Fishing Gear Congress convened 
by F.A.O. in Hamburg, October 1957, this book has been edited in the Fishing Gear Section of the 
Fisheries Division, F.A.O., where a very big share of the work was done by Mr. P. Lusyne and 
Dr. J. Scharfe, Gear Technologists. 

Due to its origin the text is divided into more than a hundred articles written by different authors. 
During editing we have attempted to minimize repetition, unify terminology, etc., and also arranged 
the contributions into sections according to subject matter. It is, however, inevitable that informa- 
tion on one subject is often found in many widely separate parts of the book, but it is hoped that 
the detailed list of Contents and particularly the Index which appears at the end of the literary 
contents of the book will be of help when using this volume as a reference book. 

No attempt was made to include material ably covered in well known and accessible books on 
basic net making, knots and splices, nor on the English ground trawls already fully described by 
Hodson, Garner and other authors. For such general references the readers are referred to the 
Annotcd Bibliography of Fishing Gear and Methods available from F.A.O., Rome. 

HILMAR KRISTJONSSON 
Editor 



XIV 



GENERAL ILLUSTRATIONS 

To supplement the specific diagrams and illustrations in the various papers a number 
of general illustrations covering fishing craft and activities in various parts of the world have been 
included on the pages listed below. 

Page 
Making of twine fibres ..... .... 5 

Main operation stages in net manufacture ........ 7 

Throwing cast nets on a lake in Indonesia ........ 9 

Woman spinning a yarn from sun-hemp in Ceylon ...... 29 

Menhaden purse seine dories with the catch "dried up" in the bunt .... 33 

Repairing drift nets in Ceylon ......... 56 

Liftnet fishing in Jakarta harbour ......... 58 

Brailing herring from a purse seine on the West Coast of Canada .... 68 

Log-rafts returning from drift net fishing, Ceylon ...... 74 

Hand-hauling a Marlon pursed lampara seine in South Africa . . . .81 

A canoe fisherman mending his net on the Indian Malabar coast .... 86 

The 883 tons distant-water trawler Portia of Hull ...... 99 

Washing fishing nets in Pakistan . . . . . . . . .101 

Net sections being braided by hand ......... 106 

Stacking a beach seine after a haul in Ceylon ....... 109 

Drying herring drift nets at Great Yarmouth . . . . . . .132 

Two canoes fishing with a midwater bag net on the Malabar coast of India . .136 

Testing the breaking strength and extensibility of twine (left:) 138 

Hand and foot operated net weaving loom (right:) . . . . . .138 

Hand spinning of cotton yarn in an Indian fishing village ..... 146 

Bottom-set cod gillnets of nylon hauled mechanically off Iceland . . . .149 

Handling heavy ground rope with steel bobbins on an Arctic trawler .... 151 

Underwater television photo of monofilament and cotton net . . . . .158 

Underwater photo of a trawl headline with spherical floats ..... 204 

Trawl toads and wingdoor of hydrodynamical design ...... 208 

Skindiver team preparing for trawl observations . . . . . . .212 

Hydrofoil otter board with a recording angle-of-attack meter (left) .... 224 

An oval otter board with an open angle-of-attack meter (right) .... 244 

Surface dynamometer for measuring towing pull (left) : Simultaneous calibration of 4 under- 
water and 2 surface dynamometers (right) ....... 247 

Modern Mediterranean stern trawling vessel ....... 250 

Hauling salmon gillnets on a power drum ....... 263 

200 tons of herring taken in one set in Norway ....... 273 

Deckload of cod on an Arctic trawler ........ 299 

Small inshore shrimp trawler on the USA Gulf Coast 316 

Hauling the codend over the stern chute of a factory trawler ..... 324 

The Nekrasov, one of the Russian factory trawlers ...... 330 

Mothership loading catches from fishing vessels on the high seas .... 332 

[XV] 



MODERN FISHING GEAR OF THE WORLD 

Page 

Underwater photo of a midwater trawl model ....... 350 

Hydrofoil otter board with recording dynamometer ...... 356 

Echo trace of a pelagic sardine school ........ 360 

A 3-drum-trawl and anchor winch on a Swedish cutter ...... 368 

The Janet Helen, a 73 ft. modern small trawler, U.K. ...... 370 

An oval otter board for bottom trawling ........ 374 

Beach seining live bait for tuna fishing, Haiti ....... 390 

Indian fishermen hauling lampara type bagnet ....... 393 

A big set with a two-boat purse seine on the Norwegian West Coast . . . 399 
Conventional hand hauling of a Norwegian purse seine . . . . . .413 

South African fishing vessels unloading their catch by fishpump .... 417 

Taking the catch out of a big tuna trap in Lybian waters ..... 421 

Hauling up the bag of a large Japanese setnet ....... 425 

Shark longline hauled mechanically on a 22 ft. FAO motor boat, India . . . 435 

" Chinese " liftnet in Cochin, India ......... 446 

Modern Japanese tuna longline vessel for high seas fishing ..... 473 

C.R.T. echo display of herring and redfish near the bottom ..... 477 

Echogram of stratified bottom ......... 485 

Echogram showing fish concentrations in a bottom depression ..... 506 

Brailing herring from a Norwegian purse seine . . . . . . .511 

Echo traces of tuna in the North Sea ........ 522 

Conical liftnets used for light fishing in the Caspian Sea ..... 547 

Echogram showing the reaction of freshwater fish to artificial light .... 549 

Mediterranean light boat with three big gas lamps for attracting fish . . . 566 

Electro-fishing with a battery powered impulse gear in fresh water .... 580 

Electrical fish barrier ........... 591 

Electrotaxic concentration of anchovy around pump-hose opening .... 595 



XVI ] 



LIST OF CONTRIBUTORS 



No. 
\AGAARD, O. . . . . .111 

Organization of Norwegian Fishing Gear Manufacturers, 
Christiania Seildugsfabrik Tordenskioldsgt. ] Oslo, Norway. 

\KYUZ, E. F. 357 

Chief, Demersal Fish Laboratory, Fishery Research Centre 
Meat and Fish Office, Istanbul, Turkey. 

\LBRECHTSON, Gunnar . . 269, 270, 271, 272 

Technical Manager of Jul Albrechtson and Co. A.B., Kom- 
mendorsgatan 11, Goteborg V, Sweden. 



ALVERSON, D. L. 



. 317,446,537 



Fishery Biologist, Washington Department of Fisheries, 4015. 
30th Avenue West, Seattle 66, Washington, U.S.A. 



AMANO, M. 



150 



Head of Synthetic Fibres Export Section, Toyo Rayon Co. Ltd., 
No. 5, 3-chome, Nakanoshima, Kitaku, Osaka, Japan. 

ANDERSON, A. W 596, 598 

Assistant Director. Bureau of Commercial Fisheries, U.S. Fish 
and Wildlife Service, Washington 25, D.C., U.S.A. 

ARZANO, R. . . . . . .13 

Chairman, Industrial Uses Sub-Committee of International 
Rayon and Synthetic Fibres Committee, c/o Societa Rhodiatoce, 
via Rugabella 15, Milano, Italy. 



BAIRD, R. H. 



222 



Senior Experimental Officer, Ministry of Agriculture, Fisheries 
and Food Fisheries Experiment Station, Castle Bank, Conway, 
Caernarvonshire, U.K. 



BARRACLOUGH, W. E. 



351 



Associate Scientist, Fisheries Research Board of Canada, 
Biological Station, Nanaimo, B.C., Canada. 



BEN-YAMI, M. 



165,213,270 



Master Fisherman, Kibbutz "Sa'ar", D.N. Gallil Ma'aravi 
Israel. 



BlNDLOSS, E. C 



536 



Commander, Assistant Technical Manager, Marconi International 
Marine Communication Co. Ltd., Marconi House, Chelmsford, 
Essex, U.K. 



BINNS, H. N. 



297 



Managing Director, The Great Grimsby Coal, Salt and Tanning 
Co. Ltd., Fish Dock Road, Grimsby, Lines., U.K. 



BlRKHOFF, C. 



321, 329 



Naval Architect, Rickmers Werft, Lloydstrasse 34, Brcmerhaven, 
M., Germany. 



DE BOER, P. A. 



. 225, 451, 534, 597 



Deputy Inspector of Fisheries, Wasscnaarscweg 18, The Hague, 
Netherlands. 



Page 
No. 

VON BRANDT, Prof. Dr. A. 11, 95, 97, 98, 1 12, 133, 274 

598 

Director, Institut fiir Netz und Materialforschung, 
Bundesforschungsanstalt fur Fischcrei, Palmaillc 9, Hamburg 
Altona, Germany. 

BRITISH STANDARDS INSTITUTION ... 8 

2, Park Street, London, W.I, U.K. 

BUCHAN, J f . . . . . .112 

British Nylon Spinners Ltd., Pontypool, Mon., U.K. 

BURGOON, D. W. . . . . 414 

President, Yeomans Brothers Co., 1999, North Ruby Street, 
Melrose Park, III.. U.S.A. 



CARROTHERS, P. J. G. 



. 69, 95 



Technological Station, Fisheries Research Board of Canada, 
898, Richards Street, Vancouver B.C., Canada 



CARRUTHIiRS, Dr. J. N. 



254 



National Instutute of Oceanography, Wormlcy, Nr. Godalming, 
Surrey, U.K. 



CARVALHO, M. Melo 



442 



Commander, Gabinete de Estudos das Pcsca, Avenue da Liber- 
dade 211-4, Lisbon, Portugal. 



CATASTA, L. 



251 



Costruttore Navale, Via Monte S. Michele, S. Benedetto del 
Tronto, Italy. 



CRAIG, R. E. 



474 



Scottish Home Department, Marine Laboratory, Victoria Road, 
Torry, Aberdeen, U.K. 



CRECELIUS, C. A. 



369 



Manager, Olympic Instrument Laboratories, Vashon, Washing- 
ton, U.S.A. 



GUSHING, Dr. D. H. 



525, 537 



Principal Naturalist, Fisheries Laboratory, Lowestoft, Suffolk, 
U.K. 



DECCA NAVIGATOR Co. LTD., THE 



459 



Marine Sales Dept. 9, Albert Embankment, London, S.E.ll 
U.K. 

DETHLOFF, J. ..... 583 

Director. Dethloff-Electronic Lottestrasse 52, Hamburg-Lokstedt, 
Germany. 

DICKSON, W. . .166, 268, 375, 440, 443 

Senior Scientific Officer, Marine Laboratory, Victory Road, 
Torry, Aberdeen, U.K. 

DIETRICH, Prof. Dr. G. . . .453 

Oceanographer, Dcutschcs Hydrographisches Institut, Bernhard 
Nocht Strassc 78, Hamburg 11, Germany. 



[xvu] 



A2 



MODERN FISHING GEAR OF THE WORLD 



No. 

DROST, H. S. .... 270, 598 

Inspector of Fisheries, Wassenaarseweg 1 8, The Hague, Nether- 
lands. 



EDDIE, G. C. 



325 



Food Investigation Organisation, Department of Scientific and 
Industrial Research, Tony Research Station, Aberdeen, U.K. 

EINSELE, Dr. W 96 

Director, Bundesinstirut fur Gewasserforschung und 
Fischereiwirtschaft, Scharfling am Mondsee, Austria. 

FAHRENTHOLZ, Dr. S. 504, 535, 536 

Manager, Echolote und Signalgeratc, Graswcg2-6, Kiel, Germany 

FEHER, Dr. K. 512 

F.lectroacustic G.m.b.H., Westring 425-429, Kiel, Germany. 

FINLAYSON, Capt. I. R. . . . .451 

Engineering Dept., Sub-marine Branch, British Post Office, 
Leith House, Gresham Street, London, E.C.2, U.K. 

FRIED, Z 586 

Senior Technologist, Sea Fisheries Research Station, Haifa, 
Israel. 

FUKUHARA, A. ..... 422 

Hokkaido Fisheries Experimental Station, Yoichishi, Hokkaido 
Japan. 

GERHARDSEN, Th. ..... 536 

Simonsen Radio A/S, Ensj0veien 20, Oslo, Norway. 

GEROULT, E. R 450 

Naval Architect, 26, rue Danielle Casanova, Paris (II), France 

GOODMAN, R. A. . . . 371, 597 

European Plant Engineer, The Western Union Telegraph Co., 
22, Great Winchester Street, London, fc.C.2., U.K. 

GROUSELLE, Y. . . . . 271,361 

24, Boulevard Chateaubriand, Saint- Mai o (Ils-et-Vilaine), France. 

GUNDRY, E. F. . . . . .96 

Director, Joseph Gundry and Co. Ltd., Bridport, Dorset, U.K. 

HAGENBUCII, Dr. W. . . . .137 

Sandoz A.G., Basel, Switzerland. 

HAINES, R. G 493, 534, 536 

Commander, Technical Officer, Kelvin and Hughes (Marine) Ltd. 
99, Fenchurch Street, London, E.C.3, U.K. 

HALAIN, C. P 96, 596 

Commissaire General du Fonds du Roi Gouverneur de Province 
Honoraire, B.P. 3119, Leopoldville, Congo Beige. 

HALME, Prof. Dr. E. 
Bureau for Fishery Investigations, Verkkosaari, Helsinki, Finland 

HALSBAND, Dr. E. . . . . . 575 

Institut fur Kusten- und Binnenfischerci, Palmaille 9, Hamburg 
Altona, Germany. 



HALSBAND, Dr. H. 



594 



Institut fur Kusten- und Binnenfischerei, Palmaille 9, Hamburg 
Altona, Germany. 

[ 



No. 
HAMURO, Prof. C. .... 234 

Fishing Boat Laboratory, Fisheries Agency, 1, 2-Chome, 
Kasumigaseki, Chiyoda-ku, Tokyo, Japan. 

HASHIMOTO, Prof. T. . 478, 483, 486, 499, 523 

Chief, Instrument Section Fishing Boat Laboratory, Fisheries 
Agency, 1, 2-Chomc, Kasumigaseki, Chiyoda-ku, Tokyo, Japan. 

HAYHURSI, G. A. .... 4,96,100 
William Kenyon and Sons Ltd., Dukinfield, Cheshire, U.K. 



HENNINGS, Dr. Ch. . 



. 451 



Chief. Physico-Chemical Laboratory, Institut fur Fischverar- 
bcitung, Palmaille 9, Hamburg Altona, Germany. 



HESS, Dr. E. 



Ill 



Formerly Chief, Fisheries Technology Branch FAO, now: 
Fisheries Adviser, Ministry of Agriculture, West Indies Federa- 
tion, Federal House, Port-of-Spain, Trinidad, West Indies. 



HODSON, Captain A. 



270, 445, 536 



Instructor, Grimsby College of Further Education, 80, Clee 
Road, Cleethorncs, Lines., U.K. 



HOLT, S. 



165, 471 



Chief, Research Program Section, Fisheries Biology Branch, 
Fisheries Division FAO. 



HOSL, Dr. Ing. A. 



589 



Elektro-Beratung Bayern G.m.b.H. Seidl-Strasse 25, Miinchen 2, 
Germany. 



ILES, T. D. 



95 



Fisheries Research Officer, Joint Fisheries Research Organization, 
P.O. Nkata Bay, Nyasaland. 

IMPERIAL CHEMICAL INDUSTRIES LTD. . . 43 

Fibres Division, Hookstone Road, Harrogate, Yorks., U.K. 



ISHH, Prof. K. 



234 



Fishing Boat Laboratory, Fisheries Agency, 1, 2-Chome 
Kasumigaseki, Chiyoda-ku, Tokyo, Japan. 



Izui IRON WORKS Co. LTD. 

Muroto-cho, Kochi-kcn, Japan. 
JAKOBSSON, Jakob 



. 436 



. 443, 472, 528, 536 



Fishery Biologist, Atvinnudeild Hask61ans, Fiskideild, Borgartun 
7, Reykjavik. Iceland. 

JAPAN CHEMICAL FIBRES ASSOCIATION . . 62 

3, 3-Chome Muromachi, Nihonbashi Chuo-ku, Tokyo, Japan. 
KANAMORI, Prof. M. . . . 205, 256 

Faculty of Fisheries, Kagoshima University, 470, Shimo-Arata- 
Machi, Kagoshima City, Japan. 



KAWAKAMI, M. 
XVIH ] 



597 

Chief, Trawling Department, Taiyo Fishing Co. Ltd., 1-4 
Marunouchi, Chiyoda-ku, Tokyo, Japan. 



LIST OF CONTRIBUTORS 



Page 
No. 

KAWAKAMI, Dr. T. . . . . .175 

Department of Fisheries, Faculty of Agriculture, Kyoto Uni- 
versity, Maizuru, Kyoto Prefecture, Japan. 



KAWAMOTO, Prof. Dr. N. Y. 



553 



Faculty of Fisheries, Prefectural University of Mie, Oya Mach 
Tsu City, Mie Prefecture (Japan), Lecturer, Department of 
Fisheries, Kyoto University, Japan. 



KELLER, Chem. Ing. H. 
Fibron S.A., Domat/Ems, Switzerland. 



12 



KIETZ, Dr. H 501, 536 

Chief, Electro-Acoustic Laboratory, Atlas-Werke AG, Postfach 9, 
Bremen, Germany. 



KlKUCHl, Y. 



478 



Research Institute of Electrical Communication, Tohoku 
University, Sendai, Japan. 



KLUST, Dr. G. 



93, 97, 139 



Senior Gear Technologist, Institut fiir Net/- und Materialfors- 
chung, Bundcsforschungsanstalt fur Fischerei, Palmaillc 9, 
Hamburg - Altona, Germany. 



KOBAYASIII, H. 

Nippon Seimo Co. Ltd., 6, 1-chome Ginza, Chuo-ku, Tokyo, 
Japan. 

KODAIRA, K. 465 

Anritsu Electric Co. Ltd., 39, Azabu Fijimi-cho, Minato-ku, 
Tokyo, Japan. 

KOYAMA, T 185,567 

Fishing Methods Division, Tokai Regional Fisheries Research 
Laboratory, Fisheries Agency, Tsukishima, Chuo-ku, Tokyo, 
Japan. 



KRAMER, K. M. 



96 



Chief, Sea Fisheries Section, Ministry of Agriculture, Hakirya, 
Tel-Aviv, Israel. 

KRISUONSSON, Hilmar 12, 447, 451, 535, 536, 573 

Chief, Fishing Gear Section, Fisheries Technology Branch, 
Fisheries Division, FAO. 



KROHN-HANSEN, S. 



12 



F.A. Campbell-Andersens Fnke A/S, Postbox 11, Bergen, 
Norway. 



KUREHA KASEI Co. LTD. 

Tokyo, Japan. 

KUROKI, Prof. Dr. T. 
Faculty of Fisheries, Hokkaido University. 

KUTSCH, A. 
Netmaker, Fishereihafen, Hamburg, Germany. 



57 



581 



597 



LARSSON, K. H 271, 344, 444 

Naval Architect, Stadsgarden 10, Stockholm, Sweden. 



LAWTON, C. S. 



371 



The Western Union Telegraph Co., 60 Hudson Street, New 
York 13, N.Y., U.S.A. 



LENIER, J. R. 



Page 
No. 

452, 594 



Directeur-G6neraI, S.A. "Comptoir Radio Naval" 11 bis, rue 
Saint- August in, Asnieres (Seine), France. 

LEVY, H 138 

Port de Peche, Safi, Morocco. 

LoNSDALt, J. E. . . . 10, 12, 30, 95 

British Nylon Spinners Ltd., Pontypool, Monmouthshire, U.K. 

LUSYNE, P. A. . . . . .102 

Gear Technologist, Fishing Gear Section, Fisheries Division, 
FAO. 

MANIWA, Y. ... 483, 486, 499, 523 

Fishing Boat Laboratory, Fisheries Agency, 1, 2-Chome, 
Kasumigaseki, Chiyoda-ku, Tokyo, Japan. 



MANN, H. J. 



430 



Gear Technologist, Pacific Oceanic Fishery Investigations, 
Honolulu, Hawaii, U.S.A. 



McKEE, D. 



no 



The Linen Thread Co. Ltd., 95 Bothwell Street, Glasgow, C.2. 
U.K. 



- 11 ' 112 MCNEELY, R. L. 



363 

Flcctronic Scientist, North Pacific Exploration and Gear 
Research Bureau of Commercial Fisheries, Seattle, Washington, 
U.S.A. 

Mi YFR-WAARDEN, Prof. Dr. P. F. . . 592 

Director. Institut fiir K listen- und Binnenfischerei Bundes- 
forschungsanstalt fiir Fischerei, Palmaille 9, Hamburg Altona, 
Germany. 

MIHARA, K. . . . . . . 426 

Chiba Prefectural Fisheries Experimental Station, 1510Tateyama, 
Tatcyama-shi Chiba-Ken, Japan. 



MIYAMOTO, Dr. H. 



248 



FAO Fishing Gear Technologist, Central Fisheries Technological 
Station, XXI/29, Kochangadi Cochin 5, Kerala, South India. 

MOLIN, G 156 

Fiskmaslarc, Sotvattenslaboratoriet, Drottningholm, Sweden. 

MOMOI FISHING NET MFG. Co. LTD. . .152 

Ako, Hyogo-Ken, Japan. 

MUG A AS, N. 159 

Engineer, Statens Fiskeredskapsimport Kadstuplass 10, Bergen, 
N 01 way. 

NARASAKO, Dept. Prof. Y. . . .205 

Faculty of Fisheries, Kagoshima University, 470 Shimo-Arata- 
Machi, Kagoshima City, Japan. 

NLHJUR, Dr. A. W. H. . 272, 351, 442, 471, 572 

Director, Fisheries Biological Station, Nanaimo, B.C., Canada. 

NIKONOKOV. I. V 574, 559 

Director, Caspian Institute of Marine Fisheries and Oceano- 
graphy, Astrakhan, U.S.S.R. 



NlLSSEN, E. A. 

Bergens Notforretning, P.O. Box 870, Bergen. Norway. 



96 



[XIX ] 



MODERN FISHING GEAR OF THE WORLD 



Page 

No. 

NIPPON SEIMO Co. LTD., THE . .107 

6, l-Chome Ginza, Chuo-ku, Tokyo, Japan. 

NlSHlMURA, M. . . . . .483 

Fishing Boat Laboratory, Fisheries Agency, 1, 2-Chome, 
Kasumigaseki, Chiyoda-ku, Tokyo, Japan. 



NOEL, H. S. 



348, 535 



Staff Writer "World Fishing", Temple Chambers, Temple 
Avenue, London, E.C.4, U.K. 



NOMURA, M. 



550 



Gear Technologist, Fishing Gear and Methods Section, Tokai 
Regional Fisheries Research Laboratory, Fisheries Agency, 
Tsukishima, Chuo-ku, Tokyo, Japan. 



OCRAN, R. 



97,445 



Fishing Company Owner, Mankoadze Stores, P.O. Box 1492, 
Accra, Ghana. 

O'GRADY, A. . . . . 12, 442, 451 

Technical Adviser (Fishing), Commonwealth Fisheries Office, 
Fisheries Division, Dept. of Primary Industry, Barton, Canberra, 
Australia. 

OKONSKI, S. . . . . . .196 

Sea Fisheries Institute, Al. Zjednoczenia 1, Gdynia, Poland. 

OLAFSSON, David . . . . .12 

Director of Fisheries, The Fisheries Association of Iceland, 
Reykjavik. Iceland. 

OREN, O. H. 586 

Deputy Director, Sea Fisheries Research Station, Haifa, Israel. 

PARRISH, B. B. . . . 164, 333, 444, 536 

Principal Scientific Officer, Marine Laboratory, Victoria Road, 
Torry, Aberdeen. U.K. 



VAN PEL, H. . 



574 



Fisheries Officer, South Pacific Commission, Noumea, New 
Caledonia. 



PERCIKR, A. . 



12, 260 



Institut Scientifique et Technique des Peches Maritimes, 
Laboratoire dc Biarritz, Centre Scientifiquc dc PAtalaye, 
Biarritz, France. 

PERLON-WARENZKICHEN VERBAND E. V. . . 34 

Westendstrasse 41, Frankfurt am Main, Germany. 

PHILLIPS, J. W 200, 272 

Managing Director, Phillips Trawl Products Ltd., Grimsby, 
Lines., U.K. 



DU PLESSIS, C. G. 



391 



Assistant Director, Division of Fisheries, Department of Com- 
merce and Industries, Beach Road, Sea Point, Cape Town, 
Union of South Africa. 

E. I. DU PONT DE NEMOURS AND Co. INC. . 147 

Wilmington 98, Delaware, U.S.A. 

POWELL, D. E. . . . . .517 

Exploratory Fishing and Gear Research Branch, Bureau of 
Commercial Fisheries, U.S. Fish and Wildlife Service, Washing- 
ton 25, D.C., U.S.A. 



Page 
No. 

RACK, R. S 11,95,445,597 

Fishery Advisor, Government of Northern Rhodesia, P.O. Box 1, 
Chilanga, Lusaka, Northern Rhodesia. 



RASALAN, S. B. 



418 



Chief Division of Commerical Fisheries, Bureau of Fisheries, 
Department of Agriculture and Natural Resources, Manila, 
Philippines. 

REUTER, Dr. J. 59, 82, 96, 137 

Director, Het Nederlandsche Visserij-Procfstation en Labora- 
torium voor Material-Onderzoek, Maliebaan 103, Utrecht, 
Netherlands. 

RICHARDSON, I. . . . . 272, 446 

Senior Naturalist, Fisheries Laboratory, Lowestoft, Suffolk, U.K. 

ROBAS, J. S 311,394 

Commercial Fisheries Consultant, Fernandina Beach, Florida, 
U.S.A. 



ROBERTS, D. 



12, 269, 441, 536 



Captain of deep sea trawler, Derwent Trawlers Ltd., Hutton 
Road, Grimsby Fish Docks, Grimsby, Lines., U.K. 



ROBINSON, A. 



. 4, 96, 97, 100, 111 



Technical Officer, William Kenyon and Sons Ltd., Chapelsfield 
Works, Dukinfield, Cheshire, U.K. 



Ruivo, Dr. M. 



473, 571 



Sub-Director, Institute de Biologia Marinha, Cais do Sodre, 
Lisbon, Portugal. 



RLIPERTI, A. 



123, 138 



Ciba Aktiengesellschaft, Kunststoffabteilung, Klybeckstr. 141, 
Basle, Switzerland. 



SAETERSDAL, G. 



161 



Fishery Biologist, Fiskeridirektoratets, Havforskningsinstitutt, 
Postboks 189, Bergen, Norway. 

SADOWSKI, S. . . . . .196 

Sea Fisheries Institute, Al. Zjednoczenia, Gdynia, Poland. 

SAHRHAGE, Dr. D. . . . . 453, 472 

Marine Biologist, Institut fiir Seefischerei, Bundcsforschungsan- 
stall fiir Fischerei, Palmaille 9, Hamburg Altona, Germany. 

SAITO, Prof. Dr. 1 388 

Faculty of Fisheries, Hokkaido University, 253 Minato-Machi, 
Hakodate, Japan. 

SANCHEZ ROIG, Dr. M. . . . 433 

Institute Nacional de la Pesca, Habana, Cuba. 

SAND, R. F 209 

Chief, Great Lakes Fisheries Exploration and Gear Research, 
Bureau of Commercial Fisheries, U.S. Fish and Wildlife Service, 
P.O. Box 640, Ann Harbour, Michigan, U.S.A. 

SANDOZ LTD. . . . . .125 

Department for Chemical Fibre Modification, Basle, Switzerland. 

SASAKI, Prof. T 269, 559 

Tokyo University of Fisheries and Chief Research Fellow of 
the Scientific Research Institute, 6-chome Kaigandori, Minato-ku 
Tokyo, Japan. 



[XX] 



LIST OF CONTRIBUTORS 

Page 

No. 

SCHARFE, Dr. J. . 241, 245, 269, 300, 444, 532, 537 TESTER, A. L. 



Gear Technologist, Fishing Gear Section, Fisheries Division. 
FAO. 

SCHAEFERS, E. A. . . . .517 

Acting Chief, Branch of Exploratory Fishing and Gear Research, 
Bureau of Commercial Fisheries, U.S. Fish and Wildlife Service, 
Washington 25, D.C., U.S.A. 



Sf HEFOLD, K. 



594 



Vizeprasidcnl, Osterreichische, Hschereigescllschaft, Elisabethstr. 
22, Wien I, Austria. 



SCHMIDT, P. G. 



400, 449 



President, Marine Construction and Design Co., 2300 Commo- 
dore Way, Seattle 99, Washington, U.S.A. 

S( HUBERT, Dr. K. . . . . 453 

Marine Biologist, Institut fur Seefischerci, Bundesforschungsan- 
stalt fur f ischerei, Palmaille 9. Hamburg Altona, W. Germany. 



Sen v ML, M. 



534 



Sales Manager, Flektroakustik G.m.b.H., Westring 425-429, 
Kiel, Germany. 

SHIMOZAKI, Y. . . . . 19, 113 

Gear Technologist, Fishing Gear Division, Tokai Regional 
Fisheries Research Laboratory, Tsukishima, Chuo-ku, Tokyo, 
Japan. 



SMI ni, H. C. 



11 



Managing Director, Apeldoornse Nettenfabriek von Zeppelin 
and Co. N.V., Apeldoorn, Netherlands. 



SOUBI IN, L. 



441, 452 



President, Federation des syndicats d'armuleurs a la peche, 
59, rue des Mathurins, Paris 8e, France. 

SPRINGER, S. . . . .97, 165, 445 

Chief, Exploratory Fishing Section, Bureau of Commercia' 
Fisheries, U.S. Fish and Wildlife Service, Washington 25. 
D.C., U.S.A. 

Siurz, Dipl. Ing. H. . . . . 1, 87 

Farbwerke Hocchst AG, Bobingen Mills, Germany. 

StJBERKRUB, F. ..... 359 

Naval Architect, Chile Haus C VII, Hamburg 1, Germany. 

SUIYO-KAI 438, 462 

c/o Anritsu Electric Co. Ltd., 39, Azabu-Fijimi-cho, Minato-ku, 
Tokyo, Japan. 

SVETINA, M 445 

Vice-President du C.S.P. de Slovenie, Poljanska 20B, Ljubljana, 
Yugoslavia. 

SZATYBELKO, M. . . . . 264 

Sea Fisheries Institute, Al. Zjednoczenia 1, Gdynia, Poland. 

TAKAYAMA, Prof. S. . 6, 111, 113, 185, 269, 594 

Chief, Fishing Gear and Methods Section, Tokai Regional 
Fisheries Research Laboratory, Tsukishima, Chuo-ku, Tokyo 
Japan. 

TAMURA, Prof. T 543 

Fisheries Institute, Faculty of Agriculture, Nagoya University, 
Anzyo, Aiti-Prcfecture, Japan. 



No. 
538 

Director, Pacific Oceanic Fishery Investigations, Honolulu 
Hawaii, U.S.A. 

TEIKOKU RAYON Co. LTD., Tin- ... 55 

Teviron Department. Hdobori-Mmamidori. Nishiku, Osaka, 
Japan. 

THOMAS, Dr. H. A. . . . 97, 271 

President de la Commission Technologique, Comite Inter- 
national de la Rayonne el des Fibres Synthetiques, c/o Court - 
aulds Ltd., 15 Cross Street, Manchester 2, Lanes. U.K. 

TRAUNG, J. O. . . . 266, 269, 270, 574 

Chief, Fishing Boat Section, Fisheries Division, FAO. 



TRESCHEV, A. I. 



450 



Chief, Fishing Technique Laboratory, U.S.S.R. Institute of 
Marine Fisheries and Oceanography (VNIRO), Moscow 
U.S.S.R. 

TSUDA, K. K. . . . . . 535 

Japan Radio Co. Ltd., 930 Kamirenjaku, Mitaka, Tokyo, Japan. 

Vi RHEYEN, F . J. . . . . 548, 572 

Laboratorium voor Vergehjkende, Physiologic der Rijks 
UnivcrsiteiU Jan van Galenstraat 17, Utrecht, Netherlands. 



VESINES, G. 



507 



Fiskcridirektoratets Havforskningsinstitutt. Postbox 189 
Bergen, Norway. 



WARNCKI., H. 



1, 110 



Director, Itzehoer Net/fabrik AG, Brunnenstr. 2-10, It/cnhoc 
Germany. 



WENT, Dr. A. E. J. . 



165 



Inspector and Scientific Advisor, Fisheries Branch, Department 
of Agriculture, 3, Cathal Brugha Street, Dublin, Ireland. 

WESTROP, K. J. . . . . .97 

Fibres Division, Imperial Chemical Industries Ltd., Hookstone 
Road, Harrogate, Yorks., U.K. 



VAN WlJNC.AARI>LN, J. K. 



. 12, 75 



N.V. Research Laboratory and Affiliated Companies. Velperweg 
76, Arnhem, Netherlands. 



DE WIT, J. G. 



450 



Naval Architect, P.C. Hooftlaan 38, Dnejuis (Gemccntc Velsen), 
Netherlands. 



WOLMARANS, B. J. 



95 



Cooper, Wolmarans and Co. Ltd., P.O. Box 799, Cape Town, 
Union of South Africa. 

WOODGATE, R. W 488 

Pye Marine Ltd., Oulton Works, Lowestoft, Suffolk, U.K. 

ZAUCHA, J. . . . . . .128 

Sea Fisheries Institute, Al. Zjednoczenia 1, Gdynia, Poland. 

ZEBROWSKI, Z 272, 452 

Reedcrei "Dalmor", Gdynia, Poland. 

ZEI, Prof. Dr. M 537 

Director, Institute of Marine Biology, Roving, Yugoslavia. 



[XXI] 



ABBREVIATIONS 



A - Ampere 

C. -- E>egrees Centigrade 

cm. - Centimetre(s) 

sq. cm. Square Centimetre(s) 

cu. cm. -=-- Cubic Centimetre(s) 

col. = Column 

cu. = Cubic 

diarn. == Diameter 

F. Degrees Fahrenheit 

fm. Fathom(s) 

ft. Feel 

g. Gram(s) 

gal. -^ American gallon(s) 

ha. ~ Hectare(s) 

h.p. Horsepower 

hr. -=- Hour 

hrs. ~ Hours 

in. = Inch(es) 

kg. -- Kilogram(s) 

km. --- Kilometre(s) 

kw. Kilowatt 

1. = L.itre(s) 



Ib. ^- Pound(s) avoirdupois 

m. Metre(s) 

sq. m. Square metre(s) 

cu. m. Cubic metre(s) 

mg. Milligram(s) 

min. =--' Minute(s) 

ml. =- Millilitre(s) 

mm. Millimetre(s) 

sq. mm. ---= Square millimetre(s) 

cu. mm. ~ Cubic millimetre(s) 

oz. Ounce(s) avoirdupois 

p. = Page 

pp. Pages 

p. p.m. - Parts per million 

r.p.m. Revolutions p>er minute 

sec. -- Sccond(s) 

sp. Species 

spp. - Plural of species 

V Volts 

Vol. -= Volume 

W Watt(s) 

wt. = Weight 



XXII ] 



PREFACE 

THE International Fishing Gear Congress, which was held in Hamburg, Germany in October, 
1957, was the first meeting of its kind, and it marked an important step forward in international 
cooperation in dealing with some of the many problems concerned with the development 
of fisheries throughout the world. This book contains the edited versions of more than one hundred 
technical papers presented to the Congress, as well as the gist of the discussions which took place. 

Broadly speaking, FAQ's function is to promote food production, especially through 
international cooperation. One part of the work of the Organisation is to provide, at the request 
of any of the 77 Member Governments, direct technical assistance by assigning specialists to deal 
with specific fisheries problems. 

The other part of FAO's function is to act as a clearing house for technical information, 
stimulate the exchange of ideas and experience, and to fogus attention of governments on key 
problems, particularly those which need to be dealt with through international cooperation. The 
International Fishing Gear Congress provides an example of this function of the Organisation. 

While a great deal of FAO's work concerns the fisheries in the underdeveloped countries, 
it is also of value to technically developed countries. This was shown at the Congress where a major 
part of the 540 participants were from countries in the front rank of fishing nations. These people 
found, for example, that the papers and discussions were most useful in focusing attention on the 
problems concerned with the development of fishing gear technology. This is a new concept in the 
fishing world which has emerged in recent decades because of the growing complexity of fishing. 

Literature in this field is scattered and incomplete and this book is the first comprehensive 
reference work covering net materials, rational gear design, description of modern fishing 
gear and its operation as well as the strategy and tactics of finding and attracting fish. Although 
the profession of gear technology is still in the development stage, and gear research facilities are, 
as yet, available only in a few countries, much progress has been made towards evolving the method- 
ology and tools of the trade. But experimenting with fishing gear is expensive and, in view of the 
economic pressure under which the fishing industry generally works and the need to increase gear 
efficiency, this is clearly a field for governmental action. If rapid progress is to be made, then Govern- 
ments must set up and/or support gear research institutes. Such institutes are as essential as the 
already well established biological and fish processing stations now found in all fishing countries. 
The need for such institutes is underlined by the fact that, despite the progress made, fishing is, 
broadly speaking, still a very inefficient operation. For example, in the most highly developed fishing 
countries each fisherman produces over 80 tons of fish per year but there are more than two million 
fishermen in the less advanced countries who produce only about one ton offish per man per year, i.e. a 
little over 1 per cent, of the former. This illustrates the great need to spread existing knowledge from 
those countries with the technical "know-how'* to regions where it is lacking. 

In conclusion, I must put on record the gratitude of FAO to the Government 
of the German Federal Republic and the Senate of the Frei und Hansastadt, Hamburg, for so 
generously providing the facilities for holding the Congress. Many individuals, too, from a great 
number of countries did much to assist us in preparing and conducting the Congress. There is no 
space for me to mention them all so that 1 must limit myself to naming those who were particularly 
closely associated with the Congress. Much of the burden of making local arrangements was carried 
by Prof. Dr. A. von Brandt, Director of the Netz und Material Forschungsinstitut, Hamburg, and 
his staff, and we are especially grateful to them for all their help. Special thanks are also due to Dr. 
G. Meseck, Director of Fisheries, Germany, and Mr. A. W. Anderson, Assistant Director, Bureau 
of Commercial Fisheries, United States Fish and Wildlife Service, who acted respectively as Honorary 
Chairman and General Chairman of the Congress. 

D. B. FINN 
Rome, Italy, January, 1959 

[ xxui ] 



INTRODUCTION MODERN TRENDS IN FISHING 

*HE oceans, seas and other waters cover more than 70 per cent, of the earth surface. They occupy 
about 90 million sq. miles but produce less than 10 per cent, of humanity's food. How much 
food could eventually be taken by man from the sea cannot be assessed. 

From time to time estimates are made of how much fish we might expect to catch. 
Only a few years ago, it was thought the sustained catch would hardly exceed some 25 million metric 
tons per year. But already fish production nears 30 million metric tons (1957). Biologists and other 
experts now suggest this catch might be increased to some 60 million tons a year from known stocks, 
without taking into account the possible discovery of new fisheries. 

In a recent statement summing up reasons for the increase in world fish catch since the start 
of the twentieth century, Dr. D. B. Finn, Director of the Fisheries Division, F.A.O. declared that 
progress in fisheries has been greater in the past 30 years than in the previous three thousand ! 

Modern fishing has developed through three main technological revolutions. 

The first one, mechanization, began late in the 19th century with the use of steam propulsion 
in fishing vessels later followed by steam-driven winches. Semi-diesel and diesel engines began to 
make their mark at the turn of the century and have been gaining ground steadily till now steam is 
almost displaced except in North Atlantic long distance trawlers. But even there steam is gradually 
yielding to the diesel and such innovations as diesel -electric drives and turbine propulsion are finding 
limited application- and perhaps atomic energy is not far beyond the horizon. Mechanical propul- 
sion of the craft is important in itself, but power handling of the gear greatly extends the trend towards 
fully mechanised fishing a trend which still offers great scope for development. 

The second revolution to influence modern fishing is the use of electronic echo sounding 
and echo ranging equipment. Echo sounders had already become standard equipment in big North 
European distant water trawlers before 1939, but were only used for depth sounding. The improve- 
ment of acoustical underwater equipment during the Second World War paved the way for electronic 
fish detection and after the war recording echo sounders were speedily adopted in all medium and 
large fishing vessels in the developed fishing countries. This can be likened to giving a blind man his 
sight. Fishermen once accustomed to these facilities feel they are groping in the dark if deprived of 
them. 

The third major revolution in modern fishing is the advent of synthetic fibres. Nylon in 
various forms was the first of the man-made fibres to be widely applied in fishing nets, but in recent 
years, several other synthetics have also become important, especially in Japan, which leads the world 
in using synthetic fibres for fishing, both as regards quantities and variety. Nylon is for instance 
stimulating an important renaissance in gillnetting the world over, giving this age-old, simple but 
really basic form of fish net, a new lease of life. 

In the economically developed countries fishing has met ever keener competition from 
land industries which offer steady and relatively comfortable employment. To meet this challenge, 
the fishing industry has been forced to increase the size of fishing units, put more horse power behind 
each man on the sea, and back him with expensive shore installations for processing his catch. This 
capitalization necessitates operation at an even and high efficiency to pay dividends. Thus economic 
pressure relentlessly forces further technological development. 

Every fishing method has been affected by this development. Even handlining which 
was well on the way to becoming extinct in the Western World has gained new importance through 
the use of nylon monofilament, artificial lures and hand-powered reels. 

Longlining, both bottom set and floating, is still an important method in the North Atlantic 
cod fisheries, the North Pacific halibut fishery and the Japanese high seas tuna fishery, but technique 

f xxv ] 



MODERN FISHING GEAR OF THE WORLD 

of handling the gear has greatly improved. The lines are now streamed out at 7 to 9 knots and 
hauled in on mechanically or hydraulically driven gurdies at a rate of 2 to 5 miles/hr. Longlining is, 
however, still laborious, and formidable quantities of bait are also consumed. For each day's fishing 
an Icelandic longline boat for instance will use 700 to 1,000 Ibs. of frozen herring which is caught in 
another season and stored frozen for several months. It is therefore tempting to contemplate the 
savings in bait and labour which could be achieved if an effective artificial bait were developed such 
as possibly pieces of spongy material, suitably shaped and coloured, permanently attached on each 
hook. The line might then be immersed in, doused with, or drawn through a tank with a liquified fish, 
fish oil or other natural or artificial liquid attractant. The testing of such sponge baits, suitably 
treated is certainly one of many interesting problems awaiting solution. 



2p r 'XPC^**ir '^^^^^B?w^^^^^ '^?SliaiBiSS^888S 






.-. \ifl!Vy *' v / ' 



Ov^r two hundred thousand fishermen in India and Ceylon fish from log rafts with primitive gear, landing on the average only 

half to one ton offish per man per yevr. Photo: FAO 



Gillnetting has been more affected by the man-made fibres than any other fishing 
method and, as already mentioned, is stimulating a renaissance in this technique. The elastic pro- 
perties of nylon, its flexibility, softness, high tensile strength and other characteristics have so pro- 
foundly enhanced the catching power of gillnets that the name itself is hardly appropriate any longer 
except where school fish of a uniform size are truly gilled. In most other forms, loosely hung gillnets 
of nylon act more as tangle nets, catching fish in a wide range of size and shape. 

One attractive feature of the gill net is that it can be used even from primitive unpowered 
craft a fact of great importance in countries with underdeveloped fisheries. In F.A.O*s Technical 
Assistance work in tropical countries, the introduction of nylon gillnets, both bottom-set and drifting, 
has invariably met with almost immediate success and acceptance by the local fishermen who are 
quick to realise the advantages. The non-rotting character of synthetics is, of course, of the greatest 
importance in hot climates. Indian fishermen operating log rafts (see above) increase their catches 5 

[xxvi] 



INTRODUCTION 

to 10 times when equipped with nylon gill nets, thus raising their income and eventually enabling them 
to replace their primitive craft with small mechanized boats. 

When selecting synthetic fibre twines for fishing, due attention should be paid to the fact 
that nylon, for instance, is drawn to different degrees during manufacture to give either high tenacity 
and relatively low extensibility or else lower tensile strength and high extensibility. For certain uses, 
the latter may be preferable. 

Initial high price of nylon has come down to a competitive level, and the early difficulties 
of knot slippage, etc., have now been largely overcome with bonded twines and/or heat-setting of 
knots. This is still not fully realized in some countries, nor is the fishing industry everywhere fully 




In sharp contrast to the facing photo, modern purse seining exemplifies the high level of efficiency of modern fishing units as 
this one on the British Columbia coast ; where hundreds of tons of herring are frequently caught in one set. 

Photo: Info. Serv. t Dcpt. of Fisheries, Ottawa 



informed of the development and rapidly increasing use of other synthetic fibres such as the polyvinyl 
alcohol and polyester fibres. While practically all new gillnets used in the North Atlantic cod 
fisheries, the Pacific salmon fisheries and in inland waters, even in the great lakes of Africa, are now 
made of synthetics, man-made fibres have not yet been adopted in European herring drift net fisheries. 
It seems, however, likely that this is only a matter of time, despite initial difficulties with thin nylon 
twine which cut herring and make it difficult to shake out of the nets. The Japanese in their drift 
netting for herring, sardines, mackerel and salmon already use man-made fibres extensively. 

In world fisheries, gillnets, bottom-set and drifting, rank next after trawls and purse seines 
in importance in terms of total catch. Growing awareness of the danger of depleting fish stocks 
which, in some cases, has led to the closing of coastal waters to trawling, is another factor in favour 
of such methods as gillnetting and longlining. 

[ xxvii ] 



MODERN FISHING GEAR OF THE WORLD 

At the turn of the century purse seining came into general use, having evolved 
basically from Mediterranean roundhaul nets. American two-boat menhaden purse seines were first 
introduced into Icelandic and Norwegian herring fisheries in 1903-4, and in a few years largely 
replaced the big locknets used previously for fencing in large schools of herring in bays and fjords. 
Until the mid-thirties, two-boat purse seine dories were rowed, but became mechanised soon after. 
While pursing is normally done with a power driven winch, the net itself is still hand hauled so this 
method of fishing requires a crew of sixteen to thirty men an increasingly serious handicap to-day. 

On the other hand significant progress has been made in the power handling of one-boat 
purse seines, on the Pacific Coast of America. The Puretic power block is the latest example of 




(j i line t ting for thread/in (" Dara") north oj Bombay where engines have been installed in almost a thousand boats, but the 
nets are still hauled by hand. With a power driven net hauler costing only about S/00, this boat could easily fish twice as 

many nets with a smaller crew. Photo : \* AO. 

this. There is great scope for saving labour and otherwise improving efficiency by applying mechanical 
power to other types of purse seines and roundhaul nets elsewhere. 

Trawling has come a long way since sailing smacks drifted downwind with beam trawls. 
Mechanization and the use of otter boards, amplified later by Vigneron-Dahl gear, led to the develop- 
ment of many widely different trawl types for various operating conditions, both on and off the bottom. 
While midwater trawling has attracted considerable attention throughout the world, other important 
developments have gone almost unnoticed outside the areas where they are used. This is true for 
instance of the high-opening trawls now widely used in Sweden, Denmark, Germany, Netherlands 
and Belgium. 

Before the war large German herring trawlers had fished for years with moderately 
high-opening bottom trawls where the headline was lifted by kites and the fish schools depressed by 

[ xxviii ] 



INTRODUCTION 

kites riding on false headlines. It was, however, mainly after the war that high-opening trawls for 
vessels in the 20 to 200 ton class were developed and came into general use. These trawls are of 
many different types but in general they have certain main features in common, i.e. they are lightly 
built of thin twine, have short but high wings and the pull of the net is transmitted to the towing 
bridles along the lastrich lines or side seams in order not to drag back the headline but release it to 
rise high. These trawls do not depend on kites or hydrodynamic floats to secure a high vertical 
opening but are so proportioned that they billow out somewhat like a parachute. 

Measurements have shown that such light trails for relatively low-powered vessels (100 
to 300 h.p.) frequently open as high as 20 to 30 ft. (6 to 9 m.) headline height. They arc therefore, 




Bottom set cod gillnets of nvlon hauled on a hydraulicaily driven gurdy off Iceland. 2,000 to 2,500 fms, of nets are operated 

by each motor boat and the average catch is 6 to 10 tons per day. Photo: FAO 



particularly efficient for catching semi-pelagic and pelagic species schooling at some distance above 
the bottom, such as herring, sprat, mackerel, etc. 

During the last decade, general adoption of this type of trawl has had a profound effect 
in certain fisheries. In Denmark, for instance, the fish catch is now five times greater than it was 
before the war, i.e. has risen from about 100,000 tons (1938) to about 530,000 tons (1957), largely 
through changing over from quality fishing with Danish seines and low opening trawls to quantity 
fishing with high-opening and midwater trawls. 

Certainly there is scope for such nets in many other parts of the world and it is hoped the 
information contained in this book will help accelerate this. 

Another rather recent development not widely appreciated is the extension of trawling 
into deeper water, even with relatively small boats of modest power. Both on the U.S. Pacific Coast 

[ xxix 1 



MODERN FISHING GEAR OF THE WORLD 

and in the Mediterranean 30 to 80 ton vessels of 150 to 250 h.p. commonly trawl down to 350 fms. 
which is as deep as the deepest grounds fished now by the biggest trawlers in Northern Europe of 
over 1,000 h.p. While the Pacific Coast deep trawlers use relatively very short warps and heavy 
doors, the Mediterranean boats commonly use about 3:1 warp/depth ratio and rather light trawl 
doors with bracket adjustment giving an outward tilt and fitted with broad mud skis to avoid wasting 
towing power on ploughing deep ditches in soft mud bottoms. To fish such depths, an echosounder 
is indispensable for staying on bottom contour lines. 

In both these regions all boats use stern trawling which, with wheelhouse forward and clear 
deck aft, facilitates mechanical handling of the gear and simplifies manoeuvring during hauling 
and shooting light trawl gear (without bobbins) as compared with side trawling. 

Yet Mediterranean trawl boats normally carry crews of 6 to 9, while comparable boats in 
the Gulf of Mexico shrimp fishery or Danish side trawlers, carry only 3 or 4. Growing demands 
for better income among Mediterranean fishermen will force streamlining and reduce the number 
of the crew. A similar need for rationalization of working methods and equipment exists in most of 
the world's fisheries and there is certainly very great scope for applying work study techniques on 
board fishing vessels of all types to accelerate this development just as is done in industry on land. 

A trend in modern trawling which must be mentioned is the big stern trawlers pioneered 
by the Fairtry. The Russians now have a sizeable fleet of such factory ships, and three distant water 
trawlers of a similar design, but smaller, have also been built for German owners. All these vessels 
are built to fish in distant waters, normally more than a thousand miles from their home port. Despite 
rational methods of handling the gear, most of these factory ships carry very large crews for filleting, 
freezing and otherwise processing the catch. Such elaboration of the catch at sea is inherently expen- 
sive, and perhaps the future trend may be towards further simplifying the handling of the catch so 
that distant water fishing vessels could carry a small crew, provided with good accommodation and 
labour-easing as well as labour-saving appliances. A similar development is long overdue on the 
conventional deep sea trawlers. 

The use of bigger and more powerful vessels has led to higher trawling speeds. This gives 
rise to various problems in relation to the hydrodynamical properties of floats and trawl boards 
and it also brings up the choice between towing a relatively small net fast or using a much bigger 
net at a slower speed. Here the decisive factors are, firstly, the fish behaviour and, secondly, the 
economical or critical speed of the gear, beyond which a doubling or trebling of the power expen- 
diture results in only insignificant increase in towing speed. A careful study of these little-known 
factors may well lead to improved fishing efficiency and saving of costly fuel. 

Hydrographic and biological observations, coupled with organized fish searching are 
now beginning to supplement the empirical knowledge and intuition of experienced fishing skippers 
in locating fish concentrations. A good example of this is the service rendered to the Norwegian 
herring industry by Asdic equipped research vessels which track the annual migration of the herring 
during its feeding run in the summer in the Norwegian Sea and the winter spawning run to the 
Norwegian west coast. Other examples lie in the large fleets of Russian herring fishing vessels which, 
serviced by mother ships, follow these same herring stocks throughout the year in the sea between 
Norway, Iceland and Scotland; also the Japanese high seas fishery for salmon in the North Pacific 
and tuna longlining in equatorial waters around the world. 

The echo sounding equipment developed for fish detection after the last war has had a pro- 
found effect on most modern methods of fishing. The latest technical developments overcome some 
of the limitations of conventional models and open up new horizons; for instance, the considerable 
increase in sound output, enlarged recording of small depth segments and suppression of the bottom 
echo greatly improve the detection of fish near the bottom and in great depths. Some of these new 
features can be built into older models. Fishing Asdic units are coming into use in the North 
Atlantic herring fisheries and in whaling. 

Apart from finding fish the new echo sounders can sometimes indicate whether to use a 
trawl of high opening (and limited spread) or of the widest possible spread (and small gape). 

Echo fish detection made midwater trawling possible. An absolute prerequisite is, of 
course, to find the fish and its depth. The next step is to regulate and determine accurately the fishing 

[ xxx 1 



INTRODUCTION 

depth of the trawl, and this has presented difficulties in the past. At the time of this writing encour- 
aging progress is, however, being made towards evolving and introducing a simple, workable and 
inexpensive arrangement of using an echo sounder transducer attached to the headline or the footrope 
of midwatcr trawls as outlined on p. 491 in this book. Not only does this clearly show the exact 
depth of the trawl but the vertical opening is also indicated and the fish entering the trawl mouth or 
evading below or above it. This may well lead to a much wider application of midwater trawling 
which is still very limited. 

The use of light for attracting fish is an important method in Japan, Philippines and the 
Mediterranean region, but amazingly enough, it is still largely neglected elsewhere. One notable 
exception is, however, the novel use of conical lift nets and, more recently, of pumping in conjunction 
with light attraction in the Caspian Sea. 

Attracting fish by light is of special value where sardine, anchovy, mackerel, saury or other 
light seeking species arc present, but do not spontaneously form dense schools that arc easily 
located. Definitely the use of lights should be thoroughly tested not only throughout the tropics, but 
in the temperate and cold-temperate zones. When experimenting with light attraction, negative 
initial results should not be taken as conclusive, as a great deal of patience is often needed to develop 
a suitable technique for each species under each set of circumstances. 

While electrical fishing is already used to some extent in fresh water, serious problems 
are met with in applying it to saltwater fishing, due to the progressive increase in power requirements 
as range increases. Several years ago, optimistic reports were published heralding bright future 
prospects for revolutionary development, but this news, unfortunately, proved to be premature and 
interest in electrical fishing waned. Full-scale experimentation at sea is expensive, and while some tests 
have been made in recent years, much more work needs to be done in this field to assess the practic- 
ability of using electrofishing in salt water, and particularly in conjunction with conventional fishing 
methods, including the use of light which might possibly help to bring fish within range of the electric 
fields. Spontaneously formed dense schools of herring and other pelagic fish also appear to offer 
prospects in this connection. 

The International Fishing Clear Congress dealt mainly with the latest types of commer- 
cially important fishing gear and with current thought and experiment concerned with making it more 
efficient and operating it more effectively. This book therefore emphasizes the recent developments 
rather than describing traditional types of gear which have long been used in fishing in various 
countries. 

In the past almost all fishing gear has been evolved entirely by trial and error, but in the 
last few years a small beginning has been made towards supplementing the empirical approach by 
theoretical calculations as is clearly evidenced by Section 6 of this book. When dealing with living 
nature the use of mathematical theory and other forms of pure logic is often severely limited by our 
generally incomplete knowledge of the complex factors affecting the problems under study and 
this applies particularly to fishing where, undoubtedly, many of these factors are still unidentified 
while others have not been properly evaluated. In this respect fishing is in the same boat as many 
fields of engineering, i.e. that theoretical solutions must be carefully checked against empirical 
knowledge and tested in the field before they can be trusted. Thanks to recent technological advances 
we are, however, rapidly learning more about the behaviour of fishing gear under water and the 
reaction of fish to it, and it seems safe to say that we stand at the threshold of a new era where 
systematic gear research will be increasingly fruitful. 

Mention has been made of three major revolutionary changes which have altered the scope, 
nature and effectiveness of fishing, namely mechanization, echo fish finding and synthetic fibres. A 
fourth one is perhaps just around the corner and may be brought about by applying engineering 
theory and rational methods to the development of fishing gear and its operation. 

HILMAR KRISTJONSSON 



[ xxxi ] 



Section 1 : Materials Terminology and Numbering Systems. 



TERMINOLOGY AND COUNT OF SYNTHETIC FIBRE TWINES 

FOR FISHING PURPOSES 

by 
HANS STUTZ 

Farbwcrkc Hoechst A.G., Bobingen Mills, Germany 

Abstract 

The author, speaking as a manufacturer, tries to bring some sort of order into the present day chaos which surrounds textile fibres. 
He gives a comprehensive classification of all kinds of fibres pointing out the difficulties of using different numbering systems as well as 
different units of measurement (cm., g., lb., and inch). 



Resume 



La terniinologic et le numerotage des fils dc fibres synthetiques pour la peche 



L'auteur, parlant en tant que fabricanl, cssaie de mettre de 1'ordre dans le chaos qui regne actucllcment dans le domaine ties fibres 
textiles. II donne unc classification comprehensive de toutes les sortcs de fibres en faisant ressortir les difficultcs a ('utilisation de diffc rents 
systemes de numerotage et dc diflcrcntcs unites de mcsurc (cm., g., et pouce). 

Tcrminologia y numeracion de los hi los sinteticos para artes de pesca 
Extracto 

El autor. hablando como fabricante, trata de ordenar el caos en quc se encuentran las fibras textiles. Para este objeto clasifica 
detalladamcnte todos los tipos cxistentes, senalando las dificultades que ofrece el uso de diverse* sistemas de numeruci6n y unidades de 
mcdida (cm., g. t lb., y pgda.). 



EXTK of agreement on the definition of technical 
terms creates difficulties in translating papers from 
one language to another. Indeed, it is not always 
easy for experts speaking the same language to understand 
each other as a particular term may have several 
meanings. 

NAMES OF FIBRES 

Consider, for instance, the large number of names for 
the various fibres which arc on the market today. At 
first sight they may not seem to have any relationship 
with each other but anyone who makes an effort to 
introduce some kind of order with these fibres will 
recognise that they are connected with each other 



Editor's Note: In editing the papers and discussion for uniformity 
of terms and expression it was found necessary to adopt the following 
standard terminology for "yarn", "twine", "extension*', "elongation", 
etc.: 

1'wine Twisting Stages: 

1st step: fibres spun or twisted into yarn 
2nd step: yarns twisted into strand (or twine) 
3rd step: strands twisted into twine (or rope) 
4th step: twines twisted into cord (or cable) 

Thus nets arc normally made of "twine". 

When describing the various properties of net materials, total 
extension is the increase in length under load. This may consist of 
elastic extension (recoverable on release of stress) and permanent 
elongation. 



in certain ways. Table 1 shows one way of placing the 
variety of textile fibres into a system. 

Most of the fibres used in the manufacture of cordage 
and nets are included, although the list is by no means 
complete as far as trade names arc concerned. 

Two of the problems of terminology which concern 
manufacturers are: 

(1) Tenacity data 

(2) Determining the diameter or thickness of 
filaments, threads, etc. 

SPECIFIC WEIGHT AND TENACITY 

It is customary to measure and indicate the Breaking 
Load of a yarn, filament or thread in kilograms. For 
the purpose of comparing yarns, etc., of different 
thicknesses (yarn count or diameter), a mathematical 
factor, the "Specific Breaking Load" (G), is introduced 
and the "Break ing Length "(R) is known from the spin- 
ning and processing of natural fibres. 

The following relations exist : 

R N m v Pj Nc Yarn count in Mnglish 

Nc *- P number 

Nm metric 

P 3 number 

1 Pj Breaking-load in kg. 

p n P. - ,. Ibs. 

(g/dcn.) PV~ ", er- 

T - Titer in denier or tex. 



"Tdcn 



The specific weight of the great variety of natural and 



MODERN FISHING GEAR OF THE WORLD 

II 




*1 

if 



yacryl 
itrite 



f 













1 






il 



1 ^ 5 C 



c c c o^ S c O o O o c 

iiiHilHliil 



K Q H- K 1- >- O _i 



-O 

JI3 



E o 

3II 



s 

b o. 



Illll 

It 
s! 



"^2 

zf 



I 

- o 
w 

5^ 

I" 



II 

it 

Is 



Is 



|5 

T 

a ^ 


E"E 
E^ 



* Z . 

oj 
II 



s^ 

11 

u6 



ii 





WQ 

|| 



[2] 



SYNTHETIC FIBRE TWINES FOR FISHING PURPOSES 



man-made fibres existing today varies very much, as is 
shown in the following Table: 



Natural 
Fibre 


Y 


(I/O 


Cotton 
Wool 
Hemp 
Flax 
Jute 
Ramie 
Natural Silk 


47 
31- 
48 
43- 
43- 
50- 
25- 


56 

32 

50 
48 
52 

37 



12- 


15 


38 


40 


13- 


20 


35- 


72 


31 


60 


92 





Chemical Fibre 



Polyamids 

Polyester 

Polyacrylinitrile 

Poly vi ny Ichloridc 

Polyvinylalcohol 

Polyethylene 

Regenerated Cellulose 1 50-1 60 



The following relations exist : 

n - P x Nm --, y(kg./mm. 2 ) P -- Breaking load in kg. 
-- Rkm x v(kg./mm. 2 ) Nm Yarn count metric 
9 x G / y(kg./mm. 2 ) y ~ specific weight (g/cm. 3 ). 

With these very different specific weights, the substanc; 
cross-sections of yarns of equal weight are also different 
the cross-sectional areas are inversely proportional to 
the specific weights. When, on the other hand, tenacity 
values arc compared, only the Substance Cross Sectional 
Area is decisive. Hence in the case of two yarns, twines, 
etc., made from fibres of very different specific weights, 
far more accurate and comparable values arc obtained 
by the term "Specific Tenacity"**, which has long been 
applied in testing metals and plastics and which represents 
a force or tension related to the cross-sectional area. 

NUMBERING SYSTEMS 

The second problem, namely the indication of the dia- 
meter or thickness of the yarn, twines, etc., is considerably 
more difficult because of deep rooted and varying customs 
and traditions in the various industries and among 
processors and users. 

To achieve mutual understanding, measures and 
descriptions should as far as possible characterize un- 
equivocally the thickness of yarn, twines, ropes and 
cordage. Experience shows that the thinner the filament 
the greater the difficulty in measuring the diameter. 
Therefore the indirect course was adopted for the fine 
yarns and filaments. The length and weight of a particular 
piece of filament was determined in a relatively simple 
and unequivocal manner. Mathematical calculations 
made it possible to obtain from these quantities the 
count, the length per weight, and the titre, etc. 

Unfortunately various systems of measurements (cm., 
g., lb., inch, etc.) still exist so that even in such a small 
sector of the textile industry as throwsters, rope, cordage 



and net manufacturers there are a multitude of co- 
existing and partly confusing count systems in use as, 
for example: 

Nme, Nee, NCL, Nt, Schokker-Nr, m-weight, denier, 
tex, diameter, circumference (the latter two even in mm. 
and inches). 

it is obvious that these numerous units of measure for 
the same term are confusing, and are contrary to uniform- 
ity and rationalization. However, each industry is 
very reluctant to give up old customs so that the efforts 
made to introduce standards make little headway. 

The man-made fibres industry has always used the 
weight count in accordance with the formula: 
f-+ 

Titre: Td --(den.); G - Weight (g) 



*-* 

Tt - j-(tex); 



L, Length 
(9000 m.) 

L Length (km.) 



The weight count has certain advantages, e.g. for 
calculating more accurately the twist count of coarser 
threads. This is also shown clearly by the recommendation 
of Committee No. 38 (ISO Textiles of the 9th July 1951) 
which states that in the future a weight count with the 
units "tex" should be applied and that it would be sensi- 
ble to adjust this system to metric units of length. 
The formula for conversion of this new unit of measure 
into the units hitherto used is as follows: 



Conversion Formula 



tx 



1000 



590,541 
Ne B 



Nm 
= 0,111 Td = 



1653,52 

NCL " 
10 

Schokker No7 



1 
Nt 



Another peculiarity in establishing the count of net 
yarns and twines, although in general use, is contrary 
to the standards applicable in Germany, DIN 60900. 

A commonly used net twine or cord, is for example, 
"Nm 20/45". On further consideration, however, it is 
found that this means a multiple twist (twine or cord) 
which actually ought to be expressed as follows: 

Nm 20/5/3/3 
Using the tex unit this would be expressed as follows: 

50 tx x 5 x 3 x 3, 
which, by simple multiplication, give the total 

2250 tx (without loss of length during 
twisting) 



3] 



CONSTRUCTION AND NUMBERING OF SYNTHETIC NET TWINES 

by 
G. A. HAYHURST and A. ROBINSON 

William Kenyon & Sons Ltd., Dukinfield, Cheshire, U.K. 

Abstract 

This paper is written from the twine-maker's point of view. The construction of twines is described and the merits of 2, 3 or A 
stranded twines are mentioned. There is also a review of twine si/e descriptions. 



Resume 



Fabrication et numerotage des ills a filets synthetiques 



Ccttc etude est ccntc du point dc vue du fabricant de fil. La fabrication des fils cst dccritc ct il est fait mem ion des a vantages de* 
tils a 2, 3 on 4 brins. Lcs descriptions des dimensions des fils sont aassi passees en revue. 

Fabrication y numeracion de los hilos sinteticos para redes de pesca 
Kxtracto 

En este trabajo, desde el punto de vista del fabncante, se describe en detatle la manufactura de los hilos de 2. 3 o 4 hcbras, as 
como sus meritos. Tambien se pasa revista a las descripciones de la numeracion de los hilos. 



YARNS 

It is sufficient to mention the two main types 

(a) Continuous Filament Yarns 

These have a shiny, lustrous appearance and the 
size or length/weight ratio is usually described by 
denier measurement. Tensile strength varies from 
5 grams per denier up to 8*8 grams per denier when 
tested in the dry state on a straight pull, 

(/>) Staple Yarns 

Appearance is similar to cotton because the 
filaments are cut and spun to form a continuous 
yarn. Size may be described by reference to French 
metric count or English cotton count. Tensile 
strength varies between 2'3 and 3*3 grams per 
denier according to type of fibre, staple length, 
method of spinning, and similar considerations. 



the advantage that the strands cannot become 
displaced due to one strand "riding" over another. 
On the other hand, if one strand is slacker than the 
other, the load falls almost entirely on only half the 
total number of yarns in the cord. In all two strand 
twines the interstices are wide and the angle of lay 
is also wide, so that the twine does not have a 
round appearance. 

The three strand twine is a construction which is 
exceptionally stable and free from distortion, the 
reason being that the sectional view is in the form 
of a triangle which is not easily pushed out of shape. 




TWINES 

Basically the manufacture of twines from single yarns 
consists of two twisting operations, first twisting together 
two or more single yarns to form a strand, and then 
twisting two or more strands together to form a twine. 
This appears deceptively simple and the following points 
merit attention: 

(a) Constructions 

Nearly all fish-net twines are made up of 2 strands, 
3 strands or 4 strands. The two strand twine has 



In spite of the precautions taken in the design of 
modern machinery, one strand occasionally rides 
over another and thus creates a fault in the twine. 
Such faults are infrequent in a good quality product 
and where they do occur the load is borne by at 
least 66$ per cent, of the total yarns in the twine. The 
angle of lay is more acute (compared with 2 strand 
twines), the interstices are narrower, and the twine 
has a rounder appearance. 

Four strand twines of synthetic fibres give an 
exceptionally round formation, which some users 



[4] 



SYNTHETIC FIBRE TWINES f OR FISHING PURPOSES 



seem to prefer, but in fact the lay is easily distorted 
like this: 





This causes uneven stresses, and there is a tendency for 
"riding" strand faults to occur frequently. 

(/>) Twist Constants 

The suitability of the twine for a particular use 
is influenced by the amount of twist inserted into the 
strand and twine. However, mass production 
methods require that one standard be adopted for all 
netting twines manufactured in a factory. The twines 
are therefore a compromise of the characteristics 
most generally in demand and the economic pro- 
duction possibilities. 

Additional twist has four effects: 
(i) Breaking strength is reduced 
(ii) Extension at break is increased 
(iii) Length per weight is reduced 
(iv) Resistance to abrasion and general wear 

is improved. 

Every twine manufacturer has to compromise 
between these factors. It is impossible to have the 
advantage of item (iv) without sacrificing something 
as regards items (i) and (iii). 

(r) Twine Si/e Descriptions 

The most usual description for cotton fish-net 
twines is to state the counts of the single yarn and 
the total number of yarns, e.g. 10s/9 means 10s. 
cotton count, 3 yarns in each strand, 3 strand 
construction. 

Unfortunately, there is no universally adopted 
description method for synthetic fibre twines, and 



confusion is the result. Some Japanese manu- 
facturers have used systems similar to that for 
cotton twines, so that a twine described as 210 
Den/60 will probably be 210 denier, 20 yarns per 
strand, 3 strand construction. Note that the des- 
cription is not quite explicit, for the construction 
might possibly be 210 denier, 30 yarns per strand, 

2 strands or even 210 denier, 15 yarns per strand, 
4 strand. Yet another interpretation would be a 
cabled strand construction giving 210 denier, 15 
yarns, folded 2 ply, 2 strands in cord, or possibly 
210 denier, 10 yarns, 2 ply, 3 strands in cord. 

The Fisheries Research Board of Canada has 
adopted a system which calls for definition by yarn 
denier, number of yarns in strand and number of 
strands in twine. 

Thus 210-33 means 210 denier, 3 ends in each 
strand, 3 strand construction. Similarly 210-63 
means 210 denier, 6 yarns in each strand, 3 strand 
construction. No doubt this system is excellent 
where all persons understand fully that the Fisheries 
Research Board system is being used. It will be 
appreciated that in the Japanese system 210-63 
could mean 21 yarns per strand, 3 strand construc- 
tion. Many other systems could be mentioned as 
examples. 

We would suggest that a simple yet effective and 
easily understood size description system would be 
to state 

(i) Yarn denier 

(ii) Number of yarns in strand 

(iii) Number of strands in twine 

On this basis 210 denier, 6 yarns per strand, 

3 strand would be described as 210/6/3, and it is 
quite certain that everybody would understand this 
system, without any additional explanation and 
without the slightest doubt as to the size and 
construction required. A further advantage is that 
if the strands are sub-divided into 2 or 3 plies this 
can be clearly indicated, e.g. 210/10/2/3 would 
mean 210 denier, 10 yarns, 2 ply in each strand, 
3 strands in twine. 




MIXING 




CARDING 




SPINNING 




I 1 BREAKING- H 


L 






1 




DRAWING 








Conversion of fibres into twine. 



[5] 



TERMINOLOGY AND NUMBERING SYSTEMS USED IN JAPAN 

by 

PROFESSOR SHIGENE TAKAYAMA 

Chief, Fishing Gear and Methods Section, Tokai Regional Fisheries Research Laboratory, Tokyo, Japan 

Abstract 

Technical terms and numbering systems differ from country to country and there exists today no standard for comparison. Fisheries 
technologists find it difficult to compare the characteristics of materials and gear when studying foreign publications, and placing orders for 
gear is a problem to the fishermen. It would be beneficial to the whole industry if an international standard of terms and measurements 
could be agreed upon. As an example, a description is given of the specification of fishing twines now used in Japan. 



Resume 



Terminologie et Systemes de Numerotage au Japan Utilises 



Les termes techniques et les syst ernes de numerotage different cTun pays a 1'autrc, et actuel lenient il n'existe aucun talon de comparai- 
son. Pour les specialistes des peches il est difficile de comparer les caracteristiques des materiaux et des engins quand ils etudient les publica- 
tions etrangeres. De meme c'est un probleme pour les pecheurs quand il s'agit de commander des engins. II serait bon que toute 
1'industric se mette d'accord sur des termes et des mesures standard ct internationaux. Comme exemple, il est donn une description dc la 
specification des fits de peche utilises uctue I lenient au Japon. 

TerminoloRia y Sistemas de Numeration Usados en el Japon 
Extracto 

Los lerminos tccnicos y sistemas de numeration dificren de un pais a oiro, no exist iendo en la actual! dad norm as de comparacion. 
For estos motives, los tecnicos pcsqucros tropiezan con dificultades al cotejar las caracteristicas de los materiales o de los artes que se 
dcscribcn en publicaciones extranjeras. Estas circunstancias tambicn son un prohlema para el pescador cuando desca adquirir dicho equipo. 

Seria beneficioso para toda la industria acordar la normalization intcrnacional de terminos y medidas. Como ejemplo de esto se 
dcscriben las esnecificaciones de los hilos para artes de pcsca que se usan actualmentfc en el Japon. 



TECHNICAL terms and numbering systems related to 
fishing gear and its operation often differ from area to 
area, depending upon customary practices of fishermen. 
Thus, a standardi/ation of the terms and system is not easy 
even in a single country and still more difficult on an inter- 
national scale. In Japan, British measurements are used side 
by side with the metric system, despite the fact that the latter 
has been encouraged by the Government for years. However, 
fishermen of the country prefer their own traditional denom- 
inations, taking little heed of the other systems. 

It is felt, nevertheless, that simplification of the terminology 
and the numbering system, once established on an inter- 
national scale, would make an invaluable contribution to 
advancement of fishing techniques. It would benefit fishing 
gear technologists reading foreign publications, and fishermen 
and others in related industries. Standardized measurements 
would also eliminate many difficulties between fishermen, 
experts, gear manufacturers, their export agencies, and so 
forth in technical assistance programmes. 

We would like to make the following suggestions: 

1. That Member Governments and their qualified personnel 
be requested to report to FAO all the technical terms that 
are used in major types of commercial fisheries in their 
countries, with descriptive explanations and/or illus- 
trations. 

2. That Member Governments be requested to aim at 



adjusting or simplifying technical terms as much a 
possible in accordance with a numbering system or on 
any other rational basis. It would be desirous to set out 
the relationships between their own systems with those 
existing in other countries. 

3. That the Secretariat of FAO compile and publish, on the 
basis of the reported data, regional classifications of the 
terms, numbering systems, conversion tables and any 
other pertinent reference, for distribution among the 
countries interested. 

It is suggested that FAO endeavour to extend advice and 
assistance wherever needed on how to indicate standards for 
fishing materials and equipment. 

Furthermore, we hope that Fisheries Division of FAO will 
encourage the Member Governments to promote standard- 
ization in the various methods and procedures now employed 
in the different fisheries research organizations in experiments 
on fishing materials, equipment and methods, so that the 
results can be brought to a comparable basis. 

Such action would be in accord with the work of FAO in 
promoting the use of modern fishing gear and techniques 
throughout the world. 

SPECIFICATIONS OF FISHING MATERIALS IN 
JAPAN 

So far as Japan is concerned, this is how we specify various 
items of fishing gear materials: 



[6] 



TERMINOLOGY AND NUMBERING 



2. 



4. 



5. 



6. 



Raw Material: the raw materials used for fishing nets 
and ropes are: 

1-1. Cotton (American, Indian or Egyptian cotton) 
1-2. Flax 1-3. Hemp 1-4. Ramie 1-5. Manila 
1-6. Sisal 1-7. Maguey 1-8. Coir 1-9. Rice straw 
1-10. Silk 1-11. Synthetic fibre (Nylon, Vinylon, 

Vinylidene, etc.) 
1-12. Others 

Yarn Number: different counts of yarn are used according 
to kinds of raw material: 

2-1. For Cotton: English count system is used, in which 

840 yards X N 

Count number N = 

1 pound 

2-2. For ramie and flax: 

300 yards x N 



Count number N = 
2-3. 



2-4. 



Denier number N 



1 pound 

For silk and synthetic fibre: Denier system is used, 
in which 

For synthetic spun yarns: English cotton numbering 
is used. 

450 metres of a yarn 

0.05 gr. ~<~N 

Direction of Twisting: Left twist is indicated by *Z* 
right twist by 4 S\ 

Degree of Twisting: A degree of twist is indicated by the 
number of twists in a unit length (0-25 metre). It is 
ordinarily denoted by terms: soft, medium, hard, or 
extra hard. 

Number of Strands: is specified as 2 strands, 3 strands, 
4 strands, and so forth. The term "strand" is used as 
defined in the next paragraph. 

Denotation of Thread, Twine, Rope and Cord: The 
following formula may help one understand the relation 
between various composites of a thread and so forth. 
Fibre 1 

[ r Yarn '] 

J J- Strand 1 f Thread 

J ! J } Twine 

J I Rope 

As seen above, a number of fibres are twisted into a yarn; 
a number of yarns into a strand, and again a number of 



strands into a thread, twine or rope. Usually, the term 
thread is used for small sized material, twine for medium 
size, and rope for material large in size. 

7. Size of Thread, Twine and Rope: 

7-1 Diameter system is usually employed for indicating 
the size of thread and so forth. 

7-2 Size of twine and rope is sometimes indicated by the 
weight for a unit length as **monme"/5 ft. (One 
"monme" approximates 0*13 ounce or 3*75 grams.) 

7-3 Numbering system of cotton thread is also used by 
counting the number of yarns in one strand. Cotton 
No. 1 has two strands, one strand consisting of two 
yarns, but the other numbers of cotton thread have 
3 strands. 

8. Denotation of Net Material: By use of the above indica- 
tions, a piece of net material which consists of a thread, 
for example, count 20, 2 yarns twisted, 3 strands, may be 
expressed as 20S/2/3 or 20/2/3S. Another example, 210 
denier, 6 yarns, 3 strands left twisted thread 210d/6/3 left 

ply. 

9. Conversion Table: of various items pertaining to fishing 
gear whose indications may vary from case to case, the 
following has been prepared as an example. 

Conversion Table for Size of Yarn, etc. 
(Denier to English Count) 



Denier 


English Count 


Denier 


F-nglish Count 


10 


531-5 


90 


59 1 


20 


265*2 


100 


53-2 


30 


177-8 


120 


44'3 


40 


132-9 


150 


35-4 


50 


106-3 


200 


26-6 


60 


88*6 


250 


21-3 


70 


75-9 


300 


17-7 


80 


66*4 


500 


10-6 






1000 


5'3 








5315 


Correlation Formulae: English 


count 


denier 








5315 



Denier 



Eng. Count 




Main operation stages in net manufacture. 



[71 



YARN COUNT OR NUMBERING SYSTEMS 

by 

BRITISH STANDARDS INSTITUTION 

London, U.K. 

Abstract 

There are many different ways of designating yarn count or number, and these can be classified as either a direct system, in which 
the yarn count or number is expressed in terms of its mass per unit length or an indirect one, in which the count or number is stated in terms 
of its length per unit mass. It has been recommended that the Tex system should be universally used and, as it will take some time to 
implement this recommendation, it is suggested that whenever the traditional yarn count or number is used, the Tex equivalent should also 
be quoted. Conversion tables are given for changing from one system to another. 



Rfeumt 



Syst&mes dc numcrotage dcs fils 



11 existe un grand nombre de types de numerotage des tils. On peut les classer suivant deux met nodes: le systeme direct dans lequel 
le numdrotage du fil est exprim* d'apres son poids par unit6 de longueur, ou le systeme indirect, dans lequel il est exprim6 d'apres sa longueur 
par unite de poids. On a recommend^ 1'adoption universelle du systeme TEX et, en raison du delai n&essaire sa mise en application, il 
est suggerc de mentionncr cgalement I'equivalent d'apres le systeme TEX, chaquc fois que Ton utilise le numcrotage trad it ionnc I des fils. 
On trouve dans cet ouvrage des tables de conversion pcrmcttant de passer d'un systeme a un autre. 

Sistema de numeracion de los hilos 
Extracto 

Las sistemas de numeracion de hilos pueden clasificarse en directis, o sea, expresando el niimero en terminos de su peso por unidad 
dc longitud o, indirectos, considcrando la longitud por unidad de peso. Se ha recomendado adoptar universalmente el sistema "Tex" (peso 
de 1 Km. de hilo expresado en gramos; pero como esto tomar tiempo, se sugiere que al utilizar el sistema de numeracion tambien se dc cl 
cquivalente en unidades "Tex". 

En el trabajo tambien se incluyen tahlas de conversi6n para los diversos sistemas. 



THE many ways of designating yarn count or 
number may be classified into two systems, (a) the 
Direct System in which the yarn count or number 
is expressed in terms of its mass* per unit length, and 
(b) the Indirect System in which the yarn count or 
number is expressed in terms of its length per unit mass. 

With the increasing use of yarns containing more than 
one kind of fibre and of fabrics containing yarns made 
from different fibres, it has become evident that the 
adoption of a single yarn count or number system would 
avoid confusion and save time. 

The International Standards Organization conference 
held at Southport in 1956 recommended that a universal 
direct system should be adopted by all member nations 
and that it should be the Tex system described below. 

Inevitably, some time will be required to implement 
this recommendation. It is therefore suggested that 
wherever traditional yarn count or number is mentioned, 
the equivalent Tex value should he given in brackets. 

TEX SYSTEM 

The yarn number in the Tex system is obtained by divid- 
ing the weight of a given length of yarn (expressed in 

* The term mass is normally used to describe the quantity of matter 
in a body: the term weight describes the force exerted by gravity 
on a body. To continue to use the word weight when one means mass 
leads to confusion when the yarn number is used in derived quantities 
such as tenacity. 

Based on B.S. 947 Yarn Count Systems and their conversions. 



grams) by its length in kilometres; the unit in this system 
is the Tex multiples and submultiplcs recommended in 
preference to other possible combinations are mg. per 
km., named millitex, and g per m or kg. per km., named 
kilotex. Where a symbol is needed (e.g. in formulae) to 
represent the yarn number in Tex, it is recommended that 
this symbol should be the capital letter N. 

DIRECT SYSTEMS 

System Unit of Mass Unit of Length 

Tex Gram Kilometre 

Denier gram 9,000 metres 

Linen (dry spun), pound 14,400 yards 
Hemp, Jute (spindle) 

INDIRECT SYSTEMS 



Unit of Length Unit of Mas\ 

840 yards (hank) pound 
1,000 metres i kilogram 



System 

Cotton (British) 
Cotton 

(Continental) 
Linen (wet spun) 300 yards (lea) pound 
Metric kilometre kilogram 

CONVERSION 

Within either direct or indirect systems, conversion from 
one yarn number to another is done by means of multi- 



[81 



NUMBERING SYSTEMS 



plying factors. These factors can be conveniently arranged 
in tabular form. 

Table I gives the multiplying factors for converting 
from one to another of selected direct systems. 



For conversion from an indirect system to a direct 
system, and vice versa, a constant into which the known 
yarn number is divided is necessary. Commonly required 
constants are set out in Table 111. 



TABLE i 

Multiplying Factor for Converting from one Direct System 
to another 

Multiplying factor to give yarn numher 



Known yarn 
number in 


Tex 


Tex 

Denier 
Linen (dry spun). 
Hemp, Jute 


1 
0111 1 

34-45 



Denier 



y.ooo 

I 
310.0 



Linen (dry spun) 
Hemp* Jute 

29 03 
0-003 225 

1 



Example: The equivalent of yarn number 10 in the linen (dry 
spun) system is the yarn number 10 ,- 34 '45 or 344"5 in the Tex 
system. 

Table II gives the multiplying factors for converting 
from one to another of selected indirect systems. 

TABLL II 

Multiplying Factors for Converting from one Indirect System 
to another 



Multiplying factors to give equivalent count in 



Known count in 



Cotton and spun 

silk 

Linen (wet spun) 
Metric 



Cotton ami 
Spun Silk 



0-357 I 
0-590 5 



Linen 
(wet xpun) 

2.800 
1 
P653 5 



Metric 
Count 



1-693 4 
0*604 8 

1 



TABLE III 

Selected Constants for Converting from Direct to Indirect 
Systems and Vice Versa 



Constant into which the known yarn count is 
divided in order to obtain the equivalent yarn 
numher in the other systems 









Linen (dry spun) 




Tex 


Denier 


Hemp, Jute 


Cotton and spun 
silk 


590-5 


5 315 


17-14 


Linen (wet spun) 


I 654*0 


14 880 


48'00 


Metric 


1 000 


9 000 


29-03 





For the conversions from British units to metric units 
and vice versa the following equivalents have been used: 

1 yard -- 0-91440 metres 
1 Ib. 453-592 grams 




Throwing ca.\t nets on a lake in Indonesia. 
[9] 



Photo FAO 



TERMINOLOGY AND NUMBERING SYSTEMS DISCUSSION 



Mr. J. E. Lonsdale (U.K.) Rapporteur : Just as in this room 
we speak many languages, so do we have many ways of 
describing fishing gear, fishing methods and the properties of 
fishing materials. There is a r*~ed for all interested in fishing 
to know what other people * an when they talk about these 
subjects, particularly when .ey must compare the properties 
of different types of net. This concerns not only the fishermen, 
who want to compare the various fibres and textile materials 
from different countries, but also scientists and manufacturers. 

The first difficulty is that of translation. It is often impossible 
to find correct translations for technical words which carry 
exactly the same meaning. These papers make no specific 
references to the difficulties of translation but a good deal of 
work on this problem has been carried out by the Institut 
fur Netz-und Materialforschung, Hamburg; their Paper 
No. 77 deals with fishing gear nomenclature. The next 
difficulty is in the use of trade names, variations occurring 
even in one class of textile fibre, from country to country and 
from manufacturer to manufacturer. 

The papers before us give us two main ways of describing 
the properties of textiles. The first is the strength of the net or 
twine, and the second is the weight of the net or twine which 
is, of course, of importance commercially. But firstly the size 
of the yarn, and then the size of the twines must be described. 

To clarify the terms "twine" and "yarn" I will adopt the 
definition given in Dr. van Wijngaarden's paper (No. 6). 
A "yarn 1 * is a continuous strand of fibres and/or filaments 
from which all twist, if any, can be removed in one untwisting 
operation, and "twine" is the product of twisting together 
two or more yarns. The basic yarn may be a continuous 
monofilament, a continuous multifilament, or a yarn spun 
from short lengths of fibre. 

Yarn Size. The size of yarns cannot easily be described by 
thickness and diameter because of the practical problems 
involved. It is more common to describe size by the weight 
method either directly, that is by giving the weight for a fixed 
length, or indirectly, by comparing it to a yarn of standard size. 

The main systems in use throughout the world are: 

(1) The Tex System. Tex is a theoretically attractive unit 
but is not yet in practical use. It is attractive because it is a 
c.g.s. unit, a metric unit based on centimetres and grams. The 
tex is the weight in grams of one kilometre of the yam. 

(2) The Metric System (Nm.) giving the number of 
kilometres of the yarn which weigh one kilogram. It is 
therefore a reciprocal of tex multiplied by 1,000. You will 
notice that in the case of tex the heavier the yarn the greater 
the number, but in the case of Nm. the heavier the yarn the 
smaller the number. 

(3) The Denier System (den.) is in very widespread use. 
This is the weight in grams of 9,000 metres of the yarn. This 
is also a c.g.s. unit, but introduces a factor of 9. 



(4) The English Cotton Count (N.e.) which is an indirec 
non-c.g.s. system and is the number of hanks, each of 840 
yards which weigh one pound. 

Mr. Shimozaki (Paper No. 75) suggests relating twine 
thickness to a cotton yarn of 20*s cotton count a size in 
common use. The size will then be called the C20 equivalent. 

The papers give some 25 other methods of describing size, 
but fortunately not all of these are used in fishing technology. 
This does raise the important question of whether there should 
be one or possibly two international methods of measuring 
size, and what attempts should be made to rationalize systems 
of size numbering, particularly in view of the international 
nature of fishing. There is a natural reluctance on the part of 
manufacturers to change from their old standard of measure- 
ment. The paper that puts forward the advantages of a tex 
system (52) suggests that it should first be introduced as an 
addition to the older systems. This subject of standardization 
has been worked on by textile bodies for a number of years 
and among those who have made recommendations on the 
subject are the Bureau Internationa] pour la Standardisation 
de la Rayonne et des fibres synthetiqucs, the American 
Society for Testing Materials, BISFA, the British Standards 
Institute, the Textile Institute and a number of other bodies. 
Suggestions for standardization come mainly from technolo- 
gists and fibre manufacturers. The papers before us do not 
reveal what the fishermen think about this subject. 

Construction. A number of methods exist to describe the 
construction of the twine from individual yarn. Examples of 
methods for describing the same fishing twine are as follows: 

(1) 100 Tex Z 200 X 2 S 300 x 3 Z 400 

The term 'Z' and 4 S' refer to direction of twist, and fortunately 
are now fairly standard. The numbers 200, 300 and 400 refer 
to the degree of twist in turns per metre. 

(2) 210 X 2 X 3 

This is similar to the first example, but omits twisting descrip- 
tions. 

(3) 210 x 23 denier 

This is referred to as size 23. 

(4) 1,260 denier 
This being the total denier. 

(5) 126 obtained by dividing the gross denier by 10. 

From the papers it would appear that the lengthy and 
accurate way serves a different purpose to the shorter way, 
but obviously the quick method (which appeals to fishermen) 
can lead to confusion. Perhaps there is a need to standardize 
on two methods, a longer one for manufacturing purposes and 
a short one for commercial use. 



[10] 



DISCUSSION ON FIBRES AND SYSTEMS 



An important part of the papers is devoted to the measure- 
ment of strength. The strength of a twine is expressed as the 
breaking load in pounds or kilos. To compare different yarns 
or twines, it is necessary to express the load divided by the 
size of the yarn or twine. Usually size is measured by the 
weight system just mentioned. However, it is also an advantage 
to choose other expressions so as to compare different textile 
fibres more easily. These points are very fully discussed in the 
papers, particularly by Stutz (79), Arzano (80), and Carrothers 
(16). Two useful units for strength measurement often 
mentioned in the papers are, first the length of twine whose 
weight equals the breaking strength of that twine, i.e. breaking 
length. Second, there is the unit which is related to the 
breaking length by specific gravity, so as to compare fibres of 
different specific gravities. This measures the load per cross- 
sectional area. All these strength measurements are further 
complicated by whether c.g.s. units or other units are adopted. 

Apart from the papers listed in the programme, Papers 
Nos. 16, 80, 95 and 104 also have some relevance to this 
subject. 

Dr. A. von Brandt (Germany): In Germany there are three 
main numbering systems for materials: the English cotton 
number; the metric number; and the denier system. Sometimes 
other numbers are invented by the net makers themselves. 
Three papers propose the tex number. One proposes that 
the tex number should be in addition to the national numbers. 
That is, 1 believe, a good idea and could help us to understand 
each other. On this subject, one should hear not only the 
textile people but also and more important the fishermen 
and net makers. 

Mr. H. Warncke (Germany): My firm is a net manufacturing 
company. We have found no major difficulty in interpreting 
any definition given either by the English, metric or denier 
systems. However, a designation of international importance 
should be useful, and as a net maker 1 feel that the system used 
should be followed by a tex number in order to accustom the 
fishermen to the new system, and thus make way for the 
eventual use of the tex system alone. 

We use the metric system for the Eederal Republic of 
Germany and inside the factory, and the English system in the 
trade with foreign countries. In the net industry the composi- 
tion of twine is mainly given by one size only, and this 
complicates the use of the tex system. For instance, the 
English term 9-ply, which is always 3 times 3 strands, is 
merely designated by *9", without specifying the composition 
of the twine. This, however, has been found sufficient to 
meet our requirements. 

Mr. H. C. Smith (Netherlands): As a net maker, 1 fully agree 
with Mr. Warncke. Great confusion is caused by these 
numbering systems and we feel it would be in the best interest 
of the fisherman if all the net makers adopted the tex system. 
I am not in favour of using two systems; i.e. the old system 
followed by the tex system. We have to get the fishermen used 
to one system and 1 think it should be the tex system. It will 
certainly take some time, maybe 2 or 3 years, before the 
public will become accustomed to it, but it will contribute 
to a better understanding of the numbering of yarns. 

STATEMENT FROM NETHERLANDS 



out that four classification systems arc officially and uni- 
versally applied to yarn. 

1. The English yarn number (Ne,) for the classification of 
cotton yarns and spun yarns, manufactured from synthetic 
fibres. 

2. The English yarn number (Nc 2 ) for the designation of 
linen and hemp yarns. 

3. The metric yarn number (Nm) for the designation of 
cotton yarns and spun yarns from synthetic fibres. 

4. The denier system for the designation of yarns from 
continuous filament synthetic fibres, such as nylon. 

It is difficult even for experts in the industry to convert one 
numbering system to another to compare yarns. As far as 
synthetic yarns are concerned, it is often impossible to make 
a comparison on the basis of the number indication only. The 
composition of a yarn must be established by a test. How 
confusing therefore must the numbering be for the fisherman 
who has to be certain he buys the right yarn. 

It would be logical and most profitable to adopt the Tex 
system, rather than add it to the existing systems. 

The Tex numbers should also indicate how the yarn has 
been composed. 

This can be affected by indicating the twined yarns by num- 
bers and/or figures, connected by an X-mark and preceded by 
the indication Tex, Millitex and Kilotex The numbers in 
order of sequence could show: 

1st: which yarn has been used for the construction of the 
finished yarn in units of the Tex system. 

2nd: how many threads are twisted for the first twining. 

3rd: whether the second twining is 2, 3 or 4-ply. 

4th: the direction of the twist, indicated by the letters s 

and z behind each number. 

This system of yarn numbering, if practised universally for 
twined yarns, would enable the manufacturer and the 
trader to use the same numbering and would make a compari- 
son between various yarns and different raw materials much 
easier because all numbers would be indicated in Tex units. 

Some examples by way of illustration 

Old system 

Ne, 20/12 cotton 3-ply z-z-s. 

Nc, 20 = Tex 29,4, rounded off to e.g. Tex 30. 

Twist of yarn z, 1st twining z, second twining s. 



New system 

Tex 30z 4z 
Tex 30 ; : 4 

Old system 

Nylon Td 210 



3s cotton or 
3 z-z-s cotton. 



24 3-ply z-s. 



Apeldoornse Nettenfabriek (Netherlands): in a written 
statement on a plea for a universal numbering system. He set 



New system 

Tex 23 ;< 8z , 3s nylon or 
Tex 23 x 8 X 3 z-s nylon. 

Mr. H. Kobayashi (Japan) : As far as Japan is concerned, the 
denier system is preferred for monofilamcnts as well as 
continuous multifilaments, while English count is used for 
spun nylon yarn and also for cotton yarn. 

Mr. Rack (Northern Rhodesia): Our interest is in gillnet 
fishing and our fishermen are just emerging from very 
primitive methods. We need a system which will be uniform. 



in i 



MODERN FISHING GEAR OF THE WORLD 



Our fishermen arc primarily interested in the following: the 
diameter, expressed in a constant term; (this is important to 
the gillnet fishermen who are buying yarn for making and 
mending nets); the runnage; i.e. the amount of twine he will 
get to his given weight; and the breaking strength. At present 
large quantities of twine are sold without even a written 
guarantee that they are made of a certain synthetic fibre and 
not a blend of fibres, and it would be our suggestion to intro- 
duce Merchandise Mark Acts in which we might invite the 
manufacturer to state the specification. This would, we hope 
be one which our government officers could check in our own 
laboratories. 

Mr. S. Krohn-Hansen (Norway): It might be better to use the 
metric system than the tex system, because then the fishermen 
know the runnage how many metres there are to a kilo. 
The metric system is in use in Norway with other generally 
used numbering systems, and 1 would suggest it as an inter- 
national standard system. 

Mr. A. Percier (France) : I would support the adoption of the 
metric system which is the most widely used and because it 
is easier for the fishermen to learn and would generally be more 
useful. The Tex and the Tex and Denier systems are more 
complicated. 

Mr. J. K. van Wijngaarden (Netherlands): In the textile 
industry and in other scientific and technological fields attempts 
are being made to standardize measuring systems based on 
the c.g.s. system. The tex system does not only have a following 
in the textile industry but also throughout the scientific and 
technological fields. 

Mr. A. O'Grady (Australia): We import our netting material, 
and the fishermen are accustomed to using the English yarn 
counts number. With the introduction and growing popularity 
of the synthetic fibres, plus the added problem of import 
restrictions, we find that a fisherman will deal with a particular 
firm, changing to another only when that firm is out of stock 
of what he requires. One firm may perhaps be using the 
nylon numbering, 210/3; the alternative firm may be using 
only, say, No. 6 nylon thread number. But instead of making 
the purchase easier for the fisherman, this simple numbering 
leads to confusion. Irrespective of what system is decided 
upon, we should have one only. Initially we might, however, 
retain the old measuring system which the fisherman knows 
and also print the new equivalent on the label of the bundle 
of netting. Eventually the fisherman will get used to the new 
system and adopt it. 

Mr. H. Keller (Switzerland): I am of the opinion that the 



metric numbering system is the best and most practical for 
use between the producer and the fisherman. It is almost 
impossible to devise a system to cover all the characteristics 
of certain materials. 

Captain D. Roberts (U.K.): I am skipper of a Grimsby 
trawler. Last week I was fishing at Iceland and next week I 
shall be fishing at Iceland. 1 like to read publications from 
Holland, Norway, Germany, besides from my own country, 
and it takes me a long time to work out the difference of these 
measurements. From a practical fisherman's point of view, 
I do not mind what system is used as long as it is one system 
alone ! 

Mr. D. Olafsson (Iceland): I would like to support what has 
been said by various delegates here, on the necessity of agree- 
ing on some unification of the numbering systems. I know the 
fishermen in Iceland have great difficulties in choosing net 
materials because of the many different numbering systems 
used. There is one question I would like to ask: are these 
discussions going to be followed up by some action by FAO 
or by some other institution, or are we going to wait indefinitely 
before we get something practical done? I know that many 
of the people here would like to sec something practical 
coming out of these discussions. 

Mr. H. Kristjonsson (FAO), General Secretary: We have in 
mind to appoint today a small Working Group to study this 
complex problem, and report back to the Congress on 
Saturday. What action we can take thereafter depends on 
the findings of that Group. 

This Congress itself cannot pass any binding resolutions: 
it will be the aim of the Working Group* to indicate a 
solution to the problem. Various international bodies are 
directly concerned with the unification of standards, and FAO 
will collaborate with them. 

Mr. J. E. Lonsdale (U.K.) Rapporteur: To summarise this 
discussion, the fishermen with one voice have said "let there 
be a simple and uniform method of numbering". 

The fibre scientists and technologists have suggested the 
tex system, which is not yet in practical use. Between the 
fibre manufacturers and the fishermen there are the twine 
and net manufacturers, and any simplification of numbering 
systems inevitably start in that section. 



* Later in the day a Working Group on Terminology and Numbering 
Systems was formed, consisting of representatives from fibre manu- 
facturers, net makers and gear technologists. Mr. Lonsdale was 
appointed Chairman. 



[12] 



Section 2: Materials Characteristics of Fishing Twines and Their Testing. 



MAN-MADE FIBRES 

The Synthetic Polymer Fibres and Filaments ; their general characteristics, chemical and biological properties, with 

special reference to their use in Fishing Gear 

by 

R. ARZANO 

Chairman of the Industrial Uses Sub-Committee of International Rayon and Synthetic Fibres Committee. 



Abstract 

This paper deals with the following synthetic fibres: Polyumides (Nylon, Perlon and Rilsan); Polyesters (Terylene); Vinyl Fibres 
(Saran, Polyvinyl chloride, Courlene and Courlenc X3, and Vinylon). Basic information is given about these fibres, with special reference to 
iheir uses in fishing gear and also their employment (mixed with cotton or wool) in the manufacture of fishermen's protective clothing. The 
traditional seaman's jersey can be made of a blend of 50 per cent, viscose staple and 50 per cent, wool, or 15 per cent, nylon, 35 per cent. 
viscose rayon staple and 50 per cent, wool, anil (hese mixtures can also be used for very serviceable sea-boot stockings. 



Resume 



1/es fibres synfhetiques 



Cettc communication traite des fibres synlhetiques suivantes: Polyamides (Nylon, Perlon et Rilsan); Polyesters (T^ryldnc); Fibres 
vinyliques (Saran, chlorurc de Polyvinyl, Courlene et Courlene X3, et Vinylon). On donnc des renseignements fondamentaux sur ccs fibres, 
en particulier sur leur cmploi dans les engins de peche et aussi (melangecs au coton ou a la laine) pour la fabrication de vgtecnents pro- 
tecteurs destines aux pecheurs. Le chandail traditionnel du marin peut etre fait avec un melange de 50 pour cent, de fibres de viscose et 50 pour 
cent, de lainc, ou 15 pour cent, de nylon, 35 pour cent de fibres de viscose rayonne et 50 pour cent, de lainc, et ces melanges peuvcnt aussi 
s ervir i\ faire des bas qui sont d'une grande utility dans les bottes de mer. 

Fibres artiflciales 
Extracto 

Hste trabajo trata de las fibras sinteticas de los siguientes materiales: Poliamidas (nylon, perlon y rilsan); poliesteres (terileno); 
I'inilo (saran, cloruro de polivinilo, "courlene", "courlcne X3" y vini!6n). Tambien conticne informacion basica sobre estas fibras y su 
cmpleo (mezcladas con algoddn o lana) en la confeccion de prendas de vcstir para proteger a los Pescadores. El tradicional "sweater" 
marinero puede tejerse con una mezcla de 50 por cent de hilado de viscosa, y 50 por cent, dc lana, o 15 por cent, dc nyl6n, 35 por cent dc 
hilado de rayon con viscosa y 50 por cent de lana. hstas mezclan tambien se utilizan para tejer calcctas muy durables que se usan con botas 
de mar. 



GENERAL 

HIG H polymer chemistry, called also macromolecular 
chemistry, is a very young science, dating back only 
35 years. The term "macromolecule" was first in- 
troduced in 1922 by Staudinger, who used it to describe 
the high molecule hydrocarbon obtained by the hydro- 
genation of natural rubber. Since then a great deal of 
research has been carried out and eventually, as a result of 
work started in 1928, W. H. Carothers, discovered a fibre- 
forming synthetic condensation polymer, for which the 
name "nylon" was coined. The discovery was made public 
in 1938. 

The researches of W. H. Carothers and his associates 
led, within a relatively short time, to further important 
developments in the field of polymers, and to the 
discovery, by Whinfield and Dickson, of polyester fibres 
from polyethylene therephthalate (1939-41). 

During the period 1939-1940 a great expansion took 
place in high polymer research. Some old polymers were 
carefully reinvestigated and many new ones discovered. 
But the effect of the discoveries and researches made 



during the 1930s and the 1940s have not yet been fully 
investigated, and their impact is not yet fully realised. 

Besides polyamides and polyesters, the production of 
many new synthetic fibres -polyethylene, polyacryloni- 
trile, polyvinyl chloride, polyvinylidene chloride, poly- 
urethanes and various vinyl copolymers was also 
started and reached the commercial stage. 

The chemical industry was thus given the opportunity 
of producing a wide variety of new fibres, the character- 
istics of which could be, to a point, modified in order to 
make them suitable for specific needs and end-uses. It 
has been rightly stated by Harold DeWitt Smith 1 that 
"mankind has initiated a second great textile project, 
namely, the creation of textile fibres". This implied, 
however, extensive research for improving, on one hand, 
the characteristics of the fibres for the various applica- 
tions and developing, on the other, new uses or expanding 
already accepted ones. 

At the same time the vast industrial expansion of the 
post-war years called for ever increasing quantities of 
those specialized products known as "industrial textiles" 



f 131 



MODERN FISHING GEAR OF THE WORLD 



and imposed more and more exacting requirements. 
The new synthetic fibres have enabled the textile industry 
to keep abreast of the increased demand and to meet 
successfully the particular needs of processes and trades 
using textiles. 

The industrial use of man-made fibres has increased 
very rapidly. In the United States, industrial uses took a 
substantial proportion of man-made fibres in the early 
1950s; in England, 34 per cent, of all continuous filament 
man-made fibre yarn went to industrial uses in 1953 and 
1954 2 . 

Industrial textiles comprise, however, a very wide 
range of products, from cloth for filter presses to con- 
veyor belts, from tyre cords to tarpaulins, from ropes 
and cordages to boat sails, from cigarette filter tips to 
fishing nets. Each of these applications requires efficient 
and lasting performance, under the respective conditions 
of use, and the textile technologist has to meet very 
different needs and stringent specifications. In the case 
of industrial textiles, quality is of paramount importance 
and where these products are part of a process, a break- 
down in performance will at least cost money and may 
even cost lives. It is imperative, therefore, that quality 
and performance characteristics be of the highest possible 
standard. 

Not so many years ago, we could hardly speak of a 
"fishing industry". For thousands of years, fishing had 
been a handicraft and down the ages the methods and 
equipment showed little progress. Now the picture has 
changed, and is changing, rapidly. To keep pace with 
development, scientific and application research is 
essential; the more the properties of the various fibres are 
known, the better we shall be able to employ them in the 
most useful and appropriate way. 

PROPERTIES 

The following main properties of fibres are to be specially 
considered for use in the fishing industry: 

Density 
Tenacity 
Tensile strength 
Knot strength 
Loop strength 
Elastic properties 
Toughness 
Stiffness 
Water absorption 

Effect of: heat 
age 

sunlight 
chemicals 
sea-water 

Resistance to bacteria, mildew and insects 

Density. According to J. T. Marsh 3 "the density of a 
substance is the quantity of matter contained in unit 
volume". The relative density is the ratio of comparison 
between a given substance and a standard one (usually 
water). 

When the C.G.S. System is used (unit of volume : c.c., 
unit of mass : gram-standard substance : water at 4 deg. 
C.) the values of absolute and relative densities are 



identical. Specific gravity and specific volume are 
reciprocally proportional, so that the lower the density, 
the higher the bulk and vice versa. 

Strength is a general name for defining both tenacity and 
tensile strength of fibres. The difference between these 
two terms is clearly stated by Marsh 3 as follows: 'Ten- 
acity is the breaking force in terms of the fibre or yarn 
denier, whereas tensile strength is the breaking force in 
terms of the unit area." The first is expressed in terms of 
grams per denier, the latter in terms of grams per square 
millimetre. In this respect, it must be pointed out that 
values for tenacity are not directly comparable, as they 
do not take into account the density of the material; 
values for tensile strength, on the other hand, are directly 
comparable. 

The breaking force is often expressed as "breaking 
length" which according to "Textile Terms and Defini- 
tions" 4 is: "the length of a specimen whose weight is 
equal to the breaking load" 

The conversion formulae are: 

breaking length (in Km.) = 9 tenacity (in g/den.) 

tensile strength (kg./mm. 2 ) breaking length 

(in Km.) ** specific gravity. 

Knot strength is the tenacity of a fibre or a yarn in which 
a plain knot has been tied. As Prof. Vivianr* points out 
"the knotting test may give an idea of the transverse 
strength of the fibre". The ratio of the knot strength to 
the single fibre or yarn strength gives the effect of bending 
due to the tying of the knot. 

Loop strength. To show to what extent a fibre or a yarn 
is affected by bending, the "loop strength ratio" is a very 
useful figure. To determine this value the free ends of 
linked loops of fibre or yarn are secured in the grips of 
the testing machine, and the load required to break them 
is found. 

Elastic properties, i.e. extensibility and elastic recovery 
of a fibre are as important as strength. Too much stress 
has been placed on tenacity as the most valuable property 
of textile materials and, although high breaking load is of 
significance, extensibility is at least of equal importance. 
An inextensible fibre, or a fibre possessing very poor 
extensibility even when combined with high tenacity is 
of little actual value, if the extension at break is con- 
sidered 3 . For the evaluation of a fibre, however, the 
extension at break is not the only point to be considered; 
from the practical point of view, the behaviour of the 
fibre when stressed or extended to a degree not reaching 
the breaking point is of great value. 

The elastic behaviour of a fibre is referred to as Young's 
Modulus, which is the relationship between stress and 
strain at loads below the elastic limit. It is expressed in 
grams of stretching force per denier of fibre (g/den.) and 
corresponds to the tension required to produce an 
extension of 1 per cent. The values thus expressed are 
based on the denier of the fibre and not on the cross- 
sectional area and may be converted into kilograms per 
square millimetre by multiplying by 9 times the specific 
gravity in grams per cubic centimetre. 

It must be borne in mind, in this respect, that textile 



[14] 



SYNTHETIC FIBRE TWINES FOR FISHING PURPOSES 



fibres do not obey the physical law (Hooke's Law), 
according to which strain is proportional to stress or, to 
be more accurate, they obey this law up to a point, called 
"yield point" beyond which the fibre exhibits a 'Viscous 
or plastic flow". Consequently Young's Moduli are 
useful for comparison, but only in the region where 
Hooke's Law applies, when they are "constants". 

Elasticity is the power of recovery from strain or 
deformation. The total extension of a fibre is formed by 
two components: an elastic extension, which is recoverable 
on release of stress, and a permanent (or plastic) elonga- 
tion which is not recoverable. In its turn elastic extension 
comprises partly "immediate recovery" and partly 
"delayed recovery", so that the time factor has to be 
taken into account in determining it. 

According to Kornreich 6 "the elastic limit is reached 
when stress results in a permanent extension, known as 
'elongation'". The ability of a fibre to recover from 
strain is of importance for several end-uses. 

Toughness. Of practical importance also is the "tough- 
ness", "work of rupture", or "energy absorption" of a 
fibre. According to Kaswell 7 "the load is a force, the 
extension is a distance and the area under the load- 
extension (stress-strain or stress-elongation) diagram is 
the product of force and distance, or work (energy)". 
The area therefore depicts the fibre's ability to have work 
done upon itself, i.e. to absorb energy. The "toughness 
index" may be just the same for a fibre of high tenacity 
and low extensibility as for fibre of low tenacity and high 
extensibility. In general, the higher the "toughness 
index", the better is the fibre from the standpoint of use, 
as work of rupture shows the ability of a fibre not only 
to absorb energy, but also to withstand a sudden load, 
(i.e. a "live-load"). 

Stiffness is defined by Harold DeWitt Smith 1 as resistance 
to deformation. Average stiffness is the ratio of breaking 
stress to breaking strain; elastic stiffness the ratio of 
stress to strain at the yield point. 

Moisture content affects the physical properties of fibres 
and, in particular, their tenacity, extensibility, rigidity 
and swelling. In this respect the hygroscopic nature of 
fibres, i.e. their power to absorb and desorb water, is of 
importance, as water acts as a plasticizer to a higher 
degree for hydrophilic fibres and to a lesser degree, or 
scarcely at all, for hydrophobic ones. 

Water influences the fibres in various forms, e.g. as 
relative humidity (in the atmosphere), as liquid water 
(water or imbibition), and as steam; furthermore, the 
action of cold water is different from that of hot water. 

The amount of atmospheric moisture that a fibre is able 
to absorb when exposed, fully dried, to surrounding 
air is referred to as "regain" and is expressed as a 
percentage of the dry weight of the fibres. To ensure that 
the regain of different fibres be comparative, tests are 
conducted in a standard atmosphere. "Standard regain" 
is the amount of moisture a fibre absorbs at 65 per cent, 
relative humidity at a temperature of 20 deg. C. (inter- 
national standards). The standard testing atmosphere 
allows a tolerance of 2 per cent. R.H. and 2 deg. C. 

The moisture content of the fibres affects their tenacity 



in different degrees. Natural cellulosic fibres (cotton, 
ramie, linen) show an increase in tenacity from the dry 
to the wet state; regenerated cellulosic fibres are, on the 
contrary, stronger in the oven-dry state than moist; 
synthetic fibres show no significant variation in strength 
from the dry to the wet state. 

Liquid water, entering the fibre structure, causes 
swelling according to the water imbibition properties 
which are related inversely to wet-strength. Hot or 
boiling water affects the plastic properties of the fibres. 
For most of the synthetic fibres it causes shrinkage and, 
for some types, even degradation. 

The action of steam is dependent upon its temperature 
and saturation. It has a great influence on the plasticity 
of the fibres, and it is accompanied by shrinkage, more 
pronounced with synthetic than with other fibres. 

The property of synthetic fibres to shrink under the 
action of heat (wet or dry) is utilized by a special treat- 
ment (thermo-setting) to impart to fabrics and articles a 
dimensional stability, which is permanent as long as they 
are not treated at higher temperature than that of setting. 

Brief definitions of mechanical properties. It might be 
useful to sum up briefly the basic mechanical properties 
of textile fibre materials to be evaluated under the 
influence of tensile forces as defined by Harold De Witt 
Smith 1 : 

strength the ability to support a load 
elongation the deformation produced by a load, along 

the line of action of the load 
stiffness -resistance to deformation 
toughness - the ability to absorb work 
elasticity the ability to return to original shape and 

dimensions upon cessation of deforming 

force 
resilience the ability to absorb work without 

suffering permanent deformation. 

SYNTHETIC POLYMER FIBRES 

The physical and chemical properties of some synthetic 

polymer fibres, all satisfactorily resistant to sea water and 

fresh water, are given below: 

Polyamides: The principal commercial polyamide fibres 

are: 

polyamide 66 (Nylon) made from polyhexamethylene 

adipamide 

polyamide 6 (Perlon) made from polycaproiactam 
polyamide 1 1 (Rilsan) obtained by auto-condensation 

of o-aminoudecanoic acid (based on castor oil) 

They are produced both in the form of continuous 
filament yarn and staple fibre, in a wide range of deniers. 

As already mentioned, the discovery of polyamide 66 
is due to Dr. Wallace Hume Carothers (b. Burlington, 
Iowa, 1896 d. New York, 1937), who since 1928 had 
been entrusted with research in the laboratories of E.I. 
Du Pont de Nemours Co. 

It should be mentioned, incidentally, that many 
suppositions have been made and several explanations 
(often fantastic) given about the origin of the name 
"nylon". In a publication of E.L Du Pont de Nemours 
Co. 8 it is stated, however, that "the name given to the 
new product was 'nylon' a term just as synthetic as 



15] 



MODERN FISHING GEAR OF THE WORLD 



nylon itself. It was chosen because it was short, catchy, 
pleasant to the ear and not easily mispronounced". 

Polyamide 66 (nylon) and polyamide 6 (Perlon) yarns 
and fibres are available in normal and high-tenacity 
types. The characteristics of each quality and type are 
as follows: 

(A) Polyamide 66 (Nylon) 

Normal tenacity High tenacity 

(1) Density . . M4 

(2) Tenacity dry (g/den.) 4'5 6 6'5 8'5 
breaking length: dry (Km.) 40 54 58 76 

wet (%of dry) 8590 90 

(3) Tensile strength (Kg./mm 2 ) 46 62 67 87 

(4) Knot strength (% of tenacity) 85-90 

(5) Loop strength (% of tenacity) 84-87 

(6) Extension at Break %: dry 26 32 15 - 20 

wet 30 37 18 28 

(7) Elastic recovery . 100% 100% 

up to 8% at 4% 

(8) Toughness . . T08 0'77 

(9) Stiffness (g.p.d.) .18 32 

(10) Water absorption at 65% R.H. 4'5% 

at 100% R.H. 79% 

(11) Effect of heat melting point 250C 

softening point 235C 

Effect of age. Virtually none. 

Effect of sunlight. Loss of strength on prolonged exposure. 

Effect of chemicals. Concentrated hydrochloric acid, con- 
centrated nitric acid, sulphuric acid cause rapid dis- 
integration of the fibre. Phosphoric acid degrades the 
fibre, at elevated temperatures. Formic acid in concen- 
trations above 80 per cent, will dissolve the fibre. 

Acetic acid, oxalic acid, glycollic acid, lactic acid in high 
concentration have similar effect to that of formic acid. 
Other organic acids have little or no effect on the fibre. 

The resistance to alkalis is outstanding. 

Bleaching agents containing available chlorine will 
cause degradation on the fibre; hydrogen peroxide too 
causes degration though less rapid. 

Solution of neutral inorganic salts have no effect on the 
fibre, at room temperature. At 100 dcg. C concen- 
trated solutions of magnesium perchlorate, lithium 
bromide or lithium iodide will dissolve fibre. The 
fibre is inert towards liquid ammonia, sulphur diox- 
ide and cuprammonium solutions. 

Petrol, mineral oils, benzene, xylene, ethers, esters, 
ketones, alkyl halidcs and mercaptans have no effect, 
even at elevated temperatures. 

Alcohols (except benzyl alcohol), glycols, and alde- 
hydes (except formaldehyde, glyoxal, and chloral under 
certain conditions) have only a little effect. 

Benzyl alcohol, nitrobenzene, chlorhydrins, chloral 
hydrate, nitroalcohols, and adiponitrile are solvents for 
the fibre at high temperatures. 

Phenols, particularly phenol itself (i.e. carbolic acid), 
meta-cresol, and cresylic acid are solvents for the fibre. 
Resistance to bacteria and fungi. Untreated fibres are immune 
to attack from all micro-organisms, whether fungi or 
bacteria (i.e. air borne). Yarns and cords show extreme 
resistance to attack by marine algae. 

Resistance to insects. There is no known instance of insects 
or moth larvae deriving sustenance from polyamide 66 
fibres. 

Resistance to abrasion. In the whole field of textile fibres, 
polyamide fibres have the highest resistance to abrasion. 



Polyamide 66 fibres are also produced in the form of 
staple fibres; the characteristics of these are the same as for 
continuous filament, except for the following items: 

Tenacity: dry (g/dcn.) . 4'1 5 

wet (% of dry) . 
Breaking length : (Km.) . 
Tensile strength: (Kg/mm 2 ) 
Total extension: % dry 
wet 
Stiffness (g.p.d.) . 11 



85 
37 
42 
37 
42 



90 
45 
51 
40 
46 



(b) Polyamide 6 (Perlon) 

Normal tenacity High tenacity 

(1) Density ... 1'14 

(2) Tenacity dry (g/den.) 4'1 5'8 6'5 8 
breaking length: dry (Km.) 37 52 58 -- 72 

wet(% of dry) 85 90 

(3) Tensile strength (Vi%.lmm*) 42 60 67 82 

(4) Knot strength (% of tenacity) 85- 90 

(5) Loop strength (% of tenacity) 85- 90 

(6) Extension at Break : dry 24 30 16 24 

wet . 27 34 19 23 

(7) Elastic recovery . . 100% 100% 

up to 8% at 4% 

(8) Toughness . . 0'67 0'68 

(9) Water absorption at 65% R.H. 48% 

at 100% R.H. 79% 

(10) Effect oj heat melting point 217C 

softening point 170 -180C 

Effect of age. Virtually none. 

Effect of sunlight. Lx>ss of strength on prolonged exposure 

Effect of chemicals. 

Resistance to bacteria 






Similar to ^ amide 66 fibre 



o insects 

Resistance to abrasion J 

Polyamide 6 fibres are available also in the form of staple, 
which have as in the case of polyamide 66, a lower tenacity 
and a higher extension than continuous filament. 

(c) Polyamide 11 (Rilsan) 

Polyamide 11 (Rilsan) fibres are relatively new, as their 
production was started only a few years ago. For this reason, 
the data about the properties and characteristics of these 
fibres are not yet complete. 

(1) Density ... 1 04 

(2) Tenacity dry (g/den.) . 4'7 55 
breaking length: dry (Km.) 42 - 50 

wct(% of dry) 100% 

(3) Tensile strength (Kg.lmm 2 ) . 44-51 

(4) Extension at Break %: dry and wcl 25 40 

(5) Elastic recovery ' . " . 100% up to 8% 

(6) Water absorption &\ 65% R.H. 1'2% 

at 100% R.H. 3% 

(7) Effect of heat melting point 189C 

softening point 178C 

(8) Effect of chemicals. The resistance to chemicals (acids) 

alkalis, organic solvents, mineral salts and oxidising agents, 
is slightly superior to that for polyamide 66 and 6. 

In respect to ageing, effect of sunlight, resistance to bacteria, 
fungi, insects and to abrasion there is no substantial difference 
between Rilsan, nylon and Perlon. 

Yarns, cords and ropes made from poly am ides (66 and 6) 
are already well established in the field of fishing gear, 
because of their special characteristics, namely high strength 
combined with extensibility, low absorption of moisture and 
water, quick drying, outstanding resistance to abrasion, 
bacteria and fungi and seawater and algae. 



SYNTHETIC FIBRE TWINES FOR FISHING PURPOSES 



POLYESTER FIBRES 

The principal polyester fibre is made from polyethylene 
tercphthalate, which was first synthesized by Whinfield and 
Dickson in the laboratories of the Calico Printers Association, 
in Great Britain. 

Mr. Whinfield designated the fibre "Terylene" for conven- 
ience in writing and was surprised that the name has survived. 

We report below the data regarding polyester filament yarn ; 

Normal tenacity High tenacity 
1-38 



4 

36 



5'5 
50 



100% 



6.0 7 
54 63 



74 87 
80 
70 

15 - 7 
100% at 2% 
90% at 8% 
0-5 
51 

0-4% 

0-5% 

260C 

230--240"C 



(1) Density 

(2) Tenacity dry (g/den.) 
breaking length (Km.) 

wet (% of dry) 

(3) Tensile strength (Kg. /mm 2 ) 50 68 

(4) Loop strength (% of tenacity) 90 

(5) Knot strength (% of tenacity) 70 

(6) Extension at Break dry and wet 27 17 

(7) Elastic recovery . 97% at 2% 

80% at 8% 

(8) Toughness . . . 0*78 

(9) Stiffness (g.p.d.) . . 23 

( 10) Water absorption at 65% R.H. 

at 100% R.H. 

(11) Effect of heat melting point 

softening point 

Effect of age. Virtually none. 

Effect of sunlight. Only slight loss of strength on prolonged 
exposure. 

Effect of chemicals. Resistance of a high order to chemical 
attack; outstanding resistance to mineral and organic 
acids (expecially hydrofluoric acid). Only fair resistance 
to alkalis but adequate for most purposes. Resistant to 
oxidising agents and to organic solvents (except at the 
boiling point). Most phenols dissolve the fibre. 
Resistant to bacteria, fungi and insects. 
Resistance to abrasion: ranks second to polyamide fibres 

only. 

Polyester staple fibre is also commercially available; the 

characteristics are the same as those of continuous filament, 

except for tenacity and extension, which are respectively 

lower and higher than for filament yarn. 

Vinyl fibres 

The first vinyl fibre was described in the literature nearly 
fifty years ago. Polymer chemistry had first of all to prepare 
polymers possessing suitable properties for spinning and as a 
result of a great deal of research and experiments, fibres 
having satisfactory physical and chemical properties were 
obtained. From the standpoint of utilization in the fishing 
industry, the following vinyl fibres are to be mentioned: 
poly vinyl chloride, vinylidene chloride (Saran), polyethylene 
(Courlene and Courlene X 3) and poly vinyl alcohol (Vinylon). 
We summarize below the main properties of these fibres: 



(a) Pol> vinyl chloride fibres 

(1) Density 

(2) Tenacity dry (g/den.) 

breaking length (Km.) 
wet (% of dry) 

(3) Tensile strength (Kg./mm 2 ) 

(4) Loop strength (% of tenacity) 

(5) Knot strength (% of tenacity) 

(6) Extension at Break dry and wet 

(7) Elastic recovery 

(8) Water absorption 

(9) Effect of heat 



1'39 

2'7 3-7 
24 33 

100% 
33 46 
70% 
70% 

13 30 
80 to 85% at 3% 

O'l at 95% R.H. 
softens at 110 120C 
shrinkage starts at 60 to 70C. 



Effect of age. Virtually none. 

Effect of sunlight. Substantially unaffected after prolonged 
exposure. 

Effect of chemicals. Resistant to acids, including aqua rcgia 
and to concentrated (caustic) alkalis. Dissolves or swells 
in some aromatics, chlorinated hydrocarbons, ketones, 
esters. Generally good resistance to other chemicals. 

Resistant to bacteria, fungi, insects and algae and sea 
water. 



(b) Vinylidene chloride fibres 

(1) Density 

(2) Tenacity dry (g/den.) 

breaking length: dry (Km.) 

wet (% of dry) 

(3) Tensile strength (Kg./mm 2 ) . 

(4) I Atop strength (% of tenacity) 

(5) Knot strength (% of tenacity) 

(6) Extension at Break (%) 

dry and wet 

(7) Elastic recovery 

(8) Water absorption 

(9) Effect of heat melting point 



170 

1-5 2*6 
13*5 23 
100 
23 40 
70 80 
70 80 



18 33 

98 in 100% at 5% 
0*1% at 95% R.H. 

150 - I60C 



Effect of age. Virtually none. 

Effect of sunlight. Slight discoloration after prolonged 
exposure. 

Effect of chemicals. Unaffected by most acids, including aqua 
regia. Affected by some alkalis, including concentrated 
ammonium hydroxide, and sodium hydroxide. Sub- 
stantially inert to organic solvents. Generally good 
resistance to other chemicals. 
Resistant to bacteria, fungi, insects, moth larvae, algae 

and sea water. 

(c) Polyethylene fibres 

(The data refer to polyethylene yarns produced by 
Courtaulds Ltd. under the registered trade-names of "Cour- 
lene" and "Courlene X 3".) 

C 'ourlene Com lene X 3 

(1) Density . . . (V93 096 

(i.e. the lowest density of all the 
synthetic polymer fibres giving 
good flotation properties). 
. 1 1-5 4-0 6-0 

) 9 - 13-5 36 54 

100% 
. 8'5 - 12*5 34-5- 52 

25 - 50 20 40 

90 to 95% at 5% 
practically none 
Courlene softens above 90C; 
melts between 110' and 120"C. 

Courlene X 3 (High tenacity) 
softens at 120 C; melts at 135'C. 

Effect of age. Virtually none. 

Effect of sunlight. Loss of strength after prolonged exposure. 
Effect of chemicals. Remarkable resistance to attack by alkali, 
acids, solvents, organic salts, unequalled in this respect 
by other fibres. 

Resistant to bacteria, fungi, insects, moth larvae, algae 
and sea water. 

The abrasion and electrical resistance of Courlene X 3 is 
very good and both Courlene and Courlene X 3 are flexible 
at very low temperatures such as 70 deg. C. 



(2) Tenacity dry (g/den.) 

break i ng lengt h : d ry ( K m 
wet (% of dry) 

( 3 ) Tensile strength ( Kg./mm 2 ) 

(4) Extension at Break (%) 

dry and wet 

(5) Elastic recovery 

(6) Water absorption 

(7) Effect of heat 



[17] 



MODERN FISHING GEAR OF THE WORLD 



(d) Poly vinyl alcohol fibres 

Vinylon is the generic term for polyvinyl alcohol fibres: 
these are produced in staple and in filament. 

Staple filament 

Normal High Normal High 

Tenacity Tenacity Tenacity Tenacity 

(1) Density 1 -261 30 1 2(v-l - 30 

(2) Tenacity dry 

(g/den) . 4-2-6-0 6-78-0 3-5- 45 77-92 

breaking length: 

dry (Km.) . 3854 60-72 32-41 6983 
wet ( of dry) 77~85 80 85 8O-90 80 90';; 

(3) Tensile strength 

(Kg./mm) . 50 70 78-94 4153 90 110 

(4) Loop strength 

( of tenacity) 35 43% 35 40 90 95 n 58 65 " 

(5) Knot strength 

( % of tenacity ) 60 -67 " ; 64- 70 ; 7580 u 3952 

(6) Extension at break 

(? ) dry . 17-26 13- 16 1419 920 
Wet . 1930 1417 14 22 12-22 

(7) Elastic recovery 75 -80 ^ 78 82 70 90 8598 

at 3 at 3 at 3 at 3 

(8) Water absorption 

(at65r,R.H.) 4-5 5'0 4-5 5'0 3'5 4V\ 3'0 5'0 
(at95 R.H.) 10 -12'0 

(9) Effect of heat 

melting point 220 225 C 

shrinkage . starts at abt. 200 C 

Effect of age. Virtually none. 

Effect of sunlight. Loss of strength after prolonged exposure. 

Effect of chemicals. Concentrated sulphuric, hydrochloric, 
formic acids cause decompositions or swelling. Strong 
alkalis cause yellowing but do not affect strength. Good 
resistance to organic solvents. Soluble in hot pyridine, 
phenol, cresol. Resistant to oils. 
Resistance to bacteria, fungi, insects: not affected. 

Polyvinyl chloride, polyvinyl alcohol and polyvinyl- 
idene chloride fibres are being used in making set nets, 
trawl nets and seine nets. Polyethylene is the only textile 
fibre that has a specific gravity lower than that of water. 
Owing to this low density, the diameters of Courlenc 
filaments are greater than those of other textile fibres of 
the same denier. In the case of 125 denier monofilaments, 
for instance, the diameters in l/1000ths/inch are Cour- 
lene 5'4, nylon 4*9, acetate 4*5, viscose 4'2. 

Courlene and Courlene X3 are used in making ropes 
of all kinds for use on board ship. The tensile strength is 
sufficient to make it suitable for most applications, 
while improvements being made may increase the tensile 
strength from 4 to 6 g/den. to 8 g/den. The yarn is spun- 
dyed, which makes it easy to produce coloured ropes; 
it does not absorb water and therefore does not swell; 
ice does not form inside it, and snow, etc. can easily be 
brushed or shaken off. Its specific gravity is low and ropes 
made from it will float on water. The yarns, being inert, 
will not support fungal or weed growth. 

The fibre is useful where tensile strength and buoyancy 
are important, as in trawl nets where the upper net will 
tend to rise of its own volition ; it is claimed that con- 
sequently fewer floats are required. The fibre has been 
used both for the main-lines and snoods in longline 
fishing, and for weaving canvases which do not become 



hard and are relatively easy to handle in wet, cold 
conditions. Insoles made from Courlene provide thermal 
insulation in the fisherman's boots. 

MAN-MADE FIBRES AND FINISHES IN PROTEC- 
TIVE CLOTHING FOR FISHERMEN 

The fishermen are exposed to wet, cold climatic con- 
ditions and must, to work efficiently, receive adequate 
protection. In the past they wore oilskins, made of a 
heavy cotton, flax or similar fabric, coated with many 
layers of linseed oil. Today many of the basic fabrics are 
made from 100 per cent, viscose rayon staple or blends 
with cotton. The fabrics are produced with good tear and 
tensile strength and a surface smooth enough to allow 
even coatings, now generally of p.v.c. All types of gar- 
ments, such as coats, sou'westers and leggings, are made 
from them. 

One of nylon's chief contributions is as a lightweight 
base for waterproof clothing. Fabric of 1^ to 2J ozs./sq. 
yd. can be successfully proofed with p.v.c. neoprene and 
polyurethane resins. These cloths have the advantages 
of lightness, flexibility and a smooth p.v.c. coating which 
is of special advantage in collar fittings where the fabric 
may be flat against the wearer's face. 

Another innovation is the double textured rainproof 
jackets, coats and leggings. These are made from two 
similar fabrics laminated with rubber. The textile fabric 
provides resistance to abrasion and the rubber lamination 
provides waterproofing. 

The traditional seamen's jersey can be made in a blend 
of 50 per cent, viscose staple, 50 per cent, wool or 15 per 
cent, nylon, 35 per cent, viscose rayon staple, 50 per cent, 
wool. The latter blend has good resistance to abrasion 
and can be made to resist shrinkage. The same yarns 
have also been used in heavyweight half-hose and seamen's 
stockings, comfortable in use and hard wearing. 

Yarns made from 100 per cent, viscose rayon staple and 
viscose rayon/staple cotton blends can be knitted on 
interlock machines, and lend themselves to coating with 
vinyl compounds, rubber or p.v.c. Gloves are now made 
of this type of fabric and also rubber leggings and 
waders. The fabrics can be raised to give a fleecy lining. 



REFERENCES 

1 Harold De Witt Smith "Textile Fibres An Engineering 

Approach to their Properties and Utilization", ASTM 
Proceedings, 1944. 

2 Douglas C. Hague "The Economics of Man-Made Fibres", 

London, 1957. 

3 J. T. Marsh "Textile Science* 1 , London, 1949. 

4 "Textiles Terms and Definitions"- The Textile Institute, Man- 

chester. 3rd Edition, 1957. 

8 E. Viviani and L. Graziano "Fibre Artificial! e Sintetiche", 
Turin, 1952. 

6 E. Kornreich "Introduction to Fibres and Fabrics", London, 

1952 

7 E. R. Kaswell "Textile Fibres, Yarns and Fabrics". New 

York, 1953. 

8 E. I. Du Pont de Nemours Co. "Nylon Textile Fibres in In- 

dustry", Wilmington, 1947. 



18] 



CHARACTERISTICS OF SYNTHETIC TWINES USED FOR FISHING 

NETS AND ROPES IN JAPAN 

by 
YOSHINOR1 SHIMOZAKI 

Tokai Regional Fisheries Research Laboratory, Tokyo, Japan 

Abstract 

The main physical properties of synthetic netting twine used for fishing gear in Japan are discussed in this paper. The items con- 
sidered include the sinking speed, breaking strength, knot strength, friction resistance, resistance to sunlight, and seawatcr, etc. and reference 
is also made to treatments by tar and resin for improving the characteristics of nets and ropes. 



Resume 



Caracteristiqucs des ficelles synthetiqucs utilisees pour les filets et les cordes de peche au Japon 



Cet article examine les principals proprietes physiques des ficelles a filets synthctiqucs utilisees pour les engins de peche au Japon. 
Les sujets traites comprcnnent la vitesse de plongec, la resistance A la rupture, la resistance des noeuds, la resistance a la friction, Ja resistance 
a la lumiere solaire et a Peau de mer, etc. el il est aussi fait mention des traitements par le goudron et la resine pour amdliorcr les caracter- 
istiques des filets et des cordes. 



Extracto 



Caracteristicas de los hilos sinteticos usados en la fabricaci6n de redes e hilos en el Japon 



En cste trabajo se cstudian las principales propiedades fisicas de los hilos sintciicos usados en el Japon para fabricar artes de pest a. 
Entrc los puntos considerados figuran la velocidad de inmcrsidn, resistencia a la rupture y de los nudos, asi como al roce, lu/. solar agua 
salada, etc. Tambien se mcncionan los tratamientos con alquitran de hulla y cxtractos curtientes para mejorar las caracteristicas de las 
redes e hilos. 



1. Introduction 

FISHING gear is dependent on several factors, such 
as the fishing techniques to be employed, the fish to 
be caught, the material for nets and ropes, and so 
on. With regard to the latter, there are requirements 
which largely influence characteristics and efficiency of 
the gear. They are: 

the thickness or diameter of the netting twine; 

the weight of the twine in air and in water; 

sinking speed; 

strength and extension up to the breaking point; 

strength and extension knotted; 

friction resistance; 

resistance to sunlight and seawater; 

knot fastness; 

resistance to factors such as shock, heat, chemicals and 

fatigue; 
elasticity; 

susceptibility to dye and dye fastness; 
stiffness or handiness; 
plying and fabricating capacity. 

In evaluating these properties different methods and 
means would give different values. Therefore when 
selecting one kind of material out of a group each 
attribute must be evaluated with a uniform method 



which should approximate the actual fishing conditions 
as far as possible. 

The efficiency of a fishing net is partly predictable 
from the quality of the twine, therefore the results of 
twine testing will be first described in regard to two of 
the factors (1) the nature of the fibre, and (2) the number 
of twists given to the yarn as well as the strand. 

2. How to Indicate the Structure and Size of Net Twines 

One group of synthetic fibres made of spun yarn just as 
with cotton or hemp includes Kuralon (Manryo) 
and Mulon yarns. As in cotton the strands made by 
twisting the yarn are then again plied to form twine. 
Most of the synthetic yarns used for fishing nets are made 
equivalent to English 20's of cotton yarn in size, and are 
usually of 2 or 3 plies. The size is indicated by the 
number of yarns used for a strand with the number of 
strands (e.g. No. 5 with 3 plies), or by the total number of 
yarns contained in a twine (e.g. 15 yarns in 3 plies). 
The latter is more often used. 

In another group the continuous filaments are plied 
into strands or threads. Amilan (nylon), Saran, Krehalon, 
Teviron, Envilon, Kyokurin and Kuralon No. 5 (Manryo 
No. 5) generally belong to this group. In this case, 
however, the strand may be formed by a single filament 
(monofilament) or by yarns consisting of several fila- 



[19] 



MODERN FISHING GEAR OF THE WORLD 



TABLE I. Construction of Some Kinds of Netting Twines 



Material 
Amilan 



Chemical 
name 



Construction of yarn and/or 
strand and twine 



Polyamide (250D/15F.-Y) x n,-S, S x n 2 -T 
(210D/15F1-Y) x n,-S, S x n 2 =T 
(110D/30F1-Y) x n.-S, S x n 2 =T 
( 60D/20F t -Y) x n x -S, S x n,=T 

Kuralon No. 5 Polyvinyl (500D-F 2 ) x n 3 -S, S > n 2 -T 
(Manryo No. 5) alcohol 

Saran Polyvinylidene 720D/6Fj x n S, S x n 2 --T 
Polyvinyl chloride lOSOD^FjXnr -S, S x n 2 -T 
(360D-F 2 )xn 3 -S, S >: n,-T 
(1000D-F.,) xh a -S, S s n,-T 



Krchalon 

Teviron 
Envilon 



1080D/6F 1 xn 4 -S, S x 
(360D- F 2 )xn~-S, S x n 2 -T 
(IOOOD F 2 ) A n 3 -S, S x n 2 T 

<300D/30F r Y)x ni -S, S x n 2 
(450D- F 2 )xn 3 -S. S x n 2 -T 



Cotton not applicable (20's-Y) x n,-S, S x n 2 --T 
Kuralon Polyvinyl alcohol (20's- Y)xn 1 -S, S x n 2 ~T 

D : denier. 

multifilaments. 

monofilaments. 

yarn. 

number of yarns contained in a strand. Fach yarn of this type 
comprises multifilaments. 

strand. 

number of strands (usually 3 but sometimes 2 or 4) construct- 
ing a twine. 

twine. 

number of monofilament contained in a strand. The thickness 
of a strand varies depending on n 3 . 

number of multifilaments, usually one. or two bundles. 



ments (multifilament). Amilan, Teviron, and Kyokurin, 
and small diameter twines of Saran, Krehalon have 
strands made of multifilament yarns. Kuralon No. 5 and 
other large diameter twines, such as those of Saran and 



Krehalon, have strands made of monofilament. Table I 
illustrates how these yarns, strands and twines arc 
constructed. 

In the Table, 250/15F x n A of (nylon) Amilan, for 
instance, means that a strand is made by twisting a 
number of yarns of 250 total denier, each of which is 
constructed in 15 filaments. The thickness of a filament 
in that yarn is 16*6 denier approximately. As a (nylon) 
Amilan yarn of 210 denier corresponds in thickness to 
cotton-20-counts (20's), the number of yarn of any other 
denier in this twine, equivalent to cotton 20's (hereinafter 
called C20-equivalent), is converted by dividing the total 
denier of the twine by 210 denier. The twines consist of 3 
and sometimes 4 strands, e.g. for some salmon gillncts. 
Similar calculations can be made for other synthetic 
fibres produced in Japan. 

In all these synthetic products, the numbers of yarn 
for C20-equivalent twine are obtained by dividing the 
total denier of the twines with the thickness of the 
C20-equivalent. It should be remembered, however, that 
the thickness of C20-equivalent determined for these 
twines does not necessarily represent, in a strictly physical 
sense, the true thickness of cotton 20's. 

3. Thickness of Netting Twines 

No matter how similar may be the indicated thickness 
of different kinds of twines, the indication does not 
warrant that they are all alike in diameter, circumference 
or weight per unit length (Tables III and IV). Naturally, 
the real thickness of a twine, viz. the whole area of 
the horizontal section of all the filaments of the twine, 
varies according to the kind of twine, making it impossible 
to assess the characteristics of twines on a comparable 
basis. As, however, no other standard than the conversion 
into C20-equivalent has become available for the 
purpose, characteristics of both synthetic and natural 
twines will be compared with the help of this conventional 
method. 

The thickness of net twines has been measured 
(Table III) in a wet state. The twines were immersed in 
water for 24 hours and hung until the water slopped 
dripping from them. The twines used are generally 



TABLE If. 


Number of Twist per 30 em. of Twines 


Number of yarn 


4 


6 


9 


12 


15 


18 


21 27 36 


45 


54 60 


75 


84 


Amilan 


A 132 
H 198 


123 
189 


111 
167 





72 
112 


69 
124 


64 57 
131 117 


51 
104 


43 
78 


35 
70 




Kuralon (Manryo) 


A 
B ~ 


96 
241 


81 
189 





59 
115 


50 
92 


44 38 
78 62 


36 

57 


33 

52 


29 
49 




Criran 


A 


76 


68 


64 


59 


57 


53 45 


33 


*25 


(66) 23 




daidn .... 


B ~~ 


135 


123 


110 


98 


94 


83 75 


60 


45 


41 




Krehalon 


A 
B 


68 
104 


63 
100 





56 
93 


51 
90 


48 46 
87 85 


44 
81 


39 

75 


36 
66 


33 
60 


Teviron 


A 138 
B 246 


90 
202 


% 
158 


84 
148 


- 


60 
123 


*51 (24) 48 
114 " 102 




42 
84 






Cotton 


A 
B 


102 
405 


95 
336 





75 
264 


66 
212 


60 51 

~~ 171 135 


42 
90 


38 
60 


34 
53 




Kyokurin 


A 81 
B 126 


68 
114 


57 
95 


51 
81 








42 31 

65 ' * 52 













A: twist for 


twine. 










B: twist for strand. 










* The number within 


parentheses is 


the number of yarn equivalent 


in the thickness to cotton 20's, and the 


number outside parentheses 


is the number of twist of that twine. 



[20] 



JAPANESE SYNTHETIC TWINES 



TABLE III. Diameter of Wet Netting Twines 





















(Unit: 


mm.) 




PlylNo. of yarn 
of CW-equivalent 3/6 


3/12 : 


5/18 : 


1/24 : 


*/30 : 


1/36 


3/42 


3/48 


3/54 


3/60 


3/66 


372 


Amilan . . .0-68 


0-92 


15 


-37 


56 


1-76 


1-94 


2-11 


2-26 


2-41 


2-54 


2 78 


Kuralon (Manryo) . 0-83 


1-10 


36 


60 


83 : 


!-08 


2-23 


2-42 


2-59 


2-75 


2-90 


3-04 


Saran . 66 


0-86 


-03 


-22 


-37 


-52 


1-66 


1-77 


1 88 


2-00 


2-09 


2-18 


Krehalon . .0-66 


0-88 


05 


24 


40 


-55 


1-69 


1-83 


1-95 


2-06 


2-16 


2-25 


Teviron . 0-70 


0-96 


-21 


43 


64 


84 


2-03 


2-21 


2-37 


2-03 


2-66 


2-79 


Kyokurin . 0-67 


0-90 


08 


28 


46 


63 


1-78 


1-93 


2-06 


2-18 


2-28 


2-40 


Cotton . .0-78 


1-06 


-32 


56 


77 


-98 


2-18 


2-36 


2-53 


2 70 


2-83 


2-97 



considered to be of medium twist (Table II). Roughly 
speaking, the twist below that range has about 3 to 5 per 
cent, greater thickness. 

4. Weight of Net Twines in the Air and in Water 

(1) Weight in the air: In the air, the weight of fishing 
nets has a close relation, particularly when they are wet, 
with the loading capacity of small boats as well as with 
the working conditions for fishermen. Although weight 
is largely governed by the thickness of the twine, mesh 
size and type of knot, a table of weights prepared by 
actually weighing nets in use is useful reference. In 
preparing such a table, the weight per metre of dry twine 
and the rate of weight increase for wet twine may be 
taken as the basis for estimating the wet weight of various 
types of nets. 

The wet weight of a net in air can be obtained by multi- 
plying the known dry weight of the net with the ratio 
W w /W d , as in Table IV. 

The situation is somewhat different with nets processed 
with resins. The amount of water that sticks to the nets 
differs according to the kind of fibre and thickness of the 
resin coating as well as the water absorption or repellency 
of the resin, so that it is difficult to estimate the wet 
weight of a net. However, an experiment has proved that 
resin-processed nets gain in weight over those not 
processed by 30 to 80 per cent, which includes the 
weight of the resin adhering to the material. 

Coal tar treated nets in dry state are 70 to 150 per cent, 
heavier than non-treated nets. If the coal tar is diluted 
with creosote or gasoline, the weight gain is approxi- 
mately from 50 to 100 per cent. Use of a centrifugal 
machine when dyeing can reduce the amount of tar on 
the net and bring the weight gain down to 60 to 80 per 
cent. 



(2) Underwater weight: Increase in underwater weight 
of twines implies a quicker sinking capacity and in some 
cases a better shape of the net. This is an important 
quality for fixed nets, purse seines and stickheld dip nets. 
Table V presents the underwater weight of various kinds 
of netting twines on the basis of the unit length of one 
metre measured in air. In the case of webbing, the same 
relation may be expected between synthetic twines and 
cotton (Wo/Woe) and between tarred synthetic and 
tarred twines (Wt/Wtc.) 

5. Sinking Speed 

Sinking velocity, an important factor especially for such 
types of nets as purse seines, has a close connection with 
the thickness and specific gravity of the raw material, 
is affected by the degree of twist given to the yarn, 
strand and twine, and by the smoothness of the twine 
surface. In a sinking speed test, a piece of twine, 2 cm. 
long with each end glued, was immersed in water for 
24 hours. The air bubbles were then removed from 
the surface of the twine. The terminal velocity shown 
by the test piece in sinking straight down in a salt 
solution (specific gravity 1-020) was then determined 
(fig. 1). The solid line indicates the sinking speed of 
non-treated twine, and the dotted line the sinking speed 
of the tarred twine. It is obvious that the velocity differs 
even between the same kind and quality of twines 
depending upon the thickness of the twines as well 
as on the nature of the raw material, the number of 
twists, twisting technique, dyeing and/or heating. 

Table VI shows comparative sinking speeds for various 
twines. The coal tar treatment, which was first used for 
cotton twines to increase the sinking speed by preventing 
water absorption, has been found still mote effective 



Items 

Wd (mg/m) 
Ww (mg/m) 
Ww 

Wd 



Amilan 

25-0 X n 
34-0 x n 

1-36 x n 



TABLL IV. Weight of Dry or Wei Netting Twines 



Kuralon 

36-0 X n 
64-8 x n 

1 80 x n 



Saran 

46-6 x n 
50-5 x n 

1-08 -v n 



Krehalon 



45-3 
50-3 

1-11 



Teviron 

38-0 x n 
50-0 - n 

1-32 \ n 



Kyokurin 
35-0 n 



35-0 -> n 
57-5 > n 

1-64 x n 



Ww : wet weight. 
Wd : dry weight, 
n : number of yarn equivalent in the thickness to cotton 20's. 



[21] 



MODERN FISHING GEAR OF THE WORLD 



TABLE V. Underwater weight of Netting Twines 





Kuralon 














Items 


A mi Ian (Manryo) Saran 


Krchalon 


Teviron 


Kyokurin 


Cotton 


Manila Hemp 


Wo (mg/m) 


3-33 x n 6-70 x n 17-7 x n 


17-2 x n 8-35 x n 


11-8 x n 12 


8 x n 


10-8 x 


m 


Wo/Woe 


S 0-52 1-38 


1-34 


65 


0-92 


1-00 


0-84 




Wt (mg/m) 


8-0 n 13-2 > n 24-2 x n 


23-7 x n 


15-7 x n 


25 


4 x n 


21-8 x 


n 


Wt/Wtc 


0-32 0-52 0-96 


0*94 


0-62 




1-00 


0-86 




Wt/Woc 


0-62 1-03 1-89 


1-85 


1-24 





1-98 


1-70 




Wt Wo 
















v inn 


(%) 140 97 37 


38 


88 




98 


102 








Wo 
















Wo 


the weight of non-treated netting twine. 














Woe 


the weight of non-treated cotton twine. 














Wt 


the weight of tarred twine. 














Wtc 


the weight of tarred cotton twine. 














n 


number of yarn equivalent in the thickness to cotton 20's. 


m 


monme. One monme equals 3 75 gr. The 


number of monme 


per 151-5 


cm. m abaca twine are 


used as the 


unit of 




thickness in Japan. One monme of abaca twine is equivalent to 66 


yarns of cotton 20's. 









when applied to some synthetics. For this reason, coal 
tar and similar products are widely used in Japan. 

About 80 per cent, tar adhesion results in the quickest 
sinking speed 1 while, according to our experiments, 
twines over or undercharged with tar sank slowly. 

6. Tensile Strength of Net Twine, and the Knot Strength 

(1) Differences in strength: Tensile strength of twine 
depends upon that of the raw material used, whether 



TABLF VI 

Comparison of Sinking Speed between Non-treated Twines 
and Tarred Twines 



Material 


Items 


3 plies, 
1 5 yarns 


Amilan 


Vo/Vc 
Vt/Vo 
Vt/Vtc 


0-57 
1-68 
0-55 


Kuralon 
(Manryo) 


Vo/Vc 
Vt/Vo 

Vt/Vtc 


0-74 
1-88 
0-75 


Saran 


Vo/Vc 
Vt/Vo 
Vt/Vtc 


1-77 
1-09 
1-20 


Krehalon . 


Vo/Vc 
Vt/Vo 

Vt/Vtc 


1-65 
1-14 
1-17 


Teviron 


Vo/Vc 
Vt/Vo 
Vt/Vtc 


1-43 
1 20 
0-93 


Kyokurin . 


Vo/Vc 
Vt/Vo 
Vt/Vtc 


1-37 


Cotton 


Vo/Vc 
Vt/Vo 
Vt/Vtc 


1-00 
1 63 
1-00 



3 plies, 
30 yarns 


3 plies, 
60 yarns 


0-54 
1-65 
0-60 


51 
1-75 
66 


0-73 
1-55 
0-76 


0-66 
1-53 

0-77 


1-65 
1-08 
1-18 


1-50 
1-07 
1-17 


1 56 
1 10 
1-15 


1-43 
1-10 
1-14 


1-21 
1-14 
0-92 


1-17 
1 10 
0-92 


1-27 


1 21 


1-00 
1-50 
1-00 


1-00 
1-38 
1-00 



The number of yarn is equivalent in the thickness to cotton 20's. 



Vo 
Vc 
Vt 
Vtc 



sinking speed (cm. /sec.) of non-treated twine. 

non-treated cotton twine. 
tarred twine. 

tarred cotton twine. 



the twine consists of short or long fibres, and on the 
number of twists given to the strand and twine. The 
balance between the primary twist for making the strands 
from the yarns and the secondary twist to make the twine 
from strands is also very important because, while an 
increased twist augments the tensile strength up to an 
optimal point, an excessive increase in the twist produces 
the opposite effect 2 . This also applies to the strength of 
a fishing net itself. 

Among twines with various twists used for fishing in 
Japan there is a difference of about 15 to 20 per cent, in 



Name of 
twine 

Amilan 
Manryo 

(Kuralon) 
Saran 
Krehalon 
Teviron 
Kyokurin 
Cotton 
Abaca 



Tarred Non 
twine treated 



C c 

D d 

K e 

F f 

G g 

H (i 




Fig. 1. Relation between the sinking velocity and thickness of 
netting twines of various kinds. Dotted lines show the sinking 
velocity of tarred twines, and solid lines non-treated twines. 



[22] 



JAPANESE SYNTHETIC TWINES 



50 
# 

g 45 

fc 

P 

> 

a 
g 40 

H 

35 
32 




30 l.S ^O 30 40 J>0 

Number of twist for twine per 30 cm. 



60 



fi#. 2-a. Relation between the breaking strength and number of 
twists given to twines. A, B and C, JOOO /), .? plies, 24 mono- 
filaments, produced by different makers. 

X 

a 17.5 



17.0 



16.5 



g ie.c 
H 



15.5 



15.0 




in 15 20 30 40 50 

Number of twist for strand per 30 cm. 



60 



Fig. 2-b. Relation between the breaking strength and the number 
of twists given to a strand of the twines as of fig. 10. 

tensile strength, that is, an overtwisted and weaker twine 
may be found side by side with a correctly twisted 
stronger one, as shown in fig. 2. Kondo and Koizumi 3 " 6 
pointed out the same in regard to both cotton and 
synthetic twines. Even with identical twines, and 
whether the balance is good or not, there are differences 
of 10 to 15 per cent, in the tension resistance because of 



TABLE VII 

Coefficients a. and 2 for Breaking Strength of Wet or Dry 
Twines 



Wet 



Dry 



Amilan 


89 


0-94 


Kuralon (Manryo) 


0-78 


0-% 


Saran 


0-70 


0-68 


Krehalon 


0-60 


0-56 


Teviron 


0-72 


0-68 


Kyokurin 


0-76 


0-81 


Cotton 


0-59 


0-47 


Envilon 


0-76 


0-74 



the different numbers of twists. That is why careful 
attention must be paid to the amount of the twist in the 
twine when buying fishing nets and ropes 7 . 

In regard to the difference in the wet and dry strengths 
of netting twines, an experiment proved that natural 
fibre twine is about 10 to 20 per cent, stronger wet than 
dry, but the contrary is true with Amilan and Kuralon 
(Table VII). With Teviron, Envilon, Saran and Krehalon, 
the wet twines are slightly (3-5 per cent.) stronger than 
dry ones 8 . Similar results applied to the tensile strength 
of knots of fishing nets 9 . 

Temperature is another influencing factor, the tensile 
strength of nets decreasing by 10 to 20 per cent, in 
temperatures between 30 deg. C. and deg. C., and the 
strength of twines by about 5 to 10 per cent, according to 
the kind of twine 10 . The effect of temperature on the 
tensile strength of synthetic twines and knots is greater 
than on natural twines. 

There is a disparity in the breaking strength between 
twines of less than 50 cm.; the longer the stronger they 
are, and vice versa, whereas between twines of a same 
material and thinner than 60 yarns of C20-equivalent, 
there is little difference in the breaking strength 11 . 
An approximate breaking strain for each twine specified 
in Table II can be obtained by multiplying u\ or n2 in 
Table VII with number of C20-equivalent yarn (fig. 3). 

(2) Strength at knot: A series of tests have been con- 
ducted at temperature 18-0 deg. C.-f 1 -5deg.C. for tensile 
strength at knot with 30 cm. long wet pieces of twine. 
In one test, two pairs of the legs (AB and CD) of an 
English knot were pulled asunder (figs. 4 to 6). Although 
not convincing as a proof of the tensile strength of a 




Fig. 3. Wet tensile strength of twines of various kinds, each with 
the number of yarns equivalent in thickness to cotton 20\\. 



[23] 



MODERN FISHING GEAR OF THE WORLD 

TABLE VIII 
The Constant in Proportion to Tensile Strength at the Knots of Various Kinds of Twines 



Kind of knot 
Drawing direction * 
P and Y 



English knot 
AB-CD AC 

Pi Yi P 2 



Amilan 
Kuralon 



18 
21 



Saran 
Krehalon 
Teviron 
Kyokurin 
Cotton 

Kuralon No. 5 
(Manryo No. 5) 



1-25 
0-86 
0-80 
0-78 
0-7C 
0-84 
0-93 
0-97 



30 
45 
49 
43 
35 
34 
37 
18 
39 



1-28 
0-93 
0-86 
0-83 
0-79 
0-87 
0-97 
0-99 



Y 2 

28 
40 
45 
41 
32 
32 
33 
16 
37 



AG 



1-25 
0-93 
0-90 
0-78 
0-74 
0-81 

0-96 



Flat 


knot 




CD 


AC 


BD 


Y 3 


V* 


f* 


30 


1-23 


31 


40 


0-77 


5i 


42 


0-74 


53 


43 


0-70 


50 


36 


0-68 


41 


37 


0-71 


45 



19 



0-86 27 



* Drawing direction of test twines is shown in fig. 4. 

PI, P. P 3 , and p 4 are coefficient of proportion of tensile strength at knots of various kind and in every direction. 
"it Yjj, Ys and YI are ratios of decrease in tensile strength of these twines. 





(b) 



English knot (" Kaerumata" 
in Japan). This type is most 
popular all over the world. 



Reef knot or Square knot 
("Homme"* in Japan). 




(c) 




(d) 



Double English knot (*'Niju 
kaermala'" in Japan). 



Lock Knot 



fishing net, such a test may still be significant enough for 
comparing the strength of various types of nets webbed 
by the same knotting technique. The strength of the 
knots differs considerably according to the type of knot 
and the directions in which they are drawn 12 . Figs. 7-A 
and -B show the strength of the various types of knots 
(a and b in fig. 4) when their legs were strained in either 
direction, AB apart from CD (lengthwise) or AC apart 
from BD (crosswise). 

Breaking strength of knotted twine can be regarded 
to be nearly in proportion to /i, the number of yarns of 
C20-equivalent of a twine in which the knot is constructed; 
coefficients of proportion (i^ //.,, ft^ and />'., are shown 
in Table VIII. Decreasing percentage y,, y.,, y 3 , and 7', in 
knot strengths are represented by 



Pi 



x 100 



Fig. 4. Type of Knot. 



where a, is derived from Table VII, and ft\ represents any 
one of /?, to fi 4 . 

In fig. 4, knots c and d are the types required for 
repairing broken nets and making gillnets, and nets in 
which the knots should never work loose. Knot c is 
called the double English knot, and Knot d the Lock 
knot. However, the tests showed no noticeable differences 
in strength between the English knot and those stated 
above 13 . A study is now under way in connection with 
the strength of a knotless net. 



TABLE IX 
Breaking Extension of Wet Netting Twines 



(Unit %) 



Thickness 
of twines 


3-plies 
4-9 yarns 


3 plies 
12-18 yarns 


Amilan 
Kuralon (Manryo 
Saran 
Krehalon 
Teviron 
Cotton 
Kyokurin 


30 
) 21 
23 
22 
18 
20 
21 


30 
25 
25 
25 
20 
22 
22 



3 plies 
21-30 yarns 


3 plies 
33-45 yarn* 


30 
24 
26 
26 
24 
24 
26 


32 
24 
28 
28 
24 
29 
28 



3 plies 
48-60 yarns 

35 
32 
28 
30 
26 
30 
30 



3 plies 
over 63 yarns 

40 
37 
30 
36 
26 
32 



[24] 



JAPANESE SYNTHETIC TWINES 



Number of yarn 4-15 

Kind of knots English knot Flat knot 



Drawing* 
direction 



Amilan 
Kuralon 

(Manryo) 
Saran 
Krehalon . 
Teviron 
Cotton 

Manila hemp . 
Kyokurin 
Kuralon No. 5 
Manryo No. 5) 



AB AC 



CD 

20 
21 

17 
18 
13 

22 

17 



BD 

21 

22 

18 
18 
13 
23 

18 



AB AC 
CD BD 



21 
22 

18 
18 
12 
21 



20 
21 

15 
16 
II 
20 



TABLE X 
Breaking Elasticity at Wet Knot 



(Unit ) 



18 -24 
English knot Flat knot 



AB 



20 
22 

19 
17 
19 

27 

20 



AC 


A B 


AC 


* 


t 


4- 





1 


i 


BD 


CD 


BD 


22 


21 


21 


24 


25 


24 


19 


19 


18 


18 


19 


17 


18 


18 


17 


28 


26 


24 



23 



2745 
English knot Flat knot 



AB AC AB 



CD 

25 



18 
20 
19 
30 
12 
20 



BD 



26 



19 
20 
19 
31 
13 
23 



_CD_ 

24 



19 
21 
18 
30 
13 



AC 

t 

4 

BD 

23 



17 
19 
18 
28 
11 



48 or more 


English 


knot 


Flat 


knot 


AB 


AC 


AB 


AC 


* 


t 


* 





^ 


4 


, 


+ 


CD 


BD 


CD 


BD 


30 


30 


28 


21 


30 


30 


26 


26 


18 


19 


16 


17 


23 


22 


24 


22 


20 


20 


19 


19 


34 


34 


32 


30 


14 


15 


15 


13 



24-26 25-27 



* Sec Fig. 4 for drawing direction. 



(3) Extension of twine and knots: The breaking 
extension of various kinds of twine and their knots is 
affected by the heating and stretching procedures during 
twisting (see Tables IX and X). Most of the twines tested 
were not elongated, except Amilan which was extended 
10 per cent. 



7. Abrasive Resistance 

( I ) The relation of twist to frictional pressure and strength: 
Generally speaking, there are two forms of friction which 
wear down fishing nets; one between net twines at the 
seam and the knots, and the other against comparatively 



2100 
20' a 

L'lOD of Arotli 
120D of SB ran 
3 WU> 
120Dx 3 
1ROD x 2 
20- b 




Fig. 5. Relation between wet strength of an English knot and 

the number of yarns of C20-equivalent less than 24. In the test, 

two pairs of the legs of the knot, AB and C7>, as in Jig. 4 were 

pulled asunder. 



VA 30 36 42 48 M 60 66 7 




Fig. 6. Relation between wet strength of an English knot and 

the number of yarns of C20-equivalent more than 24. The 

pulling direction was the same as in fig. 4. 



[25] 



Kind of 
products 

A 
B 
C 



MODERN FISHING GEAR OF THE WORLD 



TABLE XI 

Number of Twist of Amilan Netting Twine used for the Wear Test 

(Indicated on the basis of length 30 cm.) 



Low Twist (L) 
For twine For strand For yarn 



Medium Twist (M) 
For twine For strand For yarn 



56-4 
70-0 
54-0 



39-2 
46-3 
32-3 



56-3 
66-0 

47-3 



67-7 
65-8 
51-5 



65-7 
50-4 

35-7 



89-7 
65-6 
53-0 



A, B and C are the names of the twine manufacturers. 



Hard Twist (//) 
For twine For strand For yarn 



77-1 
78-5 
64-1 



68-0 
50 8 
55-4 



87-0 
69-9 

71-7 



hard substances, such as the sea bottom, hull of the boat, 
and net or line haulers. The friction between the net 
twines and hard objects was examined by use of a device 
shown in fig. 8. In order to keep the temperature 
constant, water was made to drip on the sample of twine 
under test. The twine stretched across an oil-stone C 
fixed on a block. The block was kept moving back and 
forth between E and F at 80 oscillations per minute, and 
the number of rubs counted. 
The results of these tests with Amilan twines of various 



twists are seen in fig. 9. The number of twists in the 
twines is shown in Table XI. Of the twists, those of the 
strand affect the abrasive resistance most, as they seem 
to play the greatest role in increasing the rigidity of the 
twine. Judging from the results, it seems that hard twisted 
twine should be used in that part of the net which comes 
into friction with hard objects. The utmost care should, 
however, be taken to ensure that the number of twists in 
the strand should not be too much to the detriment of 
tensile strength for the sake of friction resistance. 



TABLE Xll 

Decreasing Percentage of Strength of the Twines subjected to the seawater and the Sunlight 

(Unit %) 



Kind 

of 

test 



Submerged 
in the 
Sea 



Exposed 
to the 
Sunlight 



Name 

of 

twines 

Amilan 
Kuralon 

(Manryo) 
Saran 
Teviron 
Cotton 

Amilan 
Kuralon 

( Manryo) 
Saran 
Teviron 
Cotton 

(ditched) 



Non-treated 

conk except 

cotton 

8 
5 

3 



100 

16 

24 

10 
6 
8 



Tarred group A 


a 


b 


c 


8 


5 


12 


26 





31 


16 


6 


12 


14 


6 


19 











21 


9 


20 


9 


7 


18 


10 


8 


12 


1! 


7 


19 


4 


10 


4 



Tarred group B 
a b c 



8 
17 

9 
17 



18 
17 

6 

13 

8 



15 
10 

4 
6 




10 
30 

10 
16 



23 
27 

10 
18 



Refined coal tar used in treating samples in group A was different in component from 
the one used for group B. Both were used with or without other ingredients as follows : 
Sample 'a' was treated only with the tar, 'b' with emulsion of alkaline-soap-water (30%) 
and coal tar (70;,), and V with water (30%) and coal tar (70%). 

TABLE XIII 
Characteristics of Various Kinds of Synthetic Twine Comparable with Cotton Twine* 



Items 

Susceptibility to 

dye and dye fastness 
Head resistance 
Rigidity when wet 
Elasticity 

Resistance to chemicals 
Shock resistance 



Kuralon 
Amilan (Manryo) Saran Krehalon Teviron Envilon Cotton 





I 2 

2 

i 2 



2 

! 1 

2 





+ 1 



-1 
i 2 
-2 
1-1 
-1 



1 

-{ 1 

+ i 
o 



- 2 

1 

' 1 
-1 



1 

f-3 
-2 












Obtained on the basis of cotton twine regarded as standard (0). 



[26] 



JAPANESE SYNTHETIC TWINES 




AC - BD In Fig. 3{ a ) 

AB - CD in Pig. 3() 

AB - CD In Pig. 3 (b) 

AC - BD in Fig. 3 (b) 




Rural on Tovlron Saran Krahnlon Kyokurln Cotton 




Fig. 7 A-B. Relation between the knot strength and tyres of knot 

of various mines. In text /4, twines consisting of 6 yarns, and in B 

12 yarns, of C2()-equi relent were used. The pulling direction was the, 

same as in Jtg. 4. 

The size of* net twines is not always in conformity 
even when they have the same number of yarns, con- 
sequently, it is not feasible to compare the abrasive 
resistance of one type of fishing net with another that 
has different characteristics. However, for general 
purposes, comparison between various net twines made 
of C20-equivalent yarns is given in fig. 10. The method 
and the device employed for the test were identical with 
those described in the preceding paragraph. For this 
test the twines were of medium twist, having the same 
twist range as given in Table 11. 

Twine made of spun yarns, including cotton and some 

synthetics, have a comparatively greater resistance 

(figs. 9 and 10). In fig. 10 the solid lines show the abra- 

v Pouring into // 

r K ] 



M 'JiV'i'ii I !''M Pouring 




Draining our 



AB 

c 

D 
EF 
G 



Teic piece H 

Oil scon* (Frictmg object) I 

Weight j 

Reciprocating direction K 

Stopper for testpiece L 



Counting apparatus 

Crank 

Motor 

Water tank for pouring 

Water tank for draining 



Fig. 8. A device used for testing the wear resistance of twines. 
The velocity of the reciprocative abrasion is 80 per minute both 
back and forth. 



TABLE XIV 

Contraction in Length of Netting Twine by Heating in Water 

(Unit %) 



Heating 
temperature 

Amilan 
Rural on 

( Manryo) 
Saran 
Krehalon 
Teviron 

Cotton 



40 C 60C 70 'C 80 C 90C 1(XTC 





5 




5 

(3) 
6 





7 

6 

1 

15 
(8) 

7 





8 

1 

3 

25 
(15) 

8 



1 
11 

3 

5 

30 
(20) 

8 



-1 
12 

5 

7 

45 
(30) 

8 



-1 
15 

6 
11 
56 
(35) 

9 



Numerals in parentheses show the percentage of contraction 
the length of twine heated before test. 



sive resistance of tarred twine, and one may see that tar 
treatment enhances the abrasive resistance of net twine. 
As a result of tarring long fibre twines resist friction 
better than others which have the same number of 
C20-equivalent yarn. 

With resin treatment the increase in abrasive resistance 
depends upon the thickness of the coating. A 3 to 5 per 



50,000 - 



10,000 




10 



00 1.000 



3,000 



Hg. 9. Friction resistance of Amilan netting twines, A. B and C\ 
each produced by different makers with different twists. The 
test temperature was kept at 18 'Ci- /"C. The notation AH, 
for instance, indicates the twine made by A maker with hard 
twist. See Table XI for further information. 



[27] 



MODERN FISHING GEAR OF THE WORLD 



210D. 3/15 
20- . 3/li 

1/9 (210D of AmUM * 2) 
120D of 9 

. s/u 

1200x9. J/U 
ISODi 2. 3/1B 
20' . 3/18 




i may double or quadruple the strength, 
mid be washed off during fishing operati 



But, 



Fig. 10. Relation between the friction resistance of netting twines 
and the fricative load increased at the place D of fig. 8. The 
test temperature was the same as in fig. 9. 



cent, adhesion : 

as the resin would be washed oft during fishing operations 
a more practical method of fixing it must be developed 
as a counter measure to dilution. 

(2) Interfriction between twines: The results obtained 
by Miyamoto and Mori 15 may be summarized as follows: 
When synthetic fibre twines are rubbed against another, 
abrasion between hard quality twines results in quick 
snapping; when a hard twine is rubbed against a soft 
one the latter breaks first; if both are soft the abrasive 
resistance of both seems to be increased. Hardness has 
a big influence on the abrasive strength. For example, 
when cotton twine is rubbed against Kuralon twine it 
needs 260 rubbings to snap the latter, yet Kuralon can 
withstand up to 530 rubbings against the cotton. When 
Kuralon is rubbed against Saran it snaps after only 60 
rubbings and the same applies when cotton is rubbed 
against Teviron and Kyokurin. Between twines of the 
same kind, the number of rubs needed to break them is 
mostly as many as, but sometimes a little more than, 
the number required to break cotton. 

8. Other Characteristics 

(1) Knot fastness: With natural fibre twines, knot 
slippage hardly constitutes a problem as compared to 
synthetic fibre twines. In Japan, the synthetic twines 
which lend themselves best to knotting are Kuralon, 
Teviron, Envilon, Krehalon, Saran, Kuralon No. 5, 
Kyokurin and Amilan in the order named. For fixing 
the knots, various types of knots as shown in fig. 4 are 



TABLE XV. Breaking Strength of Various Kinds of Ropes in Dry State 



Thickness 


Manila hemp 


Kuralon 


Kuralon No. 5 


Diameter Circum 


- (/IS) 


Amilan 


(Manryo) 


(Manryo No. 5) Saran 


Krehalon Envilon Teviron 


mm 


inch 


inch 


w 


BS 


W 


BS 


W 


BS 


H 


BS 


W 


BS 


W 


BS W BS W BS 


3 






__ ' 





2-74 


13 


2-54 


0-085 


__ 




_ 


_1!" 




___.__ 


4 




i 


5-2 


0-13 


4-4 


0-210 


4-24 


145 





-_. 




0-130 




55 130 


5 


i 









6-6 


0-310 


6-8 


0-235 





_ 








.___ 


- 8-6 195 


6 


* 


1 


117 


0-27 


10 


0-470 


10-2 


0-335 


10-5 


0-3S7 


14 


0-250 


14 


0240 10740270 11-2 0-270 


7 






__ 





13-2 


0-630 


13-6 


0-455 


14 4 


490 


18 


325 


18 


0-310 15 34 0-350 15-7 360 


8 


A 


10 


20 7 


46 


16 6 


0-790 


17-0 


0-580 


19-2 


0-653 


24 


0-430 


24 


0-410 19 94 450 19 8 450 


9 


i 


1* 


26 2 


57 


21-6 


1-030 


21-6 


0-730 


24-0 


816 


30 


540 


30 


510 26-08 0-590 25-1 0-570 


10 


tt 


U 


32-4 


70 


26-4 


1-270 


25-6 


0-920 


30-0 


0-970 


36 


0-640 


36 


0610 33-8 0720 31 4 0-715 


11 











31-4 


1-500 








36-0 


1 160 








.- 


39-8 0-850 


12 


ti 


U 


46-6 


98 


39-6 


1-900 


39-2 


1-360 


42-0 


1-380 


54 0-970 


54 


0-930 46-0 1 000 440 1-000 


14 


* 


l* 


63-4 


1-30 


52-8 


2-530 


51 2 


1-850 


57-0 


1-870 


72 


1-300 


72 


1-240 61-4 1-350 62-2 1-380 


16 


ft 


2-0 


82-9 


1-67 


66-0 


3-170 


64-8 


2-400 


66-0 


2-460 


96 


1-730 


96 


1-650 82-8 1-830 80-5 1-830 


18 


tt 


2i 


105 


2-08 


87-8 


4-230 


85-4 


2-850 


92-0 


3-130 


120 


2-160 


120 


2 100 104-8 2 300 102-5 2-380 


20 





2* 


129-0 


2-53 


109-8 


5-290 


108-2 


3-520 


116-0 


3-800 


150 


2-700 


150 


2-570 128-8 2-850 125-5 2-860 


22 


* 


21 


157-0 


3-02 


131 8 


6-350 


131-0 


4-260 


140 


4 600 


180 


3-240 


180 


3-100 156-4 3-480 151-0 3-430 


24 


tt 


3-0 


186-0 


3-55 


151-4 


7-300 


157-2 


5 080 


162-0 


5-510 


216 


3-890 


216 


3-700 183 6 4000 175 4-000 


26 


1A 


3* 


219-0 


4-12 


177-8 


8-570 


184-4 


5-960 


192-0 


6-530 


252 


4-540 


252 


4-350 214-2 4-750 207 4-720 


28 


U 


3* 


254-0 


4-73 


210-8 


10-160 


211-8 


7-000 


222-0 


7-560 


294 


5-300 


294 


5-100 2440 5-000 245 5-570 


30 


1* 


31 


291-0 


5-38 


237-2 


11-430 


247-6 


7-940 


258-0 


8-780 


336 


6 050 


336 


5-800 287-6 6-450 277 6-280 


32 


U 


4-0 


331-0 


6 06 


270-6 


13 040 


281-8 


9-030 


294-0 


10-000 








3-242 7-300 


34 


1 


4* 


374-0 


6-79 


298 


14-390 


315-6 


10-000 


330-0 


11-300 










36 


1A 


4* 


419-0 


7-55 


336 


16-190 






372-0 


12-600 










38 


U 


4| 


467 


8-34 


374-0 


17-800 


















40 


i 


5-0 


518-0 


9 18 


410-0 


19-800 


















42 


if* 


5i 


571 


10-05 


458-0 


22 000 


















45 


1H 


58 


655-0 


11-43 


522-0 


25-200 








JIS 


Japanese Industrial 


Standard. 


50 


2-0 


6i 


809-0 


13-90 


644-0 


31-000 








W 


Weight 


in pounds per 200 metres. 


55 


2ft 


6* 


979-0 


16-60 


784-0 


37-800 








BS 


Breaking strength in metric tons 


60 


2* 


7| 


1165-0 


19-52 


932-0 


45-000 


















65 


2* 


8-0 


1367-0 


22-65 


1092-0 


52-500 



















[28] 



JAPANESE SYNTHETIC TWINES 



used by Japanese fishermen. Most synthetic fibre nets 
except Kuralon and Mulon need heat treatment to fix the 
knots. 

Heating with hot water, gas, or air, is widely applied 
to synthetic fibre nets for knot setting, as the treatment 
can reduce the amount of complicated knotting, which 
means that the finished product weighs less. Amilan 
nets may be heated at the temperature 100 deg. C. or 
higher, while the others, except Kuralon, can be treated 
at lower than 72 deg. C. 

(2) Resistance to sunlight and seawater: Table XII 
shows the results obtained from one group of tarred net 
twines immersed in the sea and another exposed to the 
sunlight, both for one year. From the table it appears 
best to use coal tar with low isolated acid content or to 
neutralize the tar with alkali before use 16 . 

(3) Characteristics of ropes: For comparison, the break- 
ing strain of manila and synthetic ropes is reproduced in 
Table XV by courtesy of the Tokyo Seiko Kaisha, 
Limited. 

REFERENCES 

1 Shimozaki, Y.: Unpublished. 

2 Tauti, M.: Studies of Netting Cords IV. Strength of Cord 

in Relation to the Twist. Vol. 25, No. 2. Jour. Imp. 
Fish. Inst. pp. 31-41, (1929). 

8 Shimozaki, Y. and K. Mori: Studies on the Breaking Strength 
of Netting Cords Made with Various Twisting Machines I. 
Bull. Tokai Reg. Fish. Res. Lab., No. 13, pp. 61-72 (1956). 



Kondo, J.: Influence of the Difference in Size of Cotton Yarns 

Composing the Netting Cord on the Breaking Strength and 

the Flexibility of the Cord. Bull. Japan. Soc. Sci. Fish. 

Vol. 4, No. 5. 
Koizuma, T. : The Tensile Strength of Saran Netting Cord of 

Various Twist. Bull. Japan. Soc. Sci. Fish. Vol. 20, No. 7 

pp. 569-570 (1954). 
The Tensile Strength of Amilan Netting Cord of Various 

Twist, Ibid. Vol. 21, No. 3, pp. 139-140 (1955). 
Shimozaki, Y. and K. Mori : Studies on the Breaking 

Strength of Netting Cords Made with Various Twisting 

Machines I; Bull. Tokai Reg. Fish, Res. Lab., No. 13, 

pp. 68-70, (1956). 
Shimozaki, Y. : Synthetic Fishing Nets and Ropes. Fish. 

Tochnol. Scries. No. 3, pp. 68-69, Assoc. Fish. Material 

(1951). 

Unpublished. 

On the Change in Strength of Netting Cords Immersed 

in the Sea I. Relation between the Strength of Synthetic 
Netting Cords and the Temperature, and Comparison of 
Power of Various Kind of Cords Changing when Immersed 
in the Sea. Bull. Japan. Soc. Sci. Fish. Vol. 20, No. 5 (1954). 

Honda, K.: Influence on the Length of Test Piece on the 

Breaking Strength and Elongation of Netting Cord. Bull. 

Japan. Soc. Sci. Fish., Vol. 22, No. 6 (1956). 
Shimozaki, Y.: Synthetic Fishing Net and Ropes. Fish. 

Technol. Series. No. 3, pp. 77-79, Assoc. Fish. Material 

(1957) 

Ibid, pp. 79-81. 

Unpublished. Lectures delivered at Japan Soc. Sci. Fish. 

April (1956) and (1957). 

Miyamoto, H. and K. Mori: How Netting Threads Wear 
Down Due to Interdiction. "TFICH" No. 12, Nippon 
Set Net Fish. Soc. pp. 9-12 (1957). 

Shimozaki, Y. : Synthetic Fishing Nets and Ropes. Fish. 
Technol. Series. No. 3, pp. 94-95 (1957). 




Although synthetic fibres are being used in ever increasing quantities even in those countries where the fishing industry is not highly developed 
technically, the majority of fishing nets are still being made of natural fibres. The woman in the photo is spinning a yarn from sun-hemp in 

Ceylon. Photo FAO. 

[29] 



NYLON IN FISHING NETS 

by 
J. E. LONSDALE 

British Nylon Spinners Ltd., Pontypool, Monmouthshire, Great Britain 

Abstract 

In this paper, the author gives an outline of the desired characteristics of the ideal fibre to be used for fishing nets, and then compares 
this specification with the properties of nylon 66. The physical properties of this material are discussed in detail yarn strength, twine strength, 
knot strength and the comparison between the strengths of wet and dry twines and in general, nylon nets are able to withstand attacks by 
chemicals, oils, insects, vermin, bacteria and moulds, and their ability to stand up to considerable flexing and abrasion is very good. Since 
the nets do not rot, it is not necessary to dry them in the sun, and in certain African fisheries it is the habit to store gillnets in the water when 
they are not being fished. 



Resume 



Le nylon dans les filets de peche 



L'auteur expose dans cette etude les caracteristiqucs de la fibre idcule destmee a la confection des filets de peche, et les compare 
avec les proprietes du nylon 66. II fait un examen approfondi des proprietes physiques de ce materiau: resistance des files, des fils, des 
noeuds, et resistance comparee des fils sees et mouilles. En general, les filets de nylon sont insensibles aux produits chimiques, aux huiles, 
aux inscctcs, la vermine, aux bacteries et aux moisissures. et la resistance A la flexion et & Pabrasion est excellence. Comme les filets ne 
pourrissent pas, il n'est pas neccssaire dc les fairc secher au soleil, et dans certaines entreprises africaines de peche on a coutumc dc conserver 
les filets maillants dans 1'eau quand ils ne sont pas utilises pour la peche. 

El nylon en las redes de pesca 
Extracto 

En este trabajo el autor hace una rcsena de las caracteristicas que debe tener una fihru ideal para red de pesca y las cornpara con las 
propiedades del nylon 66. Tambien analiza, en detalle, las propiedadcs de cste material rcsistencia de las fibras, hilos y nudos, com panic ion 
de la resistcncia de los hilos humedos y secos y expresa que, generalmente, las redes de dicha fibra resisten cl ataque dc compucstos quimicos, 
aceites minerales, insectos, gusanos, bactcrias y mohos. Ademas, dicha fibra ofrece bastante resistencia a la flexion y al desgaste causado por 
el roce. 

Como las redes de ny!6n no se pudren, es innecesario secarlas al sol, y en algunas pesquerias africanas existe la costumbre de 
mantcner los artes de enmalle en el agua cuando no se usan. 



SPECIFICATION FOR IDEAL FISH NET FIBRE 

(1) The basic cost should be low. 

(2) Processing into net form should be cheap, easy and 
efficient. For example, shrinkage on setting should 
be low. 

(3) In both wet and dry states it should have high 
strength, by which is meant: 

(a) high tensile strength; 

(b) good ability to withstand repeated shocks; 

(c) good flex strength or fatigue resistance; 

(d) high knotting efficiency and 

(e) good resistance to abrasion 

which leads to fine, long-lasting nets, capable of 
holding large catches. 

(4) It should maintain its strength in use. 

(5) It should have good dimensional stability and 
should not distort in size or shape during use. 

(6) It should have low moisture absorption so that the 
increase in weight is small when a net becomes wet 
and handling is consequently easier. 

(7) The fibre should have a low specific gravity, since 



this allows a greater length of netting for a given 
weight of yarn, and may permit lighter fittings and 
savings in power and manhandling. On the other 
hand, a low specific gravity may not be desirable 
where quick sinking of the net is required. 

(8) It should be resistant to damage and attack by 
chemicals, oils, moulds, bacteria, insects and vermin 
in order that treatments and routine maintenance 
can be kept to a minimum. 

(9) The performance of the fibre should remain constant 
at extremes of temperature. 



TABLE I 
Specific Gravity of Fibres 



Nylon 66 and nylon 6 

Polyvinyl alcohol 

Polyester fibre . 

Hemp . 

Flax 

Cotton 

Polyvinylidene chloride 



14 
30 
38 
48 
50 
52 
72 



[30] 



NYLON IN FISHING NETS 



(10) The net should hold the fish firmly when caught, yet 
not damage them. 

(11) Some types of fishing nets may demand other 
requirements, such as translucency for gill nets or 
a lower initial elastic modulus as is required for 
salmon gillnets. 

The initial modulus (calculated by measuring the 
load to produce a 5 per cent, extension under con- 
ditions of 70 deg. :i- 4 deg. F. and 67 2 per cent. 
R.H.) for nylon yarns lies in the range 20 to 40 grams/ 
denier, with nylon 66 high tenacity yarns at the top 
end of the bracket, while, for comparison, the initial 
modulus of high tenacity polyester fibre lies in the 
range 90 to 100 grams/denier. 

The basis of the specification can be extended to 
methods of fishing which do not employ nets. It 
could include the principles involved in the choice 
of fibre for long-lines or whaling foregoers, etc. 
There is now a wide range of fibres available to 
satisfy the diverse needs of the fishing industry. 
None meets, nor could meet, the specification 
completely. 

Even when one fibre is isolated and examined 
alone, it can be seen that there is ample variety of 
choice. Thus, nylon can be divided into classes 
according to the type of polymer used, and whether 
the yarn is assembled from continuous filament 



or spun fibre; within each of these classes there is 
a range of yarns with varying properties. 

The task facing a supplier of continuous filament 
nylon for the production of fishing nets is to provide 
a yarn which measures well in comparison with the 
specification. Some of the conditions are met 
automatically (e.g. low specific gravity, rot resist- 
ance, high strength, good stability and small 
temperature influence), while others have to be met 
as nearly as possible. One of the chief ways in which 
a nylon yarn can be upgraded is by increasing its 
strength. 

YARN STRENGTH 

The dry tensile strength of all nylon yarns 66 and 6 
lies in the range 4- 5 to 9-0 grams/denier. The yarns at the 
top end of the bracket are stronger than any other 
commercially available fibre. The equivalent range of 
extension at break is 25 to 12 per cent. Generally speaking 
a higher tenacity implies a lower extension at break. 

Fig. 1 shows typical load-extension curves for three 
yarns of B.N.S. nylon 66 (measured under a rate of load 
application of 0-5 grams/den ier/sec.), and illustrates the 
different forms these may take. The energy absorption of 
each, as measured by the area under the curve, is shown 
in Table II, together with values for tenacity and extension 
at break. 




TABLt II 

Load/Extension Properties of Nylon 66 Yams 



Tvp t 500 



- NM.OM T>P IOO 



Fig. L Load/ Extension Curves of BNS nylon 66 yarns. 



Yarn Reference 



B.N.S. nylon 205 denier 

type IOO 
B.N.S. nylon 210 denier 

type 300 
B.N.S. nylon 840 denier 

type 600 



Tenacity 
(gramsldeni'r) 



4-5 

7-4 
8-8 



Extension Energy 
at (break Absorption 
(%) (inch Ibs./inch) 



22 
15 
13 



0*27 
0-31 
1-11 



It will be seen that the energy absorption of 210 denier 
type 300 on a weight for weight basis is higher than the 
other two yarns. This very high energy absorption has 
been a factor in its ready acceptance for fishing nets. 

TWINE STRENGTH 

As in the case of all fibres, nylon twines are made with 
twist in order to bind the yarns together. The degree of 
twist and the construction control the feel of the twine. 
Increasing the degree of twist in a nylon yarn lowers the 
tensile strength. The ratio of twine strength to aggregate 
yarn strength is known as the doubling efficiency. Most 
nylon twines are made with a doubling efficiency of 95 
per cent, or more. This can be affected, not only by 
twist, but also by conditions of setting and heat stretching. 
Twine strength is commonly expressed in Ibs. or other 
units of weight. Another method is to refer to specific 
strength (or breaking length), this being defined as the 
greatest length of twine which can be supported by a 



[31 ] 



MODERN FISHING GEAR OF THE WORLD 



TABLE III 
Average Specific Strength of Fibres 1 



Nylon 66 
Nylon 6 
Polyester fibre 
Linen 



Twine 



Drv 



Mesh 
Single Knot Double Knot 



Wet Dry Wet Dry Wet 



(yd.) (yd.) (yd.) (yd.) (yd.) (yd). 

63700 56000 30800 28100 34300 29900 

39100 35200 24400 22000 26600 23100 

48600 50200 20000 20700 24100 23500 

44000 58800 19900 31600 



The investigation was continued by studying the effect 
of change of molecular orientation on shear, torsion and 
compression. No appreciable effect on shear and torsion 
could be detected, but compressive force, as represented 
by loop tenacity, described a parabola. From these 
facts, it was deduced that compressive and tensile forces 
act in opposition as orientation is changed (fig. 3). 

The effect of compressive forces was subsequently 
shown experimentally by knotting unstretched polythene 
and examining it visually, and subjecting broken nylon 
knots to cross-polarised light. Tests on various knots 



single piece of that twine without breaking it. The 
supporting piece may be dry, wet or knotted. 

Specific strength (or breaking length) (in yards) 
Twine strength (Ibs) ,- twine weight (yds./lb.) 
This unit is of value in comparing different fibres. 
Results on nets tested in Canada appear in Table III, 
which lists the specific strength of dry and wet twine and 
knots. Nylon 66 will be similar to type 300. 



o 



O 



KNOT STRENGTH 

When a knot is tied in a twine, it constitutes a place of 
weakness, and reduces the effective strength of the twine. 
The term "knotting efficiency" can be used to describe 
the ratio of dry knot strength to dry twine strength (or 
alternatively wet knot to wet twine strength). The knot- 
ting efficiency, measured either way, of nets made from 
nylon 66 yarn is of the order of 40 to 50 per cent, for 
single knots and 50 to 60 per cent, for double knots. 

An investigation 2 has been carried out into the factors 
influencing the loss of strength on knotting. This has 
resulted in a clearer appreciation of the mechanism of 
knotting and the effect of yarn properties on knotting 
efficiency. 

Practical tests have shown that every type of knot has 
a different knotting efficiency, and that their order of 
efficiency approximates to the same for all fibres examined 
(nylon 66, nylon 6, polyester fibre, and polyvinylidene 
chloride). The differing configurations of various knots is 
responsible for the variations; it has been shown that a 
decrease in the angle through which the loop is formed 
decreased the loop strength; increasing the number of 
loops or hitches in a knot increased the knot strength. 
The effect of molecular orientation on knotting efficiency 
was investigated to study the nature of the rupturing 
forces more closely. Nylon 66 yarn of the same nominal 
denier and number of filaments was used to tie three 
types of knots the overhand, warpers and double 
weavers. It was shown that with increasing molecular 
orientation the yarn tenacity increased linearly, knotting 
efficiency decreased linearly, whilst knot strength assumed 
a parabolic curve (fig. 2). The shape of the latter could 
be confirmed by calculation from the two straight line 
relationships. The degree of orientation of the yarn 
exhibiting maximum knot strength is of obvious practical 
importance. The manufacturer of nylon yarn, having the 
opportunity to tailor-make his fibre, should attach 
proper importance to this effect. 



MOL.ECAJL.AC 



u 
z 

UJ 

y 
C 

Lu 
UJ 

O 

z 



MOLECLUL.AQ 



t 
U 



7. 

ot 



MOLECUI.AQ 
Fig. 2. Individual Effect of Molecular Orientation. 



[32] 



NYLON IN FISHING NETS 




M oc e w_ in. AW Oft i e. rj -r > T IOINI 
/#. .?. Combined Effect of Moleculw 



showed thai the break always occurred under the looped 
section. In symmetrical knots, such as the Blood, two 
positions of stress concentration corresponding to the 
two looped sections were observed. 

WETTING 

When nylon twines are wetted lhe> lose strength but 
gain in extensibility. The loss in strength (of both type 
66 and 6) whether in yarn, twine or net form is of the 
order of 10 to 15 per cent. The increase in extension at 
break of twines made from nylon 66 is of the order of 
15 to 20 per cent, according lo size and construction. The 
importance of this effect is to counterbalance the loss of 
tensile strength when assessing the change in energy 
absorption. It is this latter property which is of critical 
importance in deciding whether a net will break or not 
under dynamic conditions. Nylon's present place in fish- 
ing nets is largely due to its comparatively high energy 
absorption under dry and, even more so, wet conditions. 
A typical 3/3/210 denier nylon 66 twine had the pro- 
perties shown in Table IV. By measuring the area under 



JABLL IV 

Comparison of Dry and Wet Twine Properties for a Typical 3/3/210 
Denier B.M.S. Nylon 66 Twine 



Breaking load 
Extension at break 
hnergy absorption 



Dry 



32-4lbs. 
21 -0 n 
3-36in.lb./in 



Wet 



28-6lbs. 



Change on 
Wetting 



3-96 in.lb./m. 




18% 



the load/extension curves, dry and wet, it was found that 
the energy absorption actually increased when wet by 
18 per cent. 

IN USE 

Nylon nets, in common with those made from all other 
fibres, slowly Jose strength in use. In certain African 
fisheries it is now the habit to store gillnets in the water 
when they are not being fished. 

The abrasion resistance, dry and wet, of nylon 66 is 
extremely good. This can be varied by choice of filament 
denier. All nylon fishing twines are based on a filament 
denier of about 6 (as opposed to 1 to 3 for most apparel 
uses), thus providing a happy compromise between 
good abrasion resistance and flexibility (which decreases 
with increased filament denier). 

ACKNOWLEDGMENTS 

The author wishes to thank the Directors of British 
Nylon Spinners Limited, Pontypool, Monmouthshire, 
Great Britain, for permission to present this paper, and 
his colleagues for help given in its preparation. 

REFERENCES. 

J *The Selection and Care of Nylon Gillnets for Salmon." 
P. J. G. Ca rot hers. Fisheries Research Board of Canada 

-"Knots, Their Effects, and the Forces Involved/' R. J. Harrison, 
Associateship Thesis, Royal College of Science and Tech- 
nology, Glasgow, June 




Menhaden purse seine dories with the catch "dried up" in the hunt. 

[33] 



Photo FAO. 



THE TECHNOLOGICAL CHARACTERISTICS OF PERLON FOR 

FISHING EQUIPMENT 

by 

PERLON-WARENZEICHENVERBAND F.V. 
Frankfurt Am Main, Westendstrasse 41 

Abstract 

Perlon is a synthetic fibre which, like nylon, is one of the polyamides. It is made as Monofilament, Continuous Filament and 
Staple Fibre and this comprehensive paper deals with its chemical and physical properties and discusses its suitability for trawls, seines, 
setnets, whaling ropes and cordage, also for tarpaulins and protective coverings. 



Resume 



caractfrristiques technologiques de Perlon pour le material de pcche 



Comme nylon, Perlon est unc fibre synthetique du groupe des polyamides. On le fabrique en monofilament, fibres continues 
et fibres filees et cette communication detaillee traite de ses proprietds chimiques et physiques et examine s f il convient pour la confection de 
chaluts, de sennes, dc filets fixes, de cables pour la chassc a la baleine et de cordes. et uussi pour faire des baches et des enveloppcs pro- 
tec trices. 

Caracteristicas tecnoldgicas del perlon para equipo de pesca 
Kxtracto 

En este trabajo se estudian las propiedadcs quimicas y fisicas del perlon qtie, como el ny!6n, cs una poliamida, y se analizan sus 
condiciones para usarlo en la fabricaci6n de redes de arrastre, fijas y dc cerco, estachas para arpones, cordeleria, encerados y cubiertas 
protectoras. Esta fibra sinletica se fabrica en forma de hilo y filamento continuos o como hilado. 



I. WHAT IS PERLON ? 

PERLON,* Jike nylon, is a synthetic fibre which 
belongs to the polyamides' group. Like all fibre- 
forming materials, it consists of large elongated 
molecules. It results from the assembly of a large number 
of molecules of a homogeneous material, caprolactam. 

Perlon: 

<CH,) S 



n. f - ..HN(CH 2 ) 6 COHN(CH 2 ) 5 CO.. 



NHOC 

E Aminocaprolactam 

Both fibres are manufactured in the United States, 
where the fibre developed by Du Pont is called Nylon 66, 
as opposed to Nylon 6 for Perlon, a fibre developed by 
the former IG-Farbenindustrie combine in Germany. 
In their technological properties Perlon and nylon are 
largely identical, except for the melting point which, in 
the case of nylon, is approximately 30 deg. C. higher. 

Both fibres are manufactured by the extrusion process. 

* The name Perlon and its emblem are registered trademarks of 
the PERLON-Waren/eichenverband e.V. (PERLON Trade Mark 
Association), Frankfurt/Main, Germany. 



As a result the fibres are cylindrical and have a smooth 
featureless surface. 

By adding titanium dioxide or other suitable substances 
during the polymerization process, a matt fibre can be 
extruded. This does not affect the physical properties of 
the fibre except resistance to sunlight which is consider- 
ably reduced. Matt fibres should not be chosen for the 
manufacture of nets. 

II. FORMS OF PERLON 

Perlon is available in 3 basic forms for the fishing industry: 
Monofil 

Continuous Filament and 
Staple Fibre. 

(a) Monofil 

Monofil has the advantage that it can be used for the 
manufacture of nets without having to undergo further 
processing (e.g. twisting or plaiting). 

Monofils are continuous transparent wires, with a 
diameter of between 0- 1 and 2 mm. (0-004 in. to 0-08 
in.). Table I gives average values of breaking load and 
length per unit weight. 

(b) Continuous Filament 

Continuous filament has greater strength and less 
extensibility than staple fibre and is lighter in weight than 



[34] 



CHARACTERISTICS OF PERLON 





TABLE 
Mono 


1 
fils 




Diameter 
In mm. 


Breaking 
Load 
In kg. 


Length per 
Unit Weight 
mlkg. 


Nm 
(Metric 
Number) 


0-10 


0-5 


app. 92,000 


92-0 


0-15 


1-1 


43,000 


43-0 


0-17 




32,200 


33-0 


0-20 


1-8 


25,000 


25-0 


25 


2-7 


15-16,000 


15-16-0 


0-30 


3-7 


10-12,000 


10-12-0 


0-35 


5-1 


8,600 


8-6 


0-40 


6-5 


6.600 


6-6 


0-45 


8-4 


5,300 


5-3 


0-50 


10-0 


4,300 


4-3 


0-55 


12-2 


3,500 


3-5 


0-60 


14-5 


3,000 


3-0 


0-65 


16-5 


2,600 


2-6 


0-70 


19-0 


2,200 


2-2 


0-75 


22-0 


,900 


9 


0-80 


25-0 


,700 


7 


0-85 


28-0 


,500 


5 


0-90 


31-5 


,300 


3 


0-95 


33-5 


,200 


2 


00 


36-0 


,100 


1 


10 


42-0 


900 


0-9 


20 


50-0 


760 


0-76 


30 


57-0 


650 


0-65 


35 




600 


0-60 


40 


66-0 


560 


0-j6 


50 


76-0 


490 


0-49 


60 


87-0 


430 


0-43 


70 


98-0 


380 


0-38 


80 


110-0 


340 


0-34 


90 


125-0 


300 


0-30 


2-00 


140-0 


270 


27 



TABLE 111 
Perlon Continuous Filaments in Heavy Deniers 



the equivalent cotton product. It is supplied in fine and 
coarse qualities. 



TABLE II 
Perlon Continuous Filaments in Fine Deniers 



Denier 


Metric 
Number 
Nm. 


Length per 
Unit Weight 
mlkg. 


Number of 
Filaments 


210 


43-0 


42.860 


35 


630 


14-0 


14,290 


105 


750 


12-0 


12,000 


125 


840 


10-7 


10,710 


140 



Heavier deniers ("cables") is used as the raw material 
for net twines subject to severe stress, and for the 
manufacture of ropes (Table HI). 

The choice of 6 and 20 filament denier allows for 
different degrees of stiffness required, the stiffness of 
Perlon increasing with the denier. 

Consequently Perlon made up to 20 denier filaments 



Denier 


Metric 
Number 

Nm. 


Length per 
Unit 1 Weight 
mlkg. 


f-'i lament 
Denier 


Number of 
Filaments 


1,050 


8-6 


8,570 


6 


175 




1,260 


7-1 


7,140 


6 


210 




2,500 


3-6 


3,600 


20 


125 




3,000 


3-0 


3,000 


6; 20 


500; 


150 


3,210 


2-8 


2,800 


20 


160 




4,500 


2-0 


2,000 


20 


225 




5,000 


1-8 


1,800 


20 


250 




6,200 


1-5 


1,500 


6 


1,035 




7,500 


1-2 


1,200 


6; 20 


1,250; 


375 


9,300 


1-0 


1,000 


6 


1,550 




10,000 


0-9 


900 


20 


500 




11,250 


0-8 


800 


6 


1,875 




12,500 


0-7 


700 


20 


625 




15,000 


0-6 


600 


6; 20 


2,600; 


750 


30,000 


03 


300 


20 


1,500 





should be used where the end product is subjected to a 
sustained process of kneading and flexing. 

However, where a highly flexible product is required 
6 denier filaments are more suitable. 

(c) Staple Fibre 

Spun staple fibre twines are particularly suitable for 
inland and coastal waters. The yarns are spun like cotton 
yarns to attain the highest possible degree of strength or 
produced from a spinning tow and then spun into yarn 
by means of a modified schappe spinning process after 
cutting. 

The following types of staple fibre are available in 
yarn numbers up to Nm. 50: 

Cotton spinning process: 

2 den., cut length 60 mm. 
27 den., cut length 60 mm. 

Schappe spinning process: 

2, 7 den. average length of staple 100 mm. 

The optimum tensile strength of spun staple fibre 
yarn should be a breaking length of 30 km. in a Nm. 
34/1 yarn. 

Where net yarns must be stiffened with black varnish, 
spun staple fibre yarn is superior to continuous filament 
yarn, since the staple fibre yam absorbs the stiffening 
preparation more thoroughly. 

III. PROCESSING INTO NET TWINES, CORDAGE 
AND ROPES 

(a) Perlon Monofils 

Table IV gives the appropriate monofil strength for 
gillnets to replace cotton net twines. 

For mesh sizes in excess of 30 mm. at least 0-20 mm. 
diameter should be chosen even for the finest types of 
nets. 

The monofils are available as fishing lines in diameters 
between 0-1 and 2 mm. The rope making industry is 



[35] 



MODERN FISHING GEAR OF THE WORLD 



TABLE IV 
Monoflls suitable for Gillnets 



TABLE VI 



Cotton Net 


renon 


Length pet- 


A//M 


twine 

Nm. 


Diameter 


Unit Weight 


/ Tffl. 

(Metric Number) 


270/6 15 


or 20 


a pp. 43,000 resp. 


43-0 resp. 25-0 


240/6 




25,000 




200/6 


20 


25,000 


25-0 


160/6 


0-20 


25,000 


25-0 


140/6 


0-20 


25,000 


25-0 


120/6 


25 


16,000 


16-0 


100/6 


25 


16,000 


16 


100/9 


0-25 


16,000 


16-0 


85/6 


0-30 


12,000 


12-0 


85/9 


0-30 


12,000 


12-0 



using Perlon monofils as raw material for the manu- 
facture of braided and twisted cordage. 



TABLF V 

Comparison in length per unit weight of coarser monofils with 
cotton twine of equal wet strength 



Cotton Net twine 



Perlon Monofils 



Cotton 


Length per 


Metric Number 


Unit Weight 


Nm. 


mfkp. 


50/9 


5,000 


50/12 


3,600 


50/15 


2,900 


50/18 


2,400 


20/6 


2,900 


20/9 


1,950 


20/12 


1,400 


20/15 


IJOO 


20/18 


940 


20/21 


830 


20/24 


680 





Mean 


Diameter 


Length pel- 


mm. 


Unit Weight 




mlkg. 


0-35 


8,600 


0-40 


6,600 


0-45 


5,300 


0-50 


4,300 


0-45 


5,300 


0-50 


4,300 


0-60 


3,000 


0-70 


2,200 


0-70 


2,200 


0-70 


2,200 


0-80 


1,700 



Mff 


Length 






Length 




/Vt 1 


per Unit 


Diameter 


Net twine 


per Unit 


Diameter 


t wine 


Weight 


mm. 


den. 


Weight 


mm. 


iten. 


m.fkg. 






m/kg. 




210/2 


20,000 


0-28 


210/18 


2,100 


0-88 


210/3 


13,000 


0-30 


210/21 


1,850 


0-95 


210/6 


6,400 


0-48 


210/24 


1,600 


1-00 


210/9 


4,300 


0-60 


210/27 


1,450 


1-10 


210/12 


3,200 


0-70 


210/30 


1,320 


1-15 


210/15 


2,480 


0-80 









Continuous filament twines are quite smooth and 
much less dirt adheres to nets made of such material than 
to nets made of cotton or spun staple fibre twines. 
Continuous filament or Perlon monofil is particularly 
suitable for heavily polluted waters. Braided or twisted 
twines of 840 denier, 1,059 denier, 1,260 denier, and 3,000 
denier are especially suitable for equipment subject to 
severe strain such as bottom trawls. Perlon continuous 
filament twisted twines are considerably stronger than 
manila twines. This makes it possible to manufacture 
lighter weight nets to reduce the towing drag and allowing 
the use of less power. 



Manila-Extra 

Length per Breaking 
Unit Weight (kg.) 

mjkg. dry 

186 120 
248 95 



375 



65 



TABLE VI 1 


Twisted 


Twines 






Perlon Continuous 


Filament 


' Load 


Length per 


Breaking Load 




Unit Weight 




(kg.) 


wet 


mlkg. 


dry 


wet 


127 


192 


260 


221 





250 


208 


177 


100 


256 


195 


165 





312 


167 


142 


_ 


315 


173 


147 


68 


385 


130 


110 





1,248 


43 


37 



(b) Twines of Perlon Continuous Filament 

Twines for equipment exposed to little or moderate 
strain differ from twines for nets subject to severe 
stresses. 
Net twines are produced from the following materials: 

Denier . . 210 630 750 840 

Metric Number 

Nm. . . 43-0 14-0 12-0 10-7 

Length per Unit Weight 

m/kg. . . 42,860 14,290 12,000 10,710 

Table VI gives examples of approximate lengths per 
unit weight and diameters of net twines made of 210 
denier filaments. 

Only the finest deniers listed in Table VI are suitable 
for bottom-set gill nets; the others, including deniers 
heavier than those listed can be used for line fishing, 
baskets, trap nets, bagnets, trawls, seines, purse seines, 
etc. 

Given an equal wet knot strength the weight of nets 
made of these twines are less than that of the equivalent 
cotton product. 



Table VIII gives examples of Perlon continuous filament 
braided twines: 

TABLE Vlll 
Perlon Continuous Filament Braided Twines 



Length per 






Unit Weight 


Breaking Load 


mlkg. 


(kg.) 




_ Q PP- 


dry 


wet 


1,440 


40 


34 


1,270 


51 


43 


1,040 


55 


47 


840 


74 


62 


690 


83 


71 


650 


101 


81 


500 


110 


94 


450 


130 


110 


402 


151 


128 


350 


160 


136 


300 


190 


162 


265 


200 


170 


190 


280 


238 



36 



CHARACTERISTICS OF PERLON 



(c) Cords and Ropes of Continuous Filament 

Manila, sisal, hemp, and cotton have up to now been 
used as raw materials for the cords and ropes used in the 
fishing industry. 

Cords and ropes of natural fibres shrink and swell 
which renders wet ropes hard and stiff. Natural fibres 
rot in the water. Coarser qualities dry very slowly and 
when stored are destroyed by mould. Synthetic fibre 
ropes should therefore be used with synthetic fibre nets. 

Allowance must be made for the extensibility of Perlon 
which is many times that of the natural fibres. To prevent 
the ropes from untwisting or developing kinks, it is 
necessary to adjust the angle and direction of the twist 
so that the individual yarn constructions reinforce each 
other within the body of the rope. 

Cords and ropes are made of Perlon continuous 
filament yarn in the heavier deniers as listed in Table III. 



TABLE IX 
Comparison of Weight and Breaking Load 



Hemp* Manila ami Sisal 
itntarred 

Weight 
Dia- Cirenm- Break- 



C 'ontinuous Filament 

Perlon 

Breaking Load 
in kg. 

m 



meter ference ing 
in in Weight Load in 
mm. inches *' m kg 


Haw- 
ser 
laid 


Cable- Hawser- Cable- 
laid laid laid and 
Twisted 


1 




2- 


6 


230 


1-5 




410 




6 


I 


3- 


6 


380 


2-25 




580 




8 


1 


5- 


8 


572 


3-7 




1,000 




10 


U 


7- 


4 


763 


5-9 




1,500 




12 


M 


11- 


5 


1,143 


8-7 




2,250 




14 


l? 


14 


4 


1,525 


12 




3,100 




16 




18-8 


1,970 


14-5 




3,800 




18 


2| 


23- 


7 


2,460 


18-5 




4,900 




20 


2* 


29- 


5 


3,000 


25 




5,700 




22 




35- 


5 


3,580 


31 




6,950 




24 


1 


42- 


3 


4,210 


36 




8,400 




26 


3] 


49 


6 


4,870 


42 




9,750 




28 


3J 


57- 


5 


5,580 


49 




11,200 




30 


31 


66- 




6,310 


57 


52 


13,000 


11,500 


32 


4 


75- 


1 


7,090 


65 


59 


14,800 


12,200 


36 


4* 


95 




8,720 


82 


74- 


5 18,700 


15,700 


40 




117- 


5 


10,500 


101 


92 


5 (23,000) 


19,500 


44 


5 A 


142 




12,500 


124 


111 


(27,800) 


23,900 


48 


6 


169 




14,700 


145 


132 


(33,000) 


29,000 


52 


6* 


198 




17,000 


170 


155 


(39,000) 


34,600 


56 


7 


230 




19,400 


197 


180 


(45,000) 


40,800 


60 


7A 


264 




21,900 


227 


208 


(52,000) 


47,500 


64 


8 


301 




24,600 


252 


236 


(59,000) 


55,000 


72 


9 


380 




30,100 


315 


299 


(75,000) 


69,000 


80 


10 


470 




36,000 


388 


367 


(92,000) 


84,000 


90 


llj 


570 




43,000 


493 


467 


(116,000) 


106,00 


100 


124 


710 




50,000 


608 


577 


(144,000) 


130,000 


The values 


in brackets merely serve purposes of comparison - 




With 


these 


sizes it is 


advisable to 


use cable-laid 


ropes, a 


construction 


which has proved particularly efficient. 



(d) Perlon Staple Fibre Twines 

Two yarn counts: Nm. 50 and Nm. 20 are mainly used 
for net twines; details of strength are given in Table X. 



TABIF X 


Cotton and Perlon Staple Fibre 


Net twines of Kqual Wet Strength 


Cotton 


Net twine 




Perlon Staple Fibre 








and Net twine 


Metric 


Length per 


Metric 


Length per 


Number 


Unit Weight 


Number 


Unit Weight 


Nm. 


mlkg. 


Nm. 


ml kg. 


50/9 


5,000 


50/6 


7,500 


50/12 


3,600 


50/9 


5,000 


50/15 


2,900 


50/12 


3,600 


50/18 


2,400 


50/15 


2.900 


20/6 


2,900 


50/9 


MXK) 


20/9 


1,950 


50/12 


3,600 


20/12 


1,400 


20/6 


2,900 


20/15 


1,100 


20/9 


1,950 


20/18 


940 


20/12 


1,400 


20/21 


830 


20/12 


1,400 


20/24 


680 


20/15 


1,100 


20/27 


620 


20/18 


940 


20/30 


540 


20/18 


940 


20/32 to 20/36 


460 


20/24 


680 



IV. PROPERTIES 

1. Specific Gravity 

Perlon has a lower specific gravity than natural fibres: 
Perlon 1-14 g/cu. cm. 



Cotton 
Hemp, jute 
Ramie 



1-54 
1-48-1-50 
I 51 



g/cu. cm. 
g/cu. cm. 
g/cu. cm. 



Coupled with a high degree of strength, this property 
enables the industry to make very light nets. 

2. Rot Resistance 

Perlon does not rot as it is not attacked by bacteria or 
fungi, nor does it need preservative treatment. 

Perlon net twines continuously immersed in the brackish 
water of a North Sea harbour for a period of 3J years 
have shown no more than a 10 per cent, loss of strength. 

3. Tensile Strength 

The specific tenacity of monofilaments is highest with 
a small diameter. The breaking length varies between 
37 and 47 kilometres. The tenacity of water-saturated 
Perlon is between 80 per cent, and 90 per cent, of its 
air-dry tenacity. The knot strength shows an equally 
close relation to the diameter: 

(in ( ', of tenacity) 

70 80 " for small diameter (0 10 30 mm.) 
60-70% medium (0-35 0-70 mm.) 
50 <*)% large ( over ) 

The strength of the filaments is determined by the 
degree to which they have been stretched or "drawn" 
during manufacture, as shown in an example of Perlon 
continuous filament of 1,060 denier: 

Special 

Ordinary Pre-stretch 

km 55 ' 71 

km 47 61 

" 20 17 

% 22 19 

km 44 41 

km 41 36 



Breaking Length air-dry 

Breaking Length wet 

Break air-dry 

Break wet 

Extension at Knot Strength air-dry 

Extension at Knot Strength wet 



[37 1 



MODERN FISHING GEAR OF THE WORLD 



A high degree of stretching results in a considerable 
increase in strength coupled with an appreciably reduced 
extension at break. However, as filament strength is 
raised, there occurs a reduction in knot strength, parti- 
cularly when water-saturated. 

This phenomenon is particularly important when the 
fibre is subjected to a specially high pre-stretch as for 
fishing net twines. High strength and a low extension at 
break are desirable, but can only be achieved at the 
price of low knot strength. 

A comparison in knot strength of filament composition 
10,000 denier, single filament denier 20, and of monofils 
with a hemp string of equal strength: 



Strength dry kg/sq. mm. 
Strength wet kg/sq. mm. 
Knot Strength dry kg/sq. mm. 
Knot Strength wet kg/sq. mm. 
Relative Knot Strength dry % 
Relative Knot Strength wet % 

Experience has shown the knot strength of all fibres 
to be below their ordinary strength. 

4. Extensibility and Elastic Properties 

The extension at break of Perlon monofil varies between 
20 and 35 per cent. 

Other characteristic values for the extensibility and 
elasticity of Perlon monofils are: 

Elastic extension 75-90% \ of the total extension at 

Permanent elongation 10-25% / 80% of breaking load 



Details of the relationship between load and total 
extension are shown in the graphs of Illustration I. 

These diagrams show that the load extension curves 
of Perlon climb at a more obtuse angle than those of 
natural fibres. 

This divergence becomes conspicuous in a comparison 
of hemp and Perlon ropes with a circumference of 1J in. 





Perlon 


Perlon 


Hemp 
35 


Filament 
59 


Monofil 

52 


38 


52 


42 


23 


26 


26 


23 


24 


20 


66 


44 


50 


66 


41 


48 




Italian hemp 

Manilla 

~ . Siva! 

Perlon accordjnjt to construction and stabilization 

Illustration 11. 

Loadj Extension curves of Ropes in Natural Fibres ami Perlon, 
circumference \\ in. 




Illustration I. % extension 

Load/ Extension cur vex of Perlon Products compared with Cotton ami 
Manila twines. 



total extension 

permanent elongation 

. elastic extension 

//lustration III. 

Elasticity Graph of Perlon Continuous Filament in Denier 7,500 
(Single Filament Denier 6). 



[381 



CHARACTERISTICS OF PERLON 



The graph shows not only the greater strength of Perlon 
rope but also its higher working capacity, which enables 
it to absorb shocks like a spring; when stretched it 
recovers its original length very soon except for a slight, 
but permanent elongation of approximately 10 per cent. 

Illustration I II gives some idea of this elasticity as 
shown by a composition of 7,500 denier, single filament 
denier 6, with a tensile strength of 64 kg. sq. mm. Natural 
fibres can achieve similar values only through special 
construction. There is complete elasticity up to approxi- 
mately 5 per cent, of the breaking load i.e. the permanent 
elongation is nil. Above this load a permanent deforma- 
tion occurs which becomes relatively less as the extension 
increases. As a result the difference between total 
extension and permanent elongation increases further. 

The relation of elastic extension to total extension gives 
the elastic ratio, which can be said to hold good for 
Perlon proportionate to the magnitude involved. 
Illustration IV compares the elastic ratios of Perlon and 
cotton yarns. 

The load/extension curve has already shown up 
fundamental differences, which occur once again in a 
comparison of elasticity. Whilst Perlon shows a high 
proportion of elasticity within the total extension, with 
cotton fibres the permanent elongation predominates and 
leads to a much steeper fall of the elasticity graph. 









<Tnted>ntrl oi i 



Illustration \'. 

Extensibility and Elasticity of Perlon Continuous hi lament 

(Denier 7,500, Single Filament Denier 6) in Relation to Time 

and Load. 

5. Flexibility 

Net twines made of continuous filament and staple fibre 
are softer than those made from natural fibres. This 
applies particularly to their wet state as shown in tables. 

Hardness, dry and wet of Net Twines of 2*3 mm. Diameter 



Raw Material 

Manila 

Hemp 

Cotton 

Perlon Filament 



Dry 

700 
120 
42 
44 



Wet 

410 
110 
140 
21 



The higher the figure the harder the net twine. 

For some fishing nets, in particular fine gillnets, 
flexibility is a very desirable quality; for others it is of 
minor importance. This can be achieved by applying 
a stiffening preparation which at the same time gives the 
nets greater resistance to abrasion and sunlight. 



PorJon continuous fila men's 



Illustration 



Elasticity Graph of Perlon Continuous Filament in Denier 7,500 
(Single Filament Denier 6) and of a Cotton Yarn. 



From Illustration V it appears that immediately the 
load has been applied a high degree of extension ensues, 
which regains its equilibrium within the next 15 and 
30 minutes respectively. The extension is not proportional 
to the increase in the load, but is relatively greater at 
low and medium loads than at high loads. 

This gives Perlon a springy quality which enables it 
to absorb kinetic energy as shown below. 

Material Dry Wet 



Manila 
Italian Hemp 
Perlon 



100 
160 
700 



60 
HO 
500 



6. Abrasion Resistance 

Perlon has a high resistance to abrasion which together 
with non-rotting quality determine the useful life of nets. 
Wet abrasion tests of net twines showed the following 
results related to their weight per metre: 



Net 
Twine 
Weight 

Kim 

1-5 

2-5 

3-0 

4-0 

4-5 



Wet Abrasion Rubs 



Hemp 

420 

630 

940 

1.210 

1,340 



Manila 

380 
400 
540 
580 



Perlon 
Filament 

660 

930 

1,510 

2,120 

2,430 



Staple fibre net twines show a lower abrasion resistance 
than those made of continuous filament but still show 
considerably greater resistance than those made of 
cotton fibres. A staple fibre net twine Nm. 20/24 has a 
wet abrasion resistance of 270 whereas a resistance of 
1 50 was shown by a cotton net twine of the same strength. 



39] 



MODHRN FISHING GEAR OF THE WORLD 




Illustration 1 7. 

Manila net twine ami Perlon continuous filament braided cord 
after 500 wet abrasion double rubs. 

Photo: Must 1957 



A breaking extension test showed a 62 per cent, loss 
of tensile strength for the manila cord, compared with 
19 per cent, for the Perlon braided cord. 



Where Perlon twines are exposed to intense sunlight 
for long periods, as for example, in the case of fyke nets, 
it is advisable to dye them. They can easily be dyed with 
Perliton dyes, which dyes must be selected with a view 
to fastness and with acid dyes Telon light and fast 
dyes respectively, which are remarkable for their fastness 
in water. Treatment with a mixture of tannic acid and 
antimony potassium tartrate is particularly durable in 
seawater. Treatment with a catechu solution has proved 
an excellent protection against sunlight. 

8. Hygroscopic Behaviour 

Perlon has a low moisture regain. An examination of 
moisture content in air-dry conditions (65 per cent, 
relative air humidity, 20 deg. C.), and swelling ratio 
(degree of saturation) shows the following results: 



/ton 
Material 

Cotton 
Bast Fibres 
Perlon 



Moisture 

Content in 

A ir- Dry- Condition* 



1 13 
4-2 



Swelling 
Ratio ,, 

45 

100 -110 
12-14 



7. Weather Resistance 

Both synthetic and natural fibres, are weakened b> 
exposure to sunlight, but monofils display a high degree 
of resistance to sunlight and weather conditions, superior 
to that of vegetable fibres, and close to the immunity 
of poly-acrylonitrile fibres. 

Net twines of staple fibre or continuous filament lose 
more strength than natural fibre twines when exposed to 
intense sunlight, but because of their high initial strength 
they remain in the last analysis superior to natural fibres. 
The bigger the diameter the less noticeable the photo- 
degradation, which is insignificant for thick ropes as the 
layers below are protected by the degraded outer layer 
and which is probably no deeper than I mm. to which 
ultraviolet rays can penetrate. 

decrease of strength , 



crlo~! t./isted and dyed 



hemp, twisted 




Illustration VII. 

Influence of weather exposure on ropes made of Perlon continuous 
filament and hemp respectively. Rope circumference: 1| in. 
Weather exposure at 6.230 ft. above sea level. 




relative air humidity 



cotton 

lute 

Perlon 



Illustration VIII. 
Absorption and Desorption of cotton, lute and Per/on. 

For Perlon, absorption and desorption are of almost 
identical magnitude in contrast with the far more 
marked "swelling hysteresis" of natural fibres and it 
therefore dries appreciably faster. 

The level of moisture regain is known to be closely 
related to the lateral and longitudinal swelling caused by 
wetting. Cotton net twines receiving a first wetting of 24 
hours, showed lateral swellings of between 5 and 15 per 
cent.; bast fibre net twines showed an increase of 20 to 
40 per cent, in their cross-sectional area whereas Perlon 
continuous filament net twines contract rather than 
swell. The following comparison in thickness of a Perlon 
cable Nm. 0-9, single filament denier 20, with a hemp 
cord of equal size may serve as an example: 

Hemp Perlon 

Diameter dry . . mm 1-65 1-42 

Diameter wet . . mm 202 1*38 

Variation in Cross-section % +22 3 



[40 



CHARACTERISTICS OF PERLON 



Net twines made of natural fibres swell considerably 
and shrink as a result. It amounts to approximately 6 to 
9 per cent, for cotton net twines, and to approximately 
2 to 8 per cent, for hard bast fibres. 

Continuous filament twine behaves quite differently. 
An immersion in water gives rise to an extension pro- 
portionate to the cross-sectional shrinkage, in the region 
of 1 to 3 per cent. The changes in length and cross-section 
are only slight and consequently assure a constant mesh 
size. 

9. Chemical Resistance 

Perlon is resistant to rot in both fresh and seawater. 
Solvents which do not affect it and may be used in 
preparations to increase resistance to sunlight or stiffness 
are listed below: 



Methyl ethyl ketone 

perchlorcthylenc 

acetone 

trichlorelhylcne 

carbon disulphide 

dimethyl formamide 

benzine 

cyclohcxanone 

chloroform 

carbon tetrachloride 

formamide 

(base) alcohols 

ethyl oxide 



( I 60 C); 

< + 20C); 
( I 56 C); 

< + 80C); 
I 20 C); 
1 20 C); 
I 6<r C); 
{ 80" C); 
f20C); 
I 60 C); 
T 20 C); 

. 35 C C); 



Perlon solvents include concentrated solutions of 
formic, hydrochloric and sulphuric acid, as well as 
phenol (carbolic acid), cresylic acid and resorcin. 

Products with a phenol content, such as tars, can in 
certain cases cause swelling and consequently a loss of 
strength. Specially treated tars contain only small 
quantities of phenol derivatives and of phenol itself. In 
crude tar, however, these substances, "acid oils", may 
be present in fairly large quantities, although there is a 
sleep variation in the percentage. It seems advisable to 
draw special attention to this aspect, since tars are also 
used as stiffeners. 

10. Thermal Properties 

Perlon has a high resistance to cold and retains its 
elasticity even when frozen. There is, in fact, an increase 
in strength and conversely a loss of extensibility down 
to a temperature of 40 deg. C. The temperature needed 
in dyeing processes does not damage the nets, but a 
certain amount of shrinkage must be expected and 
therefore ascertained by preliminary tests on small 
samples. 

11. Visibility 

Perlon net twines can be very fine and accordingly 
inconspicuous in the Water. 

The translucent monofil is almost invisible under 
water and this property has increased the catches of 
monofil setnets and fyke nets. 

12. Processing 

Staple fibre net twines can be processed into netting 
without difficulty, manually or by machinery. They can 
be tied in non-slip knots in the same way as cotton net 
twines. With monofil and continuous filament twine, 



however, slip-proof knots cannot be assured because of 
the smoothness of the fibre. Tests are about to be com- 
pleted which aim at giving monofils a rough surface while 
preserving the inherent strength to increase the knot 
fastness. 

Continuous filament net twines can be roughened by 
treating them, preferably while they are being twisted, 
with a preparation insoluble in water, which gives them 
adhesive properties (bonding). 

The resistance to slippage of Perlon continuous fila- 
merU twine has been improved by blending spun staple 
fibres. 

Another possibility is the heat-setting of the knots 
under tension, at temperatures of 150 to 180 deg. C. 
usually applied for short periods only. 

With nets it is essential to maintain an even tension and 
twist in the Perlon material. Hawser-laid or cable laid 
ropes must be heat-set if necessary. No stabilization is 
needed, however, if the individual twists reinforce each 
other. With such a construction heat-setting is only 
needed where splices have to be made. 

Cordage can be set by hot air treatment, saturated 
steam treatment or boiling. Boiling is preferable for 
heavier types since neither hot air nor saturated steam 
can penetrate evenly enough through the rope. 

In continuous filament too hard a twist should be 
avoided as this would reduce strength and increase 
extension, particularly that proportion which is per- 
manent. Braided twines for fishing nets should be braided 
with a medium degree of hardness. On no account 
should a high degree of hardness be employed. 

13. Storage 

Perlon nets and ropes should not be left exposed to the 
sun. They are best kept in dark rooms and can be stowed 
while still wet. Nets which are freshly treated with pre- 
servatives should be handled in the same way as natural 
fibre nets: they should only be stored after having been 
used at least once. This applies particularly when 
stiffening preparations have been used. 

14. Attack by Micro-Organisms 

Perlon is immune to attacks by micro-organisms such as 
bacteria or fungi, nor do molluscs, barnacles and other 
organisms harm it. However, the larvae of the mayfly 
which settle particularly on stationary fishing gear in 
inland waters can cause considerable damage to nets; 
synthetic fibres are as much affected as cotton nets. 
Treatment with pesticides (Arkotine, Dieldrin) ensures 
a high degree of protection. 

In running waters which contain organic effluents 
thick clusters of "sewage fungi" occur which soon cover 
the nets. Frequent cleaning is needed, or catches are lost. 
Rhine fishermen are particularly affected by this fouling 
of their stow nets. Nets made of Perlon filament braided 
twine are less affected because of their smooth surface 
and can be cleaned easily and quickly. 

V. USE OF PERLON IN VARIOUS TYPES OF 
FISHING GEAR 

The economics of fishing gear depend, generally speaking, 
on initial costs, useful life, costs of preparation, main- 
tenance and efficiency. 



[41 ] 



MODERN FISHING GEAR OF THE WORLD 



The initial cost for a given weight of nets is higher for 
Perlon than for cotton, hemp and especially maniia, 
but the useful life of Perlon is considerably longer because 
of the high degree of resistance to rot and abrasion. 
While these nets need little or no preservative treatment 
nets of cotton, hemp and flax must be treated frequently. 
The expenditure in money and time involved represents 
a severe burden. 

Maintenance largely consists in preventing unnecessary 
exposure to sunlight and with monofil even this protective 
measure becomes unnecessary. 

The following paragraphs outline the use of Perlon for 
some of the more important types of equipment. 

1. Trawls 

At the Fishery Industry Fair 1957 in Copenhagen was a 
still usable bottom trawl made of Perlon braided twine 
used by a German trawler to catch 128,000 cwt. of 
herrings having a performance and useful life between 
8 to 10 times as great as that of the customary manila 
trawls. Although Perlon trawls cost two or three times 
as much as manila trawls, their economic advantages are 
beyond question. Their low weight, flexibility and smooth- 
ness make them easier to handle and the finer net twines 
noticeably reduce the tow drag. 

Probably the most important advantage is the capacity 
of Perlon to absorb kinetic energy. The nets also ensure 
the safe landing of big catches on deck as shown by the 
big catches of Norway haddock when Perlon codends 
were used. About half the German cutter fishermen use 
Perlon for the codends in drag-nets for catching herring. 
The material in this case was spun staple fibre twine in 
counts Nm. 20/15 to 20/21. 

2. Purse Seines 

This type of equipment plays an important part in the 
fishing industry of many countries, although not in 
Germany. Its traditional net material is cotton twine of 
medium strength. In the Portuguese fishing industry, 
for example, cotton nets treated with preservatives may 
have a useful life of between 400 and 500 fishing days. 

Large pieces of Perlon spun staple fibre webbing have 
been employed in Portuguese purse seines for 1,300 
fishing days without becoming unusable. These nets 
were not dyed or prepared in any way. For purse seines 
Perlon has the following advantages: reduction in the 
total weight of fishing equipment (essential considering 
the size of the equipment involved); almost no expendi- 
ture on net preservatives; no necessity to keep one set of 
nets on land for preservation purposes; less labour 
required to handle the gear; water-saturated nets can be 
safely stowed and a useful life at least double compared 
with cotton nets. 

Perlon continuous filament rope of 30 mm. in diameter 
has been used for 1,164 days as a purse line. It should 
have five times the useful life of a sisal rope to justify its 



higher price; it has already had nineteen times the life 
of a sisal rope. 

3. Bottom-Set Gillnets 

Set and floating nets used as fine gillnets are highly 
selective, helping to conserve young stock and supplying 
fish of high quality. Bottom-set nets are passive rather 
than active and must be as fine and as soft as possible 
having the least degree of visibility, requirements met 
by net twines of Perlon continuous filament yarn in a 
denier even finer than that quoted in Illb (100 denier and 
finer). Monofils are particularly suitable for set gillnets 
due to their extremely low visibility in water. Now that 
the problem of providing non-slip knots has been solved 
and mechanically produced netting can be obtained, set 
gillnets of monofil assumed considerable importance for 
fishing in inland waters. 

4. Stationary Fishing Gear 

Perlon products have proved their efficiency and economy 
when used for fyke and stow nets and traps. 

A cotton eel trap such as those used by fishermen in 
the North German inland lakes, costs about DM 24.00 
and lasts 4 years with preservative treatment. A Perlon 
spun staple fibre eel trap costs DM 17.08, needs no 
additional expenditure and remains completely efficient 
for approximately four years. 

Monofils proved even more suitable for eel traps; 
owing to their translucence they catch more eels. 

Cotton stow nets have a useful life of about two years 
if treated between 7 and 10 times with hot tar to preserve 
and stiffen them. A stow net of Perlon staple fibre twine 
has been in use for six years now and has been stiffened 
twice, once with black varnish and once with tar. Total 
costs for this stow net, which is still in full use, amounts 
to DM 1,625.00. During the six years, at least 3 cotton 
stow nets would have had to be purchased, costing 
DM 3,270.00. 

5. Whaling Ropes and Cordage 

In antarctic whaling, ropes of Perlon continuous filament 
between 100 and 120 metres in length used with the 70 
kilogram explosive harpoons have proved their worth 
as "foregoers". 

The strength of the fibres makes it possible to use 
ropes with a diameter of 33 to 34 mm., as compared to 
38 mm. for manila ropes. Perlon ropes do not stiffen in 
water and hardly ever ice up. The elasticity can absorb 
the high shock loads involved and greatly reduces the 
danger of a rope breaking. 

5. Tarpaulins and Protective Covers 

Tissues of Perlon continuous filament yarns, PVC-- 
Polyvinyl Chloride coated on both sides are used for 
tarpaulins, lifeboat covers, etc. They can be folded 
quickly and require little storage space, They are rot- 
proof, watertight, tough and can be fireproof. 



42] 



"TERYLENE" POLYESTER FIBRE AND ITS RELATION 
TO THE FISHING INDUSTRY 

by 

IMPERIAL CHEMICAL INDUSTRIES LTD. 

(Fibres Division), Harrogate, U.K. 

Abstract 

"Terylene" polyester fibre is a new synthetic fibre of British manufacture which, although being of considerable importance in the 
textile trade, is comparatively new to the fishing industry. It has physical properties that make it suitable for fishing twines and nets. It 
has high tensile strength and a high wet knot strength. It is rot -proof and has good resistance to sunlight, and, under wet conditions has also 
good resistance to abrasion. Like other synthetics, knot slippage is a problem, but this can be overcome by bonding agents either before or 
after the weaving of the net. Dyeing is preferably done during the manufacture of the nets and it is not recommended that the fishermen 
should do it themselves because of difficulties in temperature control. Terylene is used with success for gillnets in many parts of the world, 
mainly for catching "hard" fish such as salmon and cod. For "soft" fish like the herring, it has not yet been fully accepted because of the 
damage done to the fish when hauling the nets. Trawls, however, have proved very successful, for on test they have lasted for 9 trips instead 
of the usual single trip with the conventional trawl. The comparatively high cost of "Terylene" is to some extent offset by the length of its life. 



Resume 



La fibre polyester "Terylene" et ses applications dans 1'industrie des Pftches 



fibre polyester "Terylene" est une fibre synth&iqiic nouvellc de fabrication britannique; bien qu'clle soit ires rcpandue dans le 
commerce textile, son emploi dans rindustrie des pdches est relativement recent. Elle possede des proprigtes physiques qui font qu'elle 
convient a la confection de fils et de filets de peche. La resistance A la traction des fibres et des noeuds mouiltes est tres dlevee. Elle est 
insensible la pourriture et possede une bonne resistance P action du soleil; a 1'gtat humide elle possede egalement une bonne resistance 
a 1'abrasion. Les noeuds executes avec des fils dc Terylene, comme avec les fils constitues par d'autres fibres synth&iques, ont tendance a 
glisser, mais on peut r&soudre ce probleme en trait ant les fils avec des adh&ifs soit avant, soit aprds la confection du filet. II est preferable 
de proddcr a la teinture au cours de la confection du filet et il est deconseilte aux pecheurs de F6xecuter aux-memes en raison des difficultes 
qu'entraine le contrdle tres exact de la temperature pendant I'op6ration. Le T6rylcne est utilise avec succes dans de nombreux pays pour 
la fabrication des filets maillants, principalement pour la capture de poissons "durs" comme le saumon et la morue. Pour des poissons "mous" 
comme le hareng, il n*a pas encore 6te universellement adoptd car il endommagc les poissons lorsque Ton embarque les filets. Mais 11 a 
donn d'excellents resultats pour la confection de chaluts qui, a la suite d'essais, ont tenu neuf campagnes au lieu d'une seule avec le chalut 
convent ionncl. Lc coQt relativement levc du Terylene est compensd dans une certaine mesure par sa plus longue duree. 

La fibra de "terileno" y su relacion con la industria pesquera 
Extracto 

La fibra sint&ica llamada "terileno" es un nuevo tipo de poliester manufacturado en Gran Bretafta, que tienc gran importancia en la 
industria textil pero es comparativementc nuevo en las faenas de pesca. Sus propiedades fisicas se prestan para fabricar hilos y redes, a 
causa de su gran resistencia a la trace ion aun cuando esta anudada y humeda; ademds no se pudre, sufre bien la acci6n de la luz solar y 
ofrece bastante resistencia al desgaste cuando esti mojada. Como en otros productos sintticos, los nudos presentan el problema de correrse 
pcro esto se soluciona mediante agcntes de uni6n que se aplican antes o despus de tejer el artc. Lucgo de confeccionar la red es p refer ible 
proccder a su entintadura, no recomendandose que la haga el pescador a causa de las dificultades que presenta la regulaci6n de la temperatura. 
HI "terileno" se usa con dxito en muchas partes del mundo, principalmente para capturar peces **duros** como el salmdn y el bacalao, pero 
no ha sido aceptado del todp para las especics "blandas" como cl arenque, a causa del dano que produce al pescado cuando se recogen las 
redes. No obstante, ha tenido ^xito en la const rucci6n de artes de arrastre, por haher resistido durante las prucbas nuevc vez de una marea- 
que dura el material corriente. El costo relativamentc alto del "terilcno" sc compcnsa, en parte, con su mayor duracion. 



GENERAL INTRODUCTION 

TERYLENE polyester fibre is a new synthetic fibre 
which has already made a considerable impact on 
the textile industry and has significantly affected 
certain fields which have hitherto been dominated by 
natural fibres. Apart from its merits in the manufacture 
of wearing apparel and for industrial use, the special 
properties of Terylene make it suitable for employment 
in the fishing industry. It has been used not only for 
netting twines, ropes and lines, but also for lifeboat and 
hatch covers, sails and tarpaulins. 

The fibre is a British discovery made by J. R. Whin- 
field and J. T. Dickson in the Laboratories of the Calico 



Printers' Association Ltd., between 1939 and 1941. Later 
the world patent rights, with the exception of the USA 
were acquired by ICI Ltd., and the name "Terylene" 
became a registered trade mark, the property of ICI Ltd. 
Recently several European companies have been licensed 
to manufacture the fibre under their own trade names, 
and it is also being made in Canada by Canadian 
Industries Ltd. 

A new factory at Wilton, Middlesbrough, Yorkshire, 
produces over 25 million pounds per annum, and larger 
outputs are envisaged. 



[43] 



MODERN FISHING GEAR OF THE WORLD 



TYPES OF YARN 



Both continuous filament yarn and staple fibre are 
manufactured. The continuous yarn can be divided into 
two categories. The first is a yarn with a tenacity of 6 to 
7 grams per denier and a corresponding extension at 



break of 12 to 7 per cent. This yarn, which is intended 
primarily for industrial uses, is being manufactured 
currently in 125 denier/24 filaments and 250 denier/48 
filaments. It enables very fine and strong twines to be 
produced. The development of a high tenacity extra heavy 
denier yarn is under way which will enable heavier nets, 



TABLE I 
Physical Properties of Fishnet Twines- Natural Fibres 



Construction 

Count 

Twist t.p.i. twine 
strand 
yarn 

Runnage (yd./lb.) 

(Breaking Load (I h.) 
DRY { Extension (%) 

[Tenacity (g.p.d.) . 

f Breaking Load (Ib.) 
WET 1 Extension (%) 

L Tenacity (g.p.d.) . 

fKnot B/L (Ib.) 
DRY <{ Extension (%) 

L Tenacity (g.p.d.) 

fKnot B/L (Ib.) 
WET J Extension (%) 

( Tenacity (g.p.d.) . 

Abrasion dry revs, 
wet revs. 



Hemp 
7-85/3 6-3.9/3 


6-9^/3 


Flax 
105/3 

3-35 

6-6S 

6-7Z 
1006 


13-25/3 


! 8-85/3/3 


Cotton 

305/7/3 

1-4 
8-3S 
9-5Z 
1 4Z 
1170 


295/5/3 

1-96 
8-6S 
12-4Z 
1-9Z 
1646 


2-6 

5*7 
5-7 
780 


2-1 

6-0 
6-OS 
630 


2-6 

3-7Z 
6-OS 
780 


4-4 

3-9Z 
6-2S 
1318 


1-1 
5-5Z 
18-7S 
1-1Z 

922 


38-3 
4-6 
3-0 


37-8 
5-8 
2-4 


28-3 
6-5 
2-3 


27-8 
6 25 
2-8 


23-8 
5-4 

3-2 


14-8 
16-0 
1-4 


15-0 
11-5 
1-8 


10-5 
14-2 
1-8 


44-8 
8-9 
3-6 


49.4 
10-0 
3-2 


45-5 
9-7 
3-6 


36-8 
7-8 
3-8 


29-4 
9-1 
3-9 


19-9 
24-2 
1-9 


19-1 
27-8 
2-3 


13-1 
27-2 
2-2 


15-7 
11-5 
1-2 


22-2 

n 


19 
9-0 
1-5 


14-8 
10-0 
1-5 


12-0 
10-0 
1-6 


8 21 
17-0 
0-77 


8-5 
10-1 
1-0 


5-5 
13-0 
0-92 


19 5 
22-4 
1-6 


18-2 
15-5 
1-J 


19 1 

'?:? 


12 8 
8-1 
13 


13-0 
10-0 
1-7 


12-6 
24-1 
1-1 


11-9 
28-9 
1-4 


8-3 
24-5 
1-4 


48 


54 


124 


60 


71 


1195 


898 


1183 


178 


201 


125 


123 


158 


208 


169 


154 



TABLE I (continued) 
Physical Properties of Fishnet Twines Synthetic Fibres 





Construction 

Denier 
Twist t.p.i. strand 
yarn 
Runnage (yds./lb.) 


250/8/3 


Terylene 
250/6/3 


250/4/3 

3342 
7-1Z 
14-9S 
1336 


210/8/3 


Amilan 
210/6/3 


210/5/3 


210/8/3 


Nylon 
210/6/3 

4160 
5-1 Z 
12-2S 
1073 


210/4/3 




6662 
6-3Z 
10-7 S 
672 


4980 
5 4Z 

12-2S 
896 


5247 
5-8Z 
10-6S 
850 


4034 
6-OZ 
1I-5S 
1106 


3323 
6-5 Z 
11-7S 
1343 


5547 
4 
11 
805 


6Z 
8S 


2784 
7-OZ 
15-OS 
1603 


DRY 


(Breaking Load (Ib.) 
*' Extension (%) 
L Tenacity (g.p.d.) 


78-0 
31-1 
5-3 


58-5 
29-4 

5-33 


38-3 
27-5 
5-2 


50-7 
56-0 
4.4 


39-3 
47-6 
4-4 


31-7 ! 63 
45-0 45 
4-3 5 


8 

-2 


52-8 
42-6 
5-8 


33-8 
41-1 

5-5 


WET 


f Break ing Load (Ib.) 
! Extension (%) 
L Tenacity (g.p.d.) 


78-4 
30-9 
5-3 


58-9 
27-6 
5-4 


38-1 1 45-9 
20-5 55-7 
5-2 4-0 


31-0 
48-9 
3-5 


29-0 
46-2 
4-0 


60 

4 l 


9 
2 



45-2 
43-7 
4-9 


27-1 
41-8 
4-4 


DRY 


fKnot B/L (Ib.) 
< Extension (%) 
(..Tenacity (g.p.d.) 


27-0 
11-1 
1-8 


17-6 
9-1 
1-6 


12-2 26-4 
9-2 : 24-6 
1-7 ; 2-3 


18-3 
24-3 
2-1 


16-6 
23-3 
2-3 


26 
18 
2 


8 

7 
2 


21-4 
17-9 
2-3 


11-6 
17-6 
1-9 


WET 


fKnot B/L (Ib.) 
1 Extension (%) 
^ Tenacity (g.p.d.) 


26-0 
9-6 
1-8 


20-8 
9-6 
1-9 


14-3 21-7 
10 5 , 26-7 
1-9 1-9 


16-4 
25-2 
1-8 


13-1 
22-5 
1-8 


20 

f 


3 

7 
7 


17-9 
21-7 
1-9 


12-1 
21-4 
2-0 




Abrasion dry revs. 


1412 


1921 


2090 


5949 


8093 


10024 


3277 




6817 


8974 




wet revs. 


1098 


1429 


1785 


1891 


1095 


1561 


1649 




1968 


2622 



[44] 



VALUE AND USE OF TERYLENE 



e.g. trawls, to be produced more economically. All the 
high tenacity yarns are bright. 

The second category comprises a yarn with a tenacity 
of 4J to 5J grams per denier and a corresponding exten- 
sion at break of 25 to 15 per cent. It is intended mainly 
for wearing apparel and is produced in deniers ranging 
from 25 to 150, most of which can be obtained in either 
bright or delustred forms. 

A staple fibre, with a tenacity of 3 to 4 grams per 
denier and a corresponding extension at break of 40 to 
25 per cent., is currently being manufactured, ranging in 
staple length from Ij to 6 in. and from Ik to 6 denier 
(that is U in. staple, 14 denier) for processing on the cotton 
system, up to 6 in. staple, 6 denier for processing on the 
flax system. All staple fibre has a heat stabilized crimp 
and is available with a dull-lustre. Filament yarn is 
twisted to three-quarters of a turn per inch and supplied 
to the trade on bobbins. 

The fibre is made from polyethylene terephthalate, a 
condensation product of terephthalic acid and ethylene 
glycol, both of which are derived through various 
chemical processes from the products of mineral oil 
cracking. The polymer is chipped, and the fibre produced 
by a melt spinning process. Molten polymer is pumped 
through a spinneret and the spun yarn is subsequently 
mechanically stretched to develop fibre-like properties. 
The filament yarn has been exported overseas to be made 
into twines and nets. In certain countries, where limited 
doubling facilities are available, twines have been ex- 
ported by manufacturers in the United Kingdom. 
Complete nets have also been supplied in certain instances. 

The fishing industry is mainly interested in the high 
tenacity filament yarn on the grounds of high strength 
and low extensibility, although the staple fibre is used 
for specialized purposes, such as net mounting ropes. 

PHYSICAL PROPERTIES 

The most important physical properties which this yarn 
can offer for use as twines or netting are: 

(i) High tensile strength which is unaffected by 
wetting. In particular, it has a high wet knot 
strength. 

(ii) Low extensibility and high modulus, 
(iii) Rot proof and not weakened by mildew, 
(iv) Good resistance to sunlight, 
(v) Stability on water immersion coupled with low 

moisture absorption. 

(vi) Good resistance to abrasion under wet con- 
ditions, 
(vii) The smooth nature and transparency of the 

material. 

Other fibres mainly used for netting twines are cotton, 
flax, manila, sisal and poly vinyl alcohol such as Kuralon, 
and the polyamides Perlon and Nylon. The general 
physical properties of a range of Terylene fishnet twines 
in comparison with twines made from the fibres men- 
tioned above are given in Table I. 

A study of this table demonstrates the advantages 
which the fibre has to offer. A loss in strength on knotting 
is common to all fibres, and synthetic fibres may lose 
relatively more strength on knotting than natural fibres, 
such as cotton and linen, but as the initial strength of 



OY 



KOT 

TCNACITV 



WET 



19O// J9O/4/9 



Single Knot Tenacity of Terylene Twines. 



Terylene is very much higher, its actual knotting strength 
remains above the level of natural fibres. 

In the dry state the twines may have a slightly lower 
dry knot tenacity than comparable nylon twines. The 
wet knot tenacities of the two are not significantly 
different (see figs. 1 and 2). The wet knot strength of a 
fishnet twine is obviously of more importance than its 
dry knot strength. The strength of a twine depends not 
only on the fibre from which it is made, but also on its 
construction (twist, number of strands, etc.). The tables 
also show the low extensibility of Terylene and its resis- 
tance to stretch. This facilitates the manufacture of nets 
with mesh sizes which conform to the required specifica- 
tion and which resist distortion in use. 

Terylene twines do not shrink when immersed in water 
at ambient temperature, but they will shrink at elevated 
temperatures. If the nets are to be subjected to various 
heat treatments, e.g. dyeing, prior to use, and the mesh 
size is critical, an allowance should be made for shrinkage. 



DRY 



KNOT 

TENACITY 



!// HO/4/1 



Fig. 2 
Single Knot Tenacity of Nylon Twines. 



[45 



MODERN FISHING GEAR OF THE WORLD 



The abrasion resistance of the twines is superior to 
those made from cotton and flax. Unlike most synthetic 
fibres, its abrasion resistance is not appreciably different 
under wet conditions. The data above were obtained 
by rubbing both wet and dry twines over a 3 mm. thick 
hardened carbide steel bar. The abrasion resistance of 
nylon twines is significantly better than that of Terylene 
twines, but the difference under wet conditions is not 
nearly so marked. In practice Terylene fishnets can be 
expected to show good wearing qualities because of their 
good wet abrasion resistance. Mention has already been 
made of the low moisture absorption of the fibre (Table J) 
and this is clearly shown in the graph (fig. 3). This means 
that on immersion in water the twines do not swell, the 
mesh sizes of the nets remain intact, little change in 
effective net weight occurs, and the twines dry quickly. 

The smoothness, fineness and transparency of the 
material eliminate air bubbles and contribute to a low 
order of visibility. 

The fibre has very good resistance to chemical attack, 
in particular to acids and oxidizing agents. It is thus 
resistant to sea water attack and unaffected by contact 



THE TWINU weI IMMIRUD IN TAP MATCH FOR >* HRI, LEFT TO 

DR FOR IS MINI TMCN WEIGHED AT HOURLY INTERVALS 




fig. 3 
The rate of drying of Manila, Sisal, Nylon and Terylene Twine\. 



with oils, cutch and tar. This has been demonstrated in 
certain areas where traditional nets were affected by 
chemical contamination which had no effect on Terylene 
nets. 

In connection with the use of Terylene in twines and 
nets, the following points are worthy of mention: 

KNOT SLIPPAGE 

In the manufacture of fishing nets, two types of knots 
are commonly used, the single sheet bend (single weaver's 
knot) and double sheet bend (double weaver's knot). 
The latter type does not slip during use and double 
knotted twines have a knot strength about 10 per cent, 
higher than single knotted twines. Both Terylene and 
nylon single knotted nets are prone to knot slippage, but 
the tendency is less with Terylene. Tests carried out on 
samples of Terylene, nylon, cotton and linen single 
knotted gill nets showed that three out of every four 
knots slipped in the case of nylon when dry and one in 
four when wet. One out of every four Terylene knots 
slipped when dry, but none when wet. No knot slippage 
occurred with the cotton net and only occasionally with 
the linen net. However, the resistance of Terylene to 
single knot slippage is not considered to be good enough 
and as more single knotted fish netting is produced than 
any other, knot slippage constitutes a problem. It is 
said that the somewhat slow rate of production of 
double knotting machines has been improved and is now 
about the same as the single knotting machine. 

Knot slippage is a result of the smoothness of synthetic 
filament yarns, and an obvious answer is to increase 
the coefficient of friction of the twines by the application 
of a surface coating. The anti-slip agent may be applied 
to the twine during manufacture of the net, or to the 
finished net to fix the knots. Some net manufacturers 
consider both pre- and post-treatments are necessary. 
The general view seems to be that the nets should be 
made from bonded twines to enable an undistorted 
net to be taken off the machine and safely transported 
to a stretching frame to tighten and fix the knots. In 
certain cases it is possible to avoid the use of prebonding 
agents by the application of very high tensions at the 
back of the loom. These consolidate the knots sufficiently 
for net handling prior to the stretching treatment. 

The bonding agents recommended for Terylene fishnet 
twine are Colophony resin and Bedesol 76. Colophony 
resin is applied from a solution in methylated spirits or 
aqueous ammonia. Bedesol 76 is applied from a solution 
in 64 deg. over proof methylated spirits. Both bonding 
agents can be applied either by single-end gumming at a 
speed of 100 to 150 yards per minute, or by hank dipping 
for 15 minutes, draining, and, in the case of the ammonia 
solution of Colophony resin, drying for one hour at 
80 deg. C. The percentage solids of resin required on the 
twines depend on the net making machine used. For a 
Seriville machine, the required pick-ups of Colophony 
resin and Bedesol 76 are 1 -0 per cent, and 2 5 to 3 5 per 
cent, respectively. The former is achieved using a 5 per 
cent, solution and the latter a 6 per cent, solution. For 
the Zang machine the respective pick-ups are 2 to 3 
per cent, and 5 to 7 per cent. In the first case a 7 to 
8 per cent, solution is required and in the latter a 12 to 



[46] 



VALUE AND USE OF TERYLENH 



15 per cent, solution. As twines bonded from methy- 
lated spirit solution may be slightly sticky and as the 
solvent is inflammable, bonding from aqueous ammonia 
should be followed by drying at 80 deg. C. It also has 
the advantage of keying the resin to the fibre. The 
differences in optimum pick-up of the bonding agent for 
the Zang and Seriville machines are a feature of the more 
critical operating conditions for the Seriville machine. 

As already mentioned, the net itself can be treated 
with bonding agents to prevent knot slippage. Both 
Colophony resin and Bedesol 76 have been satisfactorily 
used in concentrations akin to those for bonding twines. 
The net is opened out as much as possible to ensure that 
all of it comes into contact with the solutions. It is 
immersed for a minimum period of 10 minutes, with 
stirring or agitation to ensure an even application of 
solids. The net is then removed and dried. A more even 
application of the solids is obtained if the net is cen- 
trifuged to remove surplus solution before drying. 
Drying at a temperature of 80 deg. C. is preferable to 
drying in air at room temperature, since the latter 
process is very much slower, and leaves a net slightly 
sticky. About 4 per cent, allowance should be made for 
the shrinkage in drying at 80 deg. C. 

During manufacture of the net it is important to ensure 
that the tensions applied to the twine are sufficient 
to pull the knots tight. In addition to being stretched, 
nets can also be given a steam or hot air treatment to 
consolidate the knots. Steaming the nets on a frame at 
150 deg. C. for 15 minutes has been found to be most 
satisfactory. 

As an alternative method P.V.C bonded twines have 
been used (about 5 per cent, pick up). The success of nets 



produced from such twines has been reported from 
Sweden. As a means of avoiding the use of bonding 
agents, Terylene/cotton and Terylene/spun acetate 
mixture twines have been produced. Single knots pro- 
duced from such twines do not slip. It is also noteworthy 
that Terylene staple twines can be single knotted without 
slippage occurring. 

DYEING 

In many instances dyeing has been shown to give 
increased catches (e.g. blue-grey nets for Norwegian 
lake trout), but whether this applies generally to dyed 
synthetic nets has yet to be confirmed. However, fisher- 
men usually demand nets dyed to a wide variety of 
shades, from reddish-brown to green and blue, and in 
many cases they prefer to dye their own nets. 

No difficulties are to be expected in nets made from 
dyed Terylcne twines. The twist set yarns may be dyed 
by using the appropriate equipment under normal 
dyeing techniques, i.e. with disperse dyestuffs for 90 
minutes at the boil (with or without carrier), or at higher 
temperatures under superatmospheric pressures. If, 
however, the fisherman wishes to dye his own nets the 
matter is not so simple, because the necessary equipment 
is often not available for dyeing at the boil, although 
suitable dyestuflf packages are available to enable the 
fisherman to dye his nets satisfactorily to a variety of 
shades. As mentioned previously, an allowance for 
shrinkage must be made if the mesh size of the net is 
critical. 

Tinting of bonded twines at ambient temperature has 
been successfully carried out and it is possible also to tint 




4OO 41* 5OO 

HOUR* OF SUNiHINt 



F/V. 4. Weather Tendering of Terylene and other fibres. 
[47] 



MODERN FISHING GEAR OF THE WORLD 

TABIF II 
Average variation from nominal mesh size of different nets when tested dry and after immersion in water for 15 minutes and 24 hours 



Linen 
Cotton 
Nylon 
Terylene 



Dry 

1-92",, to I 1-92;, 

-1-16% to H 1-16% 

2-35% to +2-59% 

1-16% to tO-58% 



After immersion 
for 15 minutes 



2-88'; to ()-% ( , 

-- -.VS-V.'u to Nominal 

-2-22% to } 2-00" 

-1-16% to i 2-32";, 



After immersion 
for 24 hours 

2-88" u to 0-96% 
4-05% to Nominal 
2-06% to ! 2-34;, 
0-58% to i 2-32% 



(Data supplied by Dominium Textile Company Limited prepared for Canadian Government Specification Board). 



the unbonded twine or net at ambient temperature by 
using disperse dyestuffs dissolved in chlorinated hydro 
carbons, but some shrinkage of the net may occur. 
Asphalt based solution can be used to stain and stiffen 
the net if required. 

MESH RETENTION 

Some tests have been carried out on the mesh stability 
of various types of net. The mesh was measured dry at 
room temperature, before being immersed in water, and 
also after the nets had been immersed for 15 minutes and 
24 hours respectively. A summary of the results is 
given in Table II, and the superiority of the fibre in 
respect of mesh size retention is clearly illustrated. It 
is interesting to note that after immersion for 24 hours 
cotton shows the greatest variation with an average 
shrinkage of 4-05 per cent., followed by linen, nylon and 
Terylene in that order. It is submitted that a tolerance of 
3 per cent, above or below the nominal mesh size is a 
realistic approach. This excellent mesh size retention of 
Terylene is of obvious importance with respect to gill- 
netting. 



SUNLIGHT EXPOSURE 

The fibre has about the same resistance to daylight and 
weather as the best of the natural fibres (see fig. 4), but 
because it has a higher strength premium and is rot 
proof it has a longer useful life. Trials have been 
carried out with Terylene and nylon twines exposed to 
daylight and weather in the United Kingdom, and the 
results are given in Table III and fig. 5. Even though 
the overall time of exposure is comparatively short the 
superiority of Terylene is clearly demonstrated. Terylene 
nets and others made from natural and synthetic fibres 
arc now being exposed in several countries, such as 
Canada, Kenya, India and Scandinavia, but it is too 
early to draw conclusions from these tests. 



DURABILITY 

The general toughness of the fibre, its very good mechan- 
ical properties, complete resistance to rotting and good 
resistance to sunlight and weather, ensure a long life for 
Terylene nets. 



TABLE III 
Comparison of Terylene and Nylon Twines after Weather Kxposure taken at Monthly Intervals 

Constructional details of Twines 

Terylene . Resultant denier 4,190 Structure 250/5/3 
Nylon . Resultant denier 3,570 Structure 210/5/3 







Total TER YLENE ,V YLON 


Exposure Dates 


Sun Hours 


H,!!n-i Breaking Extension Tenacity ;, loss in Break inK Extension Tenacity % loss in 






Loaddb.) " (*!./</.) Bk.Load Loaddb.) % (*/ff./rf.) Bk. Load 


Control 




477 23-6 52 42-5 30-6 5-4 


1st July 31st July 


137-63 


137-63 37-4 18-0 4-1 21-6 33-3 27-4 4-2 21-6 


1st Aug. 31st Aug. 


117-2 


254-83 32-0 15-9 3-5 33-2 28-4 24-8 3-6 33-2 


1st Sept. 30th Sept. 


108-7 


363-53 29-6 14-9 3-2 37-9 24 1 22-5 3-1 43-2 


1st Oct. 31st Oct. 


127-9 


491-13 29-7 18-6 3-2 37-7 22-6 21-6 2-9 46-8 


1st Nov. 30th Nov. 


55-6 


547-03 27-0 14-0 2-9 43-4 22-1 21-3 2-8 48-0 


1st Dec. 31st Dec. 


13-1 


560-13 26-0 15-0 2-8 45-8 16-2 19-8 21 61-9 


1st Jan. 31st Jan. 


30-69 


59082 26-4 14-9 2-9 446 18-7 21-1 2-4 56-0 


1st Feb. 28th Feb. 


73-3 


664-12 27-0 14-7 2-9 43-4 17-0 18-6 2-2 60-0 


1st Mar. 31st Mar. 


80-2 


744-32 27-1 16-5 2-9 43-2 14-8 195 1-9 68-2 


1st April 30th April 


133-0 


877-32 25-7 16-9 2-8 46-1 15-3 22-1 1-9 64-0 



48] 



VALUE AND USE OF TERYLENE 



NYLON HO/SJl 



1O 4O 



<\nnpanwn of 250 5 3 Tetvlenc ami 210:5/3 Nylon T\\ines after Exposure 



EASE OF HANDLING 

Nets made of the fibre are easy to handle because thinner 
twines can be used to give lighter nets. Trawl nets, tor 
example, can be towed more easily. This weight saving 
factor makes it possible to use larger nets or, alternative!), 
a small vessel can be used to handle a net. The low 
moisture uptake means little effective change in weight, 
and the net is less prone to freeze under icy conditions. 
The somewhat high specific gravity of the fibre permits 
a net to sink more rapidly, while the high resistance to 
stretch is favourable to easy hauling. 

COST 

The nets are more expensive than natural fibre nets but 
they provide considerable savings on a price/life basis. 
In fairness it must be pointed out that the initial cost of 
the netting is sometimes very considerable and may be 
more than some fishermen can afford. The risk of 
accidental damage and loss must also be borne in 
mind. The difference in price between Terylcne and the 
natural fibres becomes less marked in nets because twines 
of greater runnage can be used. The price of Terylene 
compares favourably with that of nylon in terms of 
pence per pound, but, because of its greater specific 
gravity, the twines have less runnage than nylon twines 
of equal thickness. Weight for weight, however, the 
twines have identical runnage. 



CONSTRUCTION : 

Cords and Twines 

The fishnet twines are normally produced from 125 and 
250 denier high tenacity filament yarn with plied and 
cabled constructions. In general, twist is inserted in 
the singles yarns in twines having plied constructions. 
The ply twist required to produce a ''balanced" twine 
can be obtained from the formula: 



t.p.i. strand 



t.p.i. singles 
A No. of strands 



The negative sign indicates opposite twist. No twist is 
inserted in the singles yarn of twines having cable 
constructions. The twine twist required to produce a 
balanced cord is given by the formula: 



t.p.i. twine 



t.p.i. strands 
v No. of twines 



The amount of twist inserted at each stage in tne pro- 
duction of the fishnet twines depends on the hardness 
of "handle" required and most manufacturers have 
certain twist factors which enable them to calculate the 
twist required. In order to produce a twine from Terylene 
filament yarn which has a balanced construction and a 
good yarn to twine strength conversion efficiency, twist 
factors in the range 3-6 to 4-6 are suggested. 



[49] 



MODERN FISHING GEAR OF THE WORLD 



14 



12 



TPI TWINC =z T Rl. STRAND 



/ 



No OF TWlHf 



X 



yl8 





-6 



10 12 14 

T.PI STRAND 



16 



18 



2O 



22 



24 



Note: Twist factor ~ 



t.p.i. x V denier 

73 



The construction for a range of the filament twines are 
given in Table IV. 



The information given in this table has been interpreted 
graphically (see figs. 6 and 7) and from these the twist 
required for the production of a range of twines having 
stranded constructions may be obtained. The use of 
balanced twists gives twines which are completely dead. 



TABLE IV. Terylene Fish-Net Twine Constructions 



Breaking 
load 
(lb.) 



Twist Factor 
3-6 (/./>./.) 



Strand 
Twist 



Twine 
Twist 



Twist Factor 
4 



Strand 
Twist 



Twine 
Twist 



Twist Factor 
4-6 (t.p.i.) 



Strand 
Twist 



Twine 
Twist 



125/2/3 . 


100 ! 16-5 


9-5 18-2 


10 5 


21-0 


12-2 


125/3/3 . 


15-0 14-0 


8-1 16-8 


9-75 


18-0 


10-4 


125/4/3 . 


19-8 ' 11-5 


6-7 


13-0 


7-5 


14-7 


8-5 


125/5/3 . 


24-4 


10-5 


6-1 


11-9 


6-9 


13-5 


7-8 


125/6/3 . 


29-7 j 9-5 


5-5 ; 10-75 


6-2 


12-1 


7-0 


125/7/3 . 


35-0 


9-0 


5-2 


9.9 


5-7 


11-4 


6-6 


125/8/3 . 


39-6 8-5 


4-8 


9-1 


5-25 i 10-7 


6-2 


125/9/3 . 


44-5 ' 8-3 


4-6 


8-7 


5-0 ! 10-2 


5-9 


125/10/3 . 


49-5 


7-8 


4-3 


8-25 


4-75 


9-5 


5-5 


250/2/3 . 


19-8 


11-5 


6-7 


13-0 


7-5 


14-7 


8-5 


250/3/3 . 


29-7 


9-5 


5-5 


10-75 


6-2 


12-1 


7-0 


250/4/3 


39-6 


8-5 


4-8 


9-1 


5-25 


10-7 


6-2 


250/5/3 . 


49-5 


7-8 


4-3 


8-25 


4-75 


9-5 


5-5 


250/6/3 . 


59-5 


6-9 


3-9 


7-5 


4-3 


8-7 


5-0 


250/7/3 . 


69-3 


6-3 


3-7 


7-0 


4-0 


8-1 


4-7 


250/8/3 . 


79-3 


6-0 


3-4 


6-5 


3-75 


7-4 


4-3 


250/9/3 . 


89-0 


5-7 


3-2 


6-25 


3-6 


7-1 


4-1 


250/10/3 . 


99-0 


5-3 


3-0 


5-9 


3-4 


6-6 


3-8 



50] 



VALUE AND USE OF TERYLENE 




TWIST FACTOR = T.P.I. X VOENIER 



73 



.ISO/ft/l 



\ 



X 



. - 2SO/S/1 



\ 



\ 



- 250/1/3 



. 7 SO /2/1 




TWINE TWIST (T.P.I.) 

/'iff. 7. twine Twists foi Twines with Twist /actors of 4 ft, 4-0, 3 -ft. 



TARLF V. 1 cry lene/I ilament Acetate Twines 



Afo. 3A 



Aw. 4 



r>. 6 



,V. 7 



Construction 


5/3 


6/3 


6/3 


6/3 


10/3 


7/3 


3/3 


4/3 


3 


250 T 


4 250 T 


3 250 T 


3 250 T 


3 250 T 


4 250 1 


2 250 T 


2 250 T 


2 


.' 200 Ac 


2 200 Ac 


3 200 Ac 


3 200 Ac 


4 - 200 Ac 


3 200 Ac 


1 200 Ac 


2 200 Ac 


Nominal denier 


3450 


3700 


4050 


4050 


6900 


4800 


2100 


2700 


Resultant denier 


3574 


4380 


4216 


4368 


7348 


5066 


3172 


2801 


T.p.i. *'S" strand 


8-0 


7-5 


7-1 


6-7 


6-7 


6-9 


9-7 


8-2 


"Z" twine 


3-5 


2-5 


2-2 


6-0 


2-5 


2-8 


4-5 


3-3 


Strength 


33-5 


44-2 


35-4 


35-2 


64-0 


44.9 


23-0 


23-8 


Extension 


15-0 


15-8 


16 


17-0 


25-1 


22-6 


14-7 


15-6 


Tenacity 


4-25 


4-58 


3-81 


3-65 


3-9 


4-0 


4-8 


3-8 


Knot Strength 


16-8 


20-6 


19-4 


18-0 


33-2 


23-4 


10 8 


12-4 


Extension 


9-1 


8-3 


9-1 


10-0 


10-9 


8-8 


7-3 


9-1 


Tenacity 


2-13 


2-14 


2-08 


1-87 


2-1 


21 


2-3 


2-0 


Wet Strength . 


34-4 


44-0 


34-2 


33*0 


64-8 


44-8 


21-9 


21-9 


Extension 


14-6 


15-4 


15-0 


16-8 


24-4 


15-4 


14-7 


14-5 


Tenacity . 


4-37 


4-56 


3-68 


3-43 


4-0 


4-0 


4-6 


3-5 


Wet Knot Strength 


16-4 


19-1 


17-2 


15-9 


31-7 


20-6 


9-9 


12-1 


Extension 


11-3 


8-8 


10-3 


12-0 


12-7 


10-7 


9-3 


10-3 


Tenacity . 


2-08 


1-98 


1-85 


1-65 


19 


1-8 


2-1 


2-0 


Dry Knot Slippage 


None 


None 


None 


1 in 5 


None 


None 


None 


None 


Wet 


2 in 5 


None 


None 


None 


None 


None 


1 in 5 


None 



151 ] 



MODERN FISHING GEAR OF THE WORLD 



show no tendency to snarl and have maximum strength. 
Some net manufacturers prefer to use twines with un- 
balanced twists and these must be twist set before net 
manufacture to consolidate the twist and prevent twine 
liveliness. The twist setting process is, in essence, one of 
free shrinkage and as such the properties of the twine 
alter. The general effect is to increase the denier and 
extension at break and to decrease tenacity, shrinkage 
potential and initial modulus of elasticity, the breaking 
load remaining unchanged. Such changes may detract 
from the performance of the netting. 

Webbing 

Terylene filament twines can be handled on traditional 
net making machines and the nets are said to be easier 
to make than those of other synthetic fibres, because of 
the twine's high resistance to stretch. The twines have been 
processed satisfactorily on single knot machines, such 
as the Zang and the rather more critical Seriville machine. 
In using bonded twines care must be taken to ensure that 
the correct percentage pick-up of bonding agents has 
been achieved so that the net making machine may 
function at optimum efficiency. Certain machine adjust- 
ments are also necessary to take this into account. In 
particular, it has been found advantageous to alter the 
number of turns of twine round the emery beam and also 
round the drag rod on the shuttle holder. Terylenc 
twines have been used successfully on double knotting 
machines. 

NETS: 
Gillnets 

The gillnet market overseas is at present the largest 
consumer of synthetic twines and Terylene gillnetting 
has been used successfully in many parts of the world, 




Skill ami care ore concentrated on this stage in the manufacture 
of Tcrvlcne ffillnetx. 



TABLt VI. "Terylene'VAcefate Spun Twines 



Construction 



Nominal denier 
Resultant denier 
T.p.i. yarns Acetate 
strand "S" 
twine "Z" 

Strength (Ibs.) 
Extension (%) 
Tenacity (g.p.d.) . 

Knot strength 
Knot extension 
Knot tenacity 

Wet strength 
Wet extension 
Wet tenacity 

Wet knot strength 
Wet knot extension 
Wet knot tenacity 

Knot slippage 



No. 2 

6/3 

250 Terylene 
1/22's Acetate 
4346 
4678 
12-5 
5-8 
5-3 

43-8 
16-0 
4-25 

16-7 
10-3 
1-62 



45-5 
15-7 
4-41 

19*6 
10-6 
1-90 

None 



No. 3 

6/3 

3 -' 250 Terylene 6 
3 * 1/22's Acetate 4 
4419 
4492 
13-0 
5-4 
4-1 

36-9 
16-7 

3-73 

16-8 
10-0 
1-70 

36-3 
15-2 
3-67 

18-0 
10-0 
1-82 

None 



No. 4 

10/3 

250 Terylene 
I /22's Acetate 
7392 
7732 
12-0 
69 
3-1 

66-4 
23-9 
3-90 

29-8 
12 9 
1-75 

65-1 
22-3 
3-82 

30-0 

12-6 

1-81 

None 



4 
3 > 



No. 5 

7/3 

250 Terylene 
1/22's Acetate 
5169 
5329 
12-0 
5-5 
3-7 

46-9 
16-0 
4-0 

20-8 
14-0 

1-77 



46-4 
15-2 
3-95 

21-8 
10 
1-86 

None 



[52] 



VALUE AND USE OF TERYLENE 




i\ \httwn a 



in the manufacture of Terylene gillnets. 



principally for catching salmon and cod. It has been used 
in Canada for fishing salmon oft* the West Coast, the 
nets showing up to particular advantage in fast moving 
water or ocean currents, where lively fish can dive straight 
through a net or, when caught by the gills, escape by 
expanding the net mesh. The small diameter of the twines 
may lead to lower visibility, but it is thought that this 
very good performance can be attributed essentially to 
the high resistance to stretch. 

In certain types of synthetic fibre gillnetting it is now 
becoming customary to pull out the fish head foremost 
which is speedier than the normal practice, i.e. com- 
pressing the gills and pulling the fish out backwards. 
In such cases the high resistance to stretch is somewhat of 
a disadvantage, as it is not always possible to clear the 
nets in such a manner. 

The gillnets have been used successfully in Kenya 
lakes for fishing borus and tilapia, while cod gillnets 
have been very successfully used in Scandinavian waters. 
The gillnets are being increasingly used in India. 

Such gillnets have to date been found more suitable 
for catching hard rather than soft fish. The twines used 
have been fine and hard and have cut into soft fish, such 
as herrings, to such an extent that the fish have become 
bruised and damaged. When removed from the net by 
shaking the fish may be decapitated. Chiefly for this 
reason, Terylene has not yet been extensively used for 
British home water drift netting. However, such drift 
netting is being developed and twine constructions have 
been revised to give thicker and more suitable twines. 
Further trials are in progress to develop this market. 



A mixed high tenacity Terylene filament/spun acetate 
netting twine is being developed, principally for pilchard 
nets. It will not bruise or damage the fish and will not slip 
when single knotted. Tables V and VI give the principal 
physical properties of such twines. The use of Terylene 
core spun cotton yarns is also being considered for similar 
reasons, but, because of the cotton present, it could not 
be expected to be so rot resistant as a mixed filament/spun 
acetate yarn. 

Trawl Nets 

The filament twine has been used with success for bottom 
trawls. Trials were carried out some time ago, principally 
for the codend, because of the shortage of twine, although 
some complete trawls were also made up. These nets 
were made by the Great Grimsby Coal, Salt and Tanning 
Co. Ltd., of Grimsby, and the tests were carried out by 
distant water trawlers on various fishing grounds. It was 
found that each trawl net lasted on average about 9 trips 
and, in one case, 15 trips were made before the net was 
lost. The normal trawl net is generally good for an 
average of one trip. It was noted that the Terylene nets 
had good mesh stability and their resistance to abrasion 
reduced any chance of the codend bursting as it was 
hauled in. The nets were much easier to tow through the 
water and being completely rot-proof, drying was un- 
necessary. It is understood that cleaner catches were 
obtained. The ship's crew reported that the nets were more 
pleasant to handle than the usual nets. The lower 
moisture uptake was particularly advantageous in the 



153] 



MODERN FISHING GEAR OF THE WORLD 



icy operating conditions in Northern waters. Another 
advantage was that unloading of the codend was some- 
times done in fewer operations because of its greater 
strength. 

Risk of loss or accidental damage of the net is now 
being greatly reduced by introduction of Decca equip- 
ment, which is of special advantage when expensive 
trawls are used. The longer life and greater security 
offered by such nets outweigh the occasional losses. 
Already a number of trawler companies have started 
their own trials for near, middle and distant water fishing 
with Terylene trawl nets. 

There is perhaps a need for the use of thinner twines 
to reduce the price of the net and without doubt the 
introduction of an extra heavy denier yarn will enable 
nets to be produced more economically. 

Appreciable quantities of the fibre are now being used 
in Sweden for mid-water trawls and trials with such 
trawls arc also being conducted in the United Kingdom 
by the Ministry of Agriculture, Fisheries and Food 

Purse Seine Nets 

Until comparatively recently, little has been done with 
Teiylene purse seine nets, principally because of their 
cost, which may be as much as 5,000. 

Trials have been carried out in Canada with drum 
seines near Deep Water Bay off the West Coast. The 
netting, whilst only about a quarter of the weight of 
corresponding tarred cotton netting and with twines a 
third as fine, was about 10 per cenf. stronger in the wet 
mesh. This means that smaller vessels can be used or 
alternatively outsize seines can be carried by vessels 
which normally work with the smaller seine nets. 

The nets wound easily on to the drum, but some 
difficulty was experienced in playing out, the loose bights 
of netting tending to get entrapped. The bunt end of 
the seine was said to be easily held. There was less drag 
on the net so that it could be closed much more quickly 
than can normal purse seines. This is a real asset, 
ensuring a quicker and more efficient fishing operation. 
The nets were held more easily against the tide, which 
means, firstly, they can be used in faster waters, thus 
enabling fishermen to operate in more fishing grounds 
and, secondly, fishing time can be extended. The nets 
tended to become entangled, when fish could only be 



extracted with difficulty, a disadvantage arising from 
their high order of flexibility. This could be overcome by 
using coarser twines or applying suitable coating agents. 

Despite the disadvantages the preliminary results were 
most encouraging and, with the suggested modifications, 
it should be possible to use such purse seines with great 
profit. It is worthy of note that the somewhat higher 
specific gravity of the fibre compared with other synthetic 
fibres was an advantage, since it enabled the net to sink 
more easily. The lightness in weight of the netting is 
particularly useful for table seines. 

More extensive trials of these purse seines nets are now 
being made. 

Purse/Lampara Nets 

Many standard purse/lampara seine nets used in Walvis 
Bay, South West Africa, have failed prematurely, due it 
is thought, to chemical contamination, but a preliminary 
test of Terylene netting for use in these waters has 
proved most encouraging. Detailed trials are now in 
progress. 

Seine Nets 

Trials with Terylene seme nets arc to be carried out 
shortly in the United Kingdom. 

OTHER APPLICATIONS 

Other applications include lines and snoods. A fairly 
substantial market is developing in Norway, where the 
use of the twines has resulted in increased catches. The 
high resistance to stretch facilitates pulling in the line 
and it is easier to tell when the fish are hooked as a more 
definite response is obtained. Strength stability on wetting 
and the quick drying properties arc also important. The 
lines are slightly more expensive but this is offset by 
fishing performance. 

The twines are being tried for lobster pots in the United 
Kingdom, chiefly because of their rot resistance and 
general toughness. 

Fishnet mounting ropes of spun Terylene (flax 
system) cordage, which are used for supporting the nets, 
have been tried. The staple yarn is preferred to the 
continuous filament yarn because its hairy nature 
minimises slippage of the net and corks. Headlines of 
the fibre are also being tested. 



54 



TEVIRON FISHING NETS 

by 
THE TEIKOKU RAYON CO. LTD. 

Edobori Minamidori, Nishiku, Osaka, Japan 

Abstract 

The Teikoku Rayon Co. Ltd. introduced in October 1956 the new synthetic fibre Teviron, made from poly vinyl chloride, which can 
be obtained either as filament or staple fibre, the former having a silk-like appearance, the latter resembling wool. 

This paper deals with the use of this material in the manufacturing of fishing gear and it is pointed out that, in competition with 
other yarns, it ranks next to cotton in price. Other advantages are explained and tests have shown that Teviron can compete with Nylon 
in the Salmon and Trout fisheries, although Nylon has long been rated the best material for those fisheries. 



Resume 



Filets de peche en Teviron 



The Teikoku Rayon Co., Edobori Minamidori, Nishiku, Osaka, Japon, a mis sur le march en octobre 1956 une nouvelle fibre 
synthetique, le Teviron, obtenue partie du chlorurc de polyvinylc qui se prsente sous Paspecl soit de filaments soyeux,soitdefibresressemblant 
a la laine. 

Ce document est consacr 1' utilisation dc ce material pour la fabrication d'engins de peche et on fait remarquer que, par comparaison 
avcc d'autres filets, son prix le place juste apres le coton. D'autres avantages de cette fibre sont enumdres et des essais ont montrg que le 
teviron peut rivaliser avec le nylon pour la peche au saumon et A la truite, alsor qu'on a longtemps consider^ que le nylon dtait le meilleur 
materiel dans ce cas. 

Redes de pesca de Teviron 
Extracto 

En octubrc de 1956 la 'Teikoku Rayon Co. Ltd./ 1 Edobori- Minamidori, Nishiku -Osaka, Janon, Ianz6 al mercado una nueva fibra 
sintetica llamada "teviron", hccha a base dc cloruro de polivinilo, la cual puede obtenerse en forma dc hilo continuo o como fibra para hilar. 
El rrimero tiene el aspect o de seda y la segunda de lana. 

Este trabajo se reficrc al uso del "teviron** en la tcjeduria de artes dc pesca, senalandosc que, en compctencia de precio con otras 
fibras, figura a continuaci6n del algod6n. Tambien se dan u conocer otras ventajas, demos trando las pruebas efectuadas que puede competir 
con el nyI6n en las nesqucrias de salm6n y truchu, no obstantc considerarse desdc hace tiempo que este ultimo material es el mas apropiado 
para la pesca de dichas especies. 



CHARACTERISTICS OF TEVIRON 

TEVIRON, a polyvinyl chloride synthetic fibre first 
introduced in October 1956, is produced by 
Teikoku Rayon. The yarn is available both as 
filament and as a staple fibre: the former has a silk-like 
appearance and touch, while the latter resembles wool. 
This fibre is suitable for making fishing nets and rope. 



Filament 



Staple Fibre 



300 den. (20-60 fil.) 
1-39 
3-0-3-7g/den. 


2-15 den. 
1-39 
2-0-3-0 g/den. 


t} 14-25% 
2-0-2-7g/den. 

9-17% 


50-75% 
1-5-2 -5 g/den.. 
50-70% 



Denier 

Specific Gravity 
Normal Strength 
Extensibility (unknotted) 

(independent of humidity) 
Knot strength 
Extensibility (knotted) 
Ratio of Knot Strength to 

Normal Strength . 70-75% 80-85% 

Young's Modulus . 800-900 kg./sq. mm. 200-300 kg./sq. mm 

Elasticity at 3% . 80-85% 80-85% 

Temperature at beginning of 

Shrinkage . . 60-70 deg. C. 100 deg. C. 

Resistance to friction . Great (esp. in water) Great 

Resistance to Acid and Alkali Great Great 

Resistance to sunlight . very great very great 



TEVIRON FISHING NETS 
Cost 

A Teviron net costs less than a net of any other 
synthetic fibre yarn, and is only 30 per cent, more than 
a cotton net. 

Ease of handling 

(a) Owing to the great resistance to rot (see figs. 1 
and 2), little work is needed for drying or re-dyeing 
Teviron nets or for other maintenance services. 

(b) As the net does not absorb water, it is very light 
and can be handled by a smaller crew. 

The table below gives the results of an investi- 
gation into labour and time factors. The com- 
parison was made between two large fixed nets 
of approximately similar size, one of Teviron, the 
other of manila: 



Teviron net 
Manila net 



Number of 
Workers 

. 44 
. 60 



Time required for pulling up 

the net completely from the sea 

(Minutes) 

25 
45 



155] 



MODERN FISHING GEAR OF THE WORLD 




23456789 
TiB of iomroion (month.) 



10 11 12 




Fig. I. Results obtained from immersion in sea-water. 



012 34 5 6 789 10 11 12 
Tine of liBMraion (Months) 

Fig. 2. Results obtained from outdoor exposure. 



The Teviron net could be pulled up when the 
current was rapid; the manila net could not be 
moved. 



Suitability for various gear 

(a) Gillnets : Teviron twine is flexible, and a 
minimum of shrinkage assures stability of mesh 
size. A test of Teviron and nylon drift nets for 
salmon and trout in northern seas showed that 



the Teviron net is not inferior to nylon net: 
A verage number offish caught for each operation 
Teviron net . .2-27 

Nylon net . .2-22 

(b) Purse seine nets: Teviron needs no drying, and 
little repair and other maintenance work, allowing 
more fishing time per day, and longer trips. More 
fish can be caught because the net sinks rapidly. 

(c) Fixed nets: The fibre does not decay even in the 
warmest season of the year, and has proved a 
strong and reliable material in rough water. 




Repairing drift nets in Ceylon. 

[56] 



Photo FAO. 



KREHALON FISHING NETS AND ROPES 

by 

KUREHA KASEI CO. LTD. 

Tokyo, Japan 



Abstract 

Krehalon is a vinylidenc chloride filament which has a higher specific gravity (1-7) than other synthetic fibres. It is less affected by 
currents, sinks faster and drains water faster. The pliability of the fibre gives more strength to the knots and resistance to impact and friction. 
These characteristics make it particularly suitable for setnets. Big setnets of Krehalon have been in use since 1952 and are said to show no 
signs of wear. 

Krehalon is also used for stick-held dipnets, surrounding nets, gillnets, longlines and trawlnets. it is available both as monofilament 
and continuous-multifilament yarn; nets arc either knotless or made with English knot. Lines and ropes are also made of Krehalon. This 
fibre is sensitive to heating and should be kept off sandy beaches or cobblestones in midsummer. 



Resume 



Filets de peche et cordages en Krehalon 



Le K rehalon est un filament de chlorurc dc vinylidenc, qui possede un poids specifique plus eleve (1,7) que les autres fibres synthc- 
tiques. 11 est moins affect 6 par les courants, plonge plus rapidement et 1'eau s'en egoutte plus vite. La souplesse de la fibre donne plus de 
resistance aux noeuds, augmente la resistance aux impacts et au frottement. Ces caracteristiques le font convenir part icu I Bremen t bien pour 
les filets fixes. Dcpuis 1952 on utilise des grands filets fixes de Krehalon et on declare qu'ils ne montrent pas de signes d*usure. 

On utilise aussi le Krehalon pour les carrelets monies sur des perches, les filets-pares, les filets maillants, les palangres et les chaluts. 
Lc Krehalon est prod nil en fil monofilament et en fil multi-filaments continus; les filets sont soit sans noeuds, soit noues. On fait aussi des 
lignes et des cordages de Krehalon. Ccttc fibre est sensible a la chaleur et doit fctre maintenue a 1'ecart des plages de sable ou des galets 
pendant la saison chaudc. 

Redes de y cuerdas de "Krehalon" 
Extracto 

Desde 1952 sc han comenzado a utilizar grandes artes de "krehalon" filamento de cloruro de yinilideno. Este material tiene mayor 
peso especifico (1,7) que el resto dc las fihras sinteticas y sufre en menor grado la influencia de la corriente; ademas se hunde y deja escurrir 
cl agua con mayor rapidez. La flexibilidad dc las fibras impartc una mayor firmeza a los nudos a la vez que ofrece mas resistencia al impacto 
y a la fricci6n, haciendolo especialmente apropiado para la fabricacidn de redes fijas. 

Esta fibra tambien se usa para salabardos provistos de mango, artes de enmallc y arrastre, palangres y espineles. 

Las redes de este material pueden fabricarse sin nudos o empleando el nudo de tejedor. El "krehalon" tambien sirve para fabricar 
cabos y cuerdas, pero es muv sensible al calentamiento y no debc extenderse sobre piedras o playas de arena durante el verano. 



GENERAL 

THIS vinylidene chloride filament has the greatest 
specific gravity (J -7) of any synthetic fibre. It is 
less water absorbent and drains water faster. Nets 
made with this fibre are pliable and strong and retain 
their shape even in turbulent waters. They sink quickly. 
The tensile strength of the fibre is 120 to 130 per cent, 
higher than that of comparable cotton yarn. The flex- 
ibility of the fibre gives higher knot strength and greater 
resistance to impact and friction. 

The fibre is particularly suitable for constructing 
setnets, as fish of any size are unlikely to be injured when 
trapped because of the pliability of the fibre. Some set- 
nets made of Krehalon (see fig. 1) have been in use 
since 1 952 and show no signs of wear ( 1 957). Fishermen 
say they can withstand the buffeting of the severest 
typhoons. Stick-held dipnets (see fig. 2), surrounding 
nets, gillnets, longlines and trawlnets made of this 
fibre show similar durability. 

The mesh size of Krehalon nets is usually made 
slightly smaller than that of nets of natural fibres as it 



does not shrink in usage. The fibres can be dyed freely 
in any colour. 

Sizes: In multi-filament twines several 180 denier 
filaments are usually put together to form yarn, twine or 
line. Mono-filaments are composed of one large 




L&rg* Mtiwt BKd* of 
Kmhalon 

1. l*dr nat 

2. *nt-oliMbr 

3. funml 

4. b* 

5. floats 

6. anchoring atom* or 



Fig. I. 



[57] 



MODERN FISHING GEAR OF THE WORLD 




A tlok-hld dipiwt 
of 



t. 2. 



filament (i.e. as 1,000 denier). 360 denier is equivalent 
to cotton yarn of count 20's. Thickness and tensile 
strength have been taken into consideration. Multi- 
filament nets are more pliable than mono-filament nets. 

Nets: The nets are of the same specifications as the 
conventional cotton yarn or manila twine nets available 
in knotless or English knot. Smallest are 720 D :; 3, 
mesh size 25 knots per 6 inches. 

Ropes: Ropes, lead line, twisted twines, longlines, 
cord, etc., are manufactured according to specifications. 

Cautions regarding use: Long exposure to high temper- 
ature can cause a chemical change in the filament. For 
this reason, a sandy beach or cobblestones are best 
avoided in midsummer. 

Tarring: Krehalon nets do not normally require 
tarring, but, if necessary, put one part of refined tar 
into two parts of 5 per cent, solution of neutral soap. 
Tar at a temperature less than 40 deg. C. 

Use a hot iron knife when cutting a filament. This 
obviates the danger of fraying. 




Lifinet fishing in Jakarta harbour. 
[58] 



Photo FAO 



SOME PHYSICAL PROPERTIES OF MANILA ROPE 

by 
J. REUTER 

Nederlandsche Visscherij-Proefstation en Laboralorium voor Materialen-Onderzoek Utrecht, Netherlands 



Abstract 

Very little has been published to date on the properties of rope, in spile of its vast importance to the fishing industries of the world. 
People have learned about rope by experience but definite conclusions based on exact and concrete data are not always available. In this 
paper the author attempts to bring out some of the properties of hard-laid, medium-laid and soft-laid ropes and tables showing the physical 
characteristics in both the wet and dry state arc given. 



Resume 



Quelques proprietes physiques des cordcs de Manillc 



Jusqu'ii present tres pen d 'articles ont etc publics au sujet des proprietes des cordes malgre leur grande importance pour les industries 
des peches dans le mo rule. On a appris empiriquement a connaitrc Ics cordes mats on nc dispose pas toujours dc conclusions definitives 
hashes sur des donnees exactes et concretes. Dans cet article, Pauteur essaie de faire ressortir quelques-unes des proprietes des cordes com- 
mises lache. moyennement et serre, ct donne des tableaux montrant Ics caractcristiques physiques l'6lat sec et a Petal mouille. 

Algunas propiedades fisicas de la cucrda de abaca 
Extracto 

Sc ha publicado muy poca informacion sobre las propiedades de las cucrdas de abaca o manila no obstante la gran importancia que 
ncnen en la industria pcsquera de todo el mundo. Se sabe mucho acerca de cuerdas por experiencia, pero no siempre se dispone de con- 
clusiones definitivas basadas en datos exaclos y concrelos. En cste trabajo el amor trata de dar a conocer algunas caracteristicas de las 
cuerdas poco, medianamenlc o muy retorcidas, e incluyc tablas con las propiedades fisicas de ellas tanto humedas como secas. 



KNOWLEDGE of the various intrinsic properties 
of ropes is indispensable for the right choice and 
economic use of them. Although experience 
has resulted in some general knowledge, no definite 
conclusions based on exact and concrete data are avail- 
able and very little has been published on this matter. 
The following article is an effort to contribute some 
information for fishermen on this subject. 

Influence of basic manufacturing procedures 

During the process the fibres are twisted successively in 
opposite directions into yarns, strands, ropes and cable. 
This results in a decrease in breaking load. A remarkable 
fact is that even when the same basic fibre material is 
used, the breaking strength of "Z" yarn is different 
from that of "S" yarn. It is obvious, therefore, that the 
actual twisting process itself exercises a very considerable 
influence on the breaking strength. 

Trial I Influence of the means of manufacture 

Rope was formerly made exclusively on the rope walk 
but the process has now been mechanized. Theoretically, 
it makes no difference how rope is made, although the 
finger-tips of an experienced ropemaker possess certain 
qualities which cannot, except with great difficulty, be 
duplicated in a machine. 
To obtain more concrete information on this aspect, 



a ropemaker was found who agreed to make rope in 
three different types of machine. He was requested to use 
different ways from a given yarn, viz. on the rope walk 
and on two different types of machine. He was requested 
to do his utmost to ensure that the ropes were as identical 
as possible. Little difference was apparent in the three 
ropes at first sight, yet very marked dissimilarities were 
disclosed by investigation (see Table I). These differences 
were not apparent from the slight variations in circum- 
ference, which is generally assumed to be an indication 



TABLL 1 


Rope 


Rope 
closing 
method 


A verage 1 
weight of 
\ metre of 
rope in 
grammes 


Total 
number of 
turns per 
strand per 
metre 


Average- 
circum- 
ference 
in mm. 


Average^ 
breaking 
strength 
in kg. 


Breaking 
length in 
km. 


Rope walk 90 
Machine 1 95 


25-0 

27-3 


38-6 
38-8 


1284 
929 


14-27 
9.78 


Machine 


2 95 


26-0 


37-7 


1028 


10-82 



1 Average for 16 determinations. 

2 Average for 80 determinations. 



59] 



MODERN FISHING GEAR OF THE WORLD 



of strength when comparing ropes made of the same 
material. 

This should not be interpreted as an endeavour to 
expound a theory that rope made on the rope walk is 
"good" and machine-made rope * 4 bad". Such a 
sweeping statement could never be made on the basis of 
a single trial; the only purpose was to prove that the way 
in which a rope is made can result in significant differ- 
ences in the breaking strength even when the same fibre 
gradings are used. 

Trial II Influence of the lay 

Procedure. Three types of rope were made on the rope 
walk. The conditions, i.e. basic material, equipment, etc., 
under which the experiments were carried out were 
identical in all cases. The only intentional deviation 
was that a number of different lays was selected, so as 
to produce ropes of hard, medium and soft lay. This 
was done not only to ascertain possible modifications 
in the properties of the rope, attributable to the different 
lays, but also because these modifications are important 
in some instances in commercial fishing. 

The three different ropes were all based on 20 yarns 
per strand, made from the same fibre mixture. 



Test Methods. During the closing of the rope, 20 
bobbins (rd of the total number used) were marked. 
The yarn was subsequently examined to establish its 
various properties. Five lengths were cut off simultan- 
eously from the rope to be tested for breaking strength, 
etc. The first and third lengths (3-5 metres long) were 
examined dry, the second and fourth (4 metres long) 
were examined wet, while the fifth (1 metre long) was 
untwisted to enable the yarns to be examined dry. 

The lengths intended for use in testing the breaking 
strength at the splice, with overhand knot and as a sling, 
were then cut off successively. 

Breaking strength tests were carried out on a hydraulic 
breaking-strength machine fitted with clamps. The 
distance between clamps was ISO cm. and the rate of 
movement of the straining head approximately 12 J cm. 
per minute. 

The ropes examined "wet" were immersed in fresh 
water for at least 16 hours. Their weight was determined 
after all non-absorbed water had run off for 30 minutes. 
The yarn tensile strength iest was carried out with 
100 cm. between clamps, the rate of movement of the 
straining head being approximately 25 cm./min. 

Results. In the following the results of this experiment 



TABLE II 
Soft-laid Rope 



TABL HI 

Normal-Laid Rope 



Experiment 



Type 



dry 



3-strand, 
plain-laid 



wet 



Total number of yarns 3 x 20 60 
Weight per metre in 



grammes 



322-4 



Average number of turns 
per strand per metre 13-78 

Average circumference 
in mm. . 74-85 

Average breaking 
strength in kg. . 4930 



100 



100 



100 



100 



Average breaking length 
in km. (based on dry 
weight) . . 15-30 100 

Average breaking length 
in km. (based on 
wet weight) . 

Average duration of 
test, after application 
of initial load . 6-425ximin. 100 



3-strand, 
plain-laid 




3x20-60 




521-5 


161-7 


13-86 


100-6 


84-70 


113-2 


5205 


105-6 



16-14 



9-98 



105-5 



65 



Experiment dry 

Type . . . 3-strand, 

plain-laid 

Total number of yarns 3 x 20 -60 
333-3 



Weight per metre in 
grammes 



8-125ximin. 126-5 



Average number of turns 
per strand per metre 15-15 

Average circumference 
in mm. . 72-45 

Average breaking 
strength in kg. . 4513 

Average breaking length 
in km. (based on dry 
weight) . . 13-54 100 

Average breaking length 
in km. (based on 
wet weight) . 

Average duration of 
test, after application 
of initial load .6-75xjmin. 100 





3-strand, 
plain-laid 






3x20 60 




100 


494-2 


148-3 


100 


15-02 


99-1 


100 


80-1 


110-6 


100 


4357 


96-5 



13-06 



8-82 



96-5 



65-1 



8-05 imin. 119-3 



Breaking strength short 
splice in kg. . 4295 87-1 

Breaking strength with 
overhand knot in kg. 2033 41-2 

Breaking strength with 
sling around rods 7344 149 

10 cm. in diameter 



Breaking strength short 
4389 84-3 splice in kg. 3652 80-9 

Breaking strength with 
2333 47-3 overhand knot in kg. 1978 43-8 

Breaking strength with 

sling around rods 6789 150-4 

10 cm. in diameter 



3700 
2322 



94-9 
51-5 



[60] 



PROPERTIES OF MANILA ROPE 



are interpreted according to a system developed at the 
Nederlandsche Visscherij-Proefstation. 

(a) Dry Rope 

The increase of number of turns per unit length (lay) 
results in : 

(1) increase of weight per unit length (see below) 

relation of weight per unit length 
yarns (not twisted) rope 

Soft laid . . 1 : 1-256 

Medium laid - 1 : 1-298 

Hard laid ... 1 : 1-332 

(2) decrease in diameter (that means more material 
per unit diameter) 

(3) decrease in breaking strength (that means more 
material for unit breaking strength) 

In the present example the remaining breaking strength 
of one yarn in the rope in the three different types 
(1/60 x rope strength) is: 

In soft laid rope . 82-17 kg. (62-6%) 
In medium laid rope 75-22 kg. (57-34%) 
In hard laid rope . 56-67 kg. (43 -20%) 

The breaking strength of the yarn, prior to closing the 
rope, was 131 18 kg. (100 per cent.) (see Table V). 

(4) This means that the breaking length, the only 



accurate tensile strength criterion for rope, cannot be 
used for the comparison of ropes of different lays. 

(5) increase in knot strength. 

(6) increase in strength of a loop. 

The total extension at break is maximal in normal 
and less in hard and soft laid ropes (see Table VI). 

(b) Wet Rope 

Increase in number of turns per unit length (lay) 
results in: 

(1) less water absorption (less increase in weight). 

(2) less increase of diameter due to water absorption. 
Contrary to the dry rope, the total extension at break 

of the wet rope is higher with hard and soft lay than 
with normal lay (see Table VI). With a tension of 2,000 
kg. or less the soft laid rope has the highest extension and 
the hard laid rope the lowest. Immersion has no 
remarkable influence on the number of turns per unit 
length. There is a certain influence of immersion on the 
breaking strength but the results available at present are 
not sufficient to draw reliable conclusions. 

(c) Influence of rope manufacturing on the yarns 

in order to examine the effect of manufacturing, samples 
of the three types of rope were untwisted and the single 
yarns tested. It was found that whilst soft and normal 
lay has only very little influence (loss) on the breaking 



TABLE IV 
Hard-laid Rope 


strength 
decrease 


of the single yarn, hard 
(see Table V). 


lay results in a 


certain 


Experiment dry % wet % 








TABLE V 
Yarn 








Type . . . 3-strand, 3-strand, 
plain-laid plain-hiid 

Total number of yarns 3 x 20 -- 60 3 x 20 =- 60 
















Untwisted Untwisted Untwisted 
Before from from from 
closing soft-laid normal-laid hard-laid 
rope rope rope 


Weight per metre in 
grammes . 340-5 100 473-7 139- 1 

Average number of turns 
per strand per metre 16-81 100 16-71 99-4 

Average circumference 
in mm. . 65-8 100 69-9 106 2 

Average breaking 
strength in kg. . 3484 100 3284 94-3 

Average breaking length 
in km (based on drv 


Average breaking 
strength in kg. . 131 18 130-76 128-38 121-11 

No. of determinations 200 100 100 100 

Average weight per 
1 00 metres in grammes 428 434 -5 427-4 424-7 

Average breaking 
length in km. . 3065 30-09 3010 28-45 

Percentage of breaking 
length . . 100 98-2 98-2 92-8 


weight) . . 10-22 100 9-65 94-4 
















Average breaking length 


TABLE VI 


in km. (based on 
wet weight) . 6-94 67-9 


Total Extension 


Average duration of 
test, after application 
of initial load . 5-85ximin. 100 6-70^ min. 114-5 


Tension 
kg. 


soft 
dry 


rope 
wet 


normal 
dry 


rope 
wet 


| hard 
| dry 


rope 
wet 




250 - 


*U' 

(1 


10-8% 


5-3% 


7*9% 


1 4-0% 


6-4, 


Breaking strength short 
splice in kg. . 3407 97-7 2944 89-6 


500 


* 


13-8 


7-4 


11 


! 5-6 


9-8 




1000 


10-9 


15-8 


11-1 


13-5 


: 8-4 


13-0 


Breaking strength with 
overhand knot in kg. 1778 51-0 1878 53-9 


2000 ! 
3000 


13-2 
14-8 


18-0 
19-6 


14-8 
16-7 


16-1 
17-8 


12-8 
15-0 


16-8 
18 


Breaking strength with 
sling around rods 5878 1 68 7 


4000 


16-1 


20-8 


17-7 


19-2 


16-2 






10 cm. in diameter . 



Not determined. 



61 ] 



THE MANUFACTURE AND TESTING OF SYNTHETIC YARNS 
AND FIBRES USED IN JAPANESE FISHING GEAR 



by 

JAPAN CHEMICAL FIBRES ASSOCIATION 

Tokyo, Japan 

Abstract 

Synthetic fibre has been used for fishing gear in Japan since 1932 when it was tried out as fishing gut, and after 1948 an effort was 
made to increase its use, and now all kinds of nets and gear are made from synthetic materials. This paper gives in tabular form the physical 
properties and uses of the various fibres and also the quantity of nets and lines manufactured from both natural and synthetic fibres in 1956. 
The weight of nets exported is also given. Then follow the rules which have been designed to standardize the testing of spun vinylon, 
filament nylon, filament vinylidcnc chloride and filament vinyl chloride. 



Resume 



Fabrication et essai des fils et fibres synthetiques entrant dans la construction dcs engins de peche japonais 



Les fibres synthtiques sont utilisees au Japon pour la confection des engins dc peche dcpuis 1932, epoque a laquclle clles ont etc 
cssayees en remplacement du crin, et Ton s'effprce depuis 1948 de developper leur cmploi en sorte qifactuellement les filets et engins de tous 
types sont confectionnes en materiaux synthctiqucs. Ce document donne sous forme de tableaux les proprietes physiques ct les applications 
des diflercntes fibres ainsi que les quantites de filets et de lignes fabriquees d'une part en fibres nature-lies, et de Paul re en fibres syntheliques 
en 1956. Le poids des filets cxportes cst egalcmcnt indiqu suivant les regies adoptees pour la normalisation des essais des fils de brins de 
vinylon ainsi que dcs filaments de nylon, de chlorure de vinylidene et de chlorurc dc vinyl. 



Extracto 



La manufactura y ensayo de las fibres e hilos sinteticos usados en los artes de pesca japoneses 



A partir de 1932 la industria pcsqucra japonesa comenzo a usar fibras sinteticas en los artcs de nesca cuando las ensay6 como sedales, 
pero s6lo dcspues dc 1948 se hicieron esfuerzos para aumentar su uso y, en la actualidad, todos los tipos dc redes y artes son confeccionados 
con este material. En el trabajo matcria de cste extracto sc compendian en tablas las propiedadcs fisicas y usos de las diversas fibras, asi 
como las cantidades de redes, palangres, etc. fabricados con fibras naturales y sinteticas. Tamhien se mcluyc el peso de las redes exportadas 
y las disposiciones que se proyectaron para norrmilizar los ensayos dc vinilon hilado, nylon y cloruros dc vinilidcno y de \ inilo en hilos dc 
una sola hebra. 



SYNTHETIC fibre was first used for fishing in 
Japan in 1932, as fishing gut. Since about 1948 
experiments have been carried out on the adapt- 
ability of synthetic fibre for fishing gear through co- 
operation of the Fisheries Agency, Fisheries College, 
Fisheries Research Institute, fibre makers, fishing net 
makers, fishermen, etc. 



As a result of improvement in quality, advance in 
net-making techniques and the reduction in cost by mass 
production in 1953, the demand for synthetic fibre has 
considerably increased for seine and setnets, and salmon 
and trout gillnets (see Tables I, 11, Ml). 

The export of fishing nets has gradually increased 
since 1951, about 1 -2 million Ibs. being exported in 1956. 



TABLE I 
Production of Synthetic Fibre Nets by Netting Types for 1956 



Unit: Pounds 



Fibre 

Nylon 

Vinylon 

Poly vinylidene Chloride Fibre 

Polyvinyl Chloride Fibre 

Two Fibres Plied 

Total .... 



Type 

English Knot Reef Knot Knotle.\s Net 



4,489,213 
1,893.088 

598,034 
70,619 

631,900 

7,682,854 



50 

3,028,940 
6,454 



3,035,444 



82,287 

810,478 

1,546,712 

104,181 



2,543,658 



Moji Net 
183,394 



Total 



4,571,550 

5,915,900 

2,151,200 

174,800 

631,900 



183,394 13,445,350 



[62] 



SYNTHETIC FIBRES JN JAPAN 



TABLE II 
Production of Fishing Nets and Lines in 1956 (or 1957) 



Unit: 1,000 Pounds 



Type 



Month 
1 2 3 4 5 6 7 8 9 10 11 12 Total 1955 



Fishing Net\ 
























Cotton .... 


1,152 


1,478 1,215 


915 


730 


641 


586 


731 


774 


702 


708 


673 10,305 14,845 


Silk ... 
































12 


Manila Hemp 


HI 


117 71 


71 


43 


53 


60 


111 


168 


108 


115 


112 1,110 1,273 


Other Hard Fibres 


3 


23 19 


18 


11 


11 


49 


3 


3 


2 


2 


3 147 437 


Synthetic Fibres 


713 


1,082 1,120 


1,090 


920 


783 


829 


898 


969 


1,290 


1,101 


1,095 11,8906,923 


Sub-Total 


1,949 


2,700 2,425 


2,094 


1,704 


1,488 


1,524 


1,743 


1,914 


2,102 


1,926 


1,88323,45223,490 


Fishing Lines 
























Cotton .... 


826 


991 895 


888 


805 


885 


703 


844 


833 


775 


797 


863 10,105 12,092 


Silk .... 





























2 


025 


Manila Hemp 

(~\t\+t*r WurH T^iKr^c 


13 


8 17 


13 


15 


7 
2 




j 


9 
i 


17 


12 


17 


13 141 51 

01 A IJA 


Synthetic Fibres 


152 


229 287 


274 


234 


275 


289 


373 


330 


422 


427 


498 3,790 1,511 


Sub-Total 


994 


1,235 1,203 


1,182 


1,057 


1,169 


999 


1,227 


1,180 


1,209 


1,243 


1,37414,07213,805 


Total 


2.943 


3,935 3,628 


3,276 


2,761 


2,6^7 


2,523 


2,970 


3,094 


3,311 


3,169 


3,25737,52437,295 



TABLL 111 
Production Capacity of Fishing Nets and Lines in 1956 (or 1957) 



Hand Machine 



Power Machine 



Twister 





Machines 


Machines for 




Operable* 


Synthetic fibres 


Reef knoi 


8,258 


6,437 


English knot 


74 





Moji net 


6 




Reef knot 


87 


42 


English knot 


2,199 


2,469 


Moji net 


426 





Knot less net 


57 


56 


Hari twister 


48,038 


n. a. 


Ring twister 


181,522 






Companies concerned 



111 



64 



Machines 
Operated* 

3,898 
62 

2 



51 

1,398 
181 
44 



35,835 
163,889 

101 



Monthly Capacity 
per Machine 

150 Ibs. 



370 
540 

2,940 



Machines for natural fibre nets and lines included. 



Owing to the rapid development of different synthetic 
fishing gears, efforts are being made to determine 
suitable testing methods for synthetic yarns. 
The following methods and standards are proposed. 

Method of Testing Twines for Fishing Nets 

A Spun Vinylon. B Filament Nylon. 

C Filament Vinylidene Chloride and Filament 
Vinyl Chloride. 

In the following text, the materials to which each 
paragraph refers are shown by the letters A, B and C. 

1. Scope 

These standards shall cover the methods of testing twines 
of the materials shown above. 



2. Definition 

2-1. Standard Condition in Testing Room (A. B.C.) 
Temperature at 20 f 2 deg. C., and relative 
humidity at 65 2 per cent. 
Remark: For determining temperature and 
humidity, the Assman's Aspiration Psychro- 
meter shall be employed, and the relative 
humidity obtained from the humidity table by 
Sprung's formula. 

2-2. Standard Condition of Test Sample (A. B. C.) 
is when the sample left in a testing room under 
standard conditions (2-1) has reached moisture 
equilibrium (2-3). 

2-3. Moisture Equilibrium. (A. B.) After pre-drying a 
test sample at a temperature of 40 to 50 deg. C. 



[63] 



MODERN FISHING GEAR OF THE WORLD 



it is left in the laboratory under standard 
conditions. When the sample has been brought 
to the constant weight (2-5), being steady and 
uniform in hygroscopic state, it shall be con- 
sidered to be in moisture equilibrium. 

2-3. Constant Weight (C.) Weigh the test sample 
twice successively at intervals of one hour or 
more at the time of drying. The constant weight 
shall be considered as that when the difference 
between the two weighings is under 0-03 per 
cent. 

2-4. Absolute Dry Condition (A. B.) Is reached when 
the weight of a test sample becomes constant 
(2-5) due to being left in a drying oven at 
105 to 110 deg. C. 

2-4. Absolute Dry Weight (C.) Is the weight under 
standard conditions of test sample, also called 
the bone weight. 

Remark: Moisture regain under Standard con- 
ditions is almost nil. 

2-5. Constant Weight (A. B.) Weigh the test sample 
at intervals of one hour or more for the moisture 
equilibrium, and at 10 minutes or more for the 
absolute dry condition. Constant weight is 
reached when the difference is within 0-05 per 
cent, of the last respective weights. 

2-6. Commercial Moisture Regain. (A.) 5 per cent, 
of the absolute dry weight (B.) 4-5 per cent. 
(C.) per cent. 

2-7. Denier (A. B. C.) Denier is a unit of fineness, 
the yarn having a weight* of 0-05 gr. per 450 
metre length. The denier is equal numerically 
to the number of grams per 9,000 metres. 

2-8. Yarn Count (A). Yarn count to be expressed by 



840 yards) 



the number of hanks (One hank 
per pound in weight*. 

Indication of Yarn Count (A.) 

Yarn count to be expressed as follows. 

Single Yarn 20 yarn count ........ 20 s 

Twine 20 yarn count 2 ply ..... 20/2 s 

3 strands of 20 yarn count 2 ply 20/2/3* 

Indication of Denier (B.) 

Denier to be expressed as follows: 

Twine 3 strands of 15 filament 2 10 denier 5 ply 

2IOD/I5f 5 

Indication of Denier (C.) 
Denier to be expressed as follows: 

Twine 3 strands of 1 filament 1000 denier 8 ply . 

1000i>/lf > 8 -. 
3 strands of 10 filament 1500 denier 6 ply 

ISOOo/lOf .-63 

2-10. Indication for Direction of Twist (A. B. C.) 

The direction of twist to be expressed by S and 
Z as shown in fig. 1 : 



2-9. 



2-9. 



2-9. 



3 



3 




The direction of upper twist, middle twist and 
lower twist to be expressed as follows: 

UPPER TWIST DIRECTION MIDDLE 
TWIST DIRECTION LOWER TWIST 

DIRECTION. 



The weight includes the commercial moisture regain. 



TABLfc IV 

Export of Natural and Synthetic Fibre Fishing Gear in 1956 (or 1957) 



Unit: Pound 



Type 

Natural Fibres 
Cotton 
Silk 

Manila Hemp 
Sisal 
Flax 
Ramie 
Coil Yarn . 

Sub-Total 



1 



3 



Month 

1 8 



10 



II 



12 



Total 



363,037 532,585 528,811 448,219 494,895 401,129 412,297 361,712 424,347 426,674 351,561 473,724 5,218,991 



18.706 



20 


159 


31 





_,_ 


2 


13,345 


42,629 


2,507 


14,170 


40,159 


9,164 


32,894 


55,099 


15,815 


47,146 


25,187 


54,945 


1,230 


2,110 


-- 


1,183 


1,933 


749 


10 


2,000 




.._ 


825 







--- 






7,572 





894 
375 



5 


99 


4 





320 


21,434 


10,445 


91,330 


194,436 


459,319 


29,710 


44,826 





20,867 


326,489 




285 


2,363 


595 


10,823 


207 




440 


5 


3,487 




... 




--- 


7,572 



381,743 580,084 630,808 466,572 557,394 476,805 477,157 362,981 475,703 482,329 445,698 689,627 6,026,901 



Synthetic Fibres 

Nylon 

Vinylon 

Polyvinylidene 

Chloride Fibre 
Polyvinyl 

Chloride Fibre 
Two Fibres Plied 

Sub-Total 
Total . 



17,140 36,570 49,072 63,955 62,795 65,009 38,818 55,464 59,264 
4,797 6,877 14,148 8,776 8,217 12,789 4,060 16,938 17,616 



18,841 



850 



720 

2,672 

6,373 8,692 



992 16,047 



19 



951 



261 



622 6,698 9,004 13,872 16,871 



40,778 44,297 72,265 82,143 72,626 100,543 51,901 87,225 94,012 
422,521 624,381 703,073 548,715 630,020 577,348 529,058 450,206 569,715 



67,519 74,017 93,309 
12,6% 97,335 17,195 



682,932 
221,444 



254 44,034 316 63,594 



7 442 3,121 

24,050 27,624 31,534 165,031 

104,526 243,010 142,7% 1,136,122 

586,855 688,708 832,423 7,163,023 



[64] 



SYNTHETIC FIBRES IN JAPAN 



2-11. Indication for Number oj Twist (A. B. C.) 

The number of twist will be indicated by the 
numerical value of turns per metre (t./m.) or 
turns per inch (t./in.). Jn the case of twine the 
number of upper twist, middle twist and lower 
twist to be indicated as follows: 

LOWER TWIST NUMBER MIDDLE 

TWIST NUMBER UPPER TWIST NUM- 
BER. 

Example: Upper twist Z 120 turns per metre, 
middle twist S 5 turns per inch and lower twist Z 
10 turns per inch- Z 10 t./in. - S 5 t./in. x 
Z 120 t./m. 

2-12. Standard Initial Tension (A.) 

Standard initial tension is the first tension in 
which the yarn is suspended without any exten- 
sion. In cases where tension affects mean 
"thickness", "ply number' 1 , "apparent yarn 
count", "twist", "tensile strength and extensibil- 
ity", "knot strength", "clastic recovery" and 
"shrinkage in water", the initial tension is given 
to a yarn of 20" with a load of 5 grams. An 
initial tension other than the standard one shall 
be indicated. 

2-12. Standard Initial Tension (B. C.) 

In cases where tension affects mean "thickness", 
"ply number and filament denier", "denier", 
"twist", "tensile strength and extensibility", 
"knot strength", "clastic recovery" and "shrink- 
age in boiling water" the initial tension used is 
1/30 g. of the nominal denier (filament denier 
- ply number). An initial tension other than the 
standard one shall be noted. 

3. Sampling and Preparation (A. B. C.) 

The test sample is taken by cutting off 5 m. from the end 
of the yarn. Care must be exercised to prevent change in 
twist, and no tension given. In case of testing for "knot 
strength" and "elastic recovery", the test sample will be 
left in the testing room under ordinary conditions until 
it reaches the constant weight. When the testing room 
cannot be kept in standard condition, the lest sample will 
be put in a closed vessel (of 36 per cent, sulphuric acid) 
and the temperature be kept at the constant degree 
(20 deg. C.). 

4. Test Items (A. B. C.) 

(1) Corrected weight 

(2) Moisture regain 

(3) Standard weight 

(4) Thickness 

(5) Ply number 

(6) Yarn count or denier 

(7) Twist 

1. Upper twist number 

2. Middle twist number 

3. Lower twist number 

4. Twist shrinkage 

(8) Twist setting 

(9) Tensile strength and extensibility 

1. Dry tensile strength and extensibility 



2. Wet tensile strength and extensibility 

(10) Knot strength 

1. Wet strength of reef knot 

2. Wet strength of English knot 

(11) Elastic recovery 

(12) (a) Shrinkage in cold water; (b) in boiling water 

(13) Moisture absorption 

(14) Sinking speed 

(15) Weathering resistance 

5. Methods of Testing 

The test of "standard weight", "tensile strength and 
extensibility", "knot strength" and "elastic recovery", 
will be carried out in a testing room under standard 
conditions. When the testing room cannot be kept at the 
standard temperature, the temperature at the time of the 
test will be noted. 



5-1. 



5-2. 



5-3. 



5-4. 



5-5. 



Corrected \\ 'eigh t 

Find out the weight of gross and tare of two 

samples and get the corrected weight from the 

following formula and indicate the average 

number. 



Corrected weight 
\\here: W 
R 



W 



100 H R t 
100 * R 

weight of the test sample (gross weight 



(are weight) 

moisture regain measured (per cent.) 
R t commercial moisture regain (A 5 per 
cent., B 45 per cent., C per cent.) 

Moisture Regain (A. B.) or Absorbed Moisture (C) 
Weigh two test samples both before and after 
absolute dry condition. The average moisture 
regain is obtained from the following formula 
to (one place of decimal): 

W __ \\'d 

Moisture Regain (per cent.) Wi * 10 

where: weight before drying the test sample. 
Wd weight of absolute dr> test sample. 

Standard Weight (A. B. C.) 
Suspend a test sample 2 m. or more in length in 
a perpendicular position. Then find out the 
weight of a standard length and indicate the 
average weight. 

Thickness (A. B. C.) 

Take five test samples and wind them 20 times 
closely, parallel to each other, and with a 
standard initial tension, around a cylinder 
about 5 cm. in diameter. Measure the breadth 
and divide by 20. The average number is indi- 
cated in millimetres (to one place of decimal) as 
shown in fig. 2. 




Plv Number (A.) Ply Number and Filament 
Denier (B. C.) 

After untwisting the twine the ply number and 
filament denier are measured. 



65 



MODERN FISHING GEAR OF THE WORLD 



5-6. Yarn Count (A.) or Denier (A. B. C.) 

Give the testing sample the standard initial 
tension and cut it into ten lengths of 30 to 90 cm. 
After weighting the yarn count or denier is 
obtained from the following formula: 



VV 



Yam count (s) -- 0-5906 x 

W 

Denier (D) - 9000 x - - - 
L s 

where: W - weight of test sample (g.) 

L total length of the test sample (m.) 

Remark: The corrected denier shall be calculated 
by the following formula: 



100 + 4-5 



100 



5-7. 



Corrected denier (B) --- D x '^ ^ ; (C) - D x - 

lOU . K. 11JU t K. 

where: D ^ denier measured 

R moisture regain measured (per cent.) 

Twist (A. B. C.) 

Apply a standard initial tension to the yarn, 
with 25 cm. (10 inches) between the clamps, 
with a yarn twist tester, and test for twist as 
follows, taking an average of ten or more tests 

5-7-1 Twist Direction (A. B. C.) 

After untwisting the test sample, the twist 
directions are examined from upper twist, 
middle twist, and lower twist. 

5-7-2 Upper Twist Number (A. B. C.) 

Untwisting the upper twist thoroughly, the 
untwisted number is converted into the number 
corresponding to one meter or one inch, and 
this figure is indicated as the upper twist number. 

5-7-3 Middle Twist Number (A. B. C.) 

All but one strand of the thoroughly untwisted 
strands of the upper twist are cut out, and then 
untwisted. This untwisted number is converted 
into the number corresponding to one metre or 
one inch, and this figure is indicated as the middle 
twist number. 

5-7-4 Lower Twist Number (A. B. C.) 

All but one yarn of the thoroughly untwisted 
strand of middle twist are cut out, and then 
untwisted. This untwisted number is converted 
into the number corresponding to one metre or 
one inch, and this figure is indicated as the lower 
twist number. 

5-7 -5 Twisting Shrinkage (A. B. C.) 

After untwisting the test sample, measure the 
length of the yarn. The shrinkage percentage is 
measured from the following formula: 

j^i L 

Twisting Shrinkage (per cent.)= x 100 

!_/ 

where: L Length of the test sample 
L 1 =- Length after untwisting 

5-8 Twist Setting (A. B. C.) 

Take ten pieces of any test specimen each one 
metre long, pick up both ends and put them 
together and count their twisting number. 

5-9 Tensile Strength and Extensibility 

5-9- 1 Dry Tensile Strength and Extensibility (A. B. C.) 
Employing a suitable "Tensile Strength Tester", 
and exercising care not to untwist the test 



specimen, grip one end in the upper clamp, and 
after applying a standard initial tension, grip the 
other end in the lower clamp, the clamps being 
25 cm. apart, and tension speed being 30 cm./ 
min. Then measure the tensile strength and 
extensibility (kg. and per cent.) at the time of 
breaking. Take the mean of ten or more tests. 
(Carry to three figures.) 

5-9 2 Wet Tensile Strength and Extensibility (A. B. C.) 
The test specimen is immersed in water at room 
temperature,* and after it has thoroughly 
absorbed water, the wet tensile strength and 
extensibility is measured in a similar manner as 
described in 5 9-1. 

5-10 Knot Strength 

5-10-1 Reef Knot Wet ( A. B. C.) 

The standard initial tension is applied to the test 
specimen, and a reef knot is made as shown in 
figure 3. Then it is immersed*. After the test 
specimen has thoroughly absorbed water, it is 
gripped in the clamps, keeping the knot in the 
middle, and the wet strength (kg.) is measured as 
in 5 to 9-1. 
The average of ten tests is taken. 

5-10-2 English Knot Wet (A. B. C.) 

A standard initial tension is applied to the test 
specimen and an English knot breaking strength 
is measured as in 5 10-1. The average of 
ten tests is taken. 





Fig. 4. 



5-11 Elastic Recovery ( A. B. C.) 

Employing a suitable "Tensile Strength Tester'*, 
the test specimen is extended to 12-5 mm. (5 per 
cent, of the original length). Then the load is 
removed for two minutes, and again the 
standard initial tension is applied and the re- 
maining elongation is measured. The elastic 
recovery is measured from the following formula: 

Hlastic recovery (per cent.) ----- x 100 

Where: L -- remaining elongation (mm.) 
The average of ten tests or more is taken. 

5-12 Shrinkage in Water (A.) 

A standard initial tension is applied to the test 
specimen, and a section one meter long is 
marked. Then a loop is made by tying both ends 
together outside the marks. Immerse as for 5 
9-2 and after the specimen has thoroughly 



* The time for immersion is twelve hours. 
Remark: Tests in which the specimens break at the clamp should 
be rejected. 



[66) 



SYNTHETIC FIBRES IN JAPAN 

TABLE V 
Synthetic Fibres Produced and Used for Fishing Gear in Japan 



June , 7957 



y ' nylon Nyhn Vinvlulene Polvvinyl Chloride Fibre 
Staple Filament 


Filament Filament 


Regular High Tenacity Regular High Tenacity 


Tensile Strength Std. 4 2 to 6-0 6-5 to 7-0 5-0 to 6-0 6-4 to 7-7 1-5 to 2-6 2-7 to 3 7 


(gram per den.) Wet 3-2 to 4-8 5-2 to 5-8 4-2 to 5-0 5*4 to 6-7 I -5 to 2-6 2-7 to 3-7 


Std. Loop l-5to2-6 3-0 to 3-4 4-7to5-5 5-4to6-5 1-0to2-0 




Std. Knot 2-5 to 4-0 4-0 to 4-5 4-5 to 5-4 5-0 to 6-3 1-0 to 20 1-8 to 2-7 


Elongation Std. 17 to 26 14 to 18 


23 to 36 18 to 24 18 to 33 ! 13 to 30 


(%) Wet 19 to 30 15 to 19 


38 to 48 21 to 28 18 to 33 13 to 30 


Elastic Recovery (%) . 75 to 88 Up to 81 


98 at 3% 98 to 100 at 5% ' 80 to 85 at 3% 


at 2% at 2% 


60 to 70 65 to 70 


at 5% at 5% 


Specific Gravity 1 -26 to 1 -30 1-14 1 -70 1-39 


Moisture Regain 5-0; at standard condition 4-5% at standard condition None None 


Moisture Absorption 


120% at 95% R.H. 8-5% at 95% R.H. 0-1% at 95% R.H. 0-1% at 95% R.H. 


Effect of Heat . \ Softens at 220 to 225 deg. C. Softens at 180 deg. C. melts Softens at Softens at 1 10 to 120 deg. 


j Shrinkage starts at about at 215 deg. C. > 140 to 160 C. 


: 200 deg. C. Yellows slightly at 150 deg. 


deg. C. Shrinkage starts at 60 to 


when held for 5 hours. Self- 70 deg. C. 


extinguishing. 


Effects of Acids 


Concentrated sulphuric, Hydrochloric and Sulphuric Unaffected by Unaffected by most acids 




hydrochloric, formic acids acids cause degradation. most acids including aqua regia. 




decompose or swell. Benzoic and Oxalic acids \ including 


will cause loss in tenacity '. aqua regiu. 


and elongation depending ! 


upon time and concent ra- j 


; lions. ! 


Effect of Alkalis . | Strong alkalis cause 


Substantially inert. Unaffected bv most Not affected by con- 


yellowing but not affect 


alkalis with the centratcd alkalis. 


strength. ' exception of 


concentrated 


ammonium 


hydroxide and 


sodium hydroxide. 


Effect of Organic Solvents Good resistance. 


Generally insoluble, soluble Substantially Dissolves or swells in 






in some phenolic compounds inert. some aromat ics, chlori- 






and in concentrated formic naled hydrocarbons, 




acid. 


ketonej>, esters. 


Effect of Other Chemicals . 


Soluble in hot pyridinc Generally good 


Generally good 


Generally good 




phenol, cresol. . resistance. 


resistance. 


resistance 




Resistant to oils. 








Effect of Sunlight 


Loses tensile strength 
after prolonged exposure. 


Loses strength on prolonged 
exposure. No discoloration. 


Darkens slightly 
after 


Substantially unaffected 
after prolonged exposure. 






Bright yarn is more resist- 


prolonged 








ant than semi-dull. 


exposure. 




Remarks 


Vi nylon is the generic term 




Vinylidene is 






of polyvinylalcohol fibres. 




an abbreviation 










of Vinyl-chloridc- 










Vinylidene-chloride 










copolymer fibres 










in Japan. 




Producers and Trade Names 


Kurashiki Rayon Co. Ltd. 


Toyo Rayon Co. Ltd. 


Asahi-Dow Ltd. 


Teikoku Rayon Co. Ltd. 




"Kuralon" 


"Amilan" 


"Saran" 


"Teviron" 




Dainippon Boseki Co. Ltd. 
"Mewlon" 


Nippon Rayon Co. Ltd. 
"Grilon" 


Kureha Kasei 
Co. Ltd. 


Toyo Kagaku Co. Ltd. 
"Fnvilon" 




Kanegafuchi Boseki Co. Ltd. 




"Krehalon" 






"Kanebian" 








End Use 


Seine net Setnet 


Gillnct Seine net 


Setnet 


Setnet Trawl net 




Longline Trawl net 




Seine net 






Lift net 




Trawl net 





Notes: For making fishing gears, these fibres arc used generally in filaments, excepting vinylon which is not produced in filament form. 
In vinylon the high tenacity staple is employed for this purpose. 

[671 



MODERN FISHING GEAR OF THE WORLD 



absorbed water, dry it in the air. Apply an 
initial tension again and then measure the length 
of the marked section. The shrinkage in water is 
obtained from the following formula (to one 
decimal): 

. . , 1000 L 

Shrinkage (per cent.) 



5-12 



5-13 



5-14 



1000 



100 



where: L 



length (mm.) of the air dry test specimen 
after treatment. 

Shrinkage in Hoi/ing Water (B.) 
Take the test sample of 1 m. or more in length, 
fix both ends of the yarn together to overlap 
two-fold, and then measure a length of 50 cm., 
marking the two end points. Apply the weight to 
give the standard initial tension. Remove the 
weight, immerse the test specimen in boiling 
water for 30 minutes, and then take out of water 
to allow to dry in the air. Applying the same 
weight again, measure the length of the air dried 
sample. Calculate the shrinkage according to 
the following formula and take mean value of 
5 tests or more (to one place of decimal). 

Shrinkage in boiling water (per cent.) " - 100 

where: L length of air-dried test specimen after 

immersion (mm.) 

Moisture Absorption (A. B. C.) 
Take about 2 m. length (if this weighs less than 
2 g., take about 2 g.) of the test specimen, and 
after measuring the weight in air dry condition, 
immerse it in water at room temperature*. Then 
take the specimen out of the water and allow the 
water to drip for two minutes; take the weight, 
and calculate the moisture absorption from the 
following formula: 

w 1 w 

Water absorption (per cent.) - 



W 



100 



where: 



W 

W 1 



air dry weight of test specimen 

water absorption weight of test specimen 



Sinking Speed (A. B. C.) 

Take a piece of twine of 2 cm. in length with a 



5-15 



knot in the middle, let it sink from the surface of 
water at 20 deg. ;!_ 5 deg. C. contained in a 
glass beaker (see fig. 5). Measure the speed 
per second from AB to CD, a distance of 50 cm. 
The test specimen should be previously de- 
aerated and immersed in clear water*. Take the 
average of three or more tests. 

Remark: Tests in which the specimen sank in a diagonal 
way or sank close to the wall of the vessel should be 
rejected. 



Weathering Resistance (A. B. C.) 
Take two test specimens at random, fix them to a 
textile testing board, and measure their strength 
(ten times 2) by exposing them under the 
condition mentioned below for 20 hours with 
the weathering resistance tester made in the form 
of the weather-O-mctcr. This strength is com- 
pared with that of the control sample and the 
average value is taken in per cent. 

Arc 130 to 145 V. 50 to 00 c/s 15 to I7A to 2 sets 
Carbon for Arc " 70 (Solid) and " 20 (Core), or other 

corresponding types. 



Temperature in the icslcr 

Revolving Speed 

Exposing time 

Spraying time 

Pressure of spraying water 

Water requirement for spraying 



40 to 50 C. 

once per min. 

102 mm. 

18 min. 

25 to 30 Ibs./in.- 

20 10 30 gal./hr. 



* The time for immersion is twelve hours. 

Remark: Tests in which the specimens break at the clamp should 
be rejected. 




Broiling herring from a purse seine on the West Coast of Canada. Photo Inf. Serv. Dept., Fish., Ottawa. 

|68] 



THE PHYSICAL PROPERTIES OF NETTING AND TWINES 
SUITABLE FOR USE IN COMMERCIAL FISHING GEAR 

by 
P. J. G. CARROTHERS 

Fisheries Research Board of Canada, Technological Station, Vancouver, B.C., Canada 

Abstract 

Many new materials Kaxc recently been introduced inio commercial fishing pear, hut many oiher useful materials have been rejected 
because they have not been tried to the best advantage. Often the tensile strength of the dry, straight twine is used as the basis foi the 
substitution of new materials f >r more conventional ones, but this basis can result in serious error because the twines are invariably knotted 
and wet while fishing, and kr.c t ing and wetting affect dillcrcnt materials in different ways. Because pertinent, reliable and comparable data 
arc often not available for new materials, original tests have had to be made, and the results thereof are presented herewith. 

The materials tested, in forms generally suitable for use on the coa*t of British Columbia, include cotton, linen, ramie, hemp, Manryo, 
nylon and Tcrylcne. 

The test procedures used to measure net weight in water, change in length due to wetting, linear twine density, twine diameter, 
twine stretch under load, and tensile strength are briefly described. 

The properties of the twine and netting are divided into two groups. The first group includes the "parameters" (properties which 
have the same numerical value for all twine si/es of the same material and style), and. where available, quantitative data for these properties 
arc reported in tabular form. The second group includes properties whose values vary with and are dependent on the twine si/e. and 
formulas are presented for estimating values of this second group of properties from data for the first. Definitions and unit equivalents for 
all properties are quoted. 

Proprieties physiques de filet et des fils pouvant vtrt* utilises dans les engins de pt-chc eommereiaux 
Resume 

On a reccmment adopte pour la fabrication des engins de pcchc commcrciaux un grand nombre de matenaux nouveaux mais 
beaucoup d'autres materiaux utilcs ont etc rcjetes simplcment parce qu'ils n'ont pas etc essayes dans les mcilleures conditions. On manque 
ires souvent pour les nouveaux materiaux de donnees pert monies, dignes de foi et compatibles, et il a fallu fa ire des essais origmaux dont 
y on trouvera les resultats ci-dessous. 

Les malcriaux, essayes sous des formes convenant gencralenvjnt a P utilisation sur la cote de la Colombie britannique, comprennent 
le lin, la ramie, le chanvrc, le manryo. le nylon et le terylene. On trouvera une breve description dc* techniques utilisces pour ccs essais qui 
consistaient a mesurer le poids net dans 1'eau, les variations de longueur subies par le fil mouille. la dcn><ie lineaire du fil, le 'Jiamctrc du fil, 
Pallongcmcnt du fil sous Pmfluence d'un poids et la icsistance a la rupture. On a reparti les proprieics des fils en deux categories, les 
"parametres" (proprietes ayant la meme valeur numcriquc pour loules les dimension.** du fil fabrique avcc le memc materiel et de mcme facon) 
et les proprictcs dont les valours sont fonction de la dimension du fil et on trouvera des formules pour calculer la valeur des propnctes dc 
cctte seconde categoric a partir des donnees relatives a la premiere. On donne des definitions et des equivalents unitaires pour Unites les 
propriety's. 

Propiedades fisicas de las redes e hilos adecuados para artes de pesea comercial 
Fxtracto 

Recientemente ha comenzado a usarse gran numero de nuevos matcriales en las artes de pesca comercial, pero tambicn se han 
rechazado muchos utiles a causa de no haber sido onsayados de manera que puedan utili/arse con ventaja. Como a menudo no se dispone 
de dates seguros quo permitan comprobar nuevos productos textiles, en cste trabajo se dan a conocer las prucbas originales que debicron 
hacerse para este objeto, asi como los resultados obtemdos. 

Los materiales ensayados en las formas como generalmente sc usan a lo largo de la costa de Colombia Britanica mcluycn: algodon, 
lino, ramio, canamo, "manryo" ("vinylon"), "nylon" y "terylene". En el trabajo tambicn sc describen, en forma sucinta, los procedimientos 
usados en las pruebas de materiales para medir su peso ncto en el agua, cambio de longitud al humcdecerlo, peso lineal y diametro, alarga- 
miento del hilo con el peso y resistencia a la tensi6n. 

Las propiedades de los hilos y de las redes se dividen en dos griipos: los "parametros" (propiedades con el mismo valor numenco 
para los hilos del mismo tipo y material) y las propiedades cuyos valores varian y dependen del diametro del hilo. Tambien se dan formulas 
para estimar los valores de este segundo grupo de propiedades basandosc en datos del primcro. definiciones y cquivalencias para todas las 
propiedades. 



INTRODUCTION 

DURING the past decade, many new materials, the data describing the new and the conventional 

particularly synthetic fibres, have been introduced materials need only be relative. But where these materials 

into commercial fishing, usually being presented arc to be used in new applications, then the physical 

as substitutes for other materials. If these new materials properties should be fully described. It is the author's 

are to be substituted rationally, certain physical proper- opinion that many new materials have been rejected 

ties should be determined quantitatively a priori, although as unsatisfactory, through improper use of the material 

[69] 



MODERN FISHING GEAR OF THE WORLD 



during initial trials, a result of complete neglect of 
quantitative test data or because only irrelevant physical 
properties have been considered. 

The misuse of test results has been illustrated in the 
selection of twine sizes for salmon gillnets. Because 
fish must be caught from water, wet strength is more 
important than dry strength even though, for convenience, 
many people measure only the latter. At one time all 
salmon gillnets on the British Columbia coast were 
made of premium-grade linen which increases about 
50 per cent, in strength when wet. In contrast, nylon 
loses about 15 per cent, strength in water. Therefore, if 
a nylon twine is chosen to give the same dry strength 
as the linen it is to replace, the wet strength of the nylon 
net will be little more than half that of the linen net. 

The manufacturers of nylon gillnets were aware of 
this and, for the first experimental nets, selected twine 
sizes of sufficient wet strength to carry normal fishing 
loads. The results were satisfactory. Nevertheless 
some net men and fishermen still select their nylon gill- 
nets on the basis of hand tests applied to dry netting, 
with the result that nets are chosen too light for their 
loads. They are torn more easily, and their owners 
erroneously claim that the quality of nylon is becoming 
poorer. Because wetting affects the strength of different 
materials in different ways, wet strength tests are much 
more significant to fishing gear design than are dry 
strength tests. 

Another example of the improper use of test results 
is in the choice of the physical property which the test 
evaluates. Because twine must be knotted to form netting 
the strength of the knot or the mesh is more important 
than the strength of the straight twine. Soon after the 
introduction of nylon 66 multifilament gillnets into 
the British Columbia salmon fishery, nylon 6 multifila- 
ment gillnets began to appear. On one occasion at least, 
the tensile strength of twine from the latter nets was found 
to be about 40 per cent, weaker than nylon 66 twine of the 
same weight, and nylon 6 was rejected as being unsatisfac- 
tory for salmon gillnets. However, because these two 
nylons react differently to knotting, the mesh of a nylon 6 
is only about 20 per cent, weaker than that of a nylon 66 
net of the same weight. Considering their lower price 
nylon 6 nets do have a place in the British Columbia 
salmon fishery in competition with the nylon 66 nets. 
Because knotting affects the strength of different materials 
in different ways, knot strength or mesh strength tests 
are much more significant to fishing gear design than 
are tensile tests on the straight twine. 

Many new materials have been made available, 
unaccompanied by specific test data describing their 
physical properties. Inquiries addressed to the suppliers 
often elicit no further information, or bring data which 
have little significance to fishing gear applications. It 
has therefore been necessary for the Fisheries Research 
Board of Canada to perform its own tests prior to recom- 
mending how these materials may be used to greatest 
advantage. Obtaining our own test data has the three- 
fold advantage that: (1) pertinent properties may be 
measured; (2) the test data are reliable to the best of 
our ability; and (3) by using consistent test procedures, 
data on all materials, both conventional and new, may 
be compared. 

This paper presents the results of our many tests on 



seven different fibres in eighteen different forms suitable 
for use in commercial gear for the British Columbia 
fishery. Because different materials were designed for 
different applications, not all properties of all materials 
were measured, and the accompanying table is not 
complete. However, except for the mesh strength of 
hemp and medium-laid cotton, test procedures were 
consistent throughout and the test data presented are 
comparable between different materials. All test results 
have been reduced to "parametric" form, that is, to 
properties which are reasonably constant over the com- 
plete twine-size range of a given material and style. 
Sometimes corresponding materials from different manu- 
facturers have properties in which measured differences 
are statistically significant, but these have been grouped 
into the overall averages presented in Table I. 

MATERIALS TESTED 

The cotton netting and twine, the Manryo twine, and 
the twisted, spun, nylon 66 twine, were of "cable" 
construction: i.e., the twine contains three or four 
plies and each ply contains several yarns. The yarn 
style is identified by the British system of hanks ( 1 hank 
840 yards - 768 metres) per pound (453-6 grams). The 
twine size is identified by two numbers, the first being 
the number of yarns per ply and the second the number 
of plies in the twine. The total number of yarns in the 
twine is the product of these two numbers. In the medium- 
laid twines the helix angle of the plies was about 54 deg., 
in the soft-laid twines about 28 deg., and in the extra- 
soft-laid twines about 22 deg. 

The linen, ramie, and hemp twines were of plied 
construction, i.e., the yarns were doubled directly into 
the twine. The linen yarn is identified according to an 
arbitrary commercial numbering system, but the approxi- 
mate number of leas (1 lea 300 yards = 274-3 metres) 
per pound (453-6 grams) is quoted in parenthesis. The 
ramie yarn is identified according to this same leas-per- 
pound system, and the hemp yarn is identified by the 
number of pounds (1 pound = 453-6 grams) per spindle 
(14,400 yards = 13,167 metres). In all cases the twine 
size is identified by the number of yarns which have been 
twisted into the twine. 

The monofilament twine is identified by its nominal 
diameter. 

The continuous multifilament yarns (nylon and 
Tcrylene) are identified both as to weight or total denier 
per yarn and as to the number of filaments per yarn. 
The twisted twines were of "cable" construction and are 
described by two numbers in the same way as are the 
cotton twines. 

The braided twines are described by the total number 
of yarns in the braid. 

PROPERTIES AND TEST PROCEDURES 

The nett weight (gravitational force less buoyant force) 
of the netting in the water is an important factor in 
determining how it will lie or move in the water and how 
much lead and what float capacity is required for a 
given piece of equipment. For example, the low density 
of nylon contributes toward the fishing efficiency of 



[70] 



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1 



MODERN FISHING GEAR OF THE WORLD 



nylon gillnets but creates handling problems in nylon 
purse seines. The nett weight was measured by weighing 
an air-dry sample of netting in the air, by soaking the 
sample overnight in distilled water at 70 dcg. F. (21 -1 
deg. C.) and then reweighing while still immersed in the 
water. The weight in water was then expressed as a 
per cent, of the air-dry weight. This weight per cent, is 
numerically equal to the weight in water in pounds 
(or kilograms) per hundred pounds (or kilograms^ air-dry 
in air. The specific gravity was calculated from the 
weight per cent, in water. The nett weight (per cent.) of 
the netting in salt water or in fresh water and at any 
temperature may be estimated by the relation: 

Weight (%) | _ F __ specific gravity of sea water ~1 
in sea water f L specific gravity of material J 

The change in length due to wetting must be known 
where the mesh length is specified only for dry netting. 
In many types of fishing gear, such as gillnets and trawls, 
the mesh length of the web in the water is an important 
factor in determining the fishing efficiency of the gear 
or in releasing under-size fish for conservation purposes. 
Different materials react differently to wetting, e.g., most 
natural fibres shrink and most synthetic fibres extend, 
so that a quantitative measure of this reaction is needed 
before dry mesh length can be properly specified for a 
given application. The change in length (per cent.) due 
to wetting was determined by measuring the length of 
meshes in the sample when air-dry, by soaking the sample 
overnight in cold tap water, by measuring the length of 
meshes in the same sample while wet, and by expressing 
the change in mesh length which occurred during 
wetting as a per cent, of the average mesh length of the 
dry sample. Shrinkages are prefixed by the negative ( ) 
sign and extensions are prefixed by the positive ( + ). 

The linear density is a convenient measure of the size 
of the twine. Often twine must be purchased by weight 
but is required for use by length. A knowledge of linear 
density therefore permits estimation of the quantity 
(weight) of twine required to construct a given piece of 
equipment. In keeping with common Canadian practice, 
the indirect system (length per unit weight) is used. Ten 
one-yard (1 yard ----- 0-9144 metres) pieces of air-dry 
twine were cut under four ounces (113-4 grams) tension 
and were weighed collectively to the nearest milligram. 
The linear density of the twine (1 yard per pound ----- 
2-016 metres per kilogram) was calculated by dividing 
the weight of the ten-yard sample in grams into 4536. 
The effective linear density per yarn was then calculated 
by multiplying the linear density of the twine by the 
total number of yarns in the twine. Further division by 
1,000 reduced the number of integers required for the 
table and changed the length unit from yards to kiloyards 
(1 kiloyard 1,000 yards - 914-4 metres). 

The diameter of the twine is a major factor in deter- 
mining how strongly moving water pulls the netting, 
how easily swimming fish can move the netting, and 
what power is required or speed attained while towing 
a given piece of equipment. The diameter was measured 
by placing four parallel strands of air-dry twine under 
the 1 -25 inch (3-15 centimetres) diameter circular foot 
of a dial gauge. The total force exerted diametrically on 
the twine by the foot during measurement was 6 ounces 
(170-1 grams). The separation of the foot from the 



supporting anvil caused by the interposed twine was 
indicated by the dial gauge in mils (1 mil - 0-001 inches 
0-0254 millimetres) and was reported as the twine 
diameter. This method of measurement has certain 
defects when used to determine the diameter of twine 
for fishing gear. Twines made from staple fibres have 
loops and fibre ends protruding from the twine which 
increase the resistance to movement of the twine through 
water but which are easily pressed to the twine during 
diameter-measurement; and soft-laid twines are pressed 
out of round by the measuring device more than are 
harder laid twines. However, when interpreted in the 
light of these effects, twine diameters measured in this 
way can be useful. 

The effective cross-section area per yarn was calculated 
as a dimension which is a function of the diameter and 
yet is reasonably constant over all twine sizes for each 
yarn style and twist hardness. The effective cross-section 
area of the twine in circular mils (1 circular mil ^ 
0-0005067 square millimetres) is the square of the twine 
diameter in mils (1 mil 0-001 inches 0-0254 milli- 
metres). Further division by the total number of yarns 
in the twine gives the effective cross-section area of each 
yarn. The diameter of any size twine of the same style 
may then be estimated by multiplying the effective yarn 
area by the number of yarns in the twine and by deriving 
the square root of this product. 

Total extension and breaking load of twines were 
measured simultaneously on a Scott Model J2 recording 
tester of 100 pounds and 400 pounds maximum capacities, 
using type X-l clamps. The tester was set so that 10 
inches (25-4 centimetres) of untensioned twine lay 
between the nips of the clamps prior to test. For knot 
strength tests, the twine was cut and the appropriate 
knot, single weavers' knot or double weavers' knot, was 
tied in the twine by hand. 

For testing the mesh strength of netting for seines 
and trawls (medium-laid cotton and hemp), small panels 
of netting were cut from the sample, all the meshes 
along two opposite sides of the panel were threaded 
respectively onto \ inch (6-35 millimetres) diameter rods 
on the tester, and the sample was stressed to rupture 
through separation of the rods by the tester. The mesh 
strength was then calculated by dividing the panel 
strength by the number of meshes in the width of the 
panel. The netting was tested in both directions relative 
to the selvedge and the overall average is reflected in 
the data quoted here. Netting in seines and trawls is 
stressed in use over several meshes at a time rather than 
on single meshes; therefore, by testing panels as above, 
irregularities in the physical dimensions of the netting 
result in lowered mesh strength as is experienced in use. 
Netting in gillnets is more commonly stressed on indivi- 
dual meshes so that these materials (linen, ramie, nylon, 
and Terylene) were tested one mesh at a time. The mesh 
was placed around two one-inch-diameter (2-54 centi- 
metres) drums so that no knots touched either drum, 
and the drums were separated by the tester until the 
mesh broke. For dry strength, the materials were tested 
in their natural, air-dry state, and for wet strength, the 
materials were soaked overnight in cold tap water. 

Specific strength is dimensionally identical with tena- 
city, the only difference being in the units employed. 
Arithmetically it is the test strength per twine (i.e., 



I 721 



SUITABLE TWINES FOR FISHING GEAR 



twine strength, knot strength, or half the mesh strength) 
in pounds (1 pound - 453-6 grams) multiplied by the 
linear density of the air-dry twine in kiloyards per pcund 
(1 kiloyard-= 1,000 yards^914-4 metres). This specific 
strength 'may be converted into tenacity in grams per 
denier by further multiplying by 0-1016. For specific 
strength units, the weight or gravitational force was 
cancelled against the strength or breaking force, leaving 
length as the unit for specific strength. This permits an 
easier understanding of the physical significance of 
specific strength or tenacity than is possible with the 
metric units, grams per denier. Specific strength (and 
tenacity) is the length of twine the weight of which equals 
the breaking strength of that same twine. For the same 
strength-quality, an increase in weight per unit length 
causes an identical increase in strength, leaving the 
specific strength (and tenacity), which could well be 
called breaking length, constant. For a given material 
of a given quality the specific strength is reasonably 
constant over all twine sizes; and the breaking strength 
of a particular twine may be estimated from the specific 
strength by dividing this latter by the linear density of 
the twine. Specific strength figures may be used directly 
to compare the strength of different materials on an 
equal weight basis, e.g., high tenacity nylon 66 when wet 
is seen to be slightly weaker than wet linen, a relation 
often obscured by the fact that nylon 66 and linen 
twines are not made in identical weights. Specific strength 
may also be used as a measure of strength-quality, the 
specific strength of different specimens being directly 
comparable even though the yarns may be spun to 
slightly different weights. Finally, the tensile strength 
(breaking force per unit area normal to the direction 
of the force) of the fibre itself is related to the specific 
strength through the fibre density so that the usable 
tensile strength of the fibre in pounds per square inch 
(1 pound per square inch 70-307 grams per square 
centimetre) may be estimated from the relation: 

Tensile Strength 1,300 x Specific Gravity x 

Specific Strength. Comparison of this usable tensile 
strength with data available elsewhere for the virgin 
fibre gives an idea of the manufacturing and geometrical 
efficiencies realised in these fishing gear materials. 

The load extension characteristics on initial loading 
of each twine, both dry and wet, were drawn autographic- 
ally by the Scott tensile tester. The average often replicate 
test plots was redrawn showing the per cent, extension 
(increase in length under load expressed as a per cent, of 
the unstressed length) as a function of specific load. 
Specific load, analogous to specific strength, is the actual 
load in pounds (a pound = 453-6 grams) multiplied by 
the linear density of the air-dry twine in kiloyards per 
pound (1 kiloyard -^ 1,000 yards 914-4 metres). All 
these average curves for all twine sizes of a given material 
and style were drawn against the same reference axes 
and an average of the curves was then drawn. The 
stretch data given in Table I were read from this last 
average plot against the corresponding specific strengths 
of each material in each state. These data do not include 
elongations consequent upon tightening of knots, which 
are functions of the initial knot tightness; but they do 
include irreversible elongations in the twine itself. 
Undoubtedly, the load-extension characteristics under 



cyclic loading are more significant to fishing gear design 
than are initial loading characteristics, but the former 
cannot be obtained with our Scott tensile tester. 

Data describing the tensile strength of the dry, straight 
twine often have little application to fishing gear design; 
in fact, they can lead to serious error. Even so, such data 
are frequently all that are available. Th change (increase 
or decrease) in tensile strength which results from wetting 
the materials is reported as a per cent, of the dry strength 
to assist in estimating the strength in water where only 
dry strength data are available. Similarly, the per cent, 
of the twine strength which is- retained in knotted 
structures is reported to assist in estimating the knot 
or mesh strengths where only twine strength data are 
available. These per cent, changes in strength to wetting 
and per cent, strength efficiencies of knots and meshes 
were calculated from the specific strength data. 

The tensile strength of the fibrous materials used in 
fishing gear can be measured relatively easily, so this 
property is often the only one evaluated, and is sometimes 
blindly adopted as the only measure of quality and 
performance. Where the material is to be subjected 
only to dead loads, tensile strength is an adequate 
measure of quality. However, fighting fish are not dead 
loads, and it is more important that the material be able 
to absorb the energy inflicted on it by the fish than 
merely carry the weight of the fish. A dramatic illus- 
tration of this is that nylon gillnets for salmon need not 
be so strong as linen gillnets to hold the same fish, 
because the greater elastic extension of the nylon imparts 
greater ability to absorb the energy expended by the 
salmon. The "toughness" used here is a rough measure 
of the energy required per unit length of twine to break 
that twine, whether it be straight, knotted, or in a mesh. 
Arithmetically it is one-half the product of the breaking 
load and the fractional extension from unstressed length 
to rupture. This estimate is in error to the extent that 
the load-extension curve is assumed to be linear; but, 
whereas most fishing gear materials deviate from linearity 
toward the extension axis, the error is in the same direc- 
tion in most cases and the figures are reasonably com- 
parable. A further loss of correlation between this 
calculated "toughness" and performance toughness 
originates from use of the load-extension relation under 
initial load -permanent elongation is included. However, 
despite approximations in its estimation, "toughness" 
is more important in the design of some types of fishing 
gear than is tensile strength. "Toughness" is reduced to 
the parametric form, viz., toughness index, by multiplying 
it by the linear density of the air-dry twine. This toughness 
index is thus the energy required per unit weight of 
twine to break that twine, and is reasonably constant 
for all twine sizes of the same material in the same style. 

DEFINITIONS AND DIMENSIONS 

A. Parametric properties, quantitatively reported in 
the table, which are reasonably constant for all 
twine sizes of the same material and style. 

I. Weight (per cent.) in water is the nett weight 
(gravitational force less buoyancy) of the material 
when immersed in distilled water at 70 deg. F. 
(21-1 deg. C), expressed as a per cent, of the 
air-dry weight. 



[73] 



MODERN FISHING GEAR OF THE WORLD 



, ^ /, x - * 
Weight (%) in water - 



Nett weight in water 

-- ~ -- - - -- 



< 100 



-- ~ -- - - -- r 
Air-dry weight in air 

2. Specific gravity is the density of the material 
relative to the density of pure water al 4 deg. C. 
39 2deg. F.). 

Specific gravity ~ } ^^^^^^^^ 

3. Change in length (per cent.) to wetting is the 
increase (+) or the decrease (-) in length caused 
by soaking the material in water, expressed as a 
per cent, of the air-dry length. 

Change in length ^ Wet length Dry length 
(%) to wetting Dry length 

4. Linear density is the length per unit weight 
(indirect system). 



100 



Linear density 
per yarn 
(kyd./lb.) 



Linear density of , 



Total num- 

, j in. v x her of yarns 
twine (yd./lb.) in (he ( winc 

2-016 m./kg. 



1000 
1 yd./lb. 

1 kyd./lb.- 1000 yd./lb. 
- 2-016m./g. 

5. Effective cross-section area is the area of the 
circle whose diameter equals the measured 
diameter of the twine. 

Effective cross-section area _ (Twine diameter (mils) ) 2 
per yarn (circular mils) Number of yarns in twine 
1 circular mil - area of circle 1 mil (0-001 in. 0254 

mm.) in diameter. 
= -0005067 sq. mm. 

6. Total extension (per cent.) at break is the increase 
in the length of the twine caused by the load 
required to break the twine (straight, knotted, or 
mesh) expressed as a per cent, of the unstressed 
length. 

Total extension Twine length at break - Unstressed length 
at break Unstressed length 

7. Specific strength (kyd.) is the effective tenacity. 

Specific strength j Linear density Measured 
(kyd.) -x of air dry ? strength 

1000 twmc (yd./lb.) (Ib.) 

1 kyd. - 1000 yd. 

- 1016 g./den. 



100 



100 



x 100 



. Total extension (%) at break Specific 
ft * - x strength 



8. Strength change (per cent.) to wetting in the in- 
crease (4-) or decrease (-) in tensile strength 
caused by soaking the material in water, expressed 
as a per cent, of the dry strength. 

Change in strength _ Wet strengthDry strength 
to wetting Dry strength X 

9. Strength efficiency (per cent.) is the per cent, of the 
straight twine strength which is retained in 
knotted structures. 

Strength efficiency Knot strength 

of Knotted twine Straight Twine strength 

Strength efficiency Mesh strength 

of mesh 2x Straight twine strength 

10. Toughness index (kyd. lb./lb.) is an approximate 
estimate of the energy per unit weight of twine 
required to break the twine. 

Toughness 
index juu (Ryd) 

1 kyd. - lb./lb. - 3000 ft. - lb./lb. 
- 91440 g. - cm./g. 

B. Specific properties, variable with twine size, which 
may be estimated from the values of the parametric 
properties given in the table. 

Linear density per yarn 
Number of yarns per twine 
1 yd./lb. - 2 -01 6m. /kg. 

2. Twine diameter /Effective cross-section Number of \ \ 
(mils). y area per yarn twine / 

1 mil. 0-001 in. 

0-0254 mm. 

Specific strength of twine x no. of yarns 

Linear density per yarn 
1 Ib. 453-6 g. 

4. Mesh strength 2x Specific strength of mesh x no. of yarns 
(Ib.) Linear density per yarn 

1 Ib. - 453-6 g. 

5 ' T (ft^1b/ft ) Tou S hncss index x Number of yarns 

Linear density per yarn 
1 ft.-lb./ft. - 453-6 g. -cm./g. 



I. Twine weight (yd./lb.) - 1000 



3. Twine strength (Ib.) 




Log-rafts returning from drift net fishing, Ceylon. 
[74] 



Photo FAO. 



TESTING METHODS FOR NET TWINES AND NETS, ESPECIALLY 
THOSE MANUFACTURED FROM SYNTHETIC MATERIALS 

by 

J. K. VAN WIJNGAARDEN 

Research Laboratory, A.K.U. and Affiliated Companies, Arnhem, Netherlands 

Abstract 

This paper describes a number of tests for yarns and cords used in the fishing industry, and the author points out that, as a certain 
amount of standardization has already been achieved in the textile industry, the International Fishing Gear Congress can help in fostering 
a uniformity of measuring methods in the various branches of the fishing gear industry. 

He recommends that "TEX", the unit for yarn numbering, representing the mass in grams per kilometre of yarn, be used for net 
yarns and cords, and further that "twist", indicated by Z or S according to the direction of the turn, should be expressed as the number of 
turns per metre (t/m). 

The methods for testing for stretching, shrinkage and stiffness of yarns and cords are fully described, and the question of knot- 
strength is dealt with in detail. He discusses the different ways in which a knot can break down when tested in the clamps of a dynamometer, 
such as tip-over, breaking before and after slip and breaking after tip-over, etc., and then he tests for the "opening-up" of knots in synthetic 
materials, by putting knotted cords in a container revolving at 60 r.p.m. and finding the number of revolutions necessary to loosen the knots. 
Finally, the methods used for testing knots are applied to the testing of meshes, and mesh-strength, i.e. the load at which a mesh breaks, is 
surely one of the most important factors affecting the performance of a fishing net. 

Mtthodes d'essai pour les conies des filets et les filets, en particulier pour les articles fabriques a partir de fibres synthetiques 
Rfeume 

I /Industrie textile etant deja arrivec un certain degre dc normalisation, le Congrcs international des engins de peche peut contribucr 
1'adoption de me th odes uni formes de mesure dans les di verses branches de P Industrie des engins de pechc. L'auteur recommande d'utiliser 
pour les filets et les cordes destines aux filets, le "TtX" unite pour le numcrotagc des fils rcpresentant la masse en grammes par kilometre de 
fil et de plus d'exprimer la torsion, indiquee par Z ou S selon le sens, en nombre de tours par metre (t/m). 

Les mcthodcs servant i\ determiner 1'extension, le raccourcissement et la rigidite des files et des cordes sont decrites en detail, de 
meme que la question de la resistance des noeuds. L'auteur examine les differentes manicres dont un noeud peut se rompre au cours d'essai 
au dynamometre, et il verifie Touverture des noeuds des materiaux synthetiques en placant des cordes nouees un recipient tournant 60 t/m 
et en cherchant le nombre de revolutions nccessaires pour relacher les noeuds. Hnfin, les methodes utilisees pour verifier les noeuds sont 
appliquees & la verification des mail les et la resistance des mailles. 

Metodos para ensayar cordajes y redes, especialmente de fibres sinteticas 
Kxtracto 

Como ya se ha logrado cierto grado de normalizacion en la industria tcxtil, el Congreso International de Artes de Pesca podria 
ayudar a uniformar los metodos de medida en las diversas ramas de la industria de artes de pesca. El autor recomienda el uso dc la unidad 
'TEX** para numerar los hilos, que representa cl peso en gramos por ki!6metro de kilo o cordaje empleados en la fabricaci6n de redes, e 
insinua expresar la "torsi6n" o colchadura, indicada per Z o S segun el sentido en que se practique, en numcro de vueltas por metro (vxm). 

Tambicn describe, en detallc, los metodos usados para determinar el alargamiento, encogimiento y flexibilidad de los hilos y cordeles, 
asi como el problema dc la resistencia de los nudos. Ademas analiza las diversas maneras en que puede romperse un nudo al probarlo con 
las pinzas de un dinam6metro, como la rotura antes y despues de correrse, etc. y las pruebas para determinar su aflojamiento cuando se 
usan materiales sinteticos, poniendo las cuerdas anudadas en un recipiente que gira a 60 r.p.m. a fin de encontrar el numero de revoluciones 
necesarias para que se aflojen dichos nudos. Por ultimo, los metodos usados en las pruebas dc nudos se han aplicado a los ensayos de las 
mallas y a su resistencia. 



1. INTRODUCTION 

THE use of synthetic yarns during the last few years 
as material for nets has caused a growing interest 
in testing methods for twines and nets. This is 
expressed by more exact measuring and by development 
of new measuring methods to deal with the special 
problems which have arisen. 

The "Bureau International pour la Standardisation de 
la Rayonne et des Fibres Synthetiques" (BISFA) with a 
membership of all the main North and West European 
producers of man-made fibres, and connected with the 
International Organisation of Standardisation (ISO), 
is engaged in standardizing the different testing methods 



for textile and tyre yarns, and for this purpose publishes 
the "BISFA-rules". In the USA similar work is done by 
the American Society for Testing Materials (ASTM). 

This contribution discusses various testing methods 
for net yarns and twines, and nets. Some of these methods 
are already known in the textile industry, some, of specific 
interest to the fishing industry, relate to testing methods 
developed in our own laboratories. The BISFA rules 
are quoted with regard to the first group, but proposals 
are made for the second primarily from the point of view 
of the yarn producer. 

The term "yarn" is understood to mean a continuous 



(75) 



MODERN FISHING GEAR OF THE WORLD 



strand of fibres and/or filaments, from which twist, if any, 
can be removed in one operation; strand is the product 
obtained by twisting together two or more twisted yarns, 
twine is the product obtained by twisting two or more 
strands together. 

2. METHODS OF TESTING YARNS AND TWINES 

21 Yarn Number 

Several units are used for the numbering of net yarns 
and twines. The ISO Conference, May 1956, recom- 
mended the use of the combination of grammes per 
kilometre of yarn, called "tex*\ as a unit for yarn 
numbering and we strongly advocated the use of the same 
unit for net yarns and twines. Table I shows the num- 
bers in tex, denier and m/kg. for some yarns. 

TABLE I 

m/kg. 100 500 1,000 5,000 10,000 50,000 1,000,000 

Td 

(g./9000 

m.) 90,000 18,000 9,000 18,000 900 180 90 

Tex 

(g./IOOO 

m.) 10,000 2,000 1,000 200 100 20 10 



2 2 Twist 

Since the determination of the twist of net yarns and 
twines is the same as that of textile yarns only a few 
points will be mentioned. The direction of twist is 
normally indicated by the letters Z or S, as shown in fig. 1 . 
In order to maintain the metric system we recommend 
that the twist shall be expressed as the number of turns 
per metre of twisted yarn or twine (t/m.). 

Below is illustrated the indication of the twist con- 
struction of a twine: 




Z- twist S- twist 
fig. 1. Indication of the twist direction. 

100 tex Z 400 x 2 S 300 X 3 Z 100 means a twine 
composed of 6 yarns: every yarn is first twisted to 400 
t/m. in Z-direction, then two of these twisted yarns are 
twisted together to 300 t/m. in S-direction, and finally 3 
of these strands are twisted in Z-direction to 100 t/m. 

2-3 Strength and Extensibility 

The stress-strain curve, and the strength and total 
extension at break, are determined by the load-extension 
tester or dynamometer. The many types of dynamometer 
can be classified according to the time conditions under 
which the determination of strength and extension are 
performed. The time factor plays an important part in 
this determination for the materials used in fishing nets. 
The velocity and the way of increasing the strain have 



an influence on the shape of the stress-strain curve and 
the values of strength and extension at break. Efforts 
have been made to realise one of the following principles 
in making the dynamometers: 

1 . the length of the test object increases in proportion 
to the time; thus the rate of extension is constant; 

2. the force on the test object increases in proportion 
to time; constant rating of loading. 

The electronic recording dynamometers which are 
characterized by their stability, accuracy and versatility, 
are of recent design. 

One clamp is moved at constant speed while the force 
is measured by the other clamp, connected with an 
electric clement for measuring the force (fig. 2). 

These meters have some specific properties, viz., the 
possibility of recording both a decrease and an increase 
in stress, and the many and wide measuring ranges that 
can be covered by a single instrument. These make them 
particularly suitable for testing twines and nets. 

In practice, the wet strength and total extension at the 
breaking point of the twines are of primary importance. 
As regards modern, synthetic materials, such as e.g. 
nylon 6, nylon 66 and polyesters, the wet stress-strain 
properties do not differ very much from those measured 
in dry condition, so it sufliccs to determine the latter 
only for routine measurement. 

The BISFA rules describe the measuring conditions 
as "the length of the test specimen between the jaws shall 
be 50 cm., and the mean time to break shall be 20 i 2 




Fig. 2. A KU electronic dynamometer. 



[76] 



METHODS OF TESTING TWINES 



seconds". From a scientific point of view this may not 
be the best possibility, but this prescription of the time 
was the only solution, owing to the many different 
working principles of the dynamometers which are in 
use in the various laboratories. 

In consequence of the growing use of the electronic 
dynamometer, however, more and more laboratories 
have begun to apply a constant rate of extension, 
generally 1 per cent, of the original length between the 
clamps per second. 

To avoid slipping or breaking of the test specimen in 
the clamps, it is advisable to use clamps of such a shape 
that a very sharp kink is avoided (fig. 3). Usually only 




(c) hot water shrinkage, measured in wet condition. 

(d) hot water shrinkage, measured after conditioning. 

In figs. 5 and 6, these 4 values arc given for some twine 
samples of synthetic material as a function of the 
immersion time in water (t). 



Water 2 K -F* ""^~^ZZ_~ 

Shrinkage 




1 

1 10 (30) 

-^Immersing timp (min. ) 

:Measured after conditioning (65 % H. H. 20 C. ) 
A :Mt-asured in wcl condition 



Twine type: 

I Fnkalon 
(nylon 6) 

(93 -|- 23) 
tcx y 3 

II Hnkanylon 
(nylon 66), 
70 tcx ,- 4 



Fig. 5. Influence of the Immersing time on the cold water 
shrinkage. 



Callaway clamp. 



the strength and total extension at break are given of the 
stress-strain properties. In practice, the shape of the 
stress-strain curve, or the modulus, can, however, be of 
great importance to the behaviour of the twine. It is 
Therefore advisable to determine some points on this 
curve, for example, the extension at 25 per cent, of the 
breaking load. 

24 Shrinkage 

The amount of shrinkage, either in hot or in cold water, 
can be important as it may effect a change in size of the 
mesh when the nets receive a final treatment in hot water 
or when they are dyed. 

The method we have used is as follows: 5 knots were 
laid in a twine at distances of about 1 m., these distances 
being measured to an accuracy of 1 mm. ( l fl ) on an appar- 
atus as shown in fig. 4. The pre-tensions were taken 



Knot 



Cord 



Knot 




Pre-tension 



Fig. 4. Apparatus for measuring the shrinkage. 

according to the BISFA rules. The sample was then 
placed in cold (20 deg. C.) or in boiling water, after which 
the distance between the knots was measured again (1 ,), 
wet or after conditioning in a standard atmosphere 
according to the BISFA rules : temperature 20 deg. ri 2 
dcg. C., relative humidity 65 per cent, and to the ASTM 
standards 

70deg. I 2 F., 65 per cent. The value ~ l x 100 then 

gives the shrinkage in per cent. 

In this way we can determine 4 values of the test 
sample:. 

(a) cold water shrinkage, measured in wet condition. 

(b) cold water shrinkage, measured after conditioning. 



1 2 
10 
8 
ti 
4 
2 




Cord type I . 
I- 

1 I 

- ' Measured after condidoniriQ 

A Measured in wd condition , 



UK , 2o*C ) j I 

I 



1 10 (30) 

Immersing time in hot wat*r (min) 



Fig. 6. Influence of the immersing time on me hot water shrinkage. 

It can be seen that especially in the first minute of t. 
the shrinkage strongly increases, and that for t. = 30 min. 
a nearly constant value is reached for all the samples. 
An immersing time of 30 min. should be accepted as the 
standard immersing time for routine measurements. 

25 Stiffness 

For measuring the stiffness of twines we used the 
following method: 

Around a rod, 4 cm. in diameter, we wound 20 turns 
of the twine close to each other, held together by a narrow 
strip of adhesive tape at the turns. The coil thus formed 
is taken off the rod (fig. 7a). 



Connected to 
at r-fls- gauging 



_-_. a,ytrnv - _. . - - 

| L of thr _!/ ' T] 

{ J dynamometer I J 

' ' * > 




?f) turns of tWliu* 





T"^ T I ' "inectcd to 

I /_. L-- - moving damp 



b) At thr beginning cf 
the ti-Bt 



r) At the rod of 



Fig. 7. Stiffness test of twines. 



77] 



MODERN FISHING GEAR OF THE WORLD 



Two flat plates of about 10 cm. diameter are attached 
to the clamps of the electronic dynamometer, the 
distance between the two plates in the highest position 
of the moving clamp, being 2 5 cm. The moving clamp 
is not lowered a few centimetres and the cord cylinder 
is placed on the lower flat plate (fig. 7b). The lower 
clamp is then moved upwards until the extreme position 
is reached (fig. 7c), when the cylinder becomes an ellipse 
with a short axis of 2-5 cm. The force needed for this 
is taken as a measure of the stiffness. 

3. METHODS OF TESTING KNOTS 
31 General 

The different methods of test on knots, dealt with 
further on, refer to the single-knot, as drawn in fig. 8. In 




Fig. 8. Single knot. 

the following the knot-ends will be as indicated according 
to the letters given in this figure. 

There are various methods of loading a knot according 
to the twine ends which are clamped on the dynamo- 
meter. Table II gives these different possibilities of 
clamping, with the results obtained on loading the knots 
with an increasing force. 



Clamped 
Twine-ends 

A and B 
AandC 



A and D 
Band C 
B and D 
CandD 



Result 

tip-over of the 
knot 



TABLE U 

Clamped 
Twine-ends 

A and C4 D 



knot breakage, B and C f D 

in some cases 

after slip 

CandA + B 
D and A IB 
knot breakage 
knot breakage 

in some cases 

after tip-over 

of the knot. 



Result 

slip of AB through 
CD or knot break- 
age 



knot breakage 




|-*~ To force measuring 
system 



3* Moving clamp 
1_ 

Fig. 9. Determination of the knot strength. 

(b) the velocity of the moving clamp (range: 1 per cent, 
to 4 per cent, rate of elongation). 

(c) the waiting time, i.e. the time between the tightening 
of the knots and the beginning of the test (range: 
6 seconds to 24 hours). 

The factors were not found to influence significantly 
the knot strength. 

To find agreement between the values for the knot 
strength, an exact description of the circumstances under 
which the test is performed is therefore unnecessary. 

33 Tip-Over Resistance 

Generally, there are two causes of changes in the size of 
the meshes, viz. the tip-over, and the slip of the knots. In 
the tip-over the structure of the knot changes, after 
which the twine AB can easily shift through the knot. 
The testing method is performed as follows (fig. 10): 



To force measuring -^ 

system of the 
A dynamometer 




Moving clamp 
Moving c 

Normal knot(uidc view) Tin-over *" /'---* view) 

Fig. 10. Determination of the tip-over resistance. 



-b- 
Tin-ovpr Ur 



3-2 Knot Strength 

The knot strength, and especially the wet knot strength 
determines the strength of the nets. The twine ends B and 
D are clamped in on the dynamometer to determine the 
knot strength (fig. 9). 

The stress at which the knot breaks expressed in kg. 
or in per cent, of the breaking load of the twine is 
called the (wet or dry) knot strength. 

We investigated the influence of: 

(a) the load with which the knots were tightened 
initially (in the range from 30 per cent, to 60 per 
cent, of the twine strength). 



the twine ends A and B are clamped on the dynamometer 
and the force at which the tip-over of the knot takes 
place is determined. This force, in kg. or in per cent, of 
the knot strength, is called the tip-over resistance. 

When the tip-over begins, the stress-strain curve 
mostly shows that for a short time the force is constant 
or decreases somewhat. 

In some cases, e.g. in research on bonded twines, it 
can be of importance to the producer to determine the 
tip-over resistance of the knots without making a net. 
The knots must be tied manually and tightened in 
accordance with what happens on the stretching appara- 
tus. Subsequently, whether or not after fixation, the 



[78] 



METHODS OF TESTING TWINES 



knots are measured. In fig. 11 a, b and c the tip-over 
resistance is given as a function of the three above- 




Tip -over 

resistance 

(Kg.) 



Tightening force 
(tf> of knot strength) 



Tip-over fi " 


- - - 


- 


resistance 










I 


(Kg ) 








4 - 


1 , -in 1 


-It- 




2 





Hi 










_. 1- 

F--H- 



120 



"ml ^ 60 

Tightening time (sec. ) 

-b- 



Twine type : 

I Enkalon(93 - 23) ic\ .< 3; 
bonded 

II Enkalon 93 lex / 2x3: 
unbonded 

III fcnkanylon 70 lex < 4 ; 
unbonded 



3-4 Knot-Slip Resistance 

The slippage of the knots, while retaining the knot 
structure also causes a change in mesh size. 

To determine the resistance to this slippage, the knots 
are clamped as drawn in fig. 12. The force, in kg. or in 




The force measuring 
ystem 



Fig. 12. Determination of 
the knot-slip resistance. 



Moving clam. 

per cent, of the knot-strength, at which the slip begins is a 
measure of knot-slip resistance. The slippage can occur 
cither suddenly or gradually, depending on the specimen 
type. Fig. 1 3 shows the stress-strain curve which can be 
obtained, where S in the knot-slip resistance. 

Curves a, b and c show a sort of slip-stick effect, 
curve d shows the slippage which takes place gradually. 
Sometimes only a slight slippage occurs (see arrows in 
fig. 13, c and d). In this connection we decided to 



Fig. 11. Influence of (a) tightening force, range 30-90 per cent. 

of the knot strength; (b) tightening time, range 1-60 seconds 

(r) waiting time, range 5-120 min. on the tip-over resistance. 



mentioned factors, and the analysis of variance is given 
in Table III for twine sample II. 



t 5 






Source of variation 



A (tightening force) 
B (tightening time) 
C (waiting time) 



AB 
AC 
BC 
ABC 

Residual 

Total 



TABLE HI 

Sum of Degrees of 
squares freedom 

Main Effect : 

. 1334 2 

. 12 1 

9 I 

Interaction : 
2 2 



Fig. 13. 



Stress-strain curves which can be obtained with the 
determination of the knot-slip resistance. 



Mean Variance 
square ratio 



21 

1 

3 

469 

1851 



2 
1 

2 
108 

119 



667-00 

12-00 

9-00 



1-00 
10-50 
1-00 
1-50 
4-34 



154 
2-76 
2-07 



0-23 
2-42 
0-23 
0-34 



It appears that in the applied ranges of the factors only 
the tightening force has a significant influence. 

We have chosen for the tightening force a fairly 
arbitrary value, viz. 20 per cent, of the knot strength. 
For the rest the standard conditions were: 

rate of extension : 1 per cent, per second 
tightening time: 10 sec. 

waiting time: 5 min. 

As a chemical preparation is applied to synthetic 
materials to prevent the knots slipping, it is advisable to 
determine both the wet and the dry tip-over resistance. 



take only that force as knot-slip resistance, in which the 
slippage occurs for longer than 1 second under the 
measuring conditions mentioned below. 

We investigated the influence of various factors on the 
knot-slip resistance. First the influence of the angle (a), 
under which the twine ends c and d can be clamped. 
We determined the knot-slip resistance at a= deg., 60 deg. 
and 120 deg. In all cases it was lowest at a=0deg. Further, 
just as for the tip-over resistance (see 3-3), the influence 
of tightening force, tightening time and waiting time 
were investigated. The results are shown in fig. 14, and 




T 
i 1 




\ \ 

f'H 


: 


I 





13579 
- Tightening fore* (Kg) 



Knot - slip 6 
resistance 
(Kg) 



0.1 120 

- Waitin? time(min) 



1 60 . 
-Tightening time (aec) 



Fig. 14. Influence of (a) tight- 
ening force, range 1-9 kg. 

(b) tightening time, range 
1-60 seconds; 

(c) waiting time, range 
0, 1-120 min. on the knot- 
slip resistance. 



[79] 



MODERN FISHING GEAR OF THE WORLD 



the analysis of variance is given for one of the samples in 
Table IV. 

TABLE IV 



Source of variation 


Sum of Decrees of Mean Variance 
squares freedom square 


Main Effect : 


A (tightening force) 
B (tightening time) 
C (waiting time) 


.37773 
2 
4 


2 
1 

1 


18886 
2-00 
4-00 


176 
0-02 
0-02 




Interaction 








AB 


. 22 


2 


11-00 


0-10 


AC 


. 401 


2 


200-50 


1-87 


BC 


. 154 


1 


154-00 


1-44 


ABC 


. 384 


2 


192-00 


1-79 


Residual 


.11571 


108 


107-14 





Total 



50311 



119 



In all cases the influence of the tightening force is 
significant, and that of the tightening time is not. In the 
range investigated, the influence of waiting time is only 
significant for some samples (see e.g. sample I, fig. 14, c), 
so the influence of this factor was investigated on a 
somewhat larger scale. The results are shown in fig. 15, 



Knot-slip 

resistance 

(Kg' 






Twine type : 

I Enfcalon (93+23)tex x 3 .unbonded 
II Enkmlon (93+23Hex x 3 ; bonded 
III Enkanylon 70 tex x 4 ; unbonded 



0, 1 1 10 100 1000 
Waiting time (min > 

Fig. 15. Influence of the waiting time on the knot- slip resistance 
range 0, 1-1440. 



brought together and a weight is attached to them. The 
knots are then tightened by dropping the weight over a 
distance of about 20 cm. The weight is taken according 
to the yarn number and amounts to about 1 g. per 5 tex. 
Five knots are tested with an apparatus as shown in 
fig. 16. The knots are placed in a wooden box, which is 
rotated with a velocity of 60 r.p.m. 



20 cm 
Hox((iO R. P. M 



Motcr 
/ 



. 30 cm 



20 cm 




Fig. 16. Apparatus for determining the open-up resistance. 

This process is regularly interrupted to check on how 
many, if any, of the knots have loosened. 

From the values found, i.e. the number of revolutions 
after which each of the knots had loosened, we deduced 
that the frequency distributions of these values approxi- 
mately correspond to those given in fig. 17. 



Sample 1 




Number of revolutions 



Fig. 17. Frequency distribution of the number of revolution*, 
after which the knots have loosened. 



from which it appears that for a waiting time exceeding 
5 min. there is no further influence on the knot-slip 
resistance. 

On the basis of the above-mentioned results, we have 
chosen the following standard conditions for routine 
measurements: 

angle between the clamped specimen ends C and D: 

Odeg.; 

rate of elongation : 1 per cent, per second, 

and, if the knots are tied manually: 

tightening force: 20 per cent, of the knot-strength 
tightening time: 10 seconds 
waiting time: 5 minutes 

For some twine types the knot slip resistance appears 
to be higher and for other types lower than the tip-over 
resistance. Hence, for a complete evaluation of a twine, 
both measurements must be carried out. 

35 Open-Up Resistance 

In the use of synthetic materials, one difficulty which 
may arise is that the knots loosen just after they have been 
made on the netting machine. To evaluate a net twine in 
this respect, the following testing method has been 
developed: in two twines (length about 20 cm.) a knot is 
tied and just tightened. Two of the twine ends are 



In such a frequency distribution, the most character- 
istic value when taking a random sample is the middle or 
so-called median value. In this case, for example, if the 
number of revolutions at which the five knots loosen, is 
arranged in order of size: X,, X 2 , X 3 , X 4 and X & , then X 3 
is taken as the determining value, called the open-up 
resistance. Generally, the measurements are repeated 
several times to find an average value of X 3 , (X 3 ), and 
a measure of the spread (standard deviation s X3 ). 

In fig. 18 the^ 3 -values are given for some samples of 



Yarn type: EnkaJon, 
93 tex x2 x3 

d3=Standard deviation 



Concentration 
bonding bath: 

Fig. 18. Some values obtained with measurements of the open-up 
resistance. 



the same twine, each dipped into a bath of different 
concentration and containing a bonding preparation. 
Tests were made of 6 x 5 knots of each sample. It appears 




[80] 



IV 



III 




To force measuring syete 
of the dynamometer 



METHODS OF TESTING TWINES 

42 Mesh Strength 

The meshes are clamped as shown in fig. 19. The load ai 
which the mesh breaks is called the mesh strength, and is 
given in kg. or in per cent, of twice the twine strength 
(because, apart from the four knots, there are two ends 
between the clamps). It appears that mostly knot II or 
III (fig. 19) breaks, and sometimes knot IV. As the 
weakest of these 3 knots will determine the mesh strength, 
the latter will be somewhat lower than twice the knot 
strength. 




Moving hook 

front view aide view 

riff. J9. Determination <>J the me\h strength. 

that the difference between the X :i values arc relatively 
large as compared with the spread s x:j . 

4. METHODS OF TESTING MESHES 

41 General 

In principle, some of the methods mentioned above for 
testing knots can be applied also to testing the meshes for 
mesh strength and tip-over resistance of the mesh. As the 
remarks, made in 3-2, and 3-3 also apply partly to these 
two qualities, only a few points of the testing methods 
will he dealt with. 



4-3 Tip-Over Resistance in the Mesh 

For determining tip-over resistance the mesh is clamped 
as in the mesh strength measurement (fig. 19). There is 
usually a tip-over of knot 1 (fig. 19) before the mesh 
breaks. The load at which this happens is called the 
tip-over resistance of the mesh and is given in kg. or in 
per cent, of the mesh strength. The value is about twice 
as high as the corresponding tip-over resistance of the 
knot. 



5. CONCLUSION 

We have not, of course, given a complete survey of 
testing methods for yarns, twines, cords, knots and 
nets, but have only recorded some of the experience 
gained with the various testing methods normally used 
in our laboratory for evaluating yarns and net t\vines. 




hauling a Marlon pursed lampara se'ne in South Africa. 

[81 ] 



Pholo FAO. 



TESTING OF MATERIALS USED IN FISHING 

by 

J. REUTER 

Nederiandsche Visscherij-Proefstation en Laboratorium voor Malerialen-Onderzoek Utrecht, Netherlands 

Abstract 

This paper points out the necessity for testing under fishing conditions materials used for fishing, i.e. in the wet state instead of 
the dry. It shows how it is possible to be misled by taking only dry breaking strength as a criterion instead of testing materials wet and 
knotted. In the case of hemp, it was found that the lower grades yarn, i.e. those with low dry breaking length, possessed a superior wet, 
knotted breaking strength. Tables showing the characteristics of hemp, cotton (Egyptian and American), silk and synthetic fibres are included. 

Essais de filet et de til a filet 
Resume 

Cette communication fait ressortir la necessite d'cssayar les matcriaux utilises pout la peche dans les conditions d'emploi, c'est-a-dire 
mouilles au lieu de sees. Elle montre comment il est possible de se tromper en prcnant comme seul critere la resistance a la rupture a P6tat 
sec au lieu d' essay er les materiaux mouiltes et noues. On a trouve, dans le cas du chanvre, que les fils dc basse qualitd, c*est-a-dire a faible 
resistance a la rupture a sec, avaient une plus forte resistance a la rupture quand ils Itaicnt mouilles et noues. Des tableaux donnent les 
caraotlristiques des fibres de chanvre, de colon (gyptien et amricain), de soie et synth&iques. 

Ensayo de redes e hilos empleados en su fabricacidn 
Extracto 

En este trabajo se expone la necesidad de ensayar los materialcs de pesca en las condiciones como trabajan, e.i. humcdos en vez de 
secos. Sc ha demostrado que es posible inc^rrir en cquivocaciones utili/ando como criterio de comparaci6n la resistcncia a la tracci6n del 
material seco, en vez de humedo y amidado. fcn el caso del caftamo, sc cncontr6 que los hilos de material de calidad inferior, o sea aquellos 
con un bajo m6dulo dc ruptura cuando estan sccos, presentan una resistenua a la rolura muy superior cuando se hallan humedos y anudados. 
Se incluyen tablas con las caracteristicas de las fibras dc caftamo, algod6n (egipcio y amcricano), scda y materialcs sintcticos. 



IN most places where twine is bought or sold for 
making webbing and nets, an attempt is invariably 
made to appraise the quality. This is done in many 
ways, and attempts are usually made to define the 
various properties possessed by the material, but there 
is one property that is invariably assessed, viz. the strength 
of the twine. The average fisherman tests the strength 
by trying to break the twine with his hands; the more 
well-to-do arrange for it to be examined at a research 
laboratory under ideal test conditions (20 deg. C. 2deg. 
and 65 per cent, relative humidity). 

The greatest value is attached to the breaking strength 
and it is taken for granted that strong twine makes 
strong webbing. When various twines are to be compared 
qualitatively, this same criterion is adopted, so that the 
prospective purchaser inevitably assumes that the 
strongest twine is most advantageous. 

A fundamental misconception underlies this appraisal 
method which frequently leads to faulty conclusions, 
with all the attendant disadvantages to the fisherman, 
because the strongest twine is not always synonymous 
to the strongest net. 

Twine intended to be worked up into webbing is 
usually tested dry to determine its tensile strength. The 
way in which this is actually done is of secondary 
importance, as the process is used simply to obtain data 
on the dry breaking strength or dry breaking length of 
the twine. But the only correct basis for examining a 



twine's properties is to test it under wet conditions, i.e. 
wet and knotted, since it will be used in wet condition, 
and the properties when wet are decisive when it comes 
to comparing various twines for webbing. 

It would be of great help if both national and inter- 
national standards of testing could be established and 
the results passed on to the fishermen; this would be of 
practical value to them when buying materials. 

As a supplement, a list of tests are given here which 
have been carried out at the Netherlands Fishery 
Experimental Laboratory as a routine investigation of 
the qualities of the materials bought and for comparing 
properties of materials. It is not considered that these are 
the only suitable tests, but they are based on experience 
and have met requirements so far. 

The figures quoted for the breaking strength are the 
mean averages of 10 test samples, as customary in 
routine investigations. The usual sample lengths and 
rates of traverse were adopted. The material for the 
"wet" tests was previously immersed in water for at 
least 12 hours. 



EXAMINATION OF HEMP TWINE 

The tests were carried out in accordance with the 
normal textile method (Table I). The only possible 
conclusion under these conditions was that Quotation I 



[821 



TESTING FISHING MATERIALS 



TABLE I 
Hemp Net Twine 



Theor- Theor- 



Actual Actual 



Dry Break- 



Quota- Analy- Make etical etical 7, ' f " / breaking ing 
tion sis lays No. of wight ; ' ""* strength length 
No. No. (1) tres ingr. tr " ingr m f mkm ' 

perk8 ' purn ' 



perkg.perm. 



twine 



(2) 



, 


24 


100 


340 


2 


941 


309 


3 


240 


65-2 


20 


6 


1 


23 


130 


442 


2 


262 


412 


2 


427 


53-6 


22-1 


I 


22 


150 


510 


1 


961 


478 


2-090 


58-0 


27 


3 


I 


21 


180 


612 


1 


634 


512 


1 


952 


51-2 


26 


2 


II 


25 


100 


340 


2 


941 


378 


2 


646 


59-8 


22 


6 


II 


26 


130 


442 


2 


262 


357 


2- 


801 


52-5 


18 


7 


II 


27 


150 


510 


1 


961 


467 


2- 


141 


48-1 


22- 


5 


II 


28 


180 


612 


1 


634 


526 


1 


901 


42-9 


22- 


6 



(1) Lay -No. of 1-70 m lengths together weighing exactly 

500 grammes. 

(2) Dry breaking strength divided by dry weight per metre. 



TABLE II 
Hemp Net Twine 



W ith over- 



With overhand 



No. 



No. 



24 
23 
22 
21 

25 
26 
27 
28 



strength 



66-8 


39-4 


46-2 


23-2 


53-6 


26-8 


53-2 


28-8 


53-1 


44-4 


47-7 


41-9 


39-1 


36-9 


38-4 


33-2 



58-9 
50-2 
51-3 
54-0 

76-1 
87-8 
94-4 
86-5 



12-2 

9-6 

12-8 

14-7 

15-27 
14-96 
17-46 
16-67 



Breaking strength (wet) divided by dry weight per metre. 



was the best, as the breaking length of this material was 
considerably superior to that of Quotation II. 

As a considerable quantity of sample material remained 
unused at the end of the tests, curiosity prompted us to 
carry out the same breaking strength tests, using wet 
twine instead, incorporating an overhand knot. 

The results were surprising for we suddenly found 
ourselves confronted with the fact that this "fishery 
method" (wet, knotted breaking strength) yielded 
results diametrically opposed to those obtained by the 
textile method. Quotation II was now found to be the 
best (Table II). 

When the data in Tables I and II are compared, a 
striking fact emerges in connection with these hemp 
twines, which were of special hard twist, viz. the wet, 
knotted breaking strength of the "higher grade" twines 
deteriorates by a much greater percentage than that of 
the "lower grade" twines. 

The wet, knotted breaking length leaves no doubt 
that one type of twine was far superior to the other, and 
that there was thus every justification for purchasing 
the twine which would inevitably have been rejected, 
had the dry evaluation method been employed. 

As the hemp samples (both hard twisted) came from 
different manufacturers, samples (normal twist) from 
yet another manufacturer were tested. The results of 
this third series of tests confirmed our findings in the two 
previous tests (Table III). Here, too, it was found that: 

1. twines characterized by a good dry breaking 
length were considerably inferior in wet, knotted 
breaking strength (webbing as used under fishing 
conditions), and that lower grade twines (low dry 
breaking length) possess a superior wet, knotted 
breaking strength. 

2. as this transition is fairly rapid (between 3/36 and 
3/30), it cannot be attributed to the twist or 
diameter of the twine, but to the intrinsic properties 
of the raw material itself. 

A happy coincidence also made it possible to carry 
out this series of tests with twines made of spun yarns. 
As they were not the same as the net twines originally 
tested, the results do not correspond exactly, but the 
general principles, defined in 1 and 2 above, still hold 
good. 



TABLE III 
Hemp Net Twine 



Analysis 
No. 



Make 

of 
product 



Actual 
No. of 
metres 
per kg. 



Dry 

breaking 
strength 
in kg. 



Dry 

breaking 
in km. 



Wet 

breaking 
strength 
in kg. 



With over- 
hand, knot 
breaking 
strength 
in kg. (wet) 



36 
37 
38 
39 
40 
41 
42 
43 



3/60 
3/42 
3/36 
3/30 

3/24 
3/18 
3/15 
3/12 



1990 

1263 

1101 

964 

755 

766 

553 

371 



8-6 
15-1 
16-0 
22-9 
31*2 
33-5 
41-1 
66-1 



100 
100 
100 
100 
100 
100 
100 
100 



17-1 
19-1 
17-6 
22-1 
23-5 
25-6 
22-7 
24-5 



12-1 
20-7 
23-8 
27-0 
32-9 
36-6 
45-3 
59-0 



140 
136 
149 
118 
106 
109 
110 
89 



10-7 
16-7 
19-3 
19-7 
27-9 
28-6 
35-1 
47-9 



130 
110 
120 
88 
89 
86 
86 
73 



[83] 



MODERN FISHING GEAR OF THE WORLD 



TABLE HlA 



Make A 

Our mark . . .21 blue 

Runnage (metres/kg. ) .385-0 

Breaking strength in kg. 

dry ... 

wet 

wel overhand knot 

Breaking length in km. 

Wet overhand knot breaking 
length in km. 

Breaking strength in grammes 
per tex 

dry ... 17-48 (100",,) 
wet ... 17-56 
wet overhand knot . 14-82 



22 blue 
383-0 



45-2 (100%) 
45-6 
38-6 
17-44 (100%) 


37-8 (83-5%,) 
35-9 
34-6 
14-74(84-3%) 


14-82(100%) 


13-32(90%) 



14-47 (82 
13-75(78 
13-25 (89 



8% 

9",, 
4% 



A preliminary investigation indicated that in the case 
of flax, made from fibres of various lengths, the results 
differ to a certain extent, depending on whether the 
textile or fishery test method was used. 

The long staple fibres of this material were separated 
from their short counterparts and both were used to 
produce the same type of netting twine with precisely 
the same lay and twist. 

The results arc summarized in Table H!A. 

Considered from the dry breaking length point of 
view, it appears that sample A was the best, the ratio 
being 100 : 84-5 on the basis of breaking length. When 
the we/, knotted breaking length is taken as criterion, 
the corresponding ratio is 100 : 90. 

Here, too, there is yet another indication that the 
"poorer" yarn (shorter fibres) stands up better to knotting. 

TESTING OF COTTON NETTING 

The same characteristic deviations between the dry twine 
and the wet knotted breaking length are also found in 
the case of cotton twines. 

To ascertain whether these data could be used as 



quality indications, the figures of the wet breaking 
strength were measured at the mesh, the results being 
expressed in the number of grams breaking strength per 
fibre quantity employed. An abbreviation, "tex" was 
used for this latter unit ( 1 tex the quantity of material 
involved when 1,000 m. weigh exactly 1 g.). 

When the quality of the various net samples is evaluated 
by this method (see Table IV), it will be found that: 

1. the unit "g. tex" provides a serviceable standard 
for comparing the strength of different net twines. 

2. webbing made from Egyptian cottons is less 
strong than that made from American cottons. 

3. the breaking length of dry twine is not a suitable 
criterion for evaluating the strength of wet 
netting. The dry twine breaking length of sample h, 
for example, is very low, whereas calculated on the 
basis of g./tex, based on the wet mesh breaking 
strength, this sample is the strongest. The dry 
breaking lengths of twine samples />, d and / are 
almost identical, yet they show a difference in the 
number of g./tex calculated on the basis of the wet 
mesh breaking strength. 

4. Twine sample c is stronger than a and b\ the dry 
breaking length is also better. On the basis of 
g./tex, however, calculated from the wet mesh 
strength, a and b arc stronger than c. 

TESTING OF SILK YARNS 

Similar deviations in results when both the textile and 
fishery methods were employed are also found when 
silk yarns were tested to ascertain the number of grammes 
wet, knotted breaking strength per unit of weight The 
unit of weight "denier" was adopted (1 denier the 
quantity involved when 9,000m. of yarn weighs exactly 
Ig.). 

Two different lots ol material were tested, and here 
again it was very obvious that this "fishery test" method 
brought to light qualities which would not have been 



'lABIL IV 

Cotton Webbing 





30/12 


30/12 


30/12 


30/12 


36/12 


36/12 




< arded 


carded 


carded 


carded 


carded 


carded 


Type 


American 


American 


American 


Egyptian 


American 


/ffyptian 




cotton 


cotton 


cotton 


cotton 


cotton 


cotton 


Ply 


4*3 - 12 


4,- 3 12 


4x3 12 


4x3 12 


4-3 12 


4 -'3 12 


Twist direction 


zzs 


ZZS 


ZZS 


ZZS 


ZZS 


ZZS 


Runnage (m./kg.) 


3851 


3824 


3943 


3935 


4796 


4570 


Breaking strength (dry) 


5-21 


5-15 


5-94 


4-84 


4-48 


4-19 


Percentage 


100 


100 


too 


UK) 


100 


100 


Breaking length 


20-06 


19-69 


23-42 


19-05 


21-49 


19-15 


Breaking strength (wet) 


5-70 


5-73 


6-81 


5-60 


5-18 


4-46 


Percentage (in terms of dry twine) 


109 


111 


115 


116 


116 


106 


Breaking strength at mesh, dry 


7-20 


7-60 


7-29 


6-64 


5-93 


5-70 


Percentage (in terms of dry twine) 


138 


148 


123 


137 


132 


136 


Breaking strength at mesh, wet 


8-15 


8-68 


8-00 


7-59 


7-10 


6-24 


Percentage (in terms of dry twine) 


156 


169 


135 


157 


158 


149 


Wet breaking strength at mesh, 














grammcs/tex. 


31-382 


33-257 


31-152 


28-870 


34-053 


28-519 


[841 



TESTING FISHING MATERIALS 

TABLL V 
Silk Net Twine 



Supplier 



No. 


80/3 > 3 


80/3 - 3 


80/3 / 4 


80/3 <5 


80/3 6 


80/3 - 8 


Runnage (m./kg.) 


82.17 


8177 


5783 


5015 


4139 


3247 


Total denier 


1012-5 


1012-5 


1350-0 


1687-5 


2025-0 


2700-0 


Dry breaking strength (kg.) 


3 -58 


3 29 


4-60 


5-93 


7-35 


8-76 


Breaking length (dry) 


29-49 


26-90 


26-61 


29-74 


30-42 


28-44 


Dry breaking strength (g./denier) 


3-538 


3-259 


3-407 


3-514 


3-620 


3-244 


Wet breaking strength (kg.) 


2 64 


2-44 


3-47 


4-37 


5-37 


6-61 


Wet breaking strength (g./denier) 


2-607 


2-410 


2-570 


2-548 


2-652 


2-448 


Wet breaking strength, with 














overhand knot (kg.) 


1-57 


1-70 


2-09 


2-70 


3-45 


4-30 


Wet breaking strength, with 














overhand knot (g./denier) 


1 551 


1-679 


1-548 


1 600 


1-709 


1 593 



shown by the dry test method. As this material is 
intended solely for use as wet webbing, the number of 
g./dcnicr calculated on the basis of the wet, knotted 
breaking strength, is the only correct criterion to adopt 
when evaluating the quality of the yarns for fishery 
purposes (Table V). 

The breaking strength in g. denier, calculated on the 
basis of the dry yarn breaking strength, runs parallel with 
the dry breaking length, as this is, in point of fact, the 
same unit expressed in dilTercnl terms. When the break- 
ing strength of wet, knotted yarn, is determined, the data 
in respect of the various yarns will he found to differ 
entirely. 

TESTING SYNTHETIC FIBRE WEBBING 

The term "g./denier" is very frequently used lu express 
the breaking strength of synthetic twines. This, however, 
invariably refers to dry twines. The current trend is more 
and more in favour of the wet breaking strength. The 



fact that some manufacturers of synthetic fibre twines 
regularly indicate the wet, knotted breaking strength, is 
certainly a step in the right direction. 

Net manufacturers treat the twines (continuous 
filaments) which have previously been worked up into 
webbing, in various ways in order to "fix" the knots. The 
determination of the breaking strength in g./ denier, 
calculated on the basis of the wet, mesh breaking strength, 
also enables the investigator to ascertain whether this 
treatment has damaged the t\\ine in the knot. This 
determination is far more logical than simply testing the 
twine prior to the knot being fixed. 

Table VI summarizes certain data in respect of various 
samples, all expressed in terms of the wet, knotted 
breaking strengths of both twines and webbing. 

One cannot help being amazed by the great changes 
which nylon 6 undergoes (1 was unable to examine any 
webbing made from nylon 66), when made into \\ebbing 
with specially treated knots. 



TAUI i VI 
Synthetic Net Twine and Webbing 



Denier 
Material 

Filament 
Product 



_!: 726 :; _ 10425 | 2520 
nvlon 



nylon 
'6 



nylon 
*6 



.: 4788 

poly- 
phony 1 
alcohol 



6300 5670 



contin- 
uous 


contin- 
uous 


contin- 
uous 


fibre 


new 
twine 


new 
twine 


new 
twine 


new 
twine 



nylon 
'6 

contin- 
uous 



m Ion 
'6 



contin- 
uous 



5760 



nylon 
6 



contin- 
uous 



6930 



nylon 
6 



contin- 
uous 



I 0080 



contin- 
uous 



webbing nebbing 



new new new 

webbing \\cbbing webbing 



Dry breaking strength (kg.) 
Dry breaking strength (g.; denier) 
Wet breaking strength (kg.) 
Wet breaking strength (g./dcnicr) 

Wet breaking strength, with 
overhand knot (kg.) 

Wet breaking strength, with 
overhand knot (g./denier) 



4-78 


69-0 


9-41 


19-2 


43-06 


33-14 


6-579 


6-610 


3-734 


4-008 


6-835 


5-845 


4-27 


59-2 


8-30 


14-6 


39-95 


29-67 


5-851 


5-679 


3-532 


3-048 


6-341 


5-233 



2-62 25-6 5-80 

3-607 2-456 2-302 



6-70 



30-86 41-4 52-8 

5-445 5-973 5-23 

27-35 30-30 42-5 

4-824 4-372 4-216 



[85 1 



MODERN FISHING GEAR OF THE WORLD 



In the case of a polyalcohol yarn, the dry breaking 
strength or other evaluation figures based on such a test 
would prove misleading as a basis for the comparison. 

This fact has quite rightly been publicized by the 
manufacturers, and it is indeed encouraging to note that 
the wet, knotted breaking strength of this twine is now 
being advocated as a quality criterion. 

TESTING OF TRAWL TWINE 

A single test was carried out with trawl twine, and here, 
too, differences came to light in respect of the wet, 
knotted breaking strength, despite the fact that the manila 
twines were of the same runnage. This was fully in 
accordance with the results of our investigations on other 
yarns. 

The investigation had to be interrupted, however, as it 
proved impossible to resolve the problem of the manila 
fibre gradings employed. 

CONCLUSIONS 

1. The most widespread method in use at present for 
the comparison of net twines of different quality 
is the dry breaking strength or other criteria based 
on it, e.g. breaking length or tenacity (the breaking 
strength in denier or tex). 



2. As the twine is used wet and knotted in the form of 
webbing, it is more logical to employ an evaluation 
standard based on the wet, knotted condition of 
the twine. 

3. The wet, breaking strength of knotted twine, or 
the wet mesh breaking strength, is therefore the 
most appropriate criterion. Evaluation figures, 
derived from the wet, knotted, breaking length or 
the wet, knotted breaking strength in denier or 
tex, can also be used for this purpose. 

4. The evaluation figures, calculated according to 
1 and 3 above, do not yield parallel results. In 
fact, in some cases, they are diametrically opposed, 
as a higher dry breaking length, for instance, is 
attended by a lower wet, knotted breaking strength. 
Thus, some twines, otherwise very strong, are 
found to be highly sensitive to strong flexion, 
while less strong twines suffer to a smaller degree 
when wet and flexed, i.e., knotted. 

5. For webbing, the wet mesh breaking strength is 
the only logical strength criterion, because it 
corresponds more accurately with the conditions 
under which the webbing is used, and permits a 
more accurate comparison to be made of the 
various materials used. 




A canoe fisherman mendinp his net on the Indian Malabar coast. 

[86] 



Photo FAO. 



LATERAL STRENGTH AND KNOT-FIRMNESS OF SYNTHETIC 
TWINES FOR FISHING PURPOSES 

by 

HANS STUTZ 

Farbwerke Hoechst A.G., Bobingen Mills, Germany 

Abstract 

The author describes tests for determining lateral strength and knot -firm ness of netting twines and shows how knot-firmness can be 
improved by treating the twines with bonding agents. The paper is illustrated by numerous tables and diagrams. 



Rfeume 



Resistance aux efforts lattraux et tenue des noeuds des flls syntbttiques pour la ptehe 



L'autcur d6crit les essais pour la determination de la resistance aux efforts lateraux et la tenuc des noeuds des fils a filets. II montrc 
comment on peut ameliorer la tcnue des noeuds en traitant les fils par impregnation de divers produits. L'article est illustrl par de nombreux 
tableaux et diagrammcs. 

Resistencia lateral y firmeza de los nudos de hilos sinttticos empleados en los artcs de pesca 
Extracto 

El autor describe los ensayos hcchos para determmar la resistencia lateral y la firmeza de los nudos hechos con hilos de fibras 
sint6ticas, y la manera como esta ultima puede aumentar tratando el material con fijativos. hi trabajo tambi&n contienc numerosas tablas 
y esqucmas. 



IN spite of all well-known lest results published on the 
subject of general, physical and chemical properties 
of synthetic fibres, time and again two problems 
emerge which cause a certain amount of trouble in the 
manufacture and use of nets, twines and cordage: 
"lateral strength" and "knot-firmness". 

Lateral strength means the resistance which the 
material offers to any stress differing from the normal 
tensile stress operating in the longitudinal direction of 
the fibre axis. Well-known examples are the strength in a 
knot and loop, alternating bending strength, etc. Since 
in these cases there is an additional stress on the material 
the normal tensile strength is, as a rule, thereby reduced. 
Various materials react to this additional stress in very 
different ways and, in this connection, the type of 
material (e.g. Perlon or hemp), its special properties 
(depending on the type), the structure of the yarn or 
twine and other factors often play an important part. 

Knot-firmness concerns the reaction of a knot to 
forces which cause shifting or loosening and thereby a 
change in the size of mesh. 

TESTING METHODS 

Our investigations were limited to the two synthetic 
fibres which are at present most important for the 
fishing industry, at least in Europe: polyamides (Perlon, 
nylon) and polyesters (Terylene, Trcvira, Dacron). The 
material was tested in many different forms: filament 
yarns, staple fibre yarns, twisted twines, and braided 
twine. 



The object of the investigations was to find ways and 
means of reducing the loss in tenacity caused by knotting 
and to improve the firmness of knots, particularly in 
very smooth materials made from continuous filament. 

These efforts were successful, at least in the laboratory 
but the results will, of course, have to be confirmed in 





\\ // 



B 



Types of knots used in the tests. 
= Fishermen's knot; B - Overhand knot ; C- Double overhand knot 



[87] 



MODERN FISHING GEAR OF THE WORLD 




Apparatus used for testing knot -firmness. 

practice. In our experiments, we determined the lateral 
strength of the various materials and structures examined 
by testing the strength of normal knots and customary 
net knots both in dry and wet conditions (see fig. 1). 
Knot-firmness is more difficult to determine bv tests. 




T 



10 12 1 
Total extena 



4 Ik Ik 
ion % 



22 24 1 28% 



Fig. 3 
Load-extension properties of different materials (dry). 

7. TREVIRA 840 den. (10,300 ml kg.) 

2. PERLON 840 den. high tenacity (70,550 ml kg.). 

3. PERLON 7,750 den. (8,080 m/kg.). 

4. TREVIRA Nm 20 (79,650 mlkg.). 

5. PERLON Nm 20 (19,500 m/kg.). 



Here we also tried two ways which, although not 
corresponding exactly to the stress on the knot of the 
net in use, nevertheless allowed a comparison of the 
knot firmness. Since the problem of maximum resistance 
in a knot to displacement is obviously closely connected 
with maximum roughness of the surface of filaments, 
yarns and twines, we first tested the yarns in 'loop knot" 
or "double overhand knot" forms (see fig. 1, C) in a 
normal tensile strength testing device. The knot was 
tightened by means of a constant weight. When a load 
was applied to the knotted yarn, the knot loosened 
(meaning poor firmness), or held fast while the yarn or 
twine broke in the knot or in some other place. 

In the second method, we desisted from any tensile 
stress on the knotted yarns since in the net the knots will, 
as a rule, shift only when they are not loaded. Instead, 
we placed a number of short pieces of twine connected 
by the fishermen's knot (fig. 1, A) in a rubber-lined 
box (fig. 2). A rubber roller was also put in the box. 
The closed box was rotated for 30 minutes at about 
60 r.p.m., i.e., a total of about 1,800 revolutions. During 
this process, a number of knots will loosen, depending 
on material and previous treatment. This number is 
expressed as percentage. By this method, which corres- 
ponds approximately to the I.C.I, pilling tester, we 
were able to find very marked differences. 

TENSILE STRENGTH, LOAD-EXTENSION 

Before giving the results of the investigations, let us 
refer again to the influence of the raw materials on the 
lateral strength of the net twines. The main facts can be 
seen in the load-extension-diagrams (fig. 3). This shows 
a comparison between the two materials, Perlon and 




Fig. 4 

Load-extension properties of different twines (dry and wet). 
I. PERLON 840 3 den. (3,160 m/kg.) dry 
? .. ,. ., ,. wet 

3. TREVIK.t S40 , 3 den. (.1,000 m/kg.) dry 

4. ., wet 

5. PERLON Nm 20/2,'J (3,110 m/kg.) dry 

6. ., ,. wet 

7. TREVIRA Nm 20/2/3 (3,040 m/kg.) dry 
* .. .. ,. wet 



[88 ] 



STRENGTH AND KNOT-FIRMNESS OF SYNTHETICS 



70. 


























460 

*k 1 


,.. 


Cj 


D 


A 






















j: '50. 














D 






















^T* 40. 
















r' 


























tf 3* 














B 


























A C D 


A 


Q 


D 




20 












































B 




... 






B 

nn 




_. 




o> 55 




B 


























































S| 10. 





























































































































Per 


Ion' Perlon 




















Perlon Pcrlon 


1 840 den 1150 den 




















Nm 50 Nm 20 


11)550 m/Kg 8080 m/Kg 




















4B400 m/Kg 19500 m/KR 


M A 






















J* 60. 




A 






















tiO 


h" 




























">- 






... 
























sii extension 
sile strengt 

CO ^ 
p ( 




B 


C 


ft. 






CD 


A 


B 


C 


D 


B 
A 

C D 


A 


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C 


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A 


B 


C 


D 




A 


B 

w* 


C 





B 
A CD 


A 


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rOn 

D 




... 








... 


.- 


o g 20- 
























-.. 

















... 


























r 


































































0. 


































































Pcrlon Perlon Perlon Perlon 


Perlon 


Pcrlon 


Perlon Pcrlon Perlon Perlon 


840 x 3 den 840x2x3 1150x3 1150x2x3 
3. 160 m/Kg 1520 m/Kg 2190 m/Kg 1050 m/Kg 


1150 
219U 


X3C 
m/Kg 


1150x2x3 D 
1050 m/Kg 


Nm 50/3 Nm 50/2/3 Nm 20/3 Nm 20/2/? 
15500 m/kg 7300 m/kg 6080 m/kg 3110 m/kg 



Comparison of the relative knot strength of different yarns and of twines made thereof. A - tensile strength* B 
strength with overhand knot, I) knot strength with fishermen's knot. - --dry, . 



total extension, C -kno 
wet. 



e70 










- 










g 




B 






Sea 














x 

ft) 












n Jl 














A 






S 5a 


Vi 
























Is 


A 




C, 


D 




A 


JB 


I 
C D 


A 






D 


* 










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A 


R 


CD 


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A 




















.. 










^ 2 fx 




B 

IW! 




... 


















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B 


... 




















... 










q 


n 








i> 


43 

wlO- 

W 

> 0- 
































































































"jj Pcrlon Perfon Pcrlon Perlon 
g Nm 20 Nm 20/3 Nm 20/2/3 Nm '20/3/3 
^ 19500 m/Kg 60BO m/kg 3110 m/Kg 1980 m/Kj- 


Perlon 
Nm 20/4/3 
1380 m/Kg 


Pcrlon Pcrlon Perlon Pet Ion Pcrlon 
Nm 50/3 Nri 50/3 Nm 50/2/3 Nm 50/3/3 Nm 50/4/3 
4R400 m/Kg 15500 m/Kg 7300 m/Kg bo 10 m/Kg 38C rn/Kg 



. 

Relative krux strength of Perlon staple twines. A tensile strength, R total extension. C knot strength with overhand knot, D knot strength: 

with fishermen's knot. ---dry wet. 

[89] 



MODERN FISHING GEAR OF THE WORLD 



g - A 


JFK 






A 








A 




A 


r 












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... 












50. 






























^40. 
8 






r 


JJ 












C 

m 


,D 

n 






C D 


A 


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A 


: 


TX 


A 


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C 


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_ 








C 


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BC D 














Bj 




.., 








Cj 


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<J 


... 








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u 




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... 














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rwi 








B 














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... 








B 

M 










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m 






I 10 - 




































































































5 _ 




































































































* Nylon Nylon Pcrlon Pcrlon Perlon Perlon Perlon Pcrlon Perlon Perlon 


g 210 x 3 den 210 x 6 den 840 x 3 den 840x2x3 den 1.150x3 den 840x10x3 den 1160x3 den C 1.150x2x3 840x3x8 den 840x2x8 den 


13.400 m/Kg 6.700 rn/kg 3160 m/Kg 1520 m/Kg 2. 190 m/Kg 314 m/Kg 2. 190 m/Kg den D braided braided 


1.050 m/Kg 391 m / kg 488 j^g 



Relative knot strength of Perlon continuous filament twines. A^ tensile strength, B^ total extension, C~knot strength with overhand 

knot. D knot strength with Jishe rmens knot. dry, .... ^wet. 



Trevira, in their various forms, i.e., as continuous filaments 
and as spun yarn. The different values for breaking 
strength and extension are clearly seen as well as the very 
different behaviour under small to medium loads, i.e., 
the most important in practical use. 

The polyester yarns are distinguished by a curve which 
is relatively steep at small loads. Their extension is thus 
relatively small in this region, which is advantageous in 
nets. This material, when twisted, often shows very 
different characteristics, depending both on the material 
used and on the structure. 

Dr. Klust shows in his comprehensive report "Perlon 



Twines", the important influence of doubling, twisting, 
braiding, etc., on the physical properties of net twines, 
so that it is enough to mention this in passing. For 
instance, Perlon twines made of continuous filament 
usually have higher tenacity and lower extension than 
those made of spun yarn. 

In net twines wet tenacity is of particular interest. 
Fig. 4 shows some comparisons between Perlon and 
Trevira (Terylene), the twines being of similar thick- 
ness, although some are of filament and others of spun 
yarns. Trevira is distinguished by a very good wet 
tenacity. 



70. 



5 60. 




A 


a 50 - 






... 




s 


A 


A 


B 


C 


A 










B 


d " A 






... 












A 








A 





A 


3 






r 1 "^ 



















... 










i 




CD 


rsr! 




C30- 




. 


^ 


A-/ 






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Tl ^ 










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B C D 


^20. 






.. 


... 






























\^ 


nm 








C 


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C 










-.. 


#. 










... 






C 
















































































"10. 

** 
Q) f\ 
















































































5 

S 

Ql 


Perlon 
Nm 20/3 


Trevira Perlon Trevira Pcrlon Trevira Perlon Trevira 
Nm 20/3 Nm 20/2/3 Nm 20/2/3 Nm 20/4/3 Nm 20/4/3 Nm 50/2/3 Nm 30/2/3 


H 6080 m/Kg 6350 m/Kg 3110 m/Kg 3040 m/Kg 1380 m/Kg 1500 m/Kg 7300 m/Kg 7650 m/Kg 



Fig. 8 

Comparison of Perlon and Trevira staple twines in regard to their tensile strength (A) t total extension (B) and knot strength with overhand 

knot (C) and fishermen's knot (/)). =dry ^wet. 

[90] 



STRENGTH AND KNOT-FIRMNESS OF SYNTHETICS 



* 

s ^ 




j-x 




A 




60_ 


... 








.., 




A 

MW 




r~ 


A 


















40. 


A 




mSm 






n 








CD 




D 


jf 30_ 


... 


_ 


CD 








ft 


D 

=5 








C 


... 






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._ 


... 








C 









tt 20 








... 






B 










B 












<J 








B 
















10. 


































B 










rrra 










B 






o> 0, 




























































"2 Petlon Trevira Perlon Trevira Perlon Trevira 


g 840x2x3 den 340x2x3 den 840x10x3 den 3000x3x3 den 840x3x8 den 914x3x8 den 


H 1520 m/Kg 1545 m/Kg 314 m/Kg 312 m/Kg braided braided 


319 m/Kg 385 m/Kg 



Comparison oj Perlon and Trevira continuous filament twines in regard to their tensile strength M), total extension (B), knot strength with 

overhand knot (C) and fishermen's knot (D). ~dry wet. 



KNOT STRENGTH 

Wet tenacity, and above all, knot strength is decisive in 
judging the usefulness of the material in nets and of 
course knot strength in a wet condition is of special 
interest. 

It becomes obvious that high normal tensile strength, 
does not indicate equally good knot strength. Fig. 5 
shows these values for Perlon filament, staple fibre yarns 
and twines of different structures. The higher tensile 
strength of the continuous material can be clearly seen 
along with its higher sensitivity to knotting and plying. 
The initial differences in the knots still exist, though no 



longer in the same relation. In multiple twists, the 
knot strength of the continuous material is, under 
certain circumstances equal to, or below, that of twines 
of spun material. Braided twines, however, usually show 
a better result. 

This fact does not question the other advantages of 
twines of continuous material as far as smoothness, 
lower thickness, lower towing drag, etc., are concerned. 
Trcvira gives slightly better results, especially in regard 
to the wet knot strength of spun material. 

Twines made of Perlon (spun yarn as well as filament) 
of various structures are compared in figs. 6 and 7 where 
the influence of the structure emerges clearly. It is well 



100. 



BCD 



0. 
TO. 












A 






A 






* 














2: 














Ida 






C 










201 


- 














S 

















10. 










P 








Pcflon 840x3 iten 
-ifio m/kg 



BCD 



Prrlon H4(K2x:i Urn 



A 

I IB 



r-, A 



B C 



Aj 



'D 



lon ll&O x 2 :< P 
lo.SU m/Kg 



Trcvira 840 x i 
J2% m/K K 



Fig. JO 

Knot firmness of different Perlon and Trevira staple twines according to 1 double overhand knot and II fishermen's knot testing method. 
Auntreated, B^treatment x, C treatment y, D^treatment z. Results given in per cent, loosened knots. =*dry ^wet. 

[91 ] 



MODERN FISHING GEAR OF THE WORLD 



known that the "critical twist" in continuous filament 
twines is reached much earlier than in spun material. 
This is also true of corresponding twist structures made 
of Trevira. In this case, too, the lower extension and the 
universally high wet strength are evident. 

In figs. 8 and 9 you see pairs of twines, each of which 
contains a strand made of Perlon and the other of 
Trevira, directly comparable or, at least, very similar in 
their total thickness (length per weight). It is tempting 
in this comparison to examine in detail the influence of 
the twist, but Dr. Klust has dealt with this subject very 
extensively in his above mentioned report. 

The purpose of this comparison-test was merely to 
point out the chances open to the processors in selecting 
material and structure and to warn against jumping to 
quick conclusions regarding the suitability of a particular 
material before all factors have been taken into account. 

KNOT FIRMNESS 

The next point concerns the problem of knot firmness. 
It is well known, and seems to be confirmed in practice, 
that net twines of spun yarn show sufficient firmness of 
knots. This is probably directly connected with the con- 
siderably rougher surface produced by the many pro- 
jecting fibre ends and the position of the capillary fibres. 
This fact is also very clearly reflected by the values found 
by means of the two test methods already described. 
Furthermore, it was found that untreated twines, wetted 
for 24 hours and then dried, had a better knot firmness 
than unwetted twines. 

Subsequently, we tried to improve the knot firmness 
by treating the twines with various agents. The results 

T> -D 

100. 



90- 



80. 




0. 



obtained with three different products are given below: 

X means an adhesive which is almost water-insoluble 

and was dissolved in a solvent; 
Y is a product on poly vinyl acetate basis, likewise 

almost water-insoluble; 
Z is a product on silicate basis, likewise having a 

roughening effect on the surface. 

The influence of these agents on the firmness of the 
knots is shown by both test methods so that the stability 
in twines of spun yarns may be considered to be practically 
100 per cent, there being only slight differences between 
the various products. 

The result of the treatment of twines of continuous 
filaments is, of course, clearer (fig. 10). Although the 
various materials and structures show different reactions 
to the agents, the knot firmness of the Terylene is 
striking. 

In fig. 1 1 the results of a braided twine of Perlon and 
of Terylene compared with Perlon monofilament are 
shown. The braided twines are distinguished because of 
their structure by a better knot firmness. The results have 
been further improved by the above mentioned trca tment. 
The position of monolilaments is somewhat different. 
Although knot firmness was improved, loo, by the 
treatment, the results were not uniform. However, 
certain other possibilities are emerging for monofilaments, 
but it would be premature to report on them now. 

In conclusion, it must be pointed out that the examina- 
tion of this very interesting subject, has by no means been 
concluded. Further tests, as well as a free exchange of 
experience between all concerned, will have to follow 
if optimum results are to be achieved. 



A B 



BCD 



D 



Perlon - Monofilamem Type 
K 0,30 mm 105^0 m/kg 



Trevira 914x3x8, braided 
385 m/kg 



Perlon 840x3x8. braided 

391 m/kg 
FIR. 11 

Knot firmness of Perlon monofilament and Perlon and Trevira braided twines according to /. double overhand knot and II. Fishermen's knot testing 
method. A untreated, B- treatment x, C-^ treatment y % D^ treatment z. Results given in per cent, unloosened knot. dry wet. 

92 



DISCUSSION ON THE PROPERTIES OF TWINES AND 

TESTING METHODS 



Dr. G. Klust (Germany) Rapporteur: This subject may be 
divided into two sections: Testing Methods and the Properties 
of Twines. Among testing methods, those of prime importance 
here refer to twines, nets or ropes. 

Renter, Shimo/aki and Arzano list tests for net twines. 
These tests take into account: Construction of the twine; 
thickness of twine, dry and wet; weight in air and in water; 
length-weight unit; sinking speed; shrinkage; breaking 
strength, dry and wet; breaking length; breaking strength per 
weight unit (tcnacit\); knot strength; breaking extension; 
load-extension curve; elastic extension and permanent 
elongation; toughness or the ability to absorb work; abrasion 
resistance; rcsisfar.ee to light, weathering and to water; 
stiffness or handiness; knot-slippage or knot firmness; 
resistance to bacteria, mildew and insects. 

The^e tests were carried out under conditions as close as 
possible to those of actual fishing, therefore they will not 
always correspond with ihc methods generally used by textile 
industries. 

Different methods often give different values and van 
Wijngaardcn in his paper urged that there should be a certain 
uniformity in the measuring methods and the conditions 
under which they are performed; this, I believe, is necessary. 
This Congress will of course not be able to engage in such 
special problems, but it would be a considerable practical 
success if the papers and discussions helped promote closer 
co-operation between those who make such tests. 

Of the testing methods specified in these papers, a few, 
which are not very well known at present, may be cited. 

Japan Chemical Fibres Association gives a simple method 
of measuring the thickness of twines. Pieces of test samples arc 
wound twenty times closely in parallel around a cylinder of 
about 5 cm. in diameter with a standard initial tension. Then 
the breadth is measured and divided by twenty. The average 
number is indicated in millimetres. 

A method of testing the sinking speed is given in the same 
paper. A cylindrical glass vessel is used, having two marks at 
a distance of 50 cm. A piece of twine, 2 cm. long, with a knot 
in the middle, is put into the glass tilled with water, and the 
time taken by the twine to sink from the top to the bottom 
mark is recorded. 

There is no need to mention such important testing methods 
as those for breaking strength and extension because they are 
very well known and are dependent on the machines at the 
disposal of the examiner. In these tests too there should of 
course, be conformity in the methods in order to produce 
comparable results. 

Knot slippage or knot firmness has become of great im- 
portance. We know that the smooth surface of continuous 
filament twines does not assure absolutely slip-proof knots. 
Van Wijngaarden and Slutz describe methods for determining 
the resistance of knots to slippage. The load-extension curves 



of knotted twines are drawn by a tensile tester. When the 
knot is slipping, the arc of the curve is interrupted by the 
appearance of jags or teeth. Slippage can occur suddenly or 
gradually. The force in kilograms or per centage of the knot 
strength at which the slip begins is the measure of the 
resistance. 

Knots in smooth twines often shift without a load. To find 
differences in the behaviour of twines made of different fibres, 
Stutz placed a number of short pieces of yarn, connected by 
the usual net knots, in a rubber-lined box. A rubber roller 
was also put into the box which was then rotated for 30 
minutes. During this process a larger or smaller number of 
knots will loosen, depending on material and previous 
treatment. The number is expressed as a percentage. A similar 
method is described by van Wijngaarden. 

Van Wijngaarden also determines the moment when the 
loaded knot is changing its structure so that the twine slips 
through the knot. The force in kg. or percentage of the knot 
strength at which this takes place is called the "tip-over 
resistance." 

I or measuring the stiffness of twines, van Wijngaardcn 
winds 20 turns of the twine round a rod 4 cm. in diameter. 
The coil is taken off the rod and placed between one of the 
scales of a balance and a fixed metal plate. Weights are added 
to the other scale-pan until the coil is in the form of an ellipse, 
the short axis of which is 2-5 cm. 

In this connection there is von Brandt's method, described 
in his book "Arbcitsmethoden dcr Net/forschung". 

As expected, nearly all papers deal with synthetic fibres. 
They are now of great importance in most of the leading fish- 
ing countries and are more and more replacing natural fibres. 
Needham states in his publication on the use of nylon in 
the fishing industry: "They bring to one of man's oldest 
occupations the miracle of science and, in doing so, provide 
easier living for the fisherman." For instance, the miracle 
can be noted in the rot-proof quality of the synthetic fibres. 
1 remember the great astonishment and the scepticism of our 
inland fishermen when they first received gear made of PeCe. 
This rot-proof quality is most important in fishing gear as it 
ensures greater durability and eliminates the work and expense 
of preservation. It also enables the gear to remain in water for 
an unlimited time and eliminates the need to dry it. 

This rot-proof quality is now taken for granted, and the 
developments in synthetic fibres have considerably increased 
the demand by fishermen or these materials. 

Lonsdale outlines the desired properties of the ideal fibre 
for use in fishing gear, but adds that this fibre, of course, does 
not exist. 

Teviron seems to be the cheapest of synthetic fibres, and 
the price of Teviron fishing net is only 30 per cent, higher 
than that of cotton. Its resistance to weathering is very high. 
The same holds true for Rhovyl and PCD. 



931 



MODERN FISHING GEAR OF THE WORLD 



Polyethylene fibres have the lowest density of synthetic 
fibres, lower than that of water, therefore ropes made of this 
fibre will float and, in trawling, the upper net will tend to rise 
of its own buoyancy. 

The fibres with the greatest specific gravity are those made 
of polyvinylidcne chloride, e.g., Krchalon. This property 
enables the nets to sink faster. It makes the fibre particularly 
suitable for setnets. 

Ter>lene has a high tensile strength which is unaffected by 
wetting. The most important characteristic seems to be its 
very low extensibility. Gillnets of Terylene have been used 
successfully, principally for catching salmon and cod, but 
net herring. This soft fish becomes damaged by the fine 
twine. Trawls made of Terylene have proved very successful. 

The most important characteristic of the polyacrylonitrile 
fibres is a very good resistance of weathering, but the fibre does 
not seem to be used in fishery and none of the papers mention 
it as a net material. 

Twines made of polyamide filament or staple fibre have a 
relatively low resistance to weathering, less than that of cotton. 
This refers especially to types of polyamides which have been 
delustred, and which are not suitable for use in the fishing 
industry. For most fishing gear this sensitivity to light is not, 
however, an important disadvantage. Practical experience 
gained by Swedish freshwater fishermen has proved that 
nylon nets discarded after 3 to 4 years have become unservice- 
able because of damage by tearing and not because of the 
effect of sunlight. 

In Portugal, purse seine nets made of perlon staple, not 
dyed or prepared in any way, have been in use 1,300 fishing 
days and are still effective. Cotton nets frequently treated 
with preservatives, have a durability of 400 to 500 fishing 
days. The excellent physical properties of polyamide twines 
are of much greater importance than their resistance to 
light. 

But there are cases where the resistance to light will be 
insufficient, as, for example, when part of the fishing gear 
remains above the water level. Colouring the net may help, 
or twines made of polyester, polyvinyl chloride, polyviny- 
lonitrile or Saran may be used. Terylene polyester fibre 
has a better resistance to light and weathering than the 
polyamides and is equal to the best of the natural fibres, such 
as cotton, although the polyvinyl alcohol fibres arc better. 
These fibres, such as the polyacrylonitrile (Orion, Dralon 
and PAN) and especially the unchlorinated polyvinyl chloride 
(Rhovyl, PCU and probably the new Japanese fibre Teviron) 
have the highest resistance to weathering. 

Resistance to abrasion is very important but we do not 
know exactly the abrasion resistance of nets made of different 
types of fibres. Test methods never give absolute values, 
but only relative ones. They are in a high degree dependent 
on the method employed. 

A few papers give examples for assessing the abrasion 
resistance. Shimozaki has chafed twined across an oil stone 
and a figure shows that the resistance of non-treated twines 
increases in the following order: Saran, Krchalon, Teviron, 
Cotton, Kyokurin (a mixed twine made of Amilan and Saran), 
Kuralon and polyamide Amilan. In tests made by Imperial 
Chemical Industries Ltd. twines were abrazed over a hardened 
carbide steel bar. The abrasion resistance of Terylene twines 
was superior to that of cotton and flax, but less than that of 
nylon twines. There is a good conformity between these data 
and those of Klust. Examples of the wet abrasion resistance 
of Perlon filament tissue in comparison with those of hemp and 



manila are to be found in the Perlon- Warenzeichenverband 
paper. 

It seems certain that the polyamides have an especially high 
abrasion resistance, not equalled by any other fibre. The 
durability of fishing gear made of such fibres, such as trawl 
nets, is probably primarily due to their abrasion resistance. 

What types of fishing gear ought to be made of fibre of the 
highest strength? First, those subjected to the heaviest stress 
and strain, such as trawl nets, cxpecially those used by large 
fishing boats. But it is also profitable to use strong fibres for 
fine gillnets. The stronger the fibre the finer the twine and the 
finer the twine the greater the quantity of fish caught. 

The test records given in the papers show that two types of 
synthetic fibres arc superior to others; polyamide and poly- 
ester. But here we have to distinguish between fibres of normal 
or ordinary tenacity and fibres of high tenacity. The factor 
which determines the strength of synthetic fibres is the degree 
to which they have been drawn out during manufacture. A 
high degree of drawing cr pre-stretching results in a consider- 
able increase in tensile strength, which is connected with a 
reduced breaking extension. But high tenacity leads to loss in 
lateral strength. It is important to know the decrease in 
strength caused by knotting and by high tenacity. Tests of 
knot strength arc much more significant than those of the 
straight twine. In this connection it is interesting to note 
the physical properties of twines in Japanese knotless nets. 

Twine and knot strengths of polyamide fibres arc dependent 
on the degree of stretching, not on the type of fibre. In principle 
nylon and Perlon, for example, do not differ in strength when 
they are made with the same degree of drawing. (Thai may 
be seen in the paper by Arzano). Can-others has tested twines 
of nylon 66 and nylon 6 or Perlon. The twine made of the 
latter was found to be about 40 per cent, weaker than nylon 66 
of the same weight, but the two twines reacted differently to 
knotting. The mesh of nylon 6 or Perlon was only about 
20 per cent, weaker than the mesh of nylon 66 and not 40 
per cent, weaker as in the case of the twine. Carrothers 
has not, 1 think, compared twines with the same degree of 
tenacity, but a twine made of a highly drawn nylon with a 
twine made of normal Perlon. Lonsdale has found that every 
type of knot has a different knotting efficiency. A decrease in 
the angle through which the loop is formed weakens the 
strength. If the number of loops in a knot increases, the knot 
strength increases too. 

As Carrothers states, tensile strength is often adopted as 
the only measure of quality because it can be measured 
relatively easily. But it is important, too, that the material is 
able to absorb kinetic energy. The degree of extension 
(elastic and permanent) is sometimes of the same or of a 
greater importance than tensile strength. Statements of 
breaking extension of the twine, mostly given by manu- 
facturers, do not provide possibilities of evaluation. In 
synthetic nets, the meshes of which are formed by knots, 
knot-strength reaches only about 50 to 60 per cent, of the 
breaking load. Breaking extension of twines made of different 
fibres may be similar, but the shape of the load-extension 
curves may be different. This can be of great importance to the 
behaviour of the twine under working conditions. Van 
Wijngaarden proposes to determine extension under lower 
load, for example, extension at 25 per cent, of the breaking 
load. 

Net twine has a great capacity for working if total and 
elastic extensions are great. It will be able to absorb kinetic 
energy and will stand shock loads better than twine of lower 



[94] 



DISCUSSION: PROPERTIES AND TESTING OF TWINES 



extensibility. The demands on net materials differ very much 
between different types of gear, but for all gear it is advan- 
tageous to use fibres of high tensile strength. On the other 
hand, one type of gear may require a low extension while 
another may require a higher extension. It is always an 
advantage for a fibre to possess a high degree of elasticity 
which guarantees a good consistency of mesh size. There is 
no ideal fibre for fishing gear, but the various types of syn- 
thetic fibres each having different properties, provide a range 
of choice from which to select the best for each type of gear. 
So we can say with Amano "Modern fishing means the use of 
synthetic fibre nets". 

Mr. J. E. Lonsdale (U.K.). One problem before synthetic 
fibre makers is to determine the exact properties required in a 
fishing net fibre and on this point fibre producers can learn 
a great deal from the fishermen and from the fisheries 
technologists. As synthetic fibres are man-made, they can be 
tailored to produce the required properties but until the 
manufacturers know what the fishermen want, they cannot 
produce the best possible fibre. Even for a material such as 
nylon, which has been in existence for some twenty years, 
there is great room for exact assessment of the properties 
required by the fishermen. One major complication is to 
differentiate between the properties required in different 
types of fishing and different types of nets in different parts 
of the world. 

There has so far been no real attempt to try to rationuli/c 
these properties but once this has been done, and an attempt 
is made to find out exactly what the fishermen want, advances 
will be made in the properties of man-made fibres. 

Dr. Avon Brandt (Germany) (Chairman). The polyester and 
polyamide fibres arc used mainly in Europe and in America. 
The group of polyvinyl alcohol fibres is most important in 
Japan. 

Mr. P. J. G. Carrothers (Canada). The results of my tests 
on Manryo were published in the Progress Report of the 
Fisheries Research Board of Canada, and copies may be 
obtained from the Vancouver Technological Station. 

Manryo twine is similar to cotton in general appearance. 
Generally speaking, we found the properties of the new 
Manryo (dry twine) to be considerably better than cotton, 
hut when knotted and wetted, the properties of both twines 
were similar. 

So many of the tests have been on (he dry twine, but wet 
mesh and wet knot tests are of far greater importance than a 
straight, dry twine test. 

1 would also like to say a word about the need for standard- 
ization of tst procedures. So far, these have been primarily 
developed from the manufacturers' point of view, but nets 
are used to catch fish, so the test methods are better designed 
from the fisherman's rather than from the manufacturers' 
point of view. Pertinent properties which relate to the fishing 
function should be measured, such as handling characteristics, 
the wet mesh strength, probably also toughness, etc. 

Test procedures in most countries are fairly well standardized 
up to the stage of the dry twine, i.e., the ASTM in the States. 
Could not this Congress try to encourage some of these 
groups to consider also standard tests for netting? Many of 
the methods available have been developed solely for research 
purposes. There is a need to develop these methods further so 
that they can also be used for routine control purpose*. It 
would then be possible for netting manufacturers to state 



how strong their netting is without fear of, say, a government 
laboratory or standards laboratory testing the netting by 
another procedure, and saying that the nets are not what they 
are claimed to be. 

Mr. B. F. Wolmarans (Union of South Africa). About 2 
years ago, the first blend of Japanese synthetic netting was 
put into use in South Africa. We find this is vastly superior 
to straightforward synthetics. Other types have been imported 
from U.K., Germany and Holland, but we find Marlon very 
much rftorc resistant to the peculiar water and weather 
conditions we have in South West Africa. Firstly, nets 
manufactured of this material are reputed to sink very much 
faster; they are abrasion-resistant to a very great degree. The 
price factor also comes into consideration. After much 
experimentation our industry has concentrated on Marlon 
particularly in the Walvis Bay area where conditions are very 
bad. Kuralon is unsatisfactory, although it has been put into 
use in the areas further south where the water is clearer and 
where damage is not so noticeable. 

Mr. R. S. Rack (Northern Rhodesia). A very few years 
ago our local fishermen were taking motor car tyres to pieces, 
in order to get threads for their fishing nets. Subsequently they 
have come to use nylon, which has superseded cotton. They 
are very simple people; they know cotton and nylon; it might 
be a blow to their vanity if I say they know very little of any 
other. In fact, I believe that if I were to say "this is not nylon, 
this is Marlon", they would say "yes, you mean Marlon- 
nylon." There is a danger in this wide use of trade names which 
are being interpreted as common names. A worthless fishing 
twine may be sold under a high sounding name. I would 
therefore suggest that the trade name always be accompanied 
by a specification of performance. I would also suggest that 
the testing methods be brought under two headings: Practical 
forms of test which could be carried out on behalf of the 
fishermen to ensure that the nets sold are adequate, and more 
exhaustive tests which could be carried out for the satisfaction 
of the industry. 

Could not this matter be referred to the various standard 
institutions who, in cooperation with users and manu- 
facturers, might be able to provide tests of this nature? 

With regard to the value of synthetic fibres under tropical 
conditions in my part of the world we use practically all 
nylon. Our primary aim is to reduce the cost as much as 
possible. Many of our fishermen make their own nets, and 
therefore a nylon which is non-slipping and which could be 
knotted with a single knot, would be of great advantage. 
Abrasion is also a problem. However, the physical character- 
istics are not so vitally important to us. When 1 tell you that 
we lose a good many nets to crocodiles you will understand 
this point of view! 

Mr. T. D. lies (Nyasaland). I am concerned more with the 
biological side, the fisheries research in general, rather than 
with test of net characteristics, but 1 have had an opportunity 
on Lake Nyasa, where we arc investigating a deep water 
gillnet fishery, in comparing cotton, flax and nylon nets. 
Under our local conditions, the physical characteristics of the 
nets such as tensile strength, do not give such a great advan- 
tage as far as the fishermen are concerned. A problem in this 
particular fishery concerns a fresh water crab, which causes 
a great amount of physical damage and, in fact, whereas a 
flax net will give up tc 25 sets, a nylon net may only give up 
to 40, despite the fact that the tensile strength of the nylon is 



[95] 



MODERN FISHING GEAR OF THE WORLD 



very high, far higher than is really needed for the fish that 
are being caught. Such problems, under these conditions at 
least, are far more important than physical characteristics 
of the net. 

Mr. C. P. Halain (Belgian Congo). Nylon fishing twine 
to some extent imposed upon us, owing to difficulties in 
finding fishing twines was first used in the Belgian Congo in 
1943. The fishermen now use nylon almost solely and cotton 
or linen yarn is seldom sold, but we arc still looking for a 
better synthetic fibre. 

Incidentally, some 80,000 to 100,000 tons of river and lake 
fish are marketed in the Congo every year. 

Mr. M. K. Kramer (Israel). We have carried out three 
experiments with synthetic fibres. The first, with trawling, 
was unsuccessful, and we are now waiting for other and 
better fibres. Good results were obtained, however, with the 
fibre net in Lake Tiberias. It was found that a white fibre 
net doubled catches and these were tripled last year by using a 
red fibre net. Today there is not one gillnet in the Lake which 
is not of synthetic fibre. 

We have now begun experiments for the change-over of sea 
purse-seine nets. We have begun by using fibres from various 
countries three kinds from Germany, two from the U.K., 
and two from Japan. In 1958 we hope to experiment with 
Italian fibres also, and so arrive at some final result. 

Dr. W. Einsele (Austria). Monofilament nets have 
revolutionized our fisheries. There is very little plankton in 
our lakes and the light penetrates very deeply. Catches were 
exceedingly low, especially in the summer, not because there 
were no fish but because we were unable to catch them. This 
has changed entirely since the introduction of monofil nets 
and this summer, for the first time, enough fish has been 
caught to supply the hotels, restaurants and villages in the 
Lake region. 

Mr. E. F. Gundry (U.K.). There is a tendency, especially 
at the government fishery officer level, to assume that man- 
made fibres make the best nets to have. The biggest production 
of nets today is still from the orthodox vegetable fibres, and 
therefore the advantages of the "old-fashioned" material 
must not be overlooked. The great advantage of sisal or cotton 
over other fibres, is their lower cost, and, in an industry such 
as fishing, which is having economic difficulties, the lower the 
cost of the nets, the more attractive they are. The advantages 
of the man-made fibre will increase as their price decrease. 
Another characteristic of cctton nets is in the extensibility 
of the material. Herring constitutes a very big part of the 
fishing catch both for man and for animal feeding stuff, and 
there are many types of herring nets and herring gillncts. The 
man-made fibre herring gillncts are not entirely successful, 
the fish becoming so deeply enmeshed, that ths catch can 
be extracted only with a great amount of labour and the fish 
often being damaged. Also in the trawler field the advantages 
of synthetic nets are not so apparent, because the physical 
conditions under which the net is operated do not permit 
it to last as long as their qualities might promise. The rock or 
the wreck on the bottom of the sea is capable of tearing and 
pulling loose an expensive synthetic net as easily as the one 
made of the less expensive natural fibre. It would be a mistake 
to think that there is no future for the orthodox vegetable fibre 
materials and those in authority and responsible for advising 
fishermen should inform them that good service can be 



obtained from the vegetable fibres as long as the nets are 
kept clean and maintenance is good. 

Dr. J. Reuter (Holland). When a fisherman has to make his 
choice of material, the more figures he sees the less able he is 
to make his choice. This information about testing was 
started by scientists. Fishermen are not scientifically trained, 
so we should adopt test methods that are scientifically correct 
and at the same time be easily understood by the fishermen. 
Take for example the breaking strength of twine; every textile 
man has this as his main goal, because the stronger the twine 
the better it is, but he forgets that the fisherman tests his net 
wet by pulling on the mesh and not the straight twine. There 
are fibres that are strong in the dry condition but become 
weak when they are wet and knotted. 

Messrs. G. A. Hayhurst and A. Robinson (U.K.) in a 
written statement: When checking twines for breaking 
strength and extension it is essential to avoid distorting them. 
If simply secured between two grips there may be a severe 
bend in the twine which, when subjected to the test force, 
will cause a stress concentration and give a most unreliable 
result. It is therefore recommended that quarter-circle 
bollards be used to lead the twine to the grip, as shown in the 
sketch. 




When checking extension under load, the test sample must 
be prc-tcnsioned to a slight but known extent. We always 
make such measurements at 1 per cent, of breaking stress. 

Mr. E. A. Nilssen (Norway). Synthetic fibres were intro- 
duced about three years ago in Norway. 1 think that at 
present only synthetic fibres are used for the gillnets. Such 
nets bring in bigger catches, they are stronger, easier to 
handle, lighter, need not be dried and need no preservation. 
The fishermen in Norway use sisal and manila for the 
mounting, but they would also prefer synthetics in the 
mounting as they could then just leave the nets without any 
drying. We are now trying to find the right material for these 
mounting lines. We have tried monofilament nets, but without 
much success. This is rather astonishing, when one thinks of 
Sweden, where they arc using so many of these nets. As 
for the breaking strength, we use single-knot and double-knot 
nets. The double-knot nets were the best at the beginning 
because there was no knot slippage, but the single-knot nets 
have improved much in the last two years. The double-knot 



[961 



DISCUSSION: PROPERTIES AND TESTING OF TWINES 



nets give somewhat higher strength. In Norway there is a 
State import monopoly for nets and raw materials; the 
Government also uses test machines. As most Norwegian 
manufacturers send the nets, the twine, etc. to this laboratory, 
tests are therefore uniform. The most important test is that 
of the knot strength. The fishermen normally pull the net 
in a wet and in a dry condition, we must find a twine that 
gives good results in both conditions. Synthetic fibre has 
also been tried for the big purse seines (about 180 fathoms 
long) in Norway. This has resulted in an increasing demand 
for the nets. As soon as the price of synthetic fibres comes down 
more or less to the level of cotton and hemp, it is possible 
that only synthetic fibres will be used. 

Mr. R. Ocran (Ghana). In Ghana, we are trying to develop 
line fishing. We catch heavy fish and the breaking strength of 
cotton and hemp cord is not strong enough. How can synthetic 
fibre be applied to line fishing? 

Dr. H. A. Thomas (U.K.). Some of the first trials with 
Courlcne (a polyethylene material) were in fact with line 
fishing using a large number of snoods in the Irish Sea from 
Fleet wood, and remarkable catches were achieved. The 
fishermen spoke very highly of the knot strength at the point 
where the hooks were running out on the snood from the 
main line. Some purse seine nets of this yarn were then 
produced, in cooperation with the Flectwood fishermen. It 
was found that the knot with the polyethylene yarn Courlcne 
did not have to be heat-scaled; if they were tied with the 
right technique, they obtained satisfactory results. We have a 
large number of individual reports on these fishing trials, 
which we shall be pleased to give in detail to anyone who is 
interested. 

It has not been possible at this Conference to include a 
full-si/e paper dealing with materials suitable for protective 
clothing for fishermen. 1 would, however, suggest that 
perhaps at another Conference it might be possible to include 
one session on the clothing and protective equipment. 

The last pages in Dr. Arzano's paper give some details of 
the use of man-made fibres in protective equipment. There is 
a development which started in Norway, namely the string 
vest. The object of this vest is to maintain a layer of air next 
to the skin to prevent clothing from becoming moist from 
perspiration, this also being a very good heat insulant and 
thereby adding to the warmth of the body. The older esta- 
blished man-made fibres (blend or a mixture of viscose 
staple and acetate staple) can be used for the string vest. To 
maintain the warmth of the feet it is of advantage to have an 
insole or interlining between the feet and the rubber boot or 
the gumboot. For gloves, blends of viscose staple with nylon 
staple and with wool seem to achieve the best results. Viscose- 
staple and filament coated with polyvinylchloride or with 
linseed oil and rubber are used for such things as aprons, 
gumboots, overcoats and sou'westers. 

Mr. A. Robinson (U.K.). We have some experience with long- 
line fishing and particularly with snoods of nylon yarn. These 
have been found to be very successful indeed in various respects, 
not only as to durability but also for increasing the catch. 

Where the speed of replacing snoods is of great importance, 
nylon snoods have been particularly advantageous. Very few 
snoods indeed have broken when the fish has been ripped 
from the hook, and very little time has been lost in repairs. 
The line itself is usually made of staple nylon in order that 
the snoods can be attached to it securely and do not slide on 



the line. The life of the staple nylon longline is very good but, 
of course, the price is high. 

Mr. S. Springer (United States of America). In the Gulf 
of Mexico longline tuna fishery, we have been making use of 
synthetic lines both mainlines and branch lines. Here, the 
advantage of the synthetic fibre is in its great strength- 
possibly double that of the natural fibre lines. The nylon line 
that has been most successful in this fishery- is a heat-stabilized 
line, which has less tendency to twist. 

Mr. K. J. Westrop (U.K.). There is a need for standard- 
ization of testing methods. Different methods lead to different 
actual figures, which do however serve usefully for purely 
relative testing of the fibres. For instance, the abrasing 
resistance described by Dr. Klust shows the superiority of the 
polyamidc and the polyester fibres over the natural fibres, 
though just what these relative figures would mean when 
you are concerned with the actual nets, of course, is another 
story. As yarn producers, we can evaluate our yarn as a 
textile material, but the fisherman himself must obviously 
be the man to decide what is required of a net. A practical 
trial, to be valid, must be made with many nets to cover the 
whole range of different types and the different conditions 
under which the nets are used. 

Presumably something will come out of the Congress and 
these discussions as to what should be done about surveying 
such testing methods. 1 would like to add that the Imperial 
Chemical Industries could probably contribute to any future 
conference if a paper of this sort is required. 

Dr. A. von Brandt (Germany). I would propose that, in 
addition to the Working Party on Terminology and Number- 
ing Systems, we form a Working Party on Testing Methods*, 
and that the following gentlemen be appointed as members: 
Mr. Reutcr (Netherlands); Mr. Carrothers (Canada); Mr. 
Takayama (Japan); Mr. Percier (France). The standardization 
of testing methods should be considered from the fisherman's 
point of view, and not from that of the textile industry. 

Dr. G. Klust (Germany) Rapporteur. I should like to give a 
brief summary of what has been said during the discussion. 
Synthetic fibres have given good results from northern waters 
to the tropics. For instance, in the Belgian Congo, the inland 
fishermen almost exclusively fish with nylon nets. Several 
speakers stressed the extremely good results that had been 
obtained with monofilament nets. Mr. Gundry defended 
natural fibres, especially cotton which still is being used 
extensively in the fishing industry, the lower price being a vcr\ 
important factor. 

The necessity of uniformity in methods of testing net 
materials has been stressed. These test methods, it was pointed 
out, must be brought into relation with experience gained in 
practical fishing. A close relationship between the manu- 
facturers of synthetic fibres and the fishing industry could give 
extraordinarily good results, because synthetic fibres could 
be produced in such a way as to meet the requirements of the 
consumers. 

If the manufacturers know the requirements of the fishing 
industry they are in a better position to manufacture what is 
actually wanted. 



* Editor's note. This Working Party has been active since the 
Congress. Under Dr. von Brandt's leadership, considerable 
progress has been made towards reaching an agreement on uniform 
standard testing methods. \ Sec preliminary report on pages <>8and99. , 



[97] 



REPORT OF THE WORKING GROUPS ON "TERMINOLOGY AND 
NUMBERING SYSTEMS" AND "TESTING THE PROPERTIES 

OF TWINES" 



Prof, von Brandt (Germany)*: The two working parties 
have met and started to deal with the problem of standard- 
ization. Due to the little spare time left by the packed 
programme of the Congress, no definite results can be expected 
yet. The difficulties which such an attempt of standardization 
meets have been discussed and are well known by everybody 
working in this field. The quality of twines for the fishery 
or particularly the standardization of their denotation depends 
not only on the basic material which is presently often 
camouflaged under a big number of trade names, and the 
manufacture of this material into fibres but also on the 
way how the fibres are processed to the twine. The final 
goal of the Working Party for Standardization of the Num- 
bering System dealing with these questions is to find out 
and establish a simple and unmistakable system for defining 
the twines used in fishery. This system is meant to enable 
the fishermen all over the world to know what really is 
offered to them and what will best suit their purpose when 
substituting one twine or material for another. The Working 
Group consists of fibre producers, twine makers and net 
makers. Mr. J. E. Lonsdale, U.K., has been appointed 
chairman. After having discussed the matter repeated I \ 
also with many people at this Congress, the present situation 
is characterized as follows: 

1. The presently used numbering systems are too com- 
plicated and too confusing for use in the fishery. 

2. The numbering complications are caused mainly b> 
the twine and net makers who often create own systems. 

3. It is necessary for the fishing industry to use always 
a common numbering system at least in addition to 
the national or manufacturers' systems. Tt may in 
time replace those. 

4. As basic units for this common system cither Denier 
or Tex are suggested. The former is a non-decimal 
unit generally used in the textile industry and already 
introduced to a certain extent into the fishery. The 
latter one is a newer decimal system which is strong!} 
recommended for international use. 

The Working Party, having accepted English as working 
language, is undertaking to survey the numbering systems 
currently used throughout the world for fisheries purposes, 
devise methods of unification and make recommendations. 
In addition to the inquiries to be made to this effect, everybody 
who wishes to bring his view to the attention of this Working 
Party is requested to write to Mr. J. E. Lonsdale of the 
British Nylon Spinners, Ltd., Pontypool, England. 



* Editor's M?/r.--This report was given on the last day of the 
Congress. 



It is the intention of this Working Party, while endea\ourmg 
to bring order in the systems of counts and numbering, 
to take into account what has been customary in the fishing 
industry as to date, and the specific demands of this industry 
The future count system, therefore, should at the same time 
indicate the main qualities important for the various fishing 
purposes. The following list of twine and net qualities has 
been set up and may be useful as a base for discussion 

(a) tensile strength 

(b) knot strength 

(c) knot slippage 

(d) mesh si/e 

(e) permanent elongation 
(0 elastic extension 

(g) softness 

(h) resistance to abrasion 

( i ) weight 

(j) water absorption 

(k) resistance to rotting 

(I) resistance to weathering 

(m) resistance to chemicals 

If applicable, these qualities should be tested in v\et con- 
ditions. For nets the knot strength of the twine is of more 
importance than the unknottcd tensile strength. The mesh 
si/e often has to be considered in regard to economic and 
biological problems as marketing and overfishing. The 
permanent elongation may be of significance for the propei 
mesh si/e. Elastic extension or elast icily may be very effec- 
tive when dealing with shock loads. Softness comes in 
particularly with gillncts. Abrasion may be caused in 
different ways during handling or when towing a trawl net 
over the sea bed. The weight is always considered as the 
weight in water not only for easy handling but also in regard 
to operation performance for instance in bottom trav\K 
when a good and continuous contact with the bottom is 
wanted or in purse seining where the sinking speed can be 
of great importance. Water absorption has an obvious 
relation to these weight problems. Resistance to rotting 
is such a general problem in fisheries that no further comments 
are needed. Resistance to weathering is of particular impor- 
tance in tropical areas with bright sunlight. The means of 
improving the insufficient resistance to weathering of certain 
synthetic materials have been discussed. They lead to the 
question of resistance to chemicals of which the different 
dying materials consist. 

The proper selection of the optimal material for the fishing 
purpose in question is strongly affected by the mutual inter- 
ference between these qualities. With a stronger material, 
for instance, the twine diameter can be reduced saving 



[98] 



RHPORT OF WORKING GROUPS 



twine, and towing or current resistance. But, with thinner 
material there might be more abrasion or, in giilnetting, the 
fish might be damaged, or it might be inconvenient to handle. 
The choice, therefore, must be based on the main qualities 
required tor the particular purpose. This working party 
has been limited to manufacturers of twine and webbing 
because they are closest to the practical fishermen. 

It is the intention to submit the information compiled 
and the conclusions drawn in the form of a report to FAO next 
vear. FAO will then distribute this report to all people 
interested in this matter. The collaboration which is hoped 
to be created hereby, and the comments and discussions 
resulting, are expected to finally result in terms and a system 
of numbering and defining twine and net qualities which 
is acceptable and most suitable for all concerned with the 
fishing industry. 

To be comparable, the qualities listed above must, of 
course, not only have uniform units but must also be deter- 
mined in a uniform way. The standardization of the testing 
methods is the subject of the second working party having 
heen established at the beginning of this Congress. These 
methods also must apply to the demands of the fishing 
mdustry rather than to the textile industry, which mainly 
is concerned with clothing, stockings, etc. In the short 
lime available this working party has prepared the following 
>hort report. 

"The working group was formed to find a common 
agreement on test methods which will be adapted to 
test material under similar conditions as it is used in 
practice. The group has appointed Prof. A. von Brandt 
as Chairman. The various testing methods \\ere dis- 



cussed and a preliminary division agreed upon: 

( 1 ) Test methods outside the scope of the working group, 
such as determination of the specific gravity of fibres, 
etc. which are not entirely adapted to fishing con- 
ditions but absolutely necessary for manufacture and 
research. 

(2) Test methods which have already been accepted and 
standardised nationa I ly or internat tonally, as for instance 
French elongation test etc. These test methods are 
also not entirely adapted to fishing conditions but 
absolutely necessary. 

(3) Test methods of particular interest for fishery pur- 
poses on which a common agreement has still to be 
found for instance, sinking speed of the net, visibility 
in the water, mesh knot and mesh breaking strength etc. 
The last group of test methods will be the main task 
of the working group. Prof. A. von Brandt will write 
to people interested in the subject who he thinks can 
contribute to the unification of this subject. He will 
be glad to receive contributions from any participant 
to the present Congress. A full report will be written 
next year." 

The working party has decided to compile the existing 
results of tests, discuss and evaluate them, after which a 
programme of work will be set up. Testing results often 
depend on the type of test carried out, and we must determine 
how we can work in agreement since so many people through- 
out the world are carrying out tests, there is need for some 
unity in this field. FAO has also emphasized to the different 
governments that they should help in this matter. 




The 883 tons distant-water trawler Portia of HulL Her diesel-electric engines, which can be controlled directly from 

the bridge, give her a speed of nearly 16 knots. 

[991 



Section 3 : Net Making. 

PRACTICAL CONSIDERATIONS OF THE USE OF SYNTHETIC 

FIBRES IN TWINES AND NETS 

by 
G. A. HAYHURST and A. ROBINSON 

William Kenyon and Sons Ltd., Dukinfield, Cheshire, U.K. 

Abstract 

From the l wine-maker's poinl of view ihe characteristics of synthetic fibres are discussed and a comparison made of the results 
obtained from nylon nets with those from cotton nets. The heat-setting of nylon twine is discussed, and also the question of the use of 
bonded twines for single knot nets. Brief notes are given on testing methods for twines. 



Ktaime 



Considerations pratiques sur ('utilisation dcs fibres synthctiques dans les His et filets 



Cettc etude est ecritc du point de vue du fabricant de fil de peche. Les aiiteurs examinent les caractcristiqucs des fibres synihctiqucs 
et comparent les resultats obtenus avec des filets dc nylon et des filets de colon. La stabilisation a chaud du fil de nylon est etudice ainsi quc 
la question de 1'cmploi de fils impregnes pour les filets a noeuds simples. L.es methodes d'essai des fils sont exposees brievement. 

Consideraciones practicas sobre el uso de fibras sinteticas en los hilos y redes de pesca 

Extracto 

Desde el punto de vista del fabricante de hilos se analizan y comparan los resultados obtcnidos con redes dc nylon y de algod6n. 
Tambien se consideran el tratamiento termico de los hilos de nylon para dismmuir el resbalamiento de los nudes y el problema de la fijaci6n 
de los hilos en redes de nudos simples. El trabajo tambicn contiene breves descripcioncs de los metodos usados en los ensayos dc los hilos 



CONTINUOUS filament yarns of nylon and 
Terylene are extremely "lively" when twisted so 
that when twine is cut the yarns promptly untwist. 
Heat setting of the twine during manufacture reduces this 
liveliness by altering the linear molecular structure of 
the fibre. If this process is carried out when the twine is in 
relaxed state contraction takes place, and influences the 
length/weight ratio and the extensibility. The extent of 
the contraction depends upon the temperature and time 
the twine is heated. The nylon and Terylene twines are 
treated at or below 100 deg. C. for up to 10 minutes. 

If the twine is permitted to contract during this process 
a greater length will be necessary to make any particular 
specification of net and the raw material cost is therefore 
increased. The elasticity of the twine is affected and if it 
were allowed to contract during the heat setting process, 
extension under load would be increased; much depends 
on the temperature and time. For this reason the Kenlon 
brand twines are heat-set by methods, devised and 
developed within the Organization and contraction 
during heat-setting is avoided so that the length/weight 
ratio is improved. These twines show about 18 per cent, 
up to 25 per cent, extension at break whereas twines 
which have been heat-set in a relaxed state show about 
21 per cent, up to 30 per cent, extension at break. The 
difference in length/weight ratio may be anything from 
5 per cent, up to 10 per cent, in the case of nylon 66 
of 210 denier. 



IMPREGNATION 

The low coefficient of friction against itself caused some 
difficulty when synthetic fibre nets were first introduced 
and necessitated the use of double knots to prevent knot 
slippage. If suitable impregnating materials and methods 
are employed, it is possible to increase the coefficient of 
friction so that secure single knots may be achieved with 
both machine-made or hand-made nets. It goes without 
saying that coating of the twine with materials which are 
incompatible with nylon or Terylene does not give 
satisfactory results. Reasonable resistance to flaking oft 
during rubbing or surface abrasion and rapid leaching 
out in water are two of the points to be considered in this 
respect. 



KNOTS 

Where double knots are made, satisfactory results ma> 
be obtained with thermoset type twines, but where single 
knots arc made it is advisable to use bonded type twines. 
In either case heat setting of the net is usual and this 
must be done at a temperature higher than that used for 
the heat setting of the twine. It is therefore an advantage 
if the twine is heat set at a temperature less than 100 deg. 
C., so that boiling water or low pressure steam may be 
used for heat setting the net. Where possible, the net 
should be kept on tension during heat setting, otherwise 



100 



HEAT-SETTING 

some contraction will take place, thus affecting mesh size. 
To further avoid knot slippage the net can be im- 
pregnated with suitable materials. When nets are so 
treated with a recent development of our own it is 
practically impossible to move the knot in any way, 
under any conditions, wet or dry. 

SHRINKAGE IN WATER 

Where an exact match of mesh size is required a check 
should be made when both natural fibre and synthetic 
fibre nets are saturated in water. This is necessary because 
of the different water absorption characteristics. 



AND BONDING 
ROPES 

From the remarks above regarding rot-proofing, it 
will be obvious that, in order to gain the maximum 
advantage, synthetic fibre mounting ropes should be 
used where possible. It is sometimes found that ropes 
made from staple fibre yarns (instead of continuous 
filament yarns) are the most suitable as this avoids 
any possibility of the tying cords gliding on the head 
rope. On the other hand, ropes made from continuous 
filament yarn are much stronger and this consideration 
may have a bearing on the size of rope required and 
therefore on the cost. 



ro-rr*^.^ .. :.-^^,^. -_- ./,.. 
^_... .:- - ; ,v;* ^ - - ,. 

^'^^'^ ---.. '^v^ 



^;^^ 4 '^^.^;'- , , 
l**^ 3 ^^^^^-^ -:'t - r .,- 
S* -5?^.- . ^%-^X/^^ , ^ 



??-*s^:^a^T.^:.- 




Washing fishing nets in Pakistan. 

1 101 j 



Photo FAO 



SOME CONSIDERATIONS ON NETMAKING 

by 

P. A. LUSYNE 

Technology Branch, FAO Fisheries Division 



Abstract 

When designing a new net the netmaker endeavours to obtain the largest catching potential for the smallest cost in material and the 
least power output. He has to take into account many factors whose effect only become apparent when the gear is in action, a condition he 
cannot observe and has to guess at. In most cases, however, they produce deformation of meshes in the netting or leave other signs which 
become apparent during operation or when the net has been used for some time. The stress-strain reaction in webbing is dealt with and it is 
pointed out that very often a stress can be neutralised by adjusting the hanging at the stress point. The effect on the net of hanging co- 
efficients, webbing joints and tailoring are also discussed. 



Resume 



Quelques Considerations sur la Fabrication des filets 



Quand il dessine un nouveau filet, le fabricant de filets s'eflbrcc d'obtenir la plus grandc puissance de capture pour Ic coin le plus 
bas de matidre et la moindre puissance mise en jeu. 11 doit tenir compte de beaucoup de facteurs dont les effets se manifestent seulement 
quand Tengin est en action, une condition qu'il ne peut pas observer et qu'ij faut qu'il suppose. Cependant, il sc produit des deformations 
des mailles dans le filet qui a etc utilise pendant quelque temps. L'auteur traite de la reaction 1'effort dc tension dans le filet et il fait ressortir 
que tres souvent un effort peut etre neutralist en ajustant le montage au point soumis I'effbrt. II examine aussi reflet sur le filet des co- 
cffcients de montage, des assemblages des parties et de la coupe. 



Consideraciones sobre la Fabrication de redes 
Exfraeto 

Al proyectar una nueva red el fabricante trata de darle el mayor potencial de pesca posible con el menor costo dc material y el 
consumo de fuerza motriz mas pequefto. Ha de tomar en consideracibn muchos factorcs cuyo efecto no se hace evidente hasta que el arte 
esta en funcionamiento, situaci6n que, por no poder observarla, ha de tratar de adivinarla. Pero en la mayoria de los casos esos factores 
causan deformaciones de las ma lias de los panos o dejan otras senales que s61o se hacen evidentes cuando el arte esta trabajando o cuando 
se ha usado la red durante aigun tiempo. Trata el autor de la reaccibn a la tensi6n y tracci6n a que esta sometida la red y subraya que, con 
mucha frecuencia, una tensibn puede neutralizarse ajustando el montaje en el punto donde ocurre. Menciona tambien el efecto que el co- 
cfkiente de colgadura, las costuras de los panos y la manera de cortarlos ejercen en el arte. 



A FEW decades ago the construction of fishing 
nets, from the braiding of the webbing to the 
assembly of the whole gear was the task of the 
fishermen themselves. The boat owner was only interested 
in the cost and, in many cases, the fishermen had to 
help pay for the gear or even owned a part of it. In 
the driftnet and line fisheries, for instance, each fisherman 
owned a certain number of the nets that went to make 
up the set. The cost of materials was high in relation 
to earnings from the catch and very often more con- 
sideration was given to the price and durability of the 
material than to its catchability and efficiency as a part 
of the gear. 

The operating range of the vessels was small and the 
nets used were largely the same for each home port 
as the gear was adjusted to the fishing conditions pre- 
vailing on the grounds within reach of that port. Large 
differences were, however, to be noted between different 
fishing areas, in boats, in gear and even in the type 
of operation. 

The use of larger vessels, engine power and better 
material has brought many changes; fishing gear is 



now constructed to give a high degree of efficiency in 
a certain fishing method over a much greater range of 
grounds. Higher speeds of operation, with resulting 
higher strains on the nets, and the use of new materials 
and improved methods of netmaking, have brought 
changes to net manufacture. While the cost of material 
in relation to returns from the catch has decreased, 
the cost of labour has increased and the new non- 
rotting fibres have made preservative treatment practic- 
ally unnecessary, so that the conditions governing the 
cost of fishing gear are now totally different. Today the 
nets are increasingly planned and constructed ashore 
and the fishermen are relying more and more on the 
netmaker to make and improve his gear. 

Although some observations of gear in action have 
been made by frogmen and results are being obtained 
by underwater television, the netmaker himself does 
not normally see how the net he has made, functions. 
He still has to evaluate the performance of the net by 
interpreting various telltale signs which are only apparent 
when the net is back on board, such as localized tighten- 
ing of knots, deformation of meshes, gilling offish, wear 



[102] 



NETMAKING 



on knots, etc. Many of these signs only become apparent 
after some time so that the fisherman must still, as of 
old, keep his gear under close observation. His criticisms 
and suggestions, based on such observations, are of the 
greatest help to the netmaker. 

GENERAL 

When making a new design, the aim of the netmaker 
is to produce a net which will give the largest catching 
potential for the smallest cost in materials and the least 
energy output. Depending on the type of gear, many 
different factors have to be taken into account, such 
as resilience of webbing, strength and elasticity, resistance 
to flow of water, weight and bulk, speed of operation, 
cost of materials, condition of fishing ground, etc. 
However, in most cases, the most important factor is 
ihe shape the completed net will take when in action, 

Gillnets and trammel nets need no fashioning as their 
shape in operation is determined by the looseness given 
to the webbing when it is hung between the float- and 
leadlines. This not only determines the opening of the 
meshes but also the resilience and the bulge the webbing 
can take during certain types of operation. The amount 
of resilience given to these nets differs according to the 
type of operation, the net height and fish species to be 
caught. It is regulated by the amount of, and relation, 
between, the buoyancy and weight of floats and sinkers. 

A certain amount of shaping is necessary during the 
construction of roundhaul nets to give the webbing 
its bulge during operation and to take up the various 
strains on the webbing during shooting and hauling. 
This is achieved partly by using the appropriate hang-in 
coefficient but mainly by adjustment of take-up and/or 
tuck-in between the strips of webbing that go to compose 
the complete net. With trawl nets and other types of 
bagnets, the netmaker has to tailor the webbing to make 
individual net sections fit the curve of the lines to which 
they are hung and to obtain the required bagshape. 
The problem here is made more difficult by the fact that 
in some cases the operational conditions are liable to 
change; variation in resistance, or drag due to change 
in the flow of water through the net, influence the 
performance of the whole gear. Points and direction 
of forces acting on the net may change, with a resulting 
change in the shape of the net in operation. 

The strains on the net must be spread as evenly as 
possible and, in general, should be across the knots. 
The twine must everywhere be strong enough to withstand 
the strains acting upon it, yet, on the other hand, its 
weight, resistance to flow of water and cost have to be 
taken into account. 

In the case of gillnets, the mesh size must be appro- 
priate for gilling and/or entangling the particular fish 
species caught; with other nets, it must prevent such 
gilling. When deciding on the mesh size for bagnets, 
the netmaker has to take into consideration, apart from 
the resistance, the water release so as prevent "whirling" 
or backwash within the net. 

Apart from the above considerations, which are 
connected with the catchability of the net, the netmaker 
has to give thought to the handling of the net during 
the shooting and hauling operations. For instance, 
very fine twines may make hauling difficult and too much 



loose webbing may slow down the speed of operation 
as in the case of roundhaul nets. 

There is no such thing as an ideal net. All nets are 
a compromise to fit a certain set or collection of fishing 
conditions; all are subject to controversy, being praised 
by some fishermen and condemned by others. Much 
depends, of course, on how the net is used, both as to 
assembly of the net to other gear parts and the skill 
with which it is operated. A well constructed net may 
give unsatisfactory results because of defective auxiliary 
gear, such as floats and kites, sinkers and anchors, 
trawl boards, etc. All such gear must be of the right 
type and fitted in the correct position; they help the 
net to take its correct shape in operation and are there- 
fore as important as the net itself. The fisherman must 
realize that he can only get maximum efficiency from a 
given net if he uses it under the conditions and in the 
manner for which it was constructed. Finally, much 
can be done to adapt a net to the conditions prevailing, 
if the netmaker is made aware of those conditions. 

STRAINS AND STRESSES 

Although certain studies have been made on the forces 
acting on the webbing of a net, most netmakers still 
use empirical values when planning and constructing 
new nets. There is a complex stress-strain reaction in 
webbing, very much like that in an clastic fabric, i.e. 
it elongates in the direction and at the point of stress, 
while contracting in the lateral direction. In fact, the 
webbing takes up a part of the stress by yielding to it. 

The deformation of webbing due to a stress acting 
on it depends on the position of the stress point in 
relation to the whole net and the magnitude and the 
direction of the stress. Normally the stress acts "across 
the knots" and in that direction a small strain will be 
taken up completely by the partial closing of the meshes 
directly below the point of stress. Larger stresses will 
cause an increased strain reaction along the "halvers" 
until the selvedge is reached. Further increase of strain 
will result in a lateral closing of the webbing section. 

The amount of reaction to a given stress in influenced 
by the hang-in coefficient and the mesh size, increasing 
as these values increase. In general, individual stresses 
cause positive strain reaction in the area of webbing 
enclosed by those halvers which run out from the point 
of stress; the meshes along these lines are opened and 
the knots tend to slip, while directly under the point 
of stress the meshes are closed and elongated. Above 
the "halver" lines, the webbing is loose and the area of 
loose webbing is in proportion to half the area under 
stress. 

When considering the effect of the direction of strains 




light strain full strain 

Fig. 1. Effect of stre.\A on webbing 




103 ] 



MODERN FISHING GEAR OF THE WORLD 



and forces acting on webbing, it can be said that the 
more the strain acts out of the vertical (across the knots), 
the easier the webbing will give to the strain, but the 
more deformation it will cause. The onJy remedy for 
diagonal stresses is the use of tension lines to take up 
the strain. An important fact is that, by proper adjust- 
ment of the hanging in stress points, the stress can be 
neutralized to a certain extent. This is done by allowing 
the meshes to elongate by close hanging at the point 
of stress, thereby spreading the strain. 

For the rational design of fishing nets and, in par- 
ticular, of trawl nets, more accurate knowledge of the 
stress-strain behaviour in webbing is needed to counter- 
act the deformation it causes to the shape of the net and 
weaknesses which arises from it. This could well be a 
subject of practical research at one of the Research 
Institutes. 

Because of this yielding characteristic of webbing it 
is difficult to foresee the actual shape of a new designed 
net. However, to the experienced netmakcr, the con- 
dition of a used net gives much indication on its behaviour 
in operation; the tightening of knots below stress points, 
the swelling of twine in slack parts, the deformation of 
meshes, accumulation of scrap, wear on the knots, 
etc., all help to form a picture of the net's performance 
and its shape in action. 

HANGING OF WEBBING 

The correct hanging of the webbing to the framing or 
supporting lines is an important factor in all nets. At 
present there are two methods in use for expressing the 
hanging coefficient and this causes confusion when 
constructing nets from a plan. The first is to express 
the length of the line, to which the webbing is hung, 
in a percentage of the total stretched webbing: 

length of line 100 

per cent, of hanging 

length of stretched webbing 

The second method is to express the amount of excess 
or loose webbing (total webbing minus line length) 
as a percentage of the total webbing: 

excess webbing ,- 100 

per cent, of hang-in 

total webbing 

Both are reciprocal values, but as the second expression 
gives a direct proportion of the looseness or resilience 
in the net, this would appear to be the most logical 
for expressing the hanging coefficient of nets. Taking 
the stretched mesh as unity, the following table gives the 
theoretical data on the meshes for different hang-in 
coefficients. It is clear that the mesh height, for instance, 
will depend to a certain extent on the strains acting 
on the webbing. 

The resilience of a section of webbing is determined 
by the forces acting on it. With low strains, however, 
the hang-in coefficient has a big influence so that when 
hung squared, webbing has its greatest area but least 
flexibility. With increasing hang-in, it becomes looser 
in the lateral direction, whereas with less than 28 per cent, 
of hang-in the webbing has a certain vertical springiness. 

In gillnets and entangle nets the hang-in determines 
the looseness of the net, true gillnets being usually 
hung somewhat tighter than entangle nets. The resilience 



Hang-in 
or 
Looseness 
per cent. 


Ratio of 
line to 
webbing 
per cent. 


Angle 
of 
mesh 


Height 
of 
mesh 


of' 


3$% 


10 


90 


128 20' 


0-436 


0-90 


0-785 


12 


88 


123 20' 


0-475 


0-88 


0-836 


14 


86 


118 40' 


0-510 


0-86 


0-877 


16 


84 


114 20' 


0-542 


0-84 


0-911 


18 


82 


110 10' 


0-572 


0-82 


0-938 


20 


80 


106 20' 


0-599 


0-80 


0-958 


22 


78 


102 40' 


0-626 


0-78 


0-975 


24 


76 


99 - 


0-649 


0-76 


0-986 


26 


74 


95 30 


0-672 


0-74 


0-991 


28 


72 


92 10' 


0-693 


0-72 


0-998 


30 


70 


89 - 


0-713 


0-70 


0-998 


32 


68 


85 40' 


0-733 


0-68 


0-997 


34 


66 


82 40 


0-751 


66 


0-991 


36 


64 


79 30' 


0-768 


0-64 


0-983 


38 


62 


76 40' 


0-784 


0-62 


0-972 


40 


60 


73 40 


0-801 


0-60 


0-961 


42 


58 


70 50' 


0-815 


0-58 


0-945 


44 


56 


66 10 


0-829 


56 


0-928 


46 


54 


65 20' 


0-842 


0-54 


0-909 


48 


52 


62 40' 


0-854 


0-52 


0-888 


50 


50 


60 


0-866 


50 


0-866 


52 


48 


57 20' 


0-877 


48 


842 


54 


46 


54 50' 


0-888 


0-46 


0-817 


56 


44 


52 10 


0-898 


44 


0-790 


58 


42 


49 40' 


0-907 


0-42 


0-762 


60 


40 


47 10 


0-916 


0-40 


0-733 


62 


38 


44 40' 


0-925 


38 


0-703 


64 


36 


42 10' 


0-933 


0-36 


0-672 


66 


34 


39 50' 


0-940 


0-34 


0-639 


68 


32 


17 20' 


0-947 


0-32 


0-606 


70 


30 


34 50' 


0-954 


0-30 


0-572 



and fishing height of these nets is, of course, largely 
influenced by the amount of sinker weight on buoyed-up 
nets, and the amount of buoyancy on bottom operating 
nets, which produces the strain in the webbing. 

In roundhaul nets, the hang-in is adjusted to give depth 
and bulge during operation; in the wings, however, it 
is often curtailed as too much webbing affects the speed 
of operation. 

With trawl nets, the hang-in to be given to wings, 
quarters and bosom, depends on the general shape and 
the cut of the sections of the net. It is difficult to deter- 
mine accurately, and is usually based on previous 
experience and experimenting. It is, therefore, most 
important that the amount of hang-in on wings, quarters 
and bosom is denoted on trawlnet plans. 

The fastening of the webbing to the lines is done in 
different ways according to the gear. The main require- 
ment is to ensure that the hanging cannot shift over the 
line or become loose once the net is hung. The net-line 
hitch and rolling hitch are about the best knots to use 
when making hangings to carry two or more meshes. 
The clove hitch is to be discouraged unless locked by 
an additional half hitch, as it tends to become loose. 
In most cases, it is better to use a rather heavy twine for 
the hangings as it reduces wear on, and cutting of, the 
selvedge meshes. When the nets are hauled mechanically, 
it is best to keep the hangings rather short to avoid 
snagging while in operation. 

The backhand marline hitch is still the most secure 
for rigid fixing of the webbing to the lines, but is also 
the most time-consuming to make. It has the further 



[104] 



NETMAK1NG 



disadvantage of requiring renewal every time the selvedge 
meshes need repairing. 

JOINING OF WEBBING 

When sections of webbing of the same width are joined 
together, the angle of the meshes in both sections is 
the same. When the width of the sections differs, the 
angle of the meshes in the widest section will be smaller, 
so that this piece will have more hang-in and, by the same 
token, less lateral strain. Several combinations are 
possible and each is applied according to the purpose 
of the joint: 

(a) the sections have the same width but different 

mesh size 

(b) the sections have the same mesh size but differ 

in width 

(c) the sections differ both in width and mesh size 

The first is a simple joint between sections of different 
mesh si/e and the take-up meshes are inserted at suitable 
intervals. It is, however, advisable to allow the large 
strip a little extra width to enable it to expand fully 
during operation. 

In the cases of (b) and (c) the greater width of one 
of the sections is given to allow the webbing freedom 
to bulge out laterally, as in the case of roundhaul nets 
and some types of bagnets. Under (c) is included the 
special case where, although both width and mesh size 
differ, the sections are joined mesh to mesh, which is 
very common in trawl nets. It must be borne in mind 
that in the above case the effect is more a narrowing 
of the wide section instead of bulging. It results in 
the wider webbing section reacting as if it were baited 
at a faster rate; this, at the same time, helps to shift 
the stress towards the side or selvedge of the complete 
section. 

In small-mesh webbing, it is better to make the take- 
ups by creases rather than by baitings, especially in 
the case of joining two sections of equal width, as the 
baitings tend to form a contraction in the row they 
are made, which causes slipping of knots. 

Where a tuck-in is needed in the lacing of vertical 
strips of webbing because of difference in depth or 
mesh size, the tucks should be made by half meshes or 
legs, rather than by full meshes. Full mesh tucks form 
strain points in the webbing, which soon become holes. 

In calculating the width of the sections to be joined, 
the take-up or tuck-in rate should be rounded off to 
allow for an easy sequence. This not only facilitates the 
actual work of joining but allows the sequence to be 
expressed in a simple fraction form such as 5/6, for 
example, meaning 6 meshes are joined to 5, or one 
take-up every fifth mesh. Simple take-up sequences 
are, furthermore, easy to replace in mending and when 
new webbing sections have to be inserted during over- 
hauling of nets. 

TAILORING OF WEBBING 

All bagnets need fashioning, either by braiding them 
in the round, with baitings inserted at appropriate 
intervals, or by assembly of shaped webbing sections. 
With the latter method, the sections can be braided to 
shape or they can be cut to shape from machine-made 



strips of webbing. Theoretically, it is possible to cut 
or braid webbing to any shape; in practice, however, 
all shapes are obtained by decreasing the width of sections 
at certain baiting rates, as curves give rise to many 
difficulties both in construction and in mounting the 
webbing to its supporting lines. Curves, therefore, 
are always made by a series of straight lines, each at a 
different angle to the vertical or "across the knots" 
direction. 

When drawing plans of nets, it is best to use a "1 to 2" 
ratio, i.e. all width measurements are drawn in as half 
values while heights are drawn to full value. It would 
be helpful when comparing net designs, if such a ratio 
could be adopted by all nctmakers, as a comparable 
picture of the general net shape would then be apparent 
at a glance. Apart from representing a fair mesh opening, 
53 degrees or about 56 per cent, hang-in, this ratio 
gives a fair picture of the net shape and has the advantage 
of being easy to work with on the drawing board. 
Furthermore, with this ratio the baiting rates can be 
taken directly from the drawings as they are equivalent 
to the cotangents of their angle of slope to the vertical. 
The angle of these slopes increases with the baiting 
ratio and fig. 2 shows the slopes of the most frequently 
used baiting ratios and illustrates the equivalent cutting 
rates. 

In some net sections, a faster slope is necessary to 
fit the slope of curving supporting lines as, for instance, 
at the quarterpoints where the wings join the bosom in 
trawlnets. in such cases, the slope can be increased by 
inserting baitings under the selvedge of the wing which, 
by reason of its fly meshes, already has a slope of 1 : 2. 




VM7 7 row* 
5 poiat* 4 bar* 



Tory 8 ram 
3 point* ? bar* 



vary 1O i 

2 point* 1 bar 



Fig. 2. Slope ami cutting ratios of most frequently used baiting 
rates. 



[105] 



MODERN FISHING GEAR OF THE WORLD 



The additional baitings cause a localized closing of 
the meshes and a consequently greater height, which 
allows the selvedge to stand further off. 

Where desired, the meshes can be kept lower down at 
the normal opening by inserting creases to equalize 
the number of meshes. 

When considering the dimensions of new nets, it is 
always better to overestimate the width the net will 
have in action; this is especially true of all types of trawl 
nets. Too high assessment of the opening width of a 
trawlnet may result in the use of too much webbing, 
but the net will still operate properly and catch fish. 
Underestimating the width at the trawl mouth, however, 
will cause a change in the whole shape of the net. When 
the wings are pulled further open than calculated, the 
bosom is pulled forward while the sideseams fall back; 
this causes a contraction in the webbing of the throat 
with resultant bad water release. It may even lead to 
the cod-end turning over. 

This desirability to over- rather than under-estimate 
net width does not mean that it is better to choose a 
bigger net, but that careful consideration should be 
given to the amount of webbing to be allowed to a 
headline. Indeed, where it is a question of the size of 
net to be used by a certain vessel the contrary is true: 
it is always better to under-estimate. 

fig. 3. Double baiting at the quarter points. 








Net sections being braided by hand. 
[106] 



THE KNOTLESS NET 

by 

THE NIPPON SEIMO CO. LTD. 

Tokyo, Japan 

Abstract 

This method of making nets was invented in 1922 by the Nippon Seimo Co. Ltd., in Japan and it is becoming increasingly popular 
in the fisheries of that country. It has many advantages; the meshes are not distorted under strain, and because of the absence of knots, 
less material is needed with a consequent saving of weight and bulk. 

The paper describes the manufacture of these nets and shows how easily they can be repaired. 

Le filet sans noeuds 
Kcsum 

Cette in genie use met node dc fabrication des filets a etc mventee en 1922 par la Nippon Seimo Co. Ltd., au Japon, et ce filet connait 
une vogue de plus en plus grande dans les peches de ce pays. 11 comporte de nombreux a vantages; les mailles ne se d&brmcnt pas sous la 
tension ct, du fait de Pabsence de noeuds, la fabrication exige moins de matiere premiere, d'ou economic de poids el moindre encombrement. 

I. 'article decrit la fabrication dc ces filets et montre combien leur reparation est facile. 

l^a red sin nudos 
Extracto 

F.n las pesquerias del Japon va aumentando la popularidad de un ingenioso metodo para fabricar redes, idcado en 1922 por la Nippon 
Seimo Co. Ltd., de ese pais. Entre las diversas ventajas de este procedimiento figuran el hecho de que las ma I las no se deforman con la 
tensi6n y la ausencia de nudos; ademas, se utiliza menos material con la consiguiente economia de peso y volumen. 

En el trabajo original se describe la fabricacidn de estras redes y demuestra la facilidad con que pucden reparar.se. 



THE knotless net was invented in 1922 by the Nippon 
Seimo Co. Ltd. (Japan Fishing Net Manufacturing 
Co.). In this type of webbing the twines are joined 
at the mesh corners by an interlacing of the two twine 
strands. Knotless nets did not come into general use 
while only natural fibres were available, but followed 
with the development of rotproof synthetic fibres and 
their increased use for fishing nets. Now this type of 
webbing is rapidly becoming popular for several kinds 
of nets. 

SPECIAL ADVANTAGES 

The rapid change-over to knotless nets in Japan is 
chiefly due to the following special features, of which the 
most important are: 

Less weight and bulk 

Less twine is used to make the meshes which, in some 
cases, can mean a saving of as much as SO per cent, of 
the raw material. As there are no knots, the bulk of the 
net is greatly reduced. 

Higher strength 

When knotted, twines of natural fibres lose about 
1 8 to 20 per cent, in strength. The loss is often higher 
with synthetic fibres and may reach 30 to 40 per cent. 
As the fibres undergo practically no sharp bending in 



knotless nets, there is no reduction in strength so that a 
correspondingly lighter twine can be used. 

Less resistance in water 

The aggregate resistance of the knots in a traditional 
net is considerable and becomes an important factor in 
the use of nets which are towed or set in a current. The 
resistance of knotless nets is very much less. 

Easier to handle less friction 

As there is no knot friction, the net can be hauled over 
the ship's side with less effort, so that the net can be 
lifted even during a change of current without danger of 
becoming fouled. During shooting, the net runs out 
much smoother as there is no inter-knot friction. 

Less labour and smaller tackle required 

As the whole net is lighter and less bulky, time and 
labour is saved and tackle can be lighter, factors leading 
to a saving in manpower. 

No wearing away of knots 

The damage caused by abrasion of knots in the belly of 
trawls, and other nets which are dragged over the sea 
bottom, is well known. In other types of nets the knots 
are worn away during operation by rubbing against the 
ship's side, net rollers or other gear parts. 



[107] 



MODERN FISHING GEAR OF THE WORLD 




Fig. I. Starting. 




Fig. 3. Pick-up. 



Fig. 2. Joining. 



With synthetic fibres, which are rotproof, knotwear is 
very important as it shortens the useful life of the net. 

Knotless nets, having no such "points** of wear, 
should last longer than knotted nets. 

No damage to catch 

When fish are collected in codends and bags of purse 
seines, many are damaged by rubbing and friction against 
the meshes. With knotless nets such damage is consider- 
ably reduced, which affects the quality of the catch. 

Constant mesh size 

Because there is no tightening of knots, as in knotted 
nets, the meshes undergo no change so that the mesh 
size of a knotless net is almost 100 per cent, constant 
throughout its life. 

Easy to dye 

Having no knots, the nets can be dyed more easily and 
completely. The absence of knots and the smaller bulk 
also means that less dyeing material is used and the nets 
dry quicker. 

Less liable to fouling 

There can be no deposit of dirt and micro-organisms 
between the interstices of knots, so that knotless nets are 
much less fouled and need less washing. 

MENDING OF KNOTLESS NETS 

When knotless nets were first introduced, the fishermen 
were anxious about the mending of them. In fact, torn 



parts are mended as easily as in knotted nets. The 
only difference is that, when starting, the mending twine 
should be attached from one mesh outside and all ends 
of torn meshes should be bent back within the mending 
knot, as shown in figs. 1, 2 and 3. 




Fig. 4. Knotless net. 



[108] 



JAPANESE KNOTLESS NETS 



METHOD OF MANUFACTURE 



The knotless net is manufactured in two stages. In the 
first stage the twine is prepared by doubling the appro- 
priate number of single yarns together and then twisting 
two or more of such yarns into strands with a "Z" twist. 
The strand thus obtained is wound on the bobbins of 
the net making machine. 

In the net making stage two such bobbins are attached 
to both sides of a special flat spindle. Turns of the spindle 
insert in the twine a second twisting operation in an "S" 
direction. When the necessary number of twists are made, 
the two bobbins move and exchange places with two 
neighbouring bobbins and the point of intersection of 
twine, which corresponds to a "knot" in the knotted net, 
is made accordingly. 

The construction of a "knot" is shown in the diagram 
(fig- 4). 

Strands of both twines run across and through each 
other, and are twisted in opposite directions as shown. 
Thus a "knot" or intersection is made. 



The twine in the knotless net has an "S" twist of two 
strands. 

The webbing is examined, flaws and/or irregular 
twists are corrected and each web section is then com- 
pleted by weaving on the top and bottom selvedges. 

Any size of web section can be made to suit different 
types of gear. 

The nets are heat-set so that the twist of the strands 
is fixed permanently. During this operation the tensile 
strength of the twine increases by about 15 per cent. 
By adjusting the process, the flexibility of the twines can 
be modified to suit particular purposes. Hard fibres can 
be made softer and soft fibres stiffened. 

The heat setting process is necessary for nets of filament 
yarns such as nylon, Krehalon and Saran (vinylidene), 
Teviron (polyvinylchloride) and Kuralon 5 but not for 
cotton, Kuralon (vinylon) and the other spun yarns. 

With the exception of materials belonging to the 
polyvinylchloride group, such as Krehalon and Saran, 
the nets made of nylon, Kuralon, etc. can be dyed with 
commercial dyes, pigment colours or coal tar. Heat 
setting is not generally required when coal tar is used. 




Slacking a beach seine after a haul in Ceylon. 
I 109 I 



Photo FAO. 



DISCUSSION ON RATIONAL MANUFACTURING OF FISHING GEAR 



Mr. H. Warncke (Germany) Rapporteur: Our problem 
is now to produce machine-made webbing on a more rational 
basis and so reduce costs. This aim could be achieved by: 

1. Greater uniformity and standardization of net types, 
and of the assembling components, which would 
gradually bring stock-carrying risks of manufacturers 
and dealers to a minimum; 

2. A reasonable limitation of types of synthetic materials; 

3. A general exchange of information on net-making 
problems. 

Some progress has been achieved towards such a standard- 
ization by the fishermen and gear technicians. This is illus- 
trated by Barraclough and Needier in their description of 
the construction of a midwater trawl for a 62 ft. 175 h.p. 
trawler equipped with typical British Columbia gear and 
deck layout, and by du Plcssis who describes the South 
African Pursed Lampara. These two examples show that 
by careful consideration of the many factors, fishing nets 
can be restricted to a few types. Standardization must, 
however, be based on scientific study and practical experience. 

The papers presented indicate that synthetic materials 
are becoming increasingly important to the fishing industry. 
It appears, however, that a fibre well suited for some types 
of net and gear lacks certain qualities for others. The net 
manufacturer must therefore produce and stock many types 
of gear in order to satisfy the requirements of the fishermen. 
A limitation in this ever increasing variety would enable the 
net manufacturer to reduce his stock -carry ing overheads to a 
reasonable level, and so reduce production costs. 

It was recommended that net manufacturers should 
exchange information so as to arrive at more rational pro- 
duction. However, owing to the big differences in production 
conditions between countries, created by subsidies, import 
rules, etc., most manufacturers would at present be reluctant 
to agree to such exchange as it would interfere with business 
competition. 

It would seem, therefore, that the most likely methods 
of achieving rationalization arc: 

(a) Limitation of mesh-sizes to a standard set of sizes, 
together with a standard method of measurement. 
This would reduce the need for frequent adjustments 
to the net-making machines and allow for simplifi- 
cations in their construction; 

(b) limitation of sizes and twists of twines. For instance, 
the denier system counts that are at present in pro- 
duction, should be sufficient to supply all the required 
sizes of twines. The number of different twists and 
plies could probably be reduced without disadvantage 
to the fishing industry 

Such rationalization could be discussed by working 
groups formed of representatives of all parties concerned. 

Problems of more general interest which might be con- 
sidered are: 



(a) Does dyeing really provide sufficient protection to the 
synthetic fibres against decay through exposure to 
ultra-violet rays, as seems to be widely accepted? 
Recommendations concerning the appropriate methods 
of dying synthetics are often difficult to interpret. 
Such recommendations should be consistent with the 
limited dyeing facilities of the fishermen. 

(b) Which is the appropriate size of synthetic twines 
used in place of natural fibres? To replace 210/6 ply 
and coarser twines, synthetic fibres, 25 per cent, 
lighter in weight, are generally chosen. For finer twines, 
the criterion is the same running length as the natural 
fibre. This would mean that, in some cases, the main 
advantage of synthetics, i.e. their higher tensile strength, 
is not fully utilized and unnecessarily strong and heavy 
twines are used. 

The Nippon Seimo Co. Ltd. deal with the construction 
of knotless nets designed and developed in Japan. They 
report that such nets, constructed of 2 strand twine, suffer 
no loss in strength, whereas natural fibres lose from 1 8 per cent, 
to 20 per cent, and synthetic fibres from 30 per cent, to 40 
per cent, when knotted. 

As the selvedges have to be woven separately, causing 
additional expense, it would be interesting to know if the 
initial financial advantage of lower weight is thus reduced? 
The relation between cost of production and price of material 
can perhaps explain why knotless webbing, which was not 
in demand when made of natural fibres, has increased in 
sales since it has been made of synthetic fibres. 

Mr. D. McKee (Scotland): With regard to catering to 
the wishes of the fishermen, it is necessary for the manu- 
facturers first to obtain, either from the fishermen or from 
fisheries management, information as to the thickness or 
weight by runnage of the twines or lines required. 

A good illustration of this point is the fishing line situation. 
In inshore haddock line fishing, a man uses a line weighing 
approximately 1 lb./60 fm. Now he wants a synthetic line. 
We find the breaking strength of such a line in cotton or 
hemp is, say, 20 Ib. The problem is does he want a line 
of this strength or does he want the same thickness? Generally, 
in the case of light lines, the man wants the same body or 
feel in the new line, rather than the same strength. My firm 
which is mostly concerned with inshore herring fishing, 
gillnetting and that type of gear, has published a booklet 
for the industry, on the makeup of synthetic twines. This 
gives the dry and wet breaking strength of a cotton twine and 
recommended equivalent size in nylon or other synthetic 
twines in yds./lb., and m./kg. One omission is the breaking 
strength of knotted webbing, but information on this point 
can be obtained directly from our works. There is a certain 
risk in declaring breaking strengths and giving yardages as 
the figures depend on the testing method used. We, therefore, 
would claim at least 10 per cent, margin either way. 



110] 



DISCUSSION: RATIONAL NET MANUFACTURING 



On the question of economy, I would Jike to quote an 
example. Recently, while abroad, 1 was confronted with 
general complaints about the economic failure of the fishing. 
Until a few years ago, the fishermen were using natural 
fibres and then changed to synthetics which cost double 
the price. When natural fibres were in use and the net got 
damaged, it was thrown overboard. I tried to find out 
how much more service they obtained from a synthetic net. 
I got the amazing answer little, if any. It appeared that 
when the synthetic fibre net became damaged the same pro- 
cedure was followed, and the net was thrown aside and not 
used again. It is not the part of the manufacturer to work 
down to e -onomy level of that type, although successful 
manufacturing depends on the success of fishing. 

There are many dfferent types of mesh measurement. 
In Canada, for fine gillnets, you measure between knots; 
yet, in some parts of Canada, heavier nets are measured 
from the inside of one knot to the outside of another knot. 
The best suggestion I can make to the fisherman is to rel> 
on the netting manufacturers, but to have a precise idea 
of requirements. 

Vlr. A. Robinson (U.K.): 1 full} agree with the comments 
made so far, particularly with those of Mr. McKcc. Mr. 
Warncke also has made a very strong point regarding the 
difficulties which arise due to the large stocks which arc 
necessary at present. My firm is essentially in the twine trade, 
but if the variety of sizes and special requirements can trouble 
us, how much more will they trouble the net manufacturer! 
Of course, these are difficulties inside the trade, perhaps not 
fully realised by the fishermen, but they have a very strong 
bearing indeed on the price that the fisherman is eventually 
asked to pay. 

I also feel that the twine maker, and I am sure also the not 
maker, will, if only he is given full information, do all he 
can to help the fisherman. Net and twine factories get, daily, 
numerous inquiries and orders for materials, from which it 
is difficult to determine exactly what is required. Yet this is 
necessary because the customer docs not have sufficient tech- 
nical knowledge or information. However, if he states his 
problem exactly he will get reliable information in exchange. 

With regard to the dyeing of synthetic fibres, nothing very 
definite has been proved so far as we are aware. Our tests 
have failed to prove that dyeing does give protection against 
deterioration due to sunlight. 

Most firms would, I think, be willing to issue comparative 
lists showing the conversion from natural to synthetic fibres. 
We, ourselves, give such information quite freely and I 
believe the wet knot strength should be the criterion for such 
material. A comparison on any other basis, certainly so 
far as net twine is concerned, is apt to be misleading. At the 
same time, there are circumstances where other characteristics 
of synthetic fibres can be taken into consideration as. for 
instance, the greater elasticity which improves the energy 
absorption of the twine, quite apart from its merits as to 
breaking strength. It has been mentioned that synthetics 
may be as much as 25 per cent, lighter than natural fibres. 
On the basis of wet knot strength, and also taking into con- 
sideration the high tenacity yarns available today, a fairly 
reliable changeover to cotton can be made on the basis of 
a synthetic twine giving about 50 per cent, greater length 
per unit weight. 

I would like to raise one further point, i.e. that of mutual 
understanding between fisheries workers all over the world. 



Apart from using the same standards and tests in our work, 
we should also be able to understand one another's writings 
Translation of fisheries literature is extremely difficult 
because of the different meanings given to the terms used 
in different countries and areas. 

Dr. E. Hess (FAO): As you probabl> know, FAO has for 
the last 8 years been publishing the World Fisheries Abstracts 
in English, French and Spanish. We have, during these 
years accumulated quite a lot of terms and we are now in 
the process of preparing this material for publication as a 
dictionary in the three official FAO languages, English, 
French and Spanish, at least to begin with. The form of 
these dictionaries was agreed upon with UNESCO, who has 
done much work along similar lines. 

The English dictionary will form the base and each term 
will have a definition. Each term is given a number and its 
meaning in another language can be found by simply referring 
to that same number in the other language part or book. 

The whole field of fisheries technology will be covered, 
not just gear. The first section, on fish curing, is ready now 
The section on fishing gear and boats we hoped to have read> 
for this Congress, but I am sorry to sa> we did not get that 
far. We have another section on refrigeration also in an 
advanced stage. Before long, we hope to have this published, 
but will first issue a mimeographed draft and send it to as 
many people as we can think of in various countries for their 
comments. After study of these comments and necessary 
adjustments we will then publish in book form. 

Mr. O. Aagaard (Norway): Much has been said about 
standardization as seen from the manufacturer's point 
of view. In Norwa>, a Standardization Committee was 
formed in 1930 at the request of the Fishermen's Organiza- 
tion. However, when the same fishermen discovered that 
standardization would mean that their individual taste 
and wishes as to twine and rope sizes, mesh sizes, etc. would 
be interfered with, the whole thing was dropped. 

Before going over to an> kind of standardization, it may 
be useful to hear the fishermen's opinion. 

Prof. S. Takayama (Japan): About half the knotlcss nets 
used at present in Japan, i.e. 3 million Ib. year, are made 
of synthetic fibres. All Japanese knot less nets are made of 
two strand twines*. 

There are two types of nets based on practically the same 
system of connecting. In the first type the twines run diagon- 
ally through the webbing, whilst in the second type they run 
in a zigzag line. These different directions depend on how 
many times the tyyo twines arc threaded through each other 






Fig. I Three types of joinings used in A not less nets. 

* Editors note. Knot less nets made of braided twine are noyv 
being manufactured and tested for instance in U.S.A. and Belgium 



MODERN FISHING GEAR OF THE WORLD 




Fig. 2. Diagonally constructed knotless net. 

If they pass through only once, the direction of the twines 
is diagonal; if they arc threaded twice, the zigzag line is 
obtained; if they pass through three times, a diagonal is 
obtained, and four times again a zigzag, i.e. uneven numbers 
of interweaving results in diagonal twine direction and even 
numbers in zigzag. The number of the interweavings can 
be built up until a quite unusual mesh form results which 
could be called the tortoise type. 

Knotless nets can be adapted for practically all types of 
gear, but until now, they are mainly used for big setnets, 
leader nets and gillnets. 

Mr. H. Kobayashi (Japan). As regards mending tears or 
connecting pieces of webbing, there is no remarkable differ- 
ence between knotted and knotless nets, and consequently, 
there are practically no additional costs with regard to 
selvedges. If double selvedges arc needed, they must in 
any case be hand braided. Double selvedges can, however, 
be avoided simply by taking up two meshes instead of one, 
when hanging a net to lines. This is no longer a problem 
in the commercial fishery in Japan as the remarkable increase 
in the use of knotless nets shows. 

Mr. J. Buchan (U.K.). It seems that there are two basic 
types of knotless nets, the "diagonal" and the "zigzag". 

The twines in a webbing made with conventional double 
English knot, run in a zigzag line. There arc two ways of 
testing this knot, either by pulling the two bars belonging 
to one continuing twine against the two bars belonging to 
the other twine, or by testing the two bars belonging to 
different twines against the opposite pair. The same two 
testing directions can be applied for both types of knotless net. 

We have found that the conventional double English 
knot will give an efficiency of 54-6 per cent., that is the 
breaking load of the knot is 54 per cent, of the total breaking 
load of the two twines in the first direction, and 51 per cent, 
in the second. In the first type of knotless net, that is the 




2 &2 C 2 d ? 

Fig. .?. Zigzag constructed knotless net. 

straight cross, you get 75 per cent, and 57 per cent., but the 
knot will break at the weakest point, i.e. 57 per cent. 

With the second type of knotless nets (that made by double 
inter-weaving of twine), we obtained 91 per cent, and 51 
per cent., showing that the actual lowest efficiency of the 
knotless connection is not, in fact, better than the conven- 
tional double English knot. 

Knotless nets are made in a two- fold construction, if 
one strand breaks, the twine can untwist, causing break 
in the net running, which will not happen with an ordinary 
webbing braided with double English knot. 

Prof. A. von Brandt (Germany). The fact that not only 
Japan but also Russia use knotless nets to a large extent 
indicates to me that there must be considerable advantages. 
Furthermore, the gillnctting experiments we have carried 
out with Japanese nets in Germany gave good results. We 
had no difficulties with "knot" slippage and repair, for which 
our fishermen found an even simpler way than the one 
recommended by the Japanese. 

In addition to what we have been told until now, I believe 
that knotless nets should have great value for trawl nets. 
The limiting factor for size of the gear or towing speed is 
the relation between towing power and gear resistance. 
Dr. Schiirfe has shown how the towing resistance can be 
decreased by using hydrofoil otter boards and thinner 
synthetic twine. The smaller area of knotless nets should 
further decrease the towing resistance. This would be a 
valuable gain in addition to the savings in material resulting 
in lower weight. 



[112] 



Section 4: Net Preservation. 



DEVELOPMENT OF FISHING NET AND ROPE 
PRESERVATION IN JAPAN 

by 
SH1GENE TAKAYAMA and YOSHINORI SHIMOZAKI 

Tokai Regional Fisheries Research Laboratory, Tokyo, Japan 

Abstract 

This paper deals with the methods used in Japan for preserving different kinds of fishing gear. The methods which arc described 
are as follows: (a) Sunlight disinfection; (b) Preservation by Copper Sulphate: (c) Copper Naphthenate preservation; (d) Tannin preservation: 
(e) Bichromate treatment after tannin; (f) Coal tar and (g) Preservation by Cyanoethylation. These processes are described in detail and a 
comparison of their relatixc efficiencies is shown in tabular form. The materials concerned in the investigation arc Cotton and Abaca. 



Resume 



La preservation des cables ct filets de peche au Japon 



Les auieiirs exposent les mcihodcs appliquees au Japon pour la preservation des dirferents types d'cngins dc peche. Ces methodes 
sont les suivantes: (a) desmfection par exposition jinx rayons du solcil; (b) preservation par traitemeni an sulfate de cuivre; (c) preservation 
par traitcmcnt au naphtenate de cuivre; (d) preservation par traitement au tanin; (e) traitement au bichromate apres tannage; (e) traitement 
au goudron; et (g) traitement par cyanoethylalion. Les auteurs font unc description detaillec de ces procedes ct comparent sous forme de 
tableaux leurs eflicacites respect ives I es essais ont porte sur k* colon et r abaca. 

Dcsarrollo de la red de arrastre > preservation de cuerdas en el Japon 
Ivx tract o 

Lstc tr.ibajo irata de los mcthodos usados en el Japon para preservar diversos tipos de urtcs de pcsca, a saber: (a) desmfcccion con 
lu/ solar; (b) preservation con sulfato de cobrc; (c) preservation con naftenato dc cobre; (d) preservacion con tanino: (e) tratamiento con 
iiicromatos despucs dc la entmtadura mediante cxtractos curticntcs: (f ) alquitrande hulla, y (g) preservation mediante cianoetilacion. T.stos 
tratammetos sc dcscriben en detalle y se compendia en tablas su eficacia relativa. Fn la investigation efectuada se estudiaron materiales 
dc algodon v abaca 



INTRODUCTION 

THE various preservation methods of fishing nels 
and ropes may he grouped, according to then 
respective functions, into three categories: 

1. Sterilization to destroy putrefactive bacteria, either 
by sunlight-drying after boiling, copper sulphate 
bathing, or copper nuphthcnate bathing. 

2. Protection from bacterial putrefaction by coating 
the natural fibres with a film of cither tannin, coal-tar 
or tannin and coal-tar. 

3. Combination of these two methods, using copper 
naphthenate and coal-tar dyeing. 

Most of these methods, while they are distinguished 
from the sun-drying in which no preservatives are used, 
allow the materials to be dried in the sunlight after 
treatment. However, the materials treated in copper 
sulphate bathing and the solution itself must not be 
exposed directly to the sunlight or air. The copper 
naphthenate treatment or its combination with coal-tar 
coating recently introduced in Japan is still in the 
experimental stage. 

When a fisherman chooses one of these procedures, 
he has to consider not only the preserving effect which 



differs for each method bin also the most suitable one 
for his particular type of fishing. 

PRESERVATION BY STERILIZATION 

Sunlight disinfection: Infectious micro-organisms cannot 
survive against heat or dryness, and sunlight disinfection 
of fishing nets, therefore, is practised all over the world, 
though only applicable as a supplementary method at 
certain intervals between fishing operations or seasons 
(Table I). 

Sunlight disinfection for non-dyed nets: Since colour 
is inseparable from dyeing for some fishing gear in Japan, 
non-dyed cotton nets are preferred i.e., the boat seine 
("bacchi-ami") in Ise Bay, the purse seine for post larval 
anchovy, and the small trawl used from sailing boats 
("utase-ami") in the Seto Inland Sea. The nets are simph 
dried in the sun or in the shade after every operation, 
mostly one-day trips. In addition, the nels are sterilized 
by periodic boiling. As this method is not very effective, 
the nets are liable to decay in a short period. The only 
alternative is to adopt white synthetic fibres and for these 
reasons Vinylon is now being used to some extent. 



[ 113 1 



MODERN FISHING GEAR OF THE WORLD 

TABLt I 

Specifications for Various Preservations of Fishing Nets and Ropes 



Kind of preservation 



Type of gear 



Kind of Formula of Bath Time neede<l Redyeing 

fibres preservatives temperature for hath fishing season 

ro 



inc ' e 
1 "' 



treated 
{years) 



1 . Copper sulphate 



Small round hauls Cotton 



2. Copper naphthenatc 



3. Sunlight 

disinfection 

4. Tannin coating 



5. Improved tannin 

coating 

6. Coal tar coat ing 



7. Tannin and coal tar 

coating 

8. Resin and coal tar 

coating' 



Float lines, 
lead lines and 
ropes 



A haca 



Boat seines, and Cotton 
sailing trawl nets 



Selnets 

Round hauls and 
stick-held nets 



Cotton 

and 

abaca 
Cotton 



0* 1% for dyeing bath Normal Several hrs. 
(0-3,, if sea water is 

used). 
0-01%forsterili7ing 

bath 
(0-03",, if sea water is 

used) 



Initial onl> 

12 hrs. between trips S 



I5'0 u copper 
naphthcnate 
0-2"o sterilizer 
84 1> solvent 
0-8",, miscellaneous 



3",, cutch or tannin 
extract solution 
Same as above 



Setnets, round 
hauls and stick- 
held nets 


Cotton Apply No. 4, then 
and fix in 1% K 2 Cr 2 O 7 
abaca or Na 2 Cr 2 O 7 bath 


Trawl nets 
Setnets 


Abaca 
Cotton and 
abaca 



Setnets 



Setnets 



Same as 4 plus 6 



10-15 min. Once a season 12 



Between operations 



Boil ing for 2 hrs. then 
cooling for 12 hrs. 

For abaca, normally 
impregnate only 12 
hours 

Normal 1-2 hrs. 



30 40 C 5 10 mm. 
30 40X7. 5- 10 min. 



Same us 4 Same as 4 
plus 6 plus 6 



Once two weeks with 3-5 
weekly sun drying 

Once two weeks 3-5 

with daily sun 
drying 

Once 4 weeks for 3-5 
each with sun drying 
fortnightly 

Once three months 130 
Once three months 130 

with sun drying 

monthly. 



After treating with a Normal 
synthetic resin, treat 
with a specific coal tar 



Once 5 months 
with tar dyeing 

Same as abo\e 



150 



1 50 



3-4 
3-4 

1-2 



2-3 
2-3 

3-5 



2 
3-4 



4-f> 
5-6 



* Commercial dye H, 



H 2 , for which see footnote of Table II. 



Preservation by copper sulphate: In the Shizuoka and 
Wakayama Prefectures preservation of fishing nets by 
copper sulphate is more prevalent than in any other 
fishing community in Japan. With this treatment a life 
of three to four years is obtained. The nets are mostly 
made of cotton. They are used for sardine, anchovy, 
(and their post larvae called "shirasu"), mackerel and 
jack mackerel. 

(1) Dyeing bath: Repeated treatment is necessary for 
sufficient preservation by copper sulphate solution. The 
dyeing bath needs the strongest concentration with 0- 1 
per cent, in the case of fresh water and 0-3 per cent, for 
sea water 1 . 

The net is soaked for several hours. In sea water, the 
copper sulphate turns to basic copper chloride. If left 
exposed long to the sunlight and air, this basic copper 
chloride would deteriorate the net. The net, therefore, 
has to be kept wet after the dyeing bath and put into 
use as soon as possible. 



(2) Sterilizing baths: Following the dyeing bath, the 
net is sterilized after each fishing operation. The con- 
centration should be 0-01 per cent, in fresh water and 
0-03 per cent, in sea water. In practice, the solution for 
the sterilizing baths may be prepared by using the 
remaining solution of the dyeing bath. Copper sulphate 
is added according to the amount of water needed to 
replace that consumed. A simple method for determining 
the concentration of CuSO 4 in the serving solution has 
been established by Kanna and Matsumoto 2 . Soaking 
should last for at least several hours. The optimal length 
of time has not been ascertained. 

(3) Caution: The net should always be kept wet. Do 
not heat the bath solution as in cutch dyeing. The solution 
can be prepared at ordinary temperatures in any season. 

(4) Storage: Keep a treated net under sterilizing 
solution (0-005 to 0-001 per cent.) and cover it with a 
straw mat or canvas. When the net has to be stored in 



[1141 



JAPANESE METHODS OF PRESERVATION 




0.1 - 



20 



40 



60 



80 

Days 



100 



120 



14O 



160 



f!* I- CluiHgi' in breaking \trcnaih <>/ the cotton twitu^ MthwergctJ in \eu waiei . The test \va\ commencctf in Dcicmhcr 1955. 

7 . OrizuHil breaking strength. 

niv \trentfth ttf'ter Mibnierg'ni* in the sett. 

f 115 ] 



MODERN FISHING GFAR OF THE WORLD 




0.1 - 



20 



40 60 



80 
Days 



100 120 140 160 



Fig. 2. Change in breaking strength of the man I la twines submerged in \ea \\-atet . 

T t . Original breaking strength. 

T. Breaking strength after submerging in the sea. 



116 ] 



JAPANESE METHODS OF PRESERVATION 



TABLI II 
Specification of the Treatments shown in FIRS. 1 and 2 



First bath 



Second bath 



Third bath 



Cutch (3",,) 



HI 
I, 

B 
C 

H, 
Coal tar 

Coal tar <8()" () ) 
Gasoline (20",,) 

D, 
B 



K 2 Cr. 2 O 7 or Na 2 CY 2 <> 7 (I",,) 

Coal Tar 
Coal tar (80%) 
Gasoline (20",, 
Coal tar 

Coal tar (80" ) 
Gasoline (20,.) 

H., 



7 
X 

10 
11 
12 
13 
14 

Gasoline (20",,) 

15 D, IX 

16 Ji ^L l iM 

H, contains melanin resin etc.; H 2 a kind of coal tar dye. 

B contains copper naphlhcnate, synthetic disinfectant 3DM, etc., 

to he used in dyeing with vacuum compressors. 
C 1 has the same formula as B to be mixed with mineral oil when 

the twine is twisted. 
D, mainly consists of cutch; and D.,, CuSO 4 , alum, K.,Cr.,O 7 , or 

Na 2 Cr 2 O 7 , etc. 
l-j contains cutch, tannin, and persimmon tannin; F.,. Nu 2 Cr 2 O 7 , 

SiO 2 , etc., E 3 , coal tar and resins. 

The trade names of commercial dyes produced h\ different 

companies. Their addresses arc in possession of the authors 



the air, wash out the dye residue with fresh water, if 
available, or otherwise with sea water. After drying in 
the shade, store it in a cool dark, airy place. The value 
of sprinkling malt over the net, as is sometimes done for 
storing, has not yet been confirmed. 

(5) Life of the treated net: The net treated as above 
may last for more than three years, serving in every 
fishing season. However, one drawback is that the treat- 
ment is not applicable to those nets in continuous use in 
the sea or in high-sea operations. 

(6) Dyeing and preserving mechanisms: It is under- 
stood that CuSO 4 in the net reacts to sea water on and 
between the net fibres. It first turns into a blue hydrophile 
colloid precipitation, viz., basic copper carbonate, which 
again reacting to sea water, gradually changes into basic 
copper chloride, a light-greenish hydrophobic crystal, 
which is precipitated on the fibres. Since the precipitation 
is not so effective against micro-organisms as CuSO 4 , 
the net has to be subjected to the sterilizing bath imme- 
diately after every operation. 

COPPER NAPHTHENATE PRESERVATION 

Due to its high cost and the progress made in other 
types of dyestuffs, it was not until 1951 that copper 
naphthenate, as a preservative of fishing nets, attracted 



the attention of technologists and consumers in Japan. 
Excellent preserving qualities are obtained when copper 
naphthenate is mixed with some other sterilizers, at least 
in respect of abaca 3 . This dyestuff can be applied in a 
quick and simple way without affecting the properties 
of the treated net. 

(1) Treatment: More than 90 per cent, of the 
copper naphthenate dye consumption in Japan consists 
of three different products called A, B, C,* for the 
purposes of this paper. 

Notwithstanding an inferior preserving effect upon 
cotton or ramie twines, they are used mostly in dyeing 
fishing ropes made of Manila and Sisal, such as float 
lines for driftnets. Three different treatments are used 
to apply these dyes for nets and ropes. 

When a fisherman is about to dye his material with 
either A or B, the preservative is diluted at a normal 
temperature with kerosene, as specified for the product. 
After soaking for 15 to 20 minutes, the material is dried 
in the sun or in the shade. 

In the case of net dyers and net makers, the material 
may be treated in an autoclave. After vacuumizing, the 
solution is put into the kettle, and the material is then 
treated at about 15 to 20 Ib./sq. in. of pressure for a few 
minutes before being taken out for drying. 

In a rope factory, copper naphthenate solution 
prepared as above with the mineral oil, is usually applied 
to the strands of twines or ropes, while they are being 
twisted; thus, the rope is dyed at the same time as it is 
manufactured. 

(2) Preserving effect: Vacuum-compressing is likely 
to produce the best results of any of these methods 
(samples 10 and 1 1 in fig. 2). The first method is, 
however, as effective as the second, if the soaking time 
is more than five hours 4 . When compared with cutch 
treatment which is most commonly used in Japan, the 
effect of this preservative has been found superior, when 
applied to abaca, but inferior when applied to cotton or 
ramie (fig. 4). 

(3) Caution: Since these preservatives are inflam- 
mable due to the kerosene used as the solvent, special 
care is needed. Such nets are, however, less likely to 
suffer damage by rats or animals during storage than nets 
dyed by other means. It is recommended that the 
concentration of the dye should secure more than 0-5 
per cent, of copper to fix on the material. 

(4) Dyeing and preserving mechanisms: In per- 
forming its function, copper naphthenate is not supposed 
to require chemical combination with any other clement. 
Instead, it is precipitated on the surface of the fibres 
and penetrates between and inside them, destroying 
infectious microbes that are mainly on the surface of the 
material. 

(5) Trend in technological studies of the preservation: 

Synthetic fibres, although used increasingly by Japanese 
fishermen, will not take the place of natural fibres for 



A: "Kanadem 42", composed of copper naphthenate. synthetic 

sterilizer, and synthetic resin acid. 
B: "Ropelife", composed of copper naphthenate, organic 

preservative, and water-proofer. 
C: "Shin Asanoha", mineral oil mixed with A or B. 



[117] 



MODERN FISHING GEAR OF THE WORLD 



1.0 



0.9 _ 



0.8 



0.7 - 



0.6 - 



0.5 - 



0.4 - 



0.3 - 



0.2 ~ 



0.1 - 



20 40 



8%) 




60 80 

Days 



100 120 140 



/'if. 3. Change in breaking strength of the manila twine* treated with different concentrations oj copper nti/>hthcn<ite. 

Tf,. Original breaking strength. 

T. Breaking strength after submerging in the sea. 



[118) 



JAPANESE METHODS OF PRESERVATION 



1.0 



0.9 . 



0.8 



0.7 _ 
I 



0.6[ 




b 
c 
d 



0.5 



10 



20 



30 40 

Days 



60 



70 



Fig. 4. (Change in break i up strength ol the manila twines treated with copper naph thenate dyes /*/*<// tv/ //</;/ \ eaih <>/ \\liich has 

quantities of fungicidal agent. 

r . Onyinal breaking strength. 

T. Breaking st length after submerging in I he sea. 



some time, on account of the great difference in price, 
particularly between synthetic fibres and abaca, the 
material used for ropes and twines. For this reason, the 
adoption of synthetic fibres for fishing ropes has not yet 
made great progress. Further studies should be made on 
the technological aspects of copper naphthenate preserva- 
tion, its application to abaca described above being an 
example of the work already done (samples 10, 11, figs. 2, 
3 and 4). 

In a recent study, twines treated in the various con- 
centrations were submerged in sea water. The results 
revealed that the preserving effect depends on the 
concentrations as shown in fig. 3, in which the numerals 
enclosed in parentheses indicated the amount of pre- 
cipitant, Cu. 

Among the sample twines, each weighing approximately 
48-7 g./m. 1, 2, and 3 were washed in running water for 
5 hours, dried, then soaked for 12 hours in 40 per cent., 
30 per cent, and 20 per cent, solutions of A respectively; 
sample 4, without washing, was soaked with 20 per cent, 
solution of A. The samples were then submerged in sea 
water for about 20 days before testing the remaining 
strength. As shown in fig. 3, the preservative has been 
found effective in the decreasing order of concentration 
of 40 per cent., 30 per cent., and 20 per cent, with the 
precipitant on the samples rating 0-8 per cent., 0-5 per 
cent., 0-3 per cent, and 0-2 per cent, of the copper. 
Certainly this is suggestive of correlationship between the 



concentrations and the amounts of the precipitant. 
Despite the same concentration 20 per cent, applied to 
both samples 3 and 4, the preserving effect was much 
greater in the washed sample 3 than in 4; while no 
appreciable difference was found in the effect between 
samples 1 and 3, sample 3 according to microscopy, had 
the dyeing solution soaked much deeper into the fibres 
than sample 4, which was most likely responsible for 
making sample 3 better than sample 4. 

Experiments to establish an optimal mixing rate for 
securing the preserving at a reasonable cost by minimising 
the amount of expensive sterilizers to be mixed with copper 
naphthenate, were also conducted. Sample twines, each 
weighing approximately 48-7 g./m. washed in running 
water for 5 hours, were subjected for another 5 hours to 
copper naphthenate baths, which were prepared by 
mixing 48 per cent, copper naphthenate, less than 0-05 
per cent, synthetic resin, and either 2, 1-5, 1, or per 
cent, synthetic sterilizer 3 DM, and diluting to 30 per 
cent, with kerosene. The sample twines a, b, c, and d, 
were made to correspond to the different concentrations 
of the synthetic sterilizer in that order. After drying, 
the samples were submerged in sea water and the 
remaining breaking strength tested at intervals of about 
three weeks. Fig. 4 is indicative of efficiency of the 
synthetic sterilizer used, since all the samples but d had 
fairly good results. Comparing a, b, and c, one may 
notice that the first two with higher mixing rates were 



119 ] 



MODERN FISHING GEAR OF THE WORLD 



better than c until the 42nd day of the submergence, 
while little or no difference was apparent from the 67th 
day onward. In other words, after about 60 days of 
immersion, the precipitation of the synthetic sterilizer 
decreases nearly to the same extent among the three 
samples, and this in turn depletes their strength in the 
same degree. These findings may warrant the necessity of 
carrying out redyeing of fishing gear after about that 
period of use. 

In respect of the relationship between the preserving 
effect and the length of time for immersion, preliminary 
experiments showed no discrepancies between sample 
ropes kept for various durations over five hours in the 
dyeing bath and those treated in the vacuum-cofnpressor. 
More detailed experiments are under way. 

TANNIN PRESERVATION 

The commonest types of cutch used in Japan are dis- 
tinguished from each other by their trade names, B, R, 
and T. In addition, considerable amounts of tannin 
products, such as wattle and quebracho extracts, arc 
used, though, according to experiments by Kanna, 
there is little difference in the preserving effect 1 " 1 . 

1 I ) Dyeing bath: The cotton nets are first boiled for 
one to two hours, washed in fresh water and dried. 
They arc then boiled with 3 to 4 per cent, solution of 
culch in fresh or sea water for some 2 hours, left in the 
bath overnight for cooling, then dried in the sun or in 
the shade. Upon drying, the net is soaked once more in 
the same solution at ordinary temperature for one night. 
A 4 per cent, concentration of culch solution is the best 
for net preservatives". 

When dyeing hemp twine, the same procedure as for 
cotton materials can be employed, but heating should 
be avoided. 

(2) Redyeing for various nets: The first dyeing bath 
described above is applicable to various small types of 
fishing nets. In the case of small-sized trap nets they arc 
disinfected by sun-drying part by part after one week's 
use. In addition to that they are redyed with 3 per cent, 
solution every three weeks during the period in use. 

For other types of net, such as small purse seines, 
stick-held dip-nets and beach seines, it is recommended 
that they receive sunlight disinfection after each day's 
use and redyeing at intervals of a week to ten days in 
3 to 4 per cent, solution. The life of a small trap thus 
treated may be two or three years, and of the other 
nets, three or four years. 

BICHROMATE TREATMENT OF TANNIN 
PRESERVATION 

By impregnating with tannin products and consecutive 
sun-drying, a thin film of tannic acid is built up of the 
fibres. This film prevents infectious bacteria from getting 
into the fibres. Under conditions in the coastal waters of 
Japan, however, the acid film would remain on a net no 
longer than one week, if the net is in continuous use. 
Therefore, frequent re-dyeing is needed to maintain the 
strength of the net which otherwise would quickly 
deteriorate. Since one of the remedies, coal-tar coating, 
worked out in an attempt to prolong the life of big set- 



nets and such gear, has not yet been made free from 
certain disadvantages, another improvement has come 
into being in the form of either potassium bichromate 
or of sodium bichromate. 

(1) Treatment: A net thoroughly impregnated with 
tannin solution in the same way as described above, is 
again soaked in 1 per cent, of solution potassium bichro- 
mate or sodium bichromate at ordinary temperature for 
one or two hours. The chemicals may be dissolved by 
heating, but the dyeing bath must not be heated. After 
the two-hour immersion and subsequent washing, the net 
is ready for use or it can be dried for storing 7 . 

A defect of this treatment is that it needs a considerable 
amount of labour, and is costly and time consuming, but 
this may be offset by the prolonged life of the net, as 
tannic acid fixed by the bichromate makes it possible for 
the net to be used for twice as long as a net dyed in a 
conventional tannin bath (samples 1 and 2, figs. 1 and 2). 

(2) Commercial dyes with tannin fixation: Among 
several makes of commercial dycstuffs developed from 
the principle of tannin fixation, D* and E + showed the 
best results (samples 8 and- 15, fig. 2). 

The product D, good for preserving abaca materials, 
has been adopted with success for such gear as sctnets 
which remain in the sea for prolonged periods. However, 
a net must be put into service soon after D treatment; 
if not, it is liable to suffer from the quantities of copper 
sulphate contained along with the sodium bichromate 
in the product. Product E, comprising fine grains of 
silicic acid in the fixative, gave excellent results, parti- 
cularly when applied to cotton twine (footnote of 
Table II). 

COAIXIAR DYEING AND ITS MODIFICATION 

(1) Evaluation: Coal-tar treatment shows greater 
preservability than most of the other dyes reported 
above samples (13 and 14), fig. 1, due to the heavy 
coating on the fibre. A disadvantage is that the net 
becomes uncomfortably sticky and sometimes too 
heavy for efilcient manipulation. In addition, this would 
often result in deteriorating the structure of fibre to a 
critical extent, and increasing the weight so much that 
nets such as set nets, run a risk of being lost in an 
abnormal current or rough sea. 

(2) Treatment: Formerly coal-tar immersion was 
carried out at 100 deg. C. or higher for 5 to 10 minutes. 
However, recent experiments have established that the 
temperature need not be higher than about 60 deg. C. 
for cotton twine, or 30 to 40 deg. C. for abaca nets and 
ropes, the time required being around 10 minutes for both. 
The fractional distillation of coal tar can now be con- 
tinued further than before, making possible the utiliza- 
tion of the resulting volatile preservatives; this would 
evaporate if heated to a higher temperature. 

When either creosote or heavy oil is used as diluent to 
minimize the disadvantages, the former tends to acceler- 



* "Horyo Senryo"', requiring 3 per cent, cutch solution for the 
first bath, contains K 2 Cr 2 O 7 copper sulphate, and alum for 
the second bath. 

t "Aritoku Tannin'*, requiring 3 per cent, cutch tannic acid 
solution for the first bath, contains K 2 Cr 2 O 7 , silicic acid and 
tartar emetic for the second bath. 



[1201 



Treatment 



JAPANESE METHODS OF PRESERVATION 





Ratio of fouling (%) 
10 
1 



20 



30 



Copper naphthenate dye A A 
Coal - tar 



Manila twine 
Cotton twine 



Copper naphthenate dye B 
Coal - tar 



Cutch 

Potassium Bichromate 
Coal - tar 



Cutch 




Coal - tar 



SSSKKSS^^ 



Fig. - 5 Ratio of average weigh/ of marine plants grown on the treated twines during 60 day** sea submerging to the weight of the new twines 



ate the tar deterioration, while the latter would prevent 
the net from drying up. 

(3) Modified Coal-Tar Treatment: Further experi- 
ments in coal-tar preservation showed that re-treatment 
of a cutch-dyed set net with coal-tar or diluted coal-tar 
could extend the life of the net from three to four years to 
four to six years (samples 3 to 7 and 16, figs. 1 and 2). 

Commercial dyes D and E mentioned above, are 
successful applications born respectively from these 
ideas along with their special formulae. Tables 1 and II 
give the relative merits, as preservatives of coal-tar, 
diluted coal tar and some other dyes. 

(4) Maintenance: Creosote or heavy-oil dilution 
containing 40 to 80 per cent, coal-tar is commonly used for 
the re-dyeing bath which a setnet, for instance, requires 
only every 80 days. Meanwhile, sunlight disinfection 
should be applied to the net two to three times between 
the baths. Re-dyeing for a trawl net is required after two 
or three operations covering 60 to 90 days; for round 
haul nets, it is only necessary after each fishing sesson. 

The ideal storehouse for the treated net must have an 
elevated floor in order to secure enough ventilation with 
the lowest degree of humidity. Salt sprinkled between the 
layers of a folded net would partially check growth of 
micro-organisms and the deterioration by tar. 

(5) Trends in technological research: Technological 
research in coal-tar preservation aims at development or 
improvement of (1) the diluted coal-tar treatment; 

(2) the protection of nets against foul organisms, and 

(3) a single dyeing bath treatment. In the case of cotton 
twine, experiments have shown more or less satisfactory 
results with regard to the first two questions. However, 
much remains to be learnt in connection with abaca 
material as well as the single dyeing bath 8 (Table II; 
samples 4, 6, 9, 16, figs. 1, 2; samples 5, fig. 3; fig. 5). 

It has also been found that coal-tar treatment following 
the copper naphthenate bathing of cotton and abaca 



materials is effective against foul organisms. The twine 
samples were submerged in the sea and controls were 
carried out at 20-day intervals to dry and assess the 
amount of foul organisms, animals by number and 
plants by weight. Fig. 5 shows the average percentage 
increase of weight comparable by group of samples, on 
the basis of the total weight of plants found at the end 
of about a two-month period. The results obtained were 
nearly the same for both the plants and the animals. 
Although the treatment was also found effective for 
preserving the net (sample 16, fig. 2), further research 
is under way to obtain a similar result by a single bath 
instead of the double bath normally required. 

These procedures are based on sterilization, and pre- 
clusion of micro-organisms and any technological 
advancement of fishing gear preservation is expected to 
proceed in these directions. 

PRESERVATION BY CYANOETHYLATION 

In regard to the preservation of salmon gillnets made 
of ramie, twine treated with acrylonitrile was compared 
to those treated with cutch and sodium bichromate, by 
submerging the samples in the sea for 50 days. The 
breaking strength, tested at 10-day intervals, proved that 
the former, although it had a lower initial strength 
because of cyanoethyli/ing, can be used for a much 
longer period (Table IIT). 

Usually, the extent of cyanoethylation is indicated by 
the amount of nitrogen contained in the twine, though 
it is difficult to determine exactly to what extent it 
really is cyanoethylated. 

If the nitrogen content is 2 5 per cent., as in the present 
experiment, the treatment would cost nearly twice as 
much as the cutch treatment or about 0-22S U.S. 1 Ib. 
of the material. However, treatment in bulk reduces the 
cost to a level within the means of the fishermen. 

Caution: In using acrylonitrile, workers should be 



[121 ] 



MODERN FISHING GEAR OF THE WORLD 



TABLE III 

Decrease in Breaking Strength of Ramie Thread (17 counts, 5 plies ) 
(Submerged in the sea for 10 to 50 days) 



~,- _ t- . t-Mi Breaking strength (kg), assessed at 10 days intervals 
i wine tested - 10 days 2Q days 3Q days ^ days 5Q days 



1-0 



25-4 11-9 8-1 



Non-treated 

Treated with 

cyanoethylene 18-6 19-8 21-7 21-5 17-4 10-5 

Treated with cutch 

3 times, then with 

sodium 

bichromate 206 19-2 19 6 9-0 



protected from the hazards detrimental to their health. 

SUMMARY 

1. Disinfection by sun-drying and boiling is applied to 
certain types of nets which are used without dyeing 
because of reasons pertinent to their operation. 

2. Preservation of nets and ropes by copper suJphate 
is recommended for fisheries using sardine purse seines 
and beach seines, which are based near the shore and the 
gear can therefore be retreated daily. The first dyeing 
bath requires several hours immersion in 0-1 per cent, 
copper sulphate solution in case of fresh water or 0-3 
per cent, solution in case of sea water. After a day's 
operation, the net has to be sterilized in 0-01 per cent, 
solution (fresh water), or 0-03 per cent, solution (sea 
water). A suitable amount of the solution should be 
added to the re-dyeing bath from time to time to secure 
a constant concentration. Tn no case should a net 
treated with copper sulphate be exposed to the sunlight. 

3. Copper naphthenate has a greater preserving 
effect when mixed with organic sterilizers and similar 
dyes. The dye is not so effective for cotton or ramie 
materials as for abaca. There should be more than 
0-5 per cent, precipitation of copper on the materials 
in all cases. 

4. The optional concentration of cutch is 3 to 4 
per cent. Application of fixative such as K 2 Cr 2 O 7 or 



Na 2 CrX) 7 can double the life of the cutch-treated 
materials. Among several commercial dyes produced on 
the principle of the tannin fixation bichromates, those 
containing copper sulphate as a fixative are good for 
preserving abaca materials, and those containing tartar 
emetic or silicic acid powder are suitable for cotton. 
No appreciable efficiency has been noticed with resin 
dyes. 

5. Despite its remarkable qualities as a preservative, 
coal tar has the disadvantage of making nets sticky, 
heavy and fragile. Diluted coal-tar treatment, which 
could lessen these disadvantages, still needs to be 
improved. Experiments show that gasoline is a better 
diluent than creosote or heavy oil. The more coal tar is 
diluted, the lower its value as a preservative. However, 
pretreatment by formulae 1,2, 8, or 12 in Table II has 
been found to improve greatly the preservation of a net 
when treated v\ith diluted coal tar. 

6. It is most important to preclude foul organisms, 
such as seaweeds and shells, from growing on setnets, 
etc. Nets treated first with copper naphthenate and then 
with coal tar were proved to be markedly free from 
infectious microbes and foul organisms. Research to 
secure a similar effect by a single dyeing bath is no* 
under way. 

7. Ramie netting twines treated with icrylonitrile 
agent and submerged in sea water indicated that the 
treatment made the material strongly resistant to 
micro-organisms, without affecting other properties 
required for fishing. 

REFERENCES 

1 Matsumoto, J. : Unpublished. 

~ Migita, M., Matsumoto, J. and Karma, K. : Studies on Fish 
Net Preservation by Copper Sulphate I; A simple determination 
of Copper Sulphate. 

Bull. Japan. Soc. Sci. Fish., Vol. 18 No. 2 pp. 78-84 (1952). 

3 Shimpzaki, Y. : On the Net Preservation and some 
Characteristics of Synthetic Netting Cords. "Teich" No 10 
(1956). 

4 Shimozaki, V. : Unpublished. 

5 Kanna, K. and Migita, M. : Unpublished. 

* Migita, M. : Fixing of Tanned Nets; Journal Fish. Exp 
St., No. 13, (1943). 

7 Migita, M. : Tanning Net in Sea Water; Bull. Japan 
Soc. Sci. Fish.. Vol. 15, No. 12. pp. 781-786. (1950). 

8 Shimozaki. Y. : Unpublished. 



[122] 



ROT-RESISTANT FISHING NETS BY THE "ARIGAL" PROCESS 

by 

A. RUPERTI 

CIBA Limited, Basle, Switzerland 

Abstract 

Micro-organisms living in water attack cellulose, which is the reason why unprotected cotton nets rot. Synthetic fibres are rot-proof, 
this being one of the reasons for their increasing use in net manufacture. Impregnation of nets as carried out by fishermen does not render 
them durably rot proof; the treatment has to be repeated frequently. In the U.S.A., processes have been worked out to produce rot-proof 
cotton by chemical treatments. Acetylatcd and cyanoethylated cotton are durably rot-proof, but the chemical treatments are complicated 
and costly. CIBA's Arigal proofing process is not based on chemical treatment, but on deposition of a synthetic resin in the fibre. The 
process consists of impregnation with an aqueous Arigal solution and fixation, without intermediate drying. The Arigal is not applied to 
the finished nets by the fishermen, but to the cotton yarn in a textile mill. The process is simple and gives a degree of conservation superior 
to that of the chemical treatments, and the properties of the fibre are not adversely affected. Cotton treated with Arigal exhibits outstanding 
weather resistance. It may thus be expected that the Arigal proofing process will find use in the field of net making, and that, in all respects, 
nets proofed by this process will meet the stringent requirements placed on them. 



Resume 



Des filets de peche imputrescibles par le precede "Arigal" de CIBA 



L'eau rcnferme des micro-organismcs qui attaquent la cellulose; c'est pourquoi les filets de coton qui n'ont pas subi un traitement de 
protection, pourrissenL Les fibres synth&iques sont imputrescibles; c'cst une des raisons pour lesquelles elles sont de plus en plus employees 
dans la fabrication des filets. 1 /impregnation telle qu'clle est pratiquee par les pecheurs nc confere pas aux filets une protection durable 
contre la pourriture, et doit etre r6pclec fr&juemment. On a mis au point aux Etats-Unis des traitemcnts chimiqucs rendant le coton insensible 
a la pourriture. Le coton actyl ou cyano&yle est protege d'unc (agon durable, mais les traitements chimiques sont complexes et couteux. 
Le precede Arigal de CIBA n'est pas un traitement chimiquc; il consiste & impregner la fibre de rcsinc synthetiquc au moyen d'une solution 
aqucuse d* Arigal ct a la fixer sans sechage intermediate. L'Arigal n'est pas applique par les pecheurs aux filets fabriques, mais sur Ic fil de 
coton dans la filature. Le procede est saimple et assure un dcgrt de conservation suprieur a celui confer^ par les traitements chimiques; 
en outre, il n'exercc pas d'eflel nuisible sur les proprietes de la fibre. Le coton traite a P Arigal posscde une resistance remarquable aux 
conditions atmosph6riques. On peut done prevoir que le procedc Arigal sera adopt6 dans le domaine de la fabrication des filets et que les 
engins ainsi trailed rcsisteront an dur service qui leur est impose. 

Redes de pesca resistentes a la pudricion mediante el procedimiento "Arigal" de CIBA 
Lxtracto 

La resistcncia dc las fibras sinteticas es una de las razones que han influido sobre la popularidad de us uso en la manufactua de 
urtes de pesca, ya que los microorganismos prescntcs en el agua atacan a la cclulosa causando la pudricidn de las redes de algod6n sin tratar. 
La cniintadura hecha por los pcscadoras impide el detcrioro durante relativamcnte poco tiempo, dcbiendo rcpetirse con frecuencia. 

Ln los E.U.A. sc han ideado procedimientos quimicos para obtener algodoncs, acetilados y cianoetilados, que resistcn durante 
largo tiempo los efectos de las pudrici6n, pcro lienan el inconveniente de ser complicados y caros. El metado "Arigal" ideado por CIBA. 
no se basa en la aplicacion de un proceso quimico, si no en el deposito de resinas sinteticas en las fibras impregnandolas con una soluci6n acuosa 
dc "Arigal" que se fija sin necesidad de recurrir a una desecaci6n previa. Hste procedimincto, ademas de ser secnillo, cs aplicado en la hilanderia 
a las fibras y no por el pescador, a las redes, da una preseryaci6n superior a la obenida con procesos quimicos, no afccta adversamente a 
.is propiedades dc las fibreas y connmion al algod6n gran resistencia a los agentes climAticos. 



A THOUGH, in the main, fishing nets are still 
made from natural fibres, such as cotton, synthetic 
fibres have in recent years been used in increasing 
quantities. Synthetic fibres are very strong and light, 
absorb very little water, ase rot-proof and have good 
catching properties. Knot slippage and deterioration by 
weathering are for the present still disadvantageous 
but efforts are being made to counteract them. 

The advantages of synthetic fibres greatly outweigh 
iheir disadvantages, as is shown by the enormous 
increase in use of synthetic fibres. According to Prof, 
von Brandt, more than nine million pounds of synthetic 
fibres, primarily vinylon, were used for net manufacture 
in Japan in 1955, compared with only 110,000 pounds 
used 5 years ago. 
The high price of synthetic fibres is a drawback, but 



natural fibres, although cheaper, are not rot-proof, the 
cellulose being attacked by the micro-organisms living in 
water, so that they have to be protected. This protection 
increases costs, thus reducing the price advantage which 
cotton has over synthetics and, in some cases, making it 
quite illusory. Hitherto, preservation has been carried 
out by the fishermen who use copper preparations, 
chrome compounds, linseed oil, tar oils, etc., some 
treatments being carried out at the boil. None of these 
treatments is very durable and most have to be repeated 
periodically, which adversely affects the nets and causes 
shrinkage. 

Methods for making cotton durably rot-proof have 
been studied very intensively in recent years in the U.S.A., 
the world's greatest producer of cotton, and considerable 
efforts have been made to produce a rot-resistant 



123] 



MODERN FISHING GEAR OF THE WORLD 



cellulose fibre. Theoretically, there are two ways of 
protecting the cotton fibre from micro-organisms. First, 
the fibre can be loaded with toxic substances which kill 
the organisms. This system of active preservation is used 
by fishermen e.g. when they impregnate their nets with 
copper compounds, but it does not offer durable preserva- 
tion. In order to be effective, an active toxic agent should 
be able to penetrate into the interior of micro-organisms, 
and, to do this, it should be soluble to a certain degree. 
The drawback, is however, that even partly soluble 
substances, are eventually washed out by prolonged 
immersion in water. The second, and more promising 
method, is that of passive preservation, this being the 
method chosen by American research workers. Here the 
fibre is chemically converted into a cellulose derivative by 
csterification or etherification and thus made resistant to 
attack. The so-called chemical finishing of cotton by 
acetylation or cyanoethylation has been carried out on 
pilot plant scale in the U.S.A. and has been the subject 
of much discussion in recent years in interested circles. 

The great disadvantage of chemical treatments is their 
complexity and high cost. Processes involving the use of 
volatile and, in some cases, toxic chemicals, necessitating 
the use of enclosed equipment made of acid-resistant 
material, can be neither simple nor cheap. It is therefore 
very doubtful whether chemically-treated cotton would 
offer an appreciable price advantage over synthetic 
fibres. This is the reason why the chemical finishing of 
cotton has not been able to stem the advance of the rot- 
proof synthetic fibres. 

C1BA has attempted to solve the problem of rot-proof 
cotton by a different and considerably simpler means. 
By CIBA's Arigal process [see A. Ruperti, Mell. 
Textilberichte 37, 1419-1421 (1956)], passive protection 
is given by depositing a synthetic resin in the fibre, a 
process which gives permanent protection against attack. 

The resin is fixed by a wet treatment which has been 
patented by CIBA. The Arigal is converted into a com- 
pletely insoluble condensation product within the fibre, 
thus rendering the cotton rot-proof. This is achieved with- 
out any adverse affect on the mechanical properties of 
the fibre and without the fibre being degraded in any way 
whatever. 

The method consists in impregnating the cotton with 
an aqueous solution of Arigal C in the presence of 
a catalyst (Arigal Catalyst C) and then fixing the 
preserving agent by a heat treatment, preferably under 
pressure, the material not being dried between impregna- 
tion and fixation. This process is simple and can be 
carried out in the conventional equipment available in 
the majority of textile works. It is only the wet fixation 
treatment which does not conform to the usual type of 
operation, since hitherto it has not been the practice to 
subject resin-treated goods to a heat treatment without 
previous drying. However, the wet fixation, too, can be 
carried out quite satisfactorily, using equipment generally 
to be found in dyeworks. 

In order to ensure the maximum degree of preservation 
by this process it is essential that the Arigal be uniformly 



deposited throughout the material, the knots being 
adequately penetrated. The materials should therefore 
be treated at the textile mill, where best results are ob- 
tained by treating the untwisted yarn. 

Calculated on the weight of the treated goods, 10 per 
cent, of Arigal C, when uniformly deposited, gives a 
very high degree of protection against micro-organisms. 
Cotton net thread treated with Arigal showed absolutely 
no reduction in tensile strength after two years immersion 
in a particularly muddy part of the Rhine. 

Untreated cotton yarn immersed at the same place 
was completely destroyed in a matter of weeks. 

Comparison of tests made with chemically treated 
cotton from America showed that the Arigal treatment 
gave greater durability (A. Ruperti loc. cit.). The Arigal 
cotton showed no reduction in tensile strength after a 
4-week immersion in the Rhine followed by burial in 
compost earth for 24 weeks at 30 deg. C. The chemically 
treated cotton, on the other hand, was destroyed. 

Cotton treated with Arigal is also very resistant to 
weathering. It is well known that the tensile strength of 
textile fibres is reduced by outdoor exposure. Cotton is 
one of the more resistant of the textile fibres in this 
respect, being far superior, for example, to nylon and 
Orion 42. Chemical treatment reduces the weather 
resistance of cotton, whereas Arigal C treatment con- 
siderably increases this resistance. After a 12-month 
weathering test carried out at CIBA, a boiled out, 
untreated cotton fabric had retained 21-7 per cent, of its 
original tensile strength, and Dynel 23 per cent. The 
same quality cotton fabric proofed with 10 per cent. 
Arigal C retained 47-8 per cent, of its tensile strength, 
while Orion 42 lost all strength after 1 2 months' exposure, 
and nylon after only 6 months. 

Jute and ramie can also be treated by the Arigal C 
process with very good results. However, the degree of 
proofing obtained on hemp and linen leaves much to be 
desired, and treatment with Arigal alone cannot be 
recommended for these two fibres. 

Nets made with Arigal treated cotton do not require 
the usual cutch treatment since such a treatment would 
not give added protection. However, if cutching should 
be desirable for colouring purposes, there is no reason 
why this should not be done. Even after prolonged 
immersion, cutch is not washed off Arigal treated nets 
and they do not have to be re-treated. 

The Arigal process is still young and has yet to be 
proved in bulk application and practice before final 
judgment can be passed as to its possibilities. But even 
now its advantages are evident the simplicity with 
which it can be applied, its relatively low cost, the 
complete absence of any fibre degradation, the improve- 
ment in the weather resistance of the cotton fibre and, 
finally, the outstanding durability of the rot-proofing 
itself. 

Note: 

Arigal Trade-mark of CIBA Limited, Basle, Switzerland. 
Dynel Trade-mark of Carbide & Carbon Chemicals Co., U.S.A. 
Orion Trade-mark of E. J. DuPont de Nemours & Co., U.S.A. 



[124] 



APPLICATION OF ACETYLATED CELLULOSE FOR FISHING GEAR 

by 
SANDOZ LTD. 

Basle, Switzerland 

Abstract 

The partial acetylation of cotton, with an acetic acid content of 25-30 per cent, leaves the mechanical and technological properties 
of I he yarn unaffected. There is no change in appearance or colour of the yarn and it is odourless, non-poisonous, and insoluble in water 
or solvents and. moreover, it has an extremely high resistance to micro-organisms. Besides cotton, fibres such as jute, hemp, linen, sisal, etc. 
Ciin also be immunised to attack by bacteria without impairing their tensile strength. Tests on materials buried in compost with 30-40 per 
cent, humidity at 20-25 deg. C. showed that untreated cotton and jute yarns rotted away in 14 days while the acetylated yarns retained their 
original tensile strength after 6 months. Comparative tests in sea water showed th.-it cotton lines were very weak after two months but the 
acetylaled lines were still strong after seven months, and untreated sisal twine lost 50 per cent, of its tensile strength within one week, while 
acetylated sisal took nine weeks to lose the same amount. Lines, nets, and material for making sandbags are all improved by treatment 
and the fact that the present cost of manufacture is relatively high is offset to a large extent by the fact that partially acetylated cellulose fibres 
last 50-fcO times longer than the untreated matoitals. 

Application de la cellulose acctylee aux engins dc peche 
Resume 

l.'acetylation particllc du colon, avec une tencur de 25 a 30 pourcent d'acide aceticiue laisse intacie les proprietes mccaniques et 
chimiques du fil. II ne sc produit aucun changernent de I'aspect on de la couleur du fil: le produit est inodore, non toxiquc, insoluble dans 
I'eau et les solvants, et possede unc icsistance cxtrememcnt elevee aux microorganismes. En dehors du colon, on pcut immuniser d'autres 
!iorc % s telles quc lc jute, le chanvre, le lin, le sisal, etc., contre Pattaque des bacteries sans affcctcr leur resistance a la traction. Des essais 
cffectiics sur des lils enfouis dans un compost rcnfermant 30 a 40 pourcent d'humiditc et maintenu sa une temperature de 20 a 25 deg. C. ont 
montrc que des lils de colon et de jute non traites pourrissaient complctement en 14 jours tandis que des fils acclyles conservaient leur resistance 
primitive a la iraclion au bout de 6 mois. DCS essais comparatifs executes dans de I'eau de mer ont montre que les ligncs de colon ctaient 
devcnucs tres fragiles au bout de 2 mois, mais que les lignes acetylees etaient encore solides apres sept mois; des fils de sisal ont perdu 50 
pourcent de leur resistance en une scmaine tandis qif il a fallu neuf semaines aux fils de sisal acetylcs pour arnver au memc resultat. Les 
I'gncs. les filets et les matcriaux utilises a la confection des sacs de sable ont tons etc ameliores par le traitcment. el lc cout relativcment eleve 
de fabrication actuel est largement compcnse par le fait que les fibres de cellulose partiellement acetylees durent 50 a 60 fois plus que les 
memes matemux non traites. 

l ; sos de la celulosa acetilada en los artes de pesca 
Kxtracto 

La acetilacion del algod6n con 25 - 10 per ceni de acido acetico no afecta a las propiedades mecanicas y tecnologicas. ni produce 
cambios de aspecto o color en la libra que cs inodora, inocua c insoluble en agua o disolventes; adcmas le comunica una gran resistancia a 
los microorganismos. Fucra dc las fibras dc algodon tambien es posiblc inmunizar las de yule, canamo. lino, sisal, etc. contra el ataquede las 
hactcrias sin disminuir su rcsistcnciu a la traccion. Los ensayos dc matenales enterrados en abono vegetal con 30 a 40 per ceni. de humcdad, 
cuya tcmperaiura fluctuaba entrc 20 deg. y 25 deg. C.. dcmostraron que las fibras dc yute y de algodon sin tratar sc pudren en 14 dias y las 
.icetiladas conscrvan su resistencia a la traccion luego dc 6 mcscs. 

Los ensayos comparativos en agua salada permiticron observar que la resistencia de los hilos de algodon dismmuyc bastante despue* 
dc 2 scmanas, peio en los acctilados aunicnta despucs dc 7 mcscs. Los hilos dc sisal picrdcn un 50 per cent, dc su resistencia en 1 scmana, 
mientras que en los acctilados csta nusma disminucion sc logra al cabo dc 9 meses. I os hilos, redes, y material para fabricur sacos de arena 
mejoran con cstc tratamiento > su costo dc manufactura, relativamenie elevado. sc compensa en gran pane por el hccho de que las fibras 
pnrcialmente acctiladas duran unas 50 ; 60 \cccs mas que los matenales sin tratar. 



HISTORY 

IN 1920 C. Dorce (Biochem. J. 14, 709-14 (1920)) men- 
tioned for the first time the excellent resistance to micro- 
organisms of acetate silk and acetylated cotton (the 
latter without change of fibrous structure). A year later, a 
process of partial esterification of cotton fabrics to give 
resistance to bacterial attack was patented in U.S.A. by 
Wolcott and Jennison. (U.S.A. Patent 1.474.574). 

In 1926 A. Rheiner (Sandoz Ltd., Basle, Switzerland), 
succeeded in developing a much improved method of 
partial acetylation of cellulose (ref. DRP 525*084 and 
530'395 and A. Rheiner Angew. Ch. 46, 675 (1933) 
"Ueber niedrig acetylierte Fasercellulosen") which made 
bulk production possible. The commercial production of 



partially acetylated cellulose without change of structure, 
according to this process, was taken up by Sandoz Ltd. 
in 1927 and by their affiliated company Cotopa Ltd. in 
Horsforth (England) in 1929 and the acetylated products 
have since been marketed under the registered trade 
marks "Passivgarn", "Kristallgarn", "Cotopa", "Cres- 
tol", "Crestine", "Crestic" and "Crestose". 

After the second World War the Southern Utilization 
Research Branch, New Orleans (U.S. Department of 
Agriculture) carried out an extensive programme of 
research work in connection with partially acetylated 
cotton. Now, two U.S. firms are said to manufacture 
partially acetylated cotton in bulk. 



[125] 



PROPERTIES 



MODERN FISHING GEAR OF THE WORLD 

TEST REPORTS 



For the production of cellulose derivatives, and in 
particular, cellulose esters, it is sufficient to modify only 
the amorphous part of the fibre to obtain the maximum 
resistance to micro-organisms. This corresponds on an 
average to the substitution of one hydroxyl group for 
one glucose anhydride unit. By this means, the swelling 
and water absorption capacity of the fibre are reduced 
to such an extent that bacteria and fungi have great 
difficulties in decomposing it. The crystalline part which 
has not been modified is not easily attacked by micro- 
organisms, as was proved by P. Karrer (Kolloid-7, 52, 
304 (1930)). 

Practical experience has shown that for partial 
acetylation in bulk, an acetic acid content of 25 to 30 
per cent, should be aimed at, to leave the physical 
properties of the yarn unaffected. A modified cellulose 
with an extremely high resistance to micro-organisms is 
obtained by this method. 

The P.A. cotton does not show any change in appear- 
ance or colour. It is odourless, non-poisonous and in- 
soluble in water or solvents. It can be knotted easily, 
causes no skin irritation or corrosion and shows consider- 
ably better resistance to heat than untreated material. 
Tensile strength remains the same, but it is not immune to 
attacks by termites. 

Other fibres, such as jute, hemp, linen, sisal, ramie, 
etc., can be similarly immunised to micro-organisms. 
Acetylated bast fibres are of particular interest when the 
highest tensile strength is wanted. It is, however, ques- 
tionable whether the higher priced cellulose fibres (such 
as ramie, which shows a better natural resistance to 
micro-organisms than cotton) can stand the price 
increase imposed by the acetylation process. 

TENSILE STRENGTH AND COSTS 

Acetylation increases the weight of material by 15 to 
25 per cent., and this has to be considered in the total 
manufacturing costs. The absolute tensile strength 
remains unchanged or decreases only slightly (according 
to the yarn quality to 7 per cent.), and the breaking 
length is reduced by 20 to 30 per cent. This may have 
to be taken into account by selecting suitable raw 
materials and by paying special attention to the spinning 
and twisting of the yarn. 

A considerably increased tensile strength can be 
obtained by stretching acetylated yarn in superheated 
steam. Combinations of acetylated and synthetic fibres 
may be used. For instance, acetylated cotton is spun 
round polyamide filament or yarns made of polyester 
and acetylated fibres are twisted together, or synthetic 
staple fibres arc spun with acetylated cotton fibres. 

The partial acetylation of cellulose is dearer than most 
impregnation methods hitherto used to protect cellulose 
fibres against mildew, sea water and other forms of 
bacteria. It can only be used generally for this purpose 
if ways are found to reduce the manufacturing costs. 
But as the fibres last 50 to 60 times longer than untreated 
material there should be many possibilities for using 
them in spite of their relatively high price. 



The following reports give a vivid picture of the remark- 
able resistance of treated cotton to micro-organisms. 

1. Resistance to rot and bacteria (see Table I) in compost 
with 30 to 40 per cent, humidity at 20 to 25 deg. C. The 
yarns were wound on glass tubes of 6 cm. exterior 
diameter. After the tests, the yarns were washed and 
aired and the tensile strength was established. The cotton 
and jute yarn rotted away completely after two weeks 
but the acetylated yarn still showed the original tensile 
strength after 26J weeks. 

2. Comparative mildew resistance tests carried out by 
the Manchester Chamber of Commerce Testing House 
and Laboratory. Entry No. 342934 Prog. No. 380124 
of 15.10.1956 (see Table II). 

Hank No. 1 marked 3/10's Cotopa XL (acetylated 
cotton yarn) Howard Green (raw cotton, soap scoured 
and vat dyed, followed by acetylation). 

Hank No. 2 marked 3/1 0's Howard Green raw cotton 
treated with Copper Naphthenate (raw cotton, soap 
scoured and vat dyed and impregnated with Copper 
Naphthenate in accordance with BSS 2087). 

These samples were tested for resistance to mildew 
according to the method prescribed in the Standards 
Association of Australia Interim Specification S.A.A. 
Int. 88 Sect. 3. 

Specimens from each sample were washed in a water 
spray for 7 days and other specimens were treated 
for 5 days at 70 deg. C. : L 2 deg. C. in an oven with a 
forced air circulation. Then, with some grey cotton 
yarn as control, they were sterilized and pressed on to 
nutrient agar medium in sterile, covered, glass vessels, 
inoculated with a spore suspension of Menmoniella 
echinata, and incubated for 14 days at a temperature of 
30 deg. C. 2 deg. C. and 95 to 100 per cent, relative 
humidity. 

They were then removed, washed, aired, and their 
tensile strengths determined with the following results: 

Single thread strength on Goodbrand machine. 
Distance between jaws 12 inches. Speed of traverse of 



I \bl i I 



1 ensile im'iiKth \a\ />ei < em. of original) after interment 



raw cotton w 
( Egyptian) 



W "" d 
< onoii van, 

r.gvptian) 



Jtue 



boiled 



nun- (icervlaieil mm- acetvlated ra\\\ non- , 

/>>- 28 " mm- 28 -. ,,,- fl y- "< 
luted ineticm'id la led acetic acid la ted 



acetic acid 



100 


100 


100 


100 


100 


100 


3 25 


129 


27 A 


116 


~ 




"7 ty 


128 


23 


124 


41 


15 l > 


14 


113 





121 


n 


112 


28 


105 




124 


3 


112 


56 


117 




123 


<) 


137 


117 


104 


^. 


101 




112 


185 


108 





88J 





104 



126 ] 



ACETYLATION OF COTTON 





TABLE II. 


U.Npiu>om> GREY COMROL 


A\ 


Received 


After 


/ncubatitiK 


7-9 


8-0 


01 


01 


8-7 


8-2 


0-5 





8-9 


7-7 


02 


04 


7-9 


84 


nil 


nil 


8-0 


8-1 


nil 


0-6 


82 


91 


01 


0-4 


8-0 


8-2 


0-2 


0-1 


H-7 


8-7 


06 


01 


8-0 


8-6 


ml 


04 


X-9 


-3 


nil 


0-6 



8-3 Ihs. 

1 oss, per cent. 



2 Ihs. 

97 A 



Marked: "3/10 Coiopu XI Hovturd Green" 



4\ Received 
Ib. 


After 
Incubating 
Ib. 


After Washing 
and Incubating 
Ib. 


After Heating 
and 1m abating 
Ib. 


5-7 


46 


5-1 


5-3 


5 3 


4-6 


4 9 


44 


4-9 


5-2 


53 


5-1 


4 7 


4-7 


51 


5-2 


5-5 


4-7 


5-4 


4-9 


49 


5-7 


45 


5-3 


5-4 


51 


50 


4-7 


^ -2 


5-6 


49 


4-7 


5-9 


5 1 


51 


4 1 


5-3 


5-3 


4 7 


4-4 


4-8 


45 


49 


< *> 


^ - 


5-8 


51 


5-3 


^ -8 


51 


5-7 


42 


53 


5 2 


52 


56 


5-7 


5-1 


5-^ 


* 1 


4-7 


5-2 


51 


5-5 


4-7 


49 


5-1 


52 


S 4 


41* 


5 7 


5-2 


4-6 
5-1 


49 


5-5 


s 5 


* 1 

5 


50 


43 
5 


5-f> 



.V 


1 


2 



I oss f per cent. 



nil 



nil 



Marked: "3,10 Howard Green Ra\\ Cotton treated \\ith Copper 
Naphthenatc" 



Is Reiened 
Ib. 


After 
Im nbating 
Ib. 


After Hashing 
and IncnbafitiK 
Ib. 


Atlef Heating 
and Incubating 
Ib. 


5-7 


5 


8 


4-2 


6 





2 


4 


^ 


4 


3 


4 


42 


6-0 


V 


2 


5-7 


5 


7 




9 





7 


3 





33 


^8 


6 


2 


4-9 


5 


8 




4 


1 


4 


4 


4 


3-2 


(vl 


5 


2 


5-7 


5 


-8 




1 


- . 


4 


3 


6 


42 


4-9 


5. 


1 


5-9 


5 


4 


l 


4 





9 


3 


2 


2-9 


~ . 
















1 


6 


3 


4 


4-7 


S 6 


5 


6 


56 


5 


1 





i) 


1 


j 


3 


2 


35 


S-2 


5 


1 


5-5 


S 


6 


2 


4 





6 


3 


. 7 


\ -7 


^8 


5- 


7 


5 -ft 


5 


7 





-7 


> 


( 


4 


2 


\ 2 


5-3 


5 


(> 


51 


s 


6 





X 


"> 


3 


2' 


^ 


3 -1 



5 6 



Loss, per cent. 



3 6 



73 



lower grip 18 inches per minute. Machine capacity 10 Ib 

It will be seen that the "3/10 Cotopa XL Howard 
Green" sample was not affected by the incubation either 
before or after washing or heating. The 4k 3/10 Howard 
Green Raw Cotton treated with Copper Naphthenate" 
sample, however, lost 73 per cent, of its strength after 
washing and incubating and 36 per cent, after heating 
and incubating. 

These figures clearly show the superiority of partially 
acetylated cotton. 



3. Resistance to Sea Water 

(a) Comparative tests on fishing lines in tidal waters 
showed that cotton lines were very weak after two 
months, but the acetylated lines were still strong 
after seven months. 

(b) Similar results were obtained in testing untreated 
and acetylated sisal twine in sea water. The 
tensile strength of the untreated twine dropped 
within a week to 50 per cent.; the acetylated 
sisal material lost 50 per cent, after nine weeks. 

Application of partially acetylated cellulose fibres 

The extraordinary resistance of partially acetylated 
fibres to long immersion in water makes them most 
suitable for fishing lines, ropes and seines. Fishing nets 
made of acetylated fibres are more flexible, remain 
cleaner and are easier to handle than normal nets which 
are impregnated and must undergo regular cutch treat- 
ment, which increases costs in time and money. Nets of 
acetylated fibres or mixtures of synthetic fibres and 
acetylated cellulose do not have to be treated again. 
Another advantage is that acetylated fibres facilitate 
knotting. 

Tests in Scotland with herring nets made of partiallv 
acetylated cotton cord have shown excellent results to 
date, but more tests will be made before a conclusive 
report is issued in such mixtures. 

Tests of fishing nets made of acctylated cotton twist 
are being made in Germany, supervised by the official 
German testing station (Bundesforschungsanstalt fiir 
Fischerci, Hamburg). 



[127] 



EVALUATION OF ROT-RETARDING NET PRESERVATIVES 



by 

J. ZAUCHA 

Sea Fisheries Institute, Gdynia, Poland 

Abstract 

The most important methods of examining the effectiveness of rot-resistant proteclants are (1) the static method, (2) the aquaria I 
method, and (3) the tishing method. The author describes these in detail and points out some of their defects. In the second part of the 
paper Dr. Klust's tests on impregnated fish netting are discussed and certain amendments are suggested. 



Resume 



Evaluation des agents de preservation retardant la poupriture des filets 



Les plus importantes meihodes cTexamen de I'efficacite des agents protegeant la resistance a la pourriturc sent: (1) la m&hodc 
statique par enfouissement dans le sol, (2) Iamthodc par immersion dans un bac et (3) la mthode realisant les conditions de peche. L'autcur 
decrit ces methodcs en detail et fait ressortir quclques-uns de leurs defauts. Dans la secondc partic de la communication, 1'auteur examine 
les essais du Dr. Klust sur les filets impregnes et suggcrc certaines modifications. 



Extracto 



Evaluation del efecto de los preservatives que retardan la pudricion de las redes 



El autor describe, en detail t, los metodos mas importantes para determinar la eficacia de los preservatives que reiardan la pudrici6n 
de las redes de pesca., a saber: (I) el entierro del material tratado, (2) la inmersi6n en agua, y (3) el uso en la pesca, y senala sus defect os. 
En la segunda parte del trabajo, se analizan los ensayos del Dr. Klust con redes de pesca entmtadas y se sugicren ulgunus modificaciones. 



A PROPER and generally recognized method of 
examination of preservatives used for cellulose 
fabrics should be introduced. An ever-increasing 
number of preservatives of different rot-resistant 
strengths are appearing on the market and the indications 
of their resistant properties, as given by the manufacturers 
or by the research laboratories, are not comparable and 
can result in misuse. 

Two important factors causing deterioration of textile 
fabrics must be considered when evaluating the preserva- 
tive: (a) the decomposing effect on cellulose of cellulose- 
producing organisms, and (b) the rinsing properties of 
water, its mechanical destruction of the protective layer 
and its slow chemical effect on the cellulose of the fabric. 
The first of those factors is generally taken into considera- 
tion, whereas the second is often practically neglected. 
Even a mild preservative which is not very soluble in 
water is more effective in the first stage, than later on 
when it has been partly rinsed out and a local bacterial 
invasion has taken place, causing partial rot. If this 
bacterial invasion spreads, the fabric is regarded as 
useless, even though the chemical indicators of the 
preservative remain unchanged. 

So far, no suitable laboratory methods have been 
established which can constitute a proper examination 
of preserved textile fabrics. There is no method which 
enables one to determine and to estimate the suitability 
of various preservatives for fishing purposes. On the 
one hand, such a method would have to ensure a proper 
estimation of the intensity of bacterial degradation and the 



effect of water on the sample and, on the other, it would 
have to enable the regulation and determination in each 
case of the principal factors. It is no less important 
that other parameters, effecting the final results, should 
likewise be guaranteed. 

The most important method** of examining the 
effectiveness of rot-resistant protcctants are: 

(1) the static method 

(2) the "aquarial" method 

(3) the "fishing" method 

(1) The static method consists of burying the samples 
in soil. The soil is watered systematically at a temperature 
of 18 to 20 deg. C. thus causing the cellulose-destroying 
bacteria which live in the mouldy soil to increase abund- 
antly, and bring about a rapid decomposition of cellulose 
fabric. 

A disadvantage of this method is that there is scarcely 
any rinsing out of the preservative by the water. Another 
drawback is that the results of tests from different parts 
of the soil are always found to differ, which is particularly 
obvious in the first stage of decay, i.e., after the same 
period of time similar tests show different losses in 
initial strength. A number of factors, such as a lesser 
contact of the fabric with the soil, an unequal access of 
oxygen, etc., seem to be responsible. 

There are certain modifications, such as inoculating 
the impregnated cellulose fabric with certain bacterial 
cultures or fungi causing decomposition of the cellulose, 
and then storing the samples in thermohygrostats. 



M28] 



EVALUATION OF PRESERVATIVES 



These methods have no practical use in fishing gear 
research except in certain experiments connected with 
storage of fishing net. 

(2) With the "aquarial" method the samples arc 
immersed in an aqueous solution of mineral salts the 
nutritive components essential for the bacteria. A 
necessary amount of cellulotytic bacteria suspension is 
added to the solution. If therophilic bacteria are used, it 
is possible to evaluate the rot-resistance of the sample 
within two days. If, however, mezophilic or psychro- 
philic bacteria are applied, no results are apparent under 
a fortnight. In laboratory practice, pure cultures of 
cellulolytic bacteria are not always applied, and frequently 
river or sea water is used for the experiment with mud- 
suspension a rich source of cellulose-destroying organ- 
isms. This experiment is, however, difficult to repeat and 
the results of the examination are generally incomparable. 
Considering, however, the simplicity of the procedure, 
it is, in spite of its drawbacks, often applied to evaluate 
various kinds of netting protectants, although the rotting 
period of the examined fabrics, especially when sea 
water is used, is relatively very long. 

One of the main defects of the "aquarial" method is 
that the impregnation is not rinsed out as much as in 
natural conditions. If the water in the aquarium tank 
is not changed at all, the surroundings undergo a gradual 
intoxication by the substances rinsed out from the 
samples, which invariably stops the normal activity of 
the organisms and causes manifold biological changes 
in the medium used. A frequent changing of water, on 
the other hand, causes a change of physical conditions 
effecting the intensity of the bacterial growth. The 
results obtained by means of this method can, therefore, 
only be treated as material for further research. 

(3) The "fishing" method consists in laboratory exam- 
ination of cellulosic cotton fabric in conditions approxi- 
mating those normal to fishing gear when in use. This 
method, developed by Dr. Mcseck, seems, therefore, to 
be generally recognised as the most suitable, especially 
for industrial practice. 

The impregnated twine samples arc fixed to frames and 
immersed in deep water. At certain intervals the samples 
are taken out of the frames and tested for mechanical 
resistance. To evaluate the surrounding medium, the 
temperature, oxygen content, pH value, geographical 
conditions and the presence of hydrogensulphide at the 
bottom of the water, etc., are repeatedly tested. 

Russian scientists do not, as a rule, use twine in their 
experiments but samples of fish netting. These samples 
are either tested apart or are sewn into different parts 
of the fishing gear working on industrial scale. Sometimes 
both methods are applied simultaneously. 

From the above survey of practical methods of 
examination we see that each affects the deteriorating 
factors in a different way. Whilst the static method 
does not lay much stress on the "rinsibility" of the 
preservative, the fishing method guarantees this condition 
sufficiently but does not give any possibility of interfering 
with the parameters influencing the intensity of cellulose 
decomposition. The results obtained by the two men- 
tioned methods must necessarily be quite different and 
misleading in assessing the actual rot-resistance of the 
given fabric. 



In 1952, the laboratories of the Polish textile industries 
started to promote a very practical and cheap method of 
impregnation of cotton twine by means of copper- 
treatment, the process consisting in emulsive coating of 
the fabric with a copper naphthenate. At the same time 
the laboratory of the Sea Fisheries Institute rejected this 
method for fish netting purposes. The two contrary 
conclusions were the result of two different methods 
applied to evaluate the same rot-resistant protectant. 

'Tests were then carried out with copper-treatment of 
fish netting by two methods the "static" and the 
"fishing" method. 

"Static" method 

Samples of treated and untreated twine were buried 
in compost soil 10 cm. below the surface. The soil was 
sprayed regularly every day with distilled water in order 
to ensure its proper water content. The temperature was 
kept within the range 18 deg. to 20 deg. C. The average 
moisture of the medium was 70 per cent. The raw 
samples were removed approximately every 5 days 
and their mechanical resistance determined. Every 10 
days fresh samples of raw twine were deposited and their 
loss in strength was determined for the purpose of 
ascertaining whether the intensity of the cellulose- 
decomposition differed in the course of the tests. The 
treated samples were removed and tested for mechanical 
resistance at longer intervals. 

"Fishing" method 

Samples of twine wound into strands with 32 to 34 
strings each were fixed on frames by means of grips and 
immersed in water in a tank specially erected for testing 
fish nets. The depth of the immersion was about 0-6 m. 
below the water level. The distance from the bottom was 
about 1 m. The samples were removed from the water 
every 10 days and dried in the air, then tested for mech- 
ical resistance by means of the Schopper dynamometer 
(distance between grips 500 mm, breaking-time 10 sees.). 
During a test that lasted from 6.9.55 to 26.10.55 the 
parameters of water medium were on an average as 
follows: 



Measured parameters 
Temperature of water 



Value 

September 16 deg. 

October 1 2 deg. 
Salt content 7-2 to 7-6 per cent. 

pH 8-2 to 8-4 

For both tests, cotton twine with the following 
properties was used: 

Metric number 40/3 3 

Initial breaking strength 5-640 kg. 

Length increase 11-4 per cent. 

The impregnating solution was a water emulsion of 
copper-naphthenate, 10 g. of CuSO 4 . 5H 2 O diluted in 
100 ml. of water warm. After cooling, a quantity of 
25 ml. of 5 per cent, ammonia solution and water up to 
500 ml. were added. A separate sample of 20 g. of 
naphthenic acids was neutralized with 10 per cent, 
ammonia solution and diluted with water up to 500 ml. 
The two solutions were mixed and a "ready-for-use" 
impregnated mixture was obtained in which the cotton- 



[129] 



MODERN FISHING GEAR OF THE WORLD 




UNTREATED TWINE 
TREATED TWINE 



20 1.11.55 

Figs. 1 and 2. 



day* 



twine was copper-treated. The samples were immersed 
for 15 minutes, the surplus drained off and the twines 
dried at 80 deg. C.; after drying, the samples had a light 
green colour. The copper content in samples calculated 
as dry values was 0-65 per cent. Other properties were: 



Metric number 

Initial breaking strength 

Length increase 



4(1/3x3 
5-690 kg. 
13*5 per cent. 



Figs. 1 and 2 illustrate the results obtained during the 
experiment. Fig. 1 shows the loss in strength as 
evaluated by the "static" method, whilst fig. 2 indicates 
the results obtained by applying the "fishing" method. 
Both figures are drawn to an equal scale (of time and 
strength); they also show the loss in strength of untreated 
twine samples, in order to demonstrate the intensity of 
bacterial degradation of the examined medium. We see 
a distinct difference in the process of loss in strength of 
treated samples examined by "static" and "fishing" 
methods, although the degree of rotting, on the whole, 
is almost the same. The almost identical loss in strength 
of untreated cotton twine in both experiments can be 
seen from the parallel curves in figs. 1 and 2, whilst the 
results with treated cotton twine differ widely. Hence, the 



evaluation of fish netting twine of the same dimensions, 
treated in the same way, differs considerably according 
to the test method applied. The numbers which showed 
how many samples were decomposed up to 50 per cent, 
of their initial strength, during the time that the treated 
twine sample had lost 50 per cent, of its initial strength, 
served as comparable indicators for both method of 
protection, the condition being that each successive 
untreated twine sample was not immersed in the medium 
before the preceding one had lost 50 per cent, of its 
initial strength. 

For the treated twine samples evaluated by means of 
the "static" method, this number amounted to "PT" 
(Protection Test) =- 9, whilst for the twine samples 
evaluated by "fishing" method it was "PT" 3. The 
mere comparison of the two numbers proves sufficiently 
how different the two methods are. The obvious con- 
clusion is that for fishing purposes the so-called "fishing" 
method is the most suitable one, provided it is carried 
put under actual fishing conditions. Although, hitherto, 
it has yielded non-comparable results (which could be 
prevented by a greater number of experiments), yet it 
seems to be by far the most reliable and appropriate for 
industrial practice. 



[130] 



EVALUATION OF PRESERVATIVES 



Evaluation Tests of Protection Methods 

A great disadvantage of all the methods for testing the 
quality of impregnated fish nettings, either described in 
literature or known in laboratory practice, is that none 
of them are practically repeatable, and their results are 
therefore difficult to compare and to transfer to any other 
conditions or surroundings. Consequently, various 
research laboratories, unable to compare the results of 
their experiments, were forced to carry out the same 
investigations relating to an identical or practically 
identical protection method. 

The first efforts to compare the value of different 
protection methods were undertaken by Dr. Klust and 
put into practice in 1952. His tests consisted of deter- 
mining the so-called "rotting value" of the medium in 
which the experiments were carried out. Accordingly, 
the "rotting value" of the medium is equal to the total 
losses in strength, expressed as percentage values of the 
initial strength of the successively examined samples of 
untreated twine Nm 50/15, so that the test of Dr. Klust, 
as such, stands for the sum of "rotting values" of the 
medium during the time in which the examined sample 
of treated twine has lost 50 per cent, of its initial 
strength. 

Dr. Klust has examined a number of twine preserva- 
tives and has given them his own symbols expressed in 
numbers, the higher the number the better the quality 
of the preservative. 

From our own experiments, in completely different 
conditions, we have obtained quite different numbers for 
certain kinds of preservatives, probably resulting from 
the fact that the "rotting value" of our medium was 
2 to 2-5 lower. Another cause was the very strong 
rinsing effect of the water currents and its mechanical 
destruction of the protecting coaling of the twine 
threads. Other parameters involved in the experiments 
did not seem to have such a great effect. 

In his tests Dr. Klust has given a very exact method for 
determining the main destroying factor of the cellulosic 
fabric, i.e., the activity of the micro-organisms, thus 
enabling a proper comparison of the deteriorative effect 
of microbial activity when examining the fish netting 
fabric. Dr. Klust has, however, disregarded the 
influence of the second important factor, viz.: the 
rinsing effect of water and the mechanical destruction of 
the membranous structure of the protection layer of each 
fibre. The importance of this factor is evident when 
applying certain excellent preservatives almost insoluble 
in water; the smallest local destruction of the protective 
layer then causes an immediate invasion of bacteria and 
a complete destruction of the thread. The case is different 
with preservatives more soluble in water. A mechanical 
destruction of the layer does not, at first, provoke a 
general attack of bacteria, as the exposed area is pro- 
tected by the field of diffusion of toxic bactericidal 
components of the protectant. After some time, however, 
the process of diffusion slows down, its field diminishes 
and the bacterial activity becomes more effective. There- 
fore, when comparing different kinds of protectants, the 
influence of non-biological factors of water on the 
impregnation of fish netting fabric must be considered. 

Another minor disadvantage of Dr. Klust's tests is that 
they have no physical value and are merely symbol 



numbers comparable with each other. The way of 
obtaining them seems also rather questionable. It is 
not quite clear to us why Dr. Klust has taken as a basis 
for the treated twine the 50 per cent, of its loss in strength 
and has not applied the same principle to the untreated 
twine. Presumably, in this case Dr. Klust wanted to 
avoid any extrapolation in time of his results. 
Though, when taking into consideration the typical loss 
in strength of the untreated twine which, in the first 
stage and for quite a long period practically retains its 
initial strength, then begins to lose it rapidly, it may be 
concluded that the loss in strength taken in regard to 
time is quite different in the range to 30 per cent, and 
50 to 80 per cent. Therefore a lesser mistake would be, 
in our opinion, to extrapolate in time the results of 
the loss in strength of the examined twines down to a 
certain point of their strength, than to apply the principle 
of summing up their actual losses in strength. The extra- 
polation would have to be possibly small in time, seeing 
that it affects the exactness of the calculation of the 
protection tests. In our opinion, both treated and 
untreated twine samples should be brought down to 
50 per cent, of loss of their initial strength. 
We would suggest a modification of the test as follows: 
The protection test of the examined treated twine 
Nm 50/15 stands for a certain number of the same 
untreated twine samples which successively have lost 
50 per cent, of their initial strength in the time in which 
the sample has also lost 50 per cent, of its initial strength, 
Due to such a definition the tests acquire a real physical 
sense and the reader can see at once how many times 
stronger is the treated twine than the untreated one. 

Such a definition does not alter the principal idea of 
Dr. Klust but modifies it to a certain extent having 
eliminated the so-called "rotting value" of the medium. 
But, in spite of this definition, the test does not illustrate 
the effects of the second factor, viz.: the non-biological 
parameters, the intensity of water current in the research 
station, etc. Considering the changeability of all these 
non-biological factors, it is difficult to determine any of 
them or to choose one or more to introduce in some form 
into the test. To a certain extent, the time in which the 
experiment is carried out gives an approximate idea of 
the resultant activity of the above mentioned non- 
biological factors, and, although it does not help us 
with any indications it lets us have a general idea of their 
activity and gives us indications as to the nature of the 
medium in which the experiment has been carried out. 
The factor of time enables us to judge the degree of 
resistance of various protectants to the bacterial de- 
composition, particularly in highly infected mediums 
for, even an ineffective protectant will initially keep the 
twine from rot, until after a certain time when mechanical 
damage has taken place the micro-organisms will in- 
variably cause complete decomposition. If such a 
treatment process were only to be evaluated according to 
Dr. Klust, a very high number- denoting efficiency- 
would be obtained in a highly infected medium. The 
same treatment process evaluated in a medium with 
smaller bacterial activity (a low rotting number of the 
medium) would yield a different result a relatively low 
number. This example shows that the duration of the 
experiment has a great influence on the results. 



[131] 



MODERN FISHING GEAR OF THE WORLD 



Therefore, we would suggest that to the test of Dr. 
Klust be added a number to indicate the duration of 
time (months) in which the experiment had been carried 
out. Maybe such a test would be less comparable, 
but much more useful, for it would help to avoid greater 
mistakes which undoubtedly occur in the simple and 
attractive interpretation of Dr. Klust. 

Hence, "PT" 20/5 would signify that in the course of 
5 months the treated sample of cotton twine Nm 50/15, 
had lost 50 per cent, of its initial strength and that in the 
same period 20 successive untreated twine samples had 
also lost 50 per cent, of their initial strength. 



In spite of this modification, the k% PT" test will go on 
being a non-comparable number, as long as there is no 
better method to determine and to regulate the rotting 
processes and the "rinsibility" of the preservative. 
These demands, however, are in a technical way still 
difficult to answer. At present, there is no practical 
answer except to continue applying the classical method 
of Mescck for fishing purpose. Results obtained by any 
other method should be considered with great care. 
They can only be reliable if confirmed by the "fishing" 
method the results of which, in practice, have not been 
reported as contradicting each other. 




Herring nets used in the East Anglian fishery being dried at Ct. Yarmouth, U.K. 

1132] 



METHOD OF TESTING RESISTANCE OF NET MATERIALS 

TO MICRO-ORGANISMS 

by 

A. v. BRANDT 
Prof, und Dir., Institut fur Nctz- und Matcrialforschung, Hamburg, Germany 

Abstract 

This paper describes a method of assessing the efficiency of net preservatives independent of the rotting powers of the waters in 
which the nets are used. 

A numerical value has been found for the test figure T, which is the amount of rotting activity necessary to reduce the initial breaking 
strength of a material by 50 per cent, and the following criterion is used to assess the value of preservatives: 

T *~ 200 or less --- poor efficiency 
- 200- 500 low 
-= 500 1000 medium 
1000 2000 good 
over 2000 very good 
In this way it is possible to make comparisons which are quite independent of the type of water and time of year 



Kfeum* 



Technique d'essais de la resistance aux micro-organismcs des mattriaux employes pour la fabrication des filets 



Ce document deem une methodc permettant d'evaluer 1'efficacilc des agents de preservation des filets, mdependamment du pouvoir 
de putrefaction dc 1'eau dans laquelle ceux-ci sont utilises. 

On a trouv& pour le test de la Figure T une valeur numeric) uc qui represente le pouvoir de putrefaction necessaire pour reduire de 
50 pour cent, la resistance initiate A la rupture des materiaux et 1'echelle suivante est utilises pour evaluer rintcrdt des agents de preservation: 



T 



200 ou moins 

200 a 500 

500 a KKK) 

1000 a 2000 

plus de 2000 



mauvais 
mediocre 
passable 
bon 
tres bon 



II est ainsi possible de faire des comparisons tout a fait independantes du type de I'eau et de la saison de 1'annee. 

Metodo para determinar la resistcncia a los microorganismos de los materiales empleados en la fabricacidn de redes 
Kxtracto 

En este trabajo se describe un metodo para cvaluar la eficacia de los agentes empleados en la preservation de redes, excluyendo el 
efecto putrefactivo de las aguas donde se calan los artes. 

Al determinar los valores (T) obtenidos en las pruebas, sc han encontrado cifras que reprcscntan la cantidad de acci6n putrefactiva 
necesaria para reducir en un 50 por cent, la resistencia a la ruptura que inicialmente tenia el material. lin la evaluation del valor de los pre- 
servatives se uso el siguiente criterio: 

T 200 o menos eficacia muy baja 

- 200 500 - baja 

500 1000 mediana 

1000 2000 - buena 

mas de 2000 muy buena 

De esta manera es posible hacer comparaciones con independencia del tipo de agua y de la epoea del ano. 



NATURAL fibres tend lo rot when they are exposed 
to humidity and unfavourable temperatures. The 
destruction is caused by micro-organisms, bac- 
teria, and even by fungi, which attack the cellulose and 
protein. Numerous methods of preserving the nets have 
been developed, but their efficiency varies considerably. 
An adequate method in one kind of water may fail in 
another, not only because of the varying strains on 
fishing gear, but also because of the variable activity of 
these organisms. This activity varies in different fishing 
areas, and in a characteristic rhythm during the year 
(Diagram 1-8). 



These varying factors make it difficult to compare the 
efficiency of preservative methods, and so an attempt 
has been made to find a method of testing net preserva- 
tives irrespective of place and season. 

TESTING METHODS 

The growth of fungi and the amount of destruction in 
textiles are usually tested by the accelerated fungal 
inoculation method, or the soil burial method. Standards 
have been established in several countries for carrying 
out these tests. 



[133] 



MODERN FISHING GEAR OF THE WORLD 




100 

80 
60 

40 




Figs. 1-8. 

(1) Monthly rotting activity us compared with cotton twines in the 
course of a year in a eutrophic lake (l^owentien lake. East 
Prussia, average 1938/1942). 

(2) Monthly rotting activity as compared with cotton twines in the 
course of a year in an oligotrophic lake ( Wigry lake near SuwaJki. 
average 1940/1942). 

(J) Monthly rotting activity as compared with cotton twines in the 
course of a year in the North Sea (light vessel Elbe /, average 
1948/1956). 

(4) Monthly rotting activity as compared with cotton twines in the 
course of a year in the Baltic (light vessel Kiel, average 1952/1956). 

(5) Rotting activity (fortnight-figure) as compared with cotton 
twines in a non-polluted running water (Schlitz river near Schlitz- 
Hessen, average 19511 1956). 

(6) Rotting activity (fortnight-figure) as compared with cotton 
twines in r heavily polluted running water (Elbe estuary neat 
Cuxhaven, average 1947/1956). 

(7) Rotting activity (fortnight-figure) as compared with silk twines 
in a non-polluted running woter (Schlitz river near Schlitz- Hessen, 
average 1955/1956). 

(8) Rotting activity (fortnight-figure) as compared with silk twines 
in a heavily polluted running water (Elbe estuary near Cuxhaven, 
average 1953/1956). 



These methods cannot simpl> be adopted for fishing 
gear because fishing gear is subject to continuous 
rinsing by water. Tests therefore should be carried out 
in water. 

In testing under natural conditions, net twines, lines 
or ropes are freely immersed in water. Their breaking 
strengths are ascertained before and during the experi- 
ment. The smaller the loss in breaking strength after a 
certain period, the greater the resistance to rotting. The 
rotting action of the water is determined separately and 
related to the loss in breaking strength. Rotting activity 
and breaking strength indicate the preservation test 
figure. 



DETERMINATION OK 
OF THE WATER 



THE ROTTING ACTION 



The monthly rotting degree of the test water is deter- 
mined by immersing test-twines, cotton twines Nm 50/15 
(Ne 30/15), on the first day of each month. Before 
immersion, the twines are boiled in distilled water, and 
their initial breaking strength is determined in wet 
condition. With new cotton twines Nm 50/15 it amounts 
to about 6-0 to 6-5 kg. Four bunches of 10 twines, 
each twine 30 cm. long, are used in the experiment. 
After one, two or three weeks, and on the last day of the 
month, one bunch is taken from the water to determine 
the average loss in breaking strength of the twines. 

The loss in breaking strength of the sample remaining 
in the water throughout the month indicates the rotting 
activity for that month. By dividing it by the number of 
days the rotting activity per day is determined. 

CHANGE OF THE METHOD WITH HEAVY 
ROTTING ACTIVITY 

In heavil} rotting waters, i.e.. in running waters, a 
100 per cent, loss of breaking strength may occur before 
the end of the month, possibly already after a week, and 
in that case it is impossible to determine the rotting 
activity as described above, so the samples are replaced 
by new ones when they have lost approximately three- 
quarters of their initial breaking strength. The losses in 
breaking strength of all samples are added up to establish 
the monthly rotting activity. The loss of breaking 
strength shown in a graph has the form of an S-curve. 
The monthly figure may therefore only be computed 
from the figures, for instance, of a fortnight, if the sample 
has lost at least three-quarters of its strength (but not 
more that 90 per cent.) after 14 days. Frequently, that 
date cannot be foreseen, so it is suggested that four 
samples should be put in the water on the first day of 
the month, as described before, and subjected to a 
weekly control. This guarantees that the samples rotted 
up to three-quarters of their initial strengths are recorded 
and renewed. 

Table I is an example of recording the monthly rotting 
activity in a year in per cent, loss of breaking strength. 

In Table 1 the first four months show the loss in 
breaking strength of the cotton test twines after 1, 2 and 
3 weeks and 1 month. In the fifth month the samples 
rotted within two weeks and had to be replaced. (The 
sign "*" in the table means that the samples had been 



1341 



TESTING RESISTANCE AGAINST ROT 



TABIF I 



Test 
month 


Loss in strength after 

I 3 


4i 


m 


*, 


Value 
per 
month 


Value 
per 
day 


January 
February 
March 
April 
May 
June 


(0 
(0 
(0 
(0 
(40 


(88* 





5 
9 
93 

V 


20 
20 
40 
70 
') (50 
(88*) 


54*) 
54*) 
78*) 
100*) 
100*) 
(73*) 


i period 


54 
54 
78 
100 
193 
249 


1 
1 
2 
3 
6 
8 


7 
9 
5 
3 

3 


luly 


(88*) (100*) 


(84 


*) 


| 10 days 272 


8 


8 


August 




(84* 


) (81*) 


(90 


* V 


not 1 


255 


8 


2 


September 




(80* 


) (75*) 


(74 


*) 


| week 


229 


7 


6 


October 




(76* 


) (75*) 


(65 


*) 


I 


218 


7 





November 


(10 




40 




76*) 


(36 


*) 




112 


3 


7 


December 


(10 




40 




76*) 


(18 


*) 




94 


3 






Value p. year : 1908 



renewed.) In the following five months the samples 
lost about three-quarters of their breaking strengths 
after ten days, and had to be replaced twice. In the 
last two months the test-twines had to be replaced after 
three weeks. 

PREPARATION OF SAMPLES AND NUMBER OF 
SAMPLES 

For tests of preservatives a uniform twine Number as 
cotton Nm 50/15 (Ne 30/15) is recommended. The 
material should not be too strong, or the test will take 
too long, but it should not be too fine because the 
differences of the preservation should be distinctly 
demonstrated. 

The samples are cut into pieces of twine 60 cm. long 
and treated with the preservative. The increase in weight 
by the treatment may be determined, the stiffness 
measured and the content of certain substances deter- 
mined, etc. In any case, the wet strength after the 
treatment has to be determined. 

The twines are then folded together and bound into 
bunches 30 cm. long. It is important not to use binding 
material which may rot and influence the preservative, 
or which may even be destroyed by it. The bunches 
would get loose and be lost. 

The free end of each twine is knotted to prevent the 
bunch from becoming matted. The bunches are sufficient 
for 6 tests of 10 twines each or 12 tests of 5 twines each. 
Thicker bunches are not recommended as they might 
influence decay of breaking strength. 

It is not necessary to rinse the bunches. As with 
fishing nets, rinsing occurs automatically during the 
first days. Differently treated samples should not be 
exposed together as they may have a reciprocal influence. 

DESCRIPTION OF EXPERIMENT 

The bunches are fastened to a cord of Perlon. nylon or 
similar material, the distance between them being about 
10 cm. They are suspended so that they neither emerge nor 
touch the bottom or piles, etc. In tidal waters the samples 
must be suspended so deeply that they do not get dry. 
Tests are carried out to obtain comparative values. 



It is suggested that the preservatives should be tested 
several times, in order to obtain a sure average value of 
the method chosen as a standard. For instance, the 
following are used as standard preservatives: 

Cutch | Testalin. 

The same with Carbolineum. 

Cutch, Potassium- Bichromate (or copper vitriol with 

ammonium), 
as above, with Carbolineum. 

Others may, of course, be used for these experiments. 

All samples are simultaneously put into the test water. 
Considering the climatic conditions in Europe, it is 
thought best to remove the first sample of 5 or 10 
twines after one month, and if no decrease in the breaking 
strength is found, the next samples may be removed at 
intervals of two or even three months. A test should be 
made every two months in summer and every three 
months in winter if the initial decay does not indicate 
tighter control. 

Removed twines must be cleaned of weeds, etc., and 
their breaking strengths tested immediately in the wet 
condition. If it is impossible to do this at once, the twines 
should be dried and kept for a later test of wet-strength. 
Further decay may be prevented by using disinfectants. 
The wet-strength test is made with conventional testing 
instruments used in textile research. 

EVALUATION OF THE RESULTS 

The initial breaking strength (A) of the material to be 
tested is expressed in kg. (wet). The retained strength 
(B lf B 2 , etc. B x ) is tested after certain periods and is 
computed as percentage figures of the initial strength : 

Retained strength per cent. =- 



(1) 



(2) Loss in strength per cent. 



,oo-L- xB * 

A 



Net twines are considered to be unserviceable when 
the loss in breaking strength exceeds 50 per cent, of the 
initial strength. This loss therefore is considered the 
value-limit. 

Similarly, the loss of 50 per cent, of the initial strength 
of treated material determines the evaluation of a 
preservative. This will be explained by an example: 

In Table II the wet breaking strengths of 4 net twine 
samples preserved by methods A, B, C and D are given 
in kg. for certain days. The test No. 1 is the initial 
strength. 

TABLE II 



Test Number 
Date 


1 
1.1. 


2 
15.1V. 


3 
20.VI. 


4 
2I.VIII. 


5 
I5.XI. 


A 


6-0 


4-6 


4-1 


3-4 


l-6kg 


B 


5-9 


4.4 


3-2 


1-7 


0-3 


C 


5-8 


4-2 


2-9 


1-7 


0-3 


D 


6-4 


4.9 


1-8 


01 






Table III gives the several retained breaking strengths 
in per cent. 



M35] 



MODERN FISHING GEAR OF THE WORLD 



TABLF III 



Test Number 
Date 


1 
I.I. 


2 
15.1V. 


A 


100 


77 


B 


100 


75 


C 


100 


72 


D . 


100 


77 



3 
20. VI. 


4 
2I.VIII. 


5 

15.X1. 


68 


57 


27 


54 


29 


5 


50 


30 


5 


28 


2 





Sample A lost 50 per cent, of its strength between the 
fourth and fifth tests, sample B between the third and 
fourth, sample C in the third and sample D between 
the second and third test. It is assumed that the rotting 
activities mentioned in Table I were existent throughout 
the experiment. The rotting activity required to reduce the 
initial strengths of the test-material by 50 per cent, test 
figure T, is computed according to the following formula: 



(3) T-- 



50) 
i t. 



t x ) x (R, 
R, R 2 

In this formula t a means the rotting activity which 
became effective when the test-material had lost more 
than 50 per cent, and tj means the rotting activity before 
that state was reached. The desired test-figure T must lie 
between these two figures. R l is the breaking strength 
before and R 2 the breaking strength after the said state. 

The rotting activities, as explained in the above 
example, result according to Table I in the following: 

Period 1.1. to 15.1V.: January 54 

February 54 

March 78 

until April 1 5th 50 (15 x 3-3) 

236 

Rotting activity is computed from the daily figures for 
months which have not been completely tested. 



Period I.I. to 20.VI.: Jan. to May 
until June 20th 



Period I.I. to 21.VIII. Jan. to June 



479 
166 

645 
1000 



until August 21st 172 



Period I.I. to I5.XI. Jan. to Oct. 
until Nov. 15th 



1172 

1702 
56 

1758 



Medium A T 



Medium B T 



1172 



I 1172 13091310 



4 645 



' 645 729-730 



If the obtained values are inserted into the formula 
(3), the following values are obtained as test-figures for 
the preservatives A to D: 

(1758 1172) x (57 - 50) 
(57- 27) 

4102 
30 

(1172-645) v (54 50) 
54 29 

T 21 8 

25 

Medium C : As the date was exactly the 20th June, T 645 

(645 - 236) *' (77 50) 
(77 28) 

T M 3 236 461-460 

The greater the test-figure, the greater the performance 
of the preservative method. 

EVALUATION OF THE TEST-FIGURE 

The efficiency of the several methods of preservation 
can be summed up as follows: 

Test figure up to 200: poor effect. 

200 to 500: minor effect. 
500 to 1000: medium effect. 
1000 10 2000: good effect. 
above 2000: very good effect. 



Medium D T 



!- 236 




Two boat midwaler trawling on the Malabar coast oj India an age old method ! 

[136] 



DISCUSSION ON NET PRESERVATION 



Dr. Reuter, Rapporteur. When using natural fibres the 
fisherman must periodically treat his nets with preservatives 
against rotting, as he knows from experience that if this is 
not done regularly and properly his nets will deteriorate very 
quickly. His knowledge of preservation is based mainly on 
practical experience. The available data from preservation 
experiments with textile yarns are not directly comparable 
as these arc invariably conducted on materials in dry condition, 
whereas fishing nets are always used in wet condition. Such 
tests can therefore only be used as a guide. The fishermen in 
various countries and even in different areas of the same 
country use different preservation methods, each being con- 
vinced that his method is the best. Some only dry the nets, 
others use coaltar while a third may use cutch; others ma> 
use linseed oil, copper sulphate or a combination of two or 
three products. Very rarely can they give reasons for their 
choice and they are normally very reluctant to change the 
custom. 

In his paper, Takayama considers the different types of 
preservatives and their action, showing that some kill the 
bacteria while others make it physically impossible for the 
bacteria to attack the fibre. 

The decisive factors are the Q/-contenl in copper com- 
pounds and the tannin content in cutch or catechu. When 
buying such preservatives the fisherman is, therefore, only 
interested in the amount of these active agents, i.e. the per- 
centage of Cu or tannin but not in the bulk alone. Gear 
Research laboratories can render valuable service in analysing 
the various brands of preservatives, determine the percentage 
of active ingredients and advise on proper measures to prevent 
leaching out of the preservatives by fixing them chemically 
or by waterproofing. 

When conducting preservation experiments, one of the 
difficulties is to obtain results that can be compared with 
those obtained at a different season or in a different area. 
Dr. von Brandt gives a solution to this problem in his paper; 
his method not only gives a measure of the "rotting value" 
of the medium in which the experiment is conducted, but 
also the value of the preservation agent used. The values 
obtained are expressed in numbers by which the rotting 
value of different waters and the preserving power of different 
preservation methods can be expressed. 

The way in which this is done is as follows: While untreated 
cotton yarns are subjected to rot the loss of breaking strength 
is determined regularly and the percentage of loss added. 
This number gives the rotting power of that period. A treated 
yarn is tested in the same way, but the experiment is stopped 
as soon as the breaking strength has decreased by 50 per cent. 
The total percentage of white yarn decrease of breaking 
strength during this period is an indication of the "preserva- 
tive power.'* 

All natural fibres are open to attack by small organisms, 
so that all have to be protected against rot and loss of 
strength. In the face of growing competition of the non- 



rotting synthetic fibres, the producers of natural fibres arc 
trying to find new ways of immunizing them against micro- 
organisms, and whereas all older methods are based on 
preventing the organisms from reaching the fibre by giving 
it a protective ^coating, new methods are being considered 
which chemically change the fibres so that they become 
indigestible to the micro organisms. 

The papers by Sandoz and Ciba Ltd., both describe such 
methods which are claimed to give good and long lasting 
protection without causing major changes in the physical 
properties of the fibre. This last is very important as most 
protective preservation methods do change some of the 
physical properties. 

Although preservatives are mainly used for natural fibres, 
there are circumstances where they arc useful for the synthetic 
fibres too. Vinylon nets and lines are generally tarred in 
Japan. Other synthetics are sometimes coal-tarred to give 
them more weight or stiffness, to give protection against 
abrasion, knot slippage, etc. In some cases synthetic fibres 
are dyed or otherwise treated to prevent deterioration through 
exposure to sunlight. 

Dr. W. Hagenbuch (Switzerland). 1 am representing the 
chemical firm Sandoz in Basle, Switzerland. Dr. Renter has 
mentioned modified natural fibres which, of course, are 
something different from synthetic or man-made fibres. 1 
would like to make a few additional remarks on acctylated 
fibres such as cotton, man i la, sisal, etc. 

Acetylated cotton has been produced on an industrial scale 
for about 25 years according to a process which has been 
worked out by us in Basle, and consists in a reaction of the 
hydroxile group of cellulose with acetic acid or acetic anhy- 
dride, forming a new chemical compound. The result actually 
is a new fibre and the process is not comparable with a coating 
or a preservative. It is not cotton any more. Until now, 
acetylated fibres have been used mainly in the textile field 
because of their special properties in regard to dyeing. 
Acctylated cotton does not take up a dye-stuff as normal 
cotton does. This field, of course, is of no interest here, and 
the remark was made only to show how and why this has 
developed. Since about 10 years it has been used in the 
laundry industry because of its exceptional heat resistance, 
which is about six to seven times higher than with normal 
cotton. 

In recent times we have started studying the rot resistance 
of this acctylated material which proved to be very good in 
sea water. This rot resistance is permanent and the treatment 
does not smell or discolour the fibre and is not poisonous. 
Acetylated cotton looks exactly like normal cotton and can 
only be determined by chemical methods. 

Under the name of Otoba it has been produced in England 
since 1927. At the present experiments are going on in Scotland 
with herring nets and so far in li seasons these nets have 
been behaving exceptionally well. The price is at the moment 



137] 



MODERN FISHING GEAR OF THE WORLD 



10 to 30 per cent, less than for synthetic fibres, but it can be 
expected that with increased production a considerable 
decrease of price will take place, and then I think acctylated 
cotton will become a very interesting new fibre for the 
fishing industry. 

Mr. A. Rupert i (Switzerland): I am representing the firm 
Ciba, Basle. We also have elaborated a procedure to prevent 
rotting by converting cellulose without chemically modifying 
the fibre itself. With this socalled "Arigal" procedure we 
also achieve permanent protection, and this is what really 
counts in fishery. 



Mr. H. Levy (Morocco): For 12 years past I have been 
engaged in preserving fishing gear made of natural fibres, 
especially cotton. In Morocco we have three preservation 
methods, i.e. tarring and tanning with two different materials. 



Tarring is used only for twines that are constantly submitted 
to abrasion, i.e. certain parts of the big trap nets (madrague), 
the lower parts of trawl nets and especially the bags of sardine 
seines. Tanning with catechu gives satisfactory results, 
i.e. for the sardine net. The third method consists in tanning 
with ground pine bark which is very rich in tannin and, by 
the way, is abundant in North Africa. This gives really 
excellent results. But in recent years the Moroccan fishermen 
have found a combination of half catechu and half ground 
pine bark that gives results one would not even have dared to 
hope for. 1 would recommend strongly to all fishermen to 
give this new tanning method a test. The effect of tanning is 
improved by subsequent tarring to retard the tannin being 
washed out. Due to these preservation treatments in Mor- 
occo lines and ropes are worn out rather than deteriorated 
by putrefaction. But it must be said that this preservation 
effect is only obtained if the fishing gear is dried once every 
week, or at least twice a month. 




Left: Operator i.\ testing the breaking strength and extensibility of fishing twine. Right: With hand and fool operated net weaving looms 
such as the above, nets can he knitted three or four times faster than by hand braiding. 



( 138 ] 



Section 5 : Relative Efficiencies of Nets Made of Different Materials. 

THE EFFICIENCY OF SYNTHETIC FIBRES IN FISHING, 
ESPECIALLY IN GERMANY 

by 
GERHARD KLUST 

Institut fur Netz- und Materialforschung, Hamburg, Germany 

Abstract 

Gear is divided into three groups, according to strain on net material during operation. An attempt is (hen made to classify various 
fibres (polyvinyl chloride, polyvinyl alcohol, polyester, polyamidc, polyethylene, polypropylene) by referring them to these groups. 

Net twines of these synthetic fibres, and also net twines of vegetable fibres, are compared with regard to breaking strength (knotted 
and wet), extensibility and elasticity, and resistance to weather and abrasion. An estimate is then made of the suitability of the different 
fibres to various types of fishing gear. 

For the fine gillnets, polyamide monofi lament and twines of either polyamide high tenacity filament or of polyester filament are 
most suitable. For herring and salmon drift nets, twines of polyamide or polyester filament, and also twines of polyvinyl alcohol, are recom- 
mended. Polyamide staple should not be used. 

For standing gear, such as trap nets (especially when much exposed to sunlight), twines of polyvinyl chloride fibres (PCU, Rhovyl, 
Feviron), may be used. Plaited twine made of polyamide filament (Perlon, nylon), which has very high tensile strength, abrasion resistance 
md elasticity, is considered the best net material for very heavily strained gear, such as bottom trawl nets. 

L'efficaeite des fibres synthctiques dans la peche specialemcnt en Allemagne 
Resume 

Les engins sont divises en 3 groupes d'apres TerTort exerce sur la ma tic re du filet pendant la peche. L'auteur a fait unessaide 
classification des diverses fibres (chlorure de polyvinyle, polyacrilonitrile, alcool de polyvinyle, polyester, polyamide) en les rapportant a ces 
groupes. 

Les fits a filet de ces fibres synthetiques. et aussi les tils a filet dc fibres vegetales, sont compares en ce qui concerne la resistance a 
la rupture (noues et mouill6s), 1'extensibilite et Telasticite, et la resistance aux intempenes et a 1'anrasion. L'auteur cstime cnsuite a quel 
degr6 les differentes fibres conviennenl aux divers types d'engins de peche. 

Pour les filets maillants fins, le polyamide monofilament ct les tils dc polyamide a tenacite elevee on de filaments de polyester con 
vienncnt le mieux. Pour les filets denvunts a harengs et a saumons on recommande les files de filaments de polyamide on de polyester, et 
aussi les fils d 'alcool de polyvinyle. II ne faut pas utiliser de polyamide tresse. 

Pour les engins fixes comme les filets-trappes (specialcment quand ils sont beaucoup exposes a la lumiere solairc), les fils de fibres de 
chlorure de polyvinyle (PCU, Rhovyl, Teviron), pcuvent etre utilises. Le fil tresse de filaments de polyamide (Perlon, nylon), qui possede 
unc tres grande resistance a la traction, a Tabrasion ct une grande clasticite est considere comme etant le meilleur material! pour fabriquer 
des engins supportant de grands efforts comme les chaluts de fond. 

La eficacia de las fibras sinteticas en la pesca, espmalmenle en Aleniiinia 
Kxtracto 

Como los artes de pesca puedcn dividirsc en ires grupos segun el esfuerzo a quc se somete el material, sc ha tratado dc clasificai 
las diversas fibras (cloruro de potmnilo, policrilomtrilo, alcohol de polivinilo, poliester, poliamida) en cada uno de ellos. 

Para determmar la rcsistencia a la ruptura (anudados y hiimedos), alargamiento, clasticidad y resistencia a los agcnies climaticos 
y al roce, sc procedio a evaluar las caracteristicas de los hi los dc estos materiales smteticos con los de origen vegetal empleados en la fabricaci6n 
de redes. Luego se valoraron las maneras como se prestan las caracteristicas de las diversas fibras para tejer los artes. 

F.n el caso dc redes de enmalle finas son mas adecuados los hilos de poliamida de una sola hebra o de vanos filamentos con gran 
resistencia, ya sea dc este material o de poliesteres, asi como tambicn los de alcohol de polivinilo. Para las redes dc dcriva que se utilizan en 
la pesca de a re n que y salmon se recomiendan los hilos de poliamida o poliester y tambicn las de alcohol de polivinilo. Fn la fabricacion de 
estos no conviene usar material preparado a base dc poliamida. 

Para los artes fijos, como las redes trampas ( especial mente cuando quedan expuestas a la luz durante largo tiempo, deben usarse 
hilos formados por fibras dc cloruro de polivinilo ("PCU", "rhovyl", "teviron") al tratarse de artes sujetas a grandes esfuer/.os como las 
redes de arrastre de fondo, es mas convementc utilizar hilo de hebras de poliamida (perlon, nylon), tren/adas que poseen gran elastic id ad, 
resistencia a la tension y al roce. 



I. PROOF AGAINST ROT -THE MOST IMPORT- 
ANT PROPERTY OF SYNTHETIC FIBRES IN 
FISHING 

THE most important raw materials for nets in Factors affecting the durability of the net of vegetable 

European fisheries have been vegetable fibres fibres, and of more importance than this resistance are 
cotton, flax, hemp, sisal and manila. When 1. Duration of immersion in water: Fishing gear 

immersed in water, they are exposed to cellulose-digesting left in water for a long time arc more liable to rotting 

micro-organisms, especially bacteria. The resistance of than those used only temporarily. Rotting is stopped 

vegetable fibres increases in the following order: flax, only when the nets are dried completely, also inside the 

hemp, ramie, jute, cotton, sisal, manila, coir (Klust 1961). knots. 

[139] 



MODERN FISHING GEAR OF THE WORLD 



2. Water temperature: The warmer the water, the 
quicker the rate of rotting 1 . 

3. Kind of water: Due to intensive rotting 4 nets will 
be destroyed considerably sooner in eutrophic than in 
oligotrophic or dystrophic waters-' 3 . 

Jn middle European eutrophic water, with higher 
temperature, unpreserved cotton nets may become useless 
after 7 to 10 days. Only very intensive preservation 
methods can prolong their durability 5 - fi . Preservation 
is most effective for cotton nets whereas efficiency is poor 
with bast fibre or hard fibre nets. 

The durability of fishing gear is primarily affected by 
rotting. The original cost is increased disproportionately 
owing to frequent renewals and preservation expenses. 
The smaller the business, the greater are the relative 
expenses for nets. 

In a report on nylon as net material, Needham writes 7 : 
"Nylon brings to one of man's oldest occupations the 
miracle of science and, in doing so, provides easier living 
for the fisherman ..." This statement can apply to all 
synthetic fibres, for this miracle is apparent in their proof 
against rot. The first synthetic fibre, known as PeCe 
(polyvinyl chloride), was developed by the former 
German I.G. Farbenindustrie, in 1931. Some years later, 
twines made of these fibres began to be used for smaller 
gears in German inland fisheries 8 - y , and its rot-proof 
quality became apparent. This meant much greater 
durability of gears (fyke nets made of PeCe, have been 
in continuous use for over 15 years), less work and lower 
preservation expenses, obviating the time consuming 
drying of nets and thus ensuring longer catching periods. 
Apart from this rot-proofness which is the most import- 
ant characteristic of synthetic fibres, other important 
properties are: breaking strength, extensibility, elasticity, 
abrasion resistance, diameter, weight, stiffness, resistance 
to weathering, knot stability and behaviour in water, 
including change of length, sinking speed and visibility. 

II. TYPES OF FISHING GEAR, WITH REGARD TO 
THE MATERIAL AND KINDS OF SYNTHETIC 
FIBRES USED 

A great variety of gear is used in fishing, differing very 
much in size, structure, method and purpose of use. 
They have been classified by v. Brandt 10 . According to 
strain on the net-material German fishing gear can be 
divided into three groups 11 : 

1. Low Strain 

Fine gillnets belong to this first group. The traditional 
material is fine cotton twine of metric counts 270/6 to 
70/9 (English counts 160/6 to 40/9) or similar thickness, 
with a diameter of less than 0-40 mm. and a breaking 
load (wet) not higher than about 3 kg. 

2. Medium Strain 

This group is formed by the various fishing gears of 
the German inland, coast and deep-sea fisheries which 
formerly were made of cotton twines, of metric counts 
20 and 50 (English counts 12 and 30). Fine twines of 
flax or hemp were occasionally used. This includes: 

most fishing lines 

baskets, also trap nets and box nets 



scoops 

gape nets (without those mentioned above) 

dragged gears also bottom trawls of smaller vessels 

floating trawls of cutters 

seines and purse seines 

dip nets and lift nets 

drift nets 

3. Heavy Strain 

Bottom trawls of large vessels (trawlers and cutters) 
and gape nets set in fast running rivers belong to this 
group. They were made of thick manila, sisal or hemp 
twines, with diameters up to 3 -9 mm. and breaking loads 
up to nearly 200 kg. 

Table I gives the characteristics relevant to fisheries 
purposes for the most important synthetic fibres, and 
shows for which of the three groups these fibres could be 
used. In the column "trade names", only the best-known 
are listed. Only nylon and Perlon are given for the 



TABU 1 
Fibre Trade Nantf\ Characteri\ttc\ 



Suitable 
for u\e in 



Polyvinyl F: Rhovyl medium breaking strength. 
Chloride G: PCU, Rhovyl medium abrasion resist., group 2 

J: F.nvilon. very good resistance to 

'I eviron weathering 

Polyvinyl J: Vinylon, low price, medium breaking 

Alcohol Manryo, strength, medium abrasion group 2 

Kuralon, resistance, good resistance 

Trawlon, to weathering 

Cremona, 

Mcwlon 
G: PVA 



Polyester 



GB: Terylene 
USA: Dacron 
G: Diolen, 
Trcvira 
1: Tergal 
I: Tcrital 
J : Tetoron 



very high breaking strength, 
low extensibility, groups 1 

medium abrasion ricsistance, and 2, 
relatively good resistance group 3? 
to weathering 



Polyethylene GB: CourleneX3, high breaking strength, 

Drylene very high abrasion 
N: Nymplcx resistance, wiry, 

G: Polyathylen- swimming in water 
Hoechst 



group 2, 
group 3? 



Polypropy- 
lene 



Polyamide 
mono- 
filament 



Polyamide 
staple 



Polyamide 
continuous 
filament 



I' Meraklon 
USA 



Nylon-monofil., 
Perlon-monofil., 
Platil 

Nylon staple, 
Perlon- staple 



low price, medium to 

high breaking strength, low group 2. 

resistance to weathering, gr.la.3? 
swimming in water 

transparency (little visible- group I, 

ness in water), very good group 2: 

resistance to weathering, wiry fyke nets 



high breaking strength, 

high abrasion resistance, 

good knot stability, group 2 

very high extensibility, 

low resistance to weathering 



Nylon filament very high breaking strength, all 3 
Perlon filament very high abrasion resistance, groups 
high elasticity, low of gear 

resistance to weathering 



F=France, GB=Great Britain, G Germany, I Italy, J-Japan, 
N = Netherlands. 



f 1401 



EFFICIENCY OF SYNTHETICS FOR FISHING 



polyamides, although fibres of this group and of equal 
value to fishing gear are produced in different countries 
under various names, such as: Amilan, Anzalon, Dayan, 
Dederon, Ducilon, Enkalon, Fcfcsa, horlion, Grilon, 
Kapron, Kenlon, Knoxlock, Nylock, Rilsan, Silon, 
Steelon and Tynex. 

III. EVALUATION OF THE MOST IMPORTANT 
PROPERTIES OF SYNTHETIC FIBRES USED IN 
FISHING 

Properties of primary importance in the evaluation of 
net twine are rot-proofncss, breaking strength, extensi- 
bility and abrasion resistance. Resistance to weathering 
may be of primary importance for fishing gears, which 
arc used just below the surface or partially out of water. 
Based on experience in German fisheries and on 
investigations by the Institut fur Netz-und Material- 
forschung, an attempt is made below to evaluate these 
special properties. 

1. Breaking strength, in knotted, wet condition 

Twines of cotton, hemp and manila arc strongest in 
wet condition. With synthetic fibres there are groups 
which have the same or nearly the same strength wet or 
dry: Polyvinyl chloride (PeCc, PCU, Rhovyl), Polyester 
(Terylcne, Dacron, Trcvira, Diolen), polyethylene poly- 
propylene and some copolymcrs (Saran, Vinyon, Dyncl, 
Acrylan). Other groups show a loss of strength when 
wet, such as: polyamide (Nylon, Perlon), polyacryloni- 
trile (Orion, PAN), polyvinyl alcohol (PVA, Manryo, 
Kuralon, Vinylon). Diminution of strength occurs as 
soon as the net twines come in contact with water. After 
a 24 hour immersion the following approximate losses of 
strength were observed: twines made from polyamide 
staple and cont. filament J3 to 17 per cent., polyamide 
monofilament nearly 20 per cent., twines made from 
polyvinyl alcohol staple about 25 per cent. 

During prolonged immersion in water extending over 
several months, a further gradual decrease of strength 
takes place, 12 though by no means comparable to that 
of even well-preserved net twines of vegetable fibres. 

It is of importance to know the decrease in strength 
caused by knotting. This is connected closely with the 
properties of the fibre substance. Continuous filaments of 
polyamide and polyester are of high tenacity (highly 
stretched) in order to obtain as high a strength as possible, 
and have a lower extensibility. Unfortunately, they show 
a diminution of knot strength too. Losses of strength 
of wet twines by knotting (in the average): 

Twines made from losses 

in per cent 

manila, medium fine tw. 30 

manila, thick twines 40 

hemp 25 

cotton 30 

Perlon staple 35 

Nylon contin. fil., fine tw. 33 

Nylon contin. fil., medium fine tw. 43 

Nylon contin. fil., thick tw. 50 

Perlon contin., twisted (trawl twines) 50 

Perlon contin., braided (trawl twines) 42 

Peilon monofilament (trawl twines) M) 

Polyester contin., (trawl twines) 50 

Polyethylene 36 

Net material, therefore, has to be evaluated according 

to its strength in knotted and wet condition. Table II gives 



TABLE II 
Breaking strength of net twines, single knot and wet 



Twines matlejrom 



Break ing Length Tensile Strength 
km. kg. / mm. 2 



Polyvinyl chloride 






Rhovyl-Hbre (staple) 


6-4 


9-0 


Rhovyl, continuous filament 


7-6 


10 6 


PCU, staple 


8-2 


11-5 


Polyvinyl alcohol, staple 


10-2 


LV3 


Polyacrylonitrile, continuous filament 


14-5 


17-0 


Polyester, continuous filament 


26-3 


36-3 


Polyamide, staple 


15-7 


17-9 


Polyamide, continuous filament . 


30-1 


34-3 


Cotton .... 


12-2 


18-5 


Hemp 


28-9 


42-8 



such an evaluation for net twines from group 2. Based 
on tests of a great number of net twines of different 
thickness, the breaking length in km. and tensile strength 
have been calculated. For calculating the tensile strength 
(kg./mm. 2 ) the following specific gravities (which are 
mostly taken from the list of Grunsteidl and Preussler 16 ) 
have been used: 

Polyvinyl chloride -40 g./cm. 

Polyacrylonitrilc -17 

Polyvinyl alcohol -30 

Polyester -38 

Polyamide -14 

Cotton -52 

Hemp 1-48 

Hence of the synthetic net twines considered here, 
those of continuous polyamide and polyester are by 
far the strongest. Their wet knot-strength is twice that of 
cotton twines. 

2. Extensibility and Elasticity 

The extensibility of net twines consists of several com- 
ponents: that of the fibre, the single yarn, and finally 
extensibility of the end product or twine. The inherent 
extensibility of synthetic fibres varies, being large for the 
polyamide group and comparatively small for the 
polyester group. Short staple fibres produce a higher 
extensibility than continuous filaments. Hard twisted 
yarn is more extensible than a soft twisted one. The 
manufacturing process of the final products is also of 
great importance. The more the twine is twisted or the 
tighter the braid is plaited, the greater the extensibility. 
To obtain a high extensibility, it is better to use fibres with 
a large original extensibility than to use hard twisting of 
yarn and twine to attain this high extensibility. 

Total extensibility comprises a part of elastic extension 
and the permanent elongation. Apart from the nature of 
the fibre and the manufacturing process, their value is 
dependent on the applied load. Where the total extension 
results mainly from the manufacturing process, i.e., from 
twist of yarn and twine, elasticity will be small, and the 
permanent elongation, which remains after unloading, 
will be comparatively great. 

Net twine has a greater efficiency, if total extension and 
elasticity are high. It will be able to absorb kinetic 



[141 ] 



MODERN FISHING GEAR OF THE WORLD 




Fig. /. Load-extension curves. 

energy and will take up shock loads better than net twines 
of small extensibility. This problem was first examined 
thoroughly with nylon ropes 17 . It is of particular 
importance for gear under heavy strain where one has to 
reckon with sudden strong loads l *. 

It is difficult to evaluate the breaking extension of 
nets, as it must be expected that, for high-class fibres, 
knot-strength reaches only about 50 to 60 per cent, of 
the breaking load. Knowledge of breaking extension, is, 
therefore, not very important. The degree of extension 
with ascending load which, at the most, may amount to 
50 per cent, of the breaking load is more important. The 
relation between load and extension, up to this limit, has 
to be observed, and an example is represented by the 
load-extension curves of fig. 1 for net twines of material 
group 2. The curves have been drawn from average 
values which were calculated from the results of several 
tests of twines. 

Two different types of extensibility are represented in 
fig. 1; that of polyester and polyacrylonitrile (both of 
continuous filament), and that of polyamide, polyvinyl 
alcohol and cotton. 

The total extensibility of the first type is small, and 
such twines offer strong resistance, even at small loads. 
There is a steep ascent of the curves, as for those of 
manila twines. 

The second type is affected at low tension or pressure, 
where the increase of extension already exceeds the 
increase of load. AH curves apply to wet twines. Twines 
of staple fibres are much more extensible than those of 



Twine. 



TABU- HI 
Extension in per cent, (dry) 



jr JSST 



Immediately after 

loading . .83 3-8 

1 hour loaded . 9-0 4-2 



Immediately after 

unloading . .2-2 12 
I hour after 

unloading . . 1-7 08 

1 day after unloading 1-0 0-4 

Final condition . 0-8 0-4 



Total extension in 

per cent. . 9-0 42 

Elastic extension in 

percent. . . 8-2 38 

Permanent elongation 

in per cent. 0-8 0-4 

Degree of elasticity 
in per cent. .91 95 



22 
2-4 



14 

1-2 
1-2 
1-2 



2-4 
1-2 
12 
50 



14 2 
15-0 



8-0 

6-0 
5-0 
5-0 



15-0 

10 

5-0 

67 



continuous filaments, especially if the latter, as in the 
case in question, are of high tenacity. When cotton 
twines are wetted they show a shrinkage of nearly 10 per 
cent. With a small load, the extension of wet cotton 
twines is very great; with low tension pressure, shrinkage 
will be compensated by extension. Twines of fibres which 
have small shrinkage in water, such as twines of polyester 
or polyamide filament, will also show small differences 
between dry-extension and wet-extension. 

Extension in connection with elasticity is of special 
interest. Elasticity regarding the stronger net twines, 
which are used for large bottom trawls, is shown in 
Table 111. The twines have been loaded in dry condition 
for one hour by 30 per cent, of their breaking load. 

The thick cotton twine shows the highest extension at 
load. After unloading, a rather high permanent elonga- 
tion remains. For manila, the total extension is very 
small. Therefore, the absolute measurement of the perm- 
anent elongation is also small, though it comprises 
50 per cent, of the total extension. Polyester twine is very 
elastic, its extensibility, however, is very small. Perlon 
filament twine has a proportionately high extensibility, 
together with high elasticity. 

What significance does this difference in behaviour have 
for fishing gear? 

A fixed extensibility cannot be set for net twines, as the 
requirements differ according to the type of gear. 

In drift nets, for example, the fish will be caught in 
the meshes. The mesh sizes, which must be adapted to 
the size of the fish, should not alter, so the permanent 
elongation must be small. The twine should yield to the 
pressure of the fish caught in the mesh. Extension and 
elasticity, however, must not be too great, otherwise the 
fish would be squeezed in too tight, the quality of the 



[H21 



EFFICIENCY OF SYNTHETICS FOR FISHING 



fish would suffer, and it would be also very difficult to 
release it from the net. The very extensible twines of 
polyamide staple fibres are therefore less suitable for 
drift nets. Twines of polyester (Terylene, Dacron, 
Trevira, Diolen) (see fig. 1 and Table III) would, however, 
be especially qualified for these gears, since their perman- 
ent elongation is small, but their relative elasticity great. 

The requirements of gear exposed to strong tension 
or pressure are very different. This applies to trawls, 
especially the codends, when they are rushed up from a 
great depth to the surface or while heaving a large catch 
on deck. These nets were made of strong manila or 
sisal twines, in order to stand sudden shock loads. In 
consequence of their very small extensibility, hard fibres 
are not able to absorb kinetic energy. Best suited for large 
bottom trawls are twisted or plaited twines of polyamide 
filament (e.g. Perlon, nylon). Their extensibility is great 
enough to stand strong shock loads, and the high degree 
of elasticity guarantees a good constancy of mesh size. 
In the German trawl fishery most of the lighter bottom 
trawls and floating trawls of cutters are now also made 
of Perlon (in this case from staple fibres) because its high 
elastic extension gives the necessary strength for handling, 
also big catches. Perlon staple fibres have also proved 
suitable for ottcrboard stow nets. 

As regards extensibility, drift and trawl nets are 
examples of extreme types of gear. Between them there 
is a great range of other types of gear with different 
requirements of extensibility and elasticity. For synthetic 
fibres, polyester filament and polyamide staple fibre are 
the extremes as regards extensibility. 

3. Abrasion resistance 

In practice, it is scarcely possible to obtain exact 
knowledge of the relative abrasion resistance of nets 
made of different kinds of fibres. One is dependent on 
laboratory test methods, and only relative and never 
absolute values are obtained and these, moreover, are 
dependent on the test method employed. 

For the following tests, the machine for testing abrasion 
resistance after Sander was used, in which the wet 
net twines are chafed across a bar of carborundum Ml . 
The counts or runnages of the various types of twines 
under comparison were taken as equal as possible. 
Thicker twines for large trawl nets were compared with 
one another, and also twines for gears of material group 
2. If in the first case, abrasion resistance of thick cotton 
twine is equal to 100, the following approximate relation 
can be established: 

Cotton - 100 

Manila 130 

Hemp 280 

Polyester cont. filament = 230 

Polyamide cont. filament 460 

These figures refer to new, unused and wet twines, with 
a runnage of above 350 m./kg. The abrasion resistance 
of manila twines is very low. As some tests have shown, 
it is about the same as for sisal twines. As the breaking 
strength of nets of natural fibres is reduced by rotting, 
abrasion resistance will also be reduced. For twines of 
manila and hemp, the following relations have been 
established' : 



breaking strength 
in per cent. 



Diminution of 

abraxitm resistance 
manila, per cent. hemp, per cent . 



10 
20 
30 
40 
50 
60 
70 
80 



2 

3 

5 

(> 

15 

26 

37 

48 



5 
9 
14 
19 

23 
27 
34 
50 



Trawl nets are very much exposed to abrasion, which 
largely explains the short durability of manila nets. 
Polyamide fibres (Perlon, nylon) show the best abrasion 
resistance, and are by far superior to those of natural 
fibres. Trawl nets of Perlon filament used in the German 
trawl fishery, show about ten times the durability of 
manila nets, this is due not only to their rot-proofness, 
but also to the greater abrasion resistance of poly am ides. 
Twines of polyester filament have only half the abrasion 
resistance of twines of polyamide filament, but their 
resistance is better than that of cotton and manila twines. 

Abrasion resistance depends not only on the type of 
fibres and on the diameter, but also on the manufacturing 
process of the twine 18 . Hard twisted twines of polyamide 
filament have less abrasion resistance than soft twisted 
twines. Corresponding features apply to braids of poly- 
amide filament. 

The finer twines for gears of material group 2 have the 
following abrasion resistance (wet), when cotton is 
again equal to 100: 



cotton 

polyvinyl chloride 

Rhovyl-staple 

PCU-staple 
polyvinyl alcohol 

staple 

filament 
polyacrylonitrile 

cont. filament 
polyamide 

staple 

cont. filament 



100 

50-55 

75 

50-60 
110 

70 

170-250 
400-500 



These relative figures correspond to twines of the same 
runnage or count. If the calculation is based on the same 
diameter, the values will be somewhat displaced. The 
third possibility would be a comparison of abrasion 
resistance of twines of the same breaking strength. In 
that case twines of high tenacity fibres, such as polyamide 
filament and polyester, do not show such a great superior- 
ity, since they are much finer than twines of weaker 
types of fibres. 

4. Resistance to weathering 

There are few experiments on the resistance to weather- 
ing of nets made of vegetable fibres. These fibres are 
injured by sunlight. But such damage is small compared 
with that caused by micro-organisms in the water. Re- 
sistance to light and weathering is about the same in all 
vegetable fibres. 
Synthetic fibres show very great differences in their 



[ 143 1 



MODERN FISHING GEAR OF THE WORLD 




^ . PCU) 



Fig. 2. Relative resistance to weathering. 



degree of resistance to light and weathering. Fig. 2 
demonstrates their relative resistance to weathering 20 . 
Of the fibres represented here, delustred poly amide offers 
least resistance, so that dull polyamide twines are not 
suitable for fish nets, since their resistance to light is too 
small. 

It could be mentioned here that the USA are said to 
have succeeded in producing a dull nylon type with the 
same resistance to weathering as bright nylon. 21 The 
resistance of twines made of bright polyamide (staple and 
filament) is still below that of cotton and hemp twines. 
Polyamide monofilament and fibres of polyacrylonitrile 
and non-chlorinated polyvinyl chloride have a very 
great resistance to weathering. 

However, the other excellent physical properties of 
twines made of polyamide filament and staple more than 
compensate for their smaller resistance to light, especially 
for fishing gear of special economic significance, such as 
trawl nets. 

As an example: in the Portuguese purse seine fishery, 
nets of unprotected (uncoloured) Perlon-staple twines, 
have been used for 1,306 working days and are still 
serviceable, whereas preserved cotton nets usually last 
for no more than about 500 working days. 

For trap nets and other baskets, which stand partly 
out of the water or close below the surface, colouring of 
the material as a protection against light will often help. 
In this case nets of polyvinyl chloride, polyacrylonitrile 
and polyamide monofilament would be rather suitable. 

IV. CHOICE OF SYNTHETIC FIBRES FOR 
VARIOUS FISHING GEAR 

The discussion in Section III may now serve to answer 
the question as to the suitability of certain synthetic 
fibres for certain gear used in Germany (ref. especially 
Table I). 



Material Group 1. This comprises the different types 
of set gillnets, floating gillnets and trammel nets used in 
inland fisheries. Also fine herring nets of the Baltic 
fishery belong to this group. Gillnets are passive gears 
into which migrating fish swim by accident and become 
stuck in the meshes. Here, invisibility is of prime import- 
ance. The twines must therefore be of small diameter of 
just sufficient breaking strength, this depending on the 
species of fish to be captured. 

Accordingly, it would be advantageous to use very 
fine twines from strong types of fibres. Two types of 
synthetic fibres have a particularly high strength: 
polyester filament and polyamide filament (Table II). Very 
fine twines made of the latter have stood the test very 
well in inland fisheries, and also for herring gillnets in 
the Baltic. They catch more fish than cotton gillnets, 
since they are finer and softer and less visible. The best 
material for fine gillnets is, undoubtedly monofile 
palyamide-wire. Its translucency makes it nearly invisible 
in water. The catch of gillnets of this material is many 
times that of cotton nets, as many fishing countries can 
testify. 

Material Group 2. German fishing gear belonging to 
this group were all formerly made of cotton twines. For 
this, twines of breaking strength of 3 kg. up to about 
50 kg. were used. 

The largest gear of this group, the herring drift nets 
of the North Sea drifter, have been discussed in Section 
III, (2), showing why twines of polyester filament are 
regarded as particularly suitable. Extension and elasticity 
of twines of polyamide filament arc also suitable, but not 
twines of polyamide staple. 

For gear of such large dimensions, the initial costs must 
especially be taken into consideration. The complete 
string of herring drift nets (called "fleet'*) often consists 
of more than 1,500 kg. cotton twine. The much greater 
strength of the synthetic fibres just mentioned cannot be 
fully utilized. It is not possible to use twines as fine as 
the breaking strength would permit, because of the 
damage that could be caused to the fish. Therefore, the 
weight advantage as compared to cotton nets and, 
consequently, the lower costs, will not be as great as for 
other gears. Thus, drift nets of polyester or polyamide 
are much more expensive than cotton nets. Perhaps it 
would be better, in this case, to use polyvinyl alcohol 
which is the cheapest synthetic fibre. Drift nets made of 
that fibre are scarcely more expensive than cotton nets 
and may be completely suitable, if a good stiffening 
process is used. The production of knotless drift nets of 
polyvinyl alcohol fibres would be a great advantage. 
Satisfactory results have been obtained in a first test with 
such nets made of Japanese Manryo. 

During 1956 the German Baltic Fishery recorded very 
good results with salmon drift nets made of polyamide 
filament, and this material will probably completely 
displace the traditional hemp nets during the next few 
years. 

Passive gears, such as baskets, with the exception 
perhaps of the large trap nets (box nets, stake nets, fixed 
nets) of the coast fishery, do not generally require a very 
strong material. If fibres such as polyamide and polyester 
filament are used, then here too, may be a chance of 
catching more fish with a finer twine. Since all synthetic 



[144] 



EFFICIENCY OF SYNTHETICS FOR FISHING 



fibres are rot-proof, there is a very great choice of 
suitable materials. For trap nets, such as the Danish 
"Bundgarn", which stand partly out of the water, fibres 
of high resistance to light would be recommendable, 
e.g., polyvinyl chloride fibres PCU and Rhovyl and also 
the new Japanese Teviron or Envilon. 

Translucency, a special property of polyamide mono- 
filament, has proved to be of primary importance in 
catching more fish, also with baskets. Eel fyke nets, made 
of monofilament, caught about twice as much as those 
made of cotton; that also would be true of othtr baskets. 
But this would not seem profitable, if the long leaders and 
wings of trap nets, were also made of monofilament. 
They would not lead the fish into the trap net (net 
proper), but act as gillncts and the fish would be caught 
in the meshes. 

Dip nets, lift nets and falling nets (lantern nets, cast 
nets) are of little importance in the German fishery, but 
what has been said about material for baskets will 
mostly be applicable. 

The most important gears of German rivers are gape 
nets. According to the flowing speed of the water, they 
require material of great to very great strength, of relative 
high extension and elasticity and of great abrasion resist- 
ance. Polyamides have these requirements. For swing 
nets (stow nets) at anchor (also for otter-board stow 
nets), with the smaller mesh sizes or such nets which are in 
rivers with a flowing speed of less than 5 km./hr., twines 
of Perlon-staplc have lasted very well for more than six 
years. For stiffening, they were treated with "Black 
Varnish". Gape nets with large mesh sizes from rivers 
with strong current (e.g. the Rhine), are made either 
wholly, or in their most forward part, of plaited or 
twisted twines of polyamide filament, belonging to 
group 3. 

Two more gear types of material group 2 arc seines 
and light cutter trawls. 

For seines, and also for purse seines, there arc man> 
possibilities of choice of synthetic twines. During the 
first years of introduction of PcCc into the German 
inland fishery there were, for instance, boat seines made 
of these fibres, although breaking strength and abrasion 
resistance were less than those of cotton twines. Since 
the physical properties of the non-chlorinated polyvinyl 
chloride fibres are superior, these can also be used for 
seines. The same goes for polyvinyl alcohol twines which 
arc also inexpensive. These fibres, however, do not have 
a very high absolute strength in wet and knotted con- 
dition. Therefore, one cannot count on the gear being 
lighter than a cotton net of the same size. For polyester 
and polyamide, however, these relations are more 
favourable. If the breaking strength, wet and knotted, is 
taken as a basis, then gear of polyamide filament is only 
half as heavy as that of cotton. 

Material group 3. The requirements of the material of- 
trawls, have already been partly indicated in Section 111,2. 
They are the same as for large gape nets; very high break- 
ing strength and abrasion resistance and comparatively 
great extension and elasticity, and possibly the smallest 
weight. That goes both for lighter bottom trawls and 
floating trawls of cutters which still belong to material 
group 2, and for the large bottom trawls of deep sea 
trawlers belonging to material group 3. There are differ- 



ences only in the degree of strain and not in principle. 
By far the best material for these purposes seems to be 
polyamides. For cutter trawls, besides twines of polya- 
mide filament of liter 210 denier, weaker twines of 
polyamide staple may also be used. For heavy and large 
trawls, plaited and laid twines of polyamide filament 
have stood the test so excellently that the German trawl 
fishery works now mostly with Perlon nets for the catch 
of herring and of round fish. 

Especially in the Japanese fishery, trawl nets of poly- 
vinyl alcohol are frequently used. But their advantage 
seems to be in the low price only, as rot-proofness is 
peculiar to all synthetic fibres. They may be perfectly 
suitable for lighter trawl nets of smaller fishing boats, 
but for gears of large trawlers, twines of polyvinyl 
alcohol fibres do not seem to be very suitable. The test 
figures for one Japanese Manryo twine and for twines of 
rnanila and Perlon-filament, with nearly the same 
runnage, given in Table IV, may serve as an illustration. 

TABLE IV 



Manvro Manila 

2W SUM 'twine NmO. 7/3 



Perlon 
Km. 3/12 



Runnage, m/kg. 


239 


-230 


242 


Breaking strength. 








wet, kg. 


79 2 


~ 95 


156 


Strength, wet, 








knotted, kg. 


35-7 


~ 60 


99 



The lighter a trawl net is, the easier its handling and 
the lower its trawling resistance. These aspects are 
particularly important for large gear. From Table IV 
it can be seen that trawl nets of Manryo become much 
heavier and must have thicker twines, if they arc to be 
as strong as manilu trawl nets. The great advantages of 
trawl nets of polyamide filament in thK respect are 
apparent. 



I Klusl, Ci. iind H. Mann: txperimentellc I'nicrsuchungcn uber 
den Zelluloseubbau im Wasscr. "Vom Wasser" Bd. 21, 100-109, 
1954. 

- v. Brandt, A.: Uber den Zelluloseabbau in Seen Arch. f. 
Hydrobiol. Bd. XL. 778-821, 1944. 

;i v. Brandt, A.u. Ci. Klust: Z.elluloseabbau im Wasser. Arch. 
fur Hydrobiol. Bd. XLI1I, 223-233, 1950. 

4 v. Brandt. A.: Cellulosc-Abbuu in Fliessge\\axsern. Ber. 
Limn. Station. Freudcnthal, Bd. 4, 17-19, 1953. 

5 v. Brandt, A.: Untersuchungen zur Konservierung von 
Fischnetzen.- Prot. 7. Fischerei lechnik, H.7, Nr. 14, 1952; H.10. 
Nr, 19. 1953. 

6 Klust, G.: Die Bcurtcilung der konservicrenden, Wirkung von 
Fischnetz-Konservierungsverfahren. Mclliand Textilber., Bd. 33. 
763-764, 1952. 

Klust, G.: Testing methods of fishing net preservation. 
Cordage World, Vol. 33, Nr. 396, 1952. 

7 Nccdham. E. R.: Use of Nylon yarns in fish-netting. Canadian 
Textile Journ.. 74-76. 1953. 

8 v. Brandt, A.: Bekomnun wir unfaulbare Nelzgarne? Fischerei- 
Ztg. Bd. 42, 301-302, 1939. 

9 v. Brandt, A.: Die bisherigcn trfahrungen mit PeCc-Garnen 
in der Fischerei. Zeitschft. f. Fischerei, Bd. 42 45-65. 1944. 

10 v. Brandt, A.: Fanggerate-Systematik. Protok. z. Fischerei 
technik Bd. 2, Nr. 13, 1952. 

II Klust, G.: Zweite Ubersicht uber die Vcrwcndung von Perlon 
in der Fischerei. Prot. z. Fischereitechnik, Bd. 2, Nr. 20, 1953 



[1451 



MODERN FISHING GEAR OF THE WORLD 



12 Klust, G.: Zur Wasserbestandigkeit von Netzgarnen aus 
einigen synthetischen Faserstoffen. (vorlaufige Mittcilung) Prot. 
z. Fischereitechnik, Bd. 4, 168-174, 1957. 

18 Klust, G.: Untersuchungen an Fischnetzgarnen aus endlosen 
Polyamidfaden. ~ Arch. f. Fischereiwiss., Bd. 8, H. 1/2, 1957. 

14 Can-others, P. C: Tests on Kuralon twine. Western Fisheries, 
Vol. 50, No. 6, 1955. 

16 Klust, G.: PolyvinylalkohoI-Zwirne. Melliand Textilberichte 
-Bd. 38, 134-136, 1957. 

16 Griinsteidl, E. und H. Preussler: Chemische Faserstoffe und 
ihre Eigenschaften. St. Johann i.T., 1953. 

17 British Ropes Ltd.: Ropes made from Nylon. Leigh/Fdin- 
burgh, 1948. 



18 Klust, G.: Perlonschnure, ihre Herstellung und 
Eigenschaften unter Beriicksichtigung ihrer Verwendung in der 
Fischerei. Ulm/Donau, 1957. 

19 Klust, G.: Untersuchungen iiber die Scheuerfestigkeit von 
Fischnetz-Schnttren. Prot. z. Fischereitechnik, Bd. 3, 64-68, 1954. 

20 Klust, G.: Zur Wetterfestigkeit, von Zwirnen aus einigen 
synthetischen Faserstoffen. Textil-Praxis, Bd. 12, 233-237, 1957 
(Hier auch weitcre Literaturangaben zu dieser Fragc!) 

- 1 Ashton, H. and J. Boulton: A review of developments in the 
properties processing and utilisation of man-made fibres. Journ. 
Text. Inst. Vol. 47, No. 8, p. 532-566, 1956. 

22 Schlieker, E.: Mehr Perlongerate fiir die Fischerei. Deutsche 
Fischerei-Zeitung. Bd. 3. 356-367, 1956. 




Spinning a cotton fishing yarn in an Indian fishing village. 
[146] 



SYNTHETIC FIBRES IN THE FISHING INDUSTRY 

by 

E. I. DU PONT DE NEMOURS AND CO. 

Delaware, U.S.A. 



Abstract 

This is a general account of the use of nylon and * k Dacron" polyester fibre for all kinds of fishing gear. The lightness, elasticity and 
durability of these fibres makes them ideal for gillnets, seines, traps and pots, but the risk of total loss makes them a doubtful investment 
for bottom trawls. An important recent improvement has been the introduction of Type 330 nylon yarns which have better sunlight durability 
than cotton or previous types of nylon, an important attribute in hot and sunny climates. The use of "Taslan" textured nylon, a process 
which creates tiny loops in the individual filaments of the yarn, means better knot holding properties and easier blending of two or more 
continuous filament varns. 



Resume 



Lcs fibres synthetiques dans 1'industrie des peches 



C'est un expose general sur Femploi du nylon et du Dacron, fibre de polyester, pour Unites sortes d'engins de peche. La legerete. 
I 'elasticity et la durcc de ces fibres les rend ideales pour les filets maillants, les sennes, les trappes. les casicrs et les nasses, mais le risque de 
perte totale en fait un invcstissement douteux pour les chain Is de fond. Un important perfectionncment recent est ^'introduction des tils de 
nylon type 330 qui a une meilleure duree sous 1'action du soleil que le colon ou les types precedents de nylon, ce qui est une qualite sous les 
clirnats chauds et ensolciltts. l/emploi de nylon texture "Taslan", un precede qui cree de pelites boucles dans les filaments individuels du 
HI. signifie une meilleure tenuc des noeuds et line union plus facile de deux ou plusieurs fils du type filament continu. 



Extracto 



Las fibres sinteticas en la industria pesquera 



Description general de Jos usos ed las fibras de policsteres, nylon y dacron. en todos los tipos de artes de pesca. El poco peso, 
elasticidad y duraci6n de el las haccn que sean ideales para la confection de redes de enmalle y cerco. nasas, etc. pero el riesgo de la pcrdida total 
durante la pesca ponen en duda su empleo para fabricar redes de arrustre de fondo. Una mcjora importante introducida recientemente es 
el hilo de nylon lipo 330, mas resist entc a la action de la luz solar que el algoddn o lipos de ny!6n usados anteriormente, lo cual es una 
propiedad importante en climas calidos o con mucho sol. El uso de "taslan" nylon sometido a un procedimientoque crea pequeftos lazos 
en los filamentos individuates -permite obtener nudos no tan corredizos y un material que se retuercc en mejores condiciones al mezclarlo 
con dos o mas filamentos continues. 



WHILE Du Pont 66 nylon was first tested experi- 
mentally in the fishing industry in the United 
States for gillnets in 1939, military demand for 
nylon during the war delayed further work in the fishing 
industry. Since 1948, however, the use of nylon in gill- 
netting has grown rapidly. Recent estimates show that 
well over 90 per cent, of all Great Lakes' gillnets are now 
made of nylon. 

More recently, nylon has taken over most of the salmon 
gillnetting in the Pacific. This rapid acceptance has been 
due primarily to the great increase in numbers of fish 
caught by nylon gillnets compared to the nets they 
replaced, as well as their lower maintenance costs, longer 
life, and easier care. Gillnets made of nylon twines have 
reportedly caught from 3 to 12 times more fish per net 
than those used previously, although the reasons for 
this phenomenon are not thoroughly understood. 

In the heavier types of netting which used cotton twines 
in the past, nylon has also gained the approval of 
American fishermen. The first menhaden seine made 
entirely of nylon was placed in service in June 1954, 
and proved to be far more durable than nets previously 
used. In addition nylon nets have proved more economical 



in the long run. Significant growth has also been noted 
for nylon in lobster and shrimp gear and in tuna seining. 
Nylon is also being used in longlining for tuna and halibut. 
In addition to the wide, general use of nylon twines 
for nets, the use of ropes of nylon and "Dacron" 
polyester fibre for hanging and purse lines has become 
quite common. Present industry sales of nylon in the 
U.S.A. for fish netting and twines amount to over 
1,000,000 Ib. annually. It is expected that in about five 
years' time at least 75 per cent, of all nets used in this 
country will be made of nylon. 

FIBRE PROPERTIES 

Du Pont 66 nylon has gained acceptance in netting 
because it offers an outstanding comdination of pro- 
perties and price. Of these properties, high strength, 
wet or dry; abrasion resistance, complete resistance to 
rotting caused by marine organisms and high impact 
strength are the most important. Some specialized 
applications that call for low stretch under load have 
resulted in the use of "Dacron" polyester fibre in both 
net and rope forms. 



1147] 



MODERN FISHING GEAR OF THE WORLD 



The following table gives some of the most important 
specification properties of nylon and "Dacron" used in 
netting: 



Property 



Du Pont 66 nylon "Dacrori" 

Type 300 Type 700 7 'ype 5 1 



Denier 


210 


840 


220 


Filaments 


34 


140 


50 


Denier per filament 


6-2 


6-0 


4-3 


Tenacity Dry (grams/denier) 


8-0 


8-7 


6-4 


Tenacity Wcl (grams/denier) 


6-8 


8-1 


6-4 


Tenacity Loop (grams/denier) 


5-4 


7-1 


3-9 


Total extension dry ( ) . 


17 


17 


10 


Total extension wet (',') . 


22 


24 


10 



These properties combine to produce more economical 
or more efficient nets. 

Continuous filament nylon is the predominant 
synthetic type of raw material used by netting and rope 
manufacturers in the U.S.A., because it offers the highest 
breaking strength and maximum abrasion resistance. 
Spun nylon and combination twines are also being used 
successfully. Early problems of knot slippage or knot 
loosening have been largely overcome in nets made 
from continuous filament twines by the use of special 
resin-treated twines, special knots, or heat treatment of 
the finished nets. Spun twines of 100 per cent, nylon or 
twines made of filament nylon combined with spun 
fibres arc also used as a means of overcoming knot 
slippage without the need for any special twine treatments. 
Combination twines of filament nylon and spun fibres, 
in addition to good knot holding properties, offer the 
advantage of increased bulk at lower cost for certain 
types of netting where handling of fine twines might be a 
problem. 

GILLNETS 

The high strength of nylon allows the use of thinner 
continuous filament twines which gill fish more effectively. 
Thus, the higher initial cost of nylon is more than offset 
by the greater number offish caught per net. In addition, 
some fishermen feel that the elasticity of the nylon allows 
fish to force the twines apart and become caught. This 
may account for the fact that larger sized fish have been 
caught with a given mesh size than previously. The 
abrasion resistance of nylon is less important in this 
type of netting, but its rot resistance allows continued 
use of nets without the need for drying and treating. 

PURSE SKINES 

Abrasion resistance and resistance to rotting due to 
micro-organisms in sea water are the most important 
requirements for this type of net. It is also important to 
use twines of sufficient size to make handling easy. One 
hundred per cent, filament nylon twines are being used 
in menhaden purse seines to give maximum abrasion 
resistance as are combination twines of filament nylon 
and spun acetate, which give the required bulk and still 
achieve satisfactory strength and abrasion resistance. 
To illustrate the unusually high abrasion resistance of 



nylon, a cotton "bunt" or centre section of a menhaden 
seine used in one area lasts an average of 5,000,000 fish 
caught. A 100 per cent, nylon menhaden net placed in 
service during June 1954 has caught a total of 50,000,000 
fish; the net was still in service at the last report with the 
original bunt section intact. 

The largest nylon purse seine ever manufactured in the 
U.S.A. was produced in early 1956 for tuna seining. 
Because of the greater strength of nylon, slightly finer 
twines were used which resulted in a weight saving of 
of approximately 2,400 lb., as compared to an all-cotton 
tuna seine. The nylon tuna seine weighed a total of 
10,000 lb. and was 410 fm. long and 34 fm. deep. When 
wet, this nylon net weighs only half as much as a wet 
cotton net of the same size. 

The Pacific fishermen, after using this net for nearly 
two years, are highly enthusiastic about its light weight 
and easier handling characteristics. Jn addition, the net 
shows little wear and the fishermen estimate it will be in 
service for a number of seasons to come. 

In order to achieve optimum handling characteristics 
fishermen in the U.S.A. ordinarily dip nylon purse seines 
in a stiffening agent, such as an asphalt base tar, to 
impart required stiffness. Also, it has been found that 
slightly heavier weights should be used on the leadlines 
to provide the desired sinking qualities to the net. 

TRAP NETS 

The use of nylon in trap nets is growing slowly, although 
acceptance in the sardine industry has been widespread. 
Since these nets are stationary, rot resistance and abrasion 
resistance (particularly in the bottom section of the net) 
are important properties. Because of nylon's natural 
rot resistance, fishermen have found they can leave their 
nylon nets in the water almost indefinitely without fear 
of damage. One hundred per cent, filament nylon or 
combination twines of nylon and spun acetate are being 
used in trap netting. In the sardine fisheries experience 
has been good with a net of filament nylon, produced on 
a high speed knitting machine. This type of webbing 
has no knots and the mesh formation is made by proper 
settings on the knitting machine. 

TRAWLS 

In shrimp trawls where the sea bottoms that are fished 
are moderately level, nylon nets perform well and are 
being accepted. In the larger nets for bottom fish where 
equipment is frequently snagged and either lost or 
badly torn, the extra cost of nylon may often not be 
justified. 

FISH NET ROPES 

With the increased use of synthetic fibres in fish netting, 
ropes and lines with the same strength, elasticity and rot 
resistant properties as the net material itself are preferable 
in most cases. For this reason, the use of ropes of nylon 
and "Dacron" polyester fibre has grown considerably 
as more fishermen have switched to synthetic netting. 
Nylon ropes require no preservative treatment and give 
outstanding wear life compared to ropes made of 



[148] 



AMERICAN EXPERIENCE OF SYNTHETIC FIBRES 



natural fibres. A tuna fisherman on the Pacific coast, for 
example, has reported that his nylon net lines have been 
in service for over five years, and are still in good 
condition. 

A certain amount of difficulty was experienced at first 
in hanging nets on ropes of nylon or "Dacron". This was 
due primarily to the difference in elongation and shrink- 
age properties of ropes of these fibres as compared with 
natural fibre ropes. As a result of long experience with 
natural fibre ropes, the number of meshes of netting to 
hang per foot of rope had become well known and were 
correct for the stretch and shrinkage of such ropes. 
Fishermen have now learned that properly made ropes 
of nylon or "Dacron" stretch somewhat more than 
manila but do not shrink when wet. They have modified 
their hanging techniques to compensate for these differ- 
ences. 

Treated nylon is being used in longlining for ground 
fish such as halibut. Similar lines arc being used for 
lobster pot warps, as well as for headers in the pots. 
In these cases, the shock absorbency resulting from the 
high elasticity of nylon is a definite advantage, particu- 
larly in rough weather. 



NEW DEVELOPMENTS 

Improvement of the nylon yarn as produced by Du Pont, 
as well as improved preparation of the twine by the net 
manufacturer continues. 

An example is the recent introduction by Du Pont of 
Type 330 nylon yarn. This yarn has better resistance to 
sunlight than either cotton or previously available types 
of nylon. This yarn is now available to fish net manu- 
facturers and should insure longer life for nets when 
sunlight is a significant factor. 

A new development in the manufacture of nets of 
continuous filament yarn has been the use of "Taslan" 
textured nylon for netting twines. The texturing process 
creates tiny loops in the individual filaments, imparting 
new surface characteristics. Thus, good knot firmness 
can be obtained by the use of twines made from fc 'Taslan" 
yarns. In addition, the texturing process is useful for 
combining two or more continuous filament yarns 
intimately without the need for twisting. 

Such developments and many others are typical of 
the avenues which will continue to be explored as means 
of improving gear for the fishing industry. 




Bottom-set, cod gillnets of nylon being hauled mechanically off Iceland. 
[149] 



THE FEATURES AND USE OF "AMILAN" FISHING NETS 

by 

M. AMANO 
Toyo Rayon Co, Ltd.. Tokyo. Japan 



Abstract 



"Amilan"* is the registered trade name for nylon, made under licence hv the lo>o Ruyon Co . and ncis made \vith this material are 
at present being used extensively in Japan, and in addition, they are being exported to the U.S.A., Canada. Africa, etc. The use of "Amilan" 
nets of various kinds is discussed, and the rise in the catch of Pacific salmon and trout since the introduction of these nets is remarkable. It 
is true that the initial cost is high compared with cotton, but in spite of this, fishermen are changing over more and more to the use of these 
nets, because the physical properties of the material give it a longer life. 



Resume 



Les caracteristiuues et 1'emploi des filets dt pet he d* "Ami Ian" 



"Amilan" est le nom commercial depose du nylon fabrique sous licence par la Toyo Rayon Co. J es lilets fabriques avec ces 
matriaux sont & present largemcnt utilises an Japon et sont, de plus, exportes aux I'.-l-., an Canada, en Afrique. etc. On examine Temploi 
des filets cTAmilan de diflerents types; ('augmentation des captures de saumons et de truites du Pacifique dcpuis I'introduction de ccs filets est 
remarquable. II est vrai que le coOt initial est 61ev6 par rapport a celui du colon, malgre cela les pecheurs se rallient de plus en plus & Pemploi 
de ces filets parce que les proprietes physiques du materiau leur assurcnt une plus longue diiree d'existencc. 



Extraclo 



( 'aracteristicas y usos dtr las redes de "amilan" 



por 



Ln este trabajo se estudian los usos de los di versos tipos de redes de "amilan" (marca comercial registrada del nylon manufacturado 
la "Toyo Ray6n Co.") que se han difundido ampliamente en el Japon v. ademas, se exportan a los L.U.A., Canada. Africa, ete. La 
introduce! 6 n de estas redes en las pesquerias de salmon del Pacifico > trucha ha permit ido notables rendimientos. notandosc que, a pesar de 
su alto precio inicial comparado con las de algodon. los Pescadores las prelieren a causa de su mayor duration y propiedades fisieas del 
material. 



SYNTHETIC fibre nets are now popularly used and 
their efficiency is highly appreciated by fishermen 
all over the world. 

Amilan is the trade name of nylon produced b> the 
Toyo Rayon Co. under licence and with the technical 
cooperation of E.I. du Pont de Nemours and Co.. 
U.S.A. Amilan fishing nets are very well known todav 
among fishermen in Japan, and are also exported to 
many fishing countries. 

In the following sections the use of Amilan for nets in 
various types of fishing is described. 

SALMON AND TROUT GILLNKTS IN THF 
NORTHERN PACIFIC 

The Northern Pacific fishing has become vitally important 
to Japan, as sea products are indispensable to feed 
Japan's ever-growing population. In pre-war days, the 
main practice in the Northern Pacific was large scale 
drift net fishing near to the coast of Kamchatka Peninsula, 
under agreement with the U.S.S.R. At present, however, 
the chief fishing is based on mother-ship operation, 
which method originated around 1929. 

When the Pacific War ended, production of Amilan 
was started and by 1953, fishermen were using both 
conventional ramie and Amilan nets in the same quantity. 



\ sciics ol tests clearly indicated the superior catching 
abihiv ol in Ion nets which in addition are claimed to 
stand about three years of consecutive use as compared 
to hall a season for ramie. At that time, the price of 

\milan nets \\as twice as high as that of ramie nets, but 
uikmu into account the durability and larger catches, 
ihe> proved, however, more economical. 

The catch figures illustrate this point. In 1952, the 
first fishing Heels after the war caught 37,000 salmon and 
irout in the Northern Pacific. In 1953, the catch was 
tvMcc as much, at least partly due to the increased 
can-liability of Amilan nets. Since then, more and more 
boats have adopted the nets and thcv are now used by 
everx tishinu vessel 



//!/ v 


\uinhc' 
of 


CUH/l 


Catch 
) ship 


No. of 
Amilan / 
nets used 
(yds.) 


No. of 
Sarnie nets 
used 
(yds.) 


i9>: 


s ~ 


2,ICK) 


37 


2,784 


127,200 


1953 * 


115 


7,700 


73 


174,000 


124,800 


1954 9 


210 


20,500 


100 


780,000 





1955 14 


405 


64,040 


163 


2,040,000 





1956 16 


506 


52,000 


J03 


3,000,000 






I 150 J 



USE OF JAPANESE SYNTHETIC FIBRES 



SANMAI NET (TRAMMEL NET) 

This net is known by different names in Japan, such as 
Jigoku-Net (Hell Net), Sanzyu-Net (Three-fold Net), etc., 
and is widely used for inshore fishing. Before nylon 
made its appearance, the nets were made of natural 
fibres such as cotton, ramie and silk. Today, the nets 
are made of Amilan and about 80 or 100 times more of 
such nets are being operated. 

PURSE SEINE NET 

The use of nylon for the construction of these nets has 
great advantages owing to its increased tensile strength 
per weight unit, as compared to cotton. When Amilan 



is used the boat and crew can work a much larger net, 
or less crew is necessary to operate a purse seine of the 
size a cotton net would require. Amilan is therefore now 
used widely in the tuna and bonito fisheries of Japan. 

DRAG NET 

The strength, lightness, small moisture absorption and 
durability of Amilan trawl nets allow for increased 
trawling speed. During 1952-55 tests by Fukuoka 
Fisheries Experiment Station showed that the nets 
produced higher catches. Some small fishermen, however, 
still hesitate to use them, because of the cost, but it is 
considered that their advantages outweigh this factor 




On this Arctic trawler, the belly, codend and headline of her trawl are made from nylon which ably withstands the strain of heavy catches. 

[151 ] 



DEVELOPMENT OF SYNTHETIC NETTING AND ITS EFFECT 

ON THE FISHING INDUSTRY 

by 

MOMOI FISHING NET MFG. CO. LTD. 

Ako Hyogo-Kcn, Japan 

Abstract 

No fibre is as yet available which would suit the requirements of all types of fishing gear, although some of the new synthetic fibres 
come closer to an ideal material than the natural fibres. Blending two synthetic fibres can produce twines particularly suitable for some 
specific gears. 



Resume 



Le dSveloppement de filets des fibres synth&tiques et ses effcts sur 1'industrie de la pche 



11 n'existe pas encore dc fibre satisfaisant toutcs les exigences pour tous les types d'cngins de pcche, bien que quelqucs-uncs dcs 
nouvelles fibres synthetiqucs se rapprochent plus du materiau ideal que les fibres nature I les. Le melange de deux fibres synthetiques peut 
p rod u ire des fils particulierement appropries la construction d'engins determines. 

Perfeccionamiento de las redes de hilos sinteticos y su influencia sobre la industria pesquera 
Extracto 

Todavia no se disponc de ninguna fibra sintetica que satifaga los requisites exigidos por todos los tipos de artcs de pcsca, si bien 
muchas de las obtenidas ultimamente se acercan al producto ideal mas que las fibras naturales. Hs necesario agregar que la mezcla dc dos 
fibras sinteticas permite fabricar hilos especialmcntc adccuados para ciertos tipos de artes de pesca. 



THE Japanese fishing net manufacturing industry 
has made considerable progress in the last few years, 
due largely to the development of synthetic fibres, 
such as nylon, vinylon, vinylidene, vinyl chloride, and 
combination synthetics. The export of nets, twines and 
ropes of all types from Japan, including natural fibres, 
totalled 7,163,000 Ibs. in 1956, a 22 per cent, increase over 
the previous year's figure, compared with an increase of 
9i per cent, in exports of natural fibre fishing nets, 
twines, and ropes. 

The following are the highlights in a survey made by the 
Japanese Government's Fisheries Agency of export 
trends in fishing gears, classified according to natural 
and man-made fibres. 

NATURAL FIBRES 

The exports of cotton fishing gear continue to lead all 
other kinds of fishing nets, totalling 5,220,000 Ibs. in 
1956. This accounts for 73 per cent, of the total exports; 
460,000 Ibs. of manila hemp were exported in 1956; 
336,500 Ibs. of sisal and a total of 22,000 Ibs. of other 
natural fibres (flax, coir, ramie and silk). 

SYNTHETIC FIBRES 

The exports of nylon nets, twines and ropes amounted 
to 683,000 Ibs. and increased 158 per cent, in 1956 over 
1955. More than 91 per cent, were nylon fishing nets, 



while 8 per cent, were twines; ropes constituted 1 per cent, 
of this total. The export of other synthetic fibres in 1956 
was as follows; vinylon 221,000 Jbs. (increased 2-8 
times over the previous year); vinylidene 63,500 Ibs.; 
vinyl chloride (which is a comparatively new synthetic 
fibre) 3,000 Ibs.; combination synthetics 165,000 Ibs. 
(increased 3-8 times in 1956 and are expected to exceed 
420,000 Ibs. in 1957). 

DIFFERENT FIBRES FOR DIFFERENT FISHING 
PURPOSES 

Synthetic fibre fishing gear has contributed materially 
toward the stabilization of the fishing industry, but 
because of the industry's complexity, no synthetic fibre 
developed to date is ideal for all types of fisheries. At 
present, gillnet fisheries find nylon a satisfactory replace- 
ment for linen netting. The purse seine fisheries have 
accepted Marlon (nylon/vinylon) as a replacement for 
cotton netting, while vinylon may prove an acceptable 
replacement for cotton and manila for fishing lines and 
ropes. For trawl fishing however, no particular synthetic 
stands out as acceptable to replace natural fibres. 
Approximately 75 per cent, of the nylon netting exported 
from Japan is used in the gillnet fisheries of various 
countries. A great variety of nylon types can be produced 
by changing its chemical construction, production 
method, yarn size, degree of twist, amount and method 



[152] 



USE OF JAPANESE SYNTHETIC FIBRES 




Fig, I. Manujactnrc of synthetic twine\. 



of relieving the stress in the twine, and the different 
processes for setting the knots. 

It should be borne in mind that when selecting the 
appropriate nylon twine to replace linen for a gillnet, 
wet knot strength of nylon is less than that of first grade 
linen. So, where it is necessary to maintain the same 
strength a slightly heavier nylon twine must be chosen. 

Nylon exposed continually to sunlight of normal 
intensity for two months can lose as much as 40 per cent, 
of its tensile strength. It must therefore be kept away 
from direct sunlight. 

Nylon is not weakened by bacteria, but a nylon net 
should be kept clean, as acid caused by fish slime can 
be harmful. 

DEEP WATER G1LLNETS AND SEINES 

To determine the twine diameter most suitable for deep 
water gillnets, consideration must be given to: 

a. Strength of the twine 

b. Fishability 

c. Form of the net in the water when fishing 

d. Durability and 

e. Initial cost of the net. 

Factors a and b are opposite in function, namely 
thicker twine means higher strength, but lower catching 
ability, therefore, a compromise has to be found. 

The specific gravity of the material influences the form 
of the net when fishing and it was found that pure 



nylon nets were too light. Attempts were made to over- 
come this deficiency by hanging a strip of vinylidene 
net 360d/30 ply on a ratio of nylon 4 : vinylidene 1 under 
the nylon. This method was not entirely satisfactory. 

The later method, which proved satisfactory, was to 
combine nylon and vinylidene fibre during manufacture 
of the yarn and twine. This product called Livlon has 
considerable merit for deep sea gillnetting operations. 

It is especially important to determine accurately the 
most suitable twine size for deep water purse seine 
because the webbing is subject to much water resistance 
while sinking. The specific gravity of a fibre can be 
determined by the laws of physics, but accurate deter- 
mination of the resistance is complicated by various 
factors. 

For a comparative study, the unit of resistance K 
D/L can be used where D is the diameter of the twine 
and L the meshsize (stretched). 

The unit of resistance of a standard sardine purse 
seine made of cotton twine 20/15 ply with a mesh size 
of 20 m/m would be 0-05. 

If the influence of the surface condition of the twine 
on the resistance is called 44 R", the numerical values of 
kk R" for different types of twine are as follows: 



Cotton 

Nylon 

Vinyl Chloride 
Vinylon 



1-00 
0-75 
0-70 
1-00 



153] 



MODERN FISHING GEAR OF THE WORLD 




Fig. 2. Mechanical knitting of synthetic fibre nets. 




Fig. 3. Inspection oj machine-braided webbing. 
\ 154 ] 



USE Oh JAPANESE SYNTHETIC FIBRES 




/-'if;. 4 Fishing with iwo-hoal pin.\c M'incs <>/ Marlon (in Japan). 



These factors "K" and "R" influence the shape of 
the seine in operation, sinking speed, etc. 

It may be assumed that a set is made with a cotton 
seine 20/15 ply, 20 m m stretched mesh, 300 fathoms 
long by 10 fathoms deep, on a sardine school of 100 
tons, 20 fathoms in width, that the travelling speed 
of the school is 0-5 fathoms second, and that it takes 
2 minutes for the sardines of the lower part of (he school 
to arrive at the skirt of the net. In this case, the seine 
must be pursed within two minutes to catch the entire 
school, thus the net must sink at a rale of I fathom per 
second, which is quite difficult to accomplish with cotton 
netting. However, Livlon seine netting of smaller 
diameter twine, manufactured with a special twisting 
method equal in specific gravity to cotton, is able to 
meet the requirements. 

Marlon netting was first put to commercial use in 
1951, and many of the original nets are still giving good 
service. Its most notable characteristics are derived from 
the combination of the best features of nylon and 
vinylon fibres. 

Some of the advantages of such a combination are: 
increased specific gravity of the twine, maintenance of 



strength b> the predominance of mlon fibre in the twine 
and decreased knot slippage. 

Marlon netting is available in a \anei\ of colours, 
twine and mesh sizes, and complete!) made up purse 
seines of standard or controlled specifications art- 
available. 

Like most synthetics, it requires little maintenance, 
but reasonable precaution should be taken lo prevent 
undue exposure lo sunlight. 

CONCLUSIONS 

Synthetic fibres are rapidlv replacing natural fibres in 
the construction of all kinds of fishing gear, but an 
ideal synthetic fibre suitable to all types of gears is noi 
yet available to the fishing induslrx. 

At present the synthetic fibres most commonK used in 
the main types of fishing gear can be listed as follows 

Type i>f dear Srnihefn nn\i i/.\'/ 

Ciillncts, trammel nets, tangle nets nylon 

purse seines, beach seines. Mai Ion aiul othei combination 

lamparas, trap nets synthetics 

beam trawl, otter trawl, balloon various but none cut ircl> 

trawl satisfactorv 

twines and ropes \ my I on. n\ Ion and combinations 



[155 



TESTS WITH NYLON FISHING TACKLE IN SWEDISH 

INLAND FISHERIES 

by 

GOSTA MOLIN 

Institute of Freshwater Research, Drottningholm, Sweden 

Abstract 

It has become quite clear that nylon is, in several respects, superior to cotton, flax or hemp, and among its foremost advantages are 
its rot-resistance and its high fishing capacity. Fishing experiments have proved that continuous multifilament nylon has something like 
twice the fishing capacity of cotton, and that the monofi lament nylon has a fishing capacity about seven times as good as cotton. During 
the last five years practically every professional fisherman has changed over to nylon nets, and while it is true that the initial cost of these is 
high, this is offset by higher catches of fish and longer life for the gear. 

In the case of set nets, those parts which are constantly above the surface of the water are soon destroyed by the sun's rays and have 
to be replaced, so now these parts should better be made of such materials as Saran, Kuralon or Tcrylene which arc less sensitive to ultra- 
violet rays. The monofilament nylon is especially good for fishing in clear water because of its invisibility, but in muddy waters this advantage 
is lost. 



Resume 



Essais effectues sur des engins de pftche en nylon dans les ptehes int&ieures sutdoises 



II est devenu Evident que le nylon est supe>ieur, a plusieurs points de vue, au coton, au lin ou au chanvre; ses principaux avantages 
6tant son imputrescibilite et sa grande capacite de peche. Des essais ont montre que la capacite de peche du nylon a fibres multiples continues 
etait deux fois superieure & celle du coton, et celle du nylon monofilament, sept fois. Au cours des cinq dernieres annees, la presquc totality 
des pdcheurs professionnels ont adopte les filets de nylon, et bien que leur prix d'achat soit eleve, il est compense par leur plus longue duree et 
les pcches plus abondantes qu'ils permettent de realiser. 

En ce qui concerne les filets fixes, les parties qui se trouvent constamment au-dessus du niveau de Peau sont rapidement detruites par 
les rayons du soleil et doivent etre remplacees, en sorte qu'il serai t prf<6rablc de les fabriqucr en matdriaux tels que le saran, le Uuralon ou 
le terylene qui sont moins sens ib les a Faction des rayons ultra-violets. Le nylon monofilament est particulierement efficace en eau claire a 
cause de son invisibilite, mais il perd cet avantage en eau trouble. 



Extracto 



Pruebas hilo de nylon para aparejos de pesca usados en las pesquerias interiores de Suecia 



Es evidcnte que el ny!6n rcsulta, dcsde varios puntos de vista, superior al algod6n, lino o c&ftamo, contdndose cntre sus ventajas 
mas sobresalientes su resistencia a la pudricion y alta capacidad de pesca. Los expenmentos hechos han demostrado que los hilos de ny!6n 
formados por gran numero de filamentos continuos y los de una sola hebra, permiten obtencr el doble y siete veces mas rendimiento que los 
de algod6n. Durante los ultimos cinco anos practicamente todos los Pescadores profesionales han comenzado a usar redes de ny!6n, cuyo 
alto costo inicial se compensa con la mayor cantidad de pesca y duracidn del arte. 

En el caso de las redes fijas, las partes que estan constantemenlc sobre la superficie del agua son dcstruidas con mas rapidez por la 
acci6n de los rayos solares y deben ser reemplazadas. Para evitar este inconvenicnto se recomienda confeccionar dichas secciones con 
materiales como: saran, kura!6n o terrileno que son menos sensibles a los rayos ultraviolados. 1 ny!6n dc una hebra se presta cspccialmente 
para la pesca en aguas claras a causa de su invisibilidad, pcro en las cenagosas esta ventaja no ejerce ninguna influencia. 



THIS paper gives a description of tests which were 
begun in 1947 by the Institute of Freshwater 
Research (Sotvattenslaboratoriet), on the design of 
nets made of nylon. 

One of the greatest disadvantages, particularly of 
continuous filament or monofilament nylon, was the 
difficulty of making knots that would not slip. This was 
gradually eliminated by using various methods, such as 
the treatment e.g. chemical treatment of the material 
before or after knotting, as well as the use of double 
knots. In cases where the nets are exposed to great stress, 
the last-mentioned method is still the most generally used. 

Certain difficulties are still encountered in the manufac- 
ture of monofilament nylon nets. Apart from the use of 
double knots, the chemical treatment has proved to be 
most effective. 



One more disadvantage of nylon nets for fishing 
purposes is their relatively high sensitivity to ultra-violet 
rays. Tests carried out with both normal sunshine and 
quartz-lamps have proved multifilament nylon to be 
most sensitive to such radiation, whereas the mono- 
filament nylon is more resistant. While it is true that 
special impregnation of multifilament nylon with 
catechu offers a certain protection it cannot prevent the 
gradual reduction in strength. From the practical point 
of view this sensitivity to light is not an important 
disadvantage to the fisherman. If he knows of the 
destructive influence of light on his fishing tackle, he 
can take care that his nets and tackle are not exposed 
to sunshine more than necessary. Practical experience 
gained by Swedish fresh-water fishermen has also proved 
that nets that must be discarded after 3 to 4 years have 



[156] 



NYLON TACKLE JN SWEDISH FISHERIES 



not become unserviceable due to the destructive action 
of sunshine, but to damage through tearing during 
intensive fishing. 

Quite different are, on the other hand, the conditions 
prevailing in connection with the use of certain types of 
fixed fishing tackle such as bottom nets and fish baskets 
(bow nets), when part of the tackle often remains standing 
above the water level. In such cases the sensitivity of 
nylon to sunshine necessitates frequent replacement of 
the destroyed parts. It would be practical to use for 
these parts Terylene or Saran fibres, which are extremely 
resistant to U.V. radiation. 

It must be mentioned here that monofilament nylon 
very easily becomes slimy through the adherence of 
microscopic particles whirling about in the water, 
particularly when the wind is strong. Since the com- 
paratively high catching ability of this type of net is 
mainly dependent on its relative invisibility in water, the 
slimy coating of the net reduces its efficiency which, in 
certain cases, becomes less than that of spun nylon. 
This slimishness is particularly noticeable when the catch 
is checked without lifting the net from the water, and 
the net is thus left in a submerged position, sometimes 
for several days. The thorough rinsing of the nets is 
absolutely necessary to avoid a reduction of the catching 
ability. This disadvantage is responsible for the relatively 
limited use of monofilament nets in many flat-country 
lakes, where the water often has a high slime content. 

THE RESULTS OF COMPARATIVE FISHING 
TESTS 

In order to estimate the catching ability of continuous 
multifi lament nylon compared with cotton, fishing tests 
were carried out, using nets of equal size. Separate tests 
have proved the catching ability of nylon nets to be 
twice that of cotton nets. Other tests showed that the 
excess catch made with nylon nets varied between 
1 -75 to 3 times. 

Apart from the tests carried out by the Institute, 
supervised tests were made by professional fishermen 
and gave, on the whole, the same results. All tested 
nylon nets were manufactured from continuous-multi- 
filament twine as staple nylon twine is unsuitable for 
gillnets. The reason for the high catching ability of 
nylon is its low water absorption, relatively high elasticity 
and high breaking strength. These qualities permit the 
use of thinner twine than is possible with the weaker 
cotton. This rule is valid for all kinds of net fishing: 
the catching ability of nets increases with a reduced twine 
diameter. The choice of the proper diameter is naturally 
merely a question of experience. The twine must not, 
however, be so fine as to cause very quick wear and 
consequent need for frequent repairs. 

Since 1951 the Institute has carried out catching tests 
with nets made from monofilament nylon. This is an 
almost ideal material for certain fishing tackle as, due 
to its transparency, it is practically invisible in water. 
It was found that the monofilament gillnets caught not 
less than seven times as much fish as cotton nets, and 
approximately four times as much as nets of continuous- 
multifilament nylon. 

The tests, which were carried out during both summer 
and autumn, also proved that the catching ability of 



nets made of monofilament nylon are to a certain extent 
dependent on light conditions. Thus, the excess catches 
were higher during the light season when the advantage 
of transparency is greater. It has also proved possible to 
achieve good results with these nets in daytime in lakes 
with clear water, when cotton or continuous-mukifilament 
nylon nets were quite unsuccessful. 

A test was carried out during the same season in two 
different lakes. The degree of visibility in these lakes was 
13 yards and IJ yards respectively. In the former lake, 
the ratio of the catches made with nets of cotton, con- 
tinuous-multifilament and monofilament nylon was 
1:2:14. The corresponding figures for the lake with 
reduced degree of visibility were 1 :2 5: 1 1 . The fact that 
the catches made with monofilament nets in the latter 
lake were unexpectedly high indicates that apart from 
the positive influence of the invisibility in water on the 
fishing results, this material must possess additional 
advantages on account of its structure. 

Continuous-mukifilament nylon proved to be more 
efficient than cotton quite irrespective of the size of 
gillnets used whether high or low (superiority varying 
between 1 -75 and 3). 

When higher (18 to 22 ft.) nets made of monofilament 
nylon came into use, it was discovered that the superiority 
of this material compared with continuous-multifilament 
nylon disappeared and that the catch, in some cases, 
was even less. Professional fishermen using such high 
nets had the same experience. The reason most probably 
lies in the increased stiffness of the monofilament nylon 
used for these nets. This may have an adverse influence 
on the flexibility of the net surface, which is of importance 
when fish jostle against the net. Nevertheless, singular 
positive results were achieved and one of these cases 
may be quoted. 

In a fishing test a net of monofilament nylon caught 
60 per cent, more white fish than a corresponding net 
of continuous-multifilament nylon. The net used for this 
species of fish is 20 ft. deep, provided with extremely 
light weights, and has its floats on the water level, 
connected to the net by lines by which the net position 
between bottom and surface can be varied. 

THE SCOPE OF APPLICATION OF NYLON NETS 

The change from cotton to nylon nets among professional 
fishermen, despite their conservative attitude to 
modernization, is practically 100 per cent. They soon 
realized the great advantages of nylon, thanks to its high 
catching ability and absolute resistance to rot as compared 
with cotton. It is also undeniable that the introduction 
of the new material for fishing tackle has brought about 
a considerable improvement in the economic situation 
of professional fishermen. Today, the tackle of pro- 
fessional fishermen is mostly made of continuous- 
multifilament or staple nylon. The shallow nets used by 
the non-professional and casual fishermen are made of 
monofilament 'nylon. 

EXPERIENCE IN THE USE OF NYLON NETS 

In order to secure the greatest possible catches when 
using nets made of monofilament nylon, it is necessary 
to follow certain rules. Perhaps the choice of the right 



[157] 



MODERN FISHING GEAR OF THE WORLD 



diameter in relation both lo the mesh size and to the 
species of fish for which the net is intended, is the most 
important. There are quite a number of different species 
of fish in the same lake and consequently the material 
must be strong enough for the strongest species of fish. 
The following standard diameters are used for certain 
mesh sizes in Swedish lakes: 0-12 to 0-15 mm. for 
42 to 55 mm. stretched mesh; 0-15 to 0-20 mm. for 
60 to 75 mm.; 0-20 to 0-25 mm. for 85 to 100 mm.; 
and 0-22 to 0-30 mm. for 1 10 to 150 mm. In many lakes 
in northern Sweden, where the catches often consist 
mainly of white fish, thinner material is used for the 
respective mesh sizes, as such fish does not tear the nets 
to the same extent as pike, pike-perche, trout or char. 

Unfortunately, nets made of monofilament nylon 
earned a bad reputation, because the firms delivered 
nets where the material was too thick in relation to 
the mesh size, which resulted in inferior catching ability. 
Another reason was that with some of the nets the knots 
were slipping. 

The nets made of continuous-multifilament nylon at 



present on the market are almost without exception ol" 
good quality with good resistance against slipping. 

Fishermen using fixed fishing tackle have to a great 
extent changed over to the use of nets made of staple 
nylon twine, particularly in lakes where this kind of 
fishing is carried on practically the year round and where 
the rot-problem in connection with cotton becomes 
extremely serious. As already stated, the parts of the 
tackle remaining above water level must be renewed 
now and then, due to deterioration by sunshine. 

The staple nylon twine used for this type of tackle is 
always treated with a stiffening agent which also makes 
it less elastic. As a rule coal-tar or bituminous varnish, 
dissolved in an equal quantity of ben/ol, is used. 

The maintenance of fishing tackle made of nylon is 
extremely simple. The nets must not be exposed to 
sunshine for long periods of time. The repairs are, 
however, somewhat complicated. So far as continuous- 
multifilament twine or monofilament is concerned, 
special knots must be made since usual netting knots, 
such as those used with cotton twine, arc not firm enough. 




Photo of television screen showing monofilament (left) and ordinary cotton net under water. Photo: v. Brandt. 

f!58] 



EXPERIENCE WITH SYNTHETIC MATERIALS IN THE 

NORWEGIAN FISHERIES 

by 

N. MUGAAS 

Statens Hskcredskapsimport, Bergen, Norway 

Abstract 

Tests carried out by the Directorate of Fisheries, Bergen, showed that the use of nylon and Perlon gillnets in the commercial fisheries 
produced from twice to seven times the number of fish per net per day caught by the traditional cotton and hemp nets, and as a result of 
these tests the import of synthetic materials has risen from 15 to 20 tons in 1954/55 to 400 tons in 1956/57. Cod traps made of Rural on have 
been in continuous use for 3 to 6 months whereas traps made of cotton and hemp h;u1 to be renewed every seventh week. Experiments arc 
continuing with other kinds of gear such as purse seines and herring nets. 



Kfeume 



I /experience des pechcs norvegiennes avec les materiaux synth&iques 



Les cssais efleclues par la Direction des Peches, Bergen, ont montre que Pemploi des filets maillants de nylon ct de Perlon dans les 
pcches industriellcs produisait de deux a sept fois plus de poissons par filet et par jour dc peche quo les filets traditionnels de coton ct de chanvre. 
A la suite de ccs essais Timportation dc matdriaux symhctiques est passec dc 15 au 20 tonnes en 1954,55 a 400 tonnes en 1956/57. Les trappes 
a morues de Kuralon sont employees continucllemcnt dc 3 a 6 mois alors que celles de coton ct dc chanvre doivant etre renouvcldes toutes 
les sept semaincs. Les experiences se poursuivant avec d'autrcs sortes d'engins tcls que la scnnc tournante et les filets a harcngs. 

Experiences con materiales sinteticos en las pesqucrias noruegas 
Extracto 

Las prucbas hechas por la Direction de Pesca. en Bergen, han demos trado que el uso dc redes de enmallc de nylon y Pcrldn permite 
obtener diariamcnte entrc dos y sietc vcccs mas pescados por artc que las tradicionales dc algoddn y canamo. Como rcsultado de estas 
prucbas ha aumentado la imporlacion de materiales sinteticos desdc 15 - 20 tons en 1954-5, a 400 tons en 1956-7. Las redes "trampas" 
de "kuralon" pudicron usarse continuamente durantc 3 a 6 meses, pero las hechas de algodon y caftamo debicron reemplazarse cada semana. 
En la actual i dad se continiian los ertsayos con otros tipos dc artes dc pesca, como redes dc ccrco ce jarcta y para arenque. 



SYNTHETIC materials are mainly used in Norway 
for catching cod and coalfish with gillnets, and have 
mostly replaced the conventional cotton and hemp 
fibres. Nylon 66, nylon 6 and Terylene arc chiefly 
used, the twine being imported from Great Britain, 
Canada, U.S.A. and the continent, although a small 
amount is produced in Norway. Synthetic materials are 
also used for snoods, lines and ropes. 

The use of synthetic materials by Norwegian fishermen 
has gradually increased since 1955, following experiments 
with gillnets of nylon and Perlon which were started 
by the Directorate of Fisheries in 1951 and continued in 
1952, 1953, 1954 and 1955. On the condition that 
reports were made on catchability, etc., certain fishermen 
along the coast were given a quantity of nets of nylon 
and perlon to use alongside the conventional gillnets 
made from cotton and hemp. The number of fish caught 
by each type of net was counted in every haul and a report 
sent to the Directorate of Fisheries when fishing was 
finished. The following example is typical of the reports 
received (overleaf). 

As will be noticed from the report, the catchability 
of the nylon nets was approximately twice that of the 
conventional . nets. This figure is also typical as an 
average, although according to several reports, catches 



were sometimes seven times higher. The types of twine 
used in these experiments were comparable as to wet 
knot strength and, according to the reports, durability 
and strength were satisfactory. 

When the results of these promising experiments were 
published, the interest in the synthetic material grew 
rapidly among the fishermen and production of nylon 
gillnets was taken up by the Norwegian manufacturers 
to meet the increasing demand. The nets produced in 
Norway are mainly the single knot type. 

The following figures illustrate the growth of imports 
of synthetic material for the fisheries, including twine, 
filaments and nets (a large part of the nets are of the 
double knot type): 

1954/55 approx. 15 to 20 tons 
1955/56 290 
1956/57 400 

1954, 55 was the first season when nylon came into use. 

The strength of nylon is often overestimated when first 
used for fishing gear. The dry tensile strength of nylon 
shows a great superiority when compared to that of 
natural fibres, but it sustains a great reduction of 
strength when wetted, whereas the tensile strength of 
cotton increases in wet condition. The strength of nylon 



M59] 



MODERN FISHING GEAR OF THE WORLD 



1953 


65 ordinary codnels 
(cotton and hemp) 


10 nylon nets 


Date 


Total catch A verage catch 


Total catch A verage catch 




per day 


per net per day 


per day per net per day 


19/2 


40 


0-62 


19 


1-9 


21/2 


108 


1-66 


132 


13-2 


23/2 


168 


2-58 


170 


17-0 


24/2 


29 


0-44 


17 


1-7 


26/2 


21 


0-32 


14 


1-4 


27/2 


27 


0-42 


9 


0-9 


28/2 


71 


1-09 


11 


11 


2/3 


45 


0-69 


9 


0-9 


3/3 


371 


5-70 


112 


11-2 


4/3 


87 


1-33 


26 


2-6 


5/3 


234 


3-60 


47 


4-7 


7/3 


319 


4-90 


111 


11-1 


10/3 


323 


4-96 


133 


13-3 


11/3 


235 


3-61 


93 


9-3 


12/3 


140 


2-15 


21 


2-1 


14/3 


314 


4-83 


71 


7-1 


16/3 


221 


3-40 


83 


8-3 


17/3 


307 


3-18 


93 


9-3 


18/3 


59 


0-90 


12 


1-2 


19/3 


76 


1-16 


31 


.M 


20/3 


231 


3-55 


52 


5-2 


24/3 


498 


7-66 


129 


12-9 


25/3 


87 


1-33 


14 


1-4 


26/3 


14 


0-22 


y 


09 


27/3 


73 


1-12 


18 


1-8 


28/3 


366 


5-63 


57 


5-7 


30/3 


82 


1-26 


27 


2-7 


31/3 


140 


2-17 


16 


1-6 


1/4 


270 


4-15 


28 


2-8 


Total 


1,885 nets 4,956 fish 


290 nets 


1,564 fish 




Average - 


-2-63 fish 


Average --5 


38 fish 




per net 


per day 


per net per day. 



is further reduced by knotting. This has often led to the 
wrong selection in size of nylon twines in replacing 
cotton and hemp twines. 

For example, nylon twine, chosen on the basis of 
dry tensile strength, produced a fine netting with good 
catchability but resulted in much damage to nets in 
hauling the catch in the cod fishing season 1954/55. An 
investigation showed that the twine was too fine and the 



wet mesh strength of the nets was lower than that of 
similar nets of hemp and cotton. 

Tests, wet and dry, with and without knots, were 
carried out with nylon, hemp and cotton to find a rule 
for choosing nylon as a substitute for cotton and hemp 
for a particular net. 

As a result of these tests it was found that a nylon 
twine with 50 per cent, more runnage than the cotton 
it would replace, or which was 50 per cent, longer per 
unit weight, had a satisfactory wet knot strength. 

Knot slippage in single knot nylon netting has also 
created problems, but experiments and experience 
have led to methods being evolved to overcome this 
difficulty. The application of heat and/or bonding agents 
has made it possible to produce a single knot webbing 
which is satisfactory as regards knot slippage and 
stiffness of the netting. 

The degree of knot slippage depends on the construc- 
tion of the knot and double knots show less tendency 
to slip than single knots. On the other hand, mending 
double knot webbing requires more work. 

Polyester fibre nets of Terylene are used for catching 
cod and coalfish. Their catchability and durability seem 
to be similar to those of nets made from the polyamide 
fibres. 

In 1954/55 experiments with codtraps made from the 
Japanese poly vinyl alcohol fibre Kuralon were carried 
out by the Directorate of Fisheries. As this type of gear 
is almost continuously in the sea until it is renewed, 
traps made from hemp or cotton have a relatively short 
life, being destroyed by micro-organisms. A first report 
from fishermen said that Kuralon traps had been in the 
sea continuously for 20 weeks while, during this same 
period, traps from hemp and cotton had to be renewed 
every seventh week. Up to April 25th, 1957, seven reports 
said that Kuralon traps had been in the sea continuously 
from 3 to 6 months, averaging 4 5 months, and there were 
no signs of reduction in the strength of the twine. 

Experiments are still being carried out with most types 
of fishing gear, such as purse seines, herring nets, etc. 
made of synthetic material. Despite the high cost of 
these materials, there seems to be a great future for their 
use in the various types of fishing gear. 



160] 



ON THE FISHING POWER OF NYLON GILLNETS 

by 

G. SAETERSDAL 

Institute of Marine Research, Bergen, Norwa> 



Abstract 

A series of experiments was earned out in Noivtay to ie*t the fishing capacity of nylon nets as compared with nets made of cotton. 
In the mackerel and coalfish fishery, nylon gillnets were used; in the cod fishery, nylon and Perlon were used. It was found that the observed 
fishing power of the nets made of artificial fibres was from 2-5 to 4-4 times that of cotton in the case of cod. 1 -4 to 2-3 in the case of coal- 
fish, and 1 -2 to 1-3 in the case of mackerel. The reason for this variation between the different species may be related to the shoaling habits 
of the fish and this possibility is discussed in the report. 



Resume 



Sur la capacitc de peche des filets maillants do nylon 



t.n Norxege, on a effect uc unc serie d'cxperiences pour essayer la capacite de peche des filets de nylon computes a filets de colon 
On a utilise des filets maillants de nylon pour la peche du maquereau et du colin, et des filets dc nylon ct de perlon pour la peche de la morue. 
La capacitc de peche qui a etc observee pour les filets de fibre artificiellc etait de 2,5 4,4 fois celle du coton dans le cas de la morue, 1,4 
A 2,3 fois dans le cas du colin et 1,2 a 1,3 fois dans le cas du maquereau. La raison de cette variation entre les diflTcrcntcs especes peui 
etre attribute aux habitudes dc vivre en banes des poissons et cette possibility cst discutec en detail dans le rapport. 



I. -A capacidad de pesca de las redes de enmalle de nylon 
Extracto 

Fn Noruega sc hicieron series de cxpcrimcntos para detcrminar la capacidad de pesca de las redes de nylon en comparacion con las 
de algodon. En las pesquei las de caballa y colin se utilizaron artes del primero de estos materiales y de perlon, encontrindose que el rendi- 
miento de los tejidos con fibras artificiales era de 2,5 a 4,4, 1,4 a 4,4 y 1,2 a 1,3 veces mayor que los d algod6n en el caso del bacalao, colin 
y caballa, respect ivamentc. fcn el in for me tambien se analizan detallaclamcntc las causas de estas vanaciones entre las diversas especies, 
que se hallan relacionadas con los habitos gregarios de los peces. 



ON the provision of the Fisheries Director, Bergen, 
a few fishing experiments for cod with gillnets 
made of artificial fibres were carried out in 
northern Norway in 1952 and 1953. The results obtained 
were promising and for the season J954 a large series of 
experiments was planned in order to ascertain the fishing 
power and the practical usefulness of such nets compared 
with conventional ones. 

The experiments were planned and carried out under 
the leadership of Fisheries Consultant M. Halaas, 
Fisheries Directorate, Bergen. An agreement was made 
with a number of fishermen from different parts of the 
coast that they should include some nets of artificial 
fibres in their sets of conventional nets and report on the 
results. As a whole this arrangement proved to be 
successful. Most of the fishermen continued this work 
also in the season 1955. 

SPECIFICATIONS OF THE NETS 

The experiments include the species cod, coalfish and 
mackerel. In the Norwegian gillnet fisheries for cod and 
coalfish the mesh size and the dimensions of the nets 



\ary in the various coastal districts, in order to obtain 
comparable results the nylon nets were in each case made 
to match these different specifications as far as possible. 
The following types of artificial fibre nets were used: 

Mackerel: nylon, 210/2 s 3, 600 m./kg., breaking strength 

8 kg. 18 knots per ell (24 inch). . 
Cod: nylon, 210/5x3, 2,500 m./kg. breaking strength 

20 kg. 6] and 7 knots per ell (24 inch). 

Perlon No. 26, continuous multi-filament, 2,200 

m./kg., breaking strength 19 kg., 6J, 61 and 1\ 

knots per ell (24 inch). 
Coalfish: nylon, 210/6x3, 2,000 m./kg. breaking, 

strength 24 kg., 7,1, 8 and 8} knots per ell (24 inch). 

The knots in the Perlon nets were single, in the nylon 
nets double. 

The conventional nets used for comparison were of 
(he following types: 

Mackerel: cotton, 18 knots per ell (24 inch). 
Cod: cotton, 12/12 and 12/15, 6j and 6i knots per ell 

(24 inch). 
Coalfish: hemp, 7/3, and 8/3, 8 and 8J knots per ell 

(24 inch). 



[161 1 



MODERN FISHING GEAR OF THE WORLD 




r = 0,71 



4 6 

COTTON 
Fig. L C^-cotton. P^Perlon. 

FISHING RESULTS 



fish 
6 per net 



Fig. 2. Creation. N- nylon. 




Fig. 3. 



In the reports from the fishermen the following data were 
given for each lift: number of conventional nets used, 
number of synthetic fibre nets used, and total number of 
fish caught in each type of net. The distribution of the 
fish in the single nets is thus not available, but each lift 
can be described by a paired mean. 

In most cases the numbers of nylon nets used were 
small compared with the numbers of other nets in the 
sets, causing a large spread in the distribution of the paired 
means. This is, however, partly compensated by the 
large number of lifts in most of the series. 

Fig. 1 shows the distribution of the paired means from 
one of the experimental series. In this case the number of 
both types of nets were almost equal. The regression 
lines have been fitted by the method of least squares. 
(The fact that there was a small variation in the number 
of nets used in some of the lifts has not been accounted 
for in this calculation.) 



In our analysis there is no logical reason to prefer one 
of these regression lines to the other. They run almost 
symmetrically relative to the origin, and it seems fair 
to assume that the true relation is a simple proportionality 
The best description of this relationship is therefore 
a straight line through the origin and the paired mean 
of all the observations shown as the line P-=3-94 C in 
fig. 1. 

Fig. 2 and fig. 3 show the results of two more series of 
cod catches with regression lines calculated in the same 
way as in fig. 1 . The spread is larger, but the regression 
lines are still fairly symmetrical around the origin. 

Similar cluster diagrams were made for all the series or 
smaller groups of experimental series, and they all show 
a more or less pronounced trend in the distribution of 
the paired means. In Table I the results have been listed 
as the probable proportional relationship between the 
fishing powers of the two types of nets used, represented 
by the straight line through the origin and the paired 
mean of all the observations. 



f 162] 



NYLON GILLNETS IN NORWAY 



TABLE 1 



Series No. Species Localityyear 


Sum nets x //// 


Sum catch 
convent, 
nets 


Sum catch 
artific. 
fibre nets 


Probable relation 
of 
fishing power 


I. Cod Scnjabank, 1955 


Cotton 500, Perlon 452 


744 fish 


2,651 fish 


P 


3-94.C 


2. 


Kvaenangcn, 1954-55 


Cotton 1496, nylon/Perlon 374 


1,835 


1,396 


N/P 


3-03.C 


3. 


BAtsfjord, 1954 


Cotton 982, nylon/Perlon 44 


2,868 


430 


N/P 


: 3-37.C 


4. 


Vesteraien, 1953 


Cotton 477, nylon/Perlon 95 


1,703 


1,036 


N/P 


3-03.C 


5. 


S0r0y, 1954-55 


Cotton 1926, nylon 172 


4,830 


1,361 


N 


:3-15.C 




it 


Perlon 127 


t 


802 


P 


:2-51.C 


6. 


Mager0y, 1954-55 


Cotton 1124, nylon 175 


3,211 


2,189 


N 


:4-37.C 







Perlon 69 


>t 


735 


P 


:3-72.C 


7. Coa 


fish Karm0y, 1954-55 


Hemp 2986, nylon 436 


14,037 


4,744 


N 


:2-30.H 


8. 


Hcrdla, 1954-55 


Hemp 900, nylon 150 


2,644 


888 


N 


:2-01.H 


9. 


Herdla, 1954-55 


Hemp 2128, nylon 225 


15,253 


2,281 


N 


: 1-41.H 


10. 


Bremanger, 1954-55 


Hemp 645, nylon 100 


2,738 


923 


N 


:2-17.H 


11. 


Stad, 1954-55 


Hemp 748, nylon 114 


5,515 


1,211 


N 


: 1 -44.H 


12. Mackerel Langesund, 1954-55 


Cotton 2749, nylon 210 


30,841 kg. 


2,721 kg. 


N 


: 1-16.C 


13. Flekker0y, 1954 


Cotton 2850, nylon 150 


27,357 


1.826 


N 


: 1-27.C 



nylon; P^ Perlon; C cotton; H=hcmp. 



In the series numbered 2 to 6 in this table both nylon 
and Perlon nets were used in the same sets together with 
the conventional cotton nets. Records of the catch by 
each of these types of artificial fibres arc available only 
from the series 5 and 6. They show slightly lower values 
for Perlon than for nylon, but the number of observations 
is too small to allow conclusions. 

CONCLUSIONS 

In the case of the cod it is seen that the observed fishing 
power of the nets made of artificial fibres varies from 
2-5 to 4-4 times that of the cotton nets. The correspond- 
ing range for the coalfish is from J -4 to 2-3 and for the 
mackerel 1 -2 and 1 -3. 

The variation "within the species" may partly be 
chance variation, partly due to different experimental 
conditions such as the rigging of the nets, the arrange- 
ment of the two types of nets in the sets, etc. The variation 
"between the species" is, however, probably a true one, 
and must in some way be related to the nature of the 
higher efficiency of the artificial fibre nets. 

The observer of experiment No. 6 remarked in his 
report that the nylon nets seemed to catch a wider range 
offish sizes than usual. A sampling was planned for the 



season 1955/56 to ascertain whether such a difference in 
the selectivity really existed, but sufficient data was 
unfortunately not obtained. Such a difference could be 
caused by the higher elasticity of the nylon twine. 
Another practical experience which may touch on this 
point is that the quality of the cod caught on the nylon 
nets seems to be inferior to that of the fish caught on 
cotton nets, presumably because the fish die more 
quickly in the nylon nets. 

If the higher fishing power of the nylon nets is con- 
nected with the ability of the nets to catch a wider range 
of fish sizes, then this would offer us an explanation of 
the different efficiency of the nylon nets towards the 
different species found in these experiments. As a result 
of the pronounced schooling behaviour of the coalfish, 
the range offish sizes present in a concentration of coalfish 
is usually considerably smaller than in a concentration of 
cod. This phenomenon is even more striking in the 
mackerel. In agreement with this hypothesis is v. 
Brandt's (1955) 1 report of only up to 35 percent, increase 
of catches with Perlon nets in herring drifting. 



i Brandt, A. v., 1955. 
wirtschaft, 1955, 99-101. 



REFERENCE 

Perlon-Netze in der Loggertischcrei. Fisch- 



[163) 



DISCUSSION ON RELATIVE EFFICIENCIES OF NETS MADE 

OF DIFFERENT MATERIALS 



Mr. B. B. Parrish (U.K.) Rapporteur. When judging the 
relative efficiencies of gear made of different materials, 
selectivity must be considered. By selectivity we mean how 
much will a certain gear catch, what species and sizes of 
fish? 

All fishery workers arc concerned with this question in 
one form or another. The fisherman usually wants from each 
of his operations the greatest possible catch, but not necessar- 
ily the greatest amount of any or all kinds of fish. He tries to 
catch fish of a species and size for which there is a market in 
his particular area. The technologist sees in the catch an 
indication of the efficiency of the gear used, as compared to 
another. 

The fishery economist looks at the catch as an income 
resulting from a certain expenditure. 

The fishery biologist looks at the catch from the point of 
view of its significance with regard to the fish stock from 
which it has been taken, as that stock determines what can, 
and in part what will, be taken in the future. For him the 
catch is a proportion of the stock and the removal of this 
proportion signifies certain effects on the stock-changes 
in its size and other properties. 

Let us first of all define what selectivity really is. We can 
say that every individual in a fish population of a certain 
area has an equal chance of being caught, then the catch will 
reflect the composition of the whole population. When the 
proportions in the catch show a different composition, then 
the gear may be said to be selective. This can be due to the 
biological characteristics of the fish, to the type of the fishing 
operation, to the behaviour of the fish in relation to the 
operation or to the rig and design of the gear so that selection 
is not attributable to the characteristics of the gear alone. 

Another type of selection will operate when the fishing 
boats of a certain area fish in regions where certain high 
quality fish are to be found, to satisfy the market demands for 
a particular species. 

Perhaps the most important factor, determining the extent 
to which this type of selection process will operate, is the 
knowledge of the distribution of the species wanted. The 
collection of such knowledge should benefit from a close 
cooperation between fishery biologists and the fisherman. So 
we can say that selection begins as soon as the fishing fleet 
puts to sea and concentrates in places where the most desirable 
catch is to be found. This selection process becomes more 
complex where several types of gear operate at the same time 
to supply different market demands. A second stage of 
selection, which we can call gear selection, starts when the 
gear is put into operation. 

Gear selection can be divided into two components: that 
due to the avoidance of the gear by certain species and that 
due to the ability or tendencies to escape from the gear when 
the fish come into contact with it. If the magnitude of these 



components can be identified and measured, then the gear 
designer, the gear manufacturer and fishermen can take 
account of them in the construction and operation of the 
gear, or the fishery administrator in his fish conservation 
practices. 

In gill net fishing, for instance, the catch depends on fish 
swimming into and being meshed or entangled by a wall of 
net. The influence which biological factors may have in this 
action is illustrated very clearly by Nomura who discusses 
the factors affecting the selectivity and fishing ability of gill- 
nets in Japanese waters. This paper demonstrates that the 
behaviour of the fish in relation to the visibility of the nets, 
plays a very important part. Saetersdal and Mugaas also 
mention data which point to the inter-action of the fish 
behaviour to, and the gear selectivity of, different types of 
material used for gillnets, as being important in determining 
the si/e of catch and its composition. In line fishing, too, 
there are data which demonstrate the importance of these 
factors; fish of some sizes or ages, for example, may avoid 
baits of a particular shape or si/e, while others will take them 
A further stage at which selection takes place is the escape- 
ment of fish from the gear once they have contacted it, such 
as through the meshes of the net. 

This mesh escapement, of course, is a process which is 
well known to technologists, fishermen and fishery adminis- 
trators as well as fishery biologists. It is, in fact, the selection 
process which is utili/ed in effecting fishery conservation 
practices in some important regional fisheries. 

For example, we have learned a great deal in recent years 
about the behaviour of fish in trawl codends and seine cod- 
ends by the adoption of television techniques, under- water 
observations by frogmen, by measuring devices attached to 
nets, by controlled experiments with gears and observations 
on the catches in different parts of the net. This has shown 
that mesh escapement is effected by features of the gear as 
well as by the behaviour of the fish. One of the most important 
of the gear factors which affects escapement is the material 
from which the net is made. The results of experiments have 
shown conclusively that the escape of fish differs between 
nets having the same mesh size but made of different materials. 
Some quality -of the material which is being identified by 
many workers with the property of flexibility and stretch- 
ability of the twines is responsible for this. Mesh escapement 
is also affected by the size of the catch as fish in the codend 
will tend to block meshes and prevent further escapement. 

I do not propose to go into the methods by which the 
selection processes can be studied and examined yet I must 
draw attention to the method known as comparative fishing. 
Comparative fishing has been used almost exclusively hitherto 
to study selectivity and other features of fish operations, such 
as determining the fishing power of nets of different structures, 
different materials and so on, and in four of the present papers 



164 1 



DISCUSSION - RELATIVE EFFICIENCIES 



there arc examples of the use of the comparative fishing 
technique. That the method must be worked under strictly 
controlled conditions is apparent from the experiments 
referred to in the papers on the efficiency of gill nets made of 
natural and synthetic fibres. Whereas these papers conclude- 
that the synthetic fibres are catching much more efficiently 
than the natural fibres, the results of similar experiments 
conducted elsewhere show very little superiority of synthetic 
fibres. The higher catches of synthetic fibre nets may be due 
to the decreased visibility when they are fished in clear water. 
On the other hand, one would not expect to find a marked 
difference in very turbid water. 

Mr. S. Holt (FAO). In measuring how effective one gear 
is by comparison with another slightly different gear, we use 
the "comparative fishing method". Although it essentially 
means fishing the two gears side by side and comparing the 
results, the difficulty has been that results arc very variable 
and therefore rather complex statistical methods have to be 
used if we arc to make the correct interpretation of the results 
of such trials. The trouble is that, although we can measure 
the differences between gears, we do not know if that differ- 
ence will be true when we make the same experiment on 
another day, or in a different place, a different season, or at 
a different time of day. 

Comparative fishing experiments can give us measurements, 
they cannot Icll us the reasons why. The problem of inter- 
pretation of the results is a matter for both biological and 
technical study. There are very complex problems involved, 
as Mr. Parrish has said, but somehow they have got to be 
solved if we are to try to devise gears rationally. If we are 
going to accelerate the rate at which we can improve fishing 
gears, we must do more than just make trials working in the 
dark the whole time. To do this at all we will need to under- 
stand a lot more about the reactions of fish, particularly to 
different characteristics of fishing gear such as its visibility, 
the speed at which it moves, and so on. 

At a meeting of biologists in Lisbon this year, it was 
suggested that this Congress was the appropriate place to tell 
technologists and fishermen what kind of information biolo- 
gists expect from them. 

Fishery biologists are in general responsible for measuring 
the properties of the fish which determine its liability to 
capture. They believe it is the responsibility of gear tech- 
nologists to analyse and measure the corresponding properties 
of the gear. They believe that this work would be greatl> 
assisted if a world catalogue and description of fishing gears 
could be compiled and if a classification of gears based on 
toxonomic principles could be devised. They believe that a 
simple classification of gear would serve the following 
purposes. Firstly, it would stabilize the nomenclature of 
gears with special reference to synonymous terms used in 
various countries. Secondly, it would assist the population 
dynamic worker by indicating the essential properties of 
gears with which they are working, and thirdly it would 
facilitate the correct comparison of results obtained with 
various gears in different circumstances. 

The biologist cannot advise on the correct gear to use. 
unless he knows what is the composition of the fish stock on 
the ground. If that changes, then the choice of gear must 
also change, i.e. another gear may be more economical. The 
trouble is, we cannot wholly measure the composition of the 
fish on the ground without also knowing a great deal about 



the selectivity of the gears which .ire actually being used by 
the fishermen. The only solution is by very close co-operation 
between the fishermen, the gear technologist and the biologist. 

Mr. S. Springer (U.S.A.). In the CJulf of Mexico xve use 
shrimp trawls which run from 12 ft. across the mouth to 
125 ft. and all of these are used to a very great extent 
some on the same boats. The smaller nets are used for try 
nets to test the ground and the larger nets are used for pro- 
duction. The smaller nets are usually a lot faster than the 
larger nets. I presume that all of these nets work well enough 
but one thing that we have found in analysing the catches of 
the nets of different sizes is that the smaller nets catch smaller 
fish than the larger nets. Yet it appears that, owing to the 
greater speed of the smaller net, this should not be so. One 
explanation of why this may happen could be seen in the 
television film showing haddock inside the codend. In general, 
these haddock seemed to move and swim forward to a certain 
extent before they actually go into the tail of the codend. It 
would seem to me that we might infer from this that the net 
has to have a certain length in order to retain the large fish 
that is, a short net with a short codend would catch more small 
fish because the larger fish, being faster swimmers, can 
escape. I would be interested to know if there is any experience 
like this in other fisheries and whether there is any relation 
between the length of the throat and the codend and the size 
composition of the catch. 

Dr. Went (Ireland). I rom a point raised this morning it 
would appear that the fisherman in general is not convinced 
of the practical value of selectivity and comparative fishing 
for the industry. 1 think we must stress the very great import- 
ance of this subject to the practical fisherman who, of course 
is interested in getting tish. However, if he is to continue 
obtaining good catches, fish conservation regulations must 
be made to preserve the stock. I think the experiments on 
selectivity of fishing gear and comparative fishing will give 
us the basis on which to draw up such international regulations 

Mr. M. Ben-Vami (Israel). 1 would like to emphasi/c the 
importance of comparative fishing in assessing the relative 
value of fishing gear. We met this problem in Israel in con- 
nection with the high opening trawl we had developed. We 
were aware of the difficulties in determining the actual value 
of differences in catching efficiency between two types of 
gear accurately. But, for the commercial fishermen only very 
obvious differences count. I. therefore, think that accurate 
statistical evaluation, as applied in selection experiments, is 
not needed for such practical purposes. We actually used two 
techniques of comparative fishing: one and the same trawler 
fishing with the new gear and the conventional gear alterna- 
tively, and two boats, one with the new gear and one with 
conventional gear, towing side by side. These experiments 
were conducted for several months in commercial operation 
in various areas. After eliminating all not strictly comparable 
hauls, some 60 comparative tows remained, the evaluation of 
which indicated that the new gear gave about 20 per cent, 
better catches. For such commercial comparative fishing it is 
advisable to put a very experienced and very conservative, but 
good, fisherman in charge of the conventional gear and make 
the designer of the new gear compete against him. If a new 
design passes such a test successfully, I think one can be sure 
and the fishermen can be convinced, that something worth 
while has been achieved. 



165 



Section 6: Rational Design Use of Engineering Theory and Model Testing. 



THE USE OF MODEL NETS AS A METHOD OF DEVELOPING 

TRAWLING GEAR 

by 

W. DICKSON 

Marine Laboratory, Aberdeen, U.K. 

Abstract 

This paper deals with the theory and practice of using models in connection with the design of fishing gear and the study of fish 
behaviour in relation to the gear. A certain amount of success has been achieved by underwater photography by frogmen but there arc 
hazards and difficulties when the gear is towed quickly in areas of low visibility. The use of models in shallower water can overcome some of 
these difficulties, and the author lays down rules governing the making and operation of small-scale nets. 

Models were observed in action in a West Scottish sea loch by frogmen working in pairs and hanging on to a tow-rope instead of 
to the net itself, and several photographic records have been procured by this means. 

The need for correlating observations and measurements of models with observations on the full -sized gear is stressed and it has 
been found that the agreement between the performance of models and full-sized gear has generally been sufficiently close to conclude that 
much can be learned from models, provided that comparisons are viewed critically. Models can show fairly accurately the effect of alternate 
methods of rigging a gear and can at the same time reveal faults, but they are not intended as a substitute for instrumentation or comparative 
fishing, the latter being regarded as the final stage of gear-testing. The paper is fully illustrated. 



Rfemne 



Utilisation des modules de filets dans la tnise au point des chaluts 



Cet article traite dc la th^orie et.de la pratique des essais dc modeles en vue de la construction des engins de peche et de l*6tude du 
comportcment du poisson en fonction des engins. Des photographes sous-marines prises par des horn mes-grenoui lies ont perm is d'obtcnir 
quelques succes, mais Toperation est difficile et dangereuse lorsque 1'engin est remorque rapidemcnt dans des zones ou la visibility est faible. 
L* utilisation de modeles dans des eaux peu profondes permet dc surmonter ccrtaines de ces difticultes et 1'auteur pose des regies applicables 
a la fabrication ct 1'utilisation de filets de pctites dimensions. 

Des hommes-grenouilles travail lent deux par deux et se tenant a un cable de remorquage au lieu de se tenir au ft let lui-meme ont 
observe^ des modeles en action dans un loch, sur la cdte ouest de TEcosse et plusieurs enregistrements photographiqucs ont et obtenus dc 
cctte maniere. 

L'auteur souligne la necessity d'tablir un rapport entre les observations et les mesiircs des modeles ct les observations faites sur les 
filets et sur les engins de grandeur naturelle et il a ct constate quc le comportement des modeles et des engins de grandeur naturelle a etc 
sufhsamment analogue pour permet t re de conclure que les modeles pcuvent constituer une excel Icnte source d'enscignement, sous reserve de 
soumettre les comparaisons un examen critique. La construction de modeles peut montrcr d'une fagon assez sure 1'effet des di verses methodes 
possibles pour garnir un engin et en mme temps en montrer les defauts, mais elle n'est pas destinee remplacer les instruments ou la pche 
comparec, cette derniere etant toujours considdree comme 1'etape finale de 1'essai des encins. 



Extracto 



Uso de modelos de redes de pesca como metodo para perfeccionar artes de arrastre 



En este trabajo, que cuenta con numerosas ilustraciones, se estudia la teoria y practica del uso dc modelos a escala reducida en 
relaci6n con el proyecto de los artes de pesca y el estudio de la manera como reaccionan los peces ante las redes. Se ha logrado cierto exito 
mcdiante fotografias submarinas tomadas por "hombres ranas", pero este mtodo es peligrose y ofrcce dificultades cuando la red es arrastrada 
rfpidamente en zonas de poca visibilidad. Como el empleo de modelos en aguas menos profundas puede evitar algunas de estas dificultades. 
el autor da algunas reglas que gobiernan su const ruccion y uso. 

En una ensenada dc la costa occidental de Escocia parejas de buzos que colgaban del cable de remolque en vez de la red, observaron 
el comportamiento del modelo y tomaron varias fotografias. 

La neccsidad de cprrelacionar las observaciones y medidas de los modelos con observaciones de los artes de tamano correinte han 
permitido encontrar que existe una concordancia entre el rendimiento de los modelos a escala reducida y las redes normales, lo suficientemente 
estrecha como prra llegar a la conclusi6n de que pueden sacarsc grandes experiencias con el uso de modelos sicmpre y cuando las compara- 
ciones se analicen con sentido critico. Los modelos pueden demostrar con bastante certeza el cfecto que ofrece el empleo de mdtodos alterna- 
tivos empleados en la confecci6n de las redes y, al mismo tiempo, revelar sus inconvenientes pero no se trata dc utilizarlos para reemplazar 
el uso de instrumentos o la pesca comparativa, ya que esta ultima es considerada como la etapa final de las pruebas a que es nccesario someter 
un arte. 



WORK was begun on the observation of models 
underwater in 1954 by the Marine Laboratory 
in Aberdeen. Data obtained in the meantime, 
from measurements by instruments on the performance 
of full-sized trawling and Danish seine net gear, together 
with the underwater films and measurements already 
made, served as a comparison against which the per- 
formance of models could be judged. The comparison 
between models and fullsized gear was sufficiently 



encouraging to warrant repeating and extending the 
trials in 1955 and 1956. 

There are three reasons for observing fishing gear or 
models of it in operation: 

1 . To form an impression of the performance of the 
gear, to seek defects in its design and to try the 
effect of alterations in design and rigging. 

2. To make measurements to obtain a fuller apprecia- 
tion of the gear's hydrodynamical performance. 



M66] 



MODEL NETS FOR EXPERIMENTAL WORK 



3. To obtain information on the reactions of fish to 
the gear. 

Certain rules should be observed as closely as possible 
when modelling, and if the conditions of water-flow 
are to be similar for model and full-sized net, there should 
not be too great a change of Reynold's Number. When 
the scale becomes too small the rules cannot be followed. 
The purpose will also dictate how far the rules should 
be obeyed. Lastly, the choice of model size is dependent 
on the towing power of the available boat. 

When the purpose is to look for bad features in the 
design of a net, the model should correspond mesh for 
mesh with the original and the twine diameter should be 
proportionally reduced. Practical considerations, how- 
ever, often force a compromise. Expense and the avail- 
ability of suitable materials have to be taken into 
account and, if the setting of the net is to be altered 
during the experiment, labour costs must be considered. 
A quarter scale model with a half scale mesh, or an 
eighth scale model with a quarter scale mesh, are reason- 
able compromises. If a true scale model is required, a 
scale of one quarter is about the smallest that can reason- 
ably be used. 

Small nets of some 20 ft. headline length towed by 
the 15 h.p. coble shown in fig. 1, are big enough to be 
effective fishing instruments, and there is little likelihood 
of significant fish behaviour passing unnoticed. For this 




purpose the nets should be made with meshes of the 
size used commercially. 

COMPARISON BETWEEN AN EIGHTH SCALE 
MODEL AND THE FULL-SIZED GEAR 

Measurements on models can be taken by direct readings 
on measuring sticks, strings and spring balances, but 
to take corresponding readings on a full-sized trawl 
requires some degree of instrumentation. In most cases 
only a few spot-checks are possible. The net chosen for 
the present comparison is the small "Aberdeen" trawl 
used by most trawlers from that port. Its headline length 
is 62 ft. The model is to one-eighth scale with the mesh- 
size and twine diameter reduced to approximately one- 
quarter. The following data were obtained for the model 
and full-sized net in a series of trials. (Scaled up values of 
the model data are given in brackets.) The original and 
the model were rigged in the same way with 10 fm. 
sweep lines, bobbin danlenos and 20 ft. spreading wires. 



Warp Length 
Spread of otter 
boards 

Headline Height 
Drag of Gear 

Towing speed 


Full Size Net 

100 fm. 
105ft. (by wire angle 
at surface) 

6 ft. (by differential 
depth recorder) 
3-25 tons (by warp 
tension recorder, 
1 -63 in each warp) 

3 knots 


8/A scale Model 

10 fm. (80 fm.) 
11 ft. 8 in. (93 ft. but 
equivalent to 97 ft. 
with 100 fm. aft). 
9 in. (6 ft.) 

16 Ib. (3-7 tons lowest 
estimate) 
40 Ib. (9-2 tons highest 
estimate) 
1 knot 



The comparison is close enough to emphasize the 
value of models and yet divergent enough to give the 
hint that significant differences can arise. 

A photograph of the differential depth recorder used 
to measure the headline height is shown in fig. 2. It is 
an ordinary depth recorder, except that the pressure 
inside is maintained at headline depth through the 
collapsible rubber tyre attached to the headline, the 
recorder itself being attached to the ground rope. The 
instrument used for recording warp tension is shown in 



Fig. I. 



Coble with cameras ami breather set on the foredeck and 
winch in the stern. 




Fig. 2. Differential depth recorder. 



167 



MODERN FISHING CiF.AR OF THE WORLD 




/'iff. 3. MVwy> tension recordei . 




Fig. 4. Stui hoard winx and pan of the square of the small Aberdeen 

trawl. Shot from the film "Trawls in action' made by "Basic 

Films" for M.A.F.F. Fisheries Laboratory, Loweito//. in con/unction 

with Siehe Gorman\ I. id. 




tig. 3. It works on the principle of one wheel deflecting 
the warp a small lateral distance between the two 
outside wheels at a fixed distance apart. The deflecting 
wheel is mounted on the piston of an oil-filled cylinder 
and the oil pressure recorded. The instrument can work 
whether the rope is moving or stationary. 

As the small "Aberdeen" trawl was photographed in 
the M.A.F.F. film "Trawls in Action", we may compare 
it with a photograph of the model. Fig. 4 shows a vie\* 
of the net and fig. 5 one of the model. 

MODELLING RULES 

As a model is scaled down, all weights and floats de- 
pendent on volume decrease by the cube of the scale, 
while all lifts and drags due to water-flow and dependent 
on surface areas decrease by the square of the scale. 

Tand Ware proportional to / 3 where F and W are floatations 

and weights in the original and 
where / is a unit of length. 

D and L are proportional to where L and D are lifts and 
7 2 \ - drags due to water flow in the 

original and where v is the 
towing speed. 

where F s and W s are floatations 
and weights in the model, where 
/ is as before and s is the scale. 



K and W s arc proportional to 
<s / 3 ) 

U and D s arc proportional to 
is /)'- (si v) 2 



Fin. 5. 



Model of small Aberdeen trawl. 
Mote loose lay t rich line 



where L s and IX are lifts and 
drags due to water flow in the 
model. 

L D F W 

It may be seen that for = - = -- - - there 

L s D s F s W s 
are several requirements. 

1 . All dimensions of length must be reduced to scale. 

2. Floats and sinkers must be of the same density in 
the model as the original, otherwise the change in 
flotation or weight will not be proportional to the 
cube of the scale. Netting twine should also be of 
the same material otherwise there is a change in 
density, and here arises a difficulty. Most big nets 
are made of man i la twine, which cannot be obtained 
thin enough for model making, hence the usual 
material for model making is cotton twine. Although 
there is no very definite agreement about specific 
gravities of twine the following figures may be used: 

Manila (green proofed with cuprinol) SG T29 
Cotton (green proofed with cuprinol) SG 1*34 
Nylon SG 1'12 

3. The speed of towing must be reduced by the square 
root of the model scale. In operations such as seining 
where time is also a factor, the timing must also be 
scaled down by the square root of the scale. 

If the normal towing speed of trawls is taken as 3 
knots: 

.1 scale towing speed is 3/V2 or about 2 knots 
1 scale towing speed is 3/V4 or 1 J knots 
J scale towing speed is 3/V8 or about 1 knot 

4. It is assumed that the lift or drag due to water-flou 
changes proportionally with the square of the velocity, 
but this will only be so over a limited range of change 
in scale and change in speed. This will be discussed 
more fully later. 



f 1681 



MODEL NETS KOR FXPERI M ENTA 1. WORK 



In practice these rules are not always honoured 
accurately. It is, therefore, necessary to understand in 
each case whether and how they are being broken and 
the direction of the resulting bias, so that it may be 
allowed for or measures taken to overcome it. Consider 
only one of the probable compromises here, that on 
which the models described were made where mesh 
und twine size were reduced less than by the scale. 

I ei / be the length of twine in the original (in.) 
R be the runnage of the twine in the original 

(m./kg.) 
P be the density of the t\*ine in the original 

(g./cm. 3 ) 
W be the weight of the twine in the original 

(kg.) 
d be the diameter of the tv\ine in the original 

(mm.) 

A be the projected area of the twine in the original 

(mm.-) 

Similar letters with the suffix s refer to the model 
S be the scale of the model 
S m be the mesh scale, and 
S d be the twine diameter scale 



Then W 
A 





W * ' 



and - 
R 



R 




M 




/s 


1 S 2 / 


R> 


R\ Sm 




s 2 / 


/s 


d, Sd 




Sm 




: 1 


p- 


-d-approx.. 


4 


R, 



/ PR 

VK*: 



Hence S d 

When the model scale is a true one 



(I) 
(2) 



(4) 



P N d N 2 a pprox . ( 5 ) 
4 

(6) 



W 


- 


; S Sm S t 




R 




A 


/d 




w s 


S 31 


1 . 






R 


A, 


- S 2 


/d 


Rut take 


the 


simple case: 


S 


H! Sm Sj 




Sd 




Vv\ 


- 


S 2 / 




R 




As 


- S 2 /d 



l\s 



R 

S 2 ' 



P,; 



R 

Sd 2 



The area of twine projected to the water-flow is 
correctly scaled but the model is twice as heavy as it 
should be, and this has to be balanced by increased 
flotation. Where the model cannot be made of the same 
material as the original, similar effects occur. These 
physical difficulties in constructing an accurate model 
are not the only ones to be considered. 

Reynold's Number is a dimensionless number given 



hv R where \ is the velocity, 

n 

/ is an arbilar> length unit such as say the diameter 
of the floats or the twine diameter: 



n is the Kinematic viscosity and n 



where 



a is the viscosity of the medium 
Pin is the density of the medium 

So long as R remains constant it can be taken thai 
i he conditions of the water-flow round the immersed 
body remain the same. In model tests in the sea n 
cannot be altered, and, therefore, for constant R, the 
velocity of the model should be inversely proportional 
to the scale but for constant flotation to drag ratio, the 
velocity of the model should be directly proportional to 
the square root of the scale. Both conditions cannot be 
met at the same time and some change of Reynold's 
Number must be accepted. The question is, what change 
of drag coefficients does such a change in Reynold's 
Number bring? 

Pig. 6 shows that for the spherical headline floats there 
might be little change of drag coefficient between the 
full size and one-eighth scale at scale towing speed 1 . 



DRAG COEFFICIENT OP SPHERE 



1 DIA.MOML N.OAT -OI*. TftO 

AT 1 KNOT AT I UN! 

tl ftCALf 'till tltC 



-M -1* -10 



Fig. 6. Relation of coefficient of drag tor spherical floats to the value 
of Reynold's h'umher. 

Possibly in the full sized net the proximity of the head- 
line to the balls and their method of attachment would 
encourage the onset of turbulence, so that the drag 
coefficient might decrease to values given in the sharp dip 
in the graph. 

The drag coefficient of a sphere over a wide range of 
Reynold's Number has been thoroughly investigated but 
far less in known about how sheets of netting behave 
over a wide range of scale and speed. The indications 
are that at one-eighth scale the curve of the drag co- 
efficient rises appreciably and would rise more steeply 
at smaller scales. This, and the physical difficulty of 
making accurate small scale nets, puts a lower limit on 
scale size. 

Information on the lift and drag of otter boards is 
scanty. Gawn gives some data on flat boards of low 
aspect ratio at a Reynold's Number of about 4 x 10 6 . 8 . 
These boards (corresponding to about I/ 12th scale) 
were towed at speeds up to 5 knots without apparently 
much change in the lift and drag coefficients. These data 
cover the model range up to one-quarter scale quite well. 



[169] 



MODERN FISHING 




GEAR OF THE WORLD 

at 



0.2 

n 




N - DISTANCE OF CENT HE OF 
PRESSURE IS DIVIDED BY 
WIDTH OF PLANE IN 
DIRECTION OF MOTION. 



ASPECT RATIO 

21 
1:2 _._ 



20 30 40 

ANCLE OF INCIDENCE -DECREES 



Fig. 7. Forces on rectangular and square plates. From Cawn~. 

Some of Gawn's graphs are reproduced in figs. 7 and 8. 
Trawl boards are, however, in contact with the bottom, 
which affects their drag and alters their lift. Since an 
otter board bears down on its heel, the friction acts 
through a point aft of the centre line, bringing the 
effective centre of pressure further aft than indicated 
in fig. 8. 

Even where frogmen can observe large trawl nets in 
action, convenience and safety of underwater observers 



Fig. 8. Curves of centre of pressure of planes. From Gawri*. 

demands reduced towing speed. The flotation to drag 
ratio is then upset, giving rise to inaccuracies and prob- 
lems analogous to those met in the use of models. 

MAKING SPECIFICATION DRAWINGS 

There is no tendency towards standardization of the 
drawings and specifications of nets. Designers draw nets 
as they think best. Some drawings are made in specula- 



/ *" y 

*6~ L s'X",J 

l300"v 7~ 



100m"" 

60 ROWS 1:3"*S 

DOUBLE 




7 'SLACK IN i * 

LOWER WING ! * 
42' 



13 S'S 5" ) IN BELLY 30ROWS 

\ 110m. / J 




HEADLINE B2 1 "(' 1' ** '' *") 

CROUNDROPE BO' (JO* * 20* 30') 

FISHIN6 LINES 31* 6"* 2t* t 11" 6" 



Fig. 9. Schematical drawing of the 30 ft. Aberdeen trawl. 
1170] 



MODEL NETS FOR EXPERIMENTAL WORK 




>/.^"v 4: ^2 




HEADLINE 7'lO"(2' t/ 
CROUNDROPE 10 ' ( 3 1 9\ 2V* 3'9") 



V .3\ N. 12 /v.l 

LINEN 

THREAD 

DOUBLE 



27 ROWS 



70. Schematical drawing of the \th scale model of the 30 ft. Aberdeen trawl. 



live fashion, in an attempt to show the net in the fishing 
position with a few dimensions added for good measure. 
It is rare for any of these drawings and specifications to 
be complete and it is not easy to tell from them the 
salient features of the nets or how they compare in shape 
with other nets, but it should be possible to make such 
drawings. 

With a model net a glance at the drawings should 
show, when compared with those of the original, whether 
or not it is a fair replica. The scales can be so chosen that 
drawings of both model and original are the same size 
and can be checked by the use of tracing paper. 

The following rules have been found useful in practice: 

1. All lengths are true lengths with the netting 
stretched but any lengthways slack is noted on the 
drawing and indicated by an irregular line in the 
edge of the panel concerned. 

2. All widths are taken by setting the meshes in by 
the half, e.g. 120 meshes of Ij in. size set into 

120 

x U = 90 in. 

2 

Such rules give the drawings a "stepped" appearance 
which the net does not, of course, have in practice, but 
they show directly the lateral slack and tautness. The 
drawings do not cover the setting of the nets to their 
ropes, details which may be added in note form. Figs. 9 
and 10 show the drawings of the small "Aberdeen" 
trawl and model, according to these rules. 



Provided that the same rules are always observed the 
patterns which turn out to be good and bad can be 
remembered and take on their own significance. 

SOME UNDERWATER OBSERVATIONS 

Models of a suitable size for this work are too big to 
be used in most testing tanks, consequently, a method 
was devised for inspecting the models towed in a West 
Highland sea loch. 

The general requirements of a location are, a half mile 
stretch of clean smooth sandy bottom in depths between 
3 and 6 fathoms, not too much tide, a shore reasonably 
free from surf, good sunlight and an underwater visibility 
range of not less than 30 ft. These conditions are difficult 
to satisfy in Scottish waters and the work described 
was done in conditions which fell short of the ideal. A 
frogman may hang on to a full-sized net without dis- 
torting its shape but not a model, nor could he swim at 
towing speed for long. He therefore hangs on to a towing 
rope. The frogmen work in pairs, one making measure- 
ment and one taking photographs. The remainder of the 
team of 5 comprise the divers' attendant, who follows 
the frogmen's air bubbles in a rowing boat, and two men 
in the motor coble towing models and frogmen. 

An otter board is shown in fig. 11. The brackets and 
the "normans" to which the back strops are attached are 
set to give the board an angle of attack of about 35 
degrees, giving the maximum lift with a large concomitant 
drag. It is not worked at or near the angle of maximum 



[171 ] 



MODERN FISHING GEAR OF THE WORLD 




AV#. II. Model otit'i hoard in action. 

lift to drag ratio. Behind the otter boards come the 
sweepwires, the danleno bobbins, the legs or spreading 
wires, and then the net. 

One of the main principles in net design, and in avo id- 
ing net distortion, is to shape the net as nearly as possi ble 
to the shape assumed in its fishing position. Meshes in 
the region of the "quarter" mesh, where the inside edge 
of the top wings join the square, are often subject to high 




Fit;. 12. Tension behind quarter-meshes on model of \nudl 
Aberdeen trawl. 



% 9UARTCK 

f \ MCSNCS /TOP 

A /mm 

/ \ (a) 



\ 



tQUAMC 
COMSTftUCTION Or 




NET IN fISNINt POIITION 




SNAPC0 

Fig. 13. Piopoxal for a better construction of the \quare. 




Fig. 14. Wing tip of model V'ingc Trawl In action. 

tension (see fig. 12). The reason for this is also seen in 
the backward bend of the leading edge of the square 
where it joins the wings. It is as if the net were hinged 
about the quarter meshes as shown in fig. 13 (b). There 
appears to be some argument for shaping the square as 
shown in fig. 13 (c) by "bating" or tapering meshes in the 
middle of the net rather than in the selvedge. This 
improves the appearance and tends to give all parts an 
equal strain. 

It is not really surprising that a bulge in the selvedge 
at the join of top wings and square appears (figs. 9 and 




CLE VATIO N 

Fig. 15. Method to determine the proper length of false headline* 



\ 172 1 



MODEL NETS FOR EXPERIMENTAL WORK 



10) when the model is in fishing position (fig. 5). Con- 
versely, this method of drawing leads, with a little 
practice, to a fair idea of what shape will be assumed 
underwater by a given design of net. It seems as if some 
alteration to the design of this small "Aberdeen" net 
could be advantageous, and such trials will be made. 

To increase the headline height (particularly for 
herring trawling) has long been the objective of net 
designers. Various trials have been made to this end with 
Vinge trawls, where the wing ends are split down the 
selvedge. A model of this type was used with some 
success as a pilot in the development of a Vinge trawl 
for the 75 ft. research vessel Clupea. One wing end of 
the model is shown in fig. 14 where it is apparent that the 
net is set too loosely on the ropes, both headline and 
footrope being too short. Models are particularly 
useful for the correction of such faults. 

The use of kites is common with herring trawls. It is 
difficult to tell how the lengths of the false headlines were 
arrived at in the first place, probably on an empirical 
basis. The shape of a net in the towed position cannot 
yet be theoretically determined, but it was felt that there 
was sufficient knowledge to estimate certain critical 
dimensions and then calculate the desired lengths of false 
headlines to bring the kites to determined positions. Fig. 
15 shows the method. Values must be assigned to the 
headline height at its maximum and at its wing tips, to 
the spread of the net at its wing tips and to the angle of 
attack of the sweep wires. The agreement between the 
values predicted on the drawing and those obtained in 
practice on the model is reasonable. 



Spread of headline 
Headline height H 
Height of 1st Kite HK I 
Height of 2nd Kite HK2 



Predicted 
41 ft. 
14ft. 

22-7 ft. 
32-7 ft. 



Observed 
54 in 
21 in. 
36 in. 
45 in. 



(36 ft.) 
(14ft.) 
(24 ft.) 
(30 ft.) 



The appearance of the kites above the net is to be 
seen in fig. 16. 

REACTIONS OF FISH TO SMALL NETS 

The cin6 film is more useful than the "still" film for 
recording the reactions of fish to the gear. 

The reaction most commonly observed is that fish tend 
to swim away perpendicularly in front of a moving wire 
or rope when both are on or near the bottom. This is 
shown diagrammatically in fig. 17 (i). 

If the maximum swimming speed of the fish be Vf and 
the speed and angle of attack of the wire be Vt and ET 
respectively, then the angle of arc (E p ) from which it 




Fig- 16- Model herring Irawl kites in action. 

would be possible to shepherd fish can be calculated 
It is probably better to have ET smaller than Ep, as in 
case (ii) because the chances are that the wire will 
increase the probability of capture within its limited arc 
In case (iii) it is possible the fish are already outside the 
arc of possibility of capture when near enough to be 
influenced by the wire. Not all fish in the path of sweeps 
and wires finish up in the path of the net nor, for that 
matter does every fish in the path of the net finish up in 
the codend! 

A common line of escape from the path of a net is 
below the ground rope, so the balancing of sinkers and 
floats is critical, if good headline height is not to be 
sacrificed. There are other more interesting ways of 
escape. An observed escape between the legs or spreading 
wires is shown in fig. 18, where the usual movement 
perpendicular to the approaching wires turns into 
escape between them. Whether this is due to vision or 
discrimination between two approaching pressure waves 
or some other factor is not known. 

Flat fish are often pinned against the netting by the 
flow of water through it, even in areas of the net where 
the taper does not appear to be unduly rapid, as in fig. 19 
An outward turn of the flow lines inside the net might be 
inferred. The after end of the lower wings below the 
square is a particularly critical region and if the meshes 
there are large enough escape is possible. 

Shoaling fish appear to behave somewhat differently 
There is the shoal reaction as well as the individual 
reaction. Unfortunately, the only shoaling fish so far 



MOVEMENT 
OF FISH** 




(ii) 



ADVANCE 
OF WIRE 




UNIT DISTANCE 



('") y\Vf 

<<X\^ 
>A e > \v 

, UNIT DISTANCE 



F-T '[_ - *'" " 




PATH Or 
ESCAPE BETWEEN 
SPEADINC 
WIKES 



cos ET 



ADVANCE OF NET 



/iff. 17. Diagram of the common reaction offish to a rope. 

\ 173 1 



Fig. 18 Diagram of an observed reaction oj 
fish to two ropes 



MODERN FISHING GEAR OF THE WORLD 




BATING 



FISH PINNED 
ASAINSTNCTTlNt 




ALL SANDCCLS 
THIS REGION 
ESCAPE 



EXTENSION 
PIECE I 

I *l.'>.' 

TWINE HESH 




Fig. 79. Diagram of the way how a fish can 
become pinned to the webbing. 



Fig. 20. Diagram of the escape of a school 
of sandeel through the funnel. 



Fig. 21. Points of inflection in the shape 
of a trawl net in action. 



observed in their reactions to a net have been sandeels. 
Although the mesh size presented no barrier to their 
escape, they kept their formation, becoming concentrated 
deep in the funnel, and only sought escape there (though 
a few outriders of the shoal escaped earlier). The escapes 
took the pattern shown in fig. 20 and there is presumably 
a pressure build up ahead of the small mesh netting, with 
a consequent increase in flow through the last piece of 
the larger mesh netting. Shoaling fish are both easier and 
harder to catch than other fish: easier, because any 
favourable reaction induced in the outriders can be 
transferred to the shoal, and harder because any escape 
by outriders may be followed by the shoal, therefore any 
defect in design is doubly serious. 

The object of design must be to delay the escape 
reaction. All trawls so far observed have two points of 
inflexion at (a) and (b) as shown in fig. 21. For obvious 
reasons, as much of the net as possible should be in large 
mesh 9 but a critical region for escape lies near the first of 
these two points. If these inflexions are pronounced, the 
large mesh should be reduced short of the first one, while 
with a longer, more tapered net, in which the inflexions 
are more gradual, the large mesh may be carried farther 
aft. (In this sense a large mesh is merely designated as 
one through which the fish can pass.) The long net is 
the common type in herring trawls, often having a fairly 
rapid change from big mesh to small, escape-proof mesh, 
so that there is not a large area in which the herring 
become meshed as this is a nuisance when hauling the 
net. These considerations can also be applied to white fish 
trawls, but important compromises are required in their 
design because the groundrope is in close contact with 
the bottom, which is often rough. Firstly, the belly of 
the net should be kept as small as possible to avoid splits, 
and, secondly, most of the belly should be made in large 
mesh to allow as much bottom rubbish as possible to 
fall through, instead of passing into the codend, causing 
it to chafe. The planning of the inflexions and mesh 
reductions must be made within these limits. 

This is a preliminary report but the results to date 



suggest that observations of fish reactions to small nets 
with full sized meshes provide ideas for shaping full 
sized nets. These ideas can next be applied on the drawing 
board when designing a full sized net. 

CONCLUSIONS 

Observations and measurements on models are of little 
use unless correlated with measurements and, where 
possible, observations on a full-sized gear. These 
cross-checks are necessary to establish confidence in the 
value of modelling as an auxiliary to the rational design 
of fishing gear. Much can be learned from the observation 
of models but the agreement between performance of 
models and full-sized gear is not, however, close enough 
to be accepted uncritically. Models at one-eighth scale, 
for example, tend to give a view of gear performance 
which is on the pessimistic side. 

With care, models provide results which are difficult 
to achieve in other ways, such as the effect of alternative 
methods of rigging a gear and whether or not the ad- 
vantages are real, and how errors in rigging and setting 
may be corrected. 

Two other methods of gear testing which can be used 
to compare existing rigs or help in their design and 
development, are instrumentation and comparative 
fishing. What is claimed for modelling is not that it can 
be used as a substitute for the other two methods, but 
that it is complementary to them lending more confidence 
to the results obtained and giving a full picture of gear 
performance. Comparative fishing can be regarded as the 
final stage of gear testing the proof of the pudding 
but its results will be better and more confidently 
assessed if a fuller picture of gear performance is provided 
through the use of models. 

REFERENCES 

1 Goldstein, S. Modern Developments in Fluid Dynamics. Vol. 1, 

Sect. 5, p. 16. 

2 Gawn, R. W. L. Steering Experiments. Trans. Inst. Naval 

Archt., 1943, pp. 35-73. 



[1741 



DEVELOPMENT OF MECHANICAL STUDIES OF FISHING GEAR 

by 

TASAE KAWAKAMI 

Department of Fisheries, Kyoto University, Maizuru, Japan 

Abstract 

The efficiency of fishing gear is closely connected with the shape it assumes in the water under ordinary working conditions, and while 
underwater photography and television have helped to solve some of the problems, there still remain many to be studied. The author 
suggests experiments with models, provided that the law of similarity, by which the mechanical relation between the model and the full-scale 
gear, is observed; but the model law should be deduced from the mechanical theory of the operation of the gear. 

In this paper the author gives a series of summaries of the research work done on the hydrodynamics of Ashing gear trawls, seines, 
purse-nets, etc. and their accessories, and gives the mathematical formulae governing their optimum performance, in relation to depth and 
current strength. 

It is stressed, however, that after trials have been made with models to which the theory has been applied, the final test should 
always be on the full-scale gear in actual fishing operation. 



Rfeume 



Dcveloppcment de I 'etude des Engins de Pfehe au point de vue mecanique 



II existe un rapport etroit entre I'efficacitd d'un engin de peche et la forme qu'il prend dans 1'eau dans les conditions d'utilisation 
ordinal res; la photographic et la television sous-marines ont bicn aid a r&oudre certains problemes, mais il reste encore de nombreux points & 
ttudier. L'auteur propose de faire des experiences avec des modules, condition de respecter la loi de similitude laquelle doivent ob&r les 
rapports m&aniques entre le modele et Fcngin grandeur nalu relic; mais la loi modele devrait fctrc d6duite de la thforie m6canique du 
fonctionnement de 1'engin. 

Dans cct article, Pauteur resume une serie de rechcrchcs sur I'hydrodynamique des engins de p&che (chaluts, sennes, sennes tournantes, 
etc., et leurs acccssoires) et indique les formulcs mathcmatiques correspondant & leur meilleur rendement en fonction de la profondeur et de la 
force des courants. 

II soulignc n&inmoins qu'apres les essais de modules conformes a la thforie, 1'essai final devra toujours porter sur 1'engin grandeur 
naturelle au cours d'operations de peche rtelle. 



Desarrollo de los estudios mec&nicos sobre artes de pcsca 
Kxtracto 

La cficacia dc un arte pesca sc halla cstrechamentc relacionada con la forma que toma en el agua durante el trabajo en condiciones 
normales. Si bien la fotografia y televisidn submarinas ban ayudado a resolver algunos de estps problemas, todavia existen muchos que 
debcn ser estudiados. Por este motivo, el autor sugiere hacer pruebas con modelos siempre que rija la ley de la similitud, o sea, una relation 
mecanica entre el arte a escala reducida y el construdio a escala normal; no obstante la ley para el modelo debe deducirse de la teoria mecanica 
del funcionamiento del arte. 

En este trabajo el autor da una serie de resumenes de investigaciones sobre las caracteristicas hidrodinamicas de los artes de pesca 
redes de arrastre, de cerco, etc. y sus accessorios ademas de fbrmulas matemdticas que regulan su rcndimicnto Optimo en relacibn con la 
profundidad y la fuerza de la corrcintc. 

Sin embargo, es necesario hacer notar que despues de las pruebas hechas con modelos a los cualcs se ha aplicado la teoria, debe 
efectuarsc una prueba final con el arte a escala normal empl&indolo lances de pesca reales. 



THE efficiency of a fishing gear is closely related to 
the shape it assumes in operation. Until recently, the 
mechanical behaviour of the gear in action could only 
be assessed approximately by judging the tension and 
tilt angle of tow ropes or manipulating lines, or by the 
actual fishing results obtained with the gear. However, 
to design a gear efficiently or operate it effectively, an 
accurate knowledge is required of the mechanical 
properties of each part. 

In recent years, underwater television, filming, and 
other submarine devices, have been used to observe the 
working pattern. These are very effective for determining 
shape and behaviour, but in order to improve a fishing 
gear, extensive testing is necessary. It is, however, very 
expensive to make up a new full-size net for each trial, 
therefore tests with models may be practical. In this case 
the law of similarity, by which the mechanical relation 



between the model and the full-scale gear is governed, 
must be observed. 

Mechanical investigation of fishing nets in Japan 
started in 1915, when Dr. T. Terada and his associates 
made a series of experiments on the resistance of a plane 
net towed through the water. This paper gives a short 
review of research since then from the theoretical point 
of view, but space allows only a summary of the more 
important investigations, whilst most of the papers con- 
cerned are merely cited (see Literature). 

THE HYDRODYNAMIC FORCE ACTING ON A 
TWINE 

Fishing gears are composed mainly of twines or ropes of 
various sizes (exceptions are weirs, rakes, spears, etc.). 
Consequently it is of fundamental importance to have an 



[175] 



MODERN FISHING GEAR OF THE WORLD 



accurate knowledge regarding the hydrodynamic force 
of relative velocity of current acting upon an element of 
a twine. 

Tauti 49 assumed in his theory on the resistance of a 
fishing net to the flow of water: 

(1) That the magnitude of resisting force, Ro, per unit 
length of a twine varies proportionally with the sine of 
the angle between the twine and the current, and is 
directed normal to the twine in the plane, including 
directions of the twines and the current, i.e. 

Ro R sin 0. (1) 

where R is the drag or resisting force of the twine per 
unit length when it is supported perpendicularly to the 
current. 

Another method is given below. Resolve the velocity 
vector, U, of the current into its normal component U n 
and tangential component Ut with respect to the direc- 
tion of the twine, then if we assume that both the velocity 
components act independently with each other and 
Newton's law for hydro-dynamic drag is tenable to 
the normal component, we come to the conclusion: 

(2) That R is proportional to U 2 sin 2 0, i.e., 

Ro Rsin 2 0. (2) 

This assumption is supported by experimental evi- 
dence"- 63 . 

The tangential component, F is rather obscure. Ex- 
periments show that the tangential force is much smaller 
than the normal force, and is substantially independent 
of the angle until the twine becomes almost perpendicular 
to the current and then drops quickly to zero. Since the 
tangential force is very small, it is difficult to measure 
accurately and, hence, the precise nature of its variation 
with the angle cannot be given with any assurance. It 
may be permissible, for the sake of simplicity of calcula- 
tion, to assume: 

(3) That the tangential force is constant, F, over the 
whole range of 0. 

THE EQUILIBRIUM CONFIGURATION AND 
TENSION OF A FLEXIBLE TWINE IN A 
UNIFORM FLOW 

Thews and Landwebcr 52 have made a general analysis 
of the equilibrium configuration of a flexible twine sus- 




(G-0) T c 

Fig. I. Configuration of a twine in a flow of water. 



pended in a uniform current, under the assumptions (2) 
and (3). Pode 3!) has carried out a series of comprehensive 
numerical computations for the case in which neither 
the weight of the twine nor the tangential force of the 
hydrodynamic action can be neglected. 

Suppose the form of a twine in a uniform steady flow 
of velocity U (see fig. 1). Choose rectangular coordin- 
ates (x, y), whose origin is located at a point on the twine 
where the twine is normal to or parallel to the current. 
Let x-axis be directed parallel to the current measured 
positive up-stream and y-axis be directed vertically up- 
wards. Let s be the arc length along the twine from the 
origin O to any pont P (x, y) on the twine, T and T f , be 
the tensions in the twine at the points P and O respec- 
tively. The angle of inclination of the twine against the 
stream is measured clockwise from the direction of the 
current to the direction of increasing s. Furthermore, let 
W be the weight of the twine of unit length in water, and 
put w- W/R. These forces may be resolved to and along 
the twine as shown in fig. 2, then the equilibrium of the 
twine element ds requires: 



dT 
ds 
do 



F W sin 



R sin 2 i W cos 



(4) 



The solution of these differential equations can be 
written in a parametric form: 



T 

~ 

Jo 



Ry 

To 



r t (0) 



(5) 



where T, a, < and // are transcendental functions of 
angle 0, and also of the ratios f F/R and w-=W/R. 
Pode's numerical solutions are partly reproduced in 
Table 1 (reference point at 0=n/2) and Table II (reference 
point at = O). In these tables another expression of 
w is introduced. Suppose the cord is simply trailed by 
itself, without any towed body at the lower end, then its 



T+dT 



mirrenf 




Rfiin 2 0dS 



WdS 

Fig. 2. Forces acting on a twine subjected to flow of water. 



[176] 



MECHANICAL STUDY 

configuration may be a straight line inclined to the cur- 
rent at such an angle: 

w \/w 2 i 
O c =-- arc cos - - (6) 

This angle O c is called the critical angle, and will be used 
in place of w. 

ESTIMATION OF THE FISHING DEPTH OF A 
TOWED GEAR 

To illustrate an application of these solutions to cable 
problems, let us consider estimating the depth of a deep 
trolling gear I2 . All parameters related to the point where 
the line is attached to the depressor and where it inter- 
sects the water surface, are distinguished by subscrip- 
tions 1 and 2 respectively. It is required to find the 
depth h( y 2 y,) of the depressor when the submerged 
length 1 ( -S 2 S,) of the tow line is given. From the 
equations given in the preceding section, we have 

R . r,<0)-'iM 



R 

T 2 



! 



(7) 



where R is expressed as: 

R A CnpU 2 n 

CD being the drag coefficient of the trolling line and its 
numerical value being approximately equal to 1*5 for 
ordinary stranded twine, tj the density of fluid, U the 
velocity of motion and D the diameter of the twine. The 
relations between h/1, 0,, 2 and Rl/7' 2 can be graphically 
represented in a chart, which greatly facilitates the 
estimation of the working depth of a depressor. If the 
value of R is given, the ratio h/1 can be read directly 
from this chart by using any two values out of three 
values. 

The tension of the warp at the vessel in trawling is 
transmitted to the gear and the various modes of fishing 
performance of the gear must be contingent upon the 
magnitude and the direction of the force acting on the 
gear. The cable problems also have a bearing in this 
connection, i.e. in regard to mid-water trawling. The 
working depth of these nets can be regulated to sonic 
extent by adjusting the length of the towing warps. In 
these cases, if the weight of the warp in water is not 
negligible as compared with its resistance, similar charts 
for various values of critical angles must be prepared. 

Another example of the application of these formulae 
17t 4 , is a simple current-measuring device, the Siomi-ito, 
which is in traditional use on coastal fishing grounds in 
Japan. It consists of dropping overboard several sinkers 
attached to strings of different lengths. Each sinker is 
subjected to the current at a depth corresponding to the 
length of the string. The tilt of the string at the surface 
will be determined by both the profile of the current 
velocity and the length of the string. If the configuration 
of the string in a given current profile is known, we have 
a possibility of determining the current profile from the 
tilt angles of several strings of different lengths at the 
surface. Kawakami and litaka 17 have made some in- 
vestigations of this problem. They designed a new type 



OF FISHING GEAR 

of Siomi-itOt and proposed a proper way to manipulate 
it. 

THE RESISTANCE OF PLANE NETTING IN A 
CURRENT 

The resistance, R, acting on a plane net subjected to a 
uniform current of velocity U, was first studied experi- 
mentally by Terada, Sekine and Nozaki 52 , then by 
Tauti, Miura and Sugii 47 and by Miyake 3C . The ex- 
perimental method adapted by these workers was the 
same in principle. Two rectangular frames, on which a 
sample webbing was spread out, were connected with 
each other along one side and spread at an angle of 2<p. 
This pair of frames was put in motion through the water 
under the action of constant force of known magnitude. 

Their results are coincident in that the resistance varies 
proportionally with the area, S, of webbing and also 
approximately with the square of the velocity U, i.e., 

R-kSU 2 (8) 

where k is a coefficient of resistance depending upon the 
construction of the webbing and the angle of attack a. 
The construction of the webbing may be characterised 
by the length, L, of the bar of the mesh, diameter, D, 
of the netting twine and the angle, 2<p, between two 
adjacent bars of the mesh. 

Terada and his collaborators have proposed a supposi- 
tion that the value of k might be proportional to the 
area of webbing projected on the plane perpendicular to 
the direction of motion. Tauti and his associates showed 
that k varies linearly with the angle a. Miyake deduced 
a theory based on the supposition proposed by Terada 
and his collaborators, and verified that the theory co- 
incided approximately with his observed value. 

The most detailed theoretical analysis on the force 
acting on the webbing has been conducted by Tauti 40 
under the assumption (1). Suppose a mesh of webbing be 
suspended in a current of velocity U (see fig. 3), in which 

OA and OB are two adjacent bars and OC the velocity 




C(l.m,n) 



Fig. 3. A left-hand system of rectangular coordinates chosen in 
the mesh of webbing. 



[177] 



MODERN FISHING GEAR OF THE WORLD 



vector of the current. Denote the angle between two bars 
OA and OB by 2<p. In a left-hand system of rectangular 
coordinates (x, y, z), let x-axis be the bisector of the 
angle between two adjacent bars, y-axis be perpendicular 
to x-axis in the plane of webbing and z-axis be normal 

to the plane. Denote by (I, m, n) the direction cosines 

+ 

of the velocity vector OC. 

Mechanical analysis, after some mathematical pro- 
cedures, gives a result that the x-, y- and z- com- 
ponents of k can be represented respectively by 

/D\ 2 1 

+' ' f ' 

\ L 
D\ /D 

mcot 9 f ( 1 fy, ' (9) 



, D\ 
1 
L/ 



1 tan q> 



L/ 



V 



I i I i *z, i 

k L / sin 9 cos <p \ L / J 

where a is a constant depending on the drag co-efficient 
of the netting twine and is given by 

a = CD p/2 

in ordinary hydrodynamical expressions, and second 
terms are correction due to knots. The factors f x , f y , 
and f 7 vary with the direction of current relative to the 
coordinates system. These correction terms would be 
negligible in comparison with the first term in the case 
of large meshes of fine twine. 

When the direction of current lies in the xz plane, i.e., 
1- cos a, n-=sin a, where a is the angle of attack of the 
webbing, drag coefficient of the webbing may be re- 
presented from the expressions (9) by 



k a ( 1 cot 9 (sin 2 a j 1 ) 



(10) 



in which the correction terms are neglected. This means 
that the value of k varies linearly with sin-a. 

In these analyses, it is assumed that the knots and 
twines of meshes are mutually independent. Since, how- 
ever, the actual net is a complicated system of netting 
twine, the hydrodynamical interference between neigh- 
bouring twines and knots should be taken into account, 
when the net is kept in a certain range of attack-angle. 
Fujita and his collaborator" 6 have investigated this 
phenomenon. 

Miyamoto and his associates 31 ' 3G have made a series 
of experiments to secure accurate data for different types 
of webbing. They measured the drag of a piece of web- 
bing when 90 degrees and ^-45 degrees, then the 
value of k / were determined. The results are given by 



a (_- - 10*) 
\2L / 



-\ b[ xlO* ) 2 , (kg.wt. sec 2 ./i 
\2L I 



where numerical values of a and b are tabulated below: 



Kind of webbing 

Knotless 
Flat-knot 
Trawler-knot 



1-72 
1-70 
1-68 



0-370 
0-433 
0-475 



The value of k z becomes greater with decreasing or in- 
creasing of q> from <p=45 degrees. As regards the material 
of the netting cord, the value of k is somewhat larger in 
staple fibres than in continuous fibres. In general, it may 
be concluded that the fibre ends sticking out of a twine 



made of short fibres have a tendency to catch dirt and 
create more resistance. 

EQUILIBRIUM CONFIGURATION OF WEBBING 
IN A CURRENT 

A stretched piece of webbing may be considered as a 
continuous membrane, in the case where differences in 
physical states between neighbouring meshes are negli- 
gible. This membrane will be subjected to two kinds of 
external force, i.e., the hydrodynamic force due to the 
current, and the apparent weight in water. The hydro- 
dynamic force is given by kU 2 . Let W be its apparent 
weight of unit area in water, (l g , m g , n g ) be its direction 
cosines referred to coordinate axes O-x, O-y, and 
O-z, which are chosen in such a way that the principal 
curvatures at the elemental portion of webbing membrane 
lie on the xz- and yz- planes. Let r x and r y respectively 
be the radii of curvature on these planes, and T y and 
T x be the tensions of the webbing per unit length along 
the x- and y- directions respectively. Tauti r>0 pro- 
posed the following differential equations required to 
maintain a mechanical equilibrium of the webbing mem- 
brane: 



dT x 

dx 

dTy 

dy 



k x V 2 * 1 B W O, 



I k y V 2 f m K W 

+T*.-y 

TV 



(II) 



n B W. 






In the analytical treatment of mechanical problems of 
fishing nets, it is of fundamental importance to know 
exactly the configuration of a strip of net and the distri- 
bution of tension when subjected to a current. Miya- 
moto 6 *, Fujita 6 , and Kawakami l!i have made a theoret- 
ical analysis on this problem, based on Tauti's law. 

Suppose that a long narrow strip of webbing of a 
constant width is supported vertically by both ends, A 




Fig. 



Configuration of a rectangular strip of webbing subjected 
to flow of water. 



[178] 



MECHANICAL STUDY OF FISHING GEAR 



and B, in a uniform current and is in equilibrium con- 
dition. A system of coordinate axes, O-x and O-y, is 
chosen as shown in fig. 4, i.e., the origin is located at 
the point on the webbing where the webbing is perpendic- 
ular to the current, and the x- and y-axes are directed 
upstream and upward respectively. Then let s be the arc 
length of the net from the origin, O, to any point P 
(x, y) and T and to be the tensions of the webbing per 
unit length at the points P and O respectively. Denote 
the angle of the netting membrane against the current 
at the point P by 0. If the net is of homogeneous mesh of 
2L in stretched measure, woven with a netting twine of 
diameter D, and hung to the framing lines with such a 
degree of slack as to make an angle 7q> between two 
adjacent bars, then the equilibrium equations (11) take 
the form: 



dT 

ds 



- K sin 2 rp cos \ W sin 



dO 
ds 



K sin -I W cos 6 



(12) 



(13) 



where K is the normal component of the resisting force 
per unit area of the webbing when the webbing is per- 
pendicular to the current and W is the weight of unit 
area of the webbing in water. 

Let a be the area enclosed by the x-axis, the arc of the 
webbing, and the straight line parallel to the y-axis, 
x=x, then the solution of these equations may be 
written in a parametric form: 

~ 



Ks 
To 
Kx 



to 



To 



- (0), 



- /Jn (). 



(14) 



(0), 



where r n , <r n , n, ^n, and a n are transcendental functions 
of angles and y, and the ratio r~K/W. A part of these 
relations has been calculated numerically by Miya- 
moto HH . 

If the weight of the webbing be negligible compared 
to its resistance, the solutions will be simplified to: 

r n -- (sin 0) -* in2 9, 

f 
o n - ] (sin 6)-0 4- sin- 9) d0 

1 
sin 2 * (15) 

"0 
do 

f 7C/2 

ro 

otn ~ ' r t d !; 
Jic/2 

The numerical solutions have been calculated by Kawa- 
kami 16 . 

MECHANICS OF AUXILIARY GEAR (Floats, 
sinkers, shearing devices, mooring equipment.) 



The buoyancy or specific gravity of floats and sinkers 
is given by elementary mechanics. The reserve buoyancy 
of gillnets has been discussed by Miyamoto 31 . 

These accessories, however, are subjected to currents 
of various speeds, which cause the unfavourable deforma- 
tion of the gear. It is essential, therefore, that the shape 
of these accessories be streamlined to reduce the drag to 
a minimum. 

Apart from floats and sinkers which work on the static 
principle, other such accessories based on dynamic 
principles are used, such as: otter boards, kites and de- 
pressors. 

The action of the otter board has, by some authors, 
been treated as that of a flat plate in a current. When a 
flat plate of a length c is subjected to a current at an 
angle of attack a, to the direction of flow, its resistance 
force, P, is approximately normal to the plane and the 
magnitude is given by Duchcmin's equation: 

p p -,4 si V . no 

Po 1 +sm 2 

where PO is the value of P when the plate is normal to 
the flow. The distance ft from the centre of the plate to 
the point through which the total resisting force acts is 
given by 

S3 cos a 

- (17) 

C 4 4 \ n sin a 

If the board is a hydrofoil, its hydrodynamic character- 
istics must be investigated in advance by a model ex- 
periment. Polar diagrams of various types of hydrofoil 
depressors for trolling gear have been drawn by Okuno 36 . 
To fix a trap net at a point in the sea, sand bags or 
anchors are commonly used. The holding power, H, of 
a sand bag falls off as the angle, ft, of the mooring rope 
with the horizontal at the bag end is increased. The 
variation of the holding power with this angle has been 
investigated by Tauti 47 . He assumed the ordinary fric- 
tional resistance, the coefficient of which is represented 
by /*, between the under surface of the bag and the sea- 
bed, and obtained the following result: 
H ,1 



W 1 jz tan 3 
where W is the weight of the bag in water. 

With regard to the anchor, the circumstances differ. 
The holding power of an anchor is due to the action of 
its fluke which digs into the sea-bed. Assuming that the 
resistance is proportional to the total quantity of bottom 
material scooped by the fluke when the anchor is pulled, 
Tauti has derived the following relation: 

H - p tan ( a - p ) sin ( a - 3 ) (19) 
where a is the angle between the shank and the fluke 
and p is the proportionality constant depending upon the 
type and size of the anchor, and also upon the physical 
properties of the bottom material. 

ANALYTICAL STUDIES ON TOWED GEAR 

For analytical studies of the mechanical characters of 
trawl nets KaWakami 16 designed a mechanically simple 
model. It had two wings of narrow rectangular webbing 
and a kind of codend simple enough to make mechanical 
analysis possible. He solved a set of equilibrium equations 



[1791 



MODERN FISHING GEAR OF THE WORLD 



for each portion of the net and obtained the theoretical 
relation between the tension of the warp, the angle of its 
inclination to the flow, and the horizontal spread of the 
wings. This relation is of fundamental importance in 
designing a precise assembly of the net rigging such as 
headline and otter boards. 

As regards the codend, Taniguchi 43 - 46 has made a 
series of studies on various types of bagnets. He pointed 
out that the main factors affecting its resistance are total 
area of webbing used, the working gape of the bag, and 
the ratio D/L as defined in the previous section, and that 
the shape or mode of assembly has little bearing upon 
the total resistance. His further experiments showed that 
the length of the bag has also relatively little effect on its 
resistance. 

It is doubtful whether the shearing action of otter 
boards is purely hydrodynamical or whether the plough- 
ing action on the sea bottom contributed in some 
measure. Kawakami 14 , using Duchemin's equation, made 
an analytical treatment of otter boards attached to the 
end of a rectangular strip of webbing. Fig. 5 shows the 
variation of spreading action of the otter boards accord- 




ing to the adjustment of the brackets. The optimum 
spread can be obtained theoretically. 

A series of experimental studies as well as a theoretical 
discussion on the midwater trawl has been made by 
Kobayashi and his associates 19 - 23 . Their net was fitted 
with specially designed depressors and otter boards. They 
obtained fairly good working stability. The mechanical 
calculation of the working depth and of the towing re- 
sistance were found to coincide fairly well with the 
results of full-scale tests. 

PRACTICAL PROCEDURES OF MODEL EXPERI- 
MENTS (GENERAL RULES) 

The applicability of analytical methods is, of course, 
limited, in which case model experiments are often use- 
ful. In making a model test, it is essential to know what 
conditions have to be fulfilled to ensure similar mechan- 
ical and geometrical relations between the full-scale net 
and the model. This law of similarity was first deduced 
by Tauti 50 , based on the assumptions: 

1. That the elongation of the net twine is negligible 
when in operation; 

2. That the net twines arc perfectly flexible; 

3. That the change in the form of the net occurs so 
slowly that the external forces acting on each 
element of the net can be considered to be in quasi- 
equilibrium, and 

4. That Newton's law of hydrodynamic force is valid 
for every portion of the net, irrespective of its 
Reynolds' Number. 

Model experiments are generally conducted in an ex- 
perimental tank, using either one of two different 
methods. With the first the water is at rest and the gear 
is towed as in the testing of ship resistance. The net is 
attached to a carriage moving on rails and towed through 
the water by means of the towline. This method is con- 
venient for the trawl net. The still water tank is also 
suitable for such gear as encircling or lift nets. 

The second method, where the net is stationary and 
the water flows, is comparable to a wind tunnel in an 
aeronautics laboratory. This method has sometimes an 
advantage, especially for the fixed net, because changes 
in shape of the net can be photographed easily. Fig. 6 



Fig. 5. Showing the variation of shearing action of the otter 
board according to the adjustment of the brackets. 




Fig. 6. Model tank of circulation type. 



[180] 



MECHANICAL STUDY OF FISHING GEAR 



shows an experimental water tank of circulation type. 

Practical procedures of model experiments are as 
follows: 

(') following a value denotes a full-scale test. 
O denotes a model test. 

I. In the first place, define the reduction ratio, J, of 
the model as large as the circumstances permit, i.e. 



A 



(20) 



where / is the linear dimension of each section ot 
the net. 

2. Next, determine the diameter, D, of the net twine 
and the density, >, of its material such that the ratio: 

D" f/' - p^' 

t (21) 

D' p' - p w ' 

has the same value for all sets of corresponding 
portions of model and full-scale, where ft* is the 
density of water. 

3. Then, the length, L, of the bar of a mesh should he 
determined so that the ratio: 

IV I 

- M (22) 

D I 

has the same value throughout all parts of the web- 
bing. Thus the reduction ratio of mesh is not neces- 
sarily the same as that of the net itself. 

4. Assemble the webbing of the model net with the 
the same ratio of take-up or slack for all correspond- 
ing part* of both nets. This means: 

9" - <p'. (23) 

5 For the model thus made up, the ratio of velocitv. 
V. between model and full-scale is given by: 
v 

\ I (24} 

v 

1 he ratio of tension, T, m the webbing and the 
ratio of tension, T r , in the manipulating rope are 
civen respectively by : 

T 

- - \( . 
T 

(25 
T, I 

-- - A-K I 

T, 

(>. As regards the ropes in the net, the density o r ol 
its material and the diameter, D r . should be chosen 
so as to hold the next relations simultaneously: 



(26) 



D, 

=. A 
Or 



7. The size, D a , and the density, (* u * of the material 
of the accessories such as floats and sinkers should 
be chosen so as to satisfy simultaneously the 
relations: 



10. 



II 



P"a .-", / n l 

p- a -T." Vn-; 7 x' 

rr a / 

D.,Vn VV 



f 



(27) 



where n is the number of the accessories attached 
for unit length. 

8. If the net is fixed to the sea bottom by means of 
sand bags, as in the case of fixed or trap net, the 
weight, W, of the bag in water, should be chosen 
so as to hold the relation: 



[W 1 



W" k" 
W k 



- \ 2 h. 



(28) 



where k is the holding coefficient of the bag. 

9. In the case where the accessory is made of canvas, its 
apparent weight in water being negligible, the 
dimension, / a , is given by 



(2Q> 



When the accessor} effects hydrodynamic forces as 
in the case of otter boards in a trawl gear, its size, 
/.h, and density, "t>, of the material should satisfy 
simultaneously the relations: 



> b 
.''b 



(30) 



I 



Where the shape of a net changes with the fishing 
operation, as in the case of a purse seine or Danish 
seine, additional conditions must be satisfied to 
maintain the mechanical similarity. Let V p and t be 
the corresponding velocity, and required lime to 
attain a corresponding stage of operation, then 
the next relations should be satisfied: 



vl 



I 



. X'L 

If a net is worked in relatively weak currents, as in 
the case of a fixed net in a cove, the resistance of 
the rope due to the current being negligible in com- 
parison with its apparent weight in water, the values 
of D r and y T can be chosen so as to satisfy only 
the next relation; 



IV V- 



- AE. 



(32) 



13. If a net is worked in relatively strong current, as in 
the case of high speed trawling, the weight of the 
rope being negligible compared to its resistance, 
then the next relation holds approximately: 



Dr 

-- -- A 
D'r 



(33) 



14. With regard to the sinkers or floats, if the resistance 



MODERN FISHING GEAR OF THE WORLD 



is negligible, compared to the apparent weight or 
buoyancy, the relations (27) are simplified to 

DV P% - P'W n* 

-._ _ __ ,- HA. (34) 

D'a 3 p'a P'W n' 

SOME MODEL TESTS OF FISHING GEAR 

A number of model experiments have been made for 
various fishing nets since Tauti presented the law of 
similarity in 1934. A short description of these studies is 
given below and an overall picture of the investigations 
is given by the bibliography. 

Fixed nets 

The fixed net is one of the most important and popular 
of gear in the coastal and inshore waters of Japan. In set- 
ting out the nets, fishermen first place the frame-work of 
ropes with the sand bags and buoys in position and 
attach the bag net or impounding net afterwards. These 
nets are subjected to tidal currents. Excessive alteration 
in shape, caused by a strong current, may hinder the 
fish from entering the net; a very strong current induces 
an enormous tension in the net, and tends to drag the 
sand bags or anchors which serve to moor it. It is very 
laborious and often impossible to haul the net under 
such conditions. Sometimes the entire net is swept away. 
Figure 7 shows a model test of a very popular trap 
net for fishing yellow-tail. The bagnet is seen at the 
right hand side, the sloping funnel for entrapping the fish 
is in the middle and the impounding portion is at the left. 
In this case the current, the full-scale speed of which is 
1 knot (50 cm./sec.) runs from left to right. It is clearly 
seen that the bottom of the net is deformed by the strong 
current. This is an extreme case which rarely occurs in 
actual practice. Under such conditions, almost all floats 
arc pulled under. Owing to the decrease of the angle // 
in the equation (18), this increases the holding power of 
the sand bags and at the same time reduces the pull they 
have to withstand. A minimum number of floats should 
therefore be used. 

Towed nets 

Almost all types of towed nets arc used in Japan. Their 
efficiency depends on their mechanical behaviour in 




action, especially the working gape, fishing depth, or 
degree of contact of the footrope with the sea-bed. Model 
experiments carried out on these problems are not yet 
satisfactory. 

Figure 8 shows an example of a model test of a shrimp 
beam trawl commonly used in the Seto Inland Sea. 

Encircling nets 

Although the purse seine is one of the most important 
gear in the commercial pelagic fisheries, few model 
experiments have been conducted. These nets undergo a 
marked change in shape during setting and pursing. The 
speed of this transformation and the maximum depth to 
which the bottom margin could reach are important 
factors in the fishing capacity of the net. 

When the purse seine is operated in a region of strong 
underwater current, the lower part of the net sometimes 
becomes entangled. The solution has yet to be found to 
this urgent problem. 

Other nets 

The Genziki-ami (105) is a bottom drift net of a rather 
peculiar type. It consists of a single wall of webbing, the 
lower margin of which is curved to form a pouch. The 
net is drifted over the sea-bed by means of the tidak 
current. It is used to catch shrimps in waters where the 
bottom current is strong. 

FULL SCALE TESTS USING UNDERWATER 
MEASURING INSTRUMENTS 

Model experiments obviously have their limitations, 
mainly due to the difficulties in complying accurately with 
the rules of similarity between the actual gear and its 
model. Therefore, final tests at sea, using the full-size 
gear, are indispensable. For this purpose underwater 
measuring instruments of various types have been de- 
vised, such as: 

Depth-meter to measure the fishing depth of the gear. 

Dynamometer to measure the tension in the warps and 
ropes. 

Clinometer to measure the tilt of a rope or other 
accessorv. 



Fig. 7. Example of a model test of a set-net. 
flow is from left to right. 



Photo by Honda. 
The direction of 




Photo by Tanigucht 

Fig. 8. Example of a model test of a trawl. 



[182] 



MECHANICAL STUDY OF FISHING GEAR 



Differential manometer to measure the vertical dis- 
tance between two points. 

Attack-angle meter to measure the angle of attack of 
an otter board. 

Spread meter to measure the horizontal distance be- 
tween two points in the net. 

These instruments are all provided with a self-record- 
ing appliance, and are constructed to withstand rough 
handling and high pressure in deep seas. 

Literature 

Parenthesized papers are written in Japanese. Asterisks before 
the titles denote that an English synopsis beside the Japanese text 
is given. The following js the key to the abbreviations of the name 
of scientific periodicals cited. 



Bulletin of the Fisheries Research Board of Canada. 

Bulletin of the Faculty of Fisheries, Hokkaido University. 

Bulletin of the Faculty of Fisheries, Nagasaki University. 

Bulletin of the Japanese Society of Scientific Fisheries. 

Bulletin of Tokai Regional Fisheries Research Laboratory. 

Deutsche Hydrographische Zeitschrift. 

FAO Fisheries Bulletin. 

Fishery Investigation (Supplementary Report), The Im- 
perial Fisheries Experimental Station. 

Journal of Applied Physics, Japan. 

Journal of the Imperil I Fisheries Institute. 

Journal of the Kagoshima Fisheries College. 

Journal of the Oceanographic Society of Japan. 

Journal of the Tokyo University of Fisheries. 

Memoirs of the College of Agriculture, Kyoto University. 

Memoirs of the Faculty of Fisheries, Kagoshima Univer- 
sity. 

Progress Report of the Pacific Coast Station. 

Report of the U.S. Experimental Model Basin. 

Report of the David W. Taylor Model Basin. 

Report of the Faculty of Fisheries, Prefect ural University 
of Mie. 

Tciti-Gyogyo-Kai (The World of the Fixed Net Fisheries), 

Technical Report of Fishing Boat. 



B.F.C. 

B.F.H. 

B.F.N. 

B.S.F. 

B.T.L. 

D.H.Z. 

F.F.B. 

F.l.S. 

J.A.P. 

J.F.I. 

J.K.C. 

J.O.S. 

J.T.F. 

M.A.K. 

M.F.K. 

P.P.C. 
R.E.M. 
R.T.M. 
R.U.M. 

TG.K. 
T.R.F. 

I Carruthers, J. N., A. J. Wood and A. J. I ce. On the instru- 
mental measurement of line shape underwater. D.H./. 7(1/2), 1954. 

- Carruthcn>, J. N. Some simple occanographical instruments to 
aid in certain forms of commercial fishing and in various problems 
of fisheries research. F.F.B. -*(3), 1955, 130. 

3 dc Boer, P.A. Trawl gear measurements obtained by under- 
water instruments. Interim copy. 

4 Fukutomi, T. *A mjthod of approximate estimation for lee 
way or oce in current from the inclination of the lead line. J.O.C. 
-?<3), 1943, 19. 

fi Fujitu. H. and T. Yokota. The drag action on a net in a uniform 
current. I. J.A.P. 20(2). 1951. 59. 

6 Fujita, H. The drau action on a net in a uniform current. II. 
M,A.K. 66, 1953, II. 

7 Hamuro, C. *A study of Danish seine by means of recording 
the height of entrance and direction of ground rope. B.S.F. 20(5), 
1954, 353. 

8 Hamuro, C. and K. Ishii. *Study on the automatic net depth 
meter, automatic net length meter for salmon gillnet and the results 
of measurement at sea. T.R.F. #, 1956, 29. 

9 Hamuro, C. *Study of the automatic net depth meter, net 
height meter for crab tangle net and its practical application. 
T.R.F. 5, 1956, 183. 

10 Hayashi, H. *An investigation of a spreading device for 
trawling net. J.F.E. .?, 1933, 37. 

II Hosino, S. and N. Sato. (An experiment on the forms of the 
fishing net piece in the air currents.) F.l.S. #, 1941, 1. 

12 Isouti, N. and T. Kawakami. Mechanical studies on the 
trolling gear. I. Estimation of the fishing depth. M.A.K. 76, 1957, 1. 

13 Kawakami, T. and H. Tubota. On the configuration and distri- 
bution of tension of a rope in a uniform stream. M.A.K. 66, 
1953, I. 

14 Kawakami, T. Mechanical action of the otter board of the 
trawl net. B.S.F. 79(4). 1953, 228. 

16 Kawakami, T. Equilibrium configuration of a rectangular 
strip of net subjected to a uniform current. M.A.K. 72, 1955, 1. 



16 Kawakami, T. Mechanical characters of the drag net. M.A.K. 
72, 1955, 5. 

17 Kawakami, T. and Y. litaka. On a simple instrument, Siomi- 
iro, for detecting underwater current. B.S.F. 20(1 Ij, 1955, 962. 

18 Ketchen, K. S. Preliminary experiments to determine the 
working gape of trawling gear. P.P.C. 88, 1951, 62. 

19 Kobayashi. K. and H. Takahashi. *A study on fishing trawl 
perated in any depth of sea-water. B.F.H. 7(3, 4), 1951, 139. 

20 Kobayashi, K. and H. Takahashi. *A study on fishing trawl 
operated in any deptn of sea-water (Continued). On the relations 
between the length of warp and the frontage of otter board. B.F.H. 
2(1), 1951, 86. 

21 Kobayashi, K. and T. Deguchi. *An experiment of a beam- 
type trawl net for fish larvae at the various depths of sea-water. 
B.F.G. j(l), 1952, 104. 

22 Kobayashi, K., H. Takahashi and M. Ucno. * Fundamental 
studies on spherical glass floats for fishing nets. II. On the water 
resistance of glass floats. B.F.H. 4(4), 1954, 348. 

- 3 Kobayashi, K. *An experiment on a mid-water trawl. IV 
On its mechanism and a trial practice. B.F.H. 7(1), 1956, 21. 

24 Koga, S. *On the extension of the wing of trawl net. B.F.N. 3 
1955, 15. 

25 Kumakori, T., C. Hamuro and K. Ishii, O. Furuya. (Catch 
gauge for two boat trawl.) T.R.F. J, 1952, 139. 

26 Kumakori, T. and K. Ishii. (F.xperiments on manufacturing 
of remote control towing thermometer for mid-water.) T.R.F. 3 
1952, 159. 

27 Kumakori, T., C. Hamuro, K. Ishii and O. Furuya. (Catch 
gauge for two boat trawler.) T.R.F. 4, 1953, 112. 

2ft Kumakori, T. and K. Ishii. * Automatic net-height meter and 
automatic ground rope indicator for two-boat trawler and results 
of experiment for these apparatuses. T.R.F. 5, 1954, 73. 

29 Kumakori. T.. C. Hamuro, and K. Ishii. *Automatic net- 
height meter and automatic ground rope indicator for trawler and 
results of experiments for these apparatuses. T.R.F. 6, 1955, 41. 

30 Miyuke, Y. On the plane net. I. Resistance of plane nets in 
water. f.F.L 23(2). 1927, 21. 

:n Miyamoto. H. *The excess buoyancy of gillnel and the ten- 
sion of them. B.S.h.^3), W4, 147. 

32 Miyamoto, H., M. Nomura and Y. Shimozaki. *Rcsistance 
of plane net against the flow of water. I. Effect of knot type on 
the resistance of net. B.S.F. 77(8, 9), 1952. 249. 

33 Miyamoto, H. and M. Nomura. *Resistancc of plane net 
against the flow of water. II. Effect of different shapes of the 
mesh upon the resistance. B.S.F. M(7), 1953, 327. 

34 Nomura, M. and Y. Nozawa. ^Resistance of plane net 
against the flow of water. IV. On the inclination of threads in a 
current. B.S.F. 20(V). 1955, 762. 

3<t) Nomura, M. and K. Mori. * Resistance of plane net against 
flow of water. III. Effect of kind of fibres on the resistance of net. 
B.S.F. 27(11), 1956, I 1 10. 

36 Nomura, M. and K. Mori. * Resistance of plane net against 
flow of water V. On the inclination of net in a current. B.S.F. 
27(11), 195(>, 1114. 

37 Okuno, H. * Model experiment on plates to sink an end 
of a trawl rope bclovt the water surface or hydrofoil sinker. 
B.S.F. 5(3). 1936, 155. 

38 Pode, L. An experimental investigation of the hydrodynumic 
forces on stranded cables. R.T.M. 77,?, 1950. 

39 Pode, 1.. Tables for computing the equilibrium configuration 
of a flexible cable in a uniform stream. RT.M. 687. 1951. 

40 Pode. L. Configuration and tension of a light flexible 
cable in a uniform stream. (Appendix to the R.T.M. 777), 1956. 

41 Sato, N. and 1. Takayama. * Experiments on hydrofoil 
sinker for a troll line. J.F.I. J, 1933. 73. 

42 Sato, N. and S. Kurita. (An experiment on the resistance 
and lift for a float of a seine net.) F.l.S. V, 1943, I. 

43 Taniguchi, T. *On the resistance of various codends fixed 
in a stream. I. B.S.F. 27(5), 1955. 291. 

44 Taniguchi, T. *On the resistance of various codends 
fixed in a stream. II. B.S.F. 27(9). 1956. 969. 

46 Taniguchi, T. *On the resistance of various codends fixed 
in a stream. 111. 27(11), 1956, 1107. 

46 Taniguchi, T. *On the resistance of various codends fixed 
in a stream. IV. B.S.F. 22(12), 1957, 727. 

47 Tauti, M., T. Miura and K. Sugii. Resistance of plane net 
in water. J.F.I. 27(2), 1925, 11. 

48 Tauti, M. (Holding power of anchors). T.G.K. 77, 1930, 16. 



[183] 



MODERN FISHING GEAR OF THE WORLD 



4tt Tauli, M. The force acting on the plane net in motion 
through the water. B.S.F. J(l). 1934, 1. 

60 Tauti, M. A relation between experiments on model and on 
full scale of fishing net. B.S.F. 3(4), 1934, 1. 

61 Terada, T., I. Sekine, and T. Nozaki. (Study on the resist- 
ance of fishing net against the flow of water.) J.F.I. 10. 1915, 1. 

52 Thews, J. G. and L. Landweber. On the resistance of a heavy 
flexible cable for towing a surface float behind a ship. R.E.M. 
418. 1936. Appendix I. 

** Thews, J. G. and L. Landweber. The tension in a loop of 
cable towed through a fluid. R.E.M. 422, 1936. Appendix. Model 
Experiment. (Fixed net). 

* 4 Honda, K. and Y. Matumoto. * Model experiment on the 
sea fixed net for fishing amber-fish. B.S.F. 72(3), 1934, 91. 

56 Honda, K. and collaborators. Model experiments on fixed 
nets for amber-fish, Seriora* used in the coast of Mie Prefecture. 
J.T.F. 47(2), 1955, 195. 

56 Kanamori, M. *A tentative experiment on the improvement 
of yellow-tail setting net (Preliminary report). J.K.C. 7, 1950, 4, 

57 Kanamori, M. and S. Enami. ^Studies on the improvement 
of yellow-tail setting net on the model experiment of mid-layer 
trap-net. I. M.F.K. 2(1), 1952, 2. 

58 Miyamoto, H. The form of amber-fish keddle net on the 
basis of model experiments. B.S.F. 4 (3), 1935, 153. 

69 Miyamoto, H. * Model experiments on sea fixed nets for 
fishing amber-fish, Scriola. I. Ettyu keddle net and ordinary keddle 
nets. B.S.F. 5(3), 1936, 158. 

60 Miyamoto, H. * Model experiments on sea fixed net for 
fishing amber-fish, Seriola. II. Trap nets set on the fishing grounds 
under strong tidal currents. B.S.F. 5(4), 1936, 227. 

61 Miyamoto, H. * Model experiments on sea fixed net for fishing 
amber-fish, Seriola. III. Trap nets. B.S.F. 5(6), 1937, 361. 

62 Miyamoto, H. * Model experiments on sea fixed net for fishing 
amber-fish, Seriola. IV. Keddle nets and trap net. B.S.F. 6(6). 
1937, 311. 

63 Miyamoto, H. * Model experiments on sea fixed net for 
fishing amber-fish, Seriola. V. The relation between the weight of 
sinkers and the deformation of amber-fish nets subjected to various 
currents. B.S.F. 7(6), 1939, 319. 

w Miyamoto, H. * Model experiments on sea fixed net for fishing 
amber-fish, Seriola. VI. Fishing gear in relation to the current 
prevailing on the fishing ground. B.S.F. 9(5), 1941, 181. 

65 Miyamoto, H. * Model and full scale experiment on set net. 
Preliminary report. I. Double trap net for cod. B.S.F. 13(2), 1947, 
51. 

66 Miyamoto, H. * Model and full scale experiment on set net. 
Preliminary report. II. Double trap net for cod. B.S.F. 7J(6), 1948, 
263. 

e7 Miyamoto, H. * Model and full scale experiments on set net. 
Preliminary report. III. Trap net for sardine. B.S.F. 74(1), 1948, 31. 

68 Miyamoto, H. 'Study on the set-net. B.T.I.. 2,1951, I. 

69 Miyazaki, T. * Model experiments on fixed nets for fishing 
salmon in Kamchatka. B.S.F. S(3) 1939, 129. 

70 Miyazaki, T. (Model experiment on the leading net). B.S.K 
77(6), 1942, 287. 

71 Miyazaki, T. (Model experiment on a leading net. II.) B.S.F, 
70(2), 1942, 63. 

72 Miyazaki, T. (Model experiment on a fixed net). B.S.F. 77(3). 
1942,101. 

73 Mori, Y. * Model experiment on the sea fixed net for fishing 
amber-fish. B.S.F. 70(6), 1942, 278. 

74 Okahe, G. * Model experiments of a fishing net, Anko-ami. 
B.S.F. 6(6), 1938, 305. 

76 Pack, Y. *A model experiment of sardine trap net "Hisaxo- 
amr. B.S.F. 22(11), 1957,657. 

76 Saito, T. *Model experiments on the two kinds of sea bottom 
fixed nets for fishing "7ar<T. B.S.F. 2(5), 1941, 185. 



77 Sato, N. *On a tank experiment with seine nets. J.F.E. .?. 
1933, 49. 

78 Sato, N. (An experiment with models of a surface seine net). 
F.I.S. 9, 1943, 35. 

79 Simizu, H. '"Model experiments on the sea bottom fixed nets 
for fishing "Tara". B.S.F. 9(5), 1941, 191. 

H0 Sugano, S. *The model experiments on fixed nets for fishing 
salmon in Kamchatka. B.S.F. 4(6), 1936, 397. 
(Towed net). 

81 Barraclough, W. E. and W. W. Johnson. A new mid-water 
trawl for herring. B.F.C 704, 1956. 

82 Imamura, Y. (Model experiment of the British herring trawl) 
B.S.F. 70(5), 1942, 221. 

83 Imamura, Y. (Model experiments on a trawl net). B.S.F. 77(2), 
1942, 61. 

84 Koike, A. * Model experiments on a Teiso-hikiami (trawl net). 
B.S.F. 79(1), 1953,8. 

86 Miyamoto, H. The model experiments on drifter drag net 
for fishing "Sirauwo" in Lake Kasumigaura. B.S.F. 4(5), 1936, 
310. 

8fl Miyamoto, H. The model experiments on sailing trawl net 
used in Mikawa Bay. B.S.F. 4(6). 1936, 391. 

87 Miyamoto, H. * Model experiments on trawl nets. B.S.F. 5(1), 
1936, 19. 

HR Miyazaki. T. Preliminary report on experiments with small 
trawl nets. I. R.U.M. 7(2), 1952, 215. 

* 9 Miyazaki, T. Preliminary report on experiments with small 
trawl nets. I. Change in the height of square part at the mouth of 
the net with changes in the tension of the rope of the net. R.U.M. 
7(2), 1952, 223. 

90 Miyazaki, T. The relation between the mouth height of the 
square part of small trawl net and its pulling velocity. B.S.F. 79(4), 
1953, 223. 

01 Nomura, M. * Model experiments on two boat type trawl net. 
B.S.F. 76(8), 1951, 347. 

92 Nomura, M. and T. Yasui. * Model experiments on trawl 
nets of various types. B.S F 7*(I2), 1953, 727. 

93 Ogura, M. *Model experiment on a Tyus(9~hikiami(\rw\ net). 
B.S.F. 20(4), 1954, 259. 

94 Saito, T. and H. Simizu. Model experiments on * 4 7>#//n-ij/w", 
a drag-net, for fishing "Tara\ B.S.F. 70(1), 1941, 11. 

95 Sato, N. (An experiment on the use of a surface trawl net.) 
F.I.S. 7, 1934, 1. 

98 Sato, N. (An experiment with models of a surface seine net). 
F.I.S. 9, 1943, 35. 

97 Sugano, S. * Experiments with models of a surface trawl net 
lor fishing salmon. B.S.F. 5(1), 1936, 12. 

(Encircling net) 

98 litaka, Y. Model experiments on the sardine purse seine 
operating in Hiuganada I. B.S.F. 20(7), 1954, 571. 

9U litaka, Y. Model experiments on the sardine purse seine 
operating in Hiuganada II. B.S.F. 27(1), 1955, 6. 

100 litaka, Y. Model experiments on the sardine purse seine 
operating in Hiuganada III. B.S.F. 27(7), 1955, 459. 

101 litaka. Y. Model experiments on the sardine purse seine 
operating in Hiuganada IV. B.S.F. 22(7). 1956, 389. 

102 I none, M. Model experiments on a sardine ringnet. B.S.I 
79(9), 1954, 942. 

103 Uno, M. The form and the tension on pursing line of a 
mackerel ring-net used at Kosaito, Tyosen, as known by a model 
experiment. B.S.F. 4(3), 1935, 147. 

(Other nets) 

104 Pack, Y. Model experiments on a saury blanket net (Boukc- 
ami). I. B.S.F. 27(9), 1956, 978. 

105 Wang, Y. Model experiments of Genziki-anu\ a kind of net 
for fishing shrimp. B.S.F. 5(6), 1937, 369. 



184 



INCREASING THE OPENING HEIGHT OF A TRAWL NET BY 

MEANS OF A KITE 

by 

S. TAKAYAMA and T. KOYAMA 

Tokai Regional Fisheries Research Laboratory, Tokyo, Japan 

Abstract 

In order to catch fish that swim close to the bottom but not actually on it, it is necessary to have the opening of the trawl as high 
as possible, without unduly distorting the shape of the net. To do this, a new type of trawl kite has been designed and tested. This paper 
describes the rigging of a model trawl and kite, which can move freely along a false headline, and shows how the experiences with the model 
were translated to a full-size trawl. In the tests, three differently rigged trawls were used, (a) without the kite, (b) with the kite but with no 
gussets between the after end of the wing and the square, and (c) with both kite and gussets. In net (c), the net mouth was raised to twice 
the height of the control net, and in net (b) it was raised 1 '5 m. more than the control. 



Resume 



L "augmentation de la Hauteur d'ouverture d'un chalut au moyen d"un panneau elevatcur 



Pour pouvoir capturer Ic poisson qui nage tout pres du fond sans le toucher, il est necessaire que 1'ou venture du chalut soit aussi 
haute que possible sans deformcr exagerement le filet. Un nouvcau type de plateau elevateur a ele mis au point et essayg a cet eflfet. Les 
auteurs dccrivent le montage de la maquette du chalut et du plateau elevateur qui peut se deplacer librement le long d'unc fausse ralinguc 
sunerieure, et notamment comment les resultats des essais cflcctucs sur la maquette ont 6te convertis en donnees applicable* a un chalut de 
dimensions normales. Les essais ont porte sur des chaluts grees de trois fagons differentes: (a) sans le plateau eJcvateur; (b) avec le plateau 
elevateur mais sans goussets entre I'extreniit^ posterieurc de Pailc ct le grand dos, et (c) avcc le plateau ct les goussets. Avec le chalut (c), 
la hauteur de gucule atteignait le double de celle du filet temoin, et avec le chalut (b), 1 m.50 de plus que celle du temoin. 



Aumento de la altura de la boca de las redes de arrastre mediante "pucrtas de clevacidn." 
fcxtracto 

A fin de capturar los peces que nadan ccrca del fondo del mar pero no immediatamente sobre el, es necesario abrir la boca de la 
red al maximo sin dcfomar excesivamentc su forma. Para lograr estc objeto, se ha proycetado y ensayado un nucvo tipo dc **puerta de 
elevaci6n." 

En este trabajo so describe la construction de un modelo dc red de arrastre con su **pucrta clevadora" que puedc movcrse a lo largo 
de una falsa relinga superior y se demuestra la manera como las experiencias con el modelos pueden aplicarse a una red de arrastre de tamafto 
normal. En las pruebas se usaron tres lipos de red arrastre, a saber: (a) sin "puerta dc clevaci6n'\ (b) con "puerta de elevaci6n" pero sin 
refuerzos triangulares entre el extremo posterior de la banda o pernada y la visera, y (c) con "puerta de elevation" y refuer/os. Fn las redes 
(c) > (b) la altura de la voca ere 2 veces y 1.5 m. mayor, respect ivamente, que en el arte usado como testigo. 



ONt of the major factors influencing the catch of 
a trawler is the area of ground fished by the net. 
But, in the case of demersal fish such as cod, sea 
bream, hairtail, and prawn, which may not always be 
quite close to the bottom, the opening height is equall> 
important. One example of the various devices being used 
for this purpose in Japan is a mouth stretcher for the 
bull-trawl, invented by Hayashi 1 . In practice the shape 
of a net should be maintained with the mouth as high as 
possible. But actually no trawl net can keep a constant 
shape all the time because of the interfering influences of 
currents, undulation of the sea-bottom and distortion of 
the wings due to movement of the boat. 

In order to overcome these difficulties, a new type of 
trawl kite has been developed. This kite adjusts its posi- 
tion automatically according to the movement of the 
net. After preliminary model tests in a tank with circulat- 



ing flow, a series of field experiments was conducted b> 
the R.V. Tenyo-Maru and the Taka Maru of the Tokai 
Regional Fisheries Research Laboratory in Tokyo Bay 
in September 1956, and more recently by Taiyo-Maru 
No. 32 of the Taiyo Fishing Company in the central part 
of the Yellow Sea from February to April 1957. This 
paper gives the results obtained from these experiments. 

MODEL EXPERIMENTS 

Method 

Model nets with and without the new device were tested 
comparatively in a glass-walled tank with an effective 
area of 65 cm.> 1 m. The nets were subjected to various 
velocities of flow. The shape of the net was controlled 
and the elevations of the net mouth and the kite were 
measured. 



M85] 



MODERN FISHING GEAR OF THE WORLD 



Construction and Specifications of the Nets 

Several arrangements were made for constructing model 
B and C, with kite (Table I and figs. 1, 2, 3). 



TABLE I 
Specifications of Model Net 

Name of part Material Length or number Remarks 



False head line 


__ 


133 cm. (total) 




Floated part 


Cotton 


106 




4 'Riding wire" for 








kite 


Copper 


27 .. 




Head line 





164 (total) 




Bo'om 


Cotton 


37 ,. 




Wings 


%< 


127 




Connecting Legs 




8.7 cm. 


Sec fig. 3-L 


Gussets* 


Silk" 


2 pieces 


See fig. 3-S 


Floats 


Cork 


16 


Total buoy- 








ancy 1.2 gr. 



* Mesh 1.3 cm., 11x11 meshes, diagonally cut into two, one of 
each inserted into the square at the quarter points. 



(1) The false headline is not fixed to the kite, but 
passes freely through rings attached to the bridles of the 
kite, which consequently can slide smoothly on the wire 
rope used for the middle part of the false headline. This 
arrangement helps to prevent deformation of the net. 

(2) Each end of the false headline is tied to either end 




Fig. I. General view of model net "C" with kite. 



2*9 



31 



r 



43 



26 

1 




10 

1 



20 30 40 60 



Fig. 2. Diagram of the model kite. 



Material 
Weight 
Buoyancy 
Volume 
Specific gravity 



Wooden board, cedar 

2-4 x. 

/-5 g. 

3-9 cm j 

0-62 



of the upper wing so as to make handling of the net as 
easy, and lift the wing as high, as possible. 

(3) A number of floats are attached to the false head- 
line to keep it clear of the net. 

(4) In type "C" net, a triangular gusset webbing is in- 
serted into the square at both quarter points to extend the 
length of the headline in the bosom. This is meant to 
prevent strain in the webbing when the upper net is 
pulled up by the kite. 

The sizes of the kite, false headline, gussets, and so 
forth, of course, have to be in correct proportion to the 
rest of the trawl gear. For that purpose their measure- 
ments have been determined on the basis of Tauti's law 
of comparison", by an experiment using a model of a 
146 ft. -trawl. Specifications of the model net were ob- 
tained as follows: 

(1 ) The measurements of the model, >.', arc reduced to one thirtieth 
of the full scale, >.". 





Fig. 3. Schematic diagrams of model nets "A'\ "/?" and "C" 

",4" Without kite. 

"B" Furnished with kite but without gussets. 

"C" Furnished with kite and gussets. 



[1861 



USING A KITE TO INCREASE VERTICAL OPENING 



(2) For the net twine of the model, silk is used on the basis of 
the ratio 

D' L' 

-.- 0-094 

D' L* 

where D' diameter of twine of the model net 
D* the full scale net 

L' mesh size of the model net 
L" ., the full scale net 

(3) Using 0-094 as the mesh size ratio between both nets, 1-25 as 
the specific gravity of silk, p', for the model net's twine and 
I -43 as the specific gravity of abaca, p", for the full scale nets, 
one may obtain 



/ L'(p'- 1) / 0-094 - (1-25 

" V L"(P" - 1) V 1-43-1 



1) 
0-234 



where V and V" denote the current velocities at which both 
model and full scale net have the same shape. 
(4) We can ignore the hydraulic resistance of the ropes of a fishing 
net. When P^represents the diameter of cotton twine used for 
the ropes of the model net: D",, the diameter of the combination 
rope for the real trawl; p' t , the specific gravity of cotton (1-5), 
and p"j, the specific gravity of the combination rope (4-6), 
then the ratio between D', and D' l in both nets conforming 
with each other is: 



D' 



30 



4-6 I 1 

0547 

1-5 1 



0-115 

For the net twines made of the same material in both nets, the 
ratio of their diameters is: 



0547 x I 1 - 0425 



(5) Disregarding the hydraulic resistance of the float, the ratio 
between the buoyancy of the model floal, F', and the full scale 
one, F*, is represented by 

F' />/\ 2 

6 



/>/\ 2 /V'\ 
(-) . ( ) 
\>.V \V"/ 



. 

This ratio may also be applied in regard to underwater gravity 
of the foot ropes of those nets. 

After the model net and the kite had been constructed 
according to the above proportions, the optimal pro- 
portion to obtain maximum height of the net mouth 
and the best shape to the net, was determined by repeated 
tests. The results are given in Table I and fig. 2. Addi- 
tional experiments with kites of different shape, i.e. 
rectangular, with the height greater than the width, 
rectangular with the width greater than the height, and 
streamlined, revealed that the first was more practical 
than the others, though somewhat less efficient, because 
of its simple construction and superior underwater 
stability. Best results were obtained with an angle of 
attack of about 30 degrees. 

Comparison of Height of Net Mouth 

The three types of model trawls tested are shown in 
fig. 3. They are: A (without kite), B (kite but no gussets), 
C (kite and gussets). In type "B" the length of the false 
headline was 124 cm. or 85 per cent, of the length of the 
headline. The specifications of "C" are given in Table I 
and figs. 1 and 2. 

The experiments show that with a distance of 26 cm. 
between the wings the opening height of the type "C" 
net is about three times that of type "A", and with 




Hg. 4, Model tests with trawl gear type "A" (top), "B" (middle} 

and "C" (below) at a speed of flow ofO 29 m.fsec., corresponding 

to 2-5 knots with full scale gear. 



53 cm. about twice. Although in no actual case would 
the distance between the wing tips be as narrow as 7*8 m., 
i.e. 26 cm. 30, this was tested for preliminary informa- 
tion. With type "C" net, the opening height depends 
obviously not only on the distance between the wings, 
but also partly on the size of the gussets. This means that 
for determining the proper size of the gussets the distance 
between the wings must be considered. Type "B" net 
was found to come between "C" and "A". Fig. 4 shows 



TABU II 
( omparison of the Height of the Net mouth of Various Model Trawls * 



Type of 
trawl 



Speed of 
flow 

(/W..AIT.) 



Distance between 
wing tips 53 cm. 



Distance between 
wing tips 26 cm. 



Height of Height of Height oj Height of 
kite net mouth kite net mouth 
(cm.) (cm.) (cm.} (cm.) 





29 




5-7 




6-3 


A 


0-35 


__ 


5-3 




60 




0-41 


._. 


5-0 




5-7 




0-29 


16-0 


9-1 


17-3 


12-7 


B 


0-35 


16-0 


93 


16-0 


11-0 




0-41 


13-0 


8-3 


15 


10-0 




0-29 


18-3 


11-7 


23-3 


17-0 


C 


0-35 


18-3 


11-7 


22-6 


16 




0-41 


17-0 


11-0 


21-7 


15 3 



* Height measured from the bottom of the tank. 



187 



MODERN FISHING GEAR OF THE WORLD 




f-'ig. 5. Schematic views of figuration oj model trawls. 
D : Normal figuration of net "C" (with kite). 
E : Kite adjust ing distortion of net "C". 
F : Distortion of net ".4" (without kite). 

I he various types of model nets with a flow speed of 
0-29 m./sec., corresponding to 2-5 knots in full scale. 

Comparison of Net Shapes 

During the tank tests observations were also made in 
regard to the deformation caused by one wing being 
fixed forward of the other. The distance between the 



11 



jra 
"if 



! 




IP-/--^- 7 

r f f:ro.n pitj 10 10 30 40 C1 " 



//#. 6. Diagram of the full scale kite constructed according t<> 
the model. 

Material Wooden board, cetlor. 

Weight 80 kg. 

Biioyancv 23 kg. 

Volume 103,000 cm* 

Specific gravity 78 

wings tips was 53 cm. and the speed of flow was 0-3 m / 
sec., 0-35 m./sec. and 0-4 m./sec. respectively. 



with klt 
(Uj:j. er part) 



without Kite 
(Upper part) 




/T^-. 7. Detailed diagram\ uf ihc full \calc trawls with ami without kite. 

Headline for the trawl without kite. Ropes and accessories jor the trawl with kite. 

Total length : 44 2 m., wings : /V- / /;/.. bosom : 6-0 m Headline, total length: 49- 2m.. wings : /V* / ///.. hositm: II V m 

False headline, total length : 40-0 m. 

for floated part, combination rope. 2 cm. diam., two lines, each: 16 -O m 
"riding wire" for kite, wire rope. 12 mm. diam. : 8-0 m. 
Connecting leg. two lines, tied at the centre of the bosom* each : 2-6 m 
Floats, cylindrical, plastic sponge, buoyancy 0-2 kg. per piece: I00piece\ 

I 188 1 



USING A KITE TO INCREASE VERTICAL OPENING 



It was found that the kite adjusted itself automatically 
according to expectation (see fct E" in fig. 5). Further- 
more, nets "D" and "E" had the same opening heights. 

Conversion of the Kite from Model to Full Scale 

The full scale kite is constructed from the model accord- 
ing to Tauti's ratio: 



/>-'(F'S D 

-"~V ; r <7V-"i; 



V 

V 
where -- speed ratio 0-234 

V" 

/ 
reduction scale 1/30 

p' 2 -- specific gravity of model kite, 0-62 

p% - specific gravity of full scale kite (calculated 
0-78) see fig. 6. 

Here, some degree of error is to be expected, partly 
because of a difference in Reynolds number for a small- 
sized model and partly because the kites' are not absolute- 
ly similar geometrically. 

The false headline and connecting leg for the full scale 
gear were also dimensioned on the basis of the conversion 
factors mentioned above (fig. 7). For the scale 1/30 the 
ratio of the number of meshes for the gussets between 
model and full scale was computed to be 0-36 and the 
ratio of mesh size 0-094 (fig. 7). On the basis of the model 
lest result (Table 11) the heights of the kite and net mouth 
in full scale were estimated for speeds of flow as shown in 
figs. 8 and 9. 

Estimation of Hydraulic Resistance in various parts of 
the Kite gear 

The extent to which the kite could affect the distance 
between the otter boards, and thus the distance between 
ihe wing tips, could not be determined by the model 
experiments. Although no reliable value for the total 
hydraulic resistance of the trawl can be given, a ver> 
rough estimate may be of interest. To simplify matters 
the problem will be considered as two dimensional, b> 



calculating first, the resistance of each part of the kite 
gear, then the ratio of the resistance of these parts to the 
total resistance. Buoyancy and underwater gravity are 
neglected. The elevation of the kite and the resulting angle 
of the ropes will be computed on the basis of the data 
obtained in the model experiments. 

The Kite 

Let P, (kg.) be the resistance of the kite when the direc- 
tion of flow is normal to its plane, then 

?! ~Cx - v 2 s 

2 g 

density of water in Kg./m. 3 
acceleration of underwater gravity in m. /sec- 
velocity of the current in m./sec. 
plane area of the board in m 2 
coefficient dependent on function of Reynolds 
number. 

If the kite has an angle of attack 0, the resistance is Po, 
according to Duchemin's equation: 

2 sin 



where 



P 

8 v 

S 
C\ 



Ptl 



I 



Assuming that the kite is 1-3 



sin 2 
0-93 m. in size: C\ 



J-13; 



0- 3T and 104 kg. sec'-VmA the resistance at differ - 

g 
ent speed of flow is given below (Table III). 



T\B1> 111 



Speed of Hov\ 
knots 

2 
3 
4 



Resistance 

kg. 

59 

134 

236 



False Headline 

As the false headline consists of wire rope for the riding 
wire of the kite, and the combination rope partly 
equipped with floats, the resistance has to be calculated 
for each part. The angle of attack of the false headline is 
assumed to be 16 degrees, as was the case with the model 





Plow apd 3,0 knots 



3,0 kn*ts 




Fig. 8. Height oj kite ami net mouth with different speeds of 
flow computed from the model test results ( Table //, Distance 
between wing tips 53 cm.) 



189 



Fig. 9. Height of kite and net mouth with different speed* oj 
flow computed from the model test results (Table //, Distance 
between wing tips 26 cm.). 



MODERN FISHING GEAR OF THE WORLD 




Fig. 10. Echoes from the trawl type **C" towed at 2-5 knots. 
Date : Sept. 8, 7956, 0735 hours. 

TENYO-MARU 

Direction : S 45 C1 W (head wind). 
Angle between warps : 77 

TAKA-MARU 

Speed : 3-8 knots. 

Direction : S 44" W. 



experiments. The resistance of a unit length of a rope at an 
angle of attack is 



PO - Cx D V 2 

2 g 

where D is the diameter of the rope in metres. 



sin 



When Cx is 1-2, and is the same as in the last equation, 

g 

the values of PO for each length of the present type at false headline 
are tabulated below: (Table IV). 



TABLL IV 



Speed of Resistance (Kg.) of 

Flow Combination rope floated part Wire rope 

(knots) D:0-021 m. L:\6m D:0-055 w,L:16 wD:0-012m, L:R 



5-9 
13-2 
23-5 



15-4 
13-2 
61-6 



1-7 

3-8 
6-7 



The Connecting Legs 

If, for the calculation, the same angle of attack is used as 
was found in the model experiments (44 degrees), the 
diameter of the rope is 0-021 m. and its length 5-2 m., 

c 
C x = 1 -2 and the same as for the combination rope, the 

g 
results obtained are given in Table V. 





YAfcfc 



Fig. II. Echoes from the trawl type "A" towed at 2-5 knots. 
Date : Sept. 8. 1956 1010 hours. 

TENYO-MARU 

Direction : N40 {1 E(fair wind). 
Angle between warps : 79 

TAKA-MARU 

Speed : 3-0 knots 

Direction : N 39 E. 




Fig. 12. Echoes from the trawl type "C" towed at 3-0 knots. 
Date : Sept. 5, 7956, 0770* hours. 

TFNYO-MARU 

Direction : S 45" W (head wind). 
Angle between warps : 77 

TAKA-MARU 

Speed : 4-2 knots. 

Direction : S 44 W. 



[190] 



USING A KITE TO INCREASE VERTICAL OPENING 



TABLE V 



Flowing velocity 


Resistance 


(knots) 


(Kg.) 


2 


4-7 


3 


10-6 


4 


18-8 



By summing up the resistance of the different parts the 
total resistance of the complete kite gear is found to be 
87, 196 and 347 kg. at the speed of flow of 2, 3 and 4 knots 
respectively. 

For trawl type "C" an additional increase in the resist- 
ance has to be expected from the modification of the 
net, i.e., the inserting of the two gussets. At present there 
are no means of calculating this increase. 

The resistance of a common 146 ft. trawl, though more 
or less variable according to the bottom conditions, has 
been found to be about 5 tons, at a towing speed of 
3 knots under normal conditions 8 . Consequently the 
resistance of the kite gear of 196 kg. can be considered 
to be of minor importance. If, in a liberal estimation, it 
is assumed that the increase of resistance caused by the 
modification of the net is of similar magnitude, the total 
increase would not greatly exceed about 400 kg. As much 



increase often occurs because of changes in bottom con- 
ditions, warp length or amount of catch in the codend, 
it may reasonably be considered that the kite gear and 
the modification of the net would not critically affect the 
angle of attack of the otter boards. 

FIELD EXPERIMENTS IN TOKYO BAY 
Method and Equipment 

In the Tokyo Bay experiments on September 7 and 8, 
1956 two 146 ft.-trawls, one of type "C" (with kite and 
gussets), the other of type "A", were towed at various 
speeds, and their characteristics were observed by means 
of an echo sounder installed in a boat following the 
trawler. Furthermore, in certain intervals the position 
and tension of the otter boards were controlled. As there 
was no intention of catching fish, the codends were left 
open. The experimental conditions arc given below: 

Place: Central area of Tokyo Bay, depth 26 to 29 m.. 

bottom flat and sandy. 

Trawler: Tenvo-Maru. 230 tons, 430 h.p. 

Sounding Boat: Taka-Maru, 15 tons. 

Trawling Speed: 2-5; 3-0; and 3-5 knots relative to the current. 

Trawl Gear: Chose i type, similar to V.D. type, in adjustment 
according to type 'A' and *C described above. 
Warp length 60 m. bridle length 100 m. Total 
length of net approximately 44 m., including 20 m. 
wing, 14 m. square and belly, and 104 m. codend 
(see fig. 7). Kite 1 -2 m. 2 (see fig. 6). 




Fig. 13. Echoes from the trawl type "A" towed at 3-0 knots. 
Date : Sept. 8, 7956, 0935 hours. 

TENYO-MARU 

Direction : S 45" W (head wind). 
Angle between warps : 22 

TAKA-MARU 

Speed : 4-5 knots. 

Direction : No specific course was set. 

Exact measurements of the figuration could not be taken because 
the boat did not pass properly over the net. 




Fig. 14. Echoes from the trawl type "C" towed at 3-5 knots. 
Date : Sept. 8, 1956, 0640 hours. 

TENYO-MARU 

Direction : S 45 W (head wind). 
Angle between warps : 2J. 

TAKA-MARU 

Speed : 5-5 knots. 

Direction : S 43" W. 

Note the net clearing off the bottom. 



[191 ] 



MODERN FISHING GEAR OF THE WORLD 



Echo-sounder: 
Log: 

Angle Meter: 



Dynamometer: 



50 kc., 50 m. range, half beam angle 30 degree. 
Current meter Model CM-3, electric, one for each 
boat. 

To determine the angle between the warps for 
calculating the approximate distance between the 
otter boards. 

Due to a fault in the instrument the measure- 
ments of the pull on the warps are not reliable. 



The results of these experiments are given in Table VI. 
The heights of the kite and the net mouth were computed 
from the recordings of the echo-sounder by the following 
method: When the trawler Tenyo-Maru tows a 44 m.-long 
net at a speed V (cm./sec.) and the Taka-Maru steams 
with the echo-sounder at V (cm./sec.), both keeping the 
same direction, the length of time required by Tako- 
Maru to pass right over the net will be 

4400 0-6x4400 

(sec.). Then (mm.) 

V -V V V 

is the length of the net as recorded on the echo-sounder 
paper running at 0-6 mm./sec. 

Since V and V were known, and if Taka-Maru, in 
following the track of her partner, passed exactly over 
the nets, the calculated value should agree with the 
observed one. If this was not the case, it would mean that 
the boat with the sounder was not following right above 



the net. By selecting some of those data which coincided 
with the calculated values, we have plotted the heights 
of the kite and the net mouth on the recording papers 
(Table VI, figs. 10-14). 

To find the distance between the wing tips, the distance 
between the otter boards was first of all calculated on the 
basis of the length-angle relationship of the warps pre- 
suming that they extend straight to the otter board. 
Then, from the isosceles triangle bounded by the dis- 
tance between the otter boards as the base, and the length 
of the bridles (100 m.) plus the length of the net (44 m.), 
both supposedly forming a straight line, the distance 
between the wings can be computed. Such a calculation 
of course contains errors, but we have used it because 
there is nothing better and also because the errors would 
be the same for both trawls. 

The data deduced from the echo-sounder records and 
the schematic views interpreted from them are presented 
figs. 10-14, with the position of the net indicated by the 
legend "mark line", which was a buoy rope tied to the 
codend to simplify the detection of the nets. 

Discussion 

The distance between the trawl wings ranged from 5-6 to 
7-4 m. (Table VI and figs. 10-14). Such a narrow distance 
would be most unlikely to occur in commercial trawl 
operation. However, since this corresponds roughly to 



TABLE VI 
Data Relevant to Comparative Experiments of a 146 ft. Trawl with and without Kite in Tokyo Bay, September 8, 1956 



R.V. Tenyo-Maru 
CRUISING Angle Revolution 



WIND 



R.V. Taka-Maru that followed the net by an echo-sounder 

CRUISING HEIGHT FROM BOTTOM Distance 



Time Speed* Direction of warp of engine Direction Force Time Speed* Direction Kite Net mouth between wings Remarks 

(m) 

5-6 

5-6 Shown in rig. 10. 
5-6 

5-7 Shown in fig. 12. 
5-3 

The net rose 4 m. above 
7 4 the bottom. 

The net rose 4 m. above 
7-4 the bottom (fig. 14) 

The net rose 3 m. above 
7-4 the bottom. 



6-2 Shown in fig. 13 
6-2 

7-4 

7-0 Shown in fig. 13. 

7 4 The net r -se too high 

7 4 The net rose too high 



[192] 



(knot} 


(knot) (m) 


(m) 


0800 


2-35 


S45W 


17 U 180 


SW 2 0748 


4-0 


S43W 7-0 


5-9 


0755 


2-30 














0750 


2-35 














| 0735 


2-5 






0738 


3-8 


S44'W 7-0 


5-8 


t- 0730 


2-8 


^, 












0725 


2-7 


^ 




0724 


3-6 


S45'W 7-0 


5-8 


0715 


3-25 




18 200 










5. 0710 


3-0 






0713 


4-2 


S44W 7-0 


5-8 


, 0705 


3-2 


,, 


16 


0703 


4-5 


S45W 7-0 


5-8 


| 0650 


3-6 




23 248 


1 0648 


5-5 


S45W 7-0 


5-6 


* 0645 


3-5 


f% 


,. 











* 
















g 0640 


3-5 






0640 


5-5 


S43W 7-0 


5-5 


** 0635 


3-5 


., 













0630 


3-4 





., 


0629 


5-6 


S43W 7-0 


5-5 


J1020 


2-6 


N40E 


20* 180 


SW 2 








1010 


2-5 


tf 


19 


1013 


3-0 


N39E 


2-0 


J8 1000 


2-6 




* j 


1008 


3-5 


N40E 


2-0 


0945 


3-0 


S35W 


23 200 


0943 


5-5 


S35W 


2-1 


g 0940 


3-1 




22 J 










| 0935 


3-0 


S45W 




I] il 0936 


4-5 





2-1 


5 0930 


2-8 




t% 











- 1035 


3-5 


N40E 


23 240 


1033 


5-5 


N40E 


2-2 


% 1030 


3-5 


" 


22 










1024 


3-4 




23 


1027 


5-5 


N39E 


2-6 


Neither applicable nor 


specified. 


* Relative speed of 


the 


boat. 





USING A KITE TO INCREASE VERTICAL OPENING 



7-8 in., obtained by the factor 30 from 26 cm. which was 
the distance between the model's wings, the observed 
heights of the net mouths seem to be comparable with 
the value calculated from the model tests (fig. 9). It will 
be recalled that for the models the net mouth of type 4fc C" 
was nearly three times as high as that of net "A" (Table 
II), which factor closely approximates 2-5 to 2-9 ob- 
tained in the full scale tests. Furthermore, it can be 
assumed that the full scale nets had at 2-5 to 3 knots 
shapes rather similar to those of the models. At 3 -5 knots, 
the full scale trawl type "C" was lifted off the bottom 
(fig. 14), and also the type "A" gear was liable to leave 
the bottom (Table VI). This is probably due to the fact 
that the footropc, which was a little too light and had 
been dried before use, hardly had time to increase its 
weight by absorbing enough water during the experiments. 
On the other hand, the model nets could not leave the 
bottom because their wings were fastened to the bottom 
of the tank. 

The height of the full scale trawi with 7-8 m. distance 
between the wing tips and at 2 to 3 knots was approximately 
in accordance with the values calculated from the model 
experiments. It, therefore, may be assumed that with 
10 m. distance between the wing tips the full scale type 
"C" trawl would maintain an opening height nearlx 
twice as great as type "A" without kite. 

The net can, of course, easily be prevented from rising 
off the bottom by adding some weight (chain) to the foot- 
rope. The data shown in Table VI mav relieve our worries 
about some other technical difficulties connected with 
the operation of the kite. For one thing, the angle be- 
tween the warps does not change to such an extent that 
a considerable decrease of the distance between the wing 
tips has to be apprehended. 

The engine revolutions at 2 to 3 knots gave no indication 
of a considerable difference in the resistance of both Upes 
of trawl. 

The present measurements of the Joad on the \\arps, 
unfortunately, arc not reliable. The lack of differences in 
(he loads, therefore, is not conclusive. Tor observing 
directl> the kite adjusting itself to the distortion of the 
net modern Jiving techniques arid underwater photo- 
graphy should be used. I'rifortunatt'K. circumstances did 



not permit the authors to use such aids. However, if the 
similarity between the results of the model and field 
experiments is considered, it may safely be assumed that 
with a towing speed limited to 2 to 3 knots, the kite would 
behave very similar as it was observed in the tank experi- 
ments. 

During the present experiments the kite and the false 
headline never became entangled with the net, and the 
work of hauling the net was no greater than with an 
ordinary trawl, because these accessories can be left 
afloat on the water while only the codend is hauled 
aboard. Of course, during a long period of continuous 
operation, the kite would become water-logged and lose 
its buoyancy, which would most likely result in certain 
difficulties. Figs. 15 and 16 show the devices used in the 
experiments. 

FIELD EXPERIMENTS IN THE YELLOW SEA 
Method and Equipment 

The second series of experiments were conducted by the 
trawler Taiyo-Maru No. 32 (369 gross tons, with 700 h.p. 
diesel engine) on a fishing ground for prawn (Penaeus 
oriental!* Kishinouye) located in the central area of the 
Yellow Sea. In rigging a trawl (TT8-B1 type by the 
Taito Fishing Co., headline 128 ft. long) with the present 
device, the kite was used as in the preceding experiments, 
while the gussets and the '"riding wire" of the false head- 
line were somewhat modified in length (fig. 17). A 
length of chain was added to the ground rope to keep it 
on the bottom. A detailed specification of the gear is 
given in the footnote of fig. 17. 

The height of the net mouth was measured b\ a height 
meter 2 attached to the centre of the head rope All 
three types of trawl gear have been tested: "A" (without 
kite); kk B" with kite but without gussets, the false headline 
being 85 per cent, of the headline length; "("" with kitcand 
gussets. The distance between the wing tips was esti- 
mated from the angle between the warps and the trawling 
speed was determined b\ the "rail log" method. 

Results and Discussion 

With a relative towing speed of 3 3 to 3 6 knots, the height 
of the net mouth was about 25 m. for the gear type "A'\ 




l : ig. 15. Kite ami false heatlline used in the experiments. 




If). Kite about to he put in use. 



I93 ] 



MODERN 

Trawl without kite 
(Upper part) 



FISHING GEAR OF THE WORLD 



Trawl with kite 
(Upper part) 




Float 




10 20 30 



i i i 



ft 



S|i 



(S|ize 
Mesh 



90 




Fig. 17. Detailed diagram oj the 128-feet-lrawl with kite used by the Taiyo-Maru No. 32. 

Ropes ami accessories for the net with kite : False headline, total length 110 feet 

for floated part, combination rope, 2 cm. diam.. two lines, each 50 

"riding wire" for kite, wire rope, 12 mm. diam. JO 

Headline, extended by 8 feet for two gussets inserted into the square 136 ,, 
Connecting legs, combination wire, 2 cm. diam., one end of each tied 3-1/2 feet apart 

from the centre of the square, the other end to the after edge of the kite, each V 

Chains, 12 mm. diam., for additional weight of foot rope 40 meters 
Floats for false headline, cylimlrical plastic sponge, buoyancy 200 gr. per piece, 60 

pieces per side 120 pieces 

for bosom, glass ball, 24-2 cm. diam. 10 

for wings, glass ball, 18 cm. diam. 3 feet distance, total number approx. 40 



about 4 m. for type "B", and about 5-4 m. for type "C" 
(see fig, 18). The angle between the warps decreased by 
2 to 3 degrees. The corresponding decrease of the distance 
between the wing tips for the trawls type "B" and "C" 
was approximately 3 to 4 m. The position of the kite would 
be some 2 m. above the headline. The frightening effect 
of the kite gear may possibly increase the effective mouth 
opening up to the level of the kite. 

The distance between the wing tips was found to be 
about 16 to 17m. The actual opening height determined 
in these experiments was considerably higher than in the 



model experiments (fig. 8). This may be ascribed partly 
to the net being smaller than it ought to be in proportion 
to the kite, and partly to the different type of net which 
for the purpose of catching prawns, is constructed for 
a higher opening than the one used on the model tests. 
The presence of a number of bottom-living flat-fish in 
the catch and of mud of the footrope was good evidence 
that the footrope had been kept on the bottom. The 
number of engine revolutions varied but little among the 
different types of trawls. In regard to handling of the 
kite gear very little difficulty was experienced during the 



1941 



USING A KITE TO INCREASE VERTICAL OPENING 



first 5 days. But later the kite became water-logged and 
could not be kept floating by the floats on the false head- 
line, thus causing considerable trouble to the crew. 

Problems to be solved 

(1) In order to prevent water-logging, the kite should 
be made either of plastic or of light metal alloy. At the 
same time, an optional weight of the footrope has to be 
determined experimentally with regard to the new type 
of kite, trawling speeds, and bottom characteristics. 
(2) The gusset as used in the present net may not 




necessarily be the best means of securing an effective 
formation of the net mouth. It is suggested that the net 
mouth should not only be raised in height but also be as 
round as possible. One suggestion would be to insert a 
rhombical piece of webbing of the proper size between 
the upper and lower net along each side. 

(3) A hydrofoil kite may provide the same lifting power 
with a smaller area. In that case, however, the underwater 
stability and the lower resistance against rough treatment 
must be considered. 

Acknowledgements 

The authors wish to express their profound gratitude for co- 
operation and suggestions rendered in the course of the present 
study by a number of persons. They are Captain S. Sakai and 
the crew of the R.V. Tenyo-Maru, Captain Oka and the crew of 
the Taiyo Maru No. 32. Messrs. M. Kawakami, Chief, Trawl 
Division of Taiyo Fishing Company, S. Suzuki, Assistant Chief 
of the same, T. Nomura, T. Kawakami, fishing technologists 
of Taiyo Fisheries Laboratory, S. Nakamura, H. Taketomi, 
Mr. Takagi, Y. Tahara, and an English writer, M. Tshida of the 
Regional Fisheries Laboratory. 

REFERENCES 

1 Hayashi, H. A study of a trawl mouth stretcher (in Japanese), 
Jour. Fish. hxp. St., 3, 1933. 

2 Imamura, Y. Model experiment of the British herring trawl 
(in Japanese). Bull. Jap. Soc. Sci. Fish. 10 (5), 1942. 

3 Nomura, M. and Yasui, T. Model experiment on various 
types of trawl net (in Japanese), Bull, Jap. Soc. Sci. Fish. 18 (12), 
1953. 

4 Kanda, K. The notes on midwater trawl. Fish. Tech. 1 (7), 
1954. 

f> Kumugori, T., Hamuro, S. and Ishii, K. Automatic net- 
height meter and ground rope indicator for trawler with the 
results of experiments (in Japanese), Tech. Rep. Fishing Boat, 
ft, 1955. 

6 Tauti, M. A relation between experiments on model and on 
full scale of fishing net, Bull, Jap. Soc. Sci. Fish. 3. (4), 1934. 

7 Tauti, M. "Physics in fishing technology" Asakura, Tokyo, 
Japan, 1949. 

8 Hayashi, H. The calculated tension in towing two-boat-type 
trawl (in Japanese), Fish. Invest. 20 (1), 1925. 

9 Hayashi, H. Ibid. 19 (7), 1924. 

10 Sato, H. and Kurita, S. An experiment on the resistance and 
buoyancy of floats for the seine (in Japanese), Fish. Invest. Fish. 
fcx. 9, 1943. 

11 Miyamoto, H. "Study on fishing gear and method," 
Kaneharu. Tokyo, Japan, 1957. 

12 Saito, I. "Trawl fishery", Maru/cn, Tokyo, Japan, 1954. 

13 Whiteleather, R. T. Commercial Fisheries Rovieu 10 (6) 
1948. PP. 1-6. 



/!/. IS. Diagrams of the net-height recorder giving the opening height of the different types of 
trawl gear tested by Taiyo- Maru No. 32, 

Type of net 
With or without kite 
With or without gussets 
Headline length, total 
Force of wind 
Depth 

Relative towing speed 
Engine revolution 
Warp length 

Angle between the warps 
Chains added to foot 

rope 
Major kind of catch 



A 


A' 


B 


C 


C 


Without 


Without 


With 


With 


With 


Without 


Without 


Without 


With 


With 


128ft. 


128 ft. 


128ft. 


136ft. 


136ft. 


I ^ fair wind 


1, head wind 


2, fair winti 


3 , fan wind 


2, head wind 


70m. 


70 in. 


75 in. 


75 m. 


80 m. 


3-3 knots 


3-5 knots 


3-6 knots 


3-5 knots 


3-5 knots 


222lmin. 


226/ min. 


230/min. 


220/min. 


220fmin. 


220 in. 


220 m. 


230 m. 


230m. 


250 m. 


16 


15-5" 


13-5 


13 


13 






12 mm. diam. 


12 mm. diam. 


12 mm. diam. 


Without 


Without 


40 m. 


40m. 


40 m. 


Croaker, 


Prawn and 


Prawn and 


Prawn, flat- 


Prawn and 


prawn and 


croaker 


croaker 


fish and 


flatfish 


flatfish 






maker 





195 ] 



THE HEADLINE, THE FOOTROPE AND THEIR INFLUENCE ON 
THE VERTICAL OPENING OF THE MOUTH OF THE TRAWL 

by 

S. OKONSKI and S. SADOWSKI 

Sea Fisheries Institute, Gdynia, Poland 

Abstract 

Although trawls have been changed frequently to increase their efficiency, designers are .still without a complete picture of how a 
trawl works. Design, so far, has been largely determined by net materials available and the power and size of trawlers. There should be 
a thorough examination of the fundamentals in construction of a trawl to determine precise rules for designing it. This paper is confined to 
giving a few examples of construction problems and suggestions for overcoming them. It deals specifically with the influence of the 
headline and footrope on the vertical opening of the mouth of the net, and proposes formulae for determining the most effective 
proportions and arrangements. 



Resume 



I A corde de dos, lc bourrclet et leur influence sur I'ouverturc vcrticale de la gueule du filet 



Bien que Ton ait modifie frequemment les chaluts pour augmcnter leur efticacite, les specialises qui Ics dessinent n'ont pas encore 
une representation complete de comment fonctionnc le chalut. Jusqif ici, le modele a surtout etc determine par les mahercs premieres 
existantes pour le filet, et la puissance et les dimensions des chalut icrs, 

On doit examiner soigneusement les principcs dc base dans la construction d'un chalut pour determiner des regies precises d'etablis- 
scmcnt du projet. Cette communication donne quelques cxemplcs de problemes de construction et des suggestions pour les resoudre. Ellc 
traite specif iquemcnt dc 1'influence de la corde dc dos et du bourrelet sur I'ouverture vcrticale de la gueule du filet et propose des formulas 
pour determiner les proportions el les dispositions les plus efficaces. 

I, as relingas superior e inferior y su influencia sobre la altura de la boca de las redes de arrastre 
Extracto 

Aunque a menudo sc ha modificado la boca dc las redes de arrastre para aumentar su clicacia, los fabricantes no uenen todavia 
una idea perfecta de como funciona el artc. Hasta ahora. la forma ha sido dctcrminada generalmente por los materiales disponiblcs. la 
potencia y tamafto de los arraslreros. Sin embargo, para determmar de mancra precisa las normas de construcci6n debe hacerse un cuidadoso 
examen de los principles fundamentals quc entran en la construccion de una red arrastre. 

Esle trabajo, que solo tiene por objeto dar unos cuantos ejemplos de los problemas de construccion y sugestiones para evitarloft 
trata, especial mente, de la influencia que tienen las relingas superior e inferior sobre la altura dc la boca y propone formulas para determiner 
las proporciones y a r ma dura mas adecuados. 



DETAILS of the construction of trawl nets shov\ 
substantial differences from place to place. This 
situation appears to result from the lack of a com- 
plete picture of the trawl in operation. 

Although underwater films throw some light upon the 
subject, they do not tell us all we need to know; nor do 
the empirical investigations made by fishermen. What 
we need to determine are the precise rules on which the 
designs of the trawls should be based and, as designing 
a trawl is a complicated business involving a diversity of 
factors, it is necessary to start with an examination of the 
foundations of the construction of the trawl. 

The opening height of the net must suit the particular 
fishing conditions. There are, therefore, constructional 
differences between trawl nets used for catching fish 
living on or very near the bottom and nets for catching 
fish normally found some distance off the bottom. 

So far, this problem is being solved by using lifting 
devices and different qualities of net materials, and by 
the power and size of the ship. In the cutter trawls, made 
of cotton or synthetic fibres which are extensible, the 
vertical opening of the mouth depends mainly on the 



length of headline and footrope. In the bigger trawls 
made of less extensible materials (sisal, manila, hemp), 
the length of the bosom part of headline and footrope is 
probably most important. 

A cutter trawl 18/23 and a trawl 22/24 (72 ft.) for big 
deep sea trawlers are used as examples in this study as 
they are common in the Polish commercial fishery. The 
indicated fractions denote the size of the trawl nets, the 
numerator indicates the length of the headline (in metres) 
occupied by the webbing, and the denominator half of 
the circumference of the front edge of the belly measured 
with stretched meshes. 



THE POLISH HERRING 
CUTTERS 



TRAWL NET 18/23 FOR 



This trawl is rigged with headline, footrope and belly 
lines seized to the side seams linking the upper with the 
lower net (fig. 1). 

One of the most essential points in the construction of 
such trawls with sidelines is the proper length relation 
between the three elements: headline, footrope and 



196 



ADJUSTING THE TRAWL MOUTH OPENING 



L__ _ _, _ 




Fig. I. The Polhlt Herring trawl net 18123, foi cutler\. 



sidelines. This can be affected either by adding triangular 
wedges to the wing ends, or by increasing the length 
of the headline and the footrope beyond the webbing. 

The length of the triangular wedges is variable but, in 
practice, it never exceeds half of the number of meshes 
of the wing end multiplied by the stretched mesh size. 

In fig. 2 the top wing of the trawl is outlined (A BC D), 
to which a triangular wedge of webbing (ABE) has 




-*--* \ 

^^ -i 

riff. 2. The effect oj lengthening on the shape of the headline. 



been added. The wing there has the shape A E D C. From 
point A and E the wing legs, sideline leg and headline 
leg lead to the danlcno. As both are of identical length, 
the configuration of the front part of the headline is 
changed. Point F will take the place of point B, which 
in turn will be shifted to point F, and consequently 
point D to point G. The position of points A and C on 
the side seam (BE BF- DG) remain unaltered. In the 
case shown in fig. 2 the lengthening of the headline is 
effected by inserting a certain amount of webbing. Of 
course, the same result can be obtained by simply 
lengthening the headline by the amount BE. The foot- 
rope can be treated similarly. In consequence of lengthen- 
ing the inner edges of upper and lower wing, there is a 
shifting of the front part of the webbing in relation to 
the body of the net, the effect of which is more difficult 
to explain. The shape the headline takes in action is 
shown in fig. 3 for three coefficients of the opening width, 
viz., 0-5, 0-6 and 0-7 of the headline length. The curves 
are calculated according to the method of Baranov 
(parabolic equations). 

The left-hand part of the drawing (a) shows the effect 
of an elongation of the headline by 1-6 m. on each side, 
while the right-hand part (b) shows the configuration 
with the original headline length of IK m. In all three 
versions the length of the side seams remains unchanged. 
In part 4k a" the figure A B O C shows the top wing with 
coefficient 0-5, i.e. the distance between the wing tips 
equals half of the headline length. Considering the effect 
of adding the triangular wedges, it appears as if a "sur- 
plus" has arisen, which may increase the vertical opening 
of the mouth. 

In order to determine this "surplus" in the drawing, a 
line is drawn from point C parallel with the line A E, 
which represents the wing tips. 

Point O denotes the spot where the foundation (C O) 
of the wing ends, and the bosom of the headline starts. 
The respective points for the other versions are Ol and 
O2. The figure COR gives the "surplus" overlapping 
the square section of the twine. 

With increasing horizontal opening, i.e. equal 0*6 or 
0-7 of the headline length, the surplus decreases. 

If the horizontal opening equals 0-5 of the length of 
the headline, the surplus of twine is considerable (C O R). 
At the opening of 0-6 it diminishes (C,O, R,) and at 0-7 
nothing is left. 

This confirms that the increase of the headline length 
ensures correct working only within the limits of the 
horizontal opening between 0-5 up to 0-6 of the head- 
line length. The amount of surplus obtained allows for 
a higher opening at 0*5 than at the 0-6 which is con- 
firmed in the survey of de Boer. For sufficient surplus 
with 0-7 opening, the headline should be further length- 
ened by about 0-6 m.; otherwise the opening height 
would be unsatisfactory and trawling forces could cause 
a break up of the webbing in the joints of the wings. 

The otter boards, consequently, have to be adjusted 
according to the constructional possibilities of the net. 
This, in practice, has led to great caution in determining 
the lengthening of the headline or footrope, and it has 
been fixed within tolerant limits to cover individual 
deviations of the trawl. 

Part (b) of fig. 3 indicates certain shortcomings in the 



M97] 



MODERN FISHING GEAR OF THE WORLD 



\ \ 




a 



\r. 

Fig. 3. The effect of lengthening the headline on i he fool rope on the wehhing* with three different ratios oj opening width to headline length. 

webbing for the same coefficients discussed above. A 
trawl of such a construction will be inefficient, causing 
excessive strain in the webbing, or will have a very small 
vertical opening. 

THE POLISH HERRING TRAWL NET 22/24/72 FT. 
FOR BIG DEEP SEA TRAWLERS 

(Fig. 4). The headline length of this net is 22 m., i.e. 
6-7 m. for the bosom and 7-65 m. for each wing. The 
headline is only slightly longer than that of the cutter 
irawl (with triangles). 

Special attention, however, is to be paid to the char- 
acter and significance of the headline bosom which, in 
our opinion, is one of the decisive elements influencing 
the vertical opening of the mouth. Fig. 5 shows the head- 
line with the same three ratios of opening width to head- 
line length (0-5, 0-6, 0-7). The headline is divided into 
the bosom part, to which the square is attached, and the 
wing sections. As the trawl has no sidelines, the analysis 
is somewhat different. 

To examine the significance of the bosom for the three 
coefficients, the quarter points are connected by the 
straight lines GH, G,Hj, G 2 H 2 , thus getting figures 
GHO, G^O,, G ? H 2 O 2 , which are characteristic for 
the opening coefficients 0-5, 0-6 and 0-7 respectively. 
They differ in height as well as in area. The headline 
enters into the square to the depth indicated by the 
curvature of the bosom, thus constituting the actual 
surplus of webbing in the square, which permits an in- 
crease in the vertical opening of the trawl. This value 
diminishes as the distance between the ends of the wings 
increases, but it always constitutes a positive, not a 




Fig. 4. The Polish Herring trawl net 22 1 24- 72ft. for large deep \ea trawler. 



\ 198 I 



ADJUSTING THE TRAWL MOUTH OPENING 



A A , B A-, B , B-, 




Fig. .\ The unpoitance of the hosom length Joi the \cnu-al opening at different ratios of opening width it) headline length 



negative factor. Contrary to the cutter trawls, an adequate 
vertical opening can be obtained by increasing the length 
of the bosom part of the headline. The same conclusion 
will, of course, be reached when reviewing the right- 
hand part of fig. 5, where the upper wing is introduced. 

The dimensions have been defined from the co- 
efficient of the horizontal opening of the headline. Con- 
sequently, the coefficient of the horizontal opening of the 
mesh fixes its length e.g. the coefficient 5 corresponds 
to 0-86, 0-6 to 0-7 and 0*7 to 0-7 (a square). 

The straight lines HC, H^, H 2 C 2 correspond to the 
foundation of the wings, whereas the lines CB, CjB,, 
C 2 B 2 indicate the seam edge of the wing. Then we join 
the centre of the headline (O, O, O 2 ) with the outer end 
of the foundation of the wing (C C, C 2 ). The angles , 
a,, and a 2 between the foundations of the wing and the 
latter lines, express the possibilities of extra lift of the 
headline, which results from the depth of the curvature 
of the headline and the length of the bosom. 

In our opinion the value of these angles is important 



in the choice of the proper length of the bosom. At 
various opening widths this value depends on the relation 
between the width of the whole square (including the 
bases of the wings) and the length of the bosom part 
Although we presume that the value of these angles will 
enable us to a certain extent to calculate theoretically the 
vertical opening of the mouth, this is a question for the 
future. 

The footrope and the lower section of the webbing of 
the belly may be treated in a similar way, mainly to keep 
the footrope to the ground, which also may help in- 
directly to increase the vertical opening. This can be 
obtained by proper arrangement of the bosom part of 
the footrope and by increasing the length of the lower 
wings in comparison with the top wings. The fact that 
with herring nets the bosom part of the lower net is 
shorter than in the square which is opposite to the 
arrangement in the trawls for demersal fish constitutes 
sufficient proof that the first argument is right. A close 
contact to the ground is not needed in the herring trawls. 



199 



THE MOUTH OF THE TRAWL 

by 
JACK PHILLIPS 

Managing Director of Phillips Trawl Products I td. of Grimsby, Fingland 

Abstract 

Since it is the amount of fish in (he codend that matters to a fisherman, nothing can be more important than to discover how best 
10 fill the codend in the shortest possible time. There are many factors concerned in this, but one of the important ones must be the size 
of the mouth of the trawl, and this paper shows the necessity for raising the headline without its being restricted by the lateral pull cf the doors 
etc. The development and application of the Trawl-plane for lifting the headline is described, and, by carrying out hydrodynamic tests in a 
600 ft. tank, meam of overcoming instability at lowing speeds greater than 3 A knots were discovered. 



Resume 



La guele du Chalut 



ttant donne que c est en definitive la quant ite de poisson capturee dans le cul-dc-chalut que imcresse le pecheur, le point Ic plus 
important consiste a trouver le moyen de remplir ce cul-de-chalut dans le minimum de temps. Ce probleme comporte un grand nombre 
de facteurs mais la dimension de la gueule du chalut en est un des principaux, et Tautcur demon t re dans cet article la necessitc de hausscr la 
ralingue supcrieure sans que ce mouvement soit contrarid par la traction laterale des plateaux, etc. II fait un expos dc la mise au point 
et de 1'application du Trawl plane destine a soulever la ralingue superieure, ct montre comment des essais hydrodynamiques entrepris 
dans un bassin de 180 metres de long ont permis de irouver Ic moyen d'elimmer les phnomenes d'mstabilite qui se manifestaieni au\ 
allures de chalutage superieures a 3.5 noeuds. 



La boca de una red de arrastre 
Extracto 

Como el interes de los Pescadores es la cantidad dc pescado en el copo, nada liene mayor importancia que descubnr la manera Je 
l.'enarlo en el menor tiempo posible. Aunque hay muchos factores relacionados con este asunto, uno de los mas importantes debe scr el 
tiniano de la boca de una red de arrastre. Por este motive, se demuestra la necesidad de elevar la relinga de boyas sin que lo impida el 
tiron lateral de las puertas. etc. Hn el trabajo, ilustrado con bastantes fotografias, tambien se describe el perfcccionamiento y uso de pianos 
de elcvacion para hacer subir la relinga superior y los dcscubrimicntos hechos mediante ensayos hidrodinamicos en un cstanquc de M)0 pies 
(181 m.) a fin de evitar su inestabilidad con velocidades de arrastre superiores a 3 1/2 nudos 



IN trawling, there is an old and often-quoted saying: 
"It all comes out of the codend". What, therefore, 
can he of greater importance than to discover hou 
best to nil the codend with fish in the shortest possible 
lime? 

RAISING THK HEADLINE 

The catch assembled in the codend has to enter lirst at 
the mouth of the trawl so that the larger the area of the 
mouth of the net, the more chance there is of catching 
fish. The example, given in figs. 1 and 2, illustrates this 
problem. Fig. 1 shows a packet of 20 cigarettes open at 
one end, exposing its contents; fig. 2 shows the same 
packet, but because the top edge has been raised, its 
capacity has been almost doubled. Note that it has been 
possible to insert no less than 17 additional cigarettes, 
without any structural alteration to the packet itself. This 
must indicate the importance of the fact that the vertical 
plane is more essential than the horizontal for high 
swimming fish and the height of the headline has a 
more direct bearing on the potential catching power 



than the spread caused by the trawl doors or oiler boards 
At low towing speeds the lateral spread does not appear 
to restrain the lift of the headline, but there is a tendencv 
loday for the more powerful trawlers to tow their gear 
at higher speeds. This gives more spread of the otter 
boards, making it necessary, in the case of the Granton 
trawl, to shorten the side line in order to overcome this 
tendency. (The shorter side line should be made of com- 
bination wire rope to withstand the additional strain.) 
Having once ensured that the headline is free to rise 
to its maximum extent at all towing speeds, it is then a 
question of selecting the most suitable method of 
achieving this. There are two major factors concerned 
with this problem of raising the headline: 

(i) the forces involved 
(ii) the towing speeds. 

THK FORCES INVOLVED 

Fig. 3 illustrates these factors in the case of a float. Lift 
represents the total vertical component being a force 
consisting of buoyancy and hydrodynamic upthrust, the 



[200] 



DEVELOPING H Y DRODYN AM 1C TRAWL FLOATS 

4 LIFT 




FLOAT 



DRAG 




DIRECTION 
OF MOTION 



HEADLINE 
Fix. ? Fwces involved. 

latter being generated by the passage of the submerged 
floats through the water. Drag is the horizontal compon- 
ent of the force generated by the passage of these floats. 
The lower the drag can be made for a given lift, the less 
the headline will be distorted backward and the greater 
the lifting result will be. Both these factors are influ- 
enced by the speed of tow. Hydrodynamically, all sub- 
merged objects in motion have critical speeds and when 
the drag force thus created overcomes that of lift, stalling 



I ami 2. 1 1 lust rut ion of the effect oj headline Iif9 ing. 




Fix. 4. Floats and kites used in h\drodynwnic tests. 
[201 1 



MODERN FISHING GEAR OF THE WORLD 




Fig. 5. Observation Cabin ami Testing Tank. 



is inevitable. This causes instability and violent oscilla- 
tion, so that the float or elevating component becomes 
useless. 

Fig. 4 illustrates a variety of experimental buoyant kites 
or elevators upon which liydrodynamic tests have been 
made, and their performances carefully recorded. Such 
considerations as simplicity of manufacture, external 
hydraulic pressure exerted on floats when submerged to 
great depths, easy handling and freedom from fouling 
the net, must all be borne in mind. Obviously a spherical 
float is better able to withstand external hydraulic press- 
ure than floats of other shapes. Its static buoyancy 
depends on its own weight subtracted from the weight 
of the water it displaces. 

By arrangement of suitable and carefully placed 
annular foils, partially or completely surrounding a 
spherical float, a substantial upthrust is obtained, giving 
a high lift/drag ratio which ensures the headline being 
elevated vertically, with the minimum distortion in the 
backward plane. 

SPEEDS OF TOW- UNDERWATER OBSERVA- 
TION 

Photographs and observations of frogmen watching gear 
being towed have answered many questions about the 



shape and behaviour of the net. These reports have, 
however, proved misleading when concerned with per- 
formances of floats towed at normal commercial speeds 
as, for obvious reasons, it was essential for the gear to 
be towed slowly during photographic operations. There 
is, for example, the experience of the Trawl Plane Float. 
Action photographs showed the Trawl Plane to be stable 
and efficient at that particular speed of tow and, thus 
encouraged, the Trawl Plane Float was assumed to be 
capable of functioning efficiently under all conditions. 
However, when the floats were put to use in commercial 
fishing, very varied opinions were expressed by the 
fishermen some skippers criticising, others praising, 
while some, who had initially been satisfied, became 
critical when they changed to newer ships. 

FURTHER RESEARCH TANK TESTS 

The Hydrodynamic Section of Messrs. Saunders Roe, the 
aircraft manufacturers of Cowes, Isle of Wight, who have 
facilities for carrying out hydrodynamic tests, assisted in 
finding the solution to this problem. Their electronically 
controlled recording and observation cabin, and the rig 
used for testing the floats in the 600 ft. tank, are shown 
in figs. 5 and 6. 

A programme for testing many varying types was de- 



[202] 



DEVELOPING HYDRODYNAMIC TRAWL FLOATS 




Fig. 6. Testing Rig. 




cided upon, and the first task was to clear up the mystery 
of the inconsistent reports received on the performance 
of the floats. The tank tests began at 3 knots, at which 
speed the Trawl Plane Float behaved with complete 
efficiency. When the speed of tow was increased to 3*1/2 
knots, both stability and efficiency were maintained 
during acceleration but, on reaching the speed, an in- 
dication of instability was noticeable. A trial at 4 knots 
revealed that the behaviour of the Trawl Plane altered 
completely; it became so unstable that the test run had 
to be abandoned to prevent the rig being damaged. These 
antics and oscillations were caused by the drag force 
overcoming the lift force. 

LATEST DEVELOPMENTS 

It is evident that optimum performance can only be 
achieved from floats or kites when a high lift/drag ratio 
is obtained. (The tests on the original Trawl Plane tended 
to show that this ratio was less than unity.) 

The necessary adjustments were then made to enable 
the Trawl Plane to operate efficiently at speeds of tow 
beyond 6 knots. So recent, however, are these experi- 
ments that at the time of the Gear Congress, the modified 
float was not available for general commercial use, as 
the tooling up and die-making involved had yet to be 
completed. 



203 ] 



MODERN FISHING GEAR OF THE WORLD 



Fig. 7 shows the fast towing hydrofoil float called the 
"Upthruster". When towed at 5-1/2 knots this float has 
a lift equal to ten ordinary spherical floats and the drag 
factor is only equivalent to three such floats and has now 
been tank tested up to 10 knots with perfect stability. 
The performance of this new float has been much im- 
proved by extending the stabilizer until it merges with 
the trailing edge of the flap to which it is attached, en- 
suring turbulent flow to eliminate a vortex forming in 
the float's wake as it passes through the water, and is 
largely responsible for the satisfactory drag factor. 

A further feature which contributes largely to its 
efficiency is the slotted flap on the trailing part of the 
foil; this controls the angle of incidence preventing the 
float from stalling at the high speeds sometimes ex- 
perienced when shooting the gear. 

The handle attachment is designed in such a way that 
a simple form of attachment is to thread a line or com- 
bination rope in and out of the handle forming a string 
of such floats which in turn can be readily lashed to the 
headline between each float, see fig. 8. 

To ensure that the float's stabilizer docs its work 
properly and the float is free to function, it is desirable 
to leave freedom for each float to move unhampered 
when lashing the string of floats to the headline. An easy 
way of accomplishing this is after threading the line 




Fig. 8. Upthf lister float a attached hy \imply threading a n>i>e 
in and out oj the handles. 



through the handle, pass the loop completely over the 
float forming a knot under the handle, making it im- 
possible for the float to slide sideways along the line 
and giving it ample freedom to work. Alternatively, when 
lashing the string of "Upthrusters" to the headline it is 
important to leave ample play between the floats to 
enable them to move freely and take up unhampered 
their working position when in use. 

Whilst this is as far as we have gone at present, two 
additional modifications to the design are being care- 
fully investigated and which show promise of even 
greater efficiency being accomplished. 




Underwater picture of the headline of a trawl with floats attached, from the film. "The Trawl in Action" . 

Crown Copyright 

[204] 



A LARGE-SIZED EXPERIMENTAL TANK OF TWIN SYMMETRIC 

ELLIPTICAL CIRCUITS 



YOSHIKAZU NARASAKO and MASAJI KANAMORI 

Faculty of Fisheries, Kagoshima University, Kagoshima-City, Japan 

Abstract 

In this paper, the authors describe the general construction and performance of the large-sized experiment-tank set in the Faculty 
of Fisheries, Kagoshima University, which is much cheaper and gives better performance than the traditional towing tank for measuring 
resistance of fishing nets and fishing ships etc. in fluids. 

Hspccially they explain the homogeneous speed field in the waterway of the tank which can be controlled more easily than with 
the old circulating tank, by moving the current blades hori/ontally, the vertically set wire netting, and the adjustable lip of the suppressor 
of wave motion. 



Resume 



I in grand bassin experimental compose de circuits elliptiques symttriques jumele* 



Dans cede communication, les autcurs decrivent la construction generate et la fonctionnement du grand bassin d 'experiences instalJe 
a la Faculte des Pechcs de I'Univcrsite de Kagoshima, qui est bien meilleur marchet donne de meilleurs resultats quo le bassin actuel a remorqu- 
age pour mesurer la resistance des filets de peche, bateaux de peche, etc., dans les fluides. 

Us cxpliquent en particulier comment le champ de vitesse homogene dans le canal d'essai du bassin peut etre controle plus facilement 
qu'avec 1'ancien bassin a circulation en dcplacant horizontalement la lame de Timpulseur et au moyen des ecrans verticaux de treillagc 
metallique et de la levre reglable de I'effaceur de vagues. Ces dernicrs dispositifs ont etc introduits par les autcurs aprcs deux ans d'essais 
effectues dans le bassin. 



Estanque experimental de gran tamano provisto de los circuitos gemolos simetricos y de forma eliptica 
Kxtracto 

fcn csic trabajo los autores describen la construction general y rendimiento del juego de estanques experimentales de gran tamano 
pertenecientes a la Facultad de Pesca de la Universidad de Kagoshima, el cual es mucho mas barato y permite obtener major resultado quo 
los eslanques de cxpcrimentaci6n utilizados en la actualidad para mcdir la resistencia de las redes y barcos de pcsca, etc., en los liquidos. 

Los autores explican especialmentc la manera dc alcanzar un campo de velocidad uni forme en la section de ensayos del estanque. 
mas facil de regular que en el antiguo estanque moviendo la hoja que ataca horizontalmente corriente, la rcjilla dc alambre dispuesta en 
sentido vertical y la paleta regulable del supresor de olas, que fueron introducidos por los autores despues de dos aftos de ensayos en dicho 
estanque. 



THE accuracy of model tests on fishing nets depends 
especially on the similarity of twine characteristics of 
real and model net. 

The tank itself must be large enough to allow the use 
of models having a construction similar to the full size 
prototype. In the present case, a large-sized tank having 
a two-metre wide waterway, was constructed for the 
experiments. 

CONSTRUCTION OF THE CIRCULATING TANK 

The tank consists of twin symmetric elliptical circuits 
14-0 m. long, 7*1 m. wide and I -0 m. deep, constructed 
of ferro-concrete (fig. 1 ). 

The central waterway is 2-0 m. wide and the right and 
left waterways are 1-0 m. wide. The water flows sym- 
metrically into the central section, forming a straight 
waterway for making tests, then branches off at the lower 
end to circulate further. 

Paddle wheels of 2-5 m. diameter and 1 -0 m. width, 
with 24 radial blades are set on each side of the waterway. 



They are driven by a vanslip A.C. motor of 10 h.p. 
which is automatically regulated and remote controlled 
The resultant flow of water is symmetrical and easil> 
adjustable. 

The maximum speed of flow is 0-8 m./sec. which can 
be increased by decreasing the depth of water. 

Observation windows, 2 -0 m. long and 1 -0 m. wide, arc 
set in the right and left side walls of the central waterway 
and measurements and photographs can be taken through 
them. 

The flow of water round the curves of a circulating 
tank is slower on the inside and faster on the outside of 
the curve. The flow near the walls and the bottom of the 
tank is decreased by drag due to the viscosity of water. 
To equalise the flow, current plates were fixed at the 
front of the paddle wheels and at the curves of the water- 
way. The plates divide the flow into several narrow paths 
(figs. 2 and 3). 

There are also movable current blades at the curves 
of the tank, and these can control the horizontal speed 
of flow according to Bernoulli's theorem. Fixed current 



[2051 



MODERN FISHING GEAR OF THE WORLD 




ffi 



*; 



NO NO NO. NO. NQ 
~" 



12345 



6 7 ? P IQ 



>3 14 IS 



18 17 18 W 70 



73 ?a 





Fig. /. Top view of the tank with reference points for waterflow 
measurements. 

plates and vertical wire netting in frames of 25 cm. 
200 cm. are set in the lower stream. The mesh size of the 
wire netting can be adjusted to each speed of flow, while 



-900- 



-1000 



Fig. 2. Size and position of current plates. 



. Uifttt 




7-7^. 3. Position oj fixed ami movable current plates in the tank . 

an adjustable lip is set in the upper waterway as a sup- 
pressor of surface waves (fig. 4), thus controlling surface 
motion. 

The carriage, consisting of three parts, moves easily 
along rails on the top of the sides of the central straight 
waterway. One part can be moved right and left, or up 
and down, and has a balance at the centre. Thus the 
point of resistance measurement is given three dimen- 
sional freedom of movement with an accuracy of 1 mm. 
The frames of the carriage are all made of steel and the 
dynamometer (the balance) is made of duralumin, 
according to Froude's system. Resistance is measured 
by the curve recorded on a revolving drum. 

THE GENERAL PERFORMANCE OF THE 
CIRCULATING TANK 

Fig. 1 shows the plan of the tank. The positions for 
measurement of speed are marked on the parts of the 
straight waterway. The speed of flow can be examined in 




r-Mro-rr 












is 

'*o 

% 


















^ 
























































1* 


M 


>* 

wr* 


w 


w 


\t' 



Fig. 4. Position of wire netting frames and wave suppressors in 
the tank. 



[206] 



CIRCULATING TYPE TANK 




Figs. 5 and 6. Distribution of flow HK, 5 without. Jig. 6 with, current 
speed in vertical (top) and hoii- plates and wave suppressors 
zontal (below} cross section. 

three dimensions, through 6 steps in the direction of 
length, 5 steps in the direction of breadth (7 steps later, 
including two supplementary steps right and left) and 
5 steps in the direction of depth. 

The current was measured with the "Hiroi" current 
meter. With no current blade and no suppressor of wave 
motion, the speed is maximum at about 0-7 of the water 
depth. The speed drops suddenly near the side wall and 
bottom (fig. 5). It can be seen that the homogeneous 
speed fields in the central vertical plane of the waterway 
are symmetric. Because of the symmetry of the water- 
way, a good natural effect is obtained as the water flows 
through the central section. 

When the current blades and wave motion suppressor 
are mounted, the standard deviation from a homogene- 
ous speed field is 0-04 (mean speed 0-55 m./sec.) (fig. 6). 
The experiment shows further that at a flow of less than 
0-6 m./sec. the water surface is so calm that the wave 
motion suppressor is not necessary. 

Fig. 7 shows that the speed field is more uniform and 
that the deviation from a homogeneous field is only 0-02 
(mean speed 0-43 m./sec.) when the vertical wire screens 
are also used. The screens are of 3 cm. and 2 cm. mesh 
size, made of 1 1 mm. wire, and are set vertically in two 
steps under the surface, from 25 cm. to 50 cm. and from 
50 cm. to 75 cm. Wire screens were used because control 
of the speed of flow is made easy in a comparatively 
shallow tank by the fluid resistance of the webbing. 

The speed of flow becomes difficult to control when 
it increases beyond a certain limit, because the resistance 
of the net is proportional to the square of the mesh size. 
Therefore, the mesh of the net had to be enlarged when 



* -!-.. 

-H (*** | 



/r 




F/#. 7. Distribution oj flow speed 
in vertical (top) and horizontal 
(helow) cross section when wire 
net frames are used in addition 
to current plates and wave 
\npprex\oi \. 



hig. <V. Distribution oj surface 

flow lines at low speed of the 

paddle wheel. 



the mean speed in the tank wai greater than 0-4 m./sec. 
At lower speeds, it is very easy to control the speed of 
flow accurately. As a rule the homogeneous speed field 
in the waterway can be set by controlling the r.p.m. of 
motor. 

When the depth of water is constant, the r.p.m. of the 
motor is proportional to the rate of flow and the distribu- 



(i) 



TABIF I 
Relation of motor revolutions to deviation of cqui- velocity 



distribution when current plates and wave suppressors are fixed 

500 (wit h- 
r.p.m. 400 300 250 out 

wire net) 



deviation 

depth 
0-05 m. 
0-225 
0-40 
0-575 
0-75 


0-43 
0-44 
0-43 
0-42 








017 
010 
Oil 
010 


Vmls 




5 


Vmls 


S 


ym/s 


00000 


S 

033 
033 
044 
034 
041 


0-32 
0-33 
0-32 
0-31 








017 
010 
Oil 
-010 


0-26 
0-27 
0-26 
0-25 
0-22 


0-020 
0-013 
0-010 
0-010 
0-027 


0-63 
0-66 
0-60 
0-52 
52 



(ii) Vertical section of velocity deviation 

r.p.m. 400 300 250 250* 

AV de^ation )City ym/s S Vmls S Vmls S Vml * S 



Vertical section 


1 


. . 


2 


0-43 0-015 0-32 0-011 0-26 0-020 0-27 0-016 


3 


0-43 0-008 0-31 0-006 0-26 0-022 0-27 0-013 


4 


0-43 0-021 0-33 0-022 0-25 0-041 0-27 0-018 


5 


0-44 0-014 0-32 0-012 0-26 0-013 0-27 0-011 


6 


0-43 0-023 0-31 0-018 0-25 0-018 0-26 0-012 


7 


,._ 



(iii) Horizontal section of velocity deviation. 
r.p.m. 400 300 J250 

Average velocity y / s y m/s s y m/s 
deviation ' ' 



250 *_ 
S 



Horizontal section 

1 0-43 0-014 0-32 0-016 0-25 0-025 0-26 0-016 

2 0-43 0-018 0-32 0-014 0-25 0-026 0-26 0-015 

3 0-43 0-019 0-32 0-013 0-26 0-022 0-27 0-013 



*ln this calculation the velocity of flow at D^O-75 m. is omitted. 



[207] 



MODERN FISHING GEAR OF THF WORLD 



lion of water speed in the tank is uniform at all points. 

When the motor revolves very slowly, the flow line of 
the surface water layer deviates about 1 per cent, inwards, 
being influenced by the hollows at the windows in the 
side walls. The flow lines are perfectly parallel to each 
other, so there is no disturbance to the model under 
experiment (fig. 8). 

Table I shows the relation between the r.p.m. of the 
motor and the deviation when the current blade, wave 
suppressor and wire netting are used. 

Table II shows the time necessary (17 mins.) for the 
speed of flow to become constant and uniform after 
starting the motor. After that, no change of speed is 
apparent. Jf an experiment is made within 7 mins. of 
starting the motor, an error of 3 per cent, should be 
allowed on resultant measurements. 



TABLI II 

Time required before speed is constant and uniform after the 
motor is started. 



Point <>/ measurement No. 4 



Velocity 



Sec. \ 'm, \ 



I m< 



\o. Iff 



Sec. I m 



Time required 














1 m:n. 


18-0 


34 


17- X 


34 


17-8 


I) 34 


12 


17-6 


0-34 


17-6 


0-34 


17-4 


0-35 


17 


17-2 


35 


17-2 


35 


17-2 


0-35 


22 


17-0 


36 


17-2 


35 


17-4 


0-35 


27 


17-0 


0-36 


17-4 


35 


17-0 


0-35 





Trawl toads and wingdooi designed hy A. //. Larsson (S\\ederi) based on model ir\ts 



208 



Section 7: Rational Design Use of Measuring Instruments ami Underwater Observation. 



MIDWATER TRAWL DESIGN BY UNDERWATER OBSERVATIONS 

by 

R. F. SAND 

Bureau of Commercial Fisheries, U.S. Fish and Wildlife Service, Washington 25 D.C., U.S.A. 

Abstract 

Underwater observations and evaluations of the I .arsson Phantom Trawl and others are described. Direct observations of the fishing 
gear in operation were obtained by the use of underwater television and divers with cameras. By means of modification and refinement a 
practical midwater trawl was developed for use by American fishing vessels. The resulting net has been used by research vessels and also 
commercial fishing boats of 200 to 750 h.p. and, at speeds between 2 and 5 knots, catches ranging from 5.000 io 20.000 pounds have been taken. 

Utilisation des observations sous-marines dans le dessin du chalut Hot Cant 
Resume 

L'auteur se fondc sur les observations cffectuees sous 1'eau pour evaluer le comportcmeru du chalut I .arsson. type Phantom, airtsi cjuc 
d'autres types dc chaluts. Des observations directes des engins en fonctionnement ont etc obtenues par des appareils de television sous- 
marine et des plongeurs munis d'appareils cinema tographiques. A la suite de modifications ct de perfect lonnements, on a mis au point un 
chalut flottant efficace a Fintention des navires de peche amdncains. Ce chalut a ete utilise par des navires de recherche et des bateaux de 
pechc d'une puissance de 2(H) a 750 c.v. et, a des vitesses de 2 a 5 noeuds les quantitcs pechees ont attcint de 5.000 a 20.000 Iivres. 

Uso de obscrvacioncs^submarinus en el proyecto de redes del arrastre polagicas 
Kxtracto 

Se describen las observaciones y evaluaciones submarmas de la red de arrastre 1 arsson y de otros tipt s de artes de pesca. Las 
observaciones directas de estas redes durante el lance cfecutaron c con aparatos de television submarina y buzos provistos de camaras foto- 
graficas. Mediante diversas modificaciones y perfeccionaniientos se logro construir una red de arnistre para profundidades intermedias, 
dcstmada a los barcos de pesca de Nortcamcmcrica. P.I equipo resultante a sido usado por embaracciones dc investigaci6n y cnmercialcs dc 
200 a 750 c.v. a velocidades que fluctuan entre 2 y 5 nudos. obteniendosc redades de 5.000 a 20.000 Ibs (2.227 a 9,072 Kg.) dc pcscado 



THE recognition of the need for new and improved 
methods in fishing gear research has resulted in some 
promising new tools and techniques. In connection 
with some midwater trawling gear research studies, the 
United States Fish and Wildlife Service has demonstrated 
the systematic application of underwater television and 
divers using self-contained breathing apparatus and 
cameras as practical fishing gear research instruments 

UNDERWATER TELEVISION 

Since 1950, the U.S. Fish and Wildlife Service has con- 
ducted experimental trials with one- and two-boat mid- 
water trawls. Results from earlier Service work had 
shown economical and operational advantages in the 
single boat type, and its continued development was 
favoured for possible use by American fishing vessels. 
In May 1954 a Service research vessel carried out some 
preliminary trials with the Larsson Phantom Trawl in 
North Pacific offshore waters. Results of fishing per- 
formance were inconclusive. The gear was then shipped 
to the Services Gear Research and Development Unit at 
Miami, Florida, for further test and evaluation, using 
underwater television and other experimental methods. 
Here Service engineers had successfully adapted in- 
dustrial type, closed-circuit television for direct observa- 



tions of fishing gear m action 4 . B> means ot progressive 
experiment and refinement of equipment a remotely con- 
trolled submersible vehicle was developed for the tele- 
vision camera 1 . 

In November 1954, a joint cruise of the Service re- 
search vessels Oregon and Pompano made the first prac- 
tical use of underwater television in fishing gear research, 
with the Phantom Trawl as the subject to be viewed. 
While under tow in clear Gulf Stream waters, the trawl 
warps, doors and net opening were observed by a tele- 
vision camera streamed between the Oregon s towing 
warps. A second television camera was streamed from 
the Pompano to make simultaneous lateral observations 
of the gear. Still picture and kinescope recordings were 
made of the entire operation. 

The first tests were made with the gear rigged as 
originally received from Sweden: cotton trawl, hydro- 
foil floats and depressors, aluminium floats, hydrofoil 
doors and 30 fathom manila towing legs with danlenos. 
Previous trials had established that this gear did open 
to an estimated 30 feet or more, but that it was unsatis- 
factory to tow the trawl at 3-0 knots and even below 
this speed. The heavy drag caused continued tearing at 
sudden speed variations or full vessel power 3 . With 50 
fathoms of cable from vessel to net, the trawl was now 
seen well below the propellor wash at speeds below 3 



209 ] 



MODERN FISHING GEAR OF THE WORLD 



knots. At a speed of 2-0 knots, the monitor screen re- 
vealed the trawl doors, warps, and net mouth to be quite 
stable in the water with the trawl in an approximately 
20 feet square opening, and the headline rising in a gentle 
arc. A close-up camera lens revealed the terrific stress on 
the twine in a rigidly appearing trawl mouth. Most of 
the patent trawl floats had been cleared only with diffi- 
culty and those still fouled were seen to produce uneven 
stress on the twine. While the patent hydrofoil floats on 
short pennants performed well, a slight tendency to 
oscillate suggested turbulence particularly at wing tips. 
This was remedied by tying off the floats close-up. Round 
aluminium float performance seemed most satisfactory 
in comparison. Increases in speed up to the 3-0 knot 
limitation resulted in the estimated 30 feet horizontal 
spread with, however, a closing of vertical opening. This 
had been suspected in previous sounding tests, but not 
confirmed until registered on the television monitor. 

In another trial the 30 fathom manila towing legs and 
danlenos were replaced by j} in. wire cable and dandy-line 
gear to facilitate handling. Observers noted no appreci- 
able change in net performance except that the trawl 
fished slightly deeper in the water and tended to close 
at the lower wings. This was remedied by adding one 
fathom of cable at each lower towing leg. No marked 
losses of horizontal or vertical spread could be attributed 
to the removal of the danlenos. There followed various 
substitutions and arrangements of floats, leads and de- 
pressors, in an effort to attain the desired vertical trawl 
opening at 2-0 to 3-0 knot speeds. With the use of 
adequate weights and depressors, the desired vertical 
opening was obtained, but at the sacrifice of horizontal 
spread in each case. Although the hydrofoil trawl doors 
had handled and performed well, they were replaced with 
standard type trawl doors of equal and of larger sizes 
in an attempt to improve performance. Apparently there 
was no appreciable change in the trawl opening. 

Most noticeable to all observers during these trials 
was the evidence of continued heavy drag and extreme 
"sweep back" of head, breast and leadlines at all test 
speeds. Completely absent during all television observa- 
tions was any appearance of the net acting as an inflated 
body containing a volume of water exerting a pressure 
on the twine. 

It was indicated to observers that, due to the excessive 
drag, the trawl could not be opened to its maximum de- 
signed displacement without some structural modifica- 
tion. 

DIVING SLED AND CAMERA OBSERVATIONS 

Through 1955, experimental trials with the modified 
Phantom Trawl continued in clear Florida Gulf Stream 
waters, subject to observations by underwater television, 
surface water glasses and divers using a towed diving 
sled and camera gear. A diving sled was made by con- 
verting a tubular steel ambulance litter for use when 
underwater television observations were not feasible 6 . 
This device was equipped with elevator controls to per- 
mit manoeuvrability. It provided a large degree of com- 
fort and protection for the pilot-observer and camera- 
man diving team while under tow from the research 
vessel. The diving sled permitted first-hand observations 
and photography of all aspects of the trawl performance 



from various angles, to detailed inspections in actual 
contact with the fishing gear. 

During some 20 towing observations at speed and 
depth ranges proximating the previous television trials, 
various trawl modifications and accessory rigs were con- 
sidered separately and in combination. Since in the pre- 
vious trials the trawl performance had not been seriously 
affected by open or closed codend, emphasis was placed 
on reducing resistance at the trawl mouth. Progressively 
the net wings were shortened, body length was reduced 
and trawl hanging and headline increased to enlarge the 
proportion of the net square dimension to the length. 
These were effected with no real improvement apparent 
to observers. The first indication that the gear was open- 
ing in a better manner was not obtained until head, 
breast- and leadlines were reduced by about one-third in 
diameter and the number of floats and weights reduced 
by one-half. 

When quarter doors or kites of equal area were affixed 
at the four wings in the same angle of attack as the trawl 
doors, greater trawl opening was achieved but drag and 
turbulence on wings greatly increased. In a similar man- 
ner, triangular pieces of heavy canvas attached to the 
wing extremities failed to assist trawl opening due to low 
attack angle made necessary to reduce drag. 

Trials were continued with the net modified to about 
two-thirds the original size and with trawl doors approxi- 
mately twice the area of the patented hydrofoil doors. 
For the first time this net was seen to open to an esti- 
mated 90 per cent, of the possible mouth aperture at a 
2-0 knot towing speed. At this speed, a bulge or lump 
in the top square was still seen to cause some uneven 
distribution of tension on the body twine. This was 
remedied by removal of two centre aluminium floats and 
replacement at wing tips. The midwater trawl now was 
completely inflated as if exerting a pressure from the 
centre outwards to all points on the twine. Meshes were 
revealed as taking the desired diamond shape under 
tension from every angle. That there was an apparent 
pressure effect within the trawl was determined by 
physical contact by the diving team who found the net 
rigid yet malleable and capable of partially supporting 
a 50 pound lead weight placed upon the twine. With 
reduced towing speed below 2 -0 knots, there was evidence 
that the net opened, more as a result of resistance to the 
water than as the result of lift by the floats. This was 
accompanied by some apparent transfer of towing strain 
to rib lines. Strong evidence had now been presented 
showing the need to restrict future midwater trawl 
construction to materials of higher strength and lower 
drag characteristics. Also, this demonstrated the need 
for float or lead and depressor rigs permitting better 
trawl opening. Recognised as of vital importance was the 
extreme need for symmetry in design, exactness in 
measurement, and careful sewing detail to ensure perfect 
twine balance. 

DISCUSSION OF RESULTS 

Within the frame of reference provided by the underwater 
determinations, an all-nylon 40 foot square opening trawl 
was constructed (see figure). Particular attention was 
given to choice of materials, twine sizes and dimensions, 
geometric configuration and proportions to permit 



[210] 



10 M 



OBSERVING MJDWATER TRAWLS UNDER WATER 

10 M 



BAR HANG MOUTH TO 1/2" COMBINATION! 
ROPE WITH DOUBLE MESH 



NET WINGS AND BODY Of NYLON 
NO. 831 110 LBS. TEST 



DOUBLE MESH Al 
SEAMS bEFORE SEWING 



TAPER 1 PI . 2 BAR 



NYLON CROSS R I bS TOP 
BOTTOM BAR HUNG 




TAPER 4 PT . 1 FAR 



12 ROUND 8 ALUMINUM 
FLOATS ON HEADLINE 



4 OZ. SEINE LEADS ON 
LEADLINE WITH 12 SPACING 



RIBLINES 1/2 NYLON FULL LENGTH 
GATHER 3 MESHES EACH SIDE AND 
HANG EVEN 



NO TAPER 



40 //. M'uhvater trawl (U.S. hi\h ami M ilit/ije Service). 



211 



MODERN FISHING GEAR OF THE WORLD 



performance of the nei as a turgid elastic body. Final 
adjustments to trawl and accessory gear were again 
subject to underwater inspection. The resulting trawl 
design has performed well in operation from Service 
research vessels in North Pacific and North Atlantic 
offshore waters, in open swells and moderate seas with 
25-30 m.p.h. winds. In fishing trials from vessels of 
200 to 750 h.p. at speeds of between 2 and approximately 
5 knots, individual trawls have withstood over 100 tows 
without serious damage attributed to excessive drag from 
towing strain in taking catches varying from 5,000 to an 
estimated 20,000 pounds. 

There remain a number of variables to be examined 
and the trawls currently in use are, of course, subject to 
continued refinement. It is noted also that the genera! 
design features compare closely with those of recently 
introduced Canadian and European midwater gears 1 . 

For more than four years, the experiments using 
conventional gear research methods were unsuccessful, 
until the application of underwater television and other 



experimental methods permitted direct observations of 
fishing gear in operation. Continued application of these 
valuable techniques should assist materially in removing 
a great barrier to research in fishing methods and equip- 
ment. 

REFERENCES 

1 Barraclough. W. E. and W. W. Johnson. A New Midwater 
Trawl for Herring, Fisheries Research Board Canada Bulletin 
No. 104, 1956, 25 pp. 

2 Margets, A. R. Some Conclusions from Underwater Observa- 
tions of Trawl Behaviour, World Fishing, August 1952, pp. 61-65. 

3 Richardson, I. D. Some Problems in Midwater Trawling, 
World Fishing, February 1957, pp. 26-31. 

4 Sand, R. F. Use of Underwater Television in Fishing Geai 
Research (Preliminary Report) U.S.F.W.S., CFR., Vol. 17, No. 4. 
1955, pp. 1-5. 

5 Sand, R. F. Underwater Television Vehicle for Use in 
Fisheries Research, U.S.F.W.S., SSR. No. 193, December 1956, 
15 pp. 

6 Sand, R. F. New Diving Sled, U.S.F.W.S.. CFR.. Vol. 18 
No. 10, 1956, pp. 6-7. 




Skindiver learn of Coral Gables preparing for Irawl observations. 
[212] 



STUDY OF THE MEDITERRANEAN TRAWL NET 

by 

MENACHEM BEN -YAM I 

Kibbutz fc 'Sa-ar", D.N. Gallil Ma'aravi, Israel 



Abstract 

This paper deals with an attempt to improve the performance of the Italian type of trawl as used in the Mediterranean Sea. Very 
little progress has been made with this gear because the fishermen considered that it represented the climax of achievement. The author has 
studied the working of the gear by means of underwater photography and direct observation by divers, and has been able to suggest ways and 
means of constructing a cheap, strong, and efficient trawl suitable not only for the Mediterranean Sea but also for other areas where the need 
for higher headlines is of greater importance. 

Discussion sur le chalut mcditemmeen 

Kcsmn 

L'auteur traite d'un essai d 'amelioration du rendement de chalut de type italien tel qu'il est utilise dans la mer Mediterranee. Get 
engin a fait tres peu de progres parce que les pecheurs consideraient qu'il rcprescntait 1'apogee de la realisation, mais I'auteur a 6tudi6 le 
fonctionnement de I'cngin au moyen de photographies sous-marines et d'observations directes effect uees par des plongeurs, et il est 
mcme de suggerer des facons et des moycns pour construire un chalut bon marche, robuste et efficace convenant non seulement pour la mer 
Mediterranee mais aussi pour d'autrcs regions oil il est tres important d'avoir la corde de dos plus 61evee. 

Examcn de la red de arrastre del Mcditerraneo 
Rxtracto 

tste trabajo trata de las tentativas que se han hecho para mejorar el rendimiento de las redes de arrastre de tipo italiano, como las 
usadas en le mar Mcditerranco. Se ha logrado mejorar muy poco a este arte por considerar los Pescadores que ha alcan/ado el mximo de 
perfeccionamiento. No obstantc, el autor al estudiar la manera de trabajo mediantc fotografia submarina y observation direct a valiendose 
de buzos, ha sugerido formas y mdeios para construir una red de arrastre barata, resistente y eficaz, apropiada para el Mediterraneo y otras 
zonas donde tiene gran importancia el empleo de una relinga superior a bastante altura de la inferior. 



SJNCH the introduction of the otter trawl into the 
Mediterranean Sea, some thirty years ago, there 
has been no report whatsoever on the performance 
of the gear. 

Attempts by the fishermen to improve the net have 
come to a standstill for, according to them, the present 
trawl gear represents the climax of achievement and an> 
change in its technical pattern is unnecessary. 

To provide at least a part of the required information, 
underwater photographs were taken of the Italian type 
trawl net in action, typical of those used in Israel and 
southern Italy 13 . Studies were also made of the" Tzofia" 
type hybrid net, and the "B" type hybrid net I - 5 - 6and7 . 
The observations were concentrated upon the trawl 
net itself, observations on other parts of the gear being 
left to the future when financial means would permit the 
work to continue. 

Underwater measuring instruments, as used by De 
Boer" and Scharfe 20 , were not available for this survey, 
so that assumptions and conclusions cannot be based on 
exact measurements. The numerous photographs, how- 
ever, and the direct observations of the divers give, at 
least, a general picture of the shape and behaviour of 
the nets in action. 



THE TRAWLER 

The underwater observations were carried out in Haifa 
Bay at a depth of 6 to 7 fathoms. The skin divers attached 
themselves to the various parts of the net or floated 
just above it on a diving sled I2 n . 

The observed gear was towed by the F.R.V. Hatzvj, a 
Danish built wooden boat of Scandinavian type with 
120 h.p. engine and converted to stern trawling. 



THE GEAR (OTHER THAN NET) 

The differences between the examined and the commercial 
trawl gear were as follows : 

The warp was of 10 mm. o steel wire, 100 m. long, 
and appeared to be proportional to the depth (under 
normal conditions 250 m. at 20 fathoms and 200 at 15 
fathoms are used in this area). The otter boards were 
160 \ 90 cm. and typical for vessels of the Hatzvi 
size in the local trawl fishery. The swecplines of 22 
mm. o combination rope were shortened from 210 
to 100 m. The mudropes, which are several pieces of 
thick rope whipped together, 5 to 7 m. long and placed 
in the gear between the sweeplines and the wings 



213 ] 



MODERN FISHING GEAR OF THE WORLD 




h'ig. 1. Italian trawl net jor 120 h.p. vessels. 
A -- wing, 10-11 m. long, 140 meshes reduced to 90, JOO mm. 

stretched. 
B - upper wedge, 5 m. long, 80 meshes reduced to 20. 80 mm. 

stretched. 
C * - belly \ 15 m. long, 220 meshes in each part, at the connection to 

the wing, 400 meshes at the throat connection, 54 to 50 mm. 

stretched. 
1) - throat, 400 meshes reduced to 360 meshes, 40 mm. stretched, 

4 m. long. 

E *- codend, 5 m. long, 400 meshes, 40 to 50 mm. stretched. 
F lower wedge, 5 m. long, 80 meshes reduced to 20, 100 mm. 

stretched. 
G - lower body, 21 to 22 m. long, 60 meshes in each part, at the 

connection to the wing, 40 to 60 meshes at the codend, 50 to 60 

mm. stretched. 

H - headline, 14 to 16 mm. & hemp rope, 28 m. 
I footrope, 40 mm. hemp rope, 34 m. The small letters: a, 

b, c, d, show how the lower body is connected to the rest oj 

the net. 

of the net, form an integral part of the Mediterranean 
trawl gear. They were only used during one of the 
tows. The divers found that they raise a cloud of mud 
which interferes with visibility to such a degree that no 
records could be taken. As the divers did not discover 
any differences in fishing spread of the net with or without 
these ropes, the latter were removed for the rest of the 
observations 151 . 

THE NET 

The observed net was of the usual Italian type used in 
commercial fishing by Mediterranean trawlers of 120 h.p. 
The top and bottom parts of the Italian net differ 
greatly. The bottom has much less webbing, made of a 
much heavier twine, than the top part. The parts are 
connected in such a way as to permit a high degree of 
slackness in the bottom (lacing coefficient: c = 0-85 to 
0-90). The codend is one tube-like piece of webbing, 



ana the wing consists of one part, also common for top 
and bottom. The front edges of the belly are completely 
connected to the wings. At the centre of the mouth there 
are two wedges, upper and lower, sewed into long clefts 
in the top and bottom of the belly. Long hangings, 
(30 to 45 cm.), connect the webbing to headline and 
footrope. The wedges are also sewn into the belly by 
means of hangings. The net parts are never cut to 
shape but the whole webbing is made by hand and 
tapered, to reduce the size and number of meshes towards 
the codend. The Italian trawl net is much longer than 
most other types of trawl nets. 

TEST RESULTS 

The Opening Width 

The method used in finding the approximate distance 
between the otter doors was based on measuring the 
distance between the warps at two particular points on 
board the vessel. Knowing the exact length of the warp, 
the spread was then calculated. This method, although 
not exact, suffices to obtain a rough appraisal of the 
fishing spread. 

Calculations showed that the distance between the 
boards of the standard gear of Hatzvi varies from 60 to 
70 m., and in the examined gear from 40 to 50 m. 11 ' 
To assess the angular difference between the net's wings 
in both cases, a comparison can be made between the 
isosceles triangles formed by the wings and the sweeplines 
and the line joining the two otter boards. 

(1) Common gear: Distance between the boards 
60 m. Length of the arm -220 m. (this includes the 
sweepline, the mudrope and the wing of the net). 

a 
Therefore the sine of will be 0*14 and the angle 

2 

itself will be about 16 degrees ( -- angle between 
the two equal arms). 

(2) Experimental gear: Distance between the boards 
40 m.; the arm 112m. (this includes the shortened 
sweepline and the wing of the net). The sine of 
a 

-equals 0-18 and the angle itself about 21 degrees. 
2 

The difference between the common and the experi- 
mental gear, regarding the angles between the wings, 
calculated in this simplified way, is about 5 degrees. There 
is no reason to believe that this value makes a great 
difference in practice, causing basic changes in the shape 
and behaviour of the net in action. 

All measurements and observations were carried out 
while the codend was empty. The current opinion of 
local fishermen is that a big catch in the codend increases 
the total resistance of the net. It is understandable that 
if the codend fills with mud, stones or any other heavy 
load, as often happens, the total resistance of the gear 
increases, the fishing spread decreases and in some cases 
the towing speed decreases as well. The reaction ma> 
be quite different if the codend fills with fish only. De 
Boer", who measured the trawl gear under water, b> 
means of special instruments, expresses the opinion that 
a big catch may cause a decrease instead of an increase 



[214] 



THE MEDITERRANEAN TRAWL NET 



of the pull in the legs of a trawl but a normal catch would 
not influence the tension. 

Influence of bottom conditions 

All observations were made on a sandy bottom. Various 
beliefs and ideas about the influence of the type of the sea 
bottom on the behaviour of the trawling gear exist among 
the fishermen. The most common opinion is that on a 
soft muddy bottom the sweeplines dig into the mud, and 
move mole-like under its surface. 

In spite of the differences between the actual fishing 
conditions and the conditions under which the study was 
made, the author believes that the over-all picture 
obtained of the Italian trawl net in action is sufficient 
to allow a preliminary analysis of the problem. 

The Shape of the trawl net in action 

Some facts concerning the shape of the net in action may 
be determined from the photographs and observations 
made by the divers (fig. 2). 

(1) The curve of the footrope is much wider than the 
curve of the headline. This suggests that the 
overhang of the net is much smaller in action than 
it appears to be when the net is spread on shore. 

(2) The wing forms a triangular wall, with its concave 
surface inwards. The height and the cross section 
of this wall increase from the danlcno towards the 
junction with the body. 

(3) The cross section of the net's body is ellipse-like, 
becoming more and more circular in form towards 
the codcnd. 

(4) The after part of the codend forms a swollen ball, 
the diameter of which is larger than the diameter 
of the cylindrical throat (fig. 3). 

(5) The fishing height, measured by the divers at the 
centre of the headline, is 90 to 1 20 cm. 




Fig. 2. Combined pliotograph-drawing oj the Italian trawl 
net in action. 

a total net resistance. 

c and f *=" spreading forces. 

d and e = towing forces. 

g lifting force of the floais. 

h = connection between the wing ami the body. 



The forces acting on the net 

Forces acting on the Atlantic type trawl gear have already 
been calculated theoretically 3 and studies of various 
types of trawls are being made in some countries 9 , lu , '- 
and 21 . But up to the present no report has been 
received on attempts to measure these forces in the 
Mediterranean trawl gear. However, the experience 
of the fishermen and netmakers, the direct underwater 
observations, and the knowledge of the construction of 
the Italian trawl net, can provide an explanation in 
general terms. The scheme of these forces is given in 
figs. 2 and 3. 

In the horizontal plane, three main forces are acting: 

(1) Total resistance of the net "a" opposes the move- 
ment of the gear. 

(2) Towing farce "e", "d", acts at an angle a to the 
direction of movement. 

(3) Spreading force "c" acts perpendicular to the 
direction of the movement and is a result of the 
action of the water stream on the webbing. 

Although we cannot deal with the actual values of 
these forces because of the absence of any measured 
data, it is clear that the resulting force acts along the net. 
parallel to the movement. This force (fig. 3-AB) will be 
called in the following "the parallel force" . 

The spreading force acts on the webbing of the net 
from inside out in all directions, causing the net's body 
to expand (fig. 2-c and f ). The action of all these forces 
together with the lifting force, if any, of the spherical 
floats (fig. 2-g), creates the final shape of the Italian 
trawl net while fishing. As whirlpools are formed by 
the net moving through the water, it is possible that 
additional mutual influences exist between them and the 
shape of the net. 

The behaviour of the gear when towing is started 

The divers found that when the net is released and the 
whole gear is loose, the height of the vertical opening 
reaches 4 or more metres, caused by the lifting force of 
the floats. But as soon as towing is started, the vertical 
opening of the net decreases rapidly and the tightened 
headline comes down to a height of about 1 m. As the 
trawl begins to move, a stream of water through the 
net body presses in all directions, which causes the bod> 
to swell. The after-end of the codend opens up into a 
ball and, being constructed from heavy webbing, causes 
a serious resistance. While the towing speed increases, the 




tig. 3. Scheme of forces acting on an Italian trawl net. 

a, r, e and d as above (fig. 2). 

AB parallel force. the angle at which the towing forces act. 



(215] 



MODERN FISHING GEAR OF THE WORLD 




Fig. 4. Top pan of net while in action, under full towing .strain. 

A distorted section of belly webbing, at rear connection of upper 

wedge. 

B distorted edge, due to wrong adjustment of hangings. 
C and D - drawing show mesh angles. 

parallel force increases and the lifting effect of the 
spherical floats decreases. As the Italian trawl net has 
no sidelines the elongation of the body, due to the resist- 
ance of the codend, is limited only by the webbing of the 
upper part. As the parallel force increases, the meshes 
close and the body of the net consequently becomes 
longer. The result is that the net body narrows and forms 
a flat, long funnel shape. 

The lifting force of spherical floats 

The headline of the experimental net was equipped with 
common spherical glass floats. The lifting force of 
these floats at usual towing speeds of about 3 knots seems 
to be almost negligible. This feature of the spherical 
floats has been described by various authors \ ni , "* 
and 23 . 

The opening height 

The headline of the Italian trawl net lifts at regular 
towing-specds to a height of 90 to 1 20 cm. The efficiency 
of the spherical floats is more than doubtful. The 



height of the wooden danlenos of the wings is 40 to 60 
cm. only, and pictures show that they move at an acute 
angle towards the bottom. This means that their 
effective height is even less. It would seem that the 
water stream, while expanding the net, meets the bell> 
webbing at a certain angle of attack and lifts the upper 
part of the net to the observed height. 

The form of the meshes in various parts of the experimental 
net 

Due to the angle taken by the camera, the angles of the 
meshes, as measured on a photograph, are not quite 
accurate (fig. 4). Those which appeared to be undis- 
torted by the perspective were measured but the results 
are still valid only for a rough comparison of the shape 
of the webbing in the various parts of the net. 

The length of the mesh bar is the only unchanging 
factor if the stretching of the twine caused by towing 
tension is disregarded. 

All other qualities of the mesh (the length, the width, 
the mesh angle) change according to the action of outside 
forces, so that trigonometric and geometric formulae can 
be used in designing nets and analysing their action. For 
this purpose the hanging coefficients are convenient and 
in common use (figs. 5 and 6), for calculating the 
relations between the webbing and the ropes. Hanging 

b 
coefficient c r , (fig. 5), gives the relation between the 

2a 
mesh length (b) and the mesh size (2a). The co-efficient 

c 
c., represents the relation of the mesh width to the 

2a 

mesh size. The bigger b, the bigger is Cj, the smaller c , 
and the mesh angle (fig. 6). The relation between these 
coefficients and the mesh angle can be calculated trigono- 
metrically, or by means of measuring the angles on 
drawings (fig. 6). A table was published by Baranov 3 
p. 168. 

As seen from the underwater observations and photo- 
graphs the mesh angles in the Italian trawl net vary from 



><* t--' 




/ /V. 5. Miape oj a net mesh in work ing position. 

a . , a ..,..., a . . . . har\ of the mesh. 



h mesh length, 
c mesh width. 
a mesh angle. 
The arrow shows the direction of movement, a . a . . 

b ( 

T/zr. Hanging coefficients: q ; r., 

2a ~ 2a 



mesh 



Fig. 6. delation between coefficient of hanging r, ami mesh anvle 
ad mesh length at (^ 99; * - 15 degrees, 
be mesh length at q - - 91 ; a - 50 degrees, 
ab cd the difference between the mesh length in both rase\ 



[2161 



THE MEDITERRANEAN TRAWL NET 



-14m 





A/#. 7. The upper belly //// the nedge adiu\teil into the r/eft. 

A upper wedge. 

B belly. 

a distorted sector of webbing. 

wide open to completely closed. In the after part of 
the upper belly, and in the throat, the meshes are almost 
completely closed. The meshes in the central and the 
front parts are closed in the sides and open in the 
upper belly. In the central sectors of the belly and 
the upper parts of the wings, the mesh angle seems to be 
not less than 40 degrees, while in some places it reaches 80 
degrees (fig. 4). The width of the webbing strips, the 
meshes of which are open, is at least 50 rows counting 
from the top edge downwards (fig. 4). Theoretically this 
fact should cause a shortage in the upper part of the 
webbing in relation to the mid and lower parts. 

The strain in the upper part of the net 

According to observations the mesh angle in the lower 
parts of the front half of the net is less than 15 degrees 
compared with the 50 degrees in the upper strips. The 
length of the mesh at 15 degrees, is only 1 -1 per cent, 
shorter than the mesh size. The length of a mesh at 
50 degrees is 9-4 per cent, shorter than the mesh size, 
(fig. 6). The difference in length between those parts of 
the upper and lower net where great differences in the 
mesh angle appear, should be approximately 8 per cent, 
particularly in the front half of the belly and in the wings. 

In action, therefore, the front 1 to 8 m. of the upper 
belly, should theoretically be about 0-5 m. shorter than 
i he lower belly. l-rom actual experience this is not found 
to be true. The stretching of the twine in the upper net 
is a general!) known fact. This can be seen when a new 
Italian trawl net is taken ashore for the first time for 
repairs and adjustment. The belly webbing is found to 
have lost its original form, and differences between the 
upper and lower parts arc apparent, the former being 
longer than the latter. The fishermen cut triangular 
strips from the stretched sectors of the webbing, to give 
the belly its original rectangular form. This proves that 
there is a greater stretching force acting on the upper 
strips than on the rest of the webbing, and this causes an 
elongation of the meshes. The wide opening of the 
meshes is not due to a weaker parallel force acting on the 
top of the net, but to additional spreading forces affecting 
the sides of the belly (figs. 2 and 3). 

Ft could be concluded that the increase in the angle of 
the meshes in the upper net is almost balanced by the 



Fig. ti. Schematical view oj the belly in action. 

a - .sectors under distortinK Jorces. 
f angle at which the belly is broken. 

stretching. In action, the strips with wide open meshes 
would be about 5 to 10 per cent, shorter than the parallel 
strips with closed meshes below. However, the actual 
stretching of the webbing in the top is less than 5 per cent, 
so that these two phenomena only balance each other in 
part. It seems, therefore, that in action the upper parti 
of the belly and of the wings arc really a little shorter 
than the rest of the webbing, although the total strans 
over the top is stronger. 

Consideration of the suitability of the Italian net design 

The upper belly of the Italian net is a trapezium which is 
almost rectangular. In the centre of its front part there 
is a cleft 6 to 7 m. long. The shape is achieved by gradually 
reducing the number of meshes per row, and/or by 
decreasing the mesh size towards the throat. All edges 
are knitted straight and no shape cutting used. A 
triangular piece of webbing is laced in the cleft by means 
of thin lines, in order to enlarge the net mouth. This part 
is called the upper wedge (fig. 7-A). While adjusting this 
wedge into the cleft the natural shape of the belly 
webbing becomes distorted. Thus, a weak constructional 
point is produced near the posterior connection of the 




Fig. 9. \et mouth in action. 

Ill opened meshes in upper strips of webbinv. 

C sector under distorting Jorce\. 

E edge of upper wedge. 

/>/ hanging* of heaiiline 



[217 ] 



MODERN FISHING GEAR OF THE WORLD 



upper wedge (fig. 7-a). This place often tears, and the 
meshes here are always distorted, so that fishermen use 
various methods to avoid such damage but with relatively 
poor results. The methods used are: connecting the 
wedge to the belly by means of a long line running along 
the centre of the belly and reaching sometimes to the 
throat or even the codend, and/or using double twined 
webbing along the cleft. 

In addition to the distortion, two more weak points 
are created on the upper edges of the belly where the 
headline, the wedge and the belly meet (fig. 8-a, fig. 9-c). 
The angle is clearly visible in the photograph, although 
the edge here was constructed straight (fig. 9). The 
fishermen waste a lot of fishing time repairing the torn 
mesh and hangings in this sector of the net. 

The form the belly webbing takes in action is recon- 
structed in fig. 8. Comparing this figure with the 
construction plan, it is clear that the construction does 
not fit the shape the belly has when in action. The angle 
resulting from the distortion at the belly edges (fig. 8-a), 
was calculated as being approximately 20 to 30 degrees, 
depending on various factors, such as opening width, 
length of hangings, etc. 

The same constructional defects appear in the lower 
part of the net along the lower wedge and the footrope. 
However, as there is less strain here and stronger twine 
is used, less damage is done than in the corresponding 
parts of the upper net. 

In most parts of the net, the meshes are closed when 
the net is in action, so that the webbing partly loses its 
filtering action. In the after part of the belly, and in the 
throat, where the body of the net takes the shape of a 
tube, the meshes are so near to closed that substituting a 
non-filtering material for net webbing, e.g. canvas, 
would have only a slight influence on the behaviour of 
the gear. The poor filtering of the webbing results in 
increased resistance of the whole net. 

The curves of headline and footrope in the sections 
connected to the wedges, are very broad, especially in 
the footrope (fig. 9). The fishermen make the hangings 
of the wedges shortest in the centre (less than 5 cm.), 
and their length is gradually increased towards the side of 
the wedge. The divers reported that the difference in 
length between the central and the side hangings is too 
great and causes increased tension in the centre of the 
wedge and some slack, in its sides. 

Possibilities for improvements of the Italian net 

A differentiation ought to be made between the term 
"improvements in the Italian trawl net" and the term 
"improvement of the Mediterranean trawl net". In the 
former, reference is made to small technical improvements 
in the present net, while conserving the characteristic 
pattern of its construction and behaviour on the sea 
bottom. In the latter, this pattern is rejected. The aim of 
the improvements in both cases is the saving of work 
and material, decreasing the net resistance to the water, 
increasing the catch in relation to the towing force 
invested and saving the young specimens of no commer- 
cial importance 17 . 

Few changes can be made in the Italian net without 
deviating from the accepted pattern. The vertical 
opening is definitely limited because the upper part of 



the body is 10 to 15 per cent, shorter than the bottom part 
The meshes in many parts of the net are closed due to the 
absence of side lines along the body, which would limit 
the stretching of the webbing (see page 220: Hybrid net). 

Reduction of the amount of webbing 

Decreasing the number of meshes in those parts of 
the webbing where the mesh is closed, without suitable 
changes in the parallel force, will not improve the 
mesh opening. The strain acting on the webbing will con- 
tinue to keep the meshes closed, with the whole tube of 
the net body becoming thinner. Since the shape of the net 
mouth and its dimensions depend mainly on the hydro- 
dynamical features of the body, any change in the size 
and shape of the body in action must produce parallel 
changes in the form and behaviour of the net. Therefore, 
only a limited decrease of the amount of webbing in the 
throat and the codend can be recommended and care 
must be taken to avoid exaggeration which can produce 
negative effects. 

Reduction of the twine strength 

The fishermen of the smaller trawlers (up to 120 h.p.), 
have upper parts made from light webbing as it is more 
efficient despite the fact that the thinner the twine the 
weaker and shorter living the net. For the bigger trawl 
nets, the light webbing proved too weak to resist the 
greater tension of the higher towing speeds of the larger 
vessels. Substituting the thin webbing by a stronger 
and heavier one, lowers the lifting abilities of the Italian 
net and reduces the catch. 

Limits of the Italian pattern 

It can be said that in the three most important aspects, 
namely: (1) saving in the amount of webbing; (2) 
lengthening the net's life by use of stronger twine without 
changing the material, and (3) increasing the fishing 
height, no full satisfactory results can be achieved, as 
long as the main pattern of the Italian net remains 
unchanged. 

Experiments should be carried out with a shortened 
body and a flapper in the throat, and with synthetic 
twine, none of which has yet been tried. 

Minor improvements of construction 

Two different methods arc suggested to decrease the 
damage due to the weak points in the upper edges of the 
belly and around the posterior connection of the wedge. 
In fig. 10 the whole wedge is made much longer, and 
in fig. 11 only the cleft is made longer, while the 




present 
" """" suggested 

Fig. JO. Longer wedge to decrease distortion in belly webbing. 
A - wedge. B belly. 



12181 



THE MEDITERRANEAN TRAWL NET 




Fig. II. Method of wedge adjustment, to reduce distortions in 
the belly webbing. 

A - the weak points performed. 
H suggested additional hanging. 
C wedge. 

hangings of both sides of the wedge unite behind its 
end and continue some metres, decreasing their length 
gradually. Although the use of these two methods will 
decrease the strain around the end of the wedge, the 
distortion in the edges of the belly will be even more 
pronounced than before (fig. 9-c.) Therefore, at the same 
time, the hangings which connect the headline to the 
belly (fig. 9 section CD), have to be gradually lengthened 
the longest hanging should be nearest to the wedge 
(fig. 9-c). This is already practised by some fishermen. 
Here the author would rather recommend, instead of 
making the hangings in the critical section longer, that 
the other hangings along the whole wing be shorter. 
This method of hanging was already successfully 
practised. The length of the hangings along the wing 
should not exceed 20 cm. (instead of 35 to 40 as used 
generally) but those along the critical section of the 
belly edge should be gradually lengthened till 40 cm. 
at the wedge. 

The side hangings connecting the wedges to the ropes 
should not exceed 20 to 25 cm. (fig. 9-t). 

A more radical solution would be to cancel the wedges 
altogether. For this purpose, however, the number of the 
meshes in the front edge of the belly must be increased 
by about one hundred. For this purpose a rectangular 
part of webbing (fig. 12-A) could be removed in order to 
form the mouth. This would simplify the construction 
of the Italian net without changing the principle of its 
action. The weak point around the wedge end disappears 
together with the wedge and its hangings. After cutting 
out two small triangular pieces of webbing (fig. 12-A), 
a form close to that appearing in action is given to the 
top of the net mouth. 

ft must be underlined that such small technical 
adjustments may improve the economy by reducing time 
and expense of maintenance but have nothing to do with 
increasing the efficiency of the Italian trawl net, for they 
do not change its towing resistance nor the size of its 
mouth. For more basic improvements the Italian pattern 
in the construction of a trawl net would have to be 
rejected. 

Considerations about the suitability of other types of trawl 
nets 

The long experience of making, and fishing with, the 
Italian trawl net, and the survey described above, has 
convinced the author that this net cannot form a basis 
for the development of an improved trawl. 




100 



Fig. 12. tront edges of upper belly cut to sha/)e. 

A triangular pieces to be removed. 
B belly. 
C-D - wings. 



Former experiences 

From publications available in Israel we learn that 
experiments made in the Mediterranean proved that the 
Atlantic or northern types of nets were in all cases less 
efficient than the Italian, although in some trials they 
caught more pelagic fish 8 . 

Experimental trawling with the Atlantic gear in 1957 
by the South African steam trawler, Drom Africa, 
yielded very poor results, taking into consideration the 
size of the vessel and her gear and the richness of the 
north-east Mediterranean where the trawling was carried 
out 18 . Some experiments were made by the late Dr. 
Lissner, Director of the Sea Fisheries Research Station, 
but the author did not succeed in getting enough informa- 
tion about them. A Yugoslavian fishing vessel, Napredak, 
arrived in Israel in 1953 to carry out experimental tuna 
fishing. This vessel, when the expected tuna did not 
appear, fished with an Atlantic type of trawl net but, 
although her power was 400 h.p., the catches were 
always less than those of the small Israeli trawlers until 
a net of Italian pattern was used. Experimental fishing 
was done by the Sea Fisheries Research Station in 1957 
in the Bay of Tarsus with Portuguese gear on board the 
F/V Lamcrchav (240 h.p.). The results were almost nil, 
and the trawling was stopped after two tows. At the 
same time and place, big catches were taken by Lamerchav 
and other Israeli trawlers fishing with their standard gear. 

The Mediterranean needs an improved trawl net, 
which has all the features of the Italian net, is economic 
to construct and has a fishing height that will ensure 
catching fish swimming some metres off the bottom. 
The mesh should be large enough to avoid catching 
young fish of non-commercial size, as recommended in 
the survey carried out by the Sea Fisheries Research 
Station 14 . 



[219 



MODERN FISHING GEAR OF THE WORLD 




Fig. 13. Hybrid net* advanced type, as n\ed on board F\ I 
Shorn ria (I /Oh. p.) Upper part. 

A headline, 12 mm. hemp, 28 m. long. 

B sideline, 12 mm. hemp, 2 X 32 m. long. 

C - footrope, 40 mm. & hemp, 34 m. long. 

D ------ wing, 140 reduced to 90 meshes, 110 rows. 100 mm. stretched 

E -= square -, 40 meshes, 24 rows, 50 mm. stretched. 

F top, 170 reduced to 120 meshes, 300 rows, 50 mm. stretched. 

G - side, 115 reduced to 80 meshes, 300 rows, 50 mm. stretched. 

H - throat, 280 meshes, 60 rows, 40 mm. stretched. 

1 - codend* 300 meshes, 100 rows, 46 to 48 mm. stretched. 

The rows are of full meshes (2 bars). 

A flapper is sewn into the throat. 

For the bottom part see fig. /--/", G, /. 



The hybrid net 

During 1956 and 1957 four different vessels fished 
commercially with hybrid nets as well as with standard 
nets, and the hybrid nets had at least the same catches 
as the standard Italian nets. The important point is thai 
a net constructed on a different pattern from the Italian 
can achieve satisfactory results ll * 15 . The main principle of 
the hybrid net is that the towing forces are acting on the 
sidelines (seized to the side-seams) (fig. 13). 

The top (F) is connected to the sidelines with a hanging 
coefficient c=0-88 to 0-90, and the sides (G) with a 
coefficient c- 0-95 to 0-97. The Italian pattern of the 
bottom parts below the sides is preserved. The loosely 
connected top part can be lifted by means of, for in- 
stance, Philip's trawl-planes, and reaches an opening 
height of 2-5 m. (twice that of the Italian net), as deter- 
mined by the divers 1 . And this is achieved with less 
webbing in the upper part of the net. 

Fig. 13 shows the plan of a hybrid net for 100 to 120 




Fig. 14. Adjustment o/ wing tips to the wooden danleno in Ih 
hybrid-net. The height of the danleno /v 70 to 80 cm. 

u - thimble, 

h wooden danleno, 

< foo trope, 

d headline. 

t' sideline. 

/ wing connecting rope. 

X wing webbing. 

h net to foot rope connection ( Italian) method, 
direct net-to-rope connection. 



h.p. trawler as now used by the F/V Shomria. (See also 
figs. 14 and 15). 

FURTHER DEVELOPMENTS 

The preliminary observations of the Italian trawl net, 
together with the theory of net construction 3 , show the 
way for further development. The way suggested by the 
author is to remove the towing strain from the net 
webbing by the use of a rope skeleton sewn into the net. 



f220) 



THE MEDITERRANEAN TRAWL NET 




Fig 15. Wing adjustment to iron pipe danleno in hybrid-net in action. 

Height of the danleno 80 cm. 
a triangular pipe danleno. 
h swivel, 
c ~ jootrope. 
d - wing connecting rope, 
e - sideline, 
f =-- headline. 

g spherical glass floats, appearing here only Jor divert 
convenience. 

Such constructional improvement will give back to the 
net webbing its original ability to filter the water and will 
save a lot of net material without decreasing the net size. 
Moreover, it will enlarge the mouth opening. These 
advantages have been proved in fishing with and under- 
water observations of hybrid nets. But the hybrid net is 
only a first step to the future Mediterranean trawl net. 
The meshes are closed in the after part of the body as in 
the Italian net. Waste of material and superfluous 
resistance are big in this net, too. In the suggested net 
the webbing will be free from the action of the parallel 
force. The relation between the webbing and the ropes 
can be calculated by the use of hanging coefficients. This 
will enable the constructor to design a net pattern 
suitable to the net shape when in action. Furthermore, in 
such a net all the meshes will be open and less webbing 
will cover a particular surface. 

According to calculations made by the author, at 
least 64 per cent, of the webbing can be saved in those 
parts where the mesh angle does not exceed 18 degrees, if 
adjusted to the side ropes with a hanging coefficient c= 
0-87. This coefficient gives a mesh angle of 60 degrees. 

The length of the whole net will be assured by means of 
sidelines preferably made of thin (12 to 14 mm.) combina- 
tion rope, while the webbing will control only the swelling 
of the net. Such an improvement leads to: (a) saving of 
net material; (b) decreasing of resistance, and (c) liber- 
ating the top of the net from horizontal strain, thus 
enabling it to attain a larger opening height. It does not 
oppose, otherwise, the Italian principle of loose bottom 
parts. This net can be constructed of stronger (heavier) 



webbing, because its shape in action will be assured b> 
the rope skeleton and the hydro-dynamic floats, and not 
only by the action of the water stream on the webbing, 
as seems to be the case in the Italian trawl net. The new 
net can be constructed of machine-made webbing. 

CONCLUSION 

A cheap, strong and efficient trawl net for the Mediter- 
ranean could be constructed as a result of technological 
surveys and experiments. The best way to develop such 
a net seems to be in rejecting the old pattern and shifting 
the towing strain from the webbing to ropes. 

The proposed pattern could be equally applied to areas 
outside the Mediterranean where an increase in the fishing 
height may be of far greater importance. 

REFERENCES 

1 Assaf, 1. Underwater Observations of the Hybrid Net.. 
Fishermen's Bulletin No. 9, Haifa 1956. (In Hebrew). 

2 Assaf, I. Personal information, 1956. 

3 Baranov, F. I. Theory and Calculations of Fishing Gear 
Moscow, 1948. (In Russian). 

4 Bar-on, E. Personal information, 1956. 

5 Ben-Yami, M. A New Trawl Net. Fishermen's Bulletin 
No. 8, Haifa, 1956. (In Hebrew). 

6 Bcn-Yami, M. The Design of the Hybrid Net Type B, 
Fishermen's Bulletin No. 9. Haifa, 1956. (In Hebrew). 

7 Ben-Yami, M. Preliminary Report on Experimental Fishing 
with a New Trawl Net. General Fisheries Council for the Mediter- 
ranean, 4th Meeting, Technical Paper No. 35, Istanbul, 1956. 

8 Bernstein, D. Three Experiments for increasing the height 
of the Head Rope. Fishermen's Bulletin No. 4, Haifa 1955. 
In Hebrew). 

9 De Boer, P. A. Trawl Gear Measurements obtained by 
Underwater Instruments. International Council for the Explora- 
tion of the Sea and North Sea Sub-Committee Comparative 
Fishing. No. 4, 1954. 

10 De Boer, P. A. Private correspondence, 1956. 

11 Crew of M. F. V. Tzofta - Preliminary Report on a New 
Type of Trawl Net. Fishermen's Bulletin No. 8, Haifa, 1956. 
(In Hebrew). 

12 Fried, Z. and Assaf, I. Aqua-lung Tests of the Italian Trawl 
Net. Fishermen's Bulletin No. 8, Haifa, 1956. (In Hebrew). 

13 Fried, Z. Underwater study of the Italian Type Trawl Gear. 

14 Gottlieb, E. and Orcn, O. H. Savings Gear Experiments with 
Trawl Nets in Israel Waters. General Fisheries Council for the 
Mediterranean, Technical Paper No. 36, Istanbul, 1956. 

15 Hamburger, E. Preliminary Results on the Operation of the 
Hybrid Net, Fishermen's Bulletin No. 9. Haifa, 1956. (In Hebrew). 

16 Hamburger, E. Personal information, 1956. 

17 Kristjonsson, H. The scope for Technological Development 
in the Mediterranean Fisheries. General Fisheries Council for the 
Mediterranean, No. 2. Technical Paper No. 36, Rome, 1954. 

18 Lissner, H. and Hirsh, H. Experimental Fishing in the Bay 
of Alexandretta. Bulletin No. 1. Sea Fisheries Research Station, 
Haifa, 1948. (In Hebrew). 

19 Percier, M. A. L'ouverture du Chalut en Hauteur. Genera 
Fisheries Council for the Mediterranean, Rome, 1952. 

20 Scharfe, J. Geraete zur Messung an Schleppnetzen. Die 
Fischwirtschaft Hefl 1 und 2, 1953. 

21 Scharfe, J. Dass Messcn dcr Zugbelastung bei Schleppnetzen. 
Die Fischwirtschaft, Heft 2, 1955. 

22 Smislov, I. G. Analysis of Action of Spherical Trawl Floats, 
V.N.I.R.O. Works, Vol. XXX, Moscow 1955. (In Russian). 

23 Yacovlcv, A. I. Results of Hydrodynamical Tests of Trawl 
Floats. V.N.I.R.O Works, Vol. XXX, Moscow. 1955. (In Russian). 



[221 



FACTORS AFFECTING THE EFFICIENCY OF DREDGES 

by 

R. H. BA1RD 

Ministry of Agriculture, Fisheries and Food, Fisheries Experiment Station, Conway, Caerns, U.K. 



Abstract 

In this paper the various factors affecting the efficiency of the dredge are discussed. The depressive effect of diving plates allows an 
increase in the towing speed, and the angle of attack of the plates has an optimum value. The angle at which the teeth of the dredge travel 
over the bottom also has an optimum value, about 45 degrees, and the selective action of the teeth is a useful method of reducing the amount 
of trash taken. Preliminary attempts have been made to assess the absolute efficiency of the standard Manx scallop dredge and it was proved 
to be low. 



Rfeum* 



Etude des facteurs conditionnant I'efficacite des drogues 



L'auteur examine dans cet article les diflferentes facteurs qui conditionnent I'efficacite de la drague.. L'eflet d'abaissement des 
plaques de plongec pcrmet d'accroitre la vitesse de remorquage, ct il cxiste unc valeur optimum dc Tangle d'attaque des plaques. L'angle 
selon lequel les dents de la drague attaquent le fond, est optimum 45 degre environ. Une bonne methode consiste a tirer parti de 1'effet 
sdectif des dents pour reduire la quantit6 de matdriaux ind&irables ramasses par la drague. Des essais pr&iminaires entrepris pour valuer 
le rendement absolu de la drague "Manx 1 * standard a coquilles St. Jacques ont montre que Pefficacite de ce modele 6tait faible. 



Exposicidn de los factorvs que f nfluyen sobrel a eficacia de los rastros 
Extracto 

En este trabajo se analizan los diversos factores que influyen sobre la eflcacia de los rastros. HI efecto de las planchas de inmersion 
permitc aumentar la velocidad de arrastre de acuerdo con su angulo de ataque hasta alcanzar un valor maximo. For su parte, el angulo de 
incidencia de los dientes de estas dragas cuando avanzan por el fondo del mar alcanza un valor opt i mo a 45 , y la acci6n selectiva de ellos 
constituye un metodo util para reducir la cantidad de desperdicios recogidos. So han hecho ensayos preliminarcs con objeto de e valuer el 
rendimiento absolute de los rastros para peregrinas o veneras utilizados corrientementc en la isla de Man, que result 6 ser bajo. 



THIS paper is intended for marine biologists as well 
as for commercial fishermen. Much of the discus- 
sion is of an elementary nature and over-simplified; 
qualifications should follow most of the statements. How- 
ever, as dredges have evolved very slowly, and nearly 
always in an empirical manner, at least in Europe, it will 
perhaps make a starting point to discuss in a general 
way some of the problems involved. 

Underwater observation of dredges in action shows 
that scallop dredges with rope warps have a tendency to 
skip over the bottom 1 and oyster dredges to slither. In- 
creases in speed of tow above a low level tend to reduce 
catches. This can be overcome to some extent by fitting 
depressors or diving plates to the dredges. One such 
dredge for scallops has already been described 2 . The 
fitting of teeth to dredge bars improves performance in 
some cases, but makes the angle of attack of the blades 
more critical than without teeth. Tooth spacing is also 
important. 

The shape of the catenary of a warp in the water will 
depend on the drag of the warp which will vary with the 
material. In general, a wire warp will have a forward and 
downward catenary, the weight in water being greater 
than the drag; a rope warp will have a backward and 
upward catenary, the drag being greater than the weight 
in water. 

In the following discussion, the weight of the warp 



will be ignored, although it can be seen that a wire warp 
can increase the effective weight of the dredge and a rope 
warp can exercise considerable lift. 

The normally used warp-depth ratio for dredging is 
3:1. The actual length of warp required disregarding 
the effect of the warp itself will be determined by the 
drag of the dredge which is proportional to the velocity 
squared (D-- KnV a ), and by its weight in water. An in- 
crease in speed of tow necessitates a much increased ratio 
of warp to depth. 

EFFECT OF DIVING PLATES 

With a diving plate, another factor lift is introduced, 
which can act upwards (positive) or downwards (nega- 
tive). In addition to the lift from a diving plate, induced 
drag occurs. Thus, there are two sources of drag, that 
from the dredge itself, called parasitic drag (D p ), and 
induced drag from the diving plate (Dj). As with drag, 
lift is proportional to velocity squared (L KtV 2 ). 
From fig. 1 it can be seen that although the negative lift 
from a diving plate increases the warp angle, increase in 
speed still decreases the warp angle and thus some more 
warp is required for a given depth. Parasitic drag should 
be kept as low as possible by the use of as large a mesh 
as possible and by avoidance of unnecessary large sur- 
faces in the construction. 



[222] 



EFFICIENCY OF DREDGES 



> 

I 




tn-C -L I 



e I 



1 1 



vcloolty 



Fig. 1. The ejjevt on warp angle of increasing speed of tow with 
diving plate. The sign of lift and weight show direction. 

The lift/drag ratio is at its maximum at rather small 
angles of attack, the drag increasing, with increased angle 
of attack, quicker than the lift which, furthermore, in- 
creases only up to the point of stall. However, when the 
parasitic drag is high, the amount of negative lift needed 
for a given size of diving plate requires a bigger and, 
therefore, less efficient angle of attack. 

A secondary effect of a diving plate is to help material 
into the bag of the dredge by deflecting upwards the 
waterflow at the mouth of the dredge. It has been ob- 
served that if the angle of attack of the diving plate is 
too great, more trash is retained. This may be explained 
by the eddies formed by the partial or complete stall of 
the plate resulting in a slowing down of the water flow 
at the mouth of the dredge, with a tendency for trash to 
accumulate in the front of the dredge bag (fig. 2). 

The use of diving plates affects the stability of the 
dredge while it is in mid-water during shooting. A 
dihedral angle on the diving plate will give lateral 
stability about the longitudinal axis. Longitudinal stab- 
ility is maintained by the point of tow. If negative lift is 
maintained on the plate with negative dihedral (an- 
hedral) while shooting, righting moments occur when the 
dredge is disturbed laterally. If the plate gives a positive 
lift with negative dihedral angle the dredge will be turned 
over. 

Fig. 3 illustrates the effect of negative dihedral and 
negative lift. When the dredge is disturbed laterally, 
weight continues to act vertically downward but the 
negative lift is inclined to the vertical. If the negative lift 
is split into its vertical and horizontal components, it 
can be seen that the horizontal component is acting to 
the right, causing a relative waterflou to the left, which 




fif. 2. Secondary effect of stalled diving plate. Eddies behind 
stalled plate can cause accumulation of trash in the dredge bag 



rdft to right 
* rltiv flow 



Fig. 3. Effect oj dihedral. Temporary displacement of plate 
results in forces righting moments. 

gives positive lift to the left plane and negative lift to 
the right plane, resulting in righting moments. How- 
ever, if, as sometimes happens, when the tow is taken 
from the leading edge of the dredge and the warp is run 
out with restraint (fig. 4), the diving plate will give posi- 
tive lift, turning the dredge on to its back; the forces 
are illustrated in fig. 5. 

In fig. 6, a dredge designed for mussel and oyster 
fishing is shown with two alternative points of tow. When 
the forward points of tow are used, the dredge has 
positive lift and is unstable in mid-water if checked 
during shooting. This had the disadvantage that when the 
depth suddenly increasedjthe dredge left the bottom and 
turned over. With the after points, a negative lift was 
always maintained and the dredge was completely stable 
and could be towed in mid-water without turning over. 

THE EFFECT OF TEETH 

Scallops normally lie recessed with the flat valve approxi- 
mately in the plane of the bottom. On escallop dredges 
the teeth penetrate the bottom and get below the edge 
of the shell, thus lifting the scallops into the bag. There 
are, however, considerable secondary effects. It has been 
shown 1 that the teeth on scallop dredges give a highly 
selective effect, operating probably more efficiently than 
the selective effect of the meshes of the bag. Quantitative 
information on this effect is limited to date, but from my 
own data and from those of Mason (1953) the suggestion 
is that the sizes at which 50 per cent, are selected are 
between 20 per cent, and 50 per cent, larger than the tooth 
spacing. The teeth, furthermore, are also sifting out trash, 
i.e. smaller organisms, shells and small stones. This allows 
a much longer tow with an increased proportion of fish- 
ing time with the dredge on the bottom. For this screen- 
ing action to be effective there must be clearance between 
the dredge bar and the bottom. With a shallow angle of 
attack of the teeth of the dredge, excessively long teeth 
are necessary to allow for sufficient clearance and pene- 
tration of the bottom. These are very easily damaged. 
With an angle of attack of the teeth approaching 90 
degrees, shorter teeth can be used, but entry of the catch 



Dirln plat* ivin* pocltiv* lift 




Relative 
flow 



Fig 4. Diving plate giving positive lift during shooting when 
tow is taken from leading edge and warp is run out with restraint. 



t 223 ] 



MODERN FISHING GEAR OF THE WORLD 



turning 




Horisoat*! oonponmit of lift Bovine 
drod** to loft 



Fig. 5. Force* capsizing dredge during shooting \\hendi\inx plate 
gives positive lift. 

into the bag is impeded. Experiments done at Conway 
with a model dredge of about 0-5 metres span, with an 
adjustable tooth angle but uniform bottom penetration, 
have suggested that, at varying speeds, entry into the bag 
is not much impeded up to angles of 45 degrees. Within 
limits, higher speeds of tow allow steeper tooth angles 
to be used before passage of scallops over the teeth is 
impeded. 

ABSOLUTE EFFICIENCY 

The catching efficiency of dredges is low and will vary 
with the type of bottom. Coral gravel bottoms in Corn- 
wall and near Port Erin, Isle of Man, at depths of about 
20 metres, have been observed to be furrowed to a depth 
up to 10 cm. with 20 to 30 cm. between the crests of the 
ridges. The passage of a dredge effectively flattens this 
type of bottom. It can be seen that a dredge will have 
a low catching efficiency on a furrowed bottom because 
it will be either skimming the crests of the ridges and 
missing many of the scallops, or digging into the ridges 
and catching a lot of trash which will soon fill the dredge. 
An increase in efficiency will occur as the bottom is 
flattened by working. (It is often stated by scallop fisher- 
men that catches increase on some grounds after some 
days of intensive working.) 

Dickie 3 measured the efficiency of Canadian dredges 
by releasing marked scallops and afterwards dredging 
in the area, assessing efficiency by the estimated number 
encountered per tow and the actual number caught. He 
found an efficiency of from 5 per cent, to 12 per cent., 
depending on the ground worked. Walne r> assessed the 
efficiency of a hand oyster dredge on slipper limpets 
(Crepidula fornicata) by comparing the catch of the 
dredge to the density of limpets as assessed by grab 
sampling. He found an efficiency of 16 per cent. Shel- 
bourne 4 measured the efficiency of a winch-operated 
oyster dredge on slipper limpets by distributing a known 
number of limpets between poles on a clean intertidal 
area at low water and fishing between the poles at high 
water. He found this dredge to be 30 per cent, efficient. 
A special sampling dredge he devised had an efficiency 
of 60 per cent. However, although it might be quite 
possible to devise a dredge that was nearly 100 per cent, 
efficient for a short tow on a soft bottom, it does not 
follow that this will give the most economical fishing. 
This is clearly demonstrated by Shelbourne where the 
ratios of catch per distance run of 3-3, I -0, 0-6 were 
obtained for the survey dredge, the winch-operated 
dredge and hand dredge respectively on oysters. The 
ratio of output of oysters per man day was 1-0, 1-1, 
1-6 for the most, medium and least efficient dredges 
respectively. This was almost entirely due to the degree 
of selectivity, the least efficient dredge being most 




/ig. ft. Mussel antt oyster dredge showing alternative to\\ 

attachments. Forward attachment results in mid- water instability 

when warp is checked. After points give complete miil-watei 

stability. 

selective and resulting in the highest daily catch ol 
oysters on a "mixed" ground. Where the organisms to 
be caught are fairly sparse on the bottom, a high selec- 
tivity is as important as a high efficiency, otherwise the 
dredge fills too quickly with unwanted material and so 
has to be handled more frequently. 

A preliminary attempt to measure the efficiency of a 
traditional scallop dredge was made at Port Erin, Isle 
of Man, with the aim of using the dredge as a quantita- 
tive sampling device and as a standard to which other 
dredges could be related. Using a self-contained breath- 
ing apparatus, the actual density of scallops was measured 
by collecting all scallops passing between the runners 
of a sledge towed slowly over a known distance. Dredge 
hauls of measured distances were made in the same area. 
If only commercial scallops, 11-5 cm., and upwards, 
are considered, diving showed these to be present at a 
mean density of 1 per 40 m.- and the dredge covered 
250 m. 2 for every one caught, giving an efficiency of 
16 per cent, for commercial scallops. The mean densitx 
of all sizes of scallops, found by diving on the bed being 
investigated, was I per II m. 2 The dredge covered 
130 m. 2 of bottom lor every scallop caught, giving an 
efficiency of 8-5 per cent. The selective effect of the 
dredge will cause this figure to vary with the si^e- 
distribution of scallops on the bed. 

It must be emphasized that the range and scatter of 
these results was such that the only inference that can 
safely be made is that dredge efficiency is of a low 
order, probably between 5 and 20 pzr cent, with a higher 
efficiency when working on the larger scallops. 

REFERENCES 

1 Baird, R. H. and Gibson, F. A. "Underwater Observations 
on Escallop (Pecten maximus) Beds." J. mar. biol. Ass. U.K. (1956) 
35, o 555-562. 

2 Baird, R. H. "A Preliminary Report on a New Type of Com- 
mercial Escallop Dredge". J. d. Con.lnt., Vol. XX, No. 3. 1955. 

3 Dickie, L. M. ''Fluctuations in Abundance of the Giant Scal- 
lop, Placopecten rnaffc/lanicus (Gmelin), in the Digby area of the 
Bav of Fundy." J. Fish. Res. Bd. Canada, 12 (6), 1955. 

4 Shelbourne, J. b. "The 1951 Oyster Stock in the Rivers Crouch 
and Roach, Essex." Fish. Invest,. Ser. II, XXI, No. 2. 

5 Walne, P. R. "The Biology and Distribution of the Slipper 
Limpet (Crepidula fornicata) in Fssex Rivers.*' Fish. Invest., Ser. 
II, XX, No. 6. 



[2241 



TRAWL GEAR MEASUREMENTS OBTAINED BY UNDERWATER 

INSTRUMENTS 

by 

P. A. de BOER 

Fisheries Inspectorate, The Hague, Netherlands 

Abstract 

The Netherlands Fishery Inspectorate has devised a series of instruments for recording the behaviour of trawl gear, as follows: 1. The 
Spread Meter, to record the distance between the after ends of the otter boards or, if the boards are attached directly to the wings, the horizon- 
tal opening of the net. 2. The Clinometer, which records the till of the otter boards sideways as well as fore and aft. 3. A Net height meter 
for measuring the vertical opening of the net. 4. An angle of attack meter, for recording the angle of attack of the otter boards. 5. An 
Hydraulic Dynamometer, for measuring the pull of the legs between the boards and the net, and also for recording the tension in the warps 
on board the ship. 

The author describes the evolution of the instruments and then gives some interesting results obtained by their use, for instance 
the relationship between warp length, the spread of otter boards, their tilt and angle of attack and the opening height of the net. 

Tests were made using different kinds of floats on the headline, and it was found that, using no floats, the headline height was 1 -2 m.,, 
while 10 spherical floats raised it to 1 -9 m., 5 "Siamese-twin" floats increased it to 2-3 m., and 10 "trawlplanes" lifted it to 2-75 m. 



Resirni* 



Matures effectives sur des chaluts au moyen d'appareils sous-marins 



Le Service d'lnsnection des peches des Pays-Bas a mis au point les ap pure! Is suivants pour cnrcgistrer le comportemcnl du chalut: 
(1) un ecartemetre pour cnrcgistrer la distance scparant les extremites posterieures des plateaux, ou, si ceux-ci sont fixe directement aux 
ailes, Pouverture horizontal de filet. (2) Un clinometre qui cnregistre Pinclinaison long*tudimilc et latcralc des plateaux. (3) Un Paravane 
avec manometre differential pour mesurer Pouvcrturc vcrticale du filet; (4) un appariel pour mesurer l"angle d^attaque des plateaux. (5; Un 
dynamometre hydranlique pour mesurer la traction des bras reliant les plateaux au filet, ainsi que la tension des funes a bord du navire. 

L'autcur decrit ('evolution des appareils et donne ensuite certains resultats inlercssants obtenus par leur ernploi, par exemple, les 
rapports entre la longueur des funes, Pecartcment des plateaux, leur mclmaison et leur angle d'attaque. 

Des essais ont ete executes avec differents types de flotteurs sur la ralingue supericure, et Pon a constate que la hauteur de la ralingue 
etait de 1,20 m. sans flolteurs, de 1m 90 avec 10 flotteurs sphcriques, dc 2m 30 avec 5 flotteurs "freres-siamois", et de 2m 75 avec 10 " trawl- 
planes". 

Mediciones en las redes de arrastre con instruments submarines 
Kxtracto 

La Inspeccion de Pcsca dc los Paiscs Bajos ha ideado los siguicntes instrumcntos para registrar la manera como se comporta una 
red de arrastre: (1) HI medidor de separacion de las puertas dc arrastre para registrar la distancia que media entre los extremes postcriores de 
ellas o, cuando estas se encucntran unidas directamente a las bandas. la anchura de la boca de la red. (2) HI clinometro que mide la inclinacion 
de dichas puertas, tanto en sentido lateral como longitudinal. (3) El paravan con manometro dijerencial para determinar la altura de la boca 
de la red. (4) El medidor del angulo de ataque para registrar cl angulo de ataque de las peurtas de arrastre. (5) El dinamometro hidrdulico 
para cvaluar la tracci6n de las mulletas y de los cables de arrastre a bordo del barco. 

HI autor describe en el trabajo, muy bien ilustrado con fotografias y esquemas, la evoluci6n de los inst rumen tos y da a conocer 
algunos resultados intcresantes obtcnidos mediante su uso; por ejemplo, la relacibn entre la longitud de los cables de arrastre, la separacion 
dc las puertas, su inclinaci6n y angulo de ataque. Se hicieron pruebas con divcrsos tipos de flotadores distribuidos a lo largo de la relinga 
superior, encontrandosc que al usar ninguno la altura de 6sta Ilegaba a 1,2 m.. mientras que con 10 flotadores esfericos subia a 1, 9 m., con 
5 flotadores siameses ("Siamese-twin") a 2, 3 m. y con 10 "trawlplanes" a 2,75 m. 



FILMS taken by frogmen, showing trawls and 
seines in action under water, have enabled fisher- 
men for the first time to see the behaviour of 
their nets on the bottom and the reaction of the fish 
to the net. 

Although helpful, underwater filming does not solve 
all the problems. It is also necessary to take measurements 
of the gear in action. For this reason the Netherlands 
Inspection of Fisheries has, during the past four years, 
developed several underwater instruments to record the 
behaviour of the gear in tow. 

Extensive experiments have been made on board the 
Netherlands F.R.V. Antoni van Leeuwenhoek (fig. 1). 
These have led to many improvements in the instruments 
which, as they were designed for work in the Southern 



North Sea, only withstand pressures to a depth of 

lOO mp.trp.fi 



DESCRIPTION OF THE INSTRUMENTS 

The instruments can be read to an accuracy of 1 centi- 
metre, half a degree or 1 kilogram. 

1. A spread meter. This records the distance between 
the after ends of the otter boards. If the boards 
are attached to the wings directly (without legs) 
this corresponds with the horizontal opening of 
the net. 

2. A clinometer. This records the tilt of the otter 
board sideways as well as fore and aft. 



[225] 



MODERN FISHING GEAR OF THE WORLD 



j^P^^i^-iWfc'-:--.^ 

^;'";u'" .';;;':',' ' 



^.v^^ftfe'^'-iwlt" 



..m 




Ffc. /. The Netherlands F.R.V. Antoni van Leeuwenhoek. 

3. A net height meter. This records the vertical 
opening of the net (Headline or kite). 

4. An angle of attack meter. This records the angle 
of attack of the otter board. 

5. An hydraulic dynamometer. This records the pull 
in the legs between the otter board and the net 
or the pull on the warps on board ship. 

SPREAD METER 

The spread between the otter boards was first measured 
by reading the angle between two rods clipped on the 
warps. At the same time, a length of twine was attached 
to one of the otter boards, the other end being wound 
round a small barrel mounted on the other otter board. 
The barrel was pulled down by springs against two 
wooden brake cleats. Pull on the twine lifted the barrel 
from its brakes so that twine unreeled according to the 



spread of the otter boards and then braked again. In 
this way, the maximum spread could be measured. 

However, the average spread measured by these two 
methods differed by about 6 metres, so a much more 
accurate instrument had to be developed. 

First it was necessary to determine the curve in a steel 
wire of 3 mm. diameter and 12, 16, 20 and 24 metres 
length pulled through the water at speeds of 2, 3, 4 and 
5 knots, and carrying longitudinal loads of from to 
500 kg. Then graphs were drawn for each speed, giving 
the difference in lengths at certain loads between the 
curved wire and a straight line, viz. the actual distance 
between the otter boards. 

Accepting an inaccuracy of 1 per cent, and with an 
expected spread between the otter boards from 12 to 
16 metres, it was found necessary to have a pull of 11 
to 15 kg. on the wire when travelling at a speed of 3 knots. 

This pull is provided by trawl planes attached to the 
free end of the wire. Tests in the towing tank in Wagenin- 
gen showed that 3 trawlplanes on a 3 mm. wire produced 
a load of 16 kgs. at 3 knots. In practice, however, this 
pull was too much for the wire, which had to be renewed 
frequently because of kinks and flattening where it 
went over the guiding reels. So, only 2 trawlplanes, 
which exerted a load of about 10 kg., were used although 
this increased the error to 2 per cent, in the spread reading. 

At a speed of 5 knots, the pull of 2 trawlplanes is 
42*2 kgs. and for 1 trawlplane about 20 kg., which is 
double the amount that can be used for 3 mm. diameter 
wire. The new spread meter therefore cannot be used 
for speeds over 3 knots without renewing the wire after 
every haul or using a stronger wire and recalculating 
all the data. 

The spread meter works as follows: a 3 mm. diameter 
steel wire is fastened to the aft part of one otter board 
and passes over guiding reels through a hole in the aft 
part of the other otter board. As shown in fig. 2, the 
wire then passes (actually in two turns) over a wheel 
and over another set of guiding reels to the two trawl- 
planes (not in the figure). 









Fig. 2. The baseplate of the spread meter showing arrangement 
of wire and rolls. 




Fig. 3. The recording device of the spread meter. 



[226 



MEASURING TRAWL GEAR UNDER WATER 




/-"iff. 4. Clinometer, showing ai fangenwnt of pendulum and 
recording device. 

In towing, when the distance between the otter boards 
increases or decreases, the wheel turns one way or the 
other and so registers changes in the spread. 

A recording device is attached to the wheel as shown 
in figs. 3 and 5. 

The distance between the otter boards is measured 
before shooting and added to the distance read on the 
meter, the total being the spread I 2 per cent. 

CLINOMETER 

The clinometer mainly consists of a pendulum arm, free 
to swing in a vertical plane, and a clockwork paper 
recorder. Changes in the tilt of the otter board are marked 
by a stylus on the pendulum arm, which carries a weight 
that can be moved up or down to regulate the sensitivity. 
Oscillations are damped by attaching the pendulum to 
a horizontal spindle, which operates a piston rod in 



two air cylinders (fig. 4). Two vent screws regulate the 
escape of air in the cylinders. 

The apparatus is shown, together with the spread 
meter, in figs. 5 and 6, attached to the otter board in 
operation position to determine the sideways tilt of the 
otter board. By unscrewing the sole plates, it can be 
fixed in a position at right angles to measure the fore 
and aft tilt of the otter board. The range is 45 degrees. 

NET HEIGHT METER 

The height of the headline is established by using a 
differential manometer to measure the difference in 
hydrostatic pressure between the bottom of the net 
and the centre of the headline (fig. 7). 

A lank (fig. 8) is attached to the footrope. It has a 
hole at one end \\hile the other is connected to a plastic 
tube, with an inside diameter of 3 mm. The tube runs 
along the headline upwards to a paravane which has 
a buoyancy of 4 kg. and is towed by a steel wire attached 
to the centre of the headline. A second tank (an ordinary 
8 in. float with a hole at the bottom) is fastened to the 
middle of the headline, and is connected by a short 
plastic tube to the paravane. 

When the net is shot, the water enters and compresses 
the air in the tanks and in the plastic tubes. The sub- 
merged capacity of the tanks is such that they only 
half fill with sea water. 

The two plastic tubes inside the paravane arc connected 
with one pair of bellows each, welded to a steel plate, 
which moves out of its zero position if the pressure in 
one pair of bellows is more than in the other. A stylus 
records the movements. The paravane is shown in 
fig. 9, while fig. 10 shows it with the head off, disclosing 
the differential manometer and paper recorder. 

As this apparatus measures the difference between 
the water levels in the two tanks, only that difference 
can give rise to inaccurate readings. If excess seawater 
enters one tank by accident, the inaccuracy will not be 
more than 5 cm. if the tanks are lowered carefully, the 




6. 



Fig. 5. Spread meter (top) find clinometer (below) attached to 
the otter board. Without underwater casings. 



Fig. 6. Spread meter and clinometer ready for operation 



221} 



MODERN FISHING GEAR OF THE WORLD 



Differential Manomete 

< 

Rope for towing the Paravane *- ; 




Plaatic tube leading from the 
--er to thr preaaurr tank 
attached to the headlim 



t'laatlr tube loading from th- manomett 
to the pressure tank attached to the 
' _ groundrope 



f IVcsaure tank Attached to the tfr 



Fig. 7. Net height meter. Arrangement of the different pans at 
the net opening. 




maximum error, therefore, will not he more than 10 cm. 

The paravane is lowered at the same time as the head- 
line, with the towing wire and plastic tubes connected 
to both sides. When the paravane is afloat the veering wire 
is disconnected at a length of 4 metres, a small plastic 
float being attached to the end. This can be picked up 
easily when the net is hauled again. 

As the first paravane could be used only between 
depths of 15 and 30 metres, measuring a maximum 
height of 5 metres, another was developed on the same 
principles, designed to withstand an outside pressure 
of 10 atmospheres. 

A new type of differential manometer divided in two 
partitions by a large brass diaphragm on a rubber disc, 
has been used with this paravane. Movements are marked 
on a recording drum by a stylus mechanism. The paravane 
can be used at all depths up to 100 metres, measuring 
a maximum height of 10 metres. 

ANGLE OF ATTACK METER 

If a rod is attached to an otter board and suspended to 
move in horizontal and vertical directions, the free end 
sliding over the ground will adopt the towing direction 
of the otter board. 

This is the principle underlying the angle of attack 
meter. 

A steel tube, about 2 metres long, and weighted at 
the end with lead, is connected by a lever with a turning 



Fig- 8. Measuring tank fixed to the foot rope, showing the hole 
for entrance of pressure and the connection of the plastic tube. 



disc operating in a sole plate attached to the otter board. 
Fig. 11 shows the registration apparatus mounted 
on the sole plate. The complete instrument fixed to the 
otter board ready for operation is shown in fig. 12. 

DYNAMOMETER 

Tension in the warps varies considerably with the move- 
ment and change in direction of the ship, and with the 
movements of the otter boards over uneven ground. For 
measuring the pull on the warps and other parts of the 
gear, two types of dynamometers were tested. 

The principle of the first dynamometer is the variation 
in electrical resistance of a thin wire when elongated. 
Fig. 13 shows this tension dynamometer fixed between 
the bollard and the warps. The electronic tension meter 
on which the pull can be read in kg., is shown underneath 
the dynamometer. This apparatus proved to be much too 
sensitive for use. 

Measurements between the otter boards and the net 
were made by using a hydraulic dynamometer (fig. 14) 




Fig. 9. The paravane of the net height meter ready for operation. 



Fig. 10. Inside view of the paravane. 



228 



MEASURING TRAWL GEAR UNDER WATER 




Fig. 11. Angle of attack meter \ inside view. 

attached to the upper leg between the otter board and 
the wing of the net. This dynamometer, attached to a 
bracket mounted to the aft side of the otter board, 
consists of an oil cylinder, with piston rod and piston 
which compresses the oil in the cylinder. The cylinder 
is connected with the registration apparatus by a high 
pressure rubber tube. A plug regulates the sensitivity. 
The pressure, which is proportional to the pull, is 
measured by a spiral hollow tube moving a stylus, 
which is supported to prevent bad recording when the 
otter board bumps. The recorder is mounted in a vertical 
position so that ink can be used instead of a pencil, 
which proved to be too unyielding. 

The best results from the instruments mentioned are 
obtained when trawling over even ground and when the 
wind force is not more than 3 to 4. These conditions 
apply to even bigger ships than the Antoni van Leeu- 
wenhoek. 

RESULTS 

Instruments 1 to 4 have been used together, or in different 
combinations, in a number of experiments. The hydraulic 



Ftp. 12. Angle of attack meter attached to the otter hoard in 
working position. 

dynamometer has been used separately in more recent 
trials. 

The depth was noted during each haul and the ratio 
of the length of the warps to the depth was determined, 
while the distance travelled per haul over the ground was 
calculated to find out the strength of the tide. Wind and 
sea conditions were noted as well. 

A manila trawl, with a headline length of 20-8 m., a 
foot rope of 25 -2 m., and with 8 cm. meshes in the codend, 
was used. The dimensions of the otter boards (fig. 15) 
were 1-10 - 2- 10 m. (weight 209 kgs. each). The wings 
of the net were attached to the otter boards without legs, 
while 10 trawlplanes of 8in. diameter, 1 m. apart, were 
attached to the headline, 5 to each side of the middle. 
The upper tank, plastic tubes and towing wire of the 
paravane were fixed to the centre of the headline. 

Hauls were made always with the running tide and 
with a constant number of propeller revolutions, giving 
the ship a fishing speed of 1 -7 to 3 knots over the ground. 

Experiments took place from 5th May to 4th July 
1953, over smooth bottom between Scheveningen and 
Katwijk at a mean depth of 17 metres. Hauls lasted 




Fig. 13. Electronic dynamometer in action. 



Fig. 14. Hydraulic underwater dynamometer attached to the 
otter hoard in working position. 



[229] 



MODERN FISHING GEAR OF THE WORLD 



Tl 



Side view 



TILT 

Fig. 17 gives a clinometer record for one haul. The first 
line shows an outward tilt about 16-5 degrees when the 
otter board is hanging in the gallows. When lowering, 
the tilt is unsteady, but becomes steady after a short 
settling period. The otter boards take a more upright 
position as the warps are lengthened and finally tilt 
inwards and become unstable when the warps become 
too long. The average tilt with the different lengths of 
warp can be read on the right of the diagram, while on 
top the arrows give the periods of shooting and hauling. 
Conclusion: the otter boards will tilt from outwards 
to inwards, becoming more unstable, as the warps are 
lengthened. 



OJm 




Top view 



Fig. 15. Schema of the otter board used. 

one and a half hours, during which the warps were 
lengthened by veering about 7-5 fathoms every 15 
minutes. 

SPREAD 

A record of the spreadmeter is shown in fig. 16. For 
convenience the scale of the total spread has been given 
at the bottom of the diagram. The distance between 
the otler boards measured on board was 9-45 m. The 
zero-position of the stylus before lowering the otter 
boards is indicated by a thick short arrow. The recording 
is unsteady at first but becomes nearly constant as the 
gear settles on the bottom. As the warps are lengthened 
by about 7-5 fathoms, the spread increases. The periods 
of shooting and hauling are indicated with arrows on 
the left of the diagram. 

Conclusion: the spread will increase by lengthening 
the warp. 



HEIGHT OF THE NET 

Fig. 18 shows a record of the net height meter. The 
conspicuous peaks indicate that the height of the net is 
temporarily increased during the veering of the warps. 
The periods of shooting and hauling are shown by 
arrows. The large peaks are formed when the net hangs 
from the side of the ship. 

Conclusion: the height of the net decreases with 
increase in warp length. 

ANGLE OF ATTACK 

A record of the angle of attack meter is shown in fig. 19. 
During the periods of shooting and hauling, the position 
of the otter board is uncontrollable. The periods of 
veering of the warps are indicated on the left of the 
diagram. Even if the angle of attack of the otter boards 
for the different lengths of the warp arc rather variable, 
it is possible to read a reliable average, indicated on the 
left in degrees. 

Conclusion: by lengthening the warps, the angle of 
attack decreases. 

The recordings of the tilt, the height of the net and the 
angle of attack (figs. 1 7, 18 and 19) show great peaks when 
the warps are veered. 

It appeared that, during the veering of the warps, the 
otter boards tilted, on average, 23 degrees inwards, while 
the angle of attack diminished by 8 degrees and the height 
of the net increased by 35 cm. In fig. 20 the position of 




Fig. 16. A record of the spread meter. 



Fig. 17. A record of the clinometer. 



( 230 ] 



MEASURING TRAWL GEAR UNDERWATER 




Fig. 18. A record of the net height metei. 

the otter boards, drawn in dotted lines, indicate the 
situation during the veering of the warps, from which 
the conclusion can be made that there is more slack 
in the headline, which will be lifted by the floats. 

There are peaks also on the other side because of the 
sudden braking of the warps after veering, in which 
case the opposite action occurs, but, with gradual braking 
no peaks appear. 

INFLUENCE OF THE INSTRUMENTS ON THE 
GEAR 

The paravane has a buoyancy of 4 kg., equal to that 
of a spherical float of 8 in. diameter, while the clinometer 
has a buoyancy of 0-8 kg. The new paravane was given 
a buoyancy of 8 kg. It may be accepted that these 
instruments will not affect the gear in any way. 

Since the spread meter, the angle of attack meter and 
the clinometer are mounted on the aft side of the otter 
boards where, as the film "Trawls in Action" shows, 
great whirls are created, the water resistance of these 
instruments is not likely to affect the action of the otter 
boards. But the angle of attack meter weighs 9 kg. and 
the spread meter 5 kg. At a speed of 3 knots, 2 trawl- 
planes pull with a force of 10 kg. on the wire of the spread 
meter. It had, therefore, to be determined what influence 
these instruments had on the gear, separately and in 
combination. 

The instruments were distributed over both otter 
boards (see Table I) in 9 series of hauls. 

Before starting // and /, the warps had to be renewed 
and shortened and since differences in lengths of warps 





angle of attack 




opening height of the net 

Normal position of net and otter boards 
Maximal change opposition when veering 
the warps 

Fin. 20. Schematic drawing, explaining the behaviour of the otter 
boards and the net opening when veering the warps. 

produce different readings, series h was made a repetition 
of series </, so that // and i could be compared. 

The net height meter and the clinometer were used 
during all these hauls. A comparison of the data obtained 
shows that the instruments exerted no influence whatso- 
ever on the operations of the otter boards. Even the 
strain on the wire of the spread meter had no influence 
on the angle of attack and the tilt of the otter boards. 

However, the height of the net became 2 20 m. when 
the spread meter was used, compared with 2*12 without 
it (see Table IV). This corresponds to a decrease in 
spread of about 52 cm. (calculated from Table II) on 
an average spread of 12-89 (see Table IV), an error of 
nearly 4 per cent., which must be added to the measured 
spread. As already mentioned, by using 2 trawlplanes, 
2 per cent, has to be subtracted for the bend in the wire, 
so the actual distance between the aft parts of the otter 
boards will be the measured distance plus 2 per cent., 
in this case 12-89 m. ; 2 per cent. 13-I5m. 

INFLUENCE OF THE LENGTHS OF THE WARPS 

After determining the influence of the instruments on 
the gear, the average was taken of the results obtained 



Fig. 19. A record of the angle of attack meter. 



TABU I 


Sptead A Icier 


Attack- Angle 


Clinometer 


\urnbei 


Series on 


metei on' 


on 


of han/.\ 


a. 


Aft ot lei 


hi on! otter 






board 


hoard, sidewavs 


7 


b front oiler 


Aft oiler 


Front otter 




hoard 


board 


board, sideways 


^ 


c. 


- 


Aft otter hoard. 








sideways 


d 


d. 


Aft oitei 


Aft otter hoard. 






hoard 


sideways 


9 


c. Front otter 


Aft otter 


Aft otter hoard. 




hoard 


hoard 


sideways 


S 


f . 




Front otte- 








hoard, fore and 








aft 


*> 


g. 




Aft otter hoard. 








fore and aft 


^ 


h. 


Aft otter 


Aft otter hoard. 






noard 


sideways 


8 


i. 


Front otter 


Front otter 






board 


sideways 


9 



[231 



MODERN FISHING GEAR OF THE WORLD 



Length 
of the 
Warps 
in m. 



Depth 
in m. 



Ratio 

between 

Length 

of Warps 

and 

Depth 



Angle 

of 
Attack 



TABLE II 



Tilt out- 
wards (o) 
or in- 
wards (/') 



Tilt 
fore 

(/) 

or aft 

(a) 



Spread 
in. m. 



Height 

of Net 

without 

Spread 

Meter 

in m. 



Height 
of Net 
with 
Spread 
Meter 
in m. 



67-21 

81-05 

94-85 

108-67 

122-42 

136-17 



17-04 
17-03 
16-97 
17-01 
16-96 
16-87 



3,9 
4,8 
5,6 
6,4 
7,2 
8, 1 



35-2' 
32-7" 
28-4' 
25 -0 J 
22-2' 
20 T 



12 -5 (o) 
7-0 (o) 
I -0 (o) 
4-4>(i) 
8-9 (i) 

12-5 (i) 



TABLL III 



3-4 (f) 
2-5 (f) 
l-7"(f) 
0-6(f) 
0-3 (a) 
0-5 (a) 



12-26 
12-53 
12-83 
13-14 
13-34 
13-40 



2-19 
2-17 
2-13 
2-08 
2-02 
1-97 



31 
26 
21 
15 
10 



2-05 



58-50 


17-10 


3,4 


37-0 


5-9 J (o) 


2-26 


72-00 


17-00 


4,2 


34-3 


9-0 (o) 


2-19 


85-50 


16-95 


5,0 


30-9 LJ 


3 -3 Mo) - 


2-16 


99-00 


16-90 


5,9 


28-6 IJ 


1-7 (i) 


2-12 


112-50 


17 10 


6,6 


26-2 


5-3 rj (i) 


2-10 


126-00 


17-30 


7,3 


24-9 


8-8(i) 


2-08 



from series a to g, and the results are given in Table II, 
while Table III gives the averages of the hauls in h and i. 
The following conclusions can be drawn from Tables 
II and III. By lengthening of the warps: 

1. the angle of attack decreases; 

2. the otter board tilts from outward to inward; 

3. the otter board tilts from forward to aftward; 

4. the spread increases; 

5. the height of the net decreases. 

We can also say that, if the depth decreases with a 
fixed length of warp, the same will happen as mentioned 
above. If the depth increases, the opposite will occur. 

RATIO BETWEEN WARP LENGTH AND DEPTH 

The effective spreading surface of the otter board is 
greatest when it takes up a position perpendicular to 
the bottom, i.e. when the sideways tilt of the otter board 
is zero. 

Interpolating the data in Table II and III for a tilt 
of degrees, the result is given in Table IV. 

The small differences between the sets of values are 
caused by a smaller ratio between the lengths of the 
warps and the depth, by small errors in the readings due 
to differences in current, wind force, swell and slight 
changes in the depth, and by small instrument errors. 

However, the results are sufficiently accurate to show 
that, while fishing at a depth of 17 metres with an upright 



TABLE IV 



Length 
ofthe 



Ratio 

between 

Length 



Height Height 

Anole Of Net of Net 

Ang - Spread without with 



From ofthe Depth Length J Spread without with 

TABLE Warps in m. of Warps A ?*t, in m. Spread Spread 

inm. and AnacK Meter Meter 

Depth in m. in m. 



II 
III 



96-9 

94-7 



16-98 
16-92 



5,7 
5,6 



27-8 
29-4 



12-89 



2-12 
2-13 



2-20 



otter board, the angle of attack is about 28-5 degrees 
the height of the net just over 2 metres and the spread 
12-89 m. -} 2 per cent. -= 13-15 metres. For an upright 
position of the otter board the length of the warps must 
be about 5-1/2 times the depth. 

INFLUENCE OF LEGS 

Two additional series of hauls have been carried out 
with the same gear but with a fixed length of the warps. 

In the first 7 hauls, legs of 3-60 m. length were used 
between the otter boards and the net; in the second 
series of 4 hauls the wings of the net were coupled to 
the otter boards directly. The tilt of the otter boards 
was not determined. 

The average readings for these series are given in 
Table V. 

These results are represented diagrammatically in 
fig. 21 (gear with the legs shown by dotted lines). 

In fishing with legs, the angle of attack is decreased 
and the spread of the otter boards is increased, but not 
the spread of the net, so there is more slack in the head- 
line, and the height of the net is increased by 41 cm. 

INFLUENCE OF DIFFERENT TYPES OF FLOATS 
ON THE OPENING HEIGHT 

With the same gear as mentioned above, using 3-70 m. 
legs between the otter boards and the net, the height of 
the net without any floats was 1 -20 m., or 10 cm. more 



TABLE V 



as 



Measured Height 

Spread of Net 

In m. in m. 



With 
Without 


95-45 
95-45 


15-2 
16-2 


6,3 
5,9 


26-0 
31-5 


14-54 
13-43 


2-76 
2-35 



232] 



MEASURING TRAWL GEAR UNDER WATER 




Legs 



Fig. 21. Schematic drawing showing the influence oj short legs 
on the net opening. 

than the height of the otter board. With 4 to 6 spherical 
8 in. floats, the increase in height was not more than 30 
cm., while with 8 floats the lift was considerably more, 
being about 55 cm. (total height 1 -75 m.). A kite (with 
two small glass floats mounted on it) was used with the 8 
floats, but it provided no increase in height. 

Comparative trials were carried out with 10 spherical 
8 in. floats, 5 Phillip's Siamese-twin floats and 10 Phillip's 
trawlplanes, all having a diameter of 8 in. Strips of about 





Fig. 23. Record of the underwater dynamometer between otter 
board and upper /or, in a calm sea. The pull decreases due to 
the net bing choked by a big catch of colony-building Hydrozoa. 

7 cm. width were out off the sides of the half circular 
plates on the Siamese-twins, giving them a winglike 
shape, which reduced resistance and increased buoyancy. 
The results were: 



10 spherical floats 

5 Siamese-twins 

10 trawlplanes . 



height of headline 1 -90 m. 
height of headline 2-30 m. 
height of headline 2-75 m. 



Fig. 22. Record of the underwater dynamometer between otter 
board and upper leg, rough sea. 



PULL ON THE LEGS AND AMOUNT OF CATCH 

The hydraulic dynamometer has only been used sub- 
merged between the otter boards and the net, and only 
a limited number of hauls have been made. In fig. 22 a 
diagram is given showing a tension of about 180 kg. in 
the upper leg. During this haul the sea was rather rough, 
with a wind force 4. 

During another haul with very calm weather (fig. 23) 
the pull decreased from 250 to 1 30 kg. The same happened 
in 6 consecutive hauls although in earlier and later 
trials a fairly constant tension was recorded. The reason 
was fo