7. DEPARTMENT OF TRANSPORTATION Sheth ata es COAST GUARD { COAST GUARD OCEANOGRAPHIC UNIT —-

Taut-Line Instrumented Arrays\ Used by the

Coast Guard Oceanographic Unit | During 1970-1971

\

‘Christopher L. Vais Thomas C. Wolford \ ‘Alan D. Rosebrook Robert Erwin Ettle /

ia we RECEIVED TECHNICAL REPORT 72-1 >| / | Hee gh OCTOBER 1972

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U.S. COAST GUARD TECHNICAL REPORT

The reports in this series are given limited distribution within agencies, universities, and institutions engaging in cooperative projects with the U.S. Coast Guard. Therefore, citing of this report should be in accordance with the accepted bibliographic practice of following the reference with the phrase UNPUBLISHED MANUSCRIPT. Reproduction of this report in whole or in part is permitted for any purpose of the U.S. government.

TAUT-LINE INSTRUMENTED ARRAYS USED BY THE COAST GUARD OCEANOGRAPHIC UNIT DURING 1970-1971

BY

Christopher L. Vais

Alan D. Rosebrook

Thomas C. Wolford Robert E. Ettle

OCTOBER 1972

U.S. COAST GUARD OCEANOGRAPHIC UNIT Washington, D.C.

ABSTRACT

The Coast Guard Oceanographic Unit (CGOU) used taut-line instru- mented arrays to investigate the current regime near the Grand Banks of Newfoundland. The instrumented arrays used were patterned after a design developed and used by Woods Hole Oceanographic Institution. G. B. Shick’s Circular Arc Approximation was used to compute the tension in the mooring line. The arrays were set and recovered by Coast Guard personnel under the supervision of CGOU field parties.

Editor’s note: Reference to a product or comment with respect to it in this publication does not indicate, or permit any person to hold out by re- publication in whole, or in part or otherwise, that the product has been endorsed, authorized, or approved by the Coast Guard.

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INTRODUCTION

Since the early 1960’s, the International Ice Patrol Research Section (IIPRS) of the U.S. Coast Guard Oceanographic Unit has used taut- line instrumented arrays to collect current veloc- ity data near the Grand Banks of Newfoundland and the Labrador continental shelf. Only the 1970-71 projects will be discussed in this report.

The taut-line instrumented arrays used by the IIPRS (Figure 1) were patterned after a de- sign developed and used successfully by Woods Hole Oceanographic Institution (Berteaux, 1968; Berteaux and Walden, 1969). The arrays con- sisted of a surface float attached to a plaited nylon mooring line with current meters attached at various positions along its length. The com- plete mooring was secured to an anchor with a release device (acoustic or time) which freed the array from the anchor when triggered.

The direct current observations collected are of interest to the Ice Patrol Research Section:

approximation.

may be used for boundary conditions in a mathematical circulation model of the region.

® To collect direct current measurements to be used in iceberg drift models.

The 1970 arrays were set off the coast of Labrador north of the Strait of Belle Isle in positions 54°30’N, 54°32’W and 54°29’N, 54°- 30’W. Both arrays were recovered successfully two weeks after they were set. In 1971, two arrays were set on the southeastern edge of the Grand Banks at positions 45°02’N, 48°55’W and 46°40’N, 47°24’W . Two weeks later, one array was recovered; the other array was apparently struck by a fishing trawl which carried away the surface float, allowing the remaining section of the array to sink. When the CGC EVERGREEN was within about two miles of the location where the buoy had been set, the acoustic release device responded when interrogated. Extensive drag- ging operations failed to recover the release or any other part of the array. (Note in proof. Two of the current meters and assorted lengths of line from the southern array were found by a Newfoundland trawler and returned to CGOU in February 1973. The acoustic release was not recovered. )

FIXED BRIDLE SLING RING AND SHACKLES

10 FEET %°" CHAIN

iO

FIXED BRIDLE SLING RING AND SHACKLES

10 FEET %°" CHAIN

@ © ——@ © (1) 9/16"* NYLON LINE a

(2) 5/8°* NYLON LINE

a ) SHACKLE mE (4) CURRENT METER a (GS) SHACKLES AND SLING RING (6) TIME RELEASE ®

7) ACOUSTIC RELEASE

ne) 99 FEET %’’ AND 1%" CHAIN STIMSON ANCHOR (4000LBS IN AIR)

FicurE 1. Single point taut-line instrumented arrays used in 1970-71.

2

BUOY ARRAY DESIGN

All of the taut-line arrays set by the IIPRS in 1970 and 1971 used surface flotation which was on hand at CGOU. The floats used were Geodyne Model A-92 toroidal instrument buoys (Figure 2). A Geodyne Model A-93 tripod tower on each buoy supported a pair of wire mesh, life- boat radar reflectors and a Geodyne Model 180 Xenon light. A rigid tripod bridle, Geodyne Model B-301, attached to the bottom of the to- roid, supported the subsurface portion of the array.

Surface buoy, Geodyne Model A-92.

FIGURE 2.

The use of surface flotation introduces major problems which can effect the survivability and reliability of taut-line arrays.

® Surface floats are susceptible to collisions with ships, fishing trawlers and seiners, ice- bergs, and, in some locations, sea ice.

If the water depth were not accurately known and the array were set in water exceeding the design depth, heavy seas, large tidal rises, or strong currents could cause the anchor to be lifted off the bottom since the reserve buoyancy of the surface float exceeded the weight of the anchor. If the anchor were carried into deep enough water, the entire array would be free to drift and could be lost. If however, the array were set in too shallow a depth of water, the mooring line could go slack and kink, or the current meters could be inclined in excess of 15° from the vertical by the current, making the readings unreliable.

To determine water depth accurately at the mooring site, a Salinity/Temperature/Depth Sys- tem (STD) cast was taken and the sound velocity was computed at various depths. A weighted mean sound velocity, R, was then calculated. The depth at the mooring site, as indicated by the vessel’s fathometer, was noted. The time (T) required for the fathometer signal to reach bot- tom and return was determined from the re- lationship :

RT Ba (1)

where: Z=fathometer indicated depth, ft.

R=4800 ft/sec (sound velocity for which the fathometer was calibrated )

T=time, sec A more accurate value of Z was then calculated by substituting the values of R and T into equation

(i),

Mooring Line Tension Calculations

In 1971, the taut-line arrays were designed to satisfy the following requirements.

® Mooring line tension must not exceed 15% of the breaking strength of the line.

BUOY

ur 1, sin ay = 0,

Forces at the Buoy

ANCHOR

Forces at the Anchor

Figure 3. Circular Arc Approximation (Berteaux, 1968).

® The arrays must be able to withstand at ® The maximum current will be 2.48 ft/sec least 30 feet of vertical movement to compen- and can be considered constant from sea sur- sate for tidal excursions and waves. face to bottom.

® Current meters should not be allowed to in- cline more than 15° from the vertical.

® Wind drag will be considered negligible.

The total tension on the mooring line was cal- culated using the Cireular Are Approximation (G. B. Shick, 1964). The shape of the mooring line was assumed to be a circular arc (Figure 3). The only force considered was the form drag on the array. The form drag (F) acting on each component of the taut-line array was calculated from:

F=0.5pv?LDC, (2) where: F=pressure drag, lbs p—density of seawater, slugs/ft* v—current velocity, ft/sec L=length of component, ft D=diameter of component, ft Ca=drag coefficient

The uncertainties in determining the drag force arose from our lack of knowledge about the ac- tual current profile and the drag coefficient.

The current velocity was assumed to be con- stant from the ocean surface to the bottom. This assumption was made to facilitate the cal- culation of F and to introduce a “worst case” situation. In 1970, a current velocity of 1.68 ft/sec (0.51 m/sec) was used; in 1971 the value was increased to 2.48 ft/sec (0.76 m/sec).

Selection of the drag coefficient (C,) was based on the Reynolds Number (Re) and the shape of the component. Reynolds Number, the ratio of inertial forces to viscous forces, is defined as:

Vi t evs (3)

Re=— = v B where: p=density of fluid, slugs/ft*

V= velocity of flow, ft/sec w=coefficient of viscosity, lb-sec/ft? v=kinematic viscosity, ft?/sec «= characteristic length, ft

A value of Re was calculated, using equation 38,

for each component in the array. Values of Re ranged from 3 X 10? to5 10%. The calculated value of Re was used as the entering argument for determining C, from a graph of Re versus Cy (Bretschneider, 1966). The drag coefficient for a right circular cylinder ranged from 0.90 to 1.20.

A Ca equal to 1.80 was used in the final calcula- tions for the current meters, release device, and the nylon line to allow an extra safety factor and to compensate for such factors as strumming of the mooring line. Strumming occurs when a cylinder is free to vibrate laterally under the effect of alternating lift forces generated by vor- tex shedding. Strumming increases turbulent flow behind the mooring line, resulting in in- creased drag. Since no graph of Re vs. Cy was available for chain, a Cy equal to 2.0 was selected based on a value used by Woods Hole Oceano- graphic Institution.

The equivalent spring constant (IX) was cal- culated for each size nylon line considered for use in the array. K was calculated from the equation :

K= T.7Ti (4) @,X— 1X where: K=spring constant, Ibs/ft T.&T,=tension, lbs e.&e, =percent elongation x=unstretched length, ft (x + per- cent initial elongation times x = water depth)

The values of T and e were taken from first load- ing curves for line similar to that actually used in the construction of the arrays (Figure 4). The expected working range was between 5% and 15% of the average breaking strength of the nylon line. In 1971, the values of K calculated were ® 90 lbs/ft for %6 inch line at the shallowest water depth (490 ft). @ 229 lbs/ft for 5¢ inch line at the shallowest water depth (490 ft). ® 40 lbs/ft for 5% inch and %c inch line at the deepest water depth (870 ft).

The total tension (T) in the mooring line was then computed using the Circular Are Approx- imation. A value of T was assumed and the angles a, and a, were computed:

D,

yD (5)

where a,=surface angle of inclination D,=surface buoy drag, lbs T=assumed tension, Ibs

a,=are sin

and

a= are sin

1D? 7 (6)

% OF BREAKING STRENGTH

TENSION (Pounds)

2400 PEAK LOAD 2000 1600 1200 Expected Working 800 400 0

0 5 10 Ge) Me a 9B 30

TENSION (Pounds) 3120

2600 5/8 INCH PLAITED NYLON:

BREAKING STRENGTH 10,400 LBS

PEAK LOAD © 9080 LBS 2080

Expected Working 1040

0 5 10 15° 20 °2 25 30 % ELONGATION

Ficure 4. First loading curve for % and % inch plaited nylon (Berteaux and Walden, 1969).

6

where a,=bottom angle of inclination D,=total subsurface drag, lbs T=assumed tension, lbs

Next the are radius was computed :

Zeal R= =, (7) R=are radius, ft Z=water depth, ft T=assumed tension, lbs D,=total subsurface drag, lbs

D,=surface buoy drag, lbs

After solving for R, the are length was calculated : S=R (a:—a;) (8) where S=arc length, ft R=are radius, ft a,—=bottom angle of inclination a,=surface angle of inclination

Finally a value for T was calculated from: T=K(S—Z)+T> (9) where K=equivalent spring constant, lbs/ft S=arc length, ft Z=water depth, ft T,= initial tension, lbs

The calculated value of T and the assumed value of T were compared, and if they were not in agreement, a new value of T was assumed and the calculation was repeated. The iterative proc-

ess was continued until the assumed and calcu- lated values of T agreed within a predetermined limit.

After the maximum tension in the mooring had been determined, the minimum underwater weight of the anchor was determined using the equation :

W=T.+ (10)

0.6

where 0.6=assumed coefficient of friction of anchor on a mud bottom

T,=vertical tension, T (cos a2), lbs Tp=horizontal tension, T (sin a,), lbs W=anchor weight, lbs

The anchors used in 1970 were single concrete blocks (5400 Ibs) with 10 feet of 34 inch buoy chain attached above each block. In 1971, Stim- son anchors (4000 lbs) with 55 feet of 34 and 14% inch chain were used. Portions of the chain could be lifted off the bottom when the array was subjected to severe storms or excessive tides, thereby increasing the length of the array and decreasing the maximum tension which would have resulted if simple anchors had been used. Thus, the possibility of failure of the array is decreased.

A Dietzgen 7410-PA Programmable Calcu- lator was used for all computations. The pro- grams used are reproduced in Appendixes 1 and 2.

CONSTRUCTION AND TESTING

Plaited nylon line was selected for use in the 1970-71 arrays because of its great strength and elasticity, as well as for its ability to stretch and then return to its original length with no loss in strength (Figures 5-6). Asa result of its elasticity, nylon is able to absorb the large amounts of energy present during launching and during severe conditions such as storm waves or strong currents (Figure 7). Plaited nylon also resists twisting and kinking, thus eliminating the need for swivels in the mooring line.

When placed under an initial load, new nylon will be permanently elongated by approximately 10% (Figure 4); thus each section of nylon line in an array was cut shorter than its designed length. During launching, the new nylon line was placed under tension by the falling anchor and permanently elongated by approximately 10%.

Each piece of nylon line was terminated at both ends with a 3 or 4 tuck eye splice whipped with nylon line or black plastic tape (nylon whipping proved superior to the plastic tape). A steel thimble was used in each eye splice to prevent the nylon line from chafing. The nylon line and eye splices were tested by suspending the anchor from one section.

Hardware items such as shackles and sling rings were selected so that the ultimate strength of any part was at least five times greater than the maximum tension the array was designed to withstand. Safety marine shackles, locked with cotter pins, were used to join sections to- gether. To reduce corrosion, the cotter pins were only slightly bent after insertion.

In 1970, two Geodyne Model 102 photo- graphically recording current meters were tested by operating them in a darkroom with the pres- sure cases removed and a test strip of film in the magazine. After it was determined that the meters were functioning and sequencing prop- erly, the meters were reloaded with film and the pressure cases were replaced.

Two Geodyne Model 850 magnetic tape re- cording current meters were also used in 1970. Four 850 current meters were used in 1971. A characteristic failure of these instruments is for the tape to wind around the capstan drive and stop the recorder. Each of our recorders was carefully tested to insure that the capstan drive functioned properly. Then the current meters were run in the lab for several days with test tapes in the recorders to determine if the tapes advanced properly. Magna-See fluid was used to insure that data were being recorded on the tape. A new piece of test equipment manufac- tured by Geodyne enabled the Instrument Sec- tion to give each current meter a comprehensive checkout before it left the lab in 1971. After testing, each meter had a new battery installed. Each battery was checked by placing it under a 100 ohm load and measuring the voltage prior to installation. Before each tape cartridge was in- stalled, it was erased to clear it of any noise which might later interfere with computer proc- essing of the recorded data. Several desiccant bags were placed into each current meter before it was sealed .

The “O” rings at the top and bottom of the case were removed and replaced with properly greased new ones before the pressure case was placed on the current meter. Care must be taken when placing the pressure case on the current meter to insure that the “O” rings are not pinched or improperly seated, or the meter will flood. Placement of the top “O” ring is especially critical. Once the pressure case was in place, the tie rods were torqued to 10 ft-lbs. The cur- rent meters were then pressure tested to 200 meters by the National Oceanographic Instru- mentation Center. In 1970, the current meters were tested by suspending them in the Anacostia River just below the surface for about 3 hours. In 1971, one of the current meters flooded as a result of an improperly installed top “O” ring which had become pinched between the cap and

the tube. The electronic components were ex- tensively damaged by the water-battery electro- lyte mixture and the pressure. After the current TIME

9.0 years

1.8 years

130 days

POLYETHYLENE 26

days

125 hours

25 hours

5.0

hours

1.0 hours

min.

0 10 20 30

meters passed the pressure test, a final check was made by activating the meters and listening for sequencing sounds with a stethoscope.

POLYESTER

MANILA

40 50 60 70

LOAD AS A PERCENT OF ULTIMATE TENSILE STRENGTH

Figure 5.

9

Comparison of rope strength (Written communication from Columbian Rope Company).

LOAD AS PERCENT OF AVERAGE BREAKING STRENGTH

50

40

MANILA

30

20

DACRON

10

15 20 25

PERCENT ELONGATION

FIGURE 6.

Typical elongation in various ropes after first loading to 50% of average breaking strength (Written

communication from Columbian Rope Company).

The Model A-393 and 855 Geodyne time re- leases used in 1970 were checked for proper opera- tion at room temperature in the laboratory on CGC EVERGREEN. They were then operated in the ship’s reefer to simulate expected water temperature (~0.0°C). One of the releases was test fired on deck.

AMF Model 242 acoustic releases were used by IITPRS in 1971. Each release was completely

10

tested prior to use in accordance with the pro- cedures in the operation manual. Before use, both acoustic releases were given an air acoustic test at CGOU and again on the EVERGREEN immediately before deployment.

The arrays were assembled on the buoy deck of EVERGREEN in accordance with a mooring order established prior to the cruise. The moor- ing order listed each component as it would ap-

LOAD-PERCENT OF BREAKING STRENGTH

MANILA

DACRON

POLYPROPYLENE

Wote-line used in these tests was subjected to a load of 50% of tensile strength before testing.

2000 4000

6000 8000 10,000

ABSORBING ENERGY OF VARIOUS TYPES OF LINE(FT-LB PER LB OF LINE?)

FIGURE 7.

Impact resistance or energy absorption properties of line (Written communication from

Columbian Rope Company).

pear in the actual array. A check-off list was completed for each instrument in the array to insure that it was ready to be set. A single inner tube was lashed to each instrument in the array to provide flotation while the array was being set and recovered. The lines used to secure

11

the flotation to the instrument were passed be- tween the tie rods and the pressure case to pre- vent the inner tube from slipping off as it was compressed by water pressure (Figure 8). After a final check to make sure that everything was assembled properly, the array was neatly laid

Table 1. Comparison of taut-line array components, 1970 and 1971.

BUOY #1 BUOY #2 BUOY #4

54°30'N 54° 29'N 45°02'N 46°40'N 54°32'W 54°30'W 48°55'W 47°24'W

712 ft 712 ft 672 £t 21 July 1970 | 21 July 1970 | 11 May 1971 12 May 1971 i, Rae SO) A Avatee leno 25 May 1971

Flotation Geodyne Model A-92 toroidal fiberglass buoy, 4300 lbs net Buoy buoyancy Tripod Tower Geodyne Model A-93

Rigid Tripod Geodyne Model B-301 Bridle Buoy Light Geodyne Model 180 Xenon

Nylon Line Columbian Rope Company P1li-moot Columbian Rope Company Pli-moor 9/16", breaking strength 5/8", breaking strength 10400 lts 8000 lbs

Sling Rings Crosby Laughlin Inc. Crosby Laughlin Inc.

Pear shaped 5/8" Pear shaped 7/8" S.W.L. 4200 lbs S.W.L. 8300 1bs

Safety Marine

Shackle

Position

1/2" S.W.L. 2900 lbs

Boston & Lockport Inc. 5/8" S.W.L. 4400 lbs 1" S.W.L. 10,000 lbs

Boston & Lockport Inc. 5/8" S.W.L.* 4200 lbs

Geodyne 850 Magnetic tape Recording

Geodyne 102 Photographic Recording

Current Meters

Releasing Geodyne A-393 | Geodyne 855 AMF 242 AMF 242 Device Time release Time release Acoustic re- Acoustic release lease and and pinger

pinger

Chain | 3/4" Buoy 3/4" Buoy 3/4" Buoy 3/4" Buoy Proof load Proof load Proof load Proof load 16000 lbs 16000 lbs 16000 lbs 16000 lbs 1 1/4" Anchor }| 1 1/4" Anchor P.L. 45500 lbs} P.L. 45500 lbs

Stimson 4000 lbs

Concrete block 5400 lbs

ere

* Safe Working Load

12

Ficure 8. Current meter with inner tube flotation eollar attached just prior to launching.

out and secured on the buoy deck. The current meters were turned on, and the safety lanyards were removed from the release devices.

Table 1 is a comparison of the components used on the 1970-71 arrays.

Setting the Array

Just prior to launching the array, the EVER- GREEN conducted a bathymetric survey of the mooring site. A suitable site was chosen and marked with a reference buoy. The two prime factors considered in site selection were water depth and a relatively flat bottom contour. The reference buoy was identical to the surface float used with parachute drogues deployed by IIPRS

The

Ficure 9. Surface buoy being swung over the side. instruments, line, and anchors are layed out on the buoy deck of the USCGC EVERGREEN.

13

(Wolford, 1966). They were moored with poly- propylene line and anchored with approximately 50 pounds of chain.

To set the array, the surface float was swung over the side and placed in the water (Figure 9). Then as the EVERGREEN backed down slowly, the line and instruments were payed out by hand (Figure 10). A small amount of stern-

Ficure 10.

Instrument and line being payed over the side as the ship backs down.

way on the ship kept the mooring line under enough tension to prevent kinking while the anchor was suspended in the port chain stopper. When the EVERGREEN was in position, the anchor was released from the chain stopper.

When the anchor reached the bottom, the acous- tic release was interrogated to determine if it was still functioning properly. The surface float and the reference buoy were watched for about three hours to determine if there was any rela- tive motion between them which would have in- dicated that either the reference marker or the array was dragging anchor. During this time, the position of the mooring site was determined using the best methods available. In 1970, LORAN A and C were used, while in 1971 NAVSAT fixes were also available.

Recovering the Array

In 1970, recovery operations had to be sched- uled when the time release was set to fire. This prevented rescheduling recovery if the weather was adverse or other operations (SAR) pre- vented being on station when the release fired. In 1971, the use of acoustic releases permitted

Figure 11. Surface float lifted onto the buoy deck.

recovery of the array when EVERGREEN was ready. During interrogation of the acoustic re- lease, it was necessary to turn off the ship’s fathometer (UQN-4) so that the fathometer signal would not be received by the release re- ceiver and mask the pinger signal.

When the EVERGREEN was in position near the surface float, the acoustic release was fired, thereby freeing the array from the anchor. The surface float was then lifted onto the buoy deck with the whip, and the chain below the fixed bridle was secured in the chain stopper (Figure 11). The chain below the bridle was then cut with an acetylene torch (Figure 12), and the buoy was secured on deck. The remaining chain was brought aboard with the boom, and the remainder of the array was pulled in by hand (Figure 13). When the entire array was on deck, it was disassembled. The current meters were secured, and all instruments were rinsed in fresh water and stowed.

14

Kicure 12. Chain being cut from the rigid bridle.

Figure 13. Line being pulled in by hand.

DRAGGING OPERATIONS

An attempt was made to recover the two cur- rent meters and the acoustic release which were lost in 1971 and thought to be lying in 108 fathoms of water in the vicinity of 45°02’N and 48°56’W. Dragging operations were conducted with a rig which consisted of 20 feet of 14 inch chain followed by 6 feet of % inch chain. Two 15 pound heat treated marine grapnels and one 10 pound galvanized marine grapnel were shackled to the chain as shown in Figure 14. The 15 pound grapnels are a standard Coast Guard supply item, and their performance was satisfactory during the dragging operations. The 10 pound galvanized grapnels were purchased from the Atlantic Marine Exchange, Boston, Mass. They were too light for the type dragging being done and were not considered satisfactory. The rig was shackled to a 5 ton Miller D-5 swivel which was then shackled to the end of

15

the STD cable. The STD cable was terminated with a Preformed Line Products Company eye grip clamped to the cable with three cable clamps for additional holding power. <A 38 foot length of 7% inch chain trailing the bottom grap- nel usually prevented the grapnels from fouling the chain when dragging downslope.

A marker buoy was set and served as a refer- ence point for navigation during the operation. Dragging runs began by lowering the grapnels until they were just off the bottom. EVER- GREEN then got underway as more wire was let out (approximately 420 meters total). The vessel maintained a speed of 1-2 knots on a heading that set the ship away from the cable and kept it clear of the serews. <A total of 109 dragging runs was made both parallel and perpendicular to the bottom contours; however, none of the missing equipment was recovered.

1/4"" STD cable

MILLER D-5 swivel

1/2"’ chain

151b marine grapnels

7/8'’ chain

101b marine grapnels

Figure 14. Bottom drag rig used for dragging operations on the Grand Banks during June 1971.

16

RECOMMENDATIONS

The following test procedures are recommended to minimize damage during pressure tests if a current meter should flood.

® Limit the test to 30 meters instead of 200

meters.

® Have experienced personnel standing by to remove and disassemble the meter if there is any indication of flooding.

® Keep the meter upright to prevent additional damage from water or battery electrolyte shorting energized circuits.

The use of subsurface flotation is recommended. While subsurface flotation is generally more ex- pensive, an array using subsurface flotation is

® As reliable as an array using surface flota-

tion.

® Less susceptible to theft or collision.

® Easier to launch because lighter anchors can be used.

It is recommended that sufficient back-up flo- tation be used to insure recovery of any portion of the array remaining if part of the array should be damaged. Corning 16 inch glass spheres, which can be attached anywhere in the array, have been used successfully by Woods Hole as secondary flotation. Two releases attached in parallel would prevent the loss of an array if a single release failed to operate. A long tag line strong enough to lift the anchor would aid the recovery ship if the releases failed and dragging operations were required.

REFERENCES

Berteaux, H. O. (1968) Introduction to the statics of single point moored systems. Woods Hole Oceano- graphic Institution Technical Memorandum No. 11-68, May 1968, (Unpublished manuscript), 52 pp.

Berteaux, H. O. and R. G. Walden (1969) Analysis and experimental evaluation of single point moored buoy systems. Woods Hole Oceanographic Institution Reference No. 69-39, May 1969, (Unpublished manu- script), 79 pp.

Bretschneider, C. L. (1966) Overwater wind and wind forces. In Handbook of Ocean and Underwater En-

1

rd

gineering, J. J. Meyers, C. H. Holm, R. F. McAllister, editors. McGraw-Hill, 12.2-12.24.

Shick, G@ B. (1964) The design of a deep moored oceano- graphic station. Buoy Technology Symposium, MTS, Washington, D. C., pp. 48-56.

Wolford, T. C. (1966) Oceanography of the Grand Banks region and the Labrador Sea in 1966. U. S. Coast Guard Oceanographic Report No. 13, (CG-373-18), 176 pp.

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APPENDIX 1

Program Title: Calculation of Mooring Line Tension

CODE BR PT Step Instruction MIL Remarks 0 000 Reset 024 001 il 001 002 Print x 026 003 Halt 401 Enter Z, water depth, ft 004 Print x 026 005 St 1 440 006 2 002 007 Print x 026 010 Halt 401 Enter D., subsurface drag, Ibs O11 Print x 026 012 St 2 441 018 3 008 014 Print x 026 015 Halt 401 Enter D,, surface buoy drag, lbs 016 Print x 026 017 St 3 442 1 020 4 004 021 Print x 026 022 Halt 401 Enter T, assumed tension, Ibs 023 Print x 026 024 St 4 443, 025 026 027 030 031 Rel 2 461 082 = 062 0383 Rel 3 462 034 = 020 035 St 6 445 T., initial tension, lbs 036 o 007 037 Print x 026 2 040 Rel 1 460 041 x 070 042 Rel 4 463 043 = 020 044. = 072 045 Rel 6 465,

19

CODE

BR PT Step Instruction MIL Remarks 046 = 020 047 Print x 026 R, ARC Radius, ft 050 St 0 457 051 8 010 052 Print x 026 053 Rel 2 461 054 + 072 055 Rel 4 463 056 -= 020 O57 Sint 042 3 060 R>O 046 061 Print x 026 a, degrees 062 St 5 444 063 9 O11 064 Print x 026 065 Rel 3 462. 066 = 072 067 Rel 4 463 070 = 020 O71 Sin 042 072 R-O 046 073 Print x 026 a,, degrees O74. St 4 443 075 1 OO1 076 0 000 O77 Print x 026 4 100 Rel 5 464 101 — 062 102 Rel 4 463 103 = 020 104 Print x 026 105 Sin 040 106 Sint 042 107 Print x 026 a.—a,, degrees 110 ST 5 444 ILL 1 OO1 1H 1 OO1 i118} eranbiex 026 114 Rel 5 464. 115 x O70 116 Rel 0 ATT IALG = O20 5 120 Print x 026 S, ARC Length, ft 2, = 062 122 Rel 1 460 123 = 020 124 Print x 026 S—Z, ft

20

CODE

BR PT Step Instruction MIL Remarks 125 ST 2 441 126 5 005 127 Print x 026 130 Halt 401 Enter K, spring constant, lbs/ft 131 Print x 026 1382 ST 5 444 133 6 006 134 Print x 026 135 y etalt 401 Enter T,, initial tension, lbs 136 Print x 026 137 ST 6 445

6 140 1 001 141 2 002 142 Print x 026 143 Rel 2 461 144 x 070 145 Rel 5 464 146 = 020 147 aP 060 150 Rel 6 465 151 = 020, 152 Print x 026 'T, calculated tension, lbs 153 To (0) 740

Nore: This program was designed for use on a Dietzgen 7410-PA Programmable Calculator.

21

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APPENDIX 2

Program Title: Normal Drag on Mooring

CODE BR PT Step Instruction MIL Remarks 0 000 Reset 024 001 1 001 002 Print x 026 003 Halt 401 Enter V, velocity, ft/sec 004 Print x 026 005 ax O74: 006 2 002 007 = 020 010 Sut i 440 V? 011 2, 002 012 Print x 026 013 Halt 401 Enter Ca, drag coefficient 014 Print x 026 015 ST 2 441 016 017 Halt 401 1 020 3 0038 021 PE 026 022 Halt 401 Enter d, diameter, ft 023 Print x 026 024 ST 3 449 025 4 004 026 Print x 026 027 Halt 401 Enter :, length, ft 030 Print x 026 O31 ST 4 443 0382 5 005 033 Print x 026 034 035 036 037 2 040 Rel 1 460 041 x 070 042 Rel 2 461 043 x O70 044 Rel 3 462

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BR PT

Step

Instruction

045 046 047 050 O51 052 053 054 055 056 057

Rel 4

Print x Halt

SFS ON SKFS JMP to 00 JMP to 16

CODE MIL

070 463 020 026 401 523 540 600 616

Remarks

F, drag force, lbs

060 061 062 063 064 065 066 067 070 071 072 073 O74. 075 076 O77

Note: This program was designed for use on a Dietzgen 7410-PA Programmable

Calculator.

24.

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