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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 /

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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UNPUBLISHED MANUSCRIPT.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

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

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.

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.

© Surface floats with radar reflectors and
lights are highly visible, and are, there-
fore, subject to well-intentioned recovery or
theft.

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:

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).

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.

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

LOAD AS PERCENT OF AVERAGE BREAKING STRENGTH

MANILA

DACRON

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

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

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

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.

(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.

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

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.

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-

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,

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

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.

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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

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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Full text of "Taut-line instrumented arrays used by the Coast Guard Oceanographic Unit during 1970-1971"

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