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TN- i^'fl



Technical Note N-1441



CEL 10K PROPELLANT-ACTUATED ANCHOR



By



J. F. Wadsworth and R. J. Taylor



June 1976



(document

V COLLECTION



Sponsored by



CHESAPEAKE DIVISION

NAVAL FACILITIES ENGINEERING COMMAND



Approved for public release; distribution unlimited.



CIVIL ENGINEERING LABORATORY

Naval Construction Battalion Center

Port Hueneme, California 93043



Unclassified



SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered)



REPORT DOCUMENTATION PAGE



1. REPORT NUMBER

TN-1441



2. GOVT ACCESSION NO

DN644157



3. RECIPIENT'S CATALOG NUMBER



4. TITLE fond Sublillc)

CEL lOK PROPELL ANT- ACTUATED ANCHOR



S. TYPE OF REPORT & PERIOD COVERED

Final; Sep 1974 -Sep 1975



6. PERFORMING ORG. REPORT NUMBER



AUTHORfsJ

J. F. Wadsworth
R. J. Taylor



CONTRACT OR GRANT NUMBERCsJ



9. PERFORMING ORGANIZATION NAME AND ADDRESS

Civil Engineering Laboratory
Naval Construction Battalion Center
Port Hueneme, CA 93043



63713N; S46-36X; WBS3.1330;
3.1330-1



CONTROLLING OFFICE NAME AND ADDRESS

Chesapeake Division (Code FPO-1E3)
Naval Facilities Engineering Command
Washington, DC 20374



12. REPORT DATE

June 1976



13. NUMBER OF



16



14. MONITORING AGENCY NAME ft ADDRESSfi/ ditferent Irom Controtline Office)



15. SECURITY CLASS, (ol Iftis roporf)

Unclassified



16. DISTRIBUTION STATEMENT CoM/iis RoporO



Approved for public release; distribution unlimited.



17. DISTRIBUTION STATEMENT (ol Ihe nSs



in l3Iock 20. if different from Report)



IB. SUPPLEMENTARY NOTES



19. KEY WORDS (Cor^tir^ue on reverse side il necessary and identity by blocif number)

Propellant-actuated anchor; land tests; sea tests; anchor performance



20. ABSTRACT (Continue on reverse side if necessary and identify by 6/och number)

CEL has developed a new lightweight propellant-actuated embedment anchor with a
nominal long-term holding capacity of 10,000 pounds (45 kN). Through the use of stock
components, the anchor can be inexpensively fabricated and used. Land tests have
demonstrated the structural integrity of the design and verified the predicted ballistic
performance. Sea tests were conducted in a coral seafloor at Midway Island. The anchors
that were successfully embedded indicated holding capacities on the order of 30,000
continued



^D 1 JAN 73 1473 EDITION OF 1 NOV 65 IS OBSOLETE



MBL/WHOI



Unclassified



SECURITY CLASSIFICATION OF THIS PAGE fl*7ien Data Entered)



D 0301 0DMD371 3



Unclassified



SECURITY CLASSIFICATION OF



Block 20 continued.

pounds (45 kN). Further testing is required to ascertain the system's reliability in other
seafloor materials, but the lOK anchor should provide the Navy with an easily handled,
medium-holding-capacity anchor.



Library Card



Civil Engineering Laboratory

CEL lOK PROPELLANT-ACTUATED ANCHOR (Final), by

J. F. Wads worth and R. J. Taylor

TN-1441 16 p. illus. June 1976 Unclassified

1. Propellant-Actuated Anchor 2. Land Tests 3. Sea Tests L 3.1330-1

CEL has developed a new lightweight propellant-actuated embedment anchor with a
nominal long-term holding capacity of 10,000 pounds (45 kN). Through the use of stock
components, the anchor can be inexpensively fabricated and used. Land tests have demonstrated
the structural integrity of the design and verified the predicted ballistic performance. Sea tests
were conducted in a coral seafloor at Midway Island. The anchors that were successfully embedded
indicated holding capacities on the order of 30,000 pounds (45 kN). Further testing is required to
ascertain the system's reliability in other seafloor materials, but the lOK anchor should provide
the Navy with an easily handled, medium-holding-capacity anchor.



Unclassified



CONTENTS

Page

INTRODUCTION ..... 1

DESCRIPTION OF EQUIPMENT 1

Functional Description 4

Anchor Design 4

PROJECTED BALLISTIC PERFORMANCE 8

TEST PROGRAM . . t 10

Land Tests 10

Sea Tests 11

EVALUATION OF ANCHOR PERFORMANCE 15

SUMMARY 15

LIST OF ILLUSTRATIONS

Figure 1. CEL 10K Propellant-actuated anchor 1

Figure 2. Schematic of the CEL 1 0K propellant-actuated anchor ... 3

Figure 3. CEL 10K anchor f luke-to-downhaul-cable connection .... 5

Figure 4. CEL 1 0K anchor firing mechanism 6

Figure 5. CEL 1 0K anchor cartridge assembly 7

Figure 6. Projectile velocity versus water depth for the CEL

1 0K anchor at various charge weights. The projectile

used is the 173-pound, 2 x 2-foot fluke; the

propellant Is M6, 0. 0579-Inch web 8

Figure 7. Projectile velocity versus water depth for the CEL

1 0K anchor at various charge weights. The projectile

used is the 148-pound, 1 x 2-foot fluke; the

propellant is M6, 0. 0579-Inch web 9

Figure 8. Charge weight versus water depth for the CEL 10K

anchor using M6 propellant with 0.0579-inch web size. . . 9

Figure 9. Plot of experimental and predicted pressures versus

charge weight 12

Figure 10. Pressure versus time for the lant tests of the 1 0K

anchor at four charge weights 13



List of Illustrations (continued)

Page

Figure 11. CEL 1 0K anchor being placed in a 35-foot work boat ... 14

Figure 12. CEL 1 0K anchor being prepared for lowering from a

35-foot work boat 14



LIST OF TABLES

Table 1. Characteristics of CEL 1 0K Propellant -Actuated Anchor . . 2
Table 2. Characteristics of CEL 10K Anchor Flukes 5



INTRODUCTION

A new propellant -actuated anchor (CEL 10K) has been designed and
fabricated for the Chesapeake Division of NAVFAC (Figure 1 ) . The expe-
rience gained during the development of the CEL 20K anchor* allowed
a straightforward 1 0K anchor design effort. During the testing phase
for the CEL 20K anchor, many improvements were envisioned that would
simplify operational and handling characteristics and reduce cost;
these improvements were incorporated in the CEL 10K anchor design.
The anchor is designed to operate at depths of 25 to 20,000 feet (7 to
6,100 m) and will develop at least 10,000 pounds (45 kN) of long-term
holding capacity in seafloor soils, rock, and coral. Holding capacity
will vary between 10 and 50,000 pounds (45 to 225 kN) depending upon
seafloor type.

Because the anchor was designed for lower holding capacity appli-
cations, it should be useful for mooring buoys, small vessels, instrument
arrays, causeways, and a variety of other surface and subsurface struc-
tures. If the anchor is to be used for these applications, it must exhibit
advantages over the conventional approaches to anchoring.

In addition to the characteristic advantages of the direct embedment
anchor - such as the ability to resist multidirectional loadings, high
anchoring efficiency, reduction in required line scope, and operability
in competent seafloors - the CEL 10K anchor was designed to be low in
cost and light weight. Total anchor system weight is about 700 pounds,
(320 kg) and the system is fabricated for less than $2,500. In shallow
water, the cost of expendable components is about $450.

This report describes the anchor and details the land testing
program used to verify gun performance and its first in-water firings.



DESCRIPTION OF EQUIPMENT

The anchor consists of two major parts (Figure 2) - the gun assem-
bly and the fluke assembly. Table 1 describes the anchor with a sand
fluke and a clay fluke attached. The new anchor weighs about 625 to 700
pounds (285 to 320 kg) and measures about 6 feet (1.8 m) in overall length
with the touchdown probe extended. The design uses stock components and
minimizes machined parts, thereby allowing faster and simpler fabrication.



* R. J. Taylor (1976). Technical Report R-837: CEL 20K Propellant-
actuated anchor. Civil Engineering Laboratory, Port Hueneme,
CA.



Table 1. Characteristics of CEL 10K Propellant-Actuated Anchor



Description


Anchor With-


Sand
Fluke


Clay
Fluke


Length, ft (m)

Diameter, ft (m)

Nominal weight, lb (kg)
Gun assembly
Fluke assembly

Total

Operating depth, ft (m)

Rated holding capacity, lb (kN)


6 (1.83)

2 (0.61)

700 (317.1)

480 (217.4)

148 (67)

628 (384.5)

25-20,000
(6.6-6,100)

10,000 (44.5)


6 (1.83)

2 (0.61)

700 (317.1)
480 (217.4)
173 (78.4)

653 (295.8)

25-20,000
(6.6-6,100)

10,000 (44.5)




Figure 1. CEL 1 0K Propellant-actuated anchor.



Gun Assembly •<



Fluke Assembly *^




reaction vessel



;Iay fluke



touchdown probe
(stowed position)



touchdown probe
(ready position)



Figure 2. Schematic of the CEL 1 0K propellant-actuated anchor.



Functional Description

The firing mechanism is mechanical; spring energy is used to drive
a firing pin into the primer. After lifting the anchor off the deck,
only the touchdown probe is lowered to prepare the anchor for installation.
The anchor is still ''safe" until it reaches a depth of 10 to 12 feet
(3 to 4 m) . At that depth, a hydrostatic lock is released, allowing the
trigger of the safe-and-arm device (S/A) free travel.

Embedment of the anchor projectile occurs when the touchdown probe
touches the seafloor. The probe slides, triggering the S/A, which in
turn detonates the propellant charge. The pins restraining the fluke
assembly shear when the barrel pressure reaches 5,000 psi (34.5 MPa)
over ambient water pressure, and the anchor projectile is propelled
downward into the seafloor with the downhaul cable. The fluke keys into
its maximum resistance position with an upward pull. The gun assembly
is expendable in deep water at present, but deep-water retrieval methods
described by Taylor* are pertinent.

Anchor Design

Fluke assembly. Three types of flukes can be used with the CEL 10K
anchor: a sand fluke (1 x 2-foot, 31 x 61 -cm), a clay fluke (2 x 2-foot,
61 X 61 -cm), and a rock fluke (to be designed). The clay fluke is square-
shaped because recent tests have indicated that a square fluke is best
for use in soft clay seafloors. In addition, the 10K anchor utilizes
a mechanical S/A, and it is advantageous to keep the touchdown rod as
short as possible to minimize potential binding. Handling and fabrication
are also further simplified by using the same length of fluke and touch-
down rod for both sand and clay anchors. Since predicted anchor performance
gave more than enough penetration to achieve the desired holding capacities,
it was possible to sacrifice some penetration in order to keep both flukes
the same length. The fluke characteristics are outlined in Table 2. The
main plate for the flukes is flat. To balance the 10K projectile the
flat plate is mounted below the piston axis enough to counteract the
weight of the keying arm plate.

The 10K fluke assemblies also have a modified connection between
the downhaul cable and fluke. The connection is a single link that leads
to the downhaul cable socket (Figure 3) . Both the socket and line are
pinned together through a plate welded to the piston.

Gun assembly. The gun assembly of the anchor is comprised of the
gun tube, the reaction vessel, the firing system, and the cartridge
assembly (Figure 2). The gun barrel of the 10K anchor is a smooth-bore
steel tube designed to operate at 50,000 psi (345 MPa). The breech
block is threaded into the end of the gun tube, and then the S/A (pur-
chased from the Magnavox Co.) is in turn threaded into the breech block.
The reaction vessel is a reinforced pipe cap 2 feet (0.6 m) in diameter
mounted at the muzzle end of the gun tube to entrap water and reduce



* Taylor (1976), Ibid.



recoil of the gun assembly; analysis indicates the recoil will be a max-
imum of 15 feet (4.6 m) . The firing assembly is a mechanical system that
triggers the embedment sequence (Figure 4). A solid steel rod, which
can be stowed with the probe above the end of the fluke, serves as the
touchdown probe. When the rod is pulled down, spring- loaded pins lock
the rod to the firing ring. Upon probe contact with the seafloor, the
firing ring is moved upward, engaging the trigger arm of the S/A and
releasing the firing pin. The S/A has a hydrostatic lock that prevents
firing above a water depth of 10 to 12 feet (3 to 4m). The cartridge
assembly consists of an aluminum or steel cartridge base that is epoxied
to a phenolic cartridge case to form the propellant container. The ord-
nance consists of 5 -inch (1-27 mm)/38 caliber gun propellant (M6) and
a shortened M58 primer (Figure 5).



Table 2. Characteristics of CEL 10K Anchor Flukes



Description


Sand


Clay


Length, in. (cm)

Width, in. (cm)

Thickness, in. (mm)

Plan area, ft2 (m2)

Material

Piston weight, lb (kg)


24 (61)

12 (30.5)

1/2 (13)

1.94 (0.148)

A514 or A517

69 (31.3)


24 (61)

24 (61)

1/2 (13)

3.66 (0.297)

A514 or A517

69 (31.3)



connecting link




ciownhaul cable
open socket



Figure 3. CEL 1 0K anchor f luke-to-downhaul-cable connection.



stowed position
of touchdown rod



firing position



spring-loaded locking
mechanism




• I



i==*'l



touchdown probe




cf



^:Si




e:?



Magnavox S/A device



firing ring



gun tube



Figure 4. CEL 1 0K anchor firing mechanism.



PROJECTED BALLISTIC PERFORMANCE



The Naval Ordnance Station, Indian Head, Maryland, selected smoke-
less propellant (M6) with 0.0579-inch (1.37 mm) web thickness (material
thickness between perforations) as the most suitable propellant for the
10K anchor.* This was based on desired performance criteria of: (1) max-
imum operating pressure of 50,000 psi (345 MPa) , (2) maximum acceleration
of 2,000 g's, and (3) minimum projectile velocity of 250 fps (76 mps) .

A computer program for simulation of propellant -actuated anchor
performance was used to predict the 1 0K anchor ballistics at a range
of depths and charge weights. The results of the simulation are presented
graphically in Figures 6, 7, and 8. Using the plots (Figures 6 and 7)
of projectile velocity versus water depth for each projectile, charge
weight for peak performance (Figure 8) was determined with the limiting
condition of 2,000 g's acceleration for the 1 x 2-foot (31 x 61 -cm)
fluke and 50,000 psi (345 MPa) for the 2 x 2 -foot (61 x 61 -cm) fluke.
These charge weights are practically similar for both flukes. It appears
that a fluke larger than the 2 x 2-foot (61 x 61 -cm) fluke could be
effectively used with this gun system to improve anticipated performance
in clay seafloors. Once the system is used more, this decision can be
made more reliably.

Projectile Velocity (FPS)




Figure 6.



Projectile velocity versus water depth for the GEL 10K
anchor at various charge weights. The projectile used is
the 173-pound, 2 x 2-foot fluke; the propellant is
M6, 0.0579-inch web.



* J. H. Holden (1975). Technical Report IHTR 438: Propulsion

system development for a 10, 000 -pound capacity embedment anchor.
Naval Ordnance Station, Indian Head, MD.

8



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TEST PROGRAM
Land Tests

The 10K anchor was tested to verify ballistic performance, water-
tight integrity, and structural soundness. The ballistics and structural
strength were checked by conducting Instrumented tests of the anchor
on land at the Pacific Missile Test Center, Point Mugu, California. The
hydrostatic seals were checked by a pressure test in CEL's Deep Ocean
Laboratory facility.

The gun tube is a watertight container with seals designed to with-
stand water pressures of 20,000-foot (6,100 m) depths. However, the
safe-and-arm device (S/A) , which was purchased as a stock item from
the Magnavox Company, was guaranteed to only 200 feet (60 m) . The S/A
and gun tube were assembled and tested to a simulated ocean depth of
600 feet (185 m) and 1,200 feet (365 m) . The test procedure was to build
up pressure to the maximum value, hold for 10 to 15 minutes, and then
gradually release pressure. Two systems were tested to 300 psi (2 kPa) ,
and, finding no leaks, the second two were tested to 600 psi (4 kPa) .
After testing, the anchors were disassembled and Inspected for signs
of leaks; each system was found to be watertight. Minor modification to
strengthen the S/A body should allow the anchor to operate to 20,000-
foot (6,100-m) depths.

The propellant system is designed to impart high velocity to the
projectile in a short distance which results in high acceleration-
induced stresses experienced by both projectile and gun assembly. By
conducting test firings on land it was possible to examine both the
ballistic performance of the gun system and the structural integrity
of the launch vehicle. It was not feasible to use the actual anchor
projectile during land tests, so an equivalent mass of steel was sub-
stituted.

The anchor was assembled and hung in a fluke-down vertical orienta-
tion from a wooden beam resting on a steel box frame. The anchor was
then loaded, armed, and fired. Six tests were conducted with charge
weights from 1.1 to 1.4 pounds (500 to 635 gm) . Each test was instrument-
ed for pressure measurements by a transducer and copper crush gages.
High-speed movies were taken of the firing to determine projectile
velocity and acceleration should the test results indicate performance
problems with the propulsion system.

The last three tests included the use of a downhaul cable to deter-
mine the effectiveness of a new wire rope packing arrangement and the
potential use of chain as a downhaul. The wire rope was used in the
first test. The wire rope was faked into a sheet metal pack attached to
the test support frame with the bitter end of the wire rope attached to
the dummy anchor projectile. The chain downhaul was used on the last two
tests. The downhaul chain was prepared by placing a length of 1 /2-lnch-
diameter (13 mm) chain in tension and coating it with a two-part urethane
epoxy. When the epoxy hardens, it holds the chain in a pretensioned con-
figuration; thus, the chain can be used much like a cable, and the urethane
coating is flexible enough to allow faking of the chain.



10



The land testing provided a severe test of the anchor's structural
design. Upon firing, the launch vehicle would recoil upward through
the wood support beam, rising as high as 200 feet (60 m) in the air
before dropping to the ground. Although the accelerations during firing
on land are similar to those attained underwater, the impact of the
launch vehicle as it lands after its recoil is much more severe on land
than in the water. No failures of major components occurred, and the
minor damage that was sustained was entirely due to the launch vehicle
impact, not to the actual firing accelerations. This problem is elim-
inated when the anchor is used underwater.

The ballistics performance indicated an under estimation of gun
barrel pressures for each charge weight. Subsequent tests of the par-
ticular lot of propellant used indicated considerably different burn
rate characteristics than are normally expected for M6 propellant.
Rerunning the computer simulation with the new values accurately pro-
filed the test pressures. Predicted and actual pressures are plotted
in Figure 9. The pressure-time curves for the tests indicated a very
smooth pressure buildup and release as is desirable. Examples of the
pressure-time curve are given in Figure 10.

The new burn rate values do not seriously affect anchor performance
above 10,000 feet (3,100 m) of water depth. However, below that depth,
the propellant is completely burned before the piston leaves the gun
barrel. No additional propulsion is available to drive the piston from
the gun barrel; thus, as the depth increases, the ambient water pressure
reduces the net propulsive force. The result is the decrease in projectile
velocities below 10,000 feet (3,100 m) apparent in Figures 6 and 7. For
anchoring below this depth a slower burning propellant must be used.

It was unnecessary to reduce the high-speed film to obtain velocity
and acceleration data, because the agreement between predicted and actual
results for the propellant system was good.

Sea Tests

The first sea tests of the 10K anchor were recently completed
at the MILS cable installation at Midway Island. The anchors were to
be used only for testing purposes, but a YTB scheduled to install heavier
20K anchors was withdrawn; therefore, the 10K anchor had to be used
to provide a temporary four-point mooring for the ARS Bet-iver . The sea-
floor was coral, and very little was known about its strength charac-
teristics. Only four sediment flukes were available; therefore, they
were slightly modified on site to accept the downhaul cable directly
into the fluke.

The anchors were installed from a 35 -foot (10.7 m) workboat. The
anchors were transported to the site slung from a small A-frame off
the bow (Figures 11 and 12). A 6-ton (5.45 metric-ton) salvage winch
was placed in the well deck, and it was used to control-lower the anchor to
the seafloor. Each anchor was installed with 1.45 pounds (657 gm) of
M6 propellant. A 1 x 2-foot (31 x 61 -cm) fluke was used for the first



11




(jOI X rsd) aanssaaj



12



and third firings, while a 2 x 2-foot (61 x 61 -cm) fluke was used for the
second and fourth firings. The first two anchors were quickly installed
in 59 feet (18 m) of water, penetrating 9 and 14 feet (2.8 and 4.3 m) ,
respectively. This deep penetration indicated a rather soft coral or
a layered media (coral/coral sand) at these two sites. The third anchor
was installed in 112 feet (34 m) of water; this anchor was to be used
as the starboard bow anchor. The fluke penetrated a short distance and
was badly damaged. The initial assumption was that the fluke was unstable
during penetration, and this caused the piston to separate from the fluke
prematurely. However, a subsequent firing with a CEL 20K anchor at roughly
the same location indicated that this coral was extremely hard. Since
divers reported shallow penetration of the 1 0K anchor, the work boat
proof -loaded the anchor to determine its status. The work boat easily
pulled the anchor out. The front of the fluke was bent back, and the
fluke could offer no holding capacity in the coral rubble produced during
this penetration. The fourth 1 0K anchor was assembled and transported
to the same site. This anchor was rapidly lowered to the seafloor and
fired in almost a prone position. The rapid (almost free-fall) lowering
caused the anchor to plane out. The fluke grazed the seafloor at a very
shallow angle and landed on the surface a short distance away. The 1 0K
with the 2 x 2-foot (61 x 61 -cm) fluke will have to be lowered at a more
reasonable rate, perhaps less than 400 fpm (120 mpm) to prevent kiting;
this rate will be determined at a later date.




1.4-lbM6



Figure 10. Pressure versus time for the land tests of the 1 0K
anchor at four charge weights.



13




Figure 11. CEL 1 0K anchor being placed
in a 35-foot workboat.




Figure 12. CEL 1 0K anchor being prepared for
lowering from a 35- foot workboat.



14



The mooring was completed using two work boats lashed together
to install two 20K anchors. Once the ARS was in its moor, the moor-
ing lines were pretensioned. During use, one of the 10K anchors pulled
out during a moderate storm, with 25-to-30-knot beam winds, 4-to-5-foot
(1 .2-to-1 .5-m) seas, and strong beam currents, estimated to 2 knots. The
peak static load sustained by the anchor was estimated to be about 30,000
pounds (135 kN) ; ship surge would increase this load. The other 1 0K anchor
remained embedded throughout the operation and was left in place for
further use or testing.



EVALUATION OF ANCHOR PERFORMANCE

The land tests verified the efficiency of the anchor's propulsion
system and the structural design. The anchor is easily and quickly as-
sembled due to its light component weight.

The firing system performed excellently; even at large angles of
tilt, the anchor fired each time. The safe-and-arm device is simple and
easily prepared for use and reuse.

The downhaul cable packing arrangement tested at Point Mugu and


1

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