vvEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-216 July 1982
Project Summary
Tests of the Shell Sock
Skimmer Aboard
USNS Powhatan
H. W. Lichte, M. Borst, and G. F. Smith
An oil skimmer was tested in a
controlled crude oil dumping off the
New Jersey Coast in early 1980. The
program was sponsored by the U.S.
Navy, Director of Ocean Engineering.
Supervisor of Salvage (SUPSALV),
through the Oil and Hazardous Mate-
rials Simulated Environment Test
Tank (OHMSETT) Interagency Techni-
cal Committee (OITC) comprised of
the U.S. Environmintal Protection
Agency (EPA), U.S. Coast Guard
(USCG), U.S. Geological Survey
(USGS), U.S. Navy (USN), and Envi-
ronment Canada. The tests were
designed to evaluate the Spilled Oil
Containment Kit (SOCK) developed
by Shell Development Company. *The
skimmer had been designed as a
physical attachment to an oil industry
work boat in a vessel-of-opportunity
deployment mode. The USNS
Powhatan T-ATF fleet tug was chosen
as a similar vessel and one that had an
oil spill recovery operations mode.
This program is believed to be the
largest, most thorough, open ocean
test of a vessel-of-opportunity oil
skimmer to date. It involved pro-
cedures for overcoming problems
similar to those that may be en-
countered during an actual oil spill
cleanup using similar equipment.
Therefore, the steps taken in this
program may be of direct interest both
to those planning open ocean tests
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
and to those planning to operate
similar equipment in the field from a
vessel-of-opportunity. Accordingly.
the steps taken to obtain a permit to
spill crude oil at sea, to obtain a
suitable support vessel and other
equipment, and to ensure accurate
data are described in detail. The
difficulties of trying to locate, charter,
and adapt to an offshore supply vessel
with the right capabilities for working
with the SOCK (or any other vessel-of-
opportunity skimmer) are considered
especially significant.
The test program is described
including the oil/water distribution
and collection system, deployment
and retrieval of the SOCK, the on-
board fluid measurement, data analy-
sis, logistics, weather and environment
measurements, and the Powhatan/
SOCK interface. The light crude oil
and ocean water collected were stored
aboard the vessel, decanted, and the
emulsified oil later sold as waste oil.
Eight experimental crude oil dumps
are described and analyzed. The sea
conditions varied from calm to 1.8m
significant heights. During the 6 days
at sea, 50 m3 of oil were dumped and
the skimmer collected 32 m3 of oil.
The program is analyzed for sug-
gestions to future open-ocean testing
plans incorporating oil skimmers with
and without vessels-of-opportunity.
This program was fortunate in having
available a skimmer that had extensive
testing as a model, seaworthiness
-------
testing on commercial work boats,
and oil collecting experience in a spill
of opportunity.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cin-
cinnati. OH, to announce key findings
of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Personnel from the SUPSALV have a
responsibility to understand oil spill
control technology. The USN has an
extensive inventory of booms and
skimming equipment that has demon-
strated high performance and efficient
deployment. Their interests lie, then, in
looking to the future and new spill
equipment. The SOCK was selected as a
possible candidate for a vessel-of-
opportunity system that could be
deployed from standard offshore supply
boats. The SOCK development proto-
type was begun in 1975.
SUPSALV is a member of the OITC. As
such, its Supervisor requested the
committee in December 1978 to formu-
late a Research Plan to test a skimming
system offshore using crude oil. The
committee membership included repre-
sentatives from SUPSALV, EPA, USCG,
and USGS. The chairman is the EPA
representative from the Oil and Haz-
ardous Materials Spills Branch, Munici-
pal Environmental Research Laboratory.
The committee assigned EPA's
OHMSETT facility the responsibility to
design and execute the test program. In
January 1979, Mason & Hanger-Silas
Mason Co., Inc..operators of OHMSETT,
drew up a budget and job order for the
program, and subsequently began
preparation of a Research Ocean
Dumping Permit Application and Vessel
Selection.
The Research Program Plan was
completed and submitted by the USN to
the EPA Region II Office, New York City,
in May 1979 Engineering was con-
tinued in parallel to design, fabricate,
test, and deploy a portable test platform
adaptable to vessels-of-opportunity for
the SOCK. High priority was placed on a
versatile system design to be used in
future testing at sea for any skimming
system, and to be available for spills-of-
opportunity testing.
In January 1980, the USNS Powhatan
was selected as the dedicated vessel for
the experiments and the permit was
issued by the EPA. One of the out-
standing capabilities of the Powhatan is
her variable-pitch propellers. The
majority of industrial work boats in this
class do not have that versatility or the
resulting sustained, controlled, low
speed capability. Use of a conventional
boat for this program would have
required a tug boat in tow astern to
restrict speed or a continuous clutching
in and out of a propeller. Hardware
designs were integrated to the T-ATF
class, and fabrication of the test
equipment began. It was also decided
that portable on-deck tankage was
required for crude oil and fluids storage.
The at-sea schedule was fixed for mid-
April 1 980. The USCG offered the USCG
cutter Reliance as an observation
platform at sea.
Portable Test Facility
USNS Powhatan
This T-ATF class ship is a new class
combining the capabilities of the USN's
tugs, ATF's, and commercial offshore
tug/supply boat. The vessel is manned
by a civilian crew (16) of the Military
Sealift Command (MSC) and a Navy
communications team (4). Good ac-
commodations exist for 20 additional
men as transients to support portable
equipment missions.
The ship utilizes twin diesel drive
supplied through separate shafts to
controllable-pitch propellers in nozzles.
Commercially proven equipment is
installed throughout the vessel. The
vessel is 226 ft long and 204 ft at the
waterline; beam width is 42 ft, draft is
15 ft and full load displacement is 2260
tons. Cruising speed is 13 kt, and
optimum towing speed is 6 kt. The
vessel forward speed was controllable
in 0.1 kt increments at low speeds. Ship
power includes two 3600 brake-horse-
power diesels, a 300 horsepower bow
thruster, and three 400 kilowatt diesel
generators.
One unusual feature is a main deck
bolt-down grid pattern consisting of
threaded recessed sockets every 2 ft (1 -
in., 8 UNC threads) in the clear deck area
rectangle of 38 by 88 ft. The allowable
deck load wa s considered to be 300 tons
for transient equipment.
Test Equipment
Most of the portable test facility
integrated to the Powhatan was de-
signed and tested at OHMSETT, based
on a 6-yr experience of testing in the
tank and recent experience of testing in
offsite spills-of-opportunity. Thirty-one
short tons of equipment were trar
ferred to the ship. The largest elemer
(not including the skimming syste
itself) were:
• Large(19m3)storagecontainers<
crude oil and collected sea water I
• Slick generator (deployed at sea
• Gasoline engine hydraulic povv
pack (1)
• Tool house with spare parts a
tools
Dockside support was vital to t
portable test facility. This progra
utilized the deepwater pier located i
Naval Weapons Station Earle
Leonardo, New Jersey. A 70-ton era
was used for lifting the SOCK equi
ment. Tractors were required to me
large equipment on flatbed trailers a
19 m3 fluid tank trailers. Each late-nic
docking required offloading of the cru
oil and sea water collections of the di
Test crude oil tanks had to be filled w
fresh crude each evening.
Fluids Management
The fluids management circuit i
eluded manifolds, sampling pipir
storage tanks, and pumps for thr
separate floating sea platforms. /
crude oil measurements were to be
least redundant. For example, crude
loaded onboard for each tank w
quantified with two dipstick measui
ments and a totalizer meter. Crude
dumped to the skimmer was quantifi
in the same way. Crude oil collected
the skimmer was measured for to
volume and flow rate, then evaluated 1
water content and stored in tanl
Decanting settled tank water at sea w
to be monitored with grab samples a
dipstick measurements, totalizer met
and an oil/water separation chemii
analysis.
Spilled Oil Containment Kit
(SOCK)
Installation and Constraints
The SOCK was loaned to the OITC 1
this program by the Shell Oil Compa
through their Emergency Response - (
Environmental Conservation Operatic
staff in Houston, Texas. The SOCK w
operated exclusively by Shell-train
personnel, two from Tidewater Cc
tractors. Inc., Amelia, Louisiana, a
one from the Westhollow Resear
Center.
The launching and retrieval requir
support from the OHMSETT staff. T
rigging and installation onboard wa:
mutually-agreed upon design th
-------
depended on the Powhatan's deck
equipment and was constrained by a
rule disallowing welding or cutting of
the vessel's structure or covering deck
bits. The need, also, to have the system
deployed as far forward of the ship
propellers as possible resulted in the
starboard side installation.
The actual installation of the SOCK
onto the Powhatan required three large
crane lifts and four small crane lifts. A
70-ton crane was required to accomplish
the reach from the dock/pier to the
vessel deck positions.
The SOCK hardware and operators
were integrated into the USNS
Powhatan and the test program. The
following items had significant impact,
floor space, and weight loads:
• Container, 8x35 ft, 32,000 Ib (dry),
• SOCK fabric/frame, 8x29,6500 Ib,
• Air tuggers (two each) 3x3 ft, 200 Ib
each,
• Fluids strainer/manifold, 3x3 ft,
200 Ib, and
• Tool house, 7x12 ft, 5000 Ib.
The container included an integrated
diesel hydraulic power plant, valves,
rigid piping, controls, launching ramps
and the positive displacement suction
pump. The fabric/frame skimmer sits
on top of the container when not
deployed; therefore its weight is im-
portant. The height of the stack was
approximately 19 ft above the deck, and
it hung 3 ft over the starboard side.
Height and overhang were important in
safely calculating ship stability and
docking constraints.
Test Procedures and Results
The test procedures were very de-
tailed to account for safety, permit
regulations, and back-up measure-
ments. The basic elements were to
deploy the skimmer in the existing seas,
deploy the oil slick generator, dump the
fresh crude on the sea, operate the
skimmer to collect the crude oil, and
then measure the skimmer performance.
The independent variables selected for
each test were forward surface speed,
head-on or following seas, crude oil
encounter rate, and skimmer pumping
speeds.
The original test plan design laid out
two different crude oils to be used. The
deployed test program used only one,
LaRosa. The second crude oil, Murban.
was not used because of sea time
constraints. These crudes were selected
for several reasons. First, they had been
studied by others for dispersant studies,
and second, they represented a span of
Table 7. SOCK Test Results*
Test
no.
HI
1
2
3
4
5
6
7
8
Fwd
speed,
kt
(2)
2.1
1.0
0.75-
2.0
1.0
1.3
1.3
1.75
2.1
Pre-
load.
m3
(3)
.0005
1.89
1.89
1.89
3.8
3.8
3.8
3.8
Dist
rate.
rrf/hr
<4)
66
35
68
47
65
23
29
SOCK
pump.
m>/hr
IS)
68
45
65
23
29
1/3
H.
m
(6)
1.5
1.3
1.4
1.2
0.9
1.4
1.0
0.7
Period
T.
s
(7>
6
7
7
7
5.5
3.7
4.3
5.8
Direct
to sea
(8)
Head
Head
Head
Head
Head
Head
Follow
Follow
RE.
%
(9)
44
89
39
43
26
TE.
%
HO)
55
93
47
43
18
ORR,
rrt>/hr
(11)
10
35
12
12
2
*H = height; T = time; RE = recovery efficiency; TE - throughput efficiency; ORR - oil
recovery rate.
API gravities common to the tanker
shipments in the world. LaRosa, a
Venezuelan crude has an API gravity of
23.9° and sulfur weight percent of 1.73.
Weathering tests were performed at
OHMSETT in 1979 for 144 hrs to
characterize the sea water mixing that
causes increases in specific gravity, an
order of magnitude increase in viscosity,
and a drop in interfacial tension.
Data were taken from both active and
passive measurements to calculate
performance of the skimmer. Through-
put efficiency is the ratio of oil collected
to oil encountered, expressed as a
percent. Recovery efficiency is the
percent of crude oil in the skimmer-
recovered oil and sea water. Oil recovery
rate is the calculated flow of oil collected
by the skimmer, exclusive of the sea
water. The sources of oil lost at sea were
estimated by trained observers and
photographic records. Losses not at-
tributable to the skimmer were sub-
tracted from the performance calcula-
tions. These included those wind driven
out of the skimmer's reach and those
passing between the Powhatan and the
skimmer. Photographs recorded these
losses and those surfacing behind the
skimmer. The resulting slick was also
monitored photographically.
The first day at sea was dedicated to
equipment checkout and deployment
practice to verify the Powhatan and
SOCK compatibility. During the next 5
days, eight tests were made with crude
oil. One of those days produced no
testing because of fog and heavy seas.
Test results of the skimmer per-
formance at sea with the LaRosa crude
oil are listed in Table 1. Column
headings 2 through 8 are considered
independent variables, and columns 9,
10, and 11 are considered dependent
performance variables. The results
listed are actual data.
Test number one was designed to
observe a half-liter of oil at sea passing
through the SOCK without the pump
operating. The loss under the SOCK was
observed in photographs and gave the
test crew an opportunity to visually
adjust to the oil slick. Test number two
was designed to observe low speed
losses, if any, with a 1.89 m3 preload in
the SOCK without pumping. Trained
observers estimated the loss rate at 1
mVhr. Because of the low loss rate in
test two, test three was conducted to
observe the effect of increasing speed
and to determine the speed at which
gross loss would occur. At 1.75-kt
forward speed, the loss surfaced about
8 m behind the SOCK in the form of
globules. Vortices were obvious im-
mediately behind the SOCK. The loss
rate estimate was 11 mVhr. The second
part of this test was designed to
estimate the preload required without
pumping great quantities of water over
a long time period. The estimate should
give the pump operator an idea for a
preload volume collected before starting
the pump flow. This portion of the test
was inconclusive, so it was decided to
proceed to test four using the 1.89 m3
preload. Tests four through seven were
designed primarily to measure the
effects of increasing forward speed and
varying the crude oil encounter rate.
The SOCK pump rate was set to match
the encounter rate so that maximum
efficiency calculations could be made.
The reader will observe that the preload
was increased beginning with test five.
This option is available to the operator
during an uncontrolled spill.
The skimmer performed well in these
sea states. Test eight was selected at
-------
the higher advancing speed to deter-
mine if a significant drop off would
occur.
Conclusions
The test program was considered a
success for many reasons. No injuries,
damage or loss to equipment, and there
were no surprises. The built-in re-
dundancy was effective and was relied
on in several instances. The integration
of the USNS Powhatan and the SOCK
produced no problems. The MSC crew
and the transient work force worked
well together. The vessel could respond
to peculiar maneuvers required by the
oil skimming system. The requirements
of the Research Dumping Permit were
met with a relatively simple audit
system and reporting procedure. The
dump of 50 m3 and the 32 m3 retrieval
was accomplished in an environmentally
acceptable manner. The test program
produced engineering and logistics data
that can be used by others in the future
at a considerable cost savings. The
Powhatan equipment has a greater
capability than the typical oil industry
work boat. In some cases, the common
workboat could be outfitted in a similar
manner. Variable-pitch propellers, not
common on these boats, could be
replaced in future experiments by
establishing astern loads with a tugboat.
The data analysis options produced
relatively consistent numbers. The per-
formance data were calculated three
different ways, depending on the
specific instrumentation, and agreed
within 15 percent in all cases. Audio
and photographic records were effective
tools during the intense 16-hr work
days.
We recommended that only skimmer
designs that have had seaworthiness
tests and large-scale tank tests with oil
be viable candidates for open ocean
testing with fresh crude. Candidates
should also have demonstrated high
performance efficiency and strength in
these tests.
The full report was submitted in fulfill-
ment of Contract No. 68-03-2642 by
Mason & Hanger-Silas Mason Co., Inc.,
Leonardo, New Jersey 07737, under
the sponsorship of the U.S.
Environmental Protection Agency.
H. W. Lichte. M. Borst. and G. f. Smith are with Mason & Hanger-Silas Mason
Co., lnc..Leonardo. NJ 07737.
Richard A. Griffiths is the EPA Project Officer (see below).
The complete report, entitled "Tests of the Shell Sock Skimmer Aboard USNS
Powhatan" (Order No. PB 82-220 849; Cost: $10.50. subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison. NJ 08837
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
0000329
AGENCY
•ft U.S. GOVERNMENT PRINTING OFFICE: 1982—saa.ot7/n7/
------- |