v>EPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-141 Aug. 1981
Project Summary
Using Coherent Water
Jets to Control Oil Spills
Michael K. Breslin
The ability of coherent water
streams to induce a surface current in
a body of water and thus control a
floating oil slick was examined in a
number of test programs conducted at
the U.S. Environmental Protection
Agency's (USEPA) Oil and Hazardous
Materials Simulated Environmental
Test Tank (OHMSETT). The objective
of the tests was to determine whether
coherent water streams could serve as
an alternative to fabric booms and
water sprays in concentrating, divert-
ing, and containing oil slicks.
The water jets were constructed
from standard pipe fittings and sup-
plied with water from common
centrifugal water pumps. The jets
were mounted at one of three loca-
tions—some on the main OHMSETT
towing bridge, others onto small
floats, and others extended from the
bow of a catamaran. Control of oil
slicks in 6-knot currents, with water
jets, was evaluated by towing the jets
with the main bridge system at 6
knots. The tank's wave generator
developed regular waves and harbor
chop or confused sea conditions.
The tests showed that coherent jets
could induce a significant surface
current and move an oil slick with little
oil entrainment. Nonbreaking waves
produced by the OHMSETT wave
generator did not greatly affect per-
formance, except where the jet
nozzles were cantilevered off the front
of the catamaran and the pitch of the
vessel caused significant changes in
the height and attitude of the jet
outlet. The best position for an un-
manned water jet of the sizes and at
the pressures tested was determined
to be vertically directed at the surface
of the water with the putlet 0.4 to 1.0 m
above the surface. These tests showed
that the vertical component of a co-
herent water stream was as useful, if
not more so, as the horizontal com-
ponent. The performance of a water
jet supplied by a 30-kW electric
motor/centrifugal pump system
exceeded that of an air jet of com-
pressed air (210 kPa) extended 0.6 m
below the surface supplied by a
50-kW gasoline-driven air compres-
sor.
This Project Summary was develop-
ed by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The development of the water jet
began as a method to increase the
accuracy of testing oil spill control and
recovery devices at OHMSETT. Other
methods such as booms, air barriers,
fire hoses, and floating ropes have been
used with limited success. This report
describes the initial experiments used
to evaluate water jets for herding oil, as
well as additional development. The
sections that follow describe the uses of
the jets and tests performed on the jets
mounted on a moving oil skimmer and
on individual floats.
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Basics of Water Jet Use
Introduction
Two primary phenomena contribute
to the success of a water jet:
1. In Phase I, current initiated by out-
ward splatter of the water stream
when it contacts the body of water
helps prevent oil from being hit by
the water jet and subsequently
entrained into the water column.
The moving jet creates a slight
elevation in water level directly in
front of the impact point. The out-
ward splatter and slight surface
elevation combine to create a
mechanism that parts an oil slick
directly forward of the impact
point.
2. Phase II is produced by the air
entrained in the water by the jet.
Rising bubbles produce a current
that displaces water from on top of
the bubbles and draws water with
them as they travel to the surface.
When the bubbles reach the
surface, they push the last layer of
water out of the way and then
burst. The water following the
bubbles continues to the surface
and dissipates radially. The larger
bubbles rise first and fastest and
produce a strong initial current;
the smaller rise slowly and main-
tain the surface current even after
the water jet has been removed
from the area. A turbulent inter-
action between jet and water body
is important to produce a large
number of small bubbles so that
the oil slick will be kept in a desired
location A stationary water jet
will develop a "crater wall" sur-
rounding the impact point due to
the bubbles trying to rise directly
up into the jet.
A third oil moving mechanism, pro-
duced only by a moving water jet, or a jet
in a current, is a wave train of rolling,
breaking waves not unlike those pro-
duced by a vertical solid staff towed
through a body of water. These waves
give an initial push to the oil by rolling it
to the side of the path of the water jet.
Each water jet produces two waves: one
is developed as a bow wave originating
at the point of impact and the other at
the point where the water surface rises
up behind the jet directly aft of the
impact depression. The turbulence pro-
duced by these waves results in some
oil entrainment, but it is not much since
these waves seldom exceed 2 cm in
height. Besides, the rising bubbles aid in
bringing any entrained oil to the surface
quickly.
The work presented in the report
summarized here shows the ability of
water jets to effectively move an oil slick
in all wave conditions at high speeds
without significantly entraining oil.
Although originally intended to prove
the feasibility of using water jets to
control oil slicks for testing, the project
was expanded to investigate the use of
water jets to converge a wide, thin slick
into a narrow, thick one. Problems en-
countered by trying to use a fabric oil
boom to converge oil slicks during
recovery operations have proved it to be
an expensive and low speed operation.
The operation could be simplified and
sped up if water jets could be substi-
tuted for the boom.
Conclusions
Vertically directed water jets proved
capable of moving and holding an oil
slick on the surface of water at all
speeds tested (up to 6 knots) and in all
wave conditions (up to 1.2 m wave
height).
Despite the turbulence produced by a
water jet when plunging into the
water's surface, a relatively high cur-
rent and thick oil slick must be present
before a substantial amount of oil can
penetrate the crater produced by the jet
and be entrained beneath the water
stream. Very little oil entrainment was
noticed, even with the thickest slick
(5 mm) tested at a tow speed of 6 knots.
The rolling waves produced by the
passage of the water jet helped to move
the oil initially. Some oil is entrained by
the rolling bow and following waves
produced by the jet, but the oil remains
near the surface and rises quickly as it is
moved with the currents produced by
the rising bubbles.
When converging an oil slick,
sufficient time must be allowed after the
water jet passes an area to enable the
surface current to fully develop and to
move the oil slick before an oil skimmer
can most effectively encounter the
thickened slick. This could be anywhere
from 3 to 60 sec, depending upon the
desired convergence.
Thick oil slicks were not moved as
easily as thin oil slicks.
The converging water jet performed
best with the use of two and three pairs
of jets at a high pressure. At 6 knots, a
4.5-m wide, 1.08-mm-thick slick was
converged to a 0.6-m wide, 8.1-mm-
thick slick in 10 sec. These results are
probably not the maximum attainable
using three pairs of jets. Since the first
pair of jets were positioned wide and
forward of the oil slick, their full effec-
tiveness was not utilized.
The most effective performance in the
single jet tests occurred at the highest
pressures with the largest nozzle, at low
tow speeds, and at a nozzle exit height of
0.4 to 1.0 m above the water's surface.
The water jet system performed well
and was free from major breakdowns
throughout the test program. A slight
burr on the inside of the nozzle, how-
ever, could cause the water stream to
lose coherence and spray more; thus,
the penetrating and air entraining
power of the jet is diminished and, sub-
sequently, oil slick movement
performance decreases. Before assem-
bly, pipes and nozzles should be
checked for imperfections and rocks and
other foreign matter should be removed
from the hoses.
Recommendations
Given the problems encountered with
the other methods, recommend using |
water jets to maintain oil slick for test
purposes at OHMSETT until a better
method is found.
Before using a water jet system to
move oil, examine it for burrs on the
insides of the nozzles and for foreign
objects (e.g., small rocks) in the piping.
Any flow disturbance decreases the jet
efficiency.
Investigate methods to increase air
entrainment by the jets. Increasing the
cohesiveness of the water stream via
nozzle design, air injection into the
nozzle before the outlet, or screening
over the exit of the nozzle are a few
ideas that warrant investigation.
Discussion of Results
In addition to the coherent jet tests
performed as part of this project, a test
run was done using a submerged pipe
discharging compressed air to part an
oil slick. A 50-kW, gasoline engine air
compressor supplied the 2.0-cm ID pipe
with 210 kPa air pressure. The tests
were run at 4 knots and calm water
through a 1-mm slick. The results
showed a very clean path cut through
the oil, but the oil slick movement was
significantly less than that produced by
a 2.1-cm ID water jet at 140 kPa water^
pressure. During tank cleanup one day,
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a 6.1-cm ID hose connected to a
225-kW, 1250-mVhr air compressor
was used to move oil away from a tank
wall. The air pressure was approxi-
mately 560 kPa pressure. Air was
directed at the oil slick from above, and it
was also submerged to bubble up air. In
all configurations attempted, the com-
pressed air source could not match the
oil slick movement capability of a single
2.1-cm ID fire hose at approximately
420-kPa water pressure. The power re-
quired to drive the fire hose was about
20 kW.
The tests were successful in
revealing how the independent param-
eters tested affect water jet perform-
ance. Direct comparison of slick
movement between the convergence
tests and oil divergent tests is difficult.
Oil movement in the convergency tests
was less than that recorded during the
slick diverging tests because of the
opposing currents developed by the
pairs of jets and the buildup of oil
between them. Other causes for the
different results were the longer pipe
nozzles used in the slick diverging tests
and the difference in height from the
water of the nozzles. The longer pipe
(length to diameter greater than 15)
resulted in a more coherent water
stream being delivered. This water
stream entrained air well without the jet
splattering onto the oil slick and thereby
entraining oil. A coherent water jet of
the size and at the pressure tested per-
formed best at a height of 0.4 to 1.0 m
above the water's surface. The parting
slick or divergent tests had the nozzle
heights within this preferred range
whereas the convergence slick tests
had nozzle heights above 1.0 m. The
general effects of the independent
variables, however, can be qualitatively
compared between the tests. In this re-
gard, the convergent and divergent tests
can be discussed together.
When the oil slick visual estimates
were compared with known widths of 5 m
over a 30-m distance, their accuracy
was within 0.3 m. Photograph compari-
son data for the slick convergence tests
were taken with a Polaroid camera; the
accuracy of this method was about the
same.
The effects c/' the independent
parameters on oil slick movement are
discussed individually.
Tow Speed
The time required to part a slick a
given distance was inversely propor-
tional to the tow speed using the same
water jet. If a water jet parted a slick 3 m
in 15 sec when run at 2 knots, the same
jet would require 30 sec to part the slick
3 m at 4 knots. This generally held for
the slick convergence tests until inter-
action occurred between the jets on
either side of the slick. Such a relation-
ship would probably break down for
smaller water jets and faster tow
speeds. Surface tension effects would
probably cause a small water jet to
splatter somewhat upon impact rather
than penetrate and entrain air.
Wave Conditions
Nonbreaking waves appeared to have
little or no effect on water jet perform-
ance. Inherent difficulties in distributing
a uniform slick onto a harbor chop sea
state resulted in oil slick width vari-
ations. Such variations can account for
the relatively minor deviations of the
harbor chop results from the calm water
results.
Number of Water Jets
The more water jets used, the greater
the control of the oil slick. This is
reasonable since surface current
controls the oil slick and the more water
jets in operation, the greater the surface
current produced. Since the slick part-
ing tests used only one nozzle, there is
no graph from those tests to illustrate
this point.
Water Jet Pressure
The greater the water jet pressure,
the greater the oil slick control. In the
convergence tests, however, there was
a point of diminishing returns. For the
first 15 m in the six-nozzle case at 4
knots, 140 kPa pressure was sufficient
to move the oil slick from 62% to 88% of
the distance that water jets using 420
kPa moved the slick. For the second 15m,
140 kPa moved the slick 100% of the
distance moved using 420 kPa. When
using only two nozzles, the higher
possible pressures resulted in greater
slick control over the entire observation
time. These tests also showed that a
converged slick will spread again quick-
ly once the currents produced by the two
water jets subside.
Slick Thickness
The slick convergence tests showed
consistently that the thicker the oil slick,
the more difficult it is to move. With the
arrangement of water jets tested, a
4.5-m-wide oil slick of 1 to 2 mm thick"
could be thickened to 5 to 6 mm (3 to 5
times as thick). The spreading forces of
the oil and jet interaction appear to limit
convergence and thickening of an oil
slick beyond this. A thicker slick of 6.23
mm was driven to a 13.35-mm
thickness. This, however, is a reduction
of width and an increase in slick thick-
ness of only a factor of 2.14.
The slick parting test results were not
as consistent. Some tests turned in
higher performance in a thicker slick
whereas others gave the expected
poorer performance. Since a thicker oil
slick spreads faster than a thin one,
parting a heavy slick should be more dif-
ficult than parting a thin one. The better
performance in heavy slicks is probably
an abnormality in the data caused by
wind and/or errors in slick sighting.
Nozzle Size
A larger ID nozzle performed better
than a smaller one at the same
pressure. The 2.7-cm-ID nozzle outper-
formed the 2.1-cm-ID nozzle at all
speeds tested. Since more water will
flow through a larger pipe than a
smaller pipe for a given pressure,
greater fluid flow should be expected to
entrain more air and thus create a
stronger surface current.
Nozzle Height
The best performance was achieved
when the nozzle exit was 0.4 to 1.0 m
above the water's surface. Above the
optimum height, the water stream was
given a chance to spread and lost its co-
herence; penetration was reduced, and
thus, the amount of air entrained was
reduced. Belowtheoptimum height, the
jet did not have enough time to fully
develop the turbulent boundary layer
that transported'air a long with it into the
receiving water. The result was the
same as having the nozzle too high—
less air was entrained into the water
column producing less surface current.
The crater that prevented oil from get-
ting beneath the jet was also reduced in
both cases and more oil entrainment
resulted. This may not hold true for
other types of nozzles or for water pres-
sures not in the range tested.
The waves produced by a moving jet
entrained oil to a maximum depth of
about 15 cm. The oil rose quickly to the
surface as it moved away from the point
of impact. The jet was recorded to
entrain air to beyond a 1-m depth. No oil
was seen to be entrained to such
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depths. This gave good evidence that
the crater could effectively part the oil
slick and keep it from beneath the water
jet. The rapid rise of the wave-entrained
oil to the surface probably resulted from
small bubbles of air entrained by the
jet rising into the oil droplets and
making the bubbles more buoyant.
A nomograph developed from the
results of the convergence tests is used
to determine the size and number of
water jets and the water pressure to the
jets needed to converge a 1 -mm oil slick
at 4 knots. A different arrangement of
water jets would render a different
nomograph.
To use the nomograph, decide how
wide a slick (e.g., 3 m) is to be converged
to the necessary width (e.g., 1 m) and
draw a straight line between the two
widths. The number of nozzles (4) and
the pressure necessary (90 kPa) is read
from the scales.
Water Jets Mounted on a
Moving Oil Skimmer
Introduction
To have a practical application to
large-scale oil spill recovery, the water
jets must be able to be mounted and per-
form well on a moving oil skimmer.
Tests conducted at OHMSETT were
designed to develop an oil converging
system to be incorporated with the U.S.
Coast Guard's Zero Relative Velocity
(ZRV) fast current oil skimmer. The
objective was to converge a 6-m-wide
slick into a 2.7-m-wide slick (oil
skimmer inlet size) at 6 knots in various
wave conditions. Since the principle of
the ZRV skimmer consisted of oil ab-
sorption and adsorption onto a floating
composite belt, the oil slick had to be on
the surface when it was in the reduced
width. Oil entrained during the slick
convergence would not be recovered by
the skimmer.
The test program looked at the ability
of a pair of water jets to converge a slick
while mounted on a catamaran and at
the entrainment developed bythe water
jets. The independent variables of the
test were water jet nozzle size, tow
speed, oil slick thickness, wave condi-
tion, water pressure, number of water
jet nozzles in service, and water jet
nozzle attitude. The dependent vari-
ables were oil slick movement and
amount of oil entrainment.
Conclusions
Water jet booms can be successfully
incorporated onto a moving oil skimmer
to converge a wide thin slick into a nar-
row thick one for easier oil recovery.
Vertically directed jets proved to be
the best all-wave performers. Angled
jets performed slightly better than the
vertical jets in calm water, but per-
formed erratically in wave situations.
With angled jets, the point of impact and
the distance between the nozzle exit
and p'oint of impact changed drastically
when the jet-mounted long booms
reacted to the catamaran's pitch and
heave in waves.
Using the electric-motor-driven fire
pump available on the OHMSETT main
bridge, the best performance at differ-
ent tow speeds by the 7.25-m wide
water jets can be found in Table 1.
A satisfactory boom length for a water
jet off the bow of a skimmer 10 to 15 m
in length is apparently from 6 to 12 m. A
longer water jet extension improves
performance in calm water. Any pitch-
ing and heaving of the vessel, however,
is amplified by the long boom. If the
boom is too long, vessel movement can
cause the water jet to be raised high
above the water's surface and plunged
into the water regularly. Such action
renders the water jets ineffective.
The stationary tests revealed that
some oil is entrained by a passing water
jet but that almost all of the oil slick
remains on the surface. Oil that is en-
trained is carried away from the water
jet impact point as it rises to the surface.
The angled jets appeared to entrain
more oil.
A pair of water jets can be expected to
essentially double the sweep width of
the U.S. Coast Guard's ZRV skimmer
from 2.7 to 5.4 m at speeds up to 4
knots. To perform well at 6 knots, a
longer boom is required.
Recommendations
Investigate the designs of collapsible
water jet booms. Transportability and
longevity of the booms would be en-
hanced if they could be folded for
storage on the bow of the skimmer.
Conduct water jet/skimmer tests
with the skimmer traveling with the
waves to reduce the pitch and heave of
the vessel.
Fit the U.S. Coast Guard ZRV skimmer
with water jet booms divided into two
3-m and two 1.5-m sections for each
side. Assemble a suitable length boom
depending upon skimming operations
and sea conditions.
Stiffen and reinforce the water jet
boom sections to eliminate whip when
operating in waves and to withstand
rough handling. Such protective con-
struction could be placed inside rather
than outside the boom pipe as was done
in these tests. Using internal reinforcing
members would require special
consideration to ensure adequate water
flow with minimal pressure drop.
Discussion of Results
The resu Its obtained from earlier tests
were again proven by these series of
tests—the larger the nozzle and the
greater the pressure, the better the
performance. This is clearly shown in
comparison of the plots of slick move-
ment using water jets from 1.25 to 2.66
cm ID.
The benefit of angling the jets was
also established in these tests. By
angling the jet in the direction of the
desired oil movement, performance was
increased on 7-m booms. Even an angle
of 10° was beneficial. Tests only
included inwardly directed angles up to
20°. The increased performance in
using the horizontal component
resulted from the force of the angled
water stream to push the oil. When the
jet was not vertical, the reduced amount
of deeply entrained air did not affect
these tests, since the objective was to
move the oil quickly, not hold it in place
after being moved. When a 7-m boom
Table 1. Performance at Different Tow Speeds
Tow
Speed
(ktsj
2
4
6
Nozzle
Size
(cm)
2,1
2.1
2.1
Pressure
(kPa)
210
560
600
Water Jet
Angle
in/fwd
(degrees)
0/0
20/0
10/45
Wave
Cond.
calm
calm
calm
Orig.
Slick
Width
(m)
6.1
4.2
6.1
Final
Slick
Width
(m)
1.7
1.1
2.9
Slick
Movement
(m)
4.4
3.2
3.2
Note: Not all nozzle sizes were tested at all pressures and tow speeds.
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(including nozzle fittings and swivel
joints at the vertical stanchion) was
used on the catamaran, the slick had to
be converged in 3.6 sec at 4 knots. For
such a short interaction interval, the
slick holding potential of the water jets
was not required, the slick was moved
further using a 12-m boom; anghnglhe
jets inward apparently did not consis-
tently increase performance.
The forward angle of the water jets
was not beneficial to performance. The
theory behind the forward angle was to
place the point of impact further ahead
of the skimmer, essentially increasing
the length of the boom. Using a longer
boom increased performance, but the
water jet nozzle needs to be relatively
close (approximately 1 m) to the point of
impact to perform well. By angling the
jet forward, the travel path of the water
stream was increased beyond the
distance where the stream began to
lose coherence. Penetration and air en-
trainment was reduced, and the impact
area of the water was increased. The
horizontal force component of the water
stream was directed forward, which did
not help to converge the slick. At times,
the forward angled jet did produce a
dramatic initial wave that rolled the oil
away from the jet. It appeared to "plow"
the surface of the water over and give
the oil a push off to the side! The plowing
effect was especially noticeable when
the jet was angled forward and inward.
This initial push was not enough, how-
ever, to make up for the loss in current
usually developed by the entrained air
and the set of rolling, breaking waves
produced by a vertically directed jet.
The pitch of the catamaran in waves
resulted in the worst performance by
the angled water jets. Vessel roll and
heave also cause changes in impact
point and length of travel of the water
jets, but the effects were not as
dramatic. Because the jets extended
over 6 m beyond the bows of the hulls,
the amplitude of pitch was increased at
the water jet nozzles. When the nozzles
were raised upward during a stern pitch
of the catamaran, the point of impact
moved dramatically forward from its
calm water or intended position. When
the jet was angled at 45° inward and
45° forward, the water sprayed over the
oil slick entraining oil and causing an
irregularly-shaped slick. This also
lengthened the water stream's path of
travel and, thus, decreased the jet's
effectiveness. When a bow pitch was
experienced, the impact point was
brought back across the slick to directly
beneath the nozzles. During some wave
tests, the performance of the water jet
was indeterminant because the result-
ing slick was so irregular.
One of the most important findings of
this test program was that angling the
water jet nozzles is not beneficial when
operating in wave conditions that cause
the vessel to pitch, roll, and heave.
Since such conditions are the norm in
oil spill recovery, a general operation
rule can be made—point the jets
straight down into the water. This
simplifies the construction and use of
the water jets. A system that has the
best chance of performing well when
used in its simplest configuration will
probably be looked upon favorably by
field operators.
Three water jets in tandem, spaced
about 1 m apart, performed as well as or
better than one water jet at the same
pressure. By using more than one jet,
however, a significant drop in available
water jet pressure was experienced. In
some instances, an increase in pressure
of one water jet could equal the per-
formance of the three jets with reduced
pressure. A possible drawback to using
the tandem arrangement at high tow
speed was that the wave train produced
by the three jets persisted longer than
that produced by a single jet. Although
the breaking waves move oil, they also
entrain it slightly belowthesurface. The
entrained oil may not have sufficient
ti me to rise if the breaking wave persists
into the mouth of the skimmer.
Using a stationary catamaran and
pivoting the water jet boom in an arc
provided an interesting view of oil slick
movement mechanisms and entrain-
ment characteristics of a water jet. From
OHMSETTs underwater observation
window, it is possible to view a particle
behind and beneath a water jet. The
vertically directed jets appeared to en-
train the most air to a greater depth,
which maintained the surface current
caused by rising air bubbles for the
longest period of time. The angled jet
moved the oil the fastest but also en-
trained the most oil.
Water Jets Mounted on
Individual Floats
Introduction
Water jets on individual floats have
the potential to solve many problems
associated with oil spill recovery opera-
tions. Equipment deployment, wave
effects, ship traffic interference, and fire
are some of the hindrances that could
be coped with by properly using water
jets on floats. The tests described here
aimed at using such floats in a fast
current situation.
Equipment Deployment
An oil barge offloading site is often
required to ring the barge with a fabric
boom before oil can be offloaded.
Obviously, the boom cannot be in place
before the barge arrives; therefore, a
trained boom deployment/retrieval
team must be used when the barge
arrives and leaves. A water jet system
could be used in place of a fabric boom.
Water jets on floats could be supplied by
submerged hoses, left in position, and
the only action required would be to
start a pump and turn a valve or two. The
water jet floats could be bumped aside
or even momentarily submerged by the
barge and tug as they arrive or leave.
Wave Effects
When using conventional fabric
booms to converge an oil slick into a
skimmer, the reflection of small waves
between the booms causes problems.
The waves are finally concentrated in
front of the skimmer inlet causing oil
entrainment, oil loss from the booms,
and a decrease in skimmer performance.
A series of water jet floats used in place
of the booms could allow waves to pass
and yet converge the oil.
Ship Traffic Interference
If an oil spill occurred and oil retaining
had to be conducted in a ship channel,
the damage caused by a wayward
vessel could be minimized if it passed
into the retained oil slick through a
water jet float line. Many a fabric boom,
while retaining oil, has been destroyed
by errant ship traffic. The result is a loss
of oil retention until the vessel is
removed and the boom repaired.
Fire
Since the floats and jets can be made
from steel, the possibility of damage to
water jet floats by a fire is less than to a
conventional fabric boom. The flames
may not even reach the water jet floats
because the action of the water jets
maintain the oil away from the equip-
ment.
Conclusions
The use of water jets mounted on
individual floats to control an oil slick is
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feasible. Problems must be solved, how-
ever, before the concept becomes
practical for field use.
Water jet floats can be constructed
using plywood, standard piping mate-
rial, and suitable floatation (e.g., infla-
table bags, steel drums, logs).
Water jet floats allow waves normally
reflected by conventional fabric booms
to pass while rataining an oil slick.
Maintaining the individual floats in a
predesigned orientation and formation
while towing proved difficult. Because
of the fluid drag, floats drifted behind
one another. Before proper counter-
weights were used to counter the
forward pitching force of the supply
hose, the floats would occasionally sub-
merge at their bow and flip over.
Recommendations
Since only one side of a converging
boom system was tested, the perform-
ance of a complete oil slick converging
system can only be extrapolated.
Conduct another test series using at
least three floats per side. Using tie lines
across the sweep width should make it
easier to maintain the proper orienta-
tion and relative position of the floats.
The tie lines would stabilize each float
by using the float's mirror image to
supply a corrective force to balance the
drag forces on the floats.
Build three prototype permanent
water jet floats and place them in the
OHMSETT tank behind the wave
generator. They would keep oil from
gaining entrance behind the flaps and
becoming emulsified and would show
possible problems when using water jet
floats in a rough environment.
Design and test a water jet float more
suitable for towing in a desired pattern
with other floats. Perhaps a circular
float such as a tire inner tube would be
advantageous, since a slight rotation of
the system would not cause a change in
the resultant drag forces.
Investigate use of a rudder skeg on
the underside of the type of floats used
in these tests.
Discussion of Results
The water jet float concept performed
well, but maintaining float position and
stability in a diversionary mode of
operation presented problems that must
be solved before the floats can be con-
sidered a viable alternative to fabric
booms. An advantage to the water jet
float system over the fabric boom is the
ease of relocating a poorly positioned
6
float to divert oil rather than realigning
an entire boom section while fighting
the current. The floats in the tests were
positioned 15m apart measuring in the
longitudinal axisof thetankand 1.8 m in
the transverse axis. These positions
were selected for tests using tow
speeds of from 4 to 6 knots. The spacing
seemed to work well for the 4-knot tests
but fell a little short-far the 6-knot tests.
the oil slick was not diverted the entire
1.8 m before the following float con-
tacted the oil slick. For 2-knot tests,
however, it appeared that the trans-
verse spacing could have been increas-
ed to about 3 m. Little effort would be
required to move a water jet over 1.2 m
if the float was positioned by a bridle to
two anchor points upstream and on
either side of it. The draft of the floats
was about 5 cm with a projected cross
current length of 0.5 m. This resulted in
a projected area of about 0.025 m2. A
fabric boom with a draft of 0.5 m and a
projected length of 3 m would have a
final projected area of 1.5 m2. The force
required to overcome the fluid drag on
the boom would be 60 times that to
move the water jet float—using VzpAv2-
CD as the equation for drag force and
letting CD = 1.5. The force to move the
fabric boom in a current of 2 knots
would be about 118 kg, whereas the
force required to move the water jet
float would be about 2 kg. Problems with
ropes stretching and breaking, knots
giving away, or anchors moving would
be greatly reduced using water jet
floats.
The structure of the water jet floats
used in the test program was dictated by
the materials on hand or readily avail-
able. Problems of front end submer-
gence, capsizing, and position drift
could be solved by proper float design
and water supply hose location. The
small work boat with a gasoline-driven
pump onboard experienced no stability
problems. Proper rigging or using a
rudder skeg could eliminate any
position drift problem. If two sets of
water jet floats are used in front of a
skimmer, the tie lines and drag force of
the skimmer should be able to keep the
floats in position.
The water jet floats performed as well
in harbor chop waves as in calm water.
The vertically directed jets maintained
their approximate point of impact
despite the roll, pitch, and heave of the
buoyant floats.
Using a high-pressure gasoline-
engine pump to power a water jet
instead of using a hose from the bridge
pump seemed to have more advantages
than' disadvantages during the tank
tests. During field operations logistic
problems may outweigh those advan-
tages An individual pump on the float
eliminated needing the heavy water
supply hose and made towing and main-
taining float position and stability
easier. In the field there would be no
hose to be deployed, rammed, ruptured,
or lost. The drawback is maintaining the
pump so that it performs continuously. |
A large gasoline supply can be included
on the float, but it must be refilled
eventually. The pump inlet may become
clogged by debris or the machinery may
break down, thus leaving a breach in the
oil spreading defenses. A more reliable
electric-driven pump mounted on shore
or a large vessel, however, would
necessitate using the supply hose.
The full report was submitted in ful-
fillment of Contract No. 68-03-2642 by
Mason & Hanger-Silas Mason Co., lnc:,
under the sponsorship of the U.S.
Environmental Protection Agency.
MichaelK. Breslin is with Mason & Hanger-Silas'Mason Co., Inc., Leonardo, NJ
07737.
John S. Farlow is the EPA Project Officer (see below).
The complete report, entitled "Using Coherent Water Jets to Control Oil Spills,"
(Order No. PB 81 -232 720; Cost: $11.00, 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
•d US GOVERNMENT PRINTING OFFICE, 1981 — 757-012/7341
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