vc/EPA
                                  United States
                                  Environmental Protection
                                  Agency
                                   Municipal Environmental Resear
                                   Laboratory
                                   Cincinnati OH 45268
                                  Research and Development
                                   EPA-600/S2-81 -229  Dec. 1981
Project  Summary
                                   Performance Testing  of the
                                   DiPerna  Sweeper
                                   Michael K. Breslin
                                    The DiPerna Sweeper, a partial-
                                  vacuum oil skimmer, was tested in a 2-
                                  week test program conducted at the
                                  U.S. Environmental Protection Agen-
                                  cy's Oil and  Hazardous Materials
                                  Simulated Environmental Test Tank
                                  (OHMSETT) in Leonardo, New Jersey.
                                  Forty-three oil  recovery tests were
                                  run. The object of the program was to
                                  establish a range of best performance
                                  for  the skimmer under various  en-
                                  vironmental  conditions in light and
                                  heavy oils.
                                    The DiPerna Sweeper is a self-
                                  contained, floating oil skimmer that
                                  can operate  in either a stationary or
                                  advancing mode. Its principle  of
                                  operation is based upon drawing oil
                                  and water into a sealed container by
                                  creating  a  slight vacuum  in the
                                  container. A floating weir serves as
                                  the inlet. The partial vacuum is created
                                  by  pumping  fluid from the sealed
                                  container. The container serves as an
                                  oil/water separator. Separate pumps
                                  draw water from the bottom of  the
                                  vessel while others draw oil from the
                                  top.
                                    The device was able to recover over
                                  75% of the oil presented to it in calm
                                  water at tow speeds up to 2 kts.
                                  Performance decreased in waves.
                                  Modifications are  suggested to  im-
                                  prove such performance. The separator
                                  functioned well. In one case, the oil
                                  offloaded from the skimmer was 95%
                                  free of water.
                                    This Project Summary was devel-
                                  oped by EPA's Municipal Environ-
                                  mental Research Laboratory. Cincin-
                                   nati, 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
                                    The DiPerna Sweeper (Figure 1) was
                                   designed by James DiPerna and built by
                                   the Brewer Dry Dock Company,* both of
                                   Staten Island, New York. In April 1979,
                                   the skimmer, which can be transported
                                   on  a  common-carrier, flatbed tractor
                                   trailer, was moved from the shipyard to
                                   OHMSETT. The original gravity flow
                                   design was modified toa partial vacuum
                                   design at OHMSETT under the direction
                                   of  Mr. DiPerna. The merits of the
                                   conversion were demonstrated using a
                                   small model built by Mr. DiPerna (Figure
                                   2). The modifications did not  affect the
                                   basic  nonmixing oil/water collection
                                   principle. Other modifications suggested
                                   by Mr. DiPerna regarding removing the
                                   skimming head and altering the skimmer
                                   to allow the fluid to flow over a weir
                                   attached to the separator were not acted
                                   upon at this time.
                                    On 14 May, the skimmer was lifted
                                   into the test tank where 43 oil recovery
                                   tests were run with light and heavy oils,
                                   which are described in Appendix  B of
                                   the full report. On 25 May, the device
                                   was removed from the tank. All  per-
                                   formance testing was conducted at
                                  "Mention of trade names or commercial products
                                  does not constitute endorsement or recommenda-
                                  tion for use.

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Figure 1.    The DiPerna Sweeper being lifted into the test tank.
OHMSETT by the operating contractor
Mason & Hanger-Silas Mason Co., with
the guidance of the U.S. EPA Project
Officer.

Device Description
  The  original design of the DiPerna
Sweeper consisted of a gravity-flow API
oil/water separator mounted between
two floatation chambers (Figure 2). A
segregated floating  head  with an
overflow weir, connected to the main
portion of  the skimmer  by  a  20-cm
diameter hose, served as a fluid inlet
(Figure 3).  Oil and water were drawn
into the skimmer over the weir by
lowering the  water level inside the
device below the outside waterline. This
was accomplished  by pumping  water
from the bottom of the  separator. Oil
collected in the first compartment was
routed to a rear compartment where it
was offloaded by a small pump. The
water was  removed from the bottom of
the separator  in the second  compart-
ment.  This design  allowed the use of
less than half of the separator volume
since a good portion of the separator
extended above the mean waterline.
Modifications  to seal the top  of  the
separator  from the atmosphere and
reroute pump piping were carried out
while  the skimmer awaited testing at
OHMSETT (Figure 4).  The  changes
permit the use of the entire volume of
the oil/water separator and simplify the
offloading of collected oil.
  With the top of the separator sealed, a
partial vacuum  is induced  inside the
separator by pumping air out from the
top of the chamber. Fluid allowed over
the inlet weir fills the evacuated area.
Thus a flow of fluid over the weir can be
maintained even though  the fluid level
inside the separator  is above the
waterline. Water is still removed from
the lower rear of the separator, but the
oil outlets are relocated to ports welded
flush with the sealed deck. The design
utilizes  the  entire volume of the
oil/water  separator with a minimum
increase in vessel draft.
  The segregated floating head was not
modified from the original design. The
design and concept of a light, wave-
following skimming weir, which was
separate  from the main body of the
skimmer, appeared sound and did not
warrant change. The head was detached
from the separator  so it could follow
waves, maintaining the weir  at the
desired depth. Swamping of the weir
and sump by waves would be avoided if
it performed as designed. The skimming
head had not been previously tested in
either a model or in full scale. Chambers
and  valves are incorporated into the
head  to permit ballasting with water.
  The sweep width of the head is 1.2 m;
the width of the weir is 0.5m. Directly
behind the weir  is a small sump that
leads to the large hose connecting the
head to the skimmer. Additional skim-
ming  heads can be attached  to  the
skimmer with  the  use of small ports
welded to the fluid inlet pipe. Because
these heads can  be used at a distance
from the skimmer,  oil can be collected
from shallow areas  or under piers while
the main skimmer sits in deeper water.

  Fluid  is  drawn into  the skimmer by
pumping water from the lower rear of
the separator. It enters the separator
chamber at the front directly beneath
the deck. Unmixed oil is delivered to the
top of the separator where it floats; the
water  seeks the lower  level.  In this
manner, oil and  water mixing is mini-
mized. The  residence time of the oil and
water in the separator can be varied
depending  on  the  offloading pumping
rate. The pumps  used in the OHMSETT
tests had a combined flow rate of about
120 mVhr. Residence time (190 sec)
with all of the pumps operating appeared
more than adequate.

  A small, sealed deck house with plexi-
glass windows  was placed  on  the
skimmer with a  pipe  running  from  it
through the deck  to the keel of the
separator.  Water is drawn from the pipe
producing fluid flow up the pipe.
Windows  allow  the operator  to  see
when oil is being drawn up the pipe and
thus slow  the water pump rate or to
offload oil.

  The vessel had an overall  length of
5.5m, a beam of  2.9m, a draft of 1.7m,
and a freeboard  of 1m. The vessel
weighed about 3000 kg.
Results

  The DiPerna Sweeper proved to be a
simple and effective design incorporating
only  pumps for oil recovery. The
skimmer can be pushed, towed, or self-
propelled  during its oil  collection
operations. The force of the water from
the pump discharge off the rear of the
skimmer is enough to propel the device
forward at about 0.25 to 0.5 kt. Such a
forward speed may be suitable for tank
testing but would not be practical for
field  use.  The skimmer  is  chiefly
designed to be attached  to oil booms
where winds and currents would drive
oil  to  the skimming head; it is not
intended for high-speed skimming.    t

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                 Mast
                              Starboard
                              Flotation Chamber
                                                          Water Outlet

                                                                 Oil Outlet
   Skimming
      Head
                                             Oil/Water Separator
                                               (in the keel only)
                                                       Oil Transfer Pipe
                                  V~^"L---—
                                 \1V-—-"^ Oil/Water
                  Oil/Water Inlet


Figure 2.    Cutaway view of original DiPerna Sweeper design.


                            Weir (inlet)
  Converging Sides
                                                      Sump

                                                          Connecting Hose
                                                         Flotation and Water
                                                         Ballast Chamber
                                                    Water (ballast) Outlet
 Figure 3.    Isometric view of the floating skimming head.
                                          Water Outlets and Filling Ports
          Mast
     Skimming
                                 Oil Outlet
                       New Welded Deck
Sealed Deck House

          Water Outlets
           Skimming
           Head

.Figure 4.    Cutaway view of the modified DiPerna Sweeper.
Floating Skimming Head

  If the skimming head is to be retained,
a major  redesign  is necessary. The
shovel-nose design of the head caused
many problems in the presence  of
waves. It acted as a damper to slow the
inlet weir's wave response; it produced
turbulence in the oil  slick when it
heaved above the waterline; it provided
a spillway for the excess oil and water
that was washed up to the weir but
could not enter. As the oil and water ran
down the nose, it mixed vigorously and
pushed  the oncoming  oil  slick away
from the  head.  The  best solution
seemed to be a deeper weir cut in waves
so the shovel nose would  never rise
high enough to cause problems. Under
tow in both calm water and waves, the
shovel  nose  acted as a diving plane
causing the weir to sink below the calm-
water setting  and the head  to pitch
forward. The nose also caused problems
with ballasting the skimming head. If
the ballast water drained to the rear
areas because of a rearward pitch of the
head, the nose became a forward
buoyancy chamber that maintained the
head in the tilted position. SCUBA diver
weights,  guy wires, and a  wire  rope
cable to a winch on the mast provided
the ballast and kept the weir at the
desired calm water setting for the tests.
An  unfortunate interference occurred,
however because of the use of the guy
ropes and the wire rope on the skimming
head. When  a wave trough was en-
countered, the  ropes  restricted the
downward travel of the head causing a
sudden stop.  This prevented the weir
from maintaining a constant depth and
allowed water and oil to flow down off
the nose onto the approaching oil slick.
Without the ropes, however, the move-
ments of the skimming head from side
to side and pitching forward would have
made oil collection much more difficult.
The removal of the shovel nose from the
skimming head and judicious placement
of floatation and ballast should solve
most of the above problems. A feature
the skimming  head lacks is a vertical
plate to prevent waves from splashing
over the head and,  thus,  losing oil.
Finally,  the weir tended to raise up
above the waterline when the fluid in
the head sump was pumped out and
thus restricted  flow  over  the weir.
However,  if the sump did not drain
somewhat in  between waves, the next
wave would swamp the sump and oil
would be washed away from the weir. A
self-compensating weir lip or inlet valve

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could be built into the skimming head to
prevent such starving of fluid flow.


Oh'/Water Inlet Hose
  The hose used in the tests was too
heavy and too stiff to allow the skimming
head to act independently of the main
body of the  skimmer. If the skimmer
operator  changed his  location on  the
deck of the vessel,  the slight tilt of the
vessel would twist  the hose and alter
the attitude of the skimming head. The
floatation of  the skimming head is not
enough to freely move the inlet hose in
response to oncoming waves.


Oil/Water Separator
  Converting the separator from gravity
flow to  partial  vacuum  made the
additional separator volume available
above the waterline. This accounted for
64% of the 6.3 m3 total  separator
volume. Oil/water separation had to be
enhanced by this change since the fluid
residence time increased along with the
volume. Only during wave tests using
low viscosity oil did any oil  reach  the
water discharge pump inlet, and then it
was very little. This  means that  the
water  discharge capacity could be
increased beyond that  used in these
tests without significantly affecting
performance of the  separator. Onboard
storage capacity of collected oil was also
increased by  the  modification.  The
changes  also provided oil offloading
ports on the  deck that could be drawn
from during a test to increase the mass
flow rate through the skimmer. This was
done by additional pumps placed on the
skimmer.
  Nonturbulent collection of  oil and
water  was  virtually unchanged  by
converting to a partial vacuum skimmer.
The inlet pipe was extended to within
150 mm  of the new decking to deliver
the oil  to the top of the collected fluid.
This prevented the oil from having to
rise up through  the fluid  inside  the
separator and perhaps be swept away
with the water under the baffles to the
water discharge pump inlet.
  The vessel was stable and had a slow
wave response because of the water-
filled keel and  the catamaran-like
arrangement of the  floatation chambers
on both sides of the vessel.


Sealed Deck House
  Purpose of the deck house was to
determine when oil reached the inlet of
the water discharge pipe located
100mm above the keel of the separator.
This would be an  indication that the
vessel was either full of oil or that the
water had been removed from beneath
the oil and oil would be offloaded next.
Since oil  was offloaded from the ports
welded flush with the deck and logistics
prevented tests with enough oil to fill
the skimmer, the deck house was not
put to its designed use. It did, however,
provide an excellent view of the amount
of oil mixed with the water at the bottom
of the skimmer. It also  provided an
additional port from which water could
be drawn to increase the mass flow rate
through the skimmer.
Oil and Water Offloading
Pumps
  The  gasoline-driven pumps that
arrived with the skimmer consisted of a
diaphragm  pump (7m3/hr) for oil
offloading and a  centrifugal pump
(70m3/hr) for water discharge. Both
pumps performed well until carburetor
trouble forced the diaphragm pump out
of service. With the increase in usable
separator  volume, the  pump capacity
could be  increased  without  fear  of
drawing the collected oil out with the
water. It was evident that an increase in
mass flow rate over the weir could
diminish the  turbulence generated  by
the headwave and thus increase the
skimmer's performance at higher tow
speeds. To accomplish this,  an air-
driven double-diaphragm pump (32
mVhr) was placed onboard to offload oil
from an exit port on deck and a gasoline
centrifugal pump (16 mVhr) was placed
onboard to discharge water drawn  up
into the sealed deck house. The resulting
increase in mass flow rate produced  an
increase in performance in both calm
water  and  in  waves. The  general
absence of oil exiting with the discharged
water  would indicate the pump  rate
could be increased to about 225 mVhr
without deleterious effects. This would
give a fluid residence time of about 100
sec in the separator. Since the oil enters
the separator only loosely mixed with
the water, there should be enough time
for the oil to stabilize at the top of the
separator and not be drawn out with the
discharged water.
 Data Discussion
   Recovery Efficiency (RE) was not
 recorded for each test because, less
than halfway through the program, the
oil was offloaded during the test rather
than following  it.  During the test,
offloading  drew an uncontrollable
amount of water  with the oil; this
lowered the RE  of the device. Under
such circumstances, comparing  the
RE's would not render  useful con-
clusions as to the causes. The quantities
of oil offloaded into the barrels gave
representative values of RE if the barrel
was not drained of much water before
the sample  was taken. This was  the
case in several tests  in which  the
procedure was to offload the oil after
completion  of the test run. The values
obtained were 86% for 0.5 kt, 91% for
0.75 kt, 91 % for 1.0 kt, 89% for 1.25 kt,
88% for 1.5 kt, and 87% for 2.0kt. These
values  should be considered below the
capability of the skimmer since  the
amount of  oil  in the one  full barrel
represented 70% of the oil collected by
the skimmer. As the oil was drawn from
the  skimmer,  the oil  layer  inside
decreased to where water was drawn
out with  the  oil.  This lowered  the
percentage of oil in the outlet stream
and subsequently that in the barrel also.
  There was not enough time in the test
program to optimize device settings for
every condition tested so the test results
should  not be considered  the  best
performance possible by the skimmer.
When  time allowed, device settings
were changed and tests were run under
the same tank conditions.
To w Speed
  Increasing tow speed raised a  head
wave in front of the floating head and
created turbulence by forcing more
water to be channeled from the sweep
width of the head (1.2 m) into the width
of the weir (0.5 m). The tow speed at
which performance would begin to
decline should  be predictable by  com-
paring the flow over a rectangular weir
(1.2 m wide) at different water depths
over the weir to the tow  speeds and
pumping capacity of the skimmer. With
the use of one pump, 70 m3/hr of water
could be discharged. A water depth of 4
cm  is needed  for a  70-m3/hr  flow.
Bernoulli's equation predicts a 1.86-kt
tow speed will produce a headwave of
4.5 cm. A  decline in  throughput effi-
ciency (TE) and oil  recovery rate (ORR)
perfomance occurred between 1.5 and
2 kt. With the use of four  pumps (125
mVhr), the point of decline should be.
about 2.2 kt. The data for TE versus tow
speed in heavy oil and calm water show

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 a significant decline in performance
 above 2 kt using four pumps. Extrapo-
 lation of these results suggest that a
 greater pumping capacity would result
 in  better performance at higher tow
 speeds. As long as the current inside the
 skimmer is not large enough to entrain
 and sweep a good deal of oi I to the water
 discharge inlet,  performance will in-
 crease with pumping capacity.
 Waves
   TE and ORR werie greatly decreased
 by the presence of waves. Below 0.75 kt
 in harbor chop  waves, the oil was
 washed away from the skimming head
 by the wave reflection. Above 1 kt, TE
 performance declined to less than 50%
 in the harbor chop. This was because of
 the inability of the skimming head  to
 respond  well to the waves, which
 caused turbulence in front  of the weir
 and allowed waves to splash over the
 head. ORR values leveled outand began
 declining at 1 kt in the harbor chop as
 pompared with 1.5 kt in calm water.
   Regular waves reduced skimming
 performance compared with that.in
 harbor chop. The  harbor chop condition
 varied the water  level at the weir at a
 greater frequency  than the regular
 waves. The skimmer head heaved only
 slightly during the harbor chop, but the
 waves slapped into and overthe weir. In
 regular waves,  the  skimming  head
 heaved a great deal and was often 180°
 out of phase with the oncoming waves.
 A great  deal more  turbulence was
 generated in front of the weir and more
 waves splashed over the skimming
 head and degraded the performance. A
 redesign of the skimming head and inlet
 hose  should increase performance  in
 waves at all tow speeds.


 Oil Viscosity
   Skimmer  TE and ORR performance
 was  superior in the high viscostiy oil.
 Driven by the turbulence  created  in
 front of the weir, the low viscosity oil
 tended to mix with the water and pass
 beneath the skimming head. Although
 the TE results were consistently lower
 in the low viscosity oil, the general
 trends in performance were  very
 similar.  Low viscosity oil reached the
 water discharge  inlet during tests  in
 waves whereas the high viscosity oil did
 not. The amount of oil discharged with
 the water was insignificant, but it points
 to a possible problem  of discharging oil
|if the pumping capacity is increased.
Weir Depth
  This variable was  not  investigated
completely  since the skimming head
rose up in the water if the fluid in its
sump was  lowered very  much. Gen-
erally, the weir was kept at about 60 to
70  mm deep in calm water. In wave
tests, the weir depth varied a great deal
because  of  the poor wave response
capability of the  skimming head. In
wave tests, skimmer performance
increased if the weir was set at a depth
of about 100 or 120 mm before the start
of the test. The lower  setting further
submerged   the shovel nose  of the
skimming head and reduced its presence
above  the  water's surface where it
produced oil-entraining  turbulence.


Slick Thickness
  TE was not noticeably affected by the
changes in  slick thickness; however,
ORR varied  in direct proportion to the
changes.
  Recovery efficiency samples indicate
the device  is capable  of  consistently
high values of RE.


Conclusions
  The DiPerna Sweeper proved effective
in recovering low and high viscosity oils
at tow speeds up to 2 kt (Tables 1  and 2).
Based on samples taken at the  oil off-
loading pump outlet, the skimmer has
the capability of collecting oil with less
than 5% water. This  is  because the
method draws oil and  water into the
skimmer without mixing them and off-
loads the oil  from top of the collected
fluid and the water from the bottom.
  Best  performance  of the skimmer
obtained during the 2-week test program
is listed below (TE in percent; and ORR
in mVhr). RE samples were not taken
on every test and do not appear in the
chart.
                     Discrete samples taken at the pump
                   outlet resulted in RE values of 95.5% at
                   1 kt in calm water and 88% at 0.5 kt in
                   the 0.3-m harbor chop.
                     The skimmer performed best in high
                   viscosity oil  in calm  water.  Waves
                   caused drastic  reductions  in perform-
                   ance, and regular-wave, head  seas
                   resulted in the poorest performance.
                     The  greater the number of pumps
                   removing fluid  from the skimmer, the
                   better  the device performed. Primary
                   objective to improve performance was
                   to get as much of the oil slick into the
                   device  as possible and not worry
                   whether  some  oil was discharged out
                   the stern with the water.
                     The shovel-nose design of the skim-
                   ming head and its attachment to the
                   main body of the device via a large stiff
                   hose  was not  conducive to optimum
                   wave following. Overall performance in
                   waves could be substantially improved
                   with the proper skimming head and inlet
                   hose.
                     The main portion of the skimmer was
                   stable  and generally  unresponsive to
                   waves. This was due to the deep, water-
                   filled keel and the floatation chambers
                   on  both sides of the vessel.

                   Recommendations
                     A redesign of the skimming head and
                   in ret  hose should be undertaken to
                   improve wave response of the hose and
                   head system, to improve the skimming
                   head water ballasting system, to prevent
                   wave  splashover response and  to
                   prevent  turbulence  and headwave
                   production while under tow in  calm
                   water and in waves.
                     The  main  portion of the  skimmer
                   should be outfitted with larger pumps
                   than  those tested.  A pump  with a
                   capacity of about 200 m /hr should be
                   used  to  remove  the  water  from the
                   bottom of the vessel, while a 50 mVhr
                   positive displacement pump should be
                       0.5 kt
               1.0 kt
1.5 kt
2.0 kt
2.5 kt
                     TE   ORR*   TE  ORR  TE  ORR  TE  ORR  TE  ORR
Calm water
0.3m harbor chop
0.3m reg.  wave
95.0  12.7+  96.2 26.3" 95.1 38.0* 75.3 40.2 33.2 22.1
44.1   5.3   72.8 19.4  46.4 18.5 27.3 14.6  ND ND
ND   ND    38.310.0-23.5  9.4 21.1 11.321.0  14.0
*ORR values are corrected to 12-mm-thick oil slicks by multiplying the measured
 ORR by 12 mm and dividing by the actual slick thickness.
*0ne water discharge pump (70 m3/hrj was used. All other tests used four pumps
 (125 rrf/hr total).

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Table 1 . Test Results of the DiPerna Sweeper
Tow Slick
Test Speed Waves Thick
No. (knots) (m x m) (mm)
SD3 0,5

1 0.5
2 0.5
3 0.75
4 0.75
5 1.0

6 1.0

7 1.0
8 1.25
9 1.25
10 1.50
11 0.5


12 1.25
Calm

Calm
Calm
Calm
Calm
Calm

Calm

Calm
Calm
Calm
Calm
0.3 mHC


Calm
11.7

12.4
12.4
13.2
13.4
12.9

12.8

12.8
12.9
10.4
9.4
11.9


10.1
in High Viscosity Oil
Weir
Depth TE
(cm) (%)
6.35

6.35
6.35
6.35
6.35
6.35

7.62

6.35
6.35
6.35
6.35
varied


7.62
95.0

91.3
93.7
91.8
95.0
94.5

84.3

96.2
97.2
95.1
95.1
25.7


93.8
ORR
(m3/hr)
12.4

12.6
12.9
20.1
20.8
27.2

24.1

27.4
28.1
27.5
29.8
3.4


26.5
Comments
140 kg ballast on vessel, wts and ropes
on head
Good test
No losses seen in underwater film footage
Ballast on skimmer raised to 340 kg
Good test, water discharge clean of oil
Small losses less than 1% at boom
attachment points
Oil not hosed in at the end of the test.
95% RE at oil/ water outlet
Good test
Oil shedding seen from the front
Same as test No. 8
Good test
Wave reflection down nose of skimming
head washed oil away, 88% RE at oil/
water outlet
Good test
     13
1.5
Calm
12.6
14
15
16
17
18
19*
2.0
2.0
2.5
0.5
2.0
2.0
Calm
Calm
Calm
0.3 mHC
Calm
Calm
13.1
12.8
12.2
12.8
8.7
9.7
7.62
6.35
6.35
varied
6.35
10.16
46.9
55.9
23.4
30.7
34.3
30.2
27.4
31.8
15.9
4.4
13.3
13.1
 7.62      87.4      36.5   A good deal of entrapment from the
                            skimming head
                            Entrainment much worse
                            Large oil losses seen due to shedding
                            Some oil escaped under the port boom
                            Main skimmer and head out of phase due
                            to waves, jerking action on head caused
                            oil losses
                            New pump on skimmer failed in middle
                            of test
                            Four pumps used - lowered weir to gain
                            flow
*Four pumps were used from this test on except for tests 24, 39, 40, 41, and 42.
     20

     21
     22

     23

     24
     25


     26

     27

     28

     29

     30
2.0

2.0
2.0

0.5

0.75
0.75
 1.0

 1.5

2.5

2.0

0.5
Calm

Calm
Calm
12.4
12.1
0.3 mHC   12.0

0.3 mHC   11.7
0.3 mHC   12.0


0.3 mHC   12.0

0.3 mHC   12.5

Calm       12.2

0.3 mHC   11.8

0.4x1.1.6    —
—          —        —    Aborted due to oil distribution pump
                            failure
11.43      75.3      41.6   Good test
11.43      69.5      37.3   Skimming head rising and falling as it
                            emptied and filled again
varied      44.1       5.3   Larger booms used to guide oil to the
                            skimmer
varied      45.2       8.9   One pump used to compare results
varied      80.7      16.2   Turbulence caused by skimming head
                            action, some oil reached the water dis-
                            charge inlet
varied      72.8      19.4   86% RE determined from grab sample
                            at oil/water outlet
varied      46.4      19.3   Skimmer head sump drained after each
                            wave, good test
12.7       33.2      22.5   Good test, vortices in front of head
                            caused losses
varied      27.3      14.4   Waves and oil splashed over skimming
                            head
—          —        —    Aborted due to lack of oil entering
                            skimming head

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Table 1.

Test
No.
31

32
33

34

Table 2.

Test
No.
35

36
37

38

39

40

41

42

43
(Continued)
Tow
Speed
(knots)
1:0

1.5
2.0

2.5

Test Results
Tow
Speed
(knots)
0.5

0.5
1.0

1.0

1.5.

2.0

2.5

1.0

1.0


Waves
(m x m)
0.4x11.6

0.4x11.6
0.4x11.6

0.4x1 1.6

of the DiPerna

Waves
(m x m)
Calm

Calm
Calm

Calm

Calm

Calm

Calm

0.4x1 1.6

0.4x11.6

Slick
Thick
(mm)
12.6

12.5
12.5

12.6

Sweeper
Slick
Thick
(mm)
	

12.2
—

12.4

12.2

12.5

12.3

12.7

—

Weir
Depth
(cm)
varied

varied
varied

varied

in Low Viscosity
Weir
Depth
(cm)
	

70.2
—

10.2

10.2

12.7

11.4

varied

—


TE
(%)
38.3

23.5
21.1

21.0

Oil

TE
(%)
	

83.1
—

73.5

78.0

32.5

8.3

7.2

—


ORR
(m3/hr)
10.5

9.8
11.8

14.7



ORR
(m3/hr)
	

11.1
—

19.9

31.8
•
18.1

5.7

2.0

—


Comments

Waves reflected from head washed on-
coming oil slick away
Same as test No. 31
Air entered skimmer because the head
drained completely at times
Losses due to shedding more than splash-
over, water discharge clean of oil


Comments

Test aborted due to obstruction in water
jet nozzle which controlled the slick width
Water discharge lightly colored by oil
Aborted, water discharge pump ran
out of gas
Vortices formed at boom attachment
points, oil drawn underwater and lost
Smallest pump failed, three pumps in
service
Three pumps in service, only 5 or 6%
decrease in pumping rate of 4 pumps
Great deal of entrapment from skimming
head
Oil pushed away from head by reflection
waves
Aborted due to break in oil boom tie line
used for offloading oil and removing air
from the top of the skimmer.
  The  oil/water separator should be
enlarged. A longer residence time and a
more stable vessel would result if the
lower portion of the oil/water separation
compartment  were extended beyond
the center to  the  port  and starboard
sides to form a  rectangular  cross-
section.
  The  full  report  was  submitted  in
fulfillment of Contract No. 68-03-2642
by Mason & Hanger-Silas Mason Co.,
Inc., under the sponsorship of the U.S.
Environmental Protection Agency.
                                                                             •ArU.S. GOVERNMENT PRINTING OFFICE:1981--559-092/3350

-------
       Michael K. Breslin is with Mason and Hanger-Silas Mason Co.. Inc., Leonardo, NJ
         07737.
       Richard A. Griffiths is the EPA Project Officer (see belowj.
       The complete report, entitled "Performance Testing of the DiPerna Sweeper,"
         (Order No. PB 82-109 174; Cost: $6.50. subject to change) will be available
         only from:
               National Technical Information Service
               5285 Port Royal Road
               Springfield, VA22161
               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
                                                                                                                           I
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

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