GB2095571A - Method and apparatus for recovering oil spillage - Google Patents

Abstract

A sweeping net assembly (3,7) is trawled from an outrigger boom (2) of a vessel (1) and comprises a convergent lead net (3) connected to a closed-ended tubular collecting net (7) by way of a connector box (6) with a quick-release fitting operable from the vessel (1). The trailing end of the lead net (3) and the leading end of the collecting net (7) can be choked in order to facilitate substitution of one laden collecting net (7) by a fresh collecting net (7) while trawling continues and the freshly swept oil is collected ahead of the location of choking the lead net (3). When the fresh collecting net (7) is attached to the connector box (6), the choke on the lead net can be released to transfer the oil swept during bag exchange from the said lead net (3) to the fresh collecting net (7). <IMAGE>

Description

SPECIFICATION Method and apparatus for recovering oil spillage The present invention relates to a method and apparatus for recovering spilt oil, and in particular for sweeping the surface of a stretch of water to clear it of spilt oil floating on the surface.

There are in existence systems for recovering crude oil spillage by sweeping them into a tubular net dragged along the surface of a stretch of water to be cleared, and subsequently the oil can be disposed of. However, these known systems suffer from serious disadvantages in that, for example, they need to be towed by means of two towing vessels and are therefore unwieldy for use with small oil slicks, and when the collecting nets are full the exchange of one laden net for a fresh net requires manoeuvering of the two vessels so that the full net can be hauled at least partially on board one vessel for net exchange.

Towing such a system from a single vessel has the disadvantage that considerable buoyancy needs to be transmitted from the towing vessel to the net, for example by way of an outrigger boom, and so the system can only safely be used in relatively calm sea states.

In accordance with the present invention we provide apparatus for sweeping oil spillage from a stretch of water, comprising a sweeping net assembly including: first and second tubular net structures of which said first tubular net structure includes suspension means at one end for connecting it to a towing vessel and said second net structure has a closed end and an open end; means for choking said first tubular net structure at a location nearer its other end; means for connecting said open end of the second net structure releasably to said other end of said first tubular net structure; and means for choking said second net structure at a location remote from said closed end thereof.

A further aspect of the present invention provides a process for collecting oil spillage from a stretch of water, comprising trawling a sweeping net assembly through the area of oil-bearing water with a lead net defining an open leading end of said sweeping net assembly serving as a mouth into which the swept oil passes, and using in said sweeping net assembly a collecting net releasably connected to a portion of the assembly defining said open leading end; when said collecting net is laden with a quantity of oil to be recovered, choking the trailing end of said lead net; choking the leading end of said collecting net; then releasing said collecting net from said lead net; attaching a fresh collecting net to said lead net and resuming trawling operations; and finally recovering said laden collecting net for stripping of the oil therefrom.

The invention further provides apparatus for recovering oil spillage from a stretch of water, comprising a sweeping net assembly having a portion of convergent tubular form, said convergent portion being defined by side walls of net material, and a ceiling, the ceiling having at least a part of water-impermeable material rearwardly of the inlet end of the convergent tubular net portion.

A fourth aspect of the invention provides apparatus for recovering oil spillage from a stretch of water, comprising a sweeping net assembly including first and second tubular net structures of which said first tubular net structure includes suspension means at one end for connecting it to a towing vessel and said second net structure has a closed end and an open end; and a connector body able to be connected to, and communicate between, the other end of said first tubular net structure and the open end of said second net structure, said connector body having a convergent-divergent configuration such that the passage cross-section at the throat of the convergent-divergent connector body is smaller than the cross-section of the open end of said second net structure when fastened to the connector body.

In order that the present invention may more readily be understood the foliowing description is given, merely by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view, in schematic form, showing a sea-sweeping vessel having an outrigger boom supporting a sweeping net assembly, in accordance with the present invention; Figure 2 is a perspective view of the lead net of the sweeping net assembly of Fig. 1; Figure 3 is a plan view, again in schematic form, of the collecting net of the sweeping net assembly of Fig. 1; Figure 4 is an enlarged view, as seen from the front, of the connector hoop between the collecting net and the lead net of Fig. 1;; Figure 5 is a schematic view showing an oil recovery vessel for recovering filled collecting nets to have the oil therein separated out from water which may have been collected therewith; and Figure 6 is a schematic perspective view showing the separator tank which may either be incorporated on the collecting vessel of Fig. 5 or be shore-based.

Fig. 1 shows a sea-sweeping vessel 1 having, on its starboard side, an outrigger boom 2 which supports a sweeping net assembly having at the mouth end thereof a lead net 3 in the form of a convergent frusto-pyramidal net structure. If desired two similar sweeping net assemblies may be deployed so as to be arranged on both port and starboard sides of the vessel 1.

The lead net 3 of Fig. 1 is shown in more detail in Fig. 2 and comprises port and starboard gable stretchers 4 (e.g. of aluminium) defining the front ends of two side walls 5 (e.g. formed of 7 > /8 mm knotless sprat netting). The side walls 5 can be seen to be of tapering construction, decreasing in height from the gable stretchers 4 at the front towards a connector box 6 which joins the lead net 3 to the collecting net 7 (Fig. 1) at the rear end of the sweeping net assembly.

The lead net 3 further includes, along the rear part, a floor 8 (e.g. of 7+/8 mm knotless sprat netting) it being understood that the purpose of the floor 8 is to avoid spilt oil being able to pass under the connector box 6 in the event of rough weather, and consequently the only region of the lead net 3 where it is necessary to have the floor 8 is at the rear end where the side walls 5 have their smallest height. By leaving the floor open at the front part of the lead net 3, it is possible to reduce hydrodynamic drag on the lead net.

The cei:ing 9 od the lead net has its front end connected to a 10 mm securing rope 10 having suspension rings 11 for connection to a supporting wire which is stretched beneath the outrigger boom 2 of vessel 1. The front part of the ceiling 9 is of 7+/8 mm knotless sprat netting, whereas the rear part 9a includes a water- and oil-impervious splash cover which firstly prevents water from being thrown upwardly through the ceiling of the lead net 3 in rough weather, secondly provides some measure of aerodynamic lift to the lead net as it is trawled forwardly through the water (usually into wind) causing the waterand oil-impervious splash cover portion 9a to trap air and deflect it downwardly deriving an upward reaction on the lead net, and thirdly prevents extrusion of any congealed oil through the ceiling.

A further strip of water- and oil-impervious material (not shown) may be incorporated into the top of each side wall 5 so as to have its upper part out of the water and its lower part (e.g. lower half) under water during normal trawling. This helps to confine the oil better during sweeping.

It will be understood that the floor 8 and the ceiling 9 of the lead net 3 are also of tapering construction between on the one hand their front ends and on the other hand their rear ends where they are connected to the connector box 6. The degree of taper may, for example, be such that the width of the mouth of the lead net 3 is 1 7 feet (5.2 metres) and the width at the connector box 6 is 5 feet (1.53 metres).

Near the narrower end of the lead net 3 is a choker line 1 2 which passes around the entire lead net 3 (outwardly across the ceiling 9, down one side wall 5, across the floor 8, up the other side wall 5 and inwardly across the ceiling 9) to allow the choker line 1 2 to be pulled taut in order to close off the back of the lead net 3, for a purpose to be described later.

The connector box 6 has its planform and side elevation rearwardly tapering to an outward flare at an adaptor collar 1 3 to support the collector net 7. The box 6 is preferably formed of a 1+" diameter aluminium tubing frame with polypropylene sheeting on it.

Another possibility is for glass fibre reinforced plastic material to be used for the frame. The thus generally convergent-divergent shape of the connector box 6 serves to generate a venturi effect on the oil-entraining water through the connector box throat to jet the oil into the centre of the collecting net 7 which is of divergent-convergent shape to avoid contact of the oil with the mouth end of the net 7, and jamming of the net mouth.

Fig. 3 shows that the collecting net 7 is of generally tubular form with its rear end closed and also has a choker line 14 similar to the choker line 12 of the lead net 3. The collecting net 7 is formed of 2 ply archery netting.

Furthermore, the collecting net 7 includes detachable buoyance chambers 1 5 along its sides and a further detachable buoyancy chamber 15a at the closed rear end. The connector box 6 includes similar and larger buoyancy chambers 1 6 (Figs. 1 and 2).

The construction of one preferred form of collecting net 7 is such that the overall length is 23 feet (7 metres) and the profile "balloons" outwardly from a 1 7.5 feet (5.34 metre) circumference at the mouth to a 22 feet (6.7 metre) circumference then tapering to zero at the rear end.

The connector hoop 1 7 can be readily detached from the remainder of the collecting net 7, but has a quick-release fastening facility to enable it, once already attached to the collecting net 7, to be rapidly connected to and released from the connector box 6. In fact the connector hoop 1 7 has a spring-clip action so that it is sprung into a smaller diameter configuration in which it is positioned just in front of the adaptor collar 1 3 of the connector box and has a diameter smaller than that of the collar 1 3 so as to trap the front rim of the collecting net 7 in position on the back of the connector box. When removal of the collecting net 7 is required, a quick-release line 1 8 to the connector hoop is pulled, releasing the sprung hoop to open and pass over the adaptor collar 1 3 of the connector box. It is then a simple matter to connect a fresh collecting net 7, by means of its connector hoop 17, on the connector box 6 in the same manner and then to resume sweeping.

The operation of the connector hoop 1 7 will be best understood by reference to Fig. 4 which shows that the hoop 1 7 has an arcuate socket portion 1 9 and a plug portion 20 having its end 20a engaged in the socket 19.

The leading end of the collecting net 7 is attached to the connector hoop 1 7 by means of beckets (not shown) fastened to the end of the net being able to be threaded over the end 20a of the connector hoop 1 7 simply by springing open the connector hoop 1 7 to release the end 20a from the socket 1 9 to facilitate threading of the suspension beckets (not shown) thereon. Then the end 20a is reinserted in the socket 1 9 and the collecting net is ready for use. The reason for removing the connector hoop 1 7 will be apparent from the description of the method of recovery of oil spillage.

The plug portion 20 has two holes 21 which can be brought into registration with a corresponding bore 22 into which a locking pin 23 is insertable. The pin 23 is attached to the quick-release line 1 8 described above with reference to Fig. 3.

In one preferred form of the connector hoop 17, the hole 21 nearest the end 20a corresponds to a circumference of 1 6 feet 3 inches (4.95 metres) for the connecting hoop 17, whereas the hole further from the end 20a corresponds to a circumference of 1 6 feet (4.88 metres) for the entire hoop 17. From this it will be appreciated that the appropriate diameter is selected simply by springing the hoop 1 7 circumferentially to push the end 20a along the socket 1 9 until one or other of the holes 21 is in registration with the bore 22 at which point the quick-release pin 23 is inserted to hold the hoop at the desired diameter.

The operation of the sweeping assembly shown in Figs. 1 to 4 will now be described, in order to give an understanding of the operation of the present invention.

As soon as an alert is given that oil spillage has occurred, the vessel 1 is mobilised with its outrigger boom or booms 2 deployed and supported by lines 24.

Spilt oil tends to collect in wind rows and it is therefore advisable for the vessel 1 to trawl up and down each wind row to collect the oil in the collecting net 7 by virtue of the oil being passed along the lead net 3 from the wide-mouthed front thereof.

Where there is no wind and the oil has not formed into wind rows the vessel 1 should work around the outer edge of the oil slick, spiralling in towards the centre. If a particular region is threatened by oil pollution, or if pollution of that area is considered more important to avoid than any other, then differing action may be required, for example by zigzagging the vessel on that particular side of the slick. The manoeuverability of the single vessel 1 having one or more of the net systems 3,7 deployed is such that several vessels can readily work the same area without difficulty.

During the net changeover procedure where only one net assembly is deployed (for example the starboard assembly 3,7 shown in Fig.

1), the vessel 1 should advantageously steer on a curved course steering towards the side being worked.

In some cases spilt crude oil is already sufficiently "solid" to enable it to be recovered by a net assembly such as the assembly 3, as shown in Fig. 1, without any gelling additive or other coagulation agent.

In other cases, it may be advisable to treat the spilt oil with a gelling agent which may, for example, be sprayed from the boom 2 so as to contact the oil as the oil enters the mouth of the lead net 3. However, alternatively it is possible for the gelling agent to be sprayed onto the oil in the connector box 6 if the activity of the gelling agent is such that the gelling action occurs virtually instantaneously. Such a system will of course be more economic in that less gelling agent will be lost outside the swept zone.

At this stage an empty collecting net 7 will have been attached to the connector box 6 by its connector hoop 1 7 having been locked in its small diameter configuration to be held captive over the flange 1 3 of the connector box 6.

During this operation, the vessel 1 may be undergoing considerable rolling, but the depth of the side walls 5 of the lead net is such that the vessel 1 may roll about 30 without the lead net side walls leaving the water. In practice the outrigger boom 2 is swivellably connected to the vessel 1 so that its weight is supported by the lines 24.and drag on the gable stretchers 4 is sustained by lines 25 shown in Fig. 1 and by the stabiliser line 25a from the end of the boom 2 to the outboard spreader 4 and a belly line 25b under the hull of vessel 1 to the inboard gable stretcher 4.

When the particular collecting bag 7 is full, the choker line 1 2 (Fig. 2) is pulled to tie off the back of the lead net 3, and then the choker line 14 (Fig. 3) of the collecting net 7 is pulled in order to tie off the rear of the collecting net 7 to contain the oil therein. In both cases the choker line is pulled while the vessel 1 is making headway. Once the two chokers are secured, further collected oil will be trapped in the inlet end of the lead net 3, allowing the vessel 1 to continue sweeping (although probably at a reduced speed), and then tension applied to the quick-release line 1 8 will allow the connector hoop 1 7 to spring open, thereby releasing the laden collecting net 7 and allowing a fresh collecting net 7 to be attached to the connector box 6 in the above described manner.

For connection of the fresh collecting net 7, the connector box 6 can if necessary be hauled on board the vessel 1 without disturbing the configuration of the mouth of the lead net 3.

The choker line 1 2 of the lead net is then released, allowing the oil which has been collected in the mouth of the lead net 3 during the net changeover operation to pass through the connector box 6 into the fresh collecting net 7, while the laden previously used collecting net 7 can be attached to a hand buoy and anchored off for subsequent collection. The dhan buoy would provide the means of re-locating the laden net 7 for subsequent recovery when convenient (e.g. in calmer sea state conditions). If the amount of oil in the laden net was sufficiently small consideration would be given to landing it on the stern of the vessel 1.

In the event of a mishap, the inherent buoyancy of the connector box 6, by virtue of its buoyancy chambers 16, ensures that it will float on the surface and can readily be located.

It will be appreciated that the above described structure, in providing means for tying off the back of the lead net 3 as the collecting net 7 is exchanged, allows the sweeping operation to continue substantially unhindered. This is assisted by the ease with which the quick-release line on the laden collecting net 7 can be operated to release the laden collecting net 7 and to allow immediate attachment of a fresh collecting net 7 with minimum delay, again by use of the convenient connector hoop 17.

The various laden collecting nets 7 are recovered by means of a recovery vessel shown schematically in Fig. 5, or indeed by any other suitable recovery means.

The preferred recovery means shown in Fig.

5 comprises a vessel 30 having a chute 31 along which the filled collecting nets 7 (not shown) are caused to move, by attaching a line to each collecting net 7 and hauling it up the chute 31, or by any other appropriate entrainment system.

As shown in Fig. 5, the chute 31 is provided with several series of non-return strips 32 which ensure that a laden collecting net 7 is unable to slip back down the chute in the event of failure of the entrainment system.

The laden collecting net 7 eventually drops into a reception container 34.

Alternatives to hauling the filled collecting net 7 up the inclined chute 31 include lifting the filled net on board the supply vessel using a canvas sling held open by spreaders.

Fig. 6 shows schematically the reception tank 40 in which the swept oil in each collecting net 7 is separated. The tank 40 may be on board the vessel 30, but is in this case shore-based and has its lower part 41 a below a grid 42 intended to receive water, and the upper part 41 b above the grid intended to accommodate the recovered oil.

Water will always be present in the bottom part 41 a of the tank 40 but may be drained off through the drainage port 43, when desired. The lower part 41 a of the tank is traversed by heating coils 44 through which steam is applied in order to heat the contents of the tank 40. Oil suction pipes 45 are disposed at diagonally opposite corners of the tank 40.

One or more of the laden collecting bags 7 can be placed in the tank 40 after removal of the buoyancy chambers 15, 15a and the connector hoop 1 7 therefrom. The heat within the chamber 40 then softens the swept oil in the collecting nets 7 and causes it to float in the portion 41 b above the water. It is then drawn off through the suction pipes 45 to be recovered.

In the event of the swept oil being particularly "solid" (i.e. gelatinous), it may be necessary for means to be incorporated in the separating tank 40 for squeezing oil out through the mouth end of the collecting net 7, since extrusion of the oil through the mesh of the collecting net 7 may be inadequate.

Each collecting net 7, being unaffected by the temperatures prevailing in the tank 40, can then be removed from the tank 40 and reconnected to its connector hoop 1 7 and buoyancy chambers 1 5 and 15a ready for reuse.

It will be readily apparent to the expert just how the rate of extraction of water and oil from the tank 40 can be carried out so as to maintain the water level substantially at the height of the grid 42.

A system in accordance with the present invention has been successfully tested with sweeping speeds of up to 2+ knots and is designed for recovering up to 50 tonnes of crude oil per hour and for operation in winds of Beaufort Scale Force 6 (22 to 27 knots and a probable mean wave height of 4 metres).

If desired, the attachment of a succession of collecting nets 7 may be dispensed with and instead the oil may be collected either by fastening a suction line to the tail end of one collecting net 7, or even attaching a suction head directly into the rear of the connector box 6.

Although, as described above, the separating tank 40 is shore-based, it is of course possible instead for the reception container 34 on the vessel 30 to form the separating tank 40b and for the recovered oil to be pumped into a storage tank on board the vessel 1.

As a modification of the process described above, the collecting nets 7 may be finally steam cleaned by draining the tank 40 of oil through the suction pipes 45, then draining the water from the lower part 41 a of the tank by way of the drainage port 43, and finally directing the flow of steam (which normally passes along the interior of the heater pipe coils 44) to contact the net or nets 7 in the tank 40 to steam clean the net before it is removed from the tank 40.

Claims (33)

1. A process for collecting oil spillage from a stretch of water, comprising trawling a sweeping net assembly through the area of oil-bearing water with a lead net defining an open leading end of said sweeping net assembly serving as a mouth into which the swept oil passes, and using in said sweeping net assembly a collecting net releasably connected to a portion of the assembly defining said open leading end; when said collecting net is laden with a quantity of oil to be recovered, choking the trailing end of said lead net; choking the leading end of said collecting net; then releasing said collecting net from said lead net; attaching a fresh collecting net to said lead net and resuming trawling operations; and finally recovering said laden collecting net for stripping of the oil therefrom.

2. A process according to claim 1, wherein headway is maintained during the exchange of the laden collecting net for a fresh collecting net.

3. A process according to claim 1 or claim 2, wherein said release of the collecting net from the lead net is accomplished by means of a quick-release line from the trawling vessel, and the trailing end of the choked lead net is then hauled aboard the vessel for attachment to a fresh collecting net.

4. A process according to any one of claims 1 to 3, wherein said sweeping net assembly is trawled from an outrigger boom.

5. A process according to claim 4, wherein there are two said outrigger booms, one on each side of the vessel, and a said sweeping net assembly suspended from each boom.

6. A process according to any one of claims 1 to 5, and including the step of stripping said oil from the laden collecting net by heating the collecting net to reduce the viscosity of the oil therein and to release the oil from within the net.

7. A process according to clairn 6, wherein said stripping process includes the step of squeezing said collecting net to remove the oil therefrom.

8. A process for recovering oil spillage from a stretch of water, substantially as hereinbefore described with reference to the accompanying drawings.

9. Apparatus for recovering oil spillage from a stretch of water, comprising a sweeping net assembly including: first and second tubular net structures of which said first tubular net structure includes suspension means at one end for connecting it to a towing vessel and said second net structure has a closed end and an open end; means for choking said first tubular net structure at a location nearer its other end; means for connecting said open end of the second net structure releasably to said other end of said first tubular net structure; and means for choking said second net structure at a location remote from said closed end thereof.

10. Apparatus according to claim 9, and including quick-release means, operable from a vessel to which said suspension means may be attached, for releasing said second net structure from said first net structure.

11. Apparatus according to claim 10, wherein said quick-release means includes a release line which may extend from the said connecting means to a said vessel.

1 2. Apparatus according to claim 1 0 or 11, wherein said quick-release means includes a spring-loaded hoop engageable over a collar of said connecting means and operable to be locked in a smaller diameter configuration and to be released to spring into a wider diameter configuration when desired, for quick release of said second tubular net structure from said first tubular net structure.

1 3. Apparatus for sweeping oil spillage from a stretch of water, comprising a sweeping net assembly having a portion of convergent tubular form, said convergent portion being defined by side walls of net material, and a ceiling, the ceiling having at least a part of water-impermeable material rearwardly of the inlet end of the convergent tubular net portion.

14. Apparatus according to claim 13, wherein said ceiling includes a first portion of netting material near the wider end of the tubular net portion and said water-impermeable portion at the narrower end of the tubular net portion.

1 5. Apparatus according to claim 1 3 or claim 14, and including a floor to said netting structure, said floor being formed of netting material.

16. Apparatus according to claim 15, wherein said floor is positioned at the narrower end of the convergent tubular net and no floor is formed at the wider end thereof.

1 7. Apparatus according to any one of claims 1 3 to 17, wherein the said convergent tubular net portion structure is convergent both in plan view and in side elevation.

18. Apparatus according to any one of claims 1 3 to 17, wherein said sweeping net assembly includes said convergent tubular net portion and a rearward closed tubular net, and including means for connecting the narrow end of said convergent net portion to the said closed tubular net.

1 9. Apparatus according to claim 18, wherein said connecting means comprises a connector box at the narrower end of said convergent tubular net portion and adapted to have the open end of said closed net releasably connected thereto by way of a divergent portion opening into said closed net.

20. Apparatus according to claim 1 8 or claim 19, and including means operable from on board a vessel from which the sweeping net assembly is supported, for releasing the said closed net from the convergent tubular net portion without lifting either of the nets on board the vessel.

21. Apparatus according to claim 18 and 19, taken together, wherein said releasing means comprise a sprung hoop which can be locked in a smaller diameter configuration in which it is too small to pass over said divergent portion of the connector box and can be released, by removal of a locking pin, for springing to a wider diameter configuration for passing over said divergent portion of the connector box.

22. Apparatus according to any one of claims 1 3 to 21, wherein said convergent tubular net portion includes means for choking the net, to close off the narrower end of said convergent net portion.

23. Apparatus according to claim 22 when appendant to any one of claims 18 to 21 and including means for choking said closed tubular net while the closed tubular net is attached to said convergent tubular net portion.

24. Apparatus for recovering oil spillage from a stretch of water, comprising a sweeping net assembly including first and second tubular net structures of which said first tubular net structure includes suspension means at one end for connecting it to a towing vessel and said second net structure has a closed end and an open end; and a connector body able to be connected to, and communicate between, the other end of said first tubular net structure and the open end of said second net structure, said connector body having a convergent-divergent configuration such that the passage cross-section at the throat of the convergent-divergent connector body is smaller than the cross-section of the open end of said second net structure when fastened to the connector body.

25. Apparatus according to claim 24, wherein said first tubular net structure has a convergent configuration and is wider at said one end than it is at said other end.

26. Apparatus according to claim 24 or 25, wherein said second net structure is shaped so as to be able to balloon outwardly from the said open end thereof, in use of the sweeping net assembly to recover oil from a stretch of water, whereby the cross-section of the second net structure at a location between the said first and second ends thereof is greater than the cross-section of the second net structure at said open end.

27. Apparatus according to any one of claims 24 to 26, wherein said second net structure includes buoyancy chambers.

28. Apparatus according to any one of claims 24 to 27, and including means operable from on board a vessel from which the sweeping net assembly is supported, for releasing the said second net structure from said first tubular net structure without lifting either of the first and second tubular net structures on board the vessel.

29. Apparatus according to claim 28, wherein said releasing means comprise a sprung hoop which can (a) be locked in a smaller diameter configuration in which it is too small to pass over said divergent portion of the connector body, and can (b) be released, by removal of a locking pin, for springing to a wider diameter configuration for passing over said divergent portion of the connector body.

30. Apparatus according to any one of claims 24 to 29, wherein said first tubular net structure includes means for choking the first net structure, to close off the narrower end of said first tubular net structure.

31. Apparatus according to claim 30 and including means for choking said second net structure while that second net structure is attached to said connector body.

32. Apparatus according to any one of claims 9 to 28, and including means for spraying the space within said sweeping net assembly with a composition for enhancing coagulation of oil being collected.

33. Apparatus for recovering spilt oil from a stretch of water, such apparatus being substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.