GB2239819A - 0il slick skimmer - Google Patents

Abstract

A self-propelled, remote-controlled boat carries means for skimming oil from the surface and feeding it into a dracone. The whole assembly is small enough to be dropped from an aircraft. The dracone may have lower outlets so that it can discharge water separating therein, or the boat may include a settling tank 4, from which water is recycled to nozzles 35 ahead of the boat and oil pumped to the dracone. In Fig. 2 the boat is a catamaran, and arcuate slots 12, 16 in the underside of float 3 pick up the floating oil. Other constructions use a single-hulled boat with various booms and pick-up devices, which can be flexible and/or inflatable. <IMAGE>

Description

OIL SLICK SKIMMER This invention relates to apparatus for recovering oil spills.

It is able to achieve this at sea or in estuaries or in inland waterways. Emphasis is on high speed of response to emergency.

Oil spills at sea recur several times every year and no effective apparatus yet exists for effectively dealing with the problems they cause. At most they are partially destroyed at great expense, but much oil usually escapes to be deposited on beaches resulting in destruction of wildlife. Existing countermeasures are generally inadequate because they are incapable of being implemented sufficiently quickly. By the time existing skimmers are able to arrive at the site of the spill the oil is thinly spread making collection difficult and oil can already have fouled beaches.

The present patent application describes apparatus which can be quickly airlifted and dropped on site to automatically deploy and then skim the oil from the surface together with some seawater, separate the seawater for return to the ocean, followed by transport of the oil for use ashore.

The novel means to be described has the overriding advantage of extreme rapidity of response. It is feasible that collection could begin within an hour from the instant at which the emergency arose for many locations. It is especially important to achieve a rapid response when spills occur close to a shore so that oil can be prevented from fouling beaches. At present it can take a week or more for ships to arrive bringing cleanup equipment. Sometimes chemicals including detergents are sprayed from the air to break up oil spills. This is known to offer only a partial solution and it is also recognised that the chemicals used cause extra environmental damage. The present invention will at least minimise the need for such undesirable measures.

Cleanup apparatus is known. One such means is a specially designed tanker built in two halves lengthwise. The halves are hinged at the stern so that the entire vessel can be opened into a vee shape so that it can be driven into an oil slick which it then collects. Such a ship takes a long time to reach any spill.

Adding to this inadequacy is the exorbitant expense of building a fleet of such ships having the capacity to provide adequate global coverage. The present invention is able to provide the speed of response which such ships lack and will provide a much cheaper solution. Collection instead of destruction of the spilled oil is however the ideal economic solution because the oil recovered has a high commercial value.

When most existing apparatus such as boom arrays are eventually in place they are found unable to cope with even quite modest waves or currents. The oil leaks underneath. No equipment is in existence which is able to remove a burning oil slick. The present invention provides means capable of being deployed with minimum delay and yet is able to operate in strong waves and currents. In one embodiment any oil or other liquid ranging from the most viscous of crude oils to gasoline can be removed. In the other the most viscous oils cannot be ingested when cold but burning oil can be removed.

To summarise; rapidity of response is a central feature of the invention and is of the greatest importance for six reasons:1 The sooner the oil slick can be removed the less likely is the pollution of beaches and the destruction of wildlife.

2 Oil will be caught before it has spread over a wide area making recovery easier. Virtually complete recovery is thereby made possible and such an advantage is unique.

3 Cost of recovery is minimised by such rapid response.

4 The oil is made recoverable before degradation has proceeded by evaporation of volatiles and by emulsification with seawater.

Then the recovered oil need not be wasted. This effects a useful cost saving.

5 The need for use of detergents to sink and disperse the oil OIL SLICK SKIMMER is eliminated with further reduction of cost. The damage which detergents themselves inflict on the environment is also obviated.

6 The need for implementation of very expensive double hulled tankers partly water filled hulls or hulls under partial vacuum is obviated. The double hull design is at present on order to minimise the danger of oil release so urgent has the problem become. The improved apparatus will be so effective as a recovery means that the very expensive alternatives previously mentioned will not be needed. The new invention will be comparatively cheap and can be utilised additionally in an alternative way carried in the manner of lifeboats. Several could be easily carried on the deck of every tanker to be deployed by lifting over the side as soon as any leak is reported. Indeed the skimmers can be also deployed as lifeboats.

The invention will therefore result in huge savings in capital cost of future oil carrying ships.

By way of example an apparatus weighing only about thirteen tonnes would be capable of removing five hundred tonnes of oil slick which it would then be capable of transporting at least 2,000 kilometres. Such units could be carried by existing military aircraft. For the fastest response the oil skimmers would be housed in sheds close to airfields rolled or folded into compact packages and ready for instant deployment. It would require only five hundred units of the size previously considered to provide the insurance required for a disaster of the magnitude of the "Torrey Canyon". Because air transport is so rapid such units could be distributed over the surface of the Earth at strategic points so providing worldwide coverage at reasonable cost.The apparatus need not be constructed in the size chosen by way of example because some other size might be a better match with the transport aircraft available. For example if transport by helicopter is chosen then the capacity might need to be reduced to about one hundred tonnes.

DECLARATION OF PRIORITY: THE FIRST SUBMISSION In the first application dated 20 November 1989 and having application number 8926152 the apparatus was described as having two main components called a skimmer head and storage means respectively which could be made disconnectable. Said skimmer head was a small specially shaped boat containing an engine and propulsion system together with means for removal of oil with some water followed by water separation and delivery of oil.

Said storage means comprised a long plastic tube of the kind already known as a "dracone" which is able to be rolled up for stowage and transport. The two main components were connected by a pipe which transferred oil from the skimmer head to said storage means and a further connection was made by at least one flexible cable which enabled the skimmer head to act as a tug for the storage means. The skimmer head was also fitted with collecting booms for scooping oil from the water surface. Said booms could be either rigid or inflatable structures which together with the storage means formed the shape of a letter Y.

The upper arms of the Y represented the booms whilst its tail represented a floating tank designed as an oil/water separating unit followed by said storage means in the form of a long flexible tube at its remote and trailing end.

When driven into an oil slick the booms funnelled oil toward the central position causing the oil depth to increase. Said separator was located at this position having an open inlet able to receive the oil together with a quantity of water. The separator consisted of a tank in which one or more grids or meshes where optionally fitted inclined to the horizontal so that the most deeply submerged ends were forward of the other end which terminated above the water surface. An oil pump which could be of centrifugal type was arranged with an inlet below the surface of the oil and an outlet connecting with said storage means. This oil pump was fitted with a speed controlled driving means. An oil depth sensor was fitted in the separating tank to form part of a mechanism able to adjust the speed of said oil pump. It was so arranged that the pump speed was reduced as oil depth reduced in order that the minimum quantity of water OIL SLICK SKIMMER transferred to the storage means.

Several kinds of depth sensor were known so a choice existed. For example it can consist of a float whose density is carefully arranged to be intermediate between that of seawater and oil so that it floats at the interface existing between these fluids.

Another alternative was an acoustic beam arranged to partially reflect from the interface. A so called water pump could also be provided having its inlet below the interface of oil and water so that it could help drain said separating means by having a rearwardly directed outlet. A water pump is optional.

A hydraulic power transmission was preferred for providing the fine speed control needed for the oil pump. A swashplate type motor could be coupled to this oil pump or a geared pelton wheel may be used having a controllable nozzle. It is important to have fine control of the speed of the oil pump because the depth of oil slicks is variable. A deeper than average slick will require a higher than average speed for the oil pump with the propulsor then driving the oil skimmer at a lower than average speed. A turndown of total power is also involved.

Said water pump could however be used as the sole means of propulsion with the propeller retracted when operation in shallow water is required. In one embodiment of the invention a multiplicity of propellers were arranged side by side to provide an efficient propulsor requiring only a shallow draft. In this arrangement power steering was also incorporated being effected by differential control of power to these propellers. With this alternative arrangement a single propeller and the control means needed for its retraction were eliminated. The storage means would be towed by whatever propulsive system was adopted. The slipstream from the propulsor would tend to impinge on the wall of the storage means with consequent increase of drag.When a single propeller or pump was used the effect was to be minimised by having the axis of the propeller shaft inclined to the horizontal to impart a downward component to the slipstream.

Multiple propulsors were arranged to impart transverse velocity components. In either case contact of the slipstream with the storage means was to be avoided.

The propulsion system could consist of any known kind of engine and propeller or could-be of novel kind. The choice had to take account of the need for highly reliable automated self starting.

Fortunately the fuel needed for several days of continuous use does not add excessive weight and so was provided in a tank incorporated as part of the invention. The overriding consideration was reliability in starting because this needed to be completely automatic. Fuels such as propane or liquid petroleum gas (LPG) would be suitable because they vaporise readily and do not freeze even in an arctic environment. A conventional spark ignition piston engine would provide a suitable; power source. It could be provided with conventional battery and starter motor or could have magneto ignition with starting arranged by cartridge again a known means.

The invention is not limited to the use of a spark ignition engine. For example a diesel engine could be used. In this case so that operation in arctic conditions is made reliable the fuel tank is fitted with a heat exchanger connecting either with the engine cooling or exhaust system in order to prevent the fuel from becoming excessively viscous.

In a preferred arrangement the engine was directly coupled with a hydraulic pump mounted on a single bedplate to form a hydraulic power unit. This so called main assembly could also include any water pumps and multiple propellers so that with rigid hydraulic pipes and the control system a single module was formed. If the main propulsor were a single large propeller and operation in shallow water were to be made possible then a separate module hinge mounted to the separating tank was provided. By such means the propeller could be made retractable. The engine could also be hinge mounted so that the more efficient geared type of drive to the propeller is used. A much smaller hydraulic pump was engine mounted and coupled to other components by flexible hydraulic pipes. Hydraulic actuators were also provided to OIL SLICK SKIMMER facilitate retraction.Drag rudders fitted with hydraulic actuators were attached to the outer ends of said booms to provide a steering means when a single propeller is used. These were also connected to the hydraulic pump by flexible hydraulic pipes and contained valves operated by servo mechanisms for control.

The "dracone" invented by Professor Hawthorne is known. It consists of a plastic tube closed at one end and necked down to a filling port at the other. It was to be filled with crude oil and towed by a ship to provide an alternative carrier. The present invention is therefore able to provide an application of this known and tested technology. A dracone is incorporated in the invention to provide said storage means. It has a filling pipe connecting with the outlet of said oil pump. The filling pipe is of flexible kind in order to permit said booms a degree of freedom. They can then be steered to collect oil not in the direct path of the dracone which will be sluggish in response when nearly full. Towing cables are fitted between skimmer head and dracone so that the filling pipe is not overstressed.There can be two such towing cables one fitted on either side in order to constrain yaw of the booms and so simplify control. In order to eliminate cable snatch in rough sea conditions a close coiled helical spring is incorporated in at least a substantial section of each of these cables. Alternatively elastic ropes can be substituted or the cables wound on drums mounted on the skimmer head. Such drums connect with hydraulic drive means able to act as either pumps or motors. A small hydraulic accumulator is also incorporated so that the cables can be wound in or paid out in order to maintain tension within specified limits.

The junction between dracone and oil pump is preferably though not necessarily made as a coupling capable of rapid connection or disconnection. Such a feature can permit more than one mode of deployment. In one mode a full dracone can be discarded after plugging the inlet and then left floating to await collection.

Then another dracone can be reconnected to said skimmer head for further use. In another mode the connection is not broken but the said booms are made retractable and being fitted with means of propulsion the said skimmer head is then able to act as a tug for towing the filled dracone for a possible long voyage.

For long voyages normal navigation lighting is required. In addition a short mast equipped with a radar reflector would be desirable. The mast is also needed for radio reception. The mast can be stepped from either towed or towing component but in either case a means will be required to limit the roll of the dracone. A pair of fins can be provided mounted at the forward end of the dracone to form an inverted "V". Each is arranged to have a pivotable mounting and is equipped with hydraulic actuators. These connect through flexible pipes to the said hydraulic pump. A sensor is provided capable of remaining horizontal and is used to provide a signal for operation of the actuators which counters the tendency to roll by continually adjusting the setting of said vanes. A mass supported near its centre of gravity can form a suitable sensing means by acting as a slowly moving pendulum.

The equipment is to be air dropped on site as a compact package so weighted as to float in a preferred orientation. It is fitted with cylinders of carbon dioxide or alternative means such as slow burning gunpowder together with a trigger operated from a time delay mechanism. By such means automatic inflation of certain components of the oil skimmer can be effected in order cause it to unfold. The booms are formed as long hollow cylinders which can be either rigid or inflatable. The inflatable kind can be deployed in the manner just described. Secondary booms and skirts are provided for reasons to be described and the secondary booms are also inflated by the means provided. Said timing mechanism is arranged to start up the propulsion system on completion of the inflation process. It is then intended that the operation be controlled subsequently by radio signals emitted initially from the aircraft used for transport. Later more economical light aircraft or helicopters would take over control until a ship could arrive.

OIL SLICK SKIMMER Each boom can be an inflatable structure able to be rolled up for stowage when not in use and the skimmer head can be deployed in permanent connection with the dracone oil store. Booms are then retracted when the dracone is full and the complete assembly proceeds under its own power to an oil terminal. A means of automatic retraction of booms is therefore needed. In the invention this requirement is met by embedding a strip of spring steel in the bottom wall of each main boom. Each spring is coiled into a spiral so that the boom is rolled up automatically when deflated. The principle is known from its use in party toys.

When rigid booms are used their outer ends are connected by a cable which is also wound around a drum. This enables the ends of the booms to be drawn together to produce a streamlined shape.

Difficulties will arise when skimming oil in severe wave conditions because each floating boom could rise above the surface of the sea in the region of wave troughs so allowing collected oil to escape. A secondary boom of much smaller diameter than the more rigid boom to be subsequently called a main boom can be provided the two being connected by a flexible skirt. The secondary boom is to be weighted to negative buoyancy and is to be so flexible that it can contour the ocean surface though constrained to a suitable depth in order to remain below a deep oil slick. At least the more deeply immersed part of said skirt can be arranged in the form of a close mesh so that it acts as an oil/water separator. A further skirt can be attached being mounted above the main boom to prevent oil loss by lapping wave crests. It has a forward inclination.

The drag of the secondary boom will tend to cause it to trail behind the main boom to which it is attached. This is not the optimum arrangement for oil collection. It is best that the secondary boom precedes the main boom. A multiplicity of supporting struts can therefore be arranged connecting the main and secondary booms. These are designed to be flexible enough to allow the secondary boom to contour the wave surfaces. Motion restricting cables attaching with the uppermost parts of the main boom can be provided to prevent the gross movement which would cause the geometry to flip to the trailing configuration.

It is best to have the secondary boom fully immersed about 0.3 metres or so below the surface in order to prevent oil slipping past underneath. To achieve this the buoyancy needed to maintain correct immersion is provided by hollow streamlined extensions of said supporting struts which are perpendicular to said struts and close to the secondary boom so arranged that they terminate in bulb shaped floats above the surface. These bulbs are so shaped as to also act as hydroplanes by being tilted up at the leading end. In this manner forward motion is also utilised to help maintain an optimum depth of immersion of the secondary booms.

The booms and skirt are preferably made from woven plastics. They can also be coated if necessary with oil resistant polymer.

By way of example only the capacity of the invention for oil removal will now be demonstrated. It will be assumed that the harvesting booms are 10 metres long and have their outer ends 10 metres apart. The storage means has the capacity to transport 500 tonnes of oil and when full would be some 50 metres long and 4 metres in diameter. It would have an empty weight of 6 tonnes if made from IOmm thick polypropylene which is an overgenerous allowance. The installed power requirement for towing at 3 m/s (10.8 km/hr) is 37 kw. With harvesting booms deployed at a depth of immersion of 0.3 m the wave drag induced would require a further ideal power of 77 kw so a total installed power of 114 kw (153 HP) is required.

An oil slick only 1 centimetre thick is assumed which is skimmed at a speed of 3 metres per second. At the mouth of the boom the average speed of entry will probably be slowed to about a half the nominal value owing to the spreading out of streamlines ahead of the booms. With this assumption it is readily estimated that a rate of collection of 11,000 tonnes of oil per 24 hour day will be achieved. It would require only twentytwo units each working OIL SLICK SKIMMER for one day for a spill of Torrey Canyon scale to be removed.

During this time five hundred dracones would be filled.

In the alternative mode of operation in which 500 complete units are distributed around the world the first could be deployed in about 30 minutes and the last would arrive in about 30 hours.

Each dracone would take one hour to fill. Then with booms retracted and full engine power available for towing the voyage to port could proceed at a speed of 14 km/hr (7.8 knots).

It is possible to quote some figures to roughly outline the economic constraints.

Exxon spent $1000,000,000 to clear up the recent Alaskan oil spill which occurred when the "Valdez" struck a reef. Cleanup is unfinished but has been abandoned and the government is to charge Exxon a further $21,000,000 for damages to 1100 miles of polluted shoreline. (Nature vol.341 p174 21/9/89). If the maximum capacity of an air lifted skimmer head and dracone unit is assumed as 500 tonnes then to accommodate a spill of this size given as 36,000 tonnes the total number of units required would be 72. For the same total cost a completely successful cleanup could have been achieved with $14,000,000 allocated to each 13 tonne skimmer.

This is a much larger budget than would ever be required.

These figures are given by way of example only and do not limit the invention in any respect.

VARIOUS EMBODIMENTS COVERED BY THE INVENTION.

A number of alternative arrangements are possible which can be advantageous and which are to be considered as included in the present invention.

It is to be observed that the booms are not actually joined together directly. Each is connected to a common member which has been called the hull consisting of floats joined by a deck.

A single propeller used in the manner described have the advantage of the high efficiency associated with mechanical drive but operation in sufficiently shallow water may not be possible.

A multiplicity of shafts can be used instead of a single shaft all connected by gearing direct to the single engine so that several smaller propellers are then used. These permit operation in shallower water. Twin engines may be used one mounted in each of the floats forming said float-pair. The central float can then be omitted.

Said oil pump can be arranged as previously described being driven by a hydraulic system from the engine. Cheaper alternatives are possible. An axial flow pump with axis horizontal can be coupled to the engine by a clutch or hydraulic coupling with a shaft included to transfer power from the central float to a point close to the rear of the float-pair where said oil pump is located. The power requirement is very small so the economy provided by a variable speed drive may be considered unimportant. Control is then arranged by providing a throttle at the inlet to said oil pump which is progressively closed by a float arranged to define the interface between oil and water. The float which has a density between that of oil and water is prevented from moving horizontally by cables or plastic strips also arranged in a substantially horizontal plane and fixed to the sides of said floats. The inlet to the oil pump is now in a vertical plane and is arranged to hang from a float less dense than oil in order to follow the surface as it moves by wave effects. In this way the suction pressure of the oil pump is prevented from affecting the throttling control.

It is possible to eliminate said oil pump. The engine power then needs to be sufficient to propel the skimmer head and store at a speed fast enough to provide a dynamic head sufficient to fill the store without the supplementary pressure provided by an oil pump.

A non return valve is provided in the connecting pipe to the storage means so that when the latter is filled to capacity oil cannot be discharged when either the oil pump or propulsion system is closed down.

OIL SLICK SKIMMER It is not essential to provide separating means in the manner proposed with water ingestion totally avoided. In the alternative to be described a mesh for providing separation is not essential.

This is because the storage means or dracone can be utilised as a separating tank. In this embodiment of the invention a mixture of oil and water is allowed to enter the storage means. It utilises the buoyancy effect of oil droplets. Heaving motion inside the store will be smaller than in the ocean outside so that the tendency toward emulsification caused by breaking waves will be smaller. To further subdue the motion baffles or perforated bulkheads can be provided to add further damping. At the bottom of the storage means and preferably at its rear end a water outlet port is provided. This is formed as a rearwardly directed nozzle. Then after separation the water component is automatically rejected. A control means is required to prevent oil from being discharged and takes the form of a shut off valve arranged to close when the oil/water interface falls below a predetermined level.So that an excessive amount of water is not carried in the belly of the storage means a local downward facing streamlined bulge or so called blister is formed in the wall and the water outlet nozzle is arranged at the lowest point of this blister.

The control means for the said shut off valve consists of a detector for the oil/water interface and has a servo mechanism for closing this valve. A simple means consists of a float having a density between that of oil and water and is loosely positioned inside the storage means by substantially horizontal cables or plastic ropes. This can connect directly with a plug which is the moveable part of said shut off valve. It is so constrained that it can enter and seal off an entry port communicating with said rearwardly directed nozzle. The float is required to be of sufficient size as to resist the tendency of the plug to be grabbed by suction pressure. This could seal off the nozzle prematurely. This is substantially avoided by making the blister sufficiently large so that it is able to house the float and yet allow adequate area around it for flow to move at low speed.

Sealing can be reinforced for example by magnets on seal faces.

A further modification to the dracone design on which the storage means is based can be made though it is not essential. Tests showed that when turns are made a crease forms which travels along the dracone. Creases in plastics are very undesirable because rapid failure by fatigue is induced. Furthermore large waves might also produce transient creases. The tendency to crease can be greatly reduced by substituting a corrugated wall for a smooth wall. The corrugations are formed so that they appear as rings in planes perpendicular to the axis of the dracone and give the wall a wave like form when a longitudinal section is viewed. Such a shape is able to bend freely without creasing. This modification is extended to the connecting pipe which is required to be flexible.A drag penalty has to accepted in return for increased working life but can be minimised by using only a small depth of crease.

The skimmer head described in this first application was therefore a specialised tug being of very small size and weight as compared with conventional craft of equal towing capacity. The size of the propellers was however little reduced from the conventional size so that it became disproportionately large as compared with normal practice.

SECOND SUBMISSION: FIRST IMPROVEMENTS TO THE OIL SKIMMER An improvement having the filing date 20 June 1990 was allocated the application number 9013739.9. The collecting booms were now arranged with spanwise slots located on the undersides of so called collecting foils. By spanwise is meant a direction parallel to that of the beam of the hull which is perpendicular to the direction of motion. It is known that oil passes under booms when the carrying water is flowing rt even a very low speed. The invention made use of this observation to ensure such an effect occurred by driving the collecting apparatus at a much greater speed. By this means all the oil could be collected even under moderate wave conditions owing to the depth of immersion of the oil collecting slot.To meet the requirement for operation in very adverse wave conditions the spanwise collecting slot was split into a multiplicity of narrower slots each housed in a OIL SLICK SKIMMER separate so called rigid foil each capable of independent vertical motion. All such rigid foils were threaded on a common cylindrical spine by a close fitting bore provided at the leading end of each foil so that each is able to trail independently by arranging their lengths to be several times greater than the height of the spine above the water. Each foil had its own suction pipe cooperating with spanwise slots which connected to suction pumps inside the hull by flexible pipes. Said common cylindrical spine was mounted on the skimmer head in a spanwise direction.The cross section of the foils viewed in a spanwise direction appeared similar to those of aerofoils with convex surface containing the oil collecting slot forming the underside.

In a preferred arrangement oil and water delivered from the thick trailing ends of the foils was collected in flexible pipes which entered the skimmer hull and connected with the inlet of a suction pump. This delivered to the separator. The metal multifoil arrangement had the advantage of being able to operate under flame conditions the entire hull of the skimmer head being cooled by water sprays. These sprays had nozzles to be fitted optionally when required which connected with the outlet of the separator.

This enabled burning oil slicks to be skimmed such as those which arise when blowouts occur on subsea oilwells. Under these conditions even the most viscous of crude oils will be hot enough to enable pumps to handle them. In another variant a plastic material was used so that the required flexibility could be obtained in a single piece construction.

A simple form of partial retraction was provided. The trailing parts are lifted by cables attached to a deck hoist or preferably by hydraulically operated actuators mounted on the spine. The said foils are thereby raised out of the water in order to limit drag when towing after the storage means is full. The spine can also be arranged to be lifted by hydraulic jacks and turned through a right angle seen in plan view so that for air transport and storage a more compact shape is presented. The same configuration can also be adopted when the storage means is full and the skimmer head acts only as a tug.

In order to ensure adequate penetration of the water surface by the trailing parts of the foils it will generally be necessary to weight them with some form of ballast. The foils are therefore formed hollow and watertight so that they can be filled with a liquid to an optimum extent. Suitable liquids are seawater or engine fuel. The foils can be used as auxiliary fuel tanks in this way so as to leave more room inside the hull.

Alternatively or in addition a separate torsion spring attached each rigid foil to the spine in order to press each foil hard against the water surface and at the same time allow the natural frequency of torsional oscillation of each foil about the spine to have an adequately high value. Then contact with the surface is not temporarily lost when waves cause the foils to oscillate.

It is difficult with these arrangements to absolutely prevent leakages of oil past the hull and each foil on both sides in the skimming mode. To limit or possibly prevent any loss the sides of both hull and all foils are made vertical at places where they cooperate so that minimum clearances can be maintained.

Collecting slots can also be open at their outer ends. The outer ends of all foils can also terminate in vertical plates so that the opening of gaps between them under strong wave conditions is prevented.

An alternative module is provided in the invention which can be substituted for use when oil slicks are not burning and which does not suffer from the possibility of leakage.

Instead a monolithic boom system can be formed as a single unit being deployed behind the hull and attached by cables.

Alternatively the monolithic boom apparatus can be deployed in front of a rigid hull to be pushed along by this hull by struts hinged to allow relative vertical movement. These are arranged as pivoted arms as in the previous description.

A third alternative is to attach a pair of such booms one on either side of the skimmer head.

The improvement overcame an instability problem which arose with OIL SLICK SKIMMER the open top type of collecting boom system described in the first application. The first collecting system tended to dive uncontrollably. Oil and water were still sucked into the hull of the skimmer head and delivered to a separator mounted inside this hull. The rejected water was delivered from ports near the base of the separator and returned by a pair of pipes to delivery nozzles ahead of the skimmer hull and on either side of its bows.

The delivery nozzles were mounted on floats designed to plane by being tilted upwards at their leading ends and so ride on the surface to contour any waves. To permit such movement said pair of pipes were made flexible. Said delivery nozzles were also directed toward each other being mounted horizontally. They had the effect of creating an inwardly directed surface cross current to increase the effective width of swath of collected oil. In addition each had a separate flow control means so that they formed a steering means for the skimmer head.

THE RIGID HULL.

With either separate halves or monolithic configuration but confined to the case in which a mixture collecting slot extends over the entire span of the collecting booms the rigid hull to which the inflatable booms are fixed need not be of compound type. It can be a single hull containing an engine and reduction gearbox with attached propeller shaft and propeller and also a drive to the suction pump. It is preferable but not essential that the suction pumps be fitted with a control means for flow rate. This might take the form of variable inlet guide vanes or better still a variable speed drive. An engine driven hydraulic pump connecting with a swashplate hydraulic motor for example can provide a suitable drive arrangement.

The propeller needs to have a relatively large diameter and is geared down from the engine to run at a low speed because the skimmer head acts as a tug for a very heavy store of collected oil. The torque is large enough to cause a considerable heel with booms retracted and so countermeasures need to be inccrporated. Either a pair of counter-rotating propellers are fitted or a single propeller has a stator placed downstream consisting of aerofoil shaped vanes arranged to remove swirl from the water.

It is advantageous though not essential to incorporate a two speed plus reversing gearbox between the engine and propeller.

THE OIL SEPARATING MEANS.

A primary oil/water separator connects with the outlet of at least one suction pump. The separator could be of any known type the simplest being a settling tank preferably containing wire mesh baffles. An oil outlet situated at the top of said separator then connects with the storage means by a flexible oil connecting pipe. At least one outlet is situated near the base of said separator to remove and recycle the residual mixture.

In a preferred arrangement there are two such outlets connecting with a pair of mixture recycle pipes arranged symmetrically one on either side at the base of the separator. A small amount of oil is expected to remain since perfect separation is difficult to achieve. At least one separator outlet recycle pipe therefore connects said separator to a pipe outlet ahead of the skimmer so that the mixture is recycled using the water surface as an additional separator.

In order to limit the quantity of water being carried into the storage means a water level sensor is incorporated within said separator which senses the position of the oil/water interface.

When the water level rises beyond a certain point a valve is closed by a servomechanism controlled by the sensor. When the water level falls beyond another specified lower limit the proportion of power diverted from propulsion to suction pumping is progressively increased.

Said sensor can take a variety of forms. For example a pair of wires could be arranged with an electrical potential difference between them to sense the conductivity or vertically propagated acoustic waves could be reflected from the oil/water interface and the time of return of reflected waves used to determine the water level.

OIL SLICK SKIMMER A float can also be used as a mechanical alternative and this will be described in detail but it is to be understood that this is by way of example only since other kinds of sensor could be substituted. A float is so made as to have a density between that of crude oil and seawater so that it sinks in oil but floats on water. It can therefore be used to locate and respond to the interface between the two fluids. The float has a central vertically oriented hole made as a loose fit over a vertical tube fixed inside the separator whereby its movement is constrained to the vertical. The tube has a number of inlet holes arranged symmetrically around its centreline to balance any pressure forces and this tube connects at its outlet with the pipe connecting with said storage means.The inlet holes are formed close to the top of the separator so that they are closed by the float when the water level rises beyond a specified limit. In this way the store will be filled at a rate which matches the rate of oil collection whilst entraining the minimum quantity of water.

When dealing with very thick oil slicks however it is possible that the skimmer could be driven at such a speed that the capacity of the suction pump is overwhelmed so that some oil is left behind on the water surface. In this case little water will be entrained and the separator will fill with oil. A lower level of the float therefore needs to be specified at which power to the propeller is reduced or power to the suction pumps increased or power diverted so that the skimmer is slowed to a speed which enables the suction pump to deliver some water along with the oil. Hence the vertical position of the float provides the indicator needed for speed control of the skimmer and no other control is necessary except for steering of the complete assembly. A sensor of known kind can be fitted to locate the position of the float and the sensor connected with a servomechanism so that when the float falls below a given level the engine throttle is progressively closed whilst simultaneously more power is diverted to the suction pump.

Further reduction of power to propulsion is needed to cope properly with very uneven oil distribution on the water surface.

Under this condition the suction slot can be taking in a large amount of water from regions where little or no oil is present and yet the speed can be too high for all the oil to be sucked away where it does exi-st. An overriding control is therefore required able to divert a greater amount of power to the suction pump or further close the engine throttle. This could be a manual override which relies on the operator to detect oil loss or could be an automatic servo control using an oil loss sensor for detection. This could comprise pairs of wires connected by battery for measurement of electrical conductivity of water behind the suction slots or for example a television camera. In these ways fully automatic control of oil recovery can be obtained.

Under rough sea conditions it is possible that some air bubbles will be entrained by the suction pump. This air needs to be made to collect above the oil surface inside the separator. Tests have shown that small air bubbles can remain in the oil without separating out. Wire mesh screens inclined to the vertical are therefore provided in the flowpath of any fluid stream entering the separator in order to help in air separation. Unless removed air will pass to the storage means to reduce its capacity. To prevent this a second float is incorporated which is of very low density so that it sits above the oil surface. It is located preferably in a cylindrical shaped extension mounted on the top of the separator in an offset position in relation to the oil delivery pipe.Said extension can be of relatively small diameter and said second float is made to be a very loose fit inside so that air can move freely into the space above. An air vent is located in the upper end wall of the cylindrical extension which is closed by a projection attached to the secondary float when the oil level rises beyond a certain value.

Air will be vented when the level falls because the internal pressure is above atmospheric when oil is being collected. The weight of the float needs to be sufficient to overcome the upward closing force produced by this internal pressure.

OIL SLICK SKIMMER However this pressure can fall below atmospheric when the stored oil is being sucked out of the storage means for delivery to a secondary store in certain arrangements. It is then important to prevent air from entering during this phase of operations and so a non return valve is fitted at the outlet of the air vent.

A similar air vent assembly can be incorporated on the upper surface of the storage means either instead of or in addition to one fitted to the oil separating means.

Even with float valve control it is unlikely that the storage means will be totally prevented from having water entrained into it. The storage means itself can however be utilised as a final separating tank and the water will separate out below the oil.

A drain pipe which can be of relatively small bore is therefore incorporated at a point about halfway along the underside of the storage means and is built into or attached to the wall of the store to be led forward to the skimmer head. It is fitted with a stop valve which needs to be closed after the filling operation is complete or when oil instead of water issues from its outlet.

Said outlet is arranged upstream of the skimmer so that the mixture discharged is recycled.

THE MAIN RECYCLING SYSTEM.

The water discharged from the separator is unlikely to be totally free from oil and so it is undesirable to discharge it astern.

Instead it is recycled to points upstream of the inlet mouth of the skimmer head by a pair of pipes one on either side.

In a preferred arrangement such separator outlet recycle pipes terminate at widely spaced outlets so arranged that substantially horizontal jets issue toward one another. These jets are arranged to lie close to the water surface either above or submerged. The outlet orifices are made so that their areas of cross section can be varied or throttles are incorporated within said pair of pipes so that a differential control of discharge is made possible.

Five important advantages accrue from this arrangement: 1 Firstly the momentum of the sprays produces an inwardly directed surface current and so increases the effective width of oil collecting mouth.

2 Secondly the mixture will tend to separate by gravity. In this way the ocean surface is utilised as a secondary separating means.

3 Thirdly the jets form an ideal steering means. By differential control of flow in said pair of pipes the momentum of one jet can be changed with respect to the other and a very strong yet highly controllable turning moment applied. No rudders need therefore be incorporated. In a preferred arrangement a spear shaped plug is moved toward the outlet orifice in order to reduce the area of cross section. The jet is of fish tail kind of large width as compared with its depth so the spear needs to be of corresponding oblong cross section.

The jets are also arranged to be substantially horizontal to maximise the surface cross currents they create and at the same time give the best conditions for mixture separation. Said plug connects with an actuator of known type which can be hydraulic or electrical.

4 The directional control system just described enables a new collection strategy to be adopted. When the storage means is partly full its inertia will be very high so that control will become sluggish. It is highly desirable therefore that a degree of freedom of movement be conferred to the much lighter skimmer head. The two are therefore connected by only a single cable which for a large part of its length is formed as a close coiled helical spring or is made from elastic rope. By such means a tension is maintained even though the distance of separation is allowed to vary. The single cable is attached to the bow of the storage means and to a point on the centreline of the skimmer head close to the stern. Both ends are attached by couplings which are pivotable so that the cable is not subjected to severe bending or wear.

OIL SLICK SKIMMER It is then possible to carry out abrupt turns of the skimmer head first in one direction and then the other so that motion takes place in a series of arcs with a superimposed progressive forward motion limited by drag of the storage means which follows in a substantially straight line. In this way the skimmer can operate at a much greater average speed and so is able to collect more oil in a given time. The width of swath can then greatly exceed the span of the skimmer head.

5 This mode of operation is particularly desirable when collecting burning oil slicks. A fleet of skimmers will be deployed to work in concert from the upwind end of the slick so that fumes are blown away from them. All the skimmers are operated so that they sweep from side to side in unison and so create a swath equal to the entire width of the slick and yet each storage means automatically remains well clear of the slick.

The improvements also increased the range of operating conditions. Furthermore alternative modes of operation were envisaged which are potentially able to minimise the number of skimmers needed.

For the last purpose an extra set of oil stop valves or an extra pump is incorporated to connect with a delivery outlet so that connection can be made between said storage means and a secondary store. Said secondary store can be a fixed shore terminal or a conventional tanker. A conventional tanker will usually be returning empty somewhere on the same sea lane. At the time of the accident a high probability exists that at least one could be closer than the nearest oil terminal. One alternative mode of deployment is then possible in which the tanker is turned toward the spill and after the skimmer has been filled it is navigated toward the tanker. On making rendezvous the oil is transferred and the fuel tanks of the skimmer are refilled so that it can be quickly turned round for re-use. In this way the time spent in transport of collected oil can be minimised so that the skimmers can be utilised to the greatest extent. The skimmer could have been either airdropped or lowered from the leaking tanker. It is possible that the skimmer could return the collected oil to the leaking tanker if spare capacity is available somewhere on the same ship.

DELIVERY MEANS TO A SECONDARY STORE Finally a means is incorporated for delivering the stored oil to a secondary store so that the skimmer can be returned for re-use or to base. Any of the suction pumps can be fitted with stop valves or switching valves to enable them to operate in this new mode. Branch pipes connect with both inlet and outlet pipes so that the pump inlet is now connected only to the storage means connecting pipe and the pump outlet connects only with a single delivery connection. This delivery connection is arranged so that it can mate temporarily with a pipe to said secondary store.

Two pipes connect with the storage means one being used for filling with oil whilst the other is used for removal of separated water from the bottom of the store. Both pipes can be utilised for oil removal in order to maximise the rate of transfer. When two suction pumps are available then both can be arranged in the manner described.

RIGID SKIMMER HEAD TYPE.

Funnelling of a swath of oil to a central collecting point is a feature which has been sacrificed to a degree in certain previously described embodiments of the present invention. It may be thought a desirable feature since the oil depth is thereby increased before collection. Satisfactory operation should be achievable without funnelling provided the oil thickness is fairly uniform as will usually be the case on the first day of occurrence. But slicks tend to break up in time to leave patches separated by clear water. Under these circumstances funnelling before collection is highly desirable so that patches are caused to merge together. A further embodiment of the invention will therefore be described which might be a better alternative under such conditions.

An improved inflatable boom system can still be incorporated JUt OIL SLICK SKIMMER is now to be regarded as an optional extra which will only need to be used when the average oil film thickness is very small.

EXAMPLE OF SKIMMING CAPACITY WITHOUT BOOMS.

A simple example will give an idea of the magnitudes involved.

A useful size seems to be a skimmer head having a collecting mouth about 12 feet wide (3.65 metres) and connecting with a storage means having a capacity of 100 tonnes. A speed of 3 metres per second is appropriate and then it is possible to calculate the time taken for filling to be completed if the average oil slick thickness is assumed. If this is taken as only one millimetre then the filling time works out at 2 hours 48 minutes which is quite acceptable. As the oil thickness is increased so the filling time is reduced in inverse ratio.

However it would clearly be advantageous to add the optional inflatable booms if the average oil thickness fell below about 0.5 millimetres. But with the advantage of rapid deployment which is incorporated in the invention it seems unlikely that the average oil thickness will be less than 3 millimetres. Then only a one hour filling time would be involved. The extra complication of inflatable booms will therefore be rarely justified.

RIGID HULL WITH DUCTED PROPELLER.

A slightly more complex arrangement which causes the collected swath to exceed hull width may be justifiable and will now be considered. It utilises ducted propellers connecting with a fishtail inlet to suck in a wide swath.

The operating system not involving inflatable booms will be described. The skimmer head is formed with a pair of main hulls side by side and connected by a deck. A smaller secondary hull can be arranged at the bow centrally located to house an engine gearing and auxiliaries. It is preferable but not essential that a pair of contra-rotating propellers be provided connecting with the engine through reduction gearing. The propeller shafts have bearings supported by skegs attached to the stern ends of said main hulls so that the shafts have a much wider spacing at the stern than at their points of entry to said secondary hull.

In the new invention the propellers are not open as in the previous embodiment but are instead housed in ducts which terminate in propulsion nozzles of circular cross section at points immediately behind the propellers. These ducts progressively change in section and merge into a single duct as reference points progress in a direction toward the bow. As the bow is approached the depth of the duct reduces and the width is increased until a wide but shallow inlet mouth is reached. In effect a jet propulsion system is the result.

The bow ends of the main hulls are separated by a distance which governs the width of mouth for oil collection. This mouth also forms a wide slot shaped inlet for the water accelerated by the propellers when the duct is shaped according to the previous description. By such means the oil slick is induced mainly by the suction effect of the propellers. The oil is carried in on top of the water and so has no chance of slipping underneath as could occur with previous boom systems.

Said duct converges and deepens in a direction toward the centre of the main hulls and near this point an oil collection means is fixed. Two kinds of oil collector can be arranged one being of open channel type and the other being closed. It is not clear at the present time which of these alternatives will prove best and so both need to be described. However the features common to both will first be described.

It is preferable though not essential that two separate pumps be provided to suck away the oil from the water surface. A first shallow inlet passage extending over the entire duct width connects with the inlet of a first oil pump and the outlet from this pump connects with said storage means through a connecting pipe. The oil collected by this pump can be maintained almost free from water by control of flow rate. At this condition however only a portion of the oil will have been collected because some of it will exist in an emulsified layer mixed with OIL SLICK SKIMMER water. A second pump is therefore provided to suck away the emulsified layer together with a layer of uncontaminated water to ensure that all the oil present in said main duct is removed.

This second pump has a wide and shallow inlet located either below or behind said first inlet in order that the two inlets collect the desired fractions of the total flow.

The delivery port of said second pump connects via a short pipe with the inlet of an oil/water separating unit. A preferred arrangement has already been described under THE OIL SEPARATING MEANS". The separator can be mounted on deck amidships toward the stern of the skimmer head. It is possible that the separated oil may be of lower quality than that which has never been mixed in which case a permanent separation may be considered desirable.

In this case å secondary storage means is provided joined to the main store by physical attachment of the skins but with interiors kept separate.

PITCH AND ROLL DAMPER.

The vertical amplitude of pitching motion of the bow of a ship can be several times greater than that of the waves causing such motion. Clearly a resonant condition must then apply with the wave frequency being close to that of the natural pitching mode of the ship. It is particularly desirable that such motion be minimised during skimming operations. Fortunately amplitudes of oscillation can be minimised by the provision of damping.

Aerofoil section dampers can be incorporated close to the bow of any rigid skimmer hull being so arranged that wave energy is absorbed. These can be defined as hydrofoils since they will be arranged substantially in a horizontal plane below the water surface and with their rounded leading edges perpendicular to the flow direction. They will have a symmetrical section.

Each hydrofoil is pivoted about a line in front of the centre of pressure even at the stalling incidence so that it tends to line up with the direction of flow. A torsion spring is incorporated of some optimum stiffness which resists deflection from the horizontal position. Under wave conditions with such an arrangement the hydrofoil will incline downwards when the bow moves downward and incline upwards when the bow rises. In each case a lift force is produced tending to resist the motion and the inclination will tend to produce a forward thrust so helping to propel the hull. Wave energy is absorbed and converted to propulsion but the important result will be a marked reduction in the amplitude of pitching motion without causing the turbulence which would result from the use of the kind of damping which destroys kinetic energy.

If two hydrofoils are provided symmetrically arranged at opposite sides near the bow then they can move independently of each other. Then any rolling motion will be damped in a similar fashion. In one embodiment of the invention a pair of hydrofoils are threaded onto a common cylindrical spine fixed to a pair of struts hinged close to the bow. Said springs are attached one end to a hydrofoil and the other to one of the struts. Each strut is fitted with a hydraulic actuator so that it can be raised or lowered. Then the hydrofoils can be lowered into the water ahead of the bow when damping of pitch and roll is required.

WATER SPRAY MEANS FOR USE IN RECOVERING BURNING OIL SLICKS.

In any of the embodiments of the invention described a pair of recycle pipes extend forwards to deliver mostly water with a small proportion of oil mixed in to utilise the water surface as a secondary separating means. A branch pipe is fitted to each recycle pipe and is fitted with a stop valve and a quick release coupling flange. In normal operation these stop valves are closed and nothing is fitted. When a burning slick is to be skimmed however a water spray pipe apparatus is attached to each quick release coupling flange and the stop valves are opened.

By this means part of the recycle fluid is diverted to a multiplicity of water sprays. These sprays are arranged to emerge from a large number of small holes made in the water spray pipe apparatus which consists of a number of pipes so arranged as to cover the entire skimmer head and foils with a coolant OIL SLICK SKIMMER supply. It is to be noted that since only a small amount of oil is mixed with recycle water there can be no danger of this oil wadding to the conflagration.

In addition it is undesirable that hot oil be passed into the plastic connecting pipe between skimmer head and storage means.

This oil is however cooled by mixing with water ahead of the separating means.

FLOTSAM AND SEAWEED ANTIFOULING DEVICES.

Floating debris and seaweed can block the oil collecting slots and can bring operations to a halt unless means are provided for their periodic removal. The invention provides a choice of two methods for keeping the slots clear of such debris.

Method 1 consists of a means for sudden temporary reversal of flow in the suction pipes. This may be achieved by the incorporation of valves and branch pipes so arranged that the suction pump intakes and delivery ports are temporarily switched or the intakes temporarily closed whilst the suction pipes are temporarily connected with the pressurised separating means.

Another means is the incorporation of a small oil store connecting with the suction pipes and provided with means for suddenly applying a high pressure capable of temporarily reversing flow in the suction pipes.

Method 2 consists of the incorporation of wedge shaped clearing spears which partly fill the slots over a very small section of the total span. Said clearing spears have attached to them arms or cables together with actuating gear so that they can be made to travel along the slots from one end to the other and then return. They can be switched in to operate continually or intermittently similar to the manner in which car windscreen wipers are operated.

ADDENDA (Ideas not incorporated in main specification) For the "MULTIPLE RIGID COLLECTING FOILS" the foils are made as light as possible and contain no ballast. Instead each foil has a spring attached to itself at one end and to said spine at the other end whereby rotation of each foil about the spine is resisted and any dynamic behaviour resulting is then made almost independent of that of any other foil. The spine is made rotatable about its axis and has an arm attached to an actuating means so that it can be set in any position within a specified arc. This enables all foils to be simply retracted from the water surface when not in use but the main function of the arrangement is to provide control of the force exerted by the foils against the surface of the water during the oil skimming operation.In this manner the natural frequency of torsional oscillation of each foil about the spine is made as high as possible for any specified ability of wave contouring. The maximum speed of the skimmer will be governed by the frequency of forced oscillation of foils which waves cause in relation to their natural frequency. Hence the higher the natural frequency the greater will be the maximum permissible skimming speed.

In an even better though more expensive embodiment of the invention no springs or at least only light springs are incorporated so that there is no need to compromise between wave contouring ability and natural frequency of oscillation. A radial arm extends from said spine at the position of each foil and has a piston and cylinder assembly pivotally mounted at its end. The said assembly is also attached to a foil so that the piston is caused to slide in the cylinder when the foil is rotated about the spine. Each foil is arranged similarly and each corresponding cylinder connects with a common reservoir mounted inside the hull. The reservoir is preferably pressurised by air or other gas though hydraulic fluid could be substituted.

This pressure governs the force exerted by the foils against the surface of the water. When made negative the foils retract above the surface. Retraction can be assisted by rotation of the spine.

The piston and cylinder can be replaced by a simpler equivalent in which the arm attached to the spine is formed as a plate lying in the plane of the axis of the spine. The edges of this plate hive a fine clearance with respect to a segmentally shaped hollow member attached to the corresponding foil.

OIL SLICK SKIMMER The known dracone to be used as a storage means is towed by the connecting pipe fixed to its forward end. Its other end is attached to the skimmer head and can provide the second function as a towing hitch. The vertical oil delivery pipe mounted inside the separator is mounted in a sleeve so that it can rotate about its axis and then the coupling its also able to swivel so that the skimmer head is able to turn without causing the pipe to kink. The pipe is shown as 22 and the coupling as 25 in figures 2 and 3. The branch pipe 38 is now made concentric with pipe 22 and is connected only by a gland so that rotation of pipe 22 can be permitted. Unfortunately this arrangement does not permit adequate flexibility between skimmer head and dracone and so the stiffness of the towing means regarded as a spring needs to be reduced.In the invention this is achieved in one of two ways.

The first method involves making at least part of the connecting pipe in the manner of a bellows by having a multiplicity of circumferential corrugations formed in its wall.

The second method arranges the connecting pipe with a loop preferably resting on the upper surface of the dracone. A pair of flanges connect the loop with the dracone and that part of the connecting pipe which is also used as a towing means between skimmer head and dracone. A pair of close coiled helical springs symmetrically arranged are fixed to these flanges and so carry the entire towing force between these flanges. In this way the pipe section between the flanges is relieved of the towing force and the shape of the loop will be able to vary as the springs stretch or contract.

THIRD SUBMISSION: SECOND IMPROVEMENTS TO THE OIL SKIMMER (MID NOVEMBER 1990. THIS IS A FIRST DECLARATION) Neither of the two previous applications provided apparatus capable of mopping up the most viscous crude oils at normal sea temperatures. These oils are so viscous that the tankers carrying them need to be steam heated in order that pumps can handle them. After a spill has occurred the temperature falls to that of the sea surface and pumping is no longer possible.

The present application provides an improvement which enables the most viscous crudes to be collected and stored and yet it combines features of the two previous applications within its structure. These are therefore incorporated and have the priority dates given above. The final and preferred arrangement of the invention will now be described. It offers the additional advantage of being able to collect floating rubbish of the kind which fouls many harbours.

Briefly the foil collection system having an array of inlet slots on its underside is retained in an embodiment proven by tests though the open top kind described in the first submission of 20 November 1989 is not precluded. Said inlet slots connect directly with the dracone type of storage means through a duct of the same or little reduced cross sectional area as compared with that of the dracone itself. No suction pump is incorporated in the simplest embodiment and the oil is allowed to flow in on the surface of a much larger volume of carrier water. The dracone has to be modified in two ways since its front end with filling pipe is removed and carrier water needs to be separated and removed from the storage means. The oil/water separator is no longer a part of the skimmer head and instead the storage means is used as a settling tank.An outlet for carrier water is arranged at the lowermost part of the dracone or the intake section being rearwardly directed and fitted with a valve which is arranged to close when the store is full of oil. Further and similarly arranged outlets can be provided on the underside of the storage means as extras to be fitted if found necessary. A sensor for oil level and sevomechanisms for control of all outlets are therefore provided.

OIL SLICK SKIMMER Arrangements are made for retraction of the array of collecting slots for minimising drag under the voyage to terminal phase of operation. The skimmer head has now been simplified to become a tug only since the collection and separating means are now incorporated as a part of the storage means. It is not essential to have this assembly towed and in a preferred embodiment of the invention the inlet apparatus is attached directly to the hull of this tug the two components being constructed to nest closely together. Other refinements will be described at a later stage.

The improved apparatus has the disadvantage of being unable to handle burning oil slicks and so for such duty an arrangement of the kind previously described needs to be adopted. Hence the invention now exists as two separate types produced by different arrangement of the basic components.

In either type the invention can be made sufficiently light and compact for transport by either a fixed wing aircraft in which case the airdrop requires a parachute or by helicopter in which case no parachute need be used.

It is now expedient to redefine the invention as consisting of four main components. These are now to be called the compact tug, the skimmer intake, the storage means and the separator respectively.

THE COMPACT TUG The compact tug is a novel form of ship owing to the comparatively large size of the propeller or propellers. It is designed to tow a cargo about one hundred times its own weight.

Although the hull can be reduced in displacement by the large factor implied as compared with conventional practice the propellers cannot be reduced very much in size without sacrificing propulsive efficiency. In consequence the sum of the diameters of the propellers is at least one quarter of the beam of the bare hull and in a preferred arrangement is more than half the beam. When a single propeller is fitted the torque would cause excessive heel if countermeasures were not incorporated.

At least one pair of deswirling vanes is therefore fixed to the hull downstream of the propeller in order to remove a large proportion of the swirl from the slipstream thereby producing a counter torque. This arrangement has the further advantage of increasing propulsion efficiency because the energy extracted from the swirling motion is converted to provide forward thrust and exceeds the friction drag of the deswirling vanes. A single pair vertically mounted has been found effective and has the additional advantage of providing an ideal housing for the propeller shaft. The complete propulsive system therefore comprises an engine mounted in the hull and preferably though not essentially having a horizontal crankshaft connecting with a bevel pinion and crown wheel forming a first stage reduction gear such that the axis of the output shaft is vertically oriented.

This output shaft then passes inside a hollow deswirling vane forming the propeller mounting to terminate at a second bevel pinion. This meshes with a second crown wheel mounted on a substantially horizontal shaft to which the said propeller is also fixed. In this way the required two stages of reduction gearing is provided. It is preferable to have the propeller shaft at a small angle to the horizontal so that the slipstream is deflected downwards away from the towed storage means so that frictional drag is not increased. A second novel feature is implied because a tractor propeller is now described. All conventional ships have pusher propellers whose skegs being mounted upstream can only cause parasitic drag whereas in the present invention the propeller mounting adds to the thrust. In one arrangement the propeller mounting is made rotatable about a vertical axis in order to provide a steering means. However a single large propeller has the disadvantage of requiring a large draft.

A multiplicity of propellers was described in the 20 November 1989 application to provide a shallow draft alternative for use close to shore or in other shallow waters. In this case each propeller was coupled to a hydraulic motor a hydraulic pump being driven direct from the engine to form a common power supply for all drives. Hydraulic drive was not essential a direct geared OIL SLICK SKIMMER drive for each propeller being a suitable alternative. The propellers had horizontal shafts inclined with respect to the direction of the keel of the hull so that slipstreams diverged away from the towed storage means to minimise frictional drag.

At least some of the propellers were specified to counter rotate with respect to the others in order to minimise the net torque reaction.

An alternative shallow draft propulsion device can be formed by using a modification of the pitch and roll dampers described in the 20 June submission. The cylindrical spine carrying the pivoted hydrofoils connects with a vertically mounted hydraulic piston in cylinder mechanism so arranged that both spine and hydrofoils can be made to perform a forced vertical oscillation.

The piston rods can be attached directly to the ends of said cylindrical spine or to arms pivotably mounted on the underside of the hull and attaching to said cylindrical spine at their outer ends. The hydrofoils are pivoted at points upstream of their centres of pressure even at stalling incidence by having close fitting bores to run on the spine so that they tend to line up with the flow. Deflection is however resisted by springs connecting hydrofoils with said cylindrical spine. With such a mechanism a vertical oscillation results in the efficient production of forward thrust. A hydraulic control system of the required inlet and outlet valves and piping connects with an engine mounted hydraulic pump and accumulator. A depth sensor is also fitted to determine the distance to the seabed and the stroke of the hydraulic piston rods is reduced to a safe value when necessary.

The first application also provided a single propeller arrangement capable of retraction by tilting the mounting toward the horizontal direction. Propulsion then relied upon water jets delivered from outlet of the oil/water separator and powered by at least one engine driven pump. This feature is retained as an optional extra with retraction effected by a hydraulic device of known kind. The direction of retraction can be so arranged as to cause the higher speed crown wheel to swing out of mesh with the bevel pinion of the engine.

LIGHTWEIGHT PROPELLERS The relatively large size of the propellers would make them excessively heavy if made of solid metal as in conventional practice. Two bladed propellers are preferred because the mechanical stresses are then smaller than when a larger number of blades is specified. The blade bending stresses are taken by a pair of spars both arranged where the blade thicknesses are close to the maximum so that torsional deflection is also resisted. These spars can be of cast steel of light alloy of carbon fibre composite or other strong and lightweight material.

The blade surface is formed from sheet or fibreglass with the internal space preferably filled with a structural foam.

To obtain adequate directional control of the compact tug when towing the storage means an additional rudder can be fitted.

This will be needed when the towing cables are attached to the propeller mounting instead of to the hull. Said rudder can be fixed either ahead or astern of the propeller.

As also stated in the first application the engine is preferably though not essentially a piston type internal combustion engine complete with battery and electric starter.

The hull can be of conventional design though to minimise weight it can be of larger beam to length ratio than is usual. To contend with heavy seas a totally enclosed deck is provided so that the interior is fully sealed by closure of access hatches except for inlet and exhaust pipes for the engine. At least the inlet pipe is made to stand high above the deck and can have baffles fitted as an extra precaution against water spray capture. The hull can have watertight compartments and to further save weight can be internally pressurised. The hull needs also to contain gas bottles or engine driven compressor for boom inflation as well as fuel tanks and the hydraulic machinery already described when appropriate.A pump can also be incorporated with stop valves and piping so that the stored oil OIL SLICK SKIMMER when of average viscosity can be pumped to a terminal or tanker or even a larger dracone used as a temporary store.

It will not be possible to empty the storage means by pumps alone when it contains the most viscous of crude oils. One of two alternative means of emptying are therefore provided but these are not a part of the skimmer. They need to be provided at the terminal whether this is shore based or mounted on a ship. In the first case a heating coil is provided in the form of tubing wrapped into the form of a hollow basket of approximately cylindrical or spherical shape for example. This hollow basket also contains a suction pump or at least the inlet to said suction pump. In either case this pump has a delivery pipe which connects with a secondary store to which the oil is to be delivered. In operation steam is supplied to the heating coil and the entire basket assembly is allowed to melt its way inside the storage means.As soon as a pool of oil of low enough viscosity has formed inside the basket the pump is started. The basket is made considerably smaller in diameter than the interior of said storage means and so can be gradually moved along from one end to the other to cause an almost complete emptying.

The second emptying means does not involve the use of either a suction pump or a heater. Instead a crane is provided capable of lifting at least one end of the storage means when full of oil.

A cylindrical roller is also provided with a stator and a turning mechanism which is operated to roll up the plastic storage means from one end as lifting proceeds. The viscous oil is thereby extruded from the opposite open end in the manner of toothpaste.

THE SKIMMER INTAKE The skimmer intake has already been described in outline but a number of refinements need to be considered. It is now defined as the inlet piece attaching to the long plastic tube which forms the storage means and is a modified dracone. Unless properly designed the skimmer intake is found to be hydrodynamically unstable tending to dive when attempt is made at towing. A satisfactory arrangement can be constructed from plastic so that it can be automatically folded in the manner described having priority date 20 November 1989 and involving an inflatable cylindrical spine having a built in skeleton which when relaxed is a flat coiled spring.

When deployed by the inflation of hollow so called frames in addition to the spine the leading end has the shape of the forward part of an inverted aerofoil forming a highly cambered surface underneath and in contact with the water surface. This shape is enclosed by a first sheet wrapped around the leading end forming a nose shaped like the segment of a cylinder. Said inlet slot is arranged at a deep point of the camber by having a second sheet forming a lower surface separated from the first sheet and carried on a multiplicity of vertical webs in line with the flow direction. These webs also form an array in line abreast and are attached at their upper and lower edges respectively to both first and second sheets.The lower cambered part of said first sheet thereby terminates as the ceiling of an array of sub inlets in line abreast which arise from the divisions formed by said vertical webs. The floors of these sub inlets are formed by the lower second sheet. Each sub inlet has a cross sectional area which increases toward its outlet by having the depth increase as a result of the floor and ceiling being divergent so that the flow velocity is gradually reduced.

The outlets from these sub inlets discharge to a plenum chamber formed by the direct junction of said first and second sheets at their outermost edges. Further vertical webs or longitudinal extensions of some of those already described located downstream of the sub inlets can be arranged to sub divide the plenum chamber into several plenum chambers. The outer shape of the plenum chamber combination gradually changes toward that of a circle as the storage means is approached and at some point any sub division is discontinued. Finally the skimmer intake and storage means meet at a joining flange. Alternatively the storage means and skimmer head can be made as an integral unit. It is not essential to split the skimmer intake into a number of plenum chambers but the advantage of doing so is to limit the degree of bulging caused by internal pressure.

OIL SLICK SKIMMER The divergent sub inlets form diffusing passages whereby the flow speed is reduced with simultaneous increase of pressure. This pressure gain is relied upon to inflate the storage means and to maintain a through flow. A carrier water outlet port cut somewhere along the underside allows carrier water to flow away leaving the oil behind. When a single such opening is placed in the skimmer intake instead of in the storage means a horizontal dividing sheet is also preferably arranged above it to prevent oil being entrained and discharged. More than one carrier outlet port can be provided. All such carrier water outlet ports are arranged to be closed by some form of shut off valve when the store is ultimately full of oil.Also the leading end of the skimmer intake is then rolled up or at least hoisted out of the water by cables connecting its forward ends to a point further to the rear to reduce drag.

The lower lip of the intake is stiffened either by metal strips crimped onto the plastic or by having it hollow and inflated.

Either way a degree of flexibility is produced so that each sub inlet can contour the wave surface to remain at some predetermined depth. In this way the invention is enabled to cope with heavy seas.

Each sub inlet of the intake has a width equal to that of a sub section forming the shape of the leading end. Each sub section is bounded at each side by a frame made to the desired cross sectional shape and each of these is joined by a cable or inflatable cylindrical spine or both and the extreme outer ends are attached to towing cables so that preferably a vee shape is formed with outer ends leading which helps trap the surface layer to cause it to enter the inlet slot. The frames already mentioned extend from the leading end to the point at which the sub inlets terminate each lying in a vertical plane in line with the flow direction. The frames can be rigid but are preferably formed from plastic sheet having a tubular rim able when inflated to form the shape of the leading part of the skimmer intake.Other tubes can be moulded into the sheet in either a vertical or inclined direction to further stiffen each structure when inflated.

Further beamwise inflatable tubes can be provided to interconnect said frames.

The structure relies upon two inflating systems operating in conjunction. First a forced inflation is provided from a pressurised supply which inflates the cylindrical spine and frames so that the skimmer intake unfolds at its forward end but hangs limp elsewhere. A natural inflation fills out the rest of both intake and storage means as soon as towing begins. This is created by the dynamic pressure caused by motion through the seawater and is exploited by the diffusing property of the sub inlets.

A problem arises with very viscous oils because the oil contacts the upper surface or ceiling of the inlet slot and is consequently slowed. This can be prevented in several ways used either separately or in conjunction. One way is provided in the invention by adding a second slot above each sub inlet which is arranged to have its outlet pointing in a rearward direction and also arranged to be supplied with so called cover water at a low pressure. This cover water pours onto the surface of the oil so preventing it contacting the ceiling walls of each sub inlet.

Only the vertical webs between sub inlets will now be wetted by oil and this wetted area is probably acceptable. Even so the drag will slow the oil to some extent and this effect is also preventable. In a further refinement said vertical webs are each fitted with a pair of nozzles mounted near the ceiling of each sub inlet and fed with some cover water. Said nozzles point in a direction which is substantially outwards from each vertical web so that surface oil is deflected and a film of cover water is caused to flank all vertical surfaces at least near the ceiling of each sub inlet. Said nozzles can be fed with a portion of cover water pressure boosted by a small pump interposed in the pipe connecting with the cover water supply duct.

This arrangement has further potential for improvement by providing means for air bubbles to be entrained with this cover water. On leaving the short sub inlets the flow enters a plenum of greater height so that a free surface is formed. Because of OIL SLICK SKIMMER the pressure increase the level therefore rises above that of the external level and this tends to cause the skimmer head to dive.

The effect can be prevented by slightly pressurising the trapped air bubble contained between the upper plastic wall and the liquid surface. This pressure causes the internal water level to be depressed. The air bubbles in the cover water separate and so maintain such a desirable overpressure. The means needed for providing air entrainment can consist of a venturi shaped portion of the duct having a ring of small holes provided at its throat section. The pressure falls temporarily below atmospheric at this throat causing air to be induced. The cover water can be provided by a pump mounted in the hull of the compact tug. Alternatively water can be recycled from some of the slightly pressurised carrier water inside the skimmer head or storage means.The design towing speed needs to be about three metres per second and then the pressure inside can be expected to be equivalent to a head of about forty centimetres. This should be sufficient without need for boosting by pumps. The height to which the water can rise can alternatively be increased by initially taking the cover water from a low level and adding air from a pressurised supply through small holes. In either case the added air can be of very small quantity because it only makes up for possible leakage losses. A model which was tested operated satisfactorily on trapped air without needing such an extra air supply. It is intended that during the greater part of the filling process the air bubble extends from the skimmer inlet and along the upper part of the trailing storage means. In this way the amount of wall in contact with viscous oil is minimised so allowing the oil to be dragged along more readily by the carrier water flowing underneath.

Even so further improvement is possible by further limiting the area of wall in contact with oil. This is achieved in a further refinement by creating an inward cross current at the upper surface of the carrier water thereby tending to sweep the oil to the centre where it will be deepened and so made shallower at the sides. These cross currents are induced by creating a vortex pair whose axes are horizontal in the carrier water at a point ahead of the storage means. Looking in the direction of flow the vortex on the right hand side needs to rotate anticlockwise with clockwise rotation of the left hand vortex. These vortices are provided in the invention by one of two means. The first means is a pair of swirl vanes mounted within the skimmer intake.The second means is a pair of contra rotating propellers which are housed within the skimmer inlet and are arranged to revolve in the same direction as the vortices previously described. A part of the slipstream from these propellers is discharged from openings underneath the skimmer inlet to augment the thrust of the main propulsion system. They can operate as the sole propulsor with the main propeller retracted when operation in shallow water is demanded the means having already been described in the submission dated 20 November 1989. It is also an application of the ducted propulsion system described in the submission dated 20 June 1990. These ducted propellers can be driven direct from gearing coupling with the engine or can be arranged with a hydraulic power transmission means.

An alternative pressurising means for preventing oil from contacting the ceilings of said sub inlets is provided by using the hovercraft principle. A fan is fitted to the roof of the skimmer head to blow air in. This all escapes forward through the upper parts of the sub inlets so maintaining a free surface for the collected oil by raising the entire set of sub inlets bodily. No carrier water is now required.

THE SEPARATOR The skimmer intake and storage means combination now acts as the separator without the assistance of a first separator mounted in the skimmer head. However features already described in the two previous submissions are utilised. These will now be specified.

One or more air vents which are closed by float valves can be incorporated along the upper portion of the storage means. These allow a free oil surface to be presented without allowing the trapped air volume to become excessive. For the final filling stage the air bubble needs to be fully vented and eliminated.

This is achieved by adding servos of electric or hydraulic type OIL SLICK SKIMMER which override the floats by pushing them downward.

The types of oil depth sensor described in the two previous submissions also need transfer to the storage means. They can be used in the present embodiment to signal the degree of filling to the operator.

When a pair of carrier water outlets are situated at the lowest points on the underside of the skimmer intake and storage means combination their throat areas need to be adjustable and subject to controlled variation as the filling process develops. Better control of filling can then be expected than when only a single outlet is provided and the surface flow of carrier water can be made to penetrate further into the storage means. The rate of closure or opening of each outlet is controlled by a servomechdnism which senses the oil level and feeds this information to some form of control means. A central computer type processor can be incorporated or instead a simple mechanical system can be utilised.The optimum setting of each outlet for any given oil level can be predetermined and the control means incorporates servomechanisms of any known kind which are set to adjust the openings to optimum values for any possible oil depth.

A suitable kind of adjustable outlet is formed by a pair of inflatable plastic lips at the outlet ends. The orifices tend to form into a circular cross section yielding maximum area due to the internal pressure of the storage means. When the pair of lips is pressurised a counter-tendency to close to a narrow slot shape arises. It can be so arranged that this closing pressure is adequate to effect complete closure when subject to the full dynamic pressure of forward motion. Hence one embodiment of the invention incorporates a forward facing pitot tube connecting with the cavity of the said lips via a control valve. A small bleed hole is provided in said cavity which can also terminate in a stop valve as an optional extra. In another embodiment the cavity inside said lips is pressurised from the compact tug by the connection of a pipe to a pressurised supply of gas or liquid.

It can happen that oil flows along to the rear end of the storage means on carrier water and then deepens as it is brought to rest.

The store then fills up from the rear end. It is then necessary to provide a multiplicity of outlets for carrier water at equally spaced intervals along the entire underside of the storage means.

Instead of a series of depth sensors it is then simpler to arrange a horizonal oil/water interface sensor running the entire length of the storage means at almost the deepest level. This sensor can depend on an ultrasonic beam or can measure the electrical resistance of the liquid between a pair of horizontal parallel wires running the entire length of the storage means.

Other kinds of sensor may alternatively be utilised. For example an oil detector could be placed at the inlet to each carrier water outlet based on the measurement of viscosity or thermal conductivity. From the signal obtained carrier water outlets are closed in a sequence starting from the rear end and at each closure all the remainder are opened a little to compensate so that the total outlet area remains nearly constant.

A possible problem is the loss of some oil with expelled carrier water so that an extra separating means then needs to be incorporated though at outlet from the storage means. All outlets from the under surface of the storage means now open to a single relatively small diameter carrier water collecting duct running the entire length of the storage means. One of a number of alternative types of oil/water separator are situated at the outlet which is located preferably though not necessarily at the rear end of the storage means. This can be one of the passive types consisting of inclined meshes. Oil caught by the strands drifts upward to pass through an opening and is returned to the storage means. This simple type described in the first submissionis however unlikely to be fully effective and so an active type needs to be considered as an alternative which has so far not been described.

This active separator consists of a multiplicity of discs carried on a common so called disc shaft mounted in a beamwise direction the entire cross section of the water collecting duct being obstructed except for the narrow gaps between said discs. The OIL SLICK SKIMMER disc shaft is so positioned that the upper part of all discs reside in the storage section so that on rotation any point on every disc passes irom one section to the other. A scraper is fixed to cooperate with each side of every disc at the point of re-entry to said water collecting duct so that the majority of the oil collected is scraped away to enter the storage section.

The disc shaft can have a hydraulic drive so that a long hydraulic pipe needs to be fixed to run all the way along the storage means to the tug. Alternatively a small water turbine can be incorporated to operate from the flowing water either outside or inside the storage means. The turbine is coupled through suitable reduction gearing to the said disc shaft.

It will be appreciated that the exact behaviour of the most viscous crude -oils is not yet understood and in the above embodiments of the invention some water is very likely to remain in the storage means. This is undesirable since storage capacity is thereby reduced. The control means for carrier water outlet ports is also an undesirable complication. A further embodiment of the invention will now be described in which the maximum utilisation is achieved by preventing any water from entering the storage means. In addition there are no outlets for carrier water in the storage means and so the control problem with which they are associated does not arise.

The skimmer intake is unchanged except that all carrier water is expelled from at least one outlet upstream of the storage means.

A horizontal sheet dividing the plenum of the skimmer intake into an upper duct and a lower duct is provided. The upper duct merges into the filling duct of large cross section associated with the storage means. The lower duct terminates in at least one rearwardly directed carrier water outlet. At the leading end of said horizontal sheet a disc shaft is provided on which an array of discs is mounted as in the separator previously described. The assembly complete with bearings and housings is made less dense than water and so floats either on the water or oil surface it is not important which. The discs are rotated by some form of motor so that the forward ends are rising and so lift oil from the lower duct to the upper duct. Fine clearance produced by scrapers on each side of each disc on the rear facing side of the discs causes all the oil to be deposited in the upper duct.An inclination of all scrapers with respect to the radial direction as measured from the axis of the disc shaft can provide a pumping action which may be sufficient to cause the oil to pass into the storage means causing it to gradually fill. This pumping action can be increased by adding wedges ahead of the scrapers so that the cross section for flow between discs and said wedges gradually reduces as the scrapers are approached. The pressure gain achieved is of the kind produced in a journal bearing and depends upon the fluid having viscosity. It is an application of the so called hydrodynamic effect. Grooves cut in the faces of the wedges and inclined to the radial direction can also be incorporated to collect the oil and deliver it to the rim of the discs.By careful design the pressure gain obtained will be sufficient to cause the oil to fill the storage means without the need for a further specialised booster pump. The addition of a booster pump is not excluded however. It is important that the ceiling of the upper duct is maintained with a reasonably fine clearance to the upper part of the discs in order to limit a return flow of the oil but a fine clearance with the floor of the lower duct is not needed. The width of the array of discs can be about the same as the diameter of the storage means although the width of the leading part of the skimmer intake can be much greater. The narrowing of the intake of the plenum toward the storage means is a desirable feature because of the funnelling action provided with consequent deepening of the oil ahead of the array of discs.

With the rotating disc array just described the slot intake has been retained but another embodiment of the invention dispenses with this intake altogether and so avoids the need for cover and the complications involved with its supply. The disc shaft with discs is placed at the most forward part of the skimmer intake to lift oil from the water and cause it to be scraped away directly into the large duct connecting with the storage means.

No carrier water is involved. The disc shaft now needs to be the OIL SLICK SKIMMER full width of the skimmer intake and in order to contour wave surfaces needs to be flexible. Either the entire disc shaft and cooperating ducting needs to be made flexible or a set of shorter disc shafts need to be arranged connected to adjacent members by flexible couplings.

COUPLING OF COMPACT TUG TO STORAGE MEANS The intake and storage means can be towed by longitudinally flexible springs or cables as already described in the first submission. It is necessary to provide a degree of independence of lateral movement for the skimmer intake so that it can be manouvered to follow the oil pattern on the sea without too accurate steering of the compact tug. At least one vertical fin of symmetrical aerofoil section is therefore provided on the underside of the skimmer intake. Such fins provide a sideways force when inclined to the flow and so provide the required means for control. In a preferred embodiment two such vertical fins are provided one on either side and at the outermost points.They are also arranged to be ahead of the intake slot so that they have the additional effect of helping to prevent loss of oil by the sideways surface flow which tends to occur. The fins enable the towed member to be swung out sideways in a controllable manner from the line of motion of the compact tug using one of two additional features.

In the first alternative said vertical fins are mounted pivotably and are each fitted with a servomechanism so that they can be turned in either direction in the manner of a rudder. Only a single towing cable made longitudinally flexible in the manner described in the submission of 20 November 1989 is required with this arrangement.

In the second alternative said vertical fins are fixed and a pair of longitudinally flexible towing cables are incorporated one cable being attached to each of the outermost points of the skimmer intake. Each cable is wound on a separate drum fixed at opposite sides of the compact tug near its rear end. Each drum is fitted with a hydraulic motor and control valve so that it can be operated independently of the other to effect the steering of the skimmer inlet as required. Each hydraulic motor connects with a separate hydraulic accumulator so that it can alternatively operate as a pump. The arrangement is described in the first submission as a means of providing the longitudinal flexibility needed to cope with severe wave conditions.In the new modified form each hydraulic accumulator connects with the said control valve and through it to the engine mounted hydraulic pump so that both functions can be simultaneously effected. To effect steering hydraulic fluid is pumped from one hydraulic accumulator to the other. This can be effected alternatively by arranging the hydraulic pump to rotate in either direction on command. The two hydraulic accumulators are then simply connected by a pipe incorporating said hydraulic pump and no valves are needed.

A preferred alternative however dispenses with towing cables altogether. Instead the skimmer intake is attached firmly to the compact tug so that together with the following storage means a single unit is effectively produced. This arrangement has several advantages. First the weight of the flexible towing means is eliminated and this is quite a large fraction of the total weight of the complete apparatus. Second the skimmer intake can now be made to fit snugly around the rear part of the hull of the compact tug. The skimmer head is now bifurcated with one set of inlets arranged on either side of the hull. Its large beam has the useful effect of narrowing the flow stream so that oil depth is deepened before collection. The third and main advantage is the improvement in accuracy of control. It is not easy to make sure the skimmer intake at considerable distance will move in the desired path.

To further improve control the neck section of the skimmer intake which joins the storage means is to be made with circumferential corrugations. Then it is made able to bend easily without kinking. The skimmer intake attached to the hull can then be steered accurately and with a degree of indzpendence of the motion of the much heavier storage means.

In a preferred alternative arrangement a hollow cylinder is provided ahead of said intake slot. A cooperating wall is provided attaching to the skimmer intake which flanks the cylinder in such a way as to form a converging passage as viewed in the direction of cylinder motion. This is a so called flanking surface. The arrangement is similar to a journal bearing with a greatly exaggerated clearance the wedge formed being known to generate a hydrodynamic pressure caused by the viscosity of the oil. A large number of perforations or holes are provided in said flanking surface to connect with the skimmer intake so that oil is forced into the following plenum chamber and storage means. The cylinder can have circumferential corrugations and be hollow so that longitudinal flexibility is provided for wave contouring. One cylinder can be provided on either side of the compact tug.No special bearings are needed since the arrangement acts as a journal but straps are needed at intervals to wrap around the forward part for retention.

OIL SLICK SKIMMER EXAMPLES DATING FROM 20 JUNE 1990.

Specific embodiments of the invention in which drawings made prior to the above date are excluded will now be described with respect to the accompanying drawings in which: Figure 1 shows the plan view of a skimmer head of triple hull type.

Figure 2 shows a longitudinal section of the same skimmer head.

Figure 3 shows a cross section of the same skimmer head.

Figure 4 shows a plan of the same skimmer head with a monolithic inflatable boom with secondary wave contouring boom attached.

Figure 5 shows a front elevation consistent with figure 4.

Figure 6 shows a side elevation consistent with figure 4.

Figure 7 shows a plan of a simple scoop attachment.

Figure 8 shows a front elevation consistent with figure 7.

Figure 9 shows plan of a single hull skimmer head pushing a monolithic inflatable boom.

Figure 10 shows a side elevation consistent with figure 9.

Figure 11 shows a plan of a single hull skimmer head with multiple rigid collecting foils.

Figure 12 shows a side elevation consistent with figure 11.

Figure 13 shows a side elevation of a storage means.

Then four new figures are described dating from mid November 1990. These are: Figure 14 showing an oil skimmer in plan constructed as a single unit with an oil storage means nesting snugly with a compact tug.

Figure 15 showing the same oil skimmer in elevation.

Figure 16 showing a detail of a skimmer intake able to cope with the most viscous of crude oils as well as all other kinds of oil or fuel or even solid floating debris.

and Figure 17 showing a skimmer intake involving rotating discs.

Referring to Figures 1, 2 and 3 the twin main hulls 1 are utilised as engine fuel tanks as well as for buoyancy and are fully sealed. They are connected by a deck which is not shown and the same deck also attaches the machinery containing central hull 2. This hull is also sealed except for a tall funnel 51 containing engine exhaust pipe 52. This is wrapped in a heat insulating blanket to prevent excessive heating of engine intake air which is supplied through the same funnel. A centrally mounted float 3 is provided for the removal of oil through slots 12 and 16 on its undersides. A separating means 4 is shown mounted on the deck. In central hull 2 an engine 5 preferably of the diesel or spark ignition kind has a reduction gearbox 6 connecting with a pair of contra-rotating propellers 8 through propeller shafts 7.The engine has the usual auxiliaries of an electric generator 9 and battery 10 and a starter motor not shown. In addition a hydraulic oil pump 11 is coupled to the engine to provide a drive for the suction pumps 15 and 18 and for operating servos and other equipment.

Most of the oil is collected by leading slot 12 cut in suction pipe 13 whilst a mixture of oil and water is collected by slot 16. In this case both slots are made in an arc shape so that clearing spears 14 can be operated by arms attached to a common pivot. An oil suction pump 15 connects with leading slot 12 and delivers to the separator through port 20 whilst a mixture pump 18 connects with slot 16 and delivers to the separator through port 21. The cut away regions shown in the hulls would be avoided in a practical design. The separator 4 contains wire mesh baffles 31 for assisting in the separation of air bubbles and water. The separator is fitted with a vertical pipe 22 on which a float 23 having a central matching bore is constrained to slide. This float 23 has a density arranged to lie between oil and water so that it tends to move with the interface between these fluids.A symmetrical ring of ports 24 is closed when the float 23 rises to its uppermost position and so cuts off oil delivery to connecting pipe 26 which couples with a storage means of the kind shown in figure 13. A quick coupling flange 38 connects connecting pipe 26 with the separator. The separator 4 also has an extension 28 which houses a float 29 of very low density so that it floats easily on oil. It has a mating surface at the top which closes an air outlet port also fitted with a OIL SLICK SKIMMER non-return valve 30 whereby any air collected with the oil and water is removed.

A towing pulley 27 is provided or a ball hitch so that a towing cable can be used able to swing freely in a sideways direction relative to the skimmer head. Mixture recycle pipes 32 are constrained laterally by adjustable cables 33 and are supported by inclined floats 34 at their forward ends so that their outlet nozzles 35 are maintained at an optimum position above the water surface moving up and down with any waves. Each nozzle 35 is fitted with a rectangular spear 36 whereby the nozzle area can be varied and so permit directional control of the skimmer head to be effected without using rudders. The spears 36 are operated by either electric or hydraulic servos not shown.

In order to provide extra buoyancy and partially shroud the propellers the hulls 1 are connected by a hollow shaped joining member 48 which also helps to provide streamlining behind float 3. This is of greatest importance when the skimmer is used with the optional false bottom to be described later.

A branch pipe with stop valve 37 is incorporated in each recycle pipe 32 and also terminates in a quick release coupling flange.

These are available for use with water spray apparatus which is arranged to drench the complete skimmer head when used to remove burning oil slicks.

In order to permit delivery of collected oil to a terminal or other secondary store a branch pipe 38 connects with pipe 22 of the separator. A three way cock 39 connecting with branch pipe 38 then enables the oil suction pump 15 to be used to withdraw oil from the storage means 52 shown in figure 13 when another stop valve 40 fitted at an outlet branch pipe from the same pump is also opened. For this operation it is also necessary to first pump water into the separator to push out the oil and so raise the float 23 to its uppermost position so that the port 24 is closed. The mixture suction pump 18 could alternatively be fitted with similar branch pipes and valves for similar use.

Other optional extras are also shown. A pitch and roll damper is shown. A spine 43 has hydrofoils 42 pivotally mounted upon it and restrained by a spring 44 so that lift forces are produced by pitch or roll which oppose the vertical motion induced by waves and convert the associated wave energy to propulsive power.

An alternative position for such dampers is shown at 45.

It may be desirable to increase the swath width when operating with very thin oil slicks. For attaching the required optional extras at least one catch 47 is provided underneath the hull and having an actuator mounted inside the hull for its withdrawal.

Pivots 46 at either side and near deck level are also provided for attaching such optional extras. A false bottom 49 can also be fitted optionally by the use of quick fixings such as cotters and pins 50. This completes the ducting of the propellers and since this false bottom extends to the bow of the skimmer head all water used for propulsion is constrained to be induced at a forwardly positioned intake.

Referring to figures 4, 5 and 6 the skimmer head is shown with swath increasing inflatable boom apparatus attached. An ariel 53 topped by a radar reflector 54 is shown and would have been shown in figure 2 if space had permitted. Extended recycle pipes 32 are also used. Inflatable main booms 55 are attached to the bow of the skimmer by means already described. Secondary flexible booms 56 are attached to the main booms by a multiplicity of struts 57 and these have vertical extensions terminating in inclined floats 58 so that the secondary booms are constrained to contour the wave surface though positioned at an optimum level below the surface. The main and secondary booms are connected by a plastic sheet so that a channel is formed for oil floating on carrier water.The hull is fitted with a false bottom so that a closed duct system is formed terminating in the propellers whereby the propulsion system is utilised as a suction means for carrier water. Connecting pipe 26 is shown between the separator 4 and storage means 52. The towing drag force is however carried by a flexible towing cable 51. This can take the form of a close coiled helical spring so that a degree of freedom OIL SLICK SKIMMER of motion between skimmer head and storage means is provided.

Referring now to figures 7 and 8 an alternative much simpler attachment is shown. Since the increase of swath width is more modest the complex inflatable main boom and secondary boom apparatus is not needed. A simple scoop is provided which could have its edges made as inflatable structures whereby weight can be minimised. The scoop can be of either metal or plastic construction and can be arranged as a foldable device.

Referring now to figures 9 and 10 a different embodiment of the invention is presented which permits of the use of a single rigid hull 1. This has the advantage of being lighter than the compound type previously described. The separating means 4 recycle apparatus 32 to 37 engine and suction pumping means 15 and 18 have already been described.

A monolithic inflatable boom 60 is pushed by struts 59 and a flexible sheet 61 connects said boom 60 with at least one trailing flexible wave contouring suction pipe 62. Two are shown the upstream one 62 being for the collection of oil through downward facing inlet slot 12 and the downstream one 63 for a mixture of oil and water through a similar slot 16. Connecting pipes with the suction pumps 15 and 18 mounted inside the hull may need to rise above the water surface as shown. In this case the pumps need to be of self priming kind or a separate priming pump is incorporated. An upper flexible connecting sheet 67 joins the inflatable boom with the flexible suction pipes so that together with the flexible bottom sheet a sealed enclosed space is formed. This provides space for water ballast which can be introduced as required to suit a range of wave and wind conditions.The introduction of ballast water requires a ballast pump with drive and control means which are not shown. Internal vertical separating sheets 68 can also be provided to form a number of almost separate tanks if found necessary so that sloshing is limited.

Retractable pitch and roll damping hydrofoils 42 are shown as an optional extra. Two hydrofoils able to move independently are threaded on a single spine 43 and butt against one another at the central point. Their inclination to the horizontal is restrained by springs not shown. The spine is carried by a pair of hinge mounted arms 68 which can be rotated together when an actuating means not shown is operated. In this way the damper can be deployed as required.

Referring now to figures 11 and 12 an alternative single hull skimmer head is shown having rigid metal collecting foils. The hull separator and recycle apparatus is exactly as previously described. This embodiment of the invention is highly suitable for the collection of burning oil slicks and yet provides an attractively large swath width so that it is also suitable for mopping up quite thin oil slicks under severe wave and wind conditions.

A hollow cylindrical spine 64 of quite large diameter is mounted close to the deck possibly in a transverse recess. A number of independent rigid hollow foils 65 have bores at their leading ends which are a running fit on the spine so that they are able to rotate about the spine. Each foil has a length several times greater than the height of the spine above the water and so the rear end trails behind the spine being supported by the dynamic pressures caused by forward motion. An inlet slot 12 on the underside of each foil and running its full span connects with a rigid suction pipe 13 which in turn connects through flexible piping to a suction pump 15 not shown but mounted inside the hull. There can be a second similar suction slot 16 located downstream of the first slot in each foil and connecting with a second suction pump 18 for a mixture of oil and water. The flexible connecting pipes can pass through the hollow spine 64 in which case the suction pumps need to be of self priming kind or a separate priming pump can be incorporated. Alternatively said flexible connecting pipes can trail in the water behind the foils and enter the hull near the stern below the waterline.

Referring now to figure 13 a storage means is shown. It > based OIL SLICK SKIMMER on the known apparatus called a dracone but contains additional features as optional extras. The known dracone has no towing cable but makes use of the connecting pipe 26 as a towing device.

This may be too stiff for towing by the very light skimmer heads described in this specification and so an additional coiled spring towing means 51 is shown. In addition a second pipe 66 is shown connecting with the lowest part of the store and permits the removal of water. Pipe 66 is preferably carried forward to the skimmer head and has an outlet positioned ahead of the skimmer. It is also fitted with a stop valve 69. To permit of air removal a valved air vent 28 29 30 is optionally fitted to the upper surface as described with reference to figure 2.

Reference is now made to drawings submitted mid November 1990.

Figures 14 and 15 showing the plan view and elevations of a complete skimmer will be described together.

The hull of the compact tug is shown at 1 and is fully sealed when access hatches are closed except for engine air inlet 51 and exhaust 52. A radio mast 53 with radar reflector 54 is provided.

The hull contains engine 5 and has a tractor propeller 8 mounted from a deswirler vane pair 90. This mounting contains a vertical shaft 91 connecting with engine and propeller through bevel gears and bevel pinions. Nesting about the rear end of the hull is skimmer intake 92. This has inlet slot 93 followed by sub inlets 94 formed with their ceilings 95 diverging from their floors 96 to form diffusing passages. A plenum chamber 97 is shown connecting with large duct 98 which forms the connection with storage means 52. The large duct has circumferential corrugations around its wall to permit it to bend without creasing. A float valve 28, 29, 30 controls the size of the air bubble in the storage means. A carrier water outlet 99 is shown rearwardly directed at a low point on the underside of the storage means and has a means for closure incorporated.A horizontal sheet 100 is provided to prevent oil being entrained.

Figure 16 shows a side elevation of a skimmer intake in section so that one of a multiplicity of inflatable frames is shown. The leading end has a rounded nose 101 being the front part of an inverted aerofoil section whose shape is controlled by inflatable tubes 102. Sub inlets 94 are shown bounded by upper sheet 103 and lower sheet 104. These sheets are connected by vertical webs 105 but these extend over the entire frame to the position 106 where the sub ducts terminate. Some of the frames extend to position 107 to subdivide plenum chamber 97 into several smaller plenums in order to limit bulging of the assembly by internal pressure.

Figure 17 shows an alternative skimmer intake having a disc shaft 108 fitted with an array of discs 109 which are rotated by a motor not shown so that the lower part moves in a counter direction to motion of the skimmer. Oil is picked up between the discs and carried over to enter the intake slot 93. The slot is divided by wedges 110 fixed to its upper and lower walls so that one wedge lies between each adjacent disc. The wedges are arranged to make the space between its surface and each disc reduce progressively in the direction of disc movement in order to generate a pressure as a consequence of oil viscosity. To assist in expulsion of the oil grooves 111 are cut in the sides of the wedges and have a flat spiral form so that rotation of the discs tends to push oil trapped in said grooves toward the intake slot. A number of disc shafts are joined end to end by flexible couplings not shown in order that the complete array is made able to contour any waves.

Claims (28)

1. OIL SLICK SKIMMER

   CLAIMS 1. Apparatus for removal of oil slicks from the sea estuaries or inland waterways comprising at least a compact tug having a hull containing an engine connecting with some form of propulsor said tug connecting with an oil storage means having flexible walls so that it can be folded or rolled to a compact shape and a slot shaped intake of shallow depth in proportion to its width arranged with its lower lip below the surface of the oil and water in such manner as to rise and fall with the surface as it moves due to waves by connection to floats having upturned leading ends said intake also connecting with said storage means.

   (Priority date 20/11/89)
2. 2. Apparatus as claimed in claim 1 which is so light and compact that it can be carried by some form of aircraft.

   (Priority date 20/11/89)
3. 3. Apparatus as claimed in both previous claims in which said slot shaped inlet is formed from flexible plastic and attached to an inflatable structure capable of being folded into a compact parcel. (Priority date 20/11/89)
4. 4. Apparatus as claimed in claim 3 in which said inflatable structure has embedded in its wall a skeleton made from spring steel which is wound in a flat spiral so that the inflatable structure winds into this shape when deflated.

   (Priority date 20/11/89)
5. 5. Apparatus as claimed in any previous claim in which an oil/water separator in the form of a settling tank is provided and in which an oil suction pump is incorporated able to transfer the separated oil through a connecting pipe to said storage means. (Priority date 20/11/89)
6. 6. Apparatus as claimed in any previous claim in which at least one flexible cable connects said compact tug with the storage means said flexible cable having a close coiled helical spring over a substantial part of its length.

   (Priority date 20/11/89)
7. 7. Apparatus as claimed in any previous claim except claim 6 in which at least one cable is wound on a drum attached to said compact tug the drum being mechanically connected to a hydraulic motor which also acts a pump depending on whether the cable is being wound in or paid out a hydraulic accumulator connecting by pipes with this machine so that a flexible towing means is provided. (Priority date 20/11/89)
8. 8. Apparatus as claimed in any previous claim in which at least one propeller is provided in connection with said engine either by a gear train or by a hydraulic transmission and which can optionally be made retractable for use in shallow water by the provision of a hinge mounting auxiliary pumps then being provided with outlet jets for use with the propeller retracted.

   (Priority date 20/11/89)
9. 9. Apparatus as claimed in any previous claim in which said slot shaped intake has a ceiling formed by a float or foil above and attached to it so that said slot tends to lie entirely below the surface the leading end of the foil being upstream of said slot and above the water surface. Claims 3 and 4 are not necessarily included because said foil can alternatively be rigid and of metal construction. (Priority date 20/6/90)
10. 10. Apparatus as claimed in any previous claim though not necessarily including claims 3 and 4 in which a multiplicity of said foils each have a bore close to their leading ends by which they are threaded onto a common cylindrical spine so that each can move rotatably and independently of the other foils and having intake slots at a point downstream so that each slot is able to contour the water surface.

    (priority date 20/6/90)
11. 11. Apparatus as claimed in any previous claim in which at least one suction pump ;s connected to said inlet slots and also has OIL SLICK SKIMMER an outlet connecting with the inlet of an oil/water separator mounted in the hull of said compact tug and two water delivery pipes leading forward from connections near the base of said separator one on either side of the hull to terminate in nozzles which point substantially toward one another and having an oil delivery pipe connecting with the upper part of said separator and connecting at its other end with said towed storage means.

    (Priority date 20/6/90)
12. 12. Apparatus as claimed in any previous claim in which said storage means is utilised at least as a secondary oil/water separator by having an outlet port for water at the deepest point on its underside said outlet port having some form of valve for closure when the store is full with oil.

    (Priority date 20/6/90)
13. 13. Apparatus as claimed in any previous claim in which said oil/water separator contains a float having a density intermediate between that of oil and seawater so that it acts as a sensor for the interface between these two liquids.

    (Priority date 20/6/90)
14. 14. Apparatus as claimed in any previous claim in- which any separator has a float controlled air valve to allow the release of air to the atmosphere when the internal oil level falls below a certain point. (Priority date 20/6/90)
15. 15. Apparatus as claimed in any previous claim except claim 11 in which said slot shaped inlet is connected to said oil storage means through a duct at least comparable in cross sectional area to that of the oil storage means. (Priority date Nov. 90)
16. 16.Apparatus as claimed in claim 15 in which said inlet slot is formed as a multiplicity of sub inlets divided by vertical webs so that a flexible structure is formed capable of contouring waves each web forming part of a frame defining the shape of the forward part of the skimmer intake said frame being either rigid or having inflatable tubes moulded into its structure and in which each sub inlet has its ceiling and floor divergent so that it acts as a diffuser to provide a pressure gain.
17. 17. Apparatus as claimed in claim 16 in which a cover water slot is arranged slightly upstream of said inlet slot so that cover water is poured on to the oil surface to prevent contact of oil with the ceiling of said sub inlets.
18. 18. Apparatus as claimed in claim 17 in which air injection ports are provided in the duct supplying cover water so that air bubbles are carried into the skimmer intake and sustain a slightly elevated internal pressure.
19. 19. Apparatus as claimed in claim 16 in which an air blower is fitted to the ceiling of the plenum chamber of the skimmer intake so that it is internally pressurised to an extent which can lift the ceilings of the skimmer inlets above the oil surface
20. 20. Apparatus as claimed in any previous claim except for claims 6, 7 and 11 in which said skimmer intake is made to fit snugly around the rear part of the compact tug and the two directly connected to one another so that no towing cables are required.
21. 21. Apparatus as claimed in claim 20 or all previous claims except claim 11 in which a disc shaft floating in the surface with its axis in a beamwise direction carries a multiplicity of discs along its length which are caused to revolve by some form of motor coupled with said disc shaft so that the lower side of the discs move in the opposite direction to that of the skimmer the upper side fitting the entrance of a duct connecting to the storage means.
22. 22. Apparatus as claimed in claim 21 in which wedge shaped obstructions are fitted between each adjacent disc and are attached to said entrance duct the wedge shapes being such as to cause the clearance between the discs and obstructions to reduce progressively as rotation proceeds until the clearance is the minimum which can be tolerated without causing wear so that a OIL SLICK SKIMMER hydrodynamic pressure is developed to provide a means of pumping the oil into the storage means spiral grooves being incorporated in the flanks of the wedges to assist in oil delivery.
23. 23. Apparatus as claimed in any previous claim except where exclusions apply in which a means of propulsion is provided for use in shallow water consisting of a horizontally disposed hydrofoil flexibly mounted on a cylindrical spine at a point before its centre of pressure but attached to said spine by a spring which resists any deflection the cylindrical spine being connected to a hydraulic actuating mechanism able to cause it to execute a substantially vertical oscillation whereby a forward thrust can be developed the stroke of the actuator being made adjustable so that in shallow water this stroke is reduced to a safe value a sea bottom sensor being incorporated to act through a servomechanism for stroke adjustment.
24. 24. Apparatus as claimed in any previous claim in which tractor propellers form at least the main propulsion means being mounted forward of a pair of deswirling vanes acting also as the mounting and containing a vertical drive shaft connecting with said propeller and an engine in the hull above by crown and pinion bevel gears whereby the high gear ratio required is provided and the propulsion efficiency improved by the deswirling action at the same time as torque reaction is minimised.
25. 25. Apparatus as claimed in claim 24 in which the propeller is made as a composite structure having a strong lightweight pair of spars covered by a skin and the internal space preferably filled with a structural foam.
26. 26. Apparatus as claimed in claim 25 in which the sum of diameters of all propellers is in excess of half the beam of the compact tug.
27. 27. Apparatus as claimed in any previous claim except 21 and 22 in which at least one hollow cylinder having alternatively circumferential corrugations to enhance longitudinal flexibility and with the option of being an inflatable structure is mounted ahead of the skimmer intake and is mechanically connected to the engine or has hydraulic drive so that it is rotated and cooperates with a skimmer intake slot which is followed by a flanking surface arranged so that it gradually converges ultimately to a fine clearance with the surface of said cylinder and in which this flanging surface is fixed to the duct leading to the storage means said flanking surface being provided with holes to permit the movement of oil from the cylinder flanking surface wedge shaped interspace. The cylinder can be revolved in either direction.
28. 28. Apparatus as claimed in any previous claim in which said intake slot is terminated by vertical surfaces preferably having the cross section of a thin symmetrical aerofoil and arranged so that their leading edges are ahead of said intake slot.

    Amendments to the claims have been filed as follows

    CLAIMS 1. An oil skimming apparatus is claimed which is capable of operating even under severe ocean wave conditions by having at least one flexible boom also defined as a secondary boom arranged perpendicular or inclined to the direction of motion and which forms the lower lip of an intake which is held below the water surface in such a manner that the depth of this lip is maintained roughly constant by at least partly contouring any wave disturbed water surface above by having an array of vertical connecting members attached at intervals along the span of said flexible boom and in which the upper end of each connecting member is attached to or is a part of a float having an upturned leading end which thereby makes additional use of hydrodynamic forces by a planing action to help counteract the downward force exerted on said flexible boom by hydrodynamic pressure produced on a trailing sheet defined as a floor which is attached downstream and in which the hydrodynamic pressure is maintained by having a restricted outlet for water as compared with the area of the intake formed by the water above said flexible boom the only other direct connection made by said floor being with an oil storage bag. (Priority date 20/11/89) (Note see critique of Ayers UK spec No 1425365 on page 4) 2. Apparatus as claimed in claim 1 in which all booms are made as foldable inflatable structures and in which each main boom has a skeleton moulded into it consisting of a flat spiral spring so that the complete assembly naturally rolls up into a compact shape when deflated. (Priority date 20/11/89) 3.Apparatus as claimed in claim 1 or 2 in which said secondary boom is deployed upstream of a more rigid main boom by a multiplicity of substantially horizontal struts each being flexibly mounted from said main boom at its trailing end and supported by a float at its forward end by connecting through a said vertical member formed as a vertical strut and in which a trailing sheet connects said secondary boom to the underside of the main boom. (Priority date 20/11/89) (See critique of Ayers UK patent No. 1425365 page 5) OIL SLICK SKIMMER 4. Apparatus as claimed in any previous claim in which a towing vessel called a tug has at least one cable having a helical spring incorporated for at least a substantial portion of its length connecting at least indirectly with an oil storage bag.

    (Priority date 20/11/89) 5. Apparatus as claimed in any previous claim in which a towing vessel connects to the oil storage bag by at least one towing cable which is wound round a drum mechanically coupled to a hydraulic motor which also acts as a pump and which is hydraulically connected by a pipe with a hydraulic accumulator so that when the system is isolated the effect of a flexible cable is produced by pump/motor action with the accumulator acting as an energy store being alternately charged and drained the cable being paid out or wound in as waves cause relative movement between towed and towing vessels to eliminate cable snatch at all times. (Priority date 20/11/89) (See critique of Weatherford USA Spec No 3862904 A on Page 5) 6.Apparatus as claimed in all previous claims in which a towing vessel is provided made light enough to be transported by some kind of aircraft yet having adequate towing capacity for pulling both skimmer intake and oil storage bag and made possible by the incorporation of at least one relatively large propeller as compared with the size of the hull of said towing vessel.

    (Priority date 20/11/89) 7. Apparatus as claimed in all previous claims in which a towing vessel has a multiplicity of propellers to limit the draught of the vessel. (Priority date 20/11/89) 8. Apparatus as claimed in all previous claims in which the sum of diameters of all propellers is in excess of one quarter of the beam of the tug. (Priority date 20/6/90) 9. Apparatus as claimed in all previous claims in which at least one propeller is fitted which is made sufficiently light by being formed as a composite structure in which at least one spanwise spar and preferably two emerge from a common hub to run the length of each blade close to the region of maximum thickness the blades being covered by a skin and the internal space preferably though not necessarily filled with a structural foam.

    (Priority date 16/11/90) 10. Apparatus as claimed in all previous claims in which a tug has at least one tractor propeller mounted from a hollow vertical strut having an aerofoil section which is so cambered in opposite directions above and below the axis of the propeller that swirl is substantially removed from the slipstream and in which a vertical shaft is housed having a pinion at its lower end which meshes with a crown wheel attached to the propeller shaft said vertical shaft having further gearing at its upper end before connection to an engine output shaft. (Priority date 20/6/90) 11.Apparatus as claimed in all previous claims in which there are two of the hydraulic pump/motor and hydraulic accumulator units described in claim 5 each mechanically connected to a cable drum so that two cables can be deployed independently but in which the two accumulators are interconnected by a pipe and pump anble to tranfer fluid in either direction or having other pipes with valves connecting with an engine driven pump so that the cables can be paid out or wound in and yet the effect of a flexible cable for coping with wave heave is retained.

    (priority date 16/11/90) 12. Apparatus as claimed in all previous claims in which said floats are arranged by having a so called upper cover formed in some way to follow round a cylindrical tube through which a towing bar or cable is threaded at its forward end so that an upper cover and lower sheet are thereby made available which are joined at least along their outer edges to form a float system and having a rear end attached to both lower sheet and floor by a multiplicity of vertical sheets spaced out side by side and lined up with the direction of flow which connect directly with the secondary boom which forms the leading edge of the floor so that said secondary boom lies below and behind said cylindrical OIL SLICK SKIMMER tube said vertical sheets having progressingly increasing height for a short distance downstream so that floor and the ceiling provided by the underside of said lower sheet diverge to produce a diffusing action known to create a hydrodynamic pressure gain when in motion so that the floor is held down without the use of weights and the pressure gain also causes oil to flow into a connected store.(Priority date 20/6/90) (See critique of the only relevant prior art of Fitzgerald, USA patent No 3,653,510 4/4/1972 page 4 13.Apparatus as claimed in claim 12 in which said floats are merged into a single flexible float by an upper sheet attached to a multiplicity of vertical sheets bounded by rims to form frames lined up in the flow direction and placed side by side at uniform intervals so that their lower parts act as the vertical webs needed to support the floor connecting with a secondary boom of very small cross section forming the lower lip of the intake and in which said lower sheet forming a so called ceiling is added to cooperate with said floor to form a divergent inlet passage whereby a pressure gain is produced and in which said ceiling is taken forward providing a convex undersurface as viewed in side elevation as it passes over the frames which have rounded leading edges and is formed around these leading edges and attaches to or is made integral with an upper cover which connects with the floor at the sides to form a closed duct and in which this connects to a storage bag so that the entire apparatus is able to ride easily on the water surface whilst flexing with waves and in which a preferably rearward facing water outlet is arranged having an adjustable cross section capable of being fully closed. (Priority date 20/11/90) 14. Apparatus as claimed in claim 13 in which said frames are made from plastic with inflatable tubular rims and in which adjacent frames are connected to each other by horizontal inflatable tubes so that the entire framework can be inflated for use yet is flexible enough to contour waves and can be folded when deflated. (Priority date 20/6/90) 15.Apparatus as claimed in any previous claim in which a multiplicity of inflatable frames are embedded in upper and lower sheets to create the desired profile and each frame has a bore close to its leading end by which it is threaded onto a common cylindrical spine or cable a pair of towing cables being fixed to the outer ends of the assembly or with one end fixed to an arm attached to the hull of the tug so that each frame can move rotatably and independently of, the other frames until restricted by their covering sheets said frames forming vertical dividing walls to split the intake slot into a multiplicity of sub-inlets whereby said frames act as structural members to maintain the desired shape yet allow the distortions required to enable each sub-inlet slot to contour waves on the water surface.

    (priority date 20/6/90) 16. Apparatus as claimed in claim 12 in which a multiplicity of rigid narrow foils made from a stiff material such as a metal are threaded onto a common cylindrical spine through cooperating bores formed in their leading ends said foils having extended vertical surfaces at least on one side so that as intake slots move up and down relative to each other said vertical surfaces maintain a close clearance to prevent the escape of oil between foils and in which a corrugated flexible pipe connects with the rear end of each foil and at the other end connects with a store or separating tank. (Priority date 20/6/90) 17.Apparatus as claimed in any previous claim in which said intake slot is terminated by a pair of vertical surfaces extending below the lowest part of the cambered undersurface of the intake and preferably having the cross section when viewed in plan of a thin symmetrical aerofoil and arranged so that their leading edges are ahead of said intake slot whereby collection effectiveness is improved by preventing sideways flow.

    (Priority date 16/11/90) 18. Apparatus as claimed in claim 17 in which the skimmer intake is able tb be steered independently of the tug by differential winding of the two towing cables by having a pair of cable drums OIL SLICK SKIMMER and their associated pump/motor accumulator units as described a in claim 5 each separately connected to an engine driven pump.

    (Priority date 16/11/90) 19. Apparatus as claimed in any previous claim in which said storage means is utilised at least as a secondary oil/water separator by having at least one outlet port for water at a deep point on its underside said outlet port having some form of valve for closure when the store is full with oil.

    (Priority date 20/6/90) 20. Apparatus as claimed in any previous claim in which any separator inclusive of said storage bag has a float controlled air valve cooperating with a port in the upper surface of the enclosure and which is closed when the float is raised above a certain level but-is openeG below this level to allow the release of air to the atmosphere when the internal oil level is below a certain point said float being fitted with an override control to be used when required. (Priority date 20/6/90) 21. Apparatus as claimed in any previous claim in which said slot shaped inlet is connected to said oil storage means through a duct at least comparable in cross sectional area to that of the oil storage means. (Priority date 16/11/90) 22. Apparatus as claimed in any previous claim in which a cover water slot is arranged slightly upstream of said inlet slot so that cover water is poured on to the oil surface to prevent contact of oil with the ceiling of said sub inlets.

    (Priority date 16/11/90) 23. Apparatus as claimed in any previous claim except for claims 4 5 11 and 18 in which said skimmer intake is made tu fit snugly around the rear part of the compact tug and :itch the storage bag directly connected by a short large bore duct so that no towing cables are required. iPriority date 16/11/90) 24. Apparatus as claimed in any previous claim in which at least one hollow cylinder having alternatively circumferential a corrugations to enhance longitudinal flexibility and with the option of being an inflatable structure is mounted ahead of the skimmer intake and is mechanically connected to the engine or has hydraulic drive so that it is rotated and cooperates with a skimmer intake slot which is followed by a flanking surface arranged so that it gradually converges ultimately to a fine clearance with the surface of said cylinder and in which this flanking surface is fixed to the duct leading to the storage means said flanking surface being provided with holes to permit the movement of oil from the cylinder flanking surface wedge shaped interspace. The cylinder can be revolved in either direction. (Priority date 16/11/90)