GB2152881A - Containment of floating material - Google Patents

Abstract

A pollution control vessel comprising means for deployment of a floating boom around the stern end of the vessel, and a steerable bow-thrust mechanism. <IMAGE>

Description

SPECIFICATION Containment of floating material ,The present invention relates to a method and apparatus for containment of floating material and particularly, but not exclusively, to containment of a floating pollutant such as oil.

It is known to use a flexible floating boom for containment of oil floating on seawater. One end of the boom is pulled along the surface of the water by a main vessel and the other end is pulled by a work boat. In this arrangement, the boom assumes an arcuate shape and oil accumulates in the curve of the boom from where it can be collected if desired. A third vessel may be deployed to collect the oil, for example by vacuum suction, and it is important that the main propeller of the collecting vessel is kept away from) the bulk of contained oil so as not to disturb and disperse the oil.

This method of oil containment is very cumbersome and expensive as it involves at least two vessels.

It is also known to deploy a U-shaped flexible boom from the side of a single vessel for containment of oil floating on the sea. A support arm is extended laterally of the vessel and the free ends of the boom are connected to the support arm so that the boom lies entirely on one side of the vessel. In this way, the boom is kept remote from the main propeller which therefore does not disturb the contained oil. To collect the contained oil, a recovery head connected to a vacuum pump may be used.

A disadvantage of this method is that it is only possible to contain the oil disposed on one side of the vessel. Furthermore it is difficult to maintain an open U-shape for the boom and many ties need to be used for this purpose. It is also difficult to maintain a desired position of the recovery head during collection. Another disadvantage is that the boom tends to act as an anchor and to drag the vessel around as it progresses.

According to the present invention there is provided a method of containment of floating material comprising deploying a floatable boom around the stern end of a vessel and propelling the vessel forwardly by means of a bow-thrust mechanism.

An advantage of the present invention is that only a single vessel is required for containment of the floating material because a boom can be deployed around the stern of the vessel owing to the use of a bow-thrust mechanism instead of the main propeller which would cause too much disturbance. Also, the motion of the vessel causes the boom naturally to assume a shape suitable for containment of the floating material and by deploying the boom around an end of the vessel the boom does not tend to drag the vessel around as it progresses.

The bow-thrust mechanism may be of a steerable type commonly called an azimuth bow-thrust unit. Such units are rotatable through 360 independently of the rudder control. They are some times employed in ferries and fishing vessels where a high degree of manoeuvrability is required e.g. for rapid docking or for assisting in maintaining steerage under low speeds where there might otherwise be insufficient steerage control available.

The present method differs from other applications of bow-thrust mechanisms in that its principle utility is in providing forward motion of the vessel. Nevertheless an azimuth bow-thrust unit is useful in the method of the invention in maintaining direction or control under low speed conditions e.g. when wind and tide are in different directions.

Oil collection is normally carried out directly into the wind whenever possible.

Fixed, transversely directed bow-thrust mechanisms are also known and are unsuitable for carrying out the method of the invention.

A preferred form of bow-thrust mechanism is located at a considerable distance below the vessel e.g. about 6 metres or more generally from 4 to 8 metres where its effect will cause the least disturbance at the water surface.

The bow-thrust mechanism may be designed to enable steerage to be maintained at a speed of not more than 10 kilometres per hour. The bow-thrust mechanism may be operable to maintain the vessel orientation when stationary.

The free ends of the boom are preferably connected by a wire to the port and starboard sides of the bow of the vessel respectively so that the boom assumes a U-shape as the vessel progresses. A recovery head connected to a vacuum pump may be deployed from the stern to collect the floating material as it accumulates.

Preferably, means are provided for spacing the free ends of the boom from the sides of the hull of the vessel.

According to another aspect of the present invention there is provided a pollution control vessel comprising means for deployment of a floating boom around the stern end of the vessel, and a bow-thrust mechanism for propelling the vessel forwardly.

The boom may be an inflatable boom. In a particular embodiment, the boom is adapted to be wound ribbonwise when in a deflated position for storing on deck.

A particular embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing which is a perspective view of a sea-going vessel incorporating the present invention.

In the drawing, a sea-going vessel is indicated generally at 10 having a stern 12, a bow 14, a deck 15 and a hull 16.

The vessel 10 is driven by a bow thrust mechanism indicated schematically at 44 rather than by the main propeller (not shown). The bow-thrust mechanism indicated at 44 is of a steerable type commonly called an azimuth bow-thrust unit. Such units are rotatable through 360 independently of the rudder control. The bow-thrust mechanism is located about 6 metres below the vessel 10 where its effect will cause the least disturbance of the water surface.

A U-shaped boom 18 having a visible floating part 19 is deployed around the stern and attached via pivotable arms 20 and 22 to port and starboard winches 25 24, 26 respectively positioned at the bow 14.

The boom 18 is inflatable and is made of a polyurethane material. The boom has four sections 27-30. Each section is sealed at both ends and the sections are bolted together using aluminium plates forming three junctions 31-33.

The floating part 19 of each of the sections 27 and 30 of the boom 18 is of circular cross-section and attached to the underside of the floating part is a skirt (not visible) in the form of a vertical fin which is weighted by incorporating a chain along its length to steady the boom 18 in the water, an arrangement known as chain ballast. The diameter of the floating part of the boom is approximately half a metre and the height of the underwater skirt is approximately two thirds of a metre. The sections 28 and 29 of the boom 18 each have two parts of circular section forming a figure of eight in section to increase their buoyancy and providing an increased freeboard which may be as much as double the freeboard of the sections 27 and 30 of the boom 18. Attached to the lower part is a flat vertical skirt with chain ballast.

The free ends 34, 36 of the boom 18 are each provided with an aluminium plate having means for attachment to wires 38, 40 leading to the port winch 24 and the starboard winch 26 respectively.

The wires 38, 40 pass through a pulley block 39 at the ends of the arms 20, 22. The arms 20, 22 serve to maintain the desired distance of the boom 18 from the sides of the hull 16 and these arms are pivotable upwardly to stand above the deck 15 so as not to project outboard when not in use.

The junctions 31-33 of the boom 18 are each joined by wires 41-43 respectively to the stern. The wires 41-43 are connected to the junctions 31-33 and can be tensioned by a tensioning device (not shown) on the deck 15 to retain the boom 18 in position.

Oil floating on the seawater is indicated generally at 46 and is collected using a funnel-shaped recovery head 48 deployed over the stern 12. The recovery head 48 is connected to a suction tube 50 which passes over the stern 12 into a housing 52 containing a hopper 54 and a vacuum pump 56.

Floats 58 are attached to the suction pipe 50. The wire 42 connecting the junction 32 of the boom 18 to the stern 12 is attached to the recovery head 48 and can be used to control the position of the recovery head 48 relative to the junction 32.

The hopper 54 is connected to a central holding tank 58 in the hull 16. The central tank 58 is connected to an oily water separator 60 which is adapted to supply oil via pipes 62 and 64 to port and starboard oil tanks 66 and 68 respectively and to return water to the sea over the starboard side of the vessel 10 via pipe 70.

When not in use, the boom 18 is stored on the deck 15 in a deflated condition by being wound ribbonwise on the main salvage winch 72. A frame 74 comprising a roller 76 overhangs the stern 12 se that the boom 18 can be paid out over the stern 12 over the roller 76. The boom is wound on the main salvage winch 72 with its four sections 27-30 connected.

The total length of the boom is approximately 150 metres.

To assemble the boom 18 into position, the deflated boom 18 is gradually unwound from the main salvage winch 72. During unwinding, each of the sections 27-30 is inflated using hand-held portable air pumps (there are inlets for air in each section of the boom and these are not shown). The free end 34 of the boom is passed over the roller 76 on the frame 74 and the wire 38 is attached thereto. As the boom 18 is gradually paid out over the stern 12, the arm 20 is pivoted outwardly and the port winch 24 is used to drag the boom 18 along the port side of the vessel 10. The arm 20 keeps the boom 18 at a fixed distance from the port side of the hull 16 during deployment. When the full length of the boom 18 has been inflated, the other free end 36 is attached to the wire 40 and drawn by the starboard winch 26 along the starboard side of the vessel 10.During deployment, the wires 41-43 are attached to the junctions 31-33 of the boom 18. The wire 42 attached to the recovery head 48 is attached to junction 32 thereby causing the suction pipe 50 and recovery head 48 to be deployed over the stern 12.

The assembly operation takes approximately half an hour to complete. In its final position, the boom 18 forms a U-shape around the stern 12 of the vessel 10 and has a sweep width of approximately 42 metres.

The vessel 10 then proceeds slowly to the polluted area under the power of the bow thrust mechanism 44. The main propeller (not shown) is not used as this would disturb the water in the containment area of the boom 18.

As the floating part 19 of the boom 18 progresses, oil passes through the open end of the Ushape and is contained in the U-bend from where it can be collected by the recovery head 48.

Oily water is sucked up through the pipe 50 and delivered to the hopper 54 which is a closed unit.

The vacuum pump 56 is controlled by a timing mechanism to perform an intermittent sucking and blowing action. When oily water is sucked up into the hopper 54 it is then blown through the hopper 54 into the central tank 58. If any relatively large objects, for example dead birds, are delivered to the hopper 54, this will. impede the sucking and blowing action and such objects need to be cleared by hand and a door is provided in the housing 52 for this purpose.

Oily water is supplied from the central tank 58 in a regulated manner to the oily water separator 60.

After separation, oil is channelled to the port and starboard containment tanks 66 and 68 respectively and water is returned to the sea via pipe 70.

In operation, the vessel 10 will travel slowly, up to 3-4 knots. The azimuth bow-thrust mechanism 44 provides a 360 degrees turning capability and very good steering control under low speed. By virtue of its position remote from the stern and its depth beneath the hull, the bow-thrust mechanism causes minimum disturbance at the water surface.

The system described above is stable in rough seas and in bad weather conditions and has proved suitable for collection of oil from the surface of the North Sea.

The system is capable of recovering 40 tons of oil per hour. The port and starboard containment tanks have a total capacity of 400 tonnes.

When collection of oil has finished and it is desired to disassemble the containment and collection apparatus, the following procedure is used.

The vacuum pump 56 is deactivated. The wire 38 is slackened to allow the free end 34 of the floating part 19 of the boom 18 to pass by the stern 12 of the vessel 10 (by virtue of the movement of the vessel 10). The wire 38 is then hooked up so as to pull the end 34 aboard and is then detached from the end 34 and wound up by the port bow winch 24. The wire 38 is retained in the pulley block on the arm 20 ready for use. The end 34 of the part 19 of the boom 18 is passed over the roller 76, deflated and wound onto the main salvage winch 72.

The wires 41-43 are detached from the junctions 31-33 as these are wound in. The recovery head is also pulled aboard. When the port side of the boom has been retrieved, the wire 40 is also slackened to allow the free end 36 to pass via the stern 12 to be wound up. The wire 40 is then detached and wound by the starboard winch 26 but does not leave the pulley block of the arm 22. The arms 20 and 22 are pulled upwardly about their pivot points 21 and 23 using a deck winch (not shown) into a vertical position.

The main propeller of the vessel 10 can then be employed to power the vessel if desired.

It will be understood that the drawing is a schematic representation of the invention and does not show parts of the vessel 10 which are not relevant to the present invention.

The present invention has the advantage that it enables a single vessel to be used for oil containment and collection. The boom is deployed in a manner which enables its position to be controlled relatively easily so that it is not necessary to use excessive ties or manpower to maintain the boom in position during use. Also, the boom naturally assumes a shape suitable for containment due to being dragged through the water behind the vessel so that no elaborate steps are needed to be taken to maintain the containment shape of the boom.

Furthermore, the arrangement is such that the bow thrust mechanism can be used to steer the vessel accurately under the low speeds necessary for collection of floating material.

Another advantage of the invention is that it provides apparatus for collection of floating material which is relatively easy to assemble and to disassemble.

It will be understood that whilst oil may be the most commonly occurring floating pollutant which requires containment, the invention may be applied to containment of any type of floating material.

The boom employed need not necessarily be inflatable so long as it is bouyant.

If it is desired only to contain floating material but not to collect the material, a longer boom may be employed for greater capacity. In the described embodiment, further sections may be added to the boom which would then extend a greater distance behind the stern of the vessel.

Claims (21)

1. A method of containment of floating material comprising deploying a floatable boom around the stern end of a vessel and propelling the vessel forwardly by means of a bow-thrust mechanism.

2. A method according to claim 1 wherein the bow thrust mechanism is an azimuth bow-thrust mechanism.

3. A method according to claim 1 or claim 2 wherein the bow-thrust mechanism is located from 4 to 8 metres below the hull of the vessel.

4. A method according to any preceding claim wherein the bow-thrust mechanism enables steerage to be maintained at a speed of not more than 1 Okmlhr.

5. A method according to any preceding claim wherein said bow-thrust mechanism can maintain the vessel orientation when stationary.

6. A method according to any preceding claim wherein the ends of the boom are maintained at a distance from respective sides of the vessel by rigid arms.

7. A method according to any preceding claim wherein oil is sucked into disposal means on the vessel through a floating pipe deployed from the vessel and accessible to the stern region of the boom.

8. A method according to claim 7 wherein an oil/water mixture sucked in through the pipe is separated on the vessel by an oil/water separator, the separated water discharged, and the oil retained.

9. A method according to claim 8 wherein the separation is carried out centrifugally.

10. A method according to any preceding claim comprising deploying a generally U-shaped floatable boom.

11. A pollution control vessel comprising means for deployment of a floating boom around the stern end of the vessel, and a bow-thrust mechanism for propelling the vessel forwardly.

12. A vessel according to claim 11 comprising an azimuth bow-thrust mechanism.

13. A vessel according to claim 11 or claim 12 wherein the bow-thrust mechanism is located from 4 to 8 metres below the hull of the vessel.

14. A vessel according to any of claims 11 to 13 wherein the bow-thrust mechanism enables steerage to be maintained at a speed of not more than 1 Okm/hr.

15. A vessel according to any of claims 11 to 14 wherein the bow-thrust mechanism can maintain the vessel orientation when stationary.

16. A vessel according to any of claims 11 to 15 including at least one lateral thrust mechanism.

17. A vessel according to any of claims 11 to 16 including rigid arms for maintaining the ends of the boom at a distance from respective sides of the vessel.

18. A vessel according to any of claims 11 to 17 comprising an oil/water separator, a floating pipe deployable from the vessel and accessible to a stern region of the boom when deployed and means for sucking an oil/water mixture through the pipe into the separator.

19. A vessel according to any of claims 11 to 18 comprising means for storing a flexible boom in reeled form and means for gradually paying the boom out over the stern end.

20. A method substantially as herein described with reference to the accompanying drawing.

21. A vessel substantially as herein described with reference to and as illustrated in the accompanying drawing.