"FLOATING CONTAINMENT BOOM"

Field of the Invention

The present invention relates to a floating containment boom for containing oil, fuel and other pollutants on water and relates particularly, though not exclusively, to a boom for containing oil at sea.

Background to the Invention

Unfortunately, it is not uncommon for oil spills to occur at sea, either as a result of damage sustained by an oil tanker or other sea-faring vessels, or as a result of spillage at a drilling platform, due to an accident or a storm at sea. With the increased awareness of the environmental damage caused by oil pollution greater efforts are now being made to contain and clean-up oil spills before they disperse. If not contained oil spills foul beaches, kill marine wildlife and damage sensitive coastal resources. However, if properly contained it is sometimes possible to recover some of the oil before it does too much damage. For this purpose a variety of different types of prior art containment booms have been produced.

There is also a need to keep oil waste, floating debris and other pollutants, away from sensitive industrial plants such as desalination plants and power stations. This is often achieved by the use of a containment system around the perimeter of the industrial plant..

A typical prior art containment boom consists of a series of floats with a fabric skirt suspended from the floats, the skirt having a ballast provided at the bottom to keep it in a generally vertical orientation. The containment boom must be of robust design as it may be required to be deployed at sea for extended periods of time where it is subject to the damaging effects of wind, waves, sunlight and corrosive seawater in all weather conditions. Prior art containment booms are typically manufactured from a variety of materials including PVC, polyethylene, polyurethane, woven polypropylene fabric, steel, aluminium and rubber. One of the problems with prior art containment booms

is producing a boom of sufficiently robust design whilst using a variety of materials with different corrosion resistant properties and differing mechanical properties such as differing tensile strengths, expansion coefficients and friction coefficients. The use of differing materials causes the components to work against each other especially in harsh environmental conditions, often resulting in tearing of the plastic components of the boom. In addition, certain prior art booms are only able to flex in one direction adding further stress to the boom.

The present invention was developed with a view to providing a floating containment boom of robust design that will operate reliably in all weather conditions in a dynamic environment.

References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.

Summary of the Invention

According to one aspect of the present invention there is provided a floating containment boom for containing oil and other pollutants on the surface of a body of water, the boom comprising:

a plurality of floats arranged serially in connection with an elongate, flexible, tension member, each float being spaced apart from an adjacent float; and,

an elongate containment skirt made from a flexible, polymer plastics material and mechanically coupled to, and supported in a vertical orientation on the water surface by, said floats, said skirt having a plurality of flexing sections folded in concertina fashion, said flexing sections being located in the spaces between the floats, wherein the boom is able to flex in both horizontal and vertical directions so as to more effectively provide containment in varying wave conditions.

Preferably said containment skirt is made from one continuous length of said polymer plastics material. Preferably said plurality of floats is one of two

strings of floats on a pair of parallel tension members, a string of floats being provided on either side of said containment skirt so that each float has a matching float adjacent to it on- the opposite side of the containment skirt. Preferably each float is of elongate configuration and each said pair of adjacent floats is fixed to opposite sides of the containment skirt adjacent an upper edge of the skirt. As an alternative, each said pair of adjacent floats may be fixed to opposite sides of the containment skirt, each respective float being spaced apart from an upper edge of the skirt.

Preferably a ballast means is provided on a lower edge of the skirt to help maintain it in a vertical orientation. In one embodiment said ballast means comprises a ballast chain which is supported in a series of conduits fixed to said lower edge of the skirt between said flexing sections.

Preferably each float has a conduit that passes through the float from end to end, an inside diameter of the conduit being adapted to receive said tension member there through in a sliding fit. Typically each said float is of triangular cross-section in a lateral direction. Preferably a plurality of spacer elements is provided on the or each tension member between each float to assist in maintaining the spacing between the floats. Alternatively, a flexing cover folded in concertina fashion is provided on the or each tension member between each float to assist in maintaining the spacing between the floats.

Preferably the or each tension member and the containment skirt are terminated at each end by a respective buoy. Preferably each buoy comprises a support float and a structural member, the structural member being adapted to allow mechanical coupling of the buoy to the containment skirt. Preferably the buoy further comprises one or more pairs of coupling members to which are attached the tension members. In a preferred embodiment, the support float is in the form of a cylindrical container. More preferably the support float forms more than about 50% of the overall weight or the volume of the buoy. The support float preferably tapers to a mooring point to allow mooring of the buoy.

Preferably each buoy further comprises a tether device for tethering the buoy to the sea bed.

More preferably the tether device comprises:

an elongate elastic tension member capable of extending to a significantly greater length from an unstretched condition to a stretched condition; and,

an anchoring means for anchoring the tension member to the sea bed wherein the elasticity of the tension member allows the floating structure to move vertically due to wave action whilst substantially maintaining its position.

Preferably said elastic tension member is designed to have a changing elastic response depending on the extent to which it is stretched. Typically the less the elastic tension member is stretched the stiffer the elastic response. In a preferred embodiment the shape of the elastic tension member is tapered, being relatively thick at one end and thinning towards the other end.

Preferably said tether device further comprises an elongate flexible sleeve member received over said elastic tension member to protect it, said sleeve member being folded in a concertina fashion to enable it to expand and contract as said elastic tension member is stretched. Advantageously said flexible sleeve member also acts as a stop member, limiting the extent to which said elastic tension member can be stretched.

Preferably the flexible, polymer plastics material is polyethylene.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred", will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of the invention.

Brief Description of the Drawings

The nature of the invention will be better understood from the following detailed description of two preferred embodiments of the containment boom, given by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a first embodiment of a floating containment boom according to the present invention;

Figure 2 is a plan view of the containment boom of Figure 1;

Figure 3 is a plan view of a buoy at one end of the containment boom of Figure 1 ;

Figure 4 is a partial section view through the buoy of Figure 3;

Figure 5 is an enlarged side elevation of a flexing section of the containment boom of Figure 1; .

Figure 6 illustrates the flexing section of Figure 5 flexing in a vertical direction;

Figure 7 illustrates a first embodiment of a tether device according to the present invention;

Figure 8 illustrates the containment boom of Figure 1 tethered at each end with the tether device of Figure 7;

Figure 9 illustrates the containment boom of Figure 8 (together with neighbouring sections on either side of the buoys) flexing in both vertical directions due to wave action;

Figure 10 illustrates a portion of the containment boom of the first embodiment showing one of the floats in perspective view;

Figure 11 illustrates a side elevation of a second embodiment of a floating containment boom according to the present invention;

Figure 12 illustrates a plan view of the containment boom of Figure 11 ;

Figure 13 illustrates an enlarged view of a portion of the containment boom as shown in Figure 12;

Figure 14 illustrates a perspective view of a buoy at each end of the containment boom of Figure 11 ;

Figure 15 illustrates a side view of the buoy of Figure 14;

Figure 16 illustrates a front view of the buoy of Figure 14;

Figure 17 is an enlarged side elevation of a flexing section of the containment boom of Figure 11 , in a flexing position;

Figure 18 illustrates a side view of the tether device of Figure 11 ;

Figure 19 is a front view of the tether device of Figure 11 ;

Figure 20 illustrates an enlarged view of the top end of the tether device of Figure 18, secured to the mooring point of a buoy;

Figure 21 illustrates an enlarged view of the top end of the tether device of Figure 19.

Detailed Description of Preferred Embodiments

A preferred first embodiment of the floating containment boom 10 according to the invention, as illustrated in the accompanying drawings, comprises a plurality of floats 12 arranged serially in connection with an elongate, flexible, tension member 14. Each float 12 on the tension member 14 is spaced apart from an adjacent float 12. An elongate containment skirt .16 made from a flexible, polymer plastics material is mechanically coupled to, and supported in a vertical orientation on the water surface by, the floats 12. In this embodiment, the floats 12 are arranged in two strings of floats 12a and 12b on a pair of parallel tension members 14a and 14b, a string of floats being provided on either side of the containment skirt 16 so that each float 12a has a matching float 12b adjacent to it on the opposite side of the containment skirt

16. However, it will be understood that in an alternative embodiment a single string of floats could be provided with the containment skirt supported thereon in a suitable manner.

In the illustrated first embodiment each float 12 is of elongate configuration and each pair of adjacent floats 12a and 12b is fixed to opposite sides of the containment skirt 16 adjacent an upper edge of the skirt. The containment skirt 16 is preferably made from one continuous length of the polymer plastics material. The skirt 16 may, for example, be made from a continuous sheet of 2mm thick high density polyethylene (HDPE), typically of width about 1000mm. Since the components are made of polymer plastics material they may be readily joined by welding with no mechanical joining required. This avoids the difficulties of prior art devices which require the interaction of different products made of different materials with their respective varying associated properties.

The containment skirt 16 has a plurality of flexing sections 18 folded in concertina fashion, the flexing sections 18 being located in the spaces between the floats 12. This feature enables the boom 10 to flex in both horizontal and vertical directions so as to more effectively provide containment in varying wave conditions.

The floats 12 are preferably also made from the same polymer plastics material as the skirt 16, for example, HDPE, and are preferably manufactured using a rotational moulding technique. Since they are made from the same material as the skirt it is a relatively straightforward matter to weld the floats 12a and 12b to either side of the skirt using a hot air extrusion gun to extrude the heated polymer. Preferably each float 12 has a conduit 75 that passes through the float from end to end as best seen in Figure 10. The inside diameter of the conduit is adapted to receive the tension member 14 there through in a sliding fit. Typically each float 12 is of generally triangular cross- section in a lateral direction. The cross-sectional shape preferably approximates that of a scalene right-angle triangle, with the face of the float

being welded to the skirt forming the base of the triangle. Each float is typically about 400mm in height and 100mm in width at its base.

Since the floats 12a and 12b are threaded on the respective tension members 14a and 14b, they are to some extent free together with the skirt to slide along the tension member which enhances the flexibility of the boom. However, preferably a plurality of spacer elements 20 is provided on each tension member 14 between each float 12 to maintain the spacing between the floats 12. The spacer members also assist in controlling the overall flexing of the boom. In this embodiment there are nine such spacer elements 20 provided between each float 12 as can be seen most clearly in Figures 5 and 6. The provision of a plurality of such spacer elements 20 ensures that the flexibility of the tension members 14 and of the boom 10 as a whole is not comprised.

Preferably a ballast means 22 is provided on a lower edge of the skirt 16 to help maintain it in a vertical orientation. In this embodiment the ballast means comprises a ballast chain 24 which is housed in a series of conduits 26 fixed to the lower edge of the skirt 16 between the flexing sections 18. The full height of the containment skirt 16 including the ballast housing 26 is typically about 1100 mm. The ballast chain 24 hangs free below the flexing sections 18, as can be seen most clearly in Figures 5 and 6.

In the illustrated first embodiment, the tension members 14 and the containment skirt 16 are terminated at each end by a respective buoy 30.

Preferably each buoy 30 comprises a support float 32 and a structural member 34 for mechanically coupling the buoy to the containment skirt. In this embodiment the float of the buoy is in the form of a cylindrical airtight container 32 with a removable inspection cover 36 provided at the top, as can be seen most clearly in Figure 4. The container 32 may be manufactured in two halves which are welded to the respective sides of the structural member

34.

In this embodiment the structural member is in the form of a plate 34 made from a rectangular sheet of 20mm thick HDPE, approximately 800mm wide

and 1.0m deep, with a tapered section that narrows to a mooring point 38 at the bottom. A cut-out section 40 of the plate 34, inside the container 32, provides easier access to a coupling point 42 fixed to the plate 34 and housed in the container. Two coupling sections 43 are provided on each side of the plate 34 protruding from either side of the container 32. One of the coupling sections 43 is coupled directly to one end of the containment skirt 16, either by welding or using suitable fasteners (not shown). The other coupling section 43 may be used to couple the buoy to the skirt of a second similar boom (not shown) to be connected in series with the first boom 10.

Two coupling members 44, in the form of two short lengths of poly pipe, extend through the wall of the container 32 to the coupling point 42. In this embodiment the tension members 14 are provided by two continuous lengths of poly pipe (with an outside diameter of 50mm) made from HDPE, and each having an 8mm galvanised chain 46 (or non-stretch rope) threaded there through from end to end. Each end of the tension members 14 is coupled to one of the coupling members 44 on the buoy 30 by a compression fitting 48, as can be seen most clearly in Figure 3. The internal chain 46 (or rope) also passes through the compression fitting 48 and the coupling members 44 and is connected to the coupling point 42 using a suitable coupling. The internal chains 46 are not load bearing under normal operating conditions, most of the load being carried by the tension members 14 and to a lesser extent by the containment skirt 16. However, in the event of a failure in one of the tension members 14 the internal chains 46 provide a back-up to prevent the boom 10 from falling apart. Typically the buoy 30 also has a second pair of coupling members 44 facing in the opposite direction, (not shown in Figure 3, however see Figure 4) to enable a second similar boom (not shown) to be connected in series with the first boom 10.

A tether means 50 is preferably provided for tethering the buoy 30 to the sea bed. A preferred embodiment of the tether means 50, according to the present invention, as illustrated in Figure 7 comprises an elongate elastic tension member 52 capable of extending to a significantly greater length from an

unstretched condition to a stretched condition. The elastic tension member 52 is preferably designed to have a changing elastic response depending on the extent to which it is stretched. Typically the less the elastic tension member is stretched the stiffer the elastic response. Hence in high seas the tension member 52 will expand and contract more easily, being already in a stretched condition, whereas in low seas the tension member 52 will expand and contract less easily, being in a less stretched condition. The elasticity of the tension member 52 thus allows the buoy 30, and hence the containment boom 10, to move vertically due to wave action whilst substantially maintaining its position. In this embodiment the shape of the elastic tension member is tapered, being relatively thick at one end and thinning towards the other end.

An anchoring means 54 is provided for anchoring the tether device to the sea bed. In the illustrated embodiment a heavy weight, for example, a concrete block 54 is used to anchor the tether device to the sea bed (see Figures 8 and 9). The tether device preferably further comprises an elongate flexible sleeve member 56 received over the elastic tension member 52 to protect it, for example, from UV radiation. The sleeve member 56 is folded in a concertina fashion to enable it to expand and contract as the elastic tension member 52 is stretched. Advantageously the flexible sleeve member 56 also acts as a stop member, limiting the extent to which the elastic tension member 52 can be stretched. The tension member 52 may be made from a rubber material, whereas the sleeve member 56 is typically made from a woven PVC fabric (for example as sold under the trade name Ripstop). In still water the tether device is typically stretched to about 6m in length, whereas in rough seas it may stretched to a maximum, for example, of 11m in length. A nylon insert 58 is preferably provided at each end to couple the tether device 50 to the mooring point 38 on the buoy 30 and to the concrete block 54 respectively with a suitable shackle.

The second embodiment of the containment boom 70 of the invention resembles the first embodiment in many respects and will therefore not be discussed in detail. As can be seen in Figures 11 and 12, the containment

boom 70 comprises a plurality of spaced apart floats 72 arranged serially in connection with an elongate, flexible, tension member 74 in the form of a galvanised chain. An elongate containment skirt 76 made from polyethylene is mechanically coupled to, and supported in a vertical orientation on the water surface by the floats 72. The floats are arranged in two strings of floats 72a and 72b on either side of the skirt 76, on a pair of tension members 74a and

74b. The containment skirt 76 is made from one continuous length of polyethylene with the floats 72 (also of polyethylene) being welded to the skirt 76.

The containment skirt 76 has a plurality of flexing sections 78 folded in concertina fashion, the flexing sections 78 being located between the floats 72. However, as can be seen in Figure 11 , and in contrast to the first embodiment, the straight non-flexing sections 80 of the skirt 76 extend into the spaces between the floats such that the relative proportion of the flexing sections 78 in the overall skirt is reduced relative to the proportion in the first embodiment. Thus, in the case of the second embodiment, the containment skirt 76 has more controlled flexing movement in a vertical direction.

A flexing cover 88 folded in concertina fashion is provided on each tension member 74 between the floats 72, as best seen in Figure 17. A ballast means 82 is provided on a lower edge of the skirt 76 in the form of a ballast chain 84 housed in a series of conduits 86, between the flexing sections 78.

The tension members 74 and the containment skirt 76 are terminated at each end by a respective buoy 90. Each buoy, also made largely of polyethylene, comprises a support float 92 and a structural member 94, as best seen in Figures 14 to 16. The structural member 94 forms a coupling section 102 provided with a series of holes 106. Bolts are placed through the holes 106 for fixing the containment skirt 76 to a respective buoy 90. The buoy 90 also includes an inspection cover 96. The buoy 90 tapers to a mooring point provided with holes 98 to which is secured a tether device 110 for mooring the buoy 90 to the sea bed.

The buoy 90 further comprises two pairs of coupling members 100 to which are attached the pairs of tension members 74 as can be seen in Figures 11 and 12. The tension members 74 are attached using bolts via coupling sections 104 on each respective tension member as can be seen in Figure 13. The coupling members 100 are formed from elongate plates (not shown) positioned through the support float 92 of the buoy 90, the ends of the steel plates forming the coupling members.

The shape of the buoy 90 is important in that it cannot readily sink ensuring that the boom is always maintained in the correct position for use. The buoy

90 would require a large amount of force to sink it to greater than half its depth. It would then require an even greater force (of extreme conditions) to sink it below this level due to the relatively larger surface area or volume of the upper half of the buoy. Thus the buoy forms an effective support system to minimise any risk of the containment boom sinking when in use.

A tether device 1 10 comprising a tension member 112, a sleeve member 116, and an anchoring means 114 is fixed to the mooring point 98 as shown in Figures 11 and 18.The upper end of the tether device 1 10 comprises a pair of plates 118 used for securing the tether.device to the mooring point 98. As best seen in Figure 21 , the tether device is secured to the mooring point by means of a locking pin 120, a locking collar 122, a washer 124, a stainless steel pin 126, and a nut 128.

The containment skirt 76 is about 12 metres in length and a number of lengths can be easily transported stacked in a container for transport to a site as required. The containment boom may then readily be assembled on site by connecting the various skirts to the buoys, and by attaching the tension members.

The typical operation of the first embodiment of the floating containment boom 10 will now be briefly described with reference to the accompanying drawings Figures 1 to 10. The boom 10 or a series of such booms would typically be deployed on the surface of the sea to contain an oil slick that has spilled from,

for example, a damaged tanker. Alternatively the boom 10 may be used to protect ocean or other water intakes from oil spills, for example water intakes used in power plants where it is essential to prevent oil from being taken into the power plant. The primary containment barrier is provided in the boom 10 by the containment skirt 16. It is essential therefore that the skirt 16 be supported in the water in a generally vertical orientation to ensure that the oil on the surface of the water is properly contained, or excluded from intakes.

The design of the boom 10 is such that approximately half the height of the skirt 16 is supported above the water level by the floats 12, and the other half is suspended below the water line, as can be seen most clearly in Figure 8.

This ensures that a minimum of oil can pass over or under the barrier created by the boom 10. However this barrier will only be effective if the skirt is always kept at approximately the same height relative to the water line. With prior art booms this becomes increasingly more difficult in rough seas as the boom is unable to flex sufficiently to follow the contours of the waves. Hence the skirt in prior art booms may at points be periodically lifted right out of the water, or become fully submerged, due to its inflexibility in a vertical direction. The boom 10 of the present invention overcomes this problem by the provision of the flexing sections 18 in the containment skirt 16.

As shown in Figure 6, the flexing sections 18 allow the boom to flex in a vertical direction between each float 12 to a considerable extent so that the boom, and hence the skirt 16, can always follow the contour of the water surface even in heavy weather conditions. Figure 9 shows the flexing of the boom 10 of Figure 8, and also shows the neighbouring sections of the boom extending on either side of the buoys 30. As can be seen in Figure 9, the buoys 30 remain substantially vertical whilst the various floats 12 and flexing sections 18 of the containment boom 10 as separated by the buoys 30 flex simultaneously in both vertical directions. These features of flexing ensure that the oil slick is more reliably contained in the floating containment boom 10.

The ability to follow the contour of the water surface in all weather conditions is further enhanced by the provision of the elastic tension member 52 in the

tether device 50 of the invention. As illustrated in Figure 8 and 9, this not only permits the boom to rise and fall with the water level during tidal movement (Figure 8), but also enables the boom to accommodate significant variations in wave height without compromising the integrity of the containment (Figure 9).

Now that preferred embodiments of the floating containment boom have been described in detail, it will be apparent that it provides a number of advantages over the prior art, including the following:

(i) Being made almost entirely from polyethylene, all the components of the boom are easily assembled, welded and connected together to produce a more robust structure that is not as susceptible to corrosion;

(ii) Being made almost entirely from polyethylene, the boom is not subject to the wear and stress common in devices made from components of varying materials such as steel, metal and rubber;

(iii) The provision of the concertinaed flexing sections in the containment skirt enables the boom to flex in a vertical direction to a much greater extent than was hitherto possible;

(iv) The concertinaed flexing sections in the containment skirt are protected by the pair of tension members so that the boom is not over-stretched thereby assisting in preventing tearing of the boom;

(v) The boom is able to flex in all directions without fatigue on the parts of the device, in particular when the boom is made of a plastics material;

(vi)The design of the tether device attached to the boom further enhances the ability of the boom to follow wave and tidal movement without compromising its containment ability;

(vii) Since polyethylene is inherently inert, the boom being comprised almost entirely from polyethylene, is generally resistant to damage by marine growth, corrosion, ultra violet radiation, sun exposure, and weathering;

(viii) Since the containment skirt which forms a major part of the boom is substantially flat, it can be readily cleaned by wiping from a nearby boat;

(ix) The containment boom is essentially formed by welding together various components made almost wholly of polyethylene to form a one-piece skirt structure which may be readily transported and assembled as required on site; and

(x) It is manufactured of relatively inexpensive and lightweight materials and can quickly and easily be deployed.

It will be readily apparent to persons skilled in the relevant arts that various modifications and improvements may be made to the foregoing embodiments, in addition to. those already described, without departing from the basic inventive concepts of the present invention. For example, in the illustrated embodiment the straight sections of the skirt, where the floats are attached, are longer than the flexing sections between the floats. However, in another embodiment it may be preferable to make the flexing sections longer than the straight sections, to further enhance the flexibility of the boom in a vertical direction. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described.