GB2148803A - Marine antifouling - Google Patents

Abstract

A marine antifouling material comprises elongate copper or copper alloy members, such as wire or strip, partially embedded in the surface of a water-insoluble substance, the members being spaced by no more than about 7 mm and at least 13% of the area of the said surface of the material being copper of copper alloy. The material can be formed in situ on a marine structure (including a ship) or pre-formed as panels and the like. Sub-sea markers can be made from the material.

Description

SPECIFICATION Marine antifouling This invention is concerned with methods and materials for reducing the fouling by marine organisms of marine structures (including vessels).

It is well known that structures which are submerged or otherwise in contact with sea water become fouled over a period of time by the attach mentthereto of various marine organisms such as barnacles. The hulls of ships suffer in this way as do off-shore oil and gas rigs, and submerged pipelines.

Power station water intakes can also be affected. The presence of the marine organisms does not normally cause any deterioration in the structure itself, but it does affect the structure in other ways. For example, fouling of ships' hulls increases the hull weight and increases the frictional resistance to motion through the water. Fouling of oil-rigs increase the platform weight and the drag imposed on it by waves. Also, it makes visual inspection of the structure (for safety purposes) much more difficult.

Various attempts have been made to reduce marine fouling. The earliest proposal, made in relation to ships' hulls, was to clad the hulls with sheet copper. Copper ions are toxic to many of the marine organisms responsible for fouling. Over-all copper cladding is very expensive and, indeed, difficu It to accomplish on steel structures where the copper must be insulated from the steel to prevent galvanic action. Another approach has been to paint structures with a copper-containing antifouling paint. The disadvantages of this are that painting cannot be effectively carried out on submerged structures and the effective life of the paint is usually not much more than about six months.

In our U.K. patent no. 1604062, we have described and claimed an antifouling material comprising a layer of carrier material and a mesh of copper or copper alloy embedded in the carrier material, the mesh being exposed at the outer surface of the layer so as to be accessible to sea water to retard or prevent marine growth thereon. Reference should be made to U.K. specification no. 1604062 for further details. This antifouling material can be formed in situ on a ship's hull, for example, or can be made in the form of panels which are subsequently applied to the hull.

Other similar types of antifouling material are described in our copending U.K. patent application no. 8324439.

Accoiding to one aspect of the present invention, we have now devised another form of antifouling material. This material comprises a layer of carrier material and, partially embedded in a surface thereof, at least one group of elongate copper or copper alloy (e.g. cupro-nickel) members extending substantially parallel in said group and being spaced by no more than about 7 mm., the percentage of the whole said surface area which is copper being at least 13%, and preferably greater than 20%.

The elongate copper members are preferably wires laid up in parallel on the carrier layer. The number of wires will depend on the thickness thereof. For the commonest wire gauges, i.e. 0.1 to 2.0 mm, there will usually be from 5 to 40 wires per linear cm. In all cases, the spacing between adjacent wires must not exceed about 7 mm and the overall percentage copper exposure must be at least 13%.

Whilst the use of wires is preferred, other elongate members may be used such as, for example, copper strip which may if desired be undercut or punched to provide areas for keying to the underlying carrier material. The width of the strips will not normally exceed about 1 cm.

There may be one group only, or two or more groups, of elongate members, the members of each different group generally extending in different directions. If one group crosses another, it will generally not be bonded thereto or interwoven.

It is not essential to have any gap between adjacent elongate members but, in practice, it is wasteful of copper not to have a gap since antifouling can be effectively achieved without covering the whole surface with copper.

The carrier layer is preferably of a plastics material, for example a thermoplastics polymer, such as polypropylene, or a curable polymer such as polyester or epoxy resin. The carrier layer may include reinforcement such as glass fibre, e.g. in the form of a mat or as random choppings or rovings. Alternatively, the carrier layer can be a rubber or rubbery material, the wires being bonded thereto by adhesive if necessary or by curing the rubber if appropriate.

The antifouling material of the present invention may be made, for example, by laying the elongate members on the carrier material and bonding them thereto. In the case of curable carrier materials, the bonding may be effected by curing. In other cases, an adhesive such as epoxy resin or the like may be used.

In our copending application no. 8324439 (specification no. 2126959A) we have described the use of the antifouling materials thereof for making sub-sea identification markers. The materials of the present invention can also be so used, for example by including colouring pigments in the carrier material.

Various arrangements are possible. For example: i) two sheets of antifouling material are made, the respective carrier materials being of contrasting colours. An alphanumeric cut from one sheet may then be adhered to the other sheet.

ii) a layer of carrier material can be formed of two contrasting colours to depict the alphanumeric, and then the elongate copper members laid up thereon.

In this case there must be a spacing between the elongate members so that the underlying alphanumeric is visible.

iii) a marker can be made from sheet copper and a material of the invention in which the carrier layer is of contrasting colour to the sheet copper. An alphanumeric of the sheet copper is then adhered to the material of the invention, or vice versa.

Reference should be made to our said copending U.K. patent application no. 8324439 for further details.

The antifouling material of the present invention may be used on any structures which are subject to marine fouling. It may be formed in situ on the structure itself, or it may be preformed as panels, preferably flexible panels, which are then fixed to the structure concerned.

In accordance with a further aspect of the present invention, we have found that it is possible in a simple and economic manner to provide an antifouling surface on elongate members such as tubes, e.g.

the structural components of offshore platforms. In one arrangement of the invention, one or more elongate pieces of copper, e.g. copper wire, are wound or wrapped around the tubular member.

Adjacent copper pieces or wires can touch or can be spaced by up to about 7 mm, provided that at least 13%, and preferably at least 20%, of the surface comprises exposed copper. In the case of copper wire, the wire will normally be a continuous winding, i.e. the wire is helically wrapped, adjacent wires being substantially "parallel".

In the case of plastic or other non-metal tubes or the like, the copper can be wrapped or wound thereon to lie directly in contact with the surface of the tube. An adhesive can be provided, if desired, to bond the wire to the surface. In another arrangement, a layer of carrier material (as previously described) may be laid on the surface and then the copper applied thereto. This will then constitute an antifouling material of the invention.

When the elongate member is made of, or coated with, metal or some other electrically conducting material, the copper must be insulated therefrom since otherwise galvanic action may occur preventing the release of copper ions. This insulation may be in the form of the carrier material previously described. One preferred form of insulation is rubber or a rubber-like material. The copper may be adhered thereto by any suitable adhesive.

The copper piece(s), e.g. thin strip or wire, may be laid on the elongate member so that some overlapping occurs. For example, copper wire may be wound as both right and left helices. One especially advantageous arrangement is to use braided wire which is itself tubular and into which the elongate member is threaded. The braided wire tube may be adhered to the tubular member if necessary. If desired, a layer of carrier material may be provided between the braid tube and the elongate member surface.

A tube of braided copper wire cannot of course be threaded on to, for example, the leg of an offshore platform. However, the braided tube can first be adhered around a cylinder of carrier material (such as rubber), and then the composite cylinder cut longitudinally to allow it to be fitted around the platform leg.

Another method of applying antifouling material to a platform leg or the like comprises winding, in helical fashion, lengths of antifouling material around the leg. The material may be a material of the present invention, or one described in our copending U.K. patent application no. 8324439. For example, strips of the material from about 7 to 15 cm.

wide are wound around the leg and secured thereto.

The securement may be effected in any convenient manner, e.g. by adhesive, or by having an uncured rubber or other material on the leg, which is then vulcanised or cured.

In order that the invention may be more fully understood, reference is made to the accompanying drawings, wherein: Figure lisa plan view of a first form of antifouling material of the invention.

Figure 2 is an end view, on an enlarged scale, of the material of Figure 1; Figure 3 is a side elevation of a cylinder made of a second form of antifouling material of the invention; Figure 4 is a plan view of a third form of antifouling material of the invention; Figure 5illustrates the steps in applying an antifouling coating to a tubular member; and Figure 6 illustrates an antifouling surface of braided wire.

Referring to the drawings, Figures 1 and 2 show a layer of carrier material 1, such as epoxy resin, having a multiplicity of fine copper or copper alloy wires 2 laid into the surface thereof. In Figure 1,two areas (3, 4) of the carrier material are differently coloured from the remainder and show up as the alphanumeric "AB". Thus, a panel in the form of Figure 1 can be used as a subsea marker.

The wires need not be laid longitudinally of the carrier material but can extend in any chosen direction. A first layer of wires (5) may be overlaid by a second layer of wires (6)-see Figure4-toform a mesh pattern. The copper wire is not a unitary mesh since it is not bonded or woven.

In Figure 3, thin strips 7 of copper are wrapped around a cylindrical carrier material 8, the spacings 9 between adjacent strips being no more than about 7mm.

Figure 5 shows the steps involved in one method of applying an antifouling material to a tubular elongate member in accordance with the invention.

As can be seen, the outer surface of the elongate member is first cleaned and roughened by, for example, grit blasting (step A). There is then applied (step B) a layer of uncured neoprene (20), over which is applied (step C) a tape (21) made of an antifouling material of this invention or as described in our copending U.K. patent application no. 8324439. After application of the tape, the assembly is heated (step D) to cure the neoprene to form the finished product (step E).

Figure 6 illustrates a tubular member 20 over which has been slid a braided copper wire tube 21.

Claims (29)

1. A marine antifouling material which comprises a layer of water-insoluble carrier material and, partially embedded in a surface thereof, at least one group of elongate copper or copper alloy members each extending substantially parallel in said groove and being spaced by no more than about 7 mm, at least 13% of the area of said surface being said copper or copper alloy.

2. A material according to claim 1 wherein at least 20% of the area of said surface is said copper or copper alloy.

3. A material according to claim 1 or 2, wherein said elongate members are or include wires.

4. A material according to claim 3 wherein the wires are of a gauge of from 0.1 to 2.0 mm.

5. A material according to claim 1 or 2, wherein said elongate members are or include strip.

6. A material according to claim 5 wherein the strip is not more than 1 cm. wide.

7. A material according to any preceding claim wherein the carrier material is a thermoplastic polymer, or a curable polymer.

8. A material according to any of claims 1 to 6, wherein the carrier material is of a rubber or of another elastomeric material.

9. A marine identification marker for attachment to a submerged or submersible structure to provide an identification memberthereon,which marker comprises a unitary support having a display surface, the display surface including an alphanumeric portion of contrasting colour to that of the remainder of said display surface, and wherein eitherthe said alphanumeric portion or the said remainder, or both, are formed from an antifouling material as claimed in any of claims 1 to 8, the said water-insoluble carrier of which includes a colouring pigment dispersed therein; and wherein any part of the display surface not so formed includes exposed metallic copper or copper alloy distributed therein so as to prevent marine fouling of said part of said surface.

10. A marker according to claim 9, wherein said unitary support comprises a self-supporting body of antifouling material as claimed in any of claims 1 to 8, and wherein said alphanumeric portion is fixed to said display surface and is also formed of an antifouling material as claimed in any of claims 1 to 8, but of contrasting colour to that of the support.

11. A marker according to claim 9, wherein said support is formed of an antifouling material as claimed in any of claims 1 to 8, and wherein the alphanumeric portion is made of copper or copper alloy and is fixed to the surface of the support, the support being of a contrasting colour to that of the alphanumeric portion.

12. A marker according to claim 9, wherein the support is a layer of copper or copper alloy and the alphanumeric portion is of an antifouling material as claimed in any of claims 1 to 8, said carrier including a pigment to contrast in colour with the copper.

13. A marker according to any of claims 9 to 12, wherein the alphanumeric portion is surrounded by a border of said display surface extending to at least half the maximum dimension of the components of the alphanumeric.

14. A marker according to any of claims 9 to 13, which also has an antifouling rear surface.

15. A material according to any of claims 1 to 8, which is in the form of a panel.

16. A marine structure comprising a surface exposable to a marine environment, said surface comprising an antifouling material as claimed in any of claims 1 to 8.

17. A method of providing a marine antifouling surface on an elongate member, which comprises providing around the member one or more lengths of copper or copper alloy, said lengths being separated by no more than about 7 mm and whereby at least 13% of the surface comprises exposed copper, and wherein the said copper or copper alloy is not in contact with any other metal to avoid galvanic action.

18. A method according to claim 17, wherein copper wire is wound around the elongate member.

19. A method according to claim 18, wherein the wire is helically wound.

20. A method according to claim 17, wherein braided copper or copper alloy wire is used.

21. A method according to claim 20, wherein the braided wire is first secured to a tube of inert carrier material to form a composite tube, and then the composite tube is provided around the elongate member.

22. A method according to claim 21, wherein the composite tube is cut longitudinally into two or more pieces which are then fitted around the elongate member.

23. A method according to claim 17,18, or 20, wherein the elongate member has a non-metal surface and the copper or copper alloy is directly on said surface, with or without adhesive.

24. A method according to claim 17, 18, 19 or 20, wherein the copper or copper alloy is wound or wrapped on a layer of water-insoluble carrier material on the said member.

25. A method according to claim 21,22 or 24, wherein the material is a thermoplastic or cured polymeric material.

26. A method according to claim 25 wherein the material is of rubber or rubber-like material.

27. A method of providing a marine antifouling surface on an elongate member which comprises securing to said member one or more lengths of antifouling material, the material being as defined in our U.K. patent specification no. 2126959 or as claimed in any of claims 1 to 8 hereof, the copper or copper alloy being kept insulated from other metals.

28. An antifouling material substantially as herein described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 6, of the accompanying drawings.

29. A method of providing a marine antifouling surface on an elongate member substantially as herein described with reference to Figure 5 of the accompanying drawings.