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Title:
A METHOD OF PREVENTING ADHERENCE AND GROWTH OF ORGANIC OBJECTS ON A BODY IN AQUATIC ENVIRONMENTS
Document Type and Number:
WIPO Patent Application WO/2000/028111
Kind Code:
A1
Abstract:
The invention relates to: A method for the hindrance of adherence and growth of living marine organic items (1) on a surface (5) of an object (2) by means of a magnetic flux (3), said surface (5) being exposed to a marine environment (7). The object of the present invention is to provide a method to achieve an anti-fouling effect on an object exposed to a marine environment, which method is flexible in use in that it may be customized to different requirements as regards placement of the sources and the distribution and the density of the magnetic flux. It is a further object of the invention to provide a method that does not require the exposed object to be treated in a magnetic field. The objects are achieved in that the magnetic flux (3) is created by one or more macroscopic discrete sources (6) carried by the object (2). The invention may be used in relation to the protection of the hull of a ship, oil-drilling rigs, oil-producing platforms, or power plants, tubes or pipes, cooling water systems, aquaria, fish tanks, other tanks, or any other submerged objects subject to adherence of living marine creatures or plants.

Inventors:
JENSEN LASSE FINN (DK)
STOLTZE SVEND TOMMAS WESS (DK)
Application Number:
PCT/DK1999/000602
Publication Date:
May 18, 2000
Filing Date:
November 05, 1999
Export Citation:
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Assignee:
MALATO APS (DK)
JENSEN LASSE FINN (DK)
STOLTZE SVEND TOMMAS WESS (DK)
International Classes:
B63B59/04; C02F1/48; E02B17/00; F16L58/00; (IPC1-7): C23F15/00; B63B59/04; F16L58/00
Foreign References:
US5116655A1992-05-26
US5683586A1997-11-04
US5227683A1993-07-13
JPH11291980A1999-10-26
GB2148803A1985-06-05
US4869016A1989-09-26
Other References:
PATENT ABSTRACTS OF JAPAN vol. 018, no. 669 (M - 1725) 16 December 1994 (1994-12-16)
DATABASE WPI Section PQ Week 200002, Derwent World Patents Index; Class P43, AN 2000-018151, XP002900880
DATABASE WPI Section Ch Week 199124, Derwent World Patents Index; Class A82, AN 1991-174964, XP002900879
Attorney, Agent or Firm:
Hofman-bang, A/s (Hans Bekkevolds Allé 7 Hellerup, DK)
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Claims:
Claims:
1. A method for the hindrance of adherence and growth of living marine organic items (1) on a surface (5) of an object (2) by means of a magnetic flux (3), said surface (5) being exposed to a marine environment (7), c h a r a c t e r i z e d in that the magnetic flux (3) is created by one or more macroscopic discrete sources (6) carried by the object (2).
2. A method according to claim 1, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are permanent magnets (21).
3. A method according to claim 1, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are current carrying electrical conductors (22).
4. A method according to claim 1, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) constitute a mixture of permanent magnets (21) and current carrying electrical conductors (22).
5. A method according to any one of claims 34, c h a r a c t e r i z e d in that the current (23) is a DC current.
6. A method according to any one of claims 35, c h a r a c t e r i z e d in that the current (23) has an AC component.
7. A method according to any one of claims 16, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are placed in a repetitive pattern (31,32; 34,35; 37,38).
8. A method according to any one of claims 17, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are placed on the surface (5) of the object (2) being exposed to a marine environment (7).
9. A method according to claim 8, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are placed in a recess (8) in the surface (5) to ensure that the surface is relatively plane.
10. A method according to any one of claims 17, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are placed behind a surface (5) of the object (2) being exposed to a marine environment (7).
11. A method according to claim 10, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are embedded in the material (9; 10) below the surface (5) of the object (2) being exposed to a marine environment (7).
12. A method according to claim 10, c h a r a c t e r i z e d in that the object (2) has an exposed side (5) and a corresponding nonexposed side (4), and the sources (6) of the magnetic flux (3) are placed on the nonexposed side (4).
13. A method according to any one of claims 812, c h a r a c t e r i z e d in that the object (2) being exposed to a marine environment (59; 79) is the hull of a ship (50; 70).
14. A method according to any one of claims 812, c h a r a c t e r i z e d in that the object (2) being exposed to a marine environment (7) is a tube or pipe (60).
15. A method according to any one of claims 814, c h a r a c t e r i z e d in that the material constituting the surface (5) of the object (2) being exposed to a marine environment (7) is a magnetic material.
16. A method according to any one of claims 814, c h a r a c t e r i z e d in that the material constituting the surface (5) of the object (2) being exposed to a marine environment (7) is fibre glass.
17. A method according to any one of claims 8 and 9, c h a r a c t e r i z e d in that the object (2) being exposed to a marine environment (79) is the hull of a ship (70), the material constituting the surface (75) of the object being exposed is iron, and the sources (6) of the magnetic flux (3) are current carrying electrical conductors (71,72,73,74).
18. A method according to any one of claims 8 and 9, c h a r a c t e r i z e d in that the object (2) being exposed to a marine environment (7) is a tube or pipe (60), and the sources (6) of the magnetic flux (3) are current carrying electrical conductors.
19. A method according to claim 10, c h a r a c t e r i z e d in that the sources (6) of the magnetic flux (3) are located in a common carrier medium (40; 401; 81).
20. A method according to claim 19, c h a r a c t e r i z e d in that said common carrier medium (40; 401; 81) is laid out in modules (41,42,43,44; 45,46,47,48; 80) that may conveniently be joined to cover a larger area.
21. A method according to any one of claims 1920, c h a r a c t e r i z e d in that the common carrier medium is fibre glass (81).
22. A method according to any one of claims 1921, c h a r a c t e r i z e d in that the object (2) being exposed to a marine environment (79) is the hull of a ship (70), the material constituting the surface (75) of the object being exposed is fibre glass (80), and the sources (6) of the magnetic flux (3) are current carrying electrical conductors (82) embedded in the fibre glass (81).
23. A method according to claim 6, c h a r a c t e r i z e d in that an AC component of the current (23) is used to loosen adhered living marine organic items (1) from the surface (5) of the object (2) being exposed to a marine environment (7).
Description:
A method of preventing adherence and growth of organic objects on a body in aquatic environments The present invention relates to the prevention of adherence and growth of organic objects on a body in an aquatic environment, such as e. g. the adherence and growth of shellfish, algae, etc. on the hull of a ship, e. g. a yacht, the legs of an oil-drilling rig, etc.

The invention relates specifically to: A method for the hindrance of adherence and growth of living marine organic items on a surface of an object by means of a magnetic flux, said surface being exposed to a marine environment.

The adherence of shellfish, algae, etc. to the hull of ships causes extra friction during sailing, resulting in an increase in the amount of energy needed to maintain a given speed. The consequence is of course an additional expense or, alternatively, a decrease in speed. The layers of organic material must be removed every now and then either by frogmen or by taking the ship ashore. In both cases at a cost.

To prevent adherence, special paints applied to the part of the outer surface of the hull of the ship that is submerged in water have been used. This has the disadvantage of necessitating a treatment ashore, which is costly and time consuming. A further disadvantage is the necessary maintenance in that the treatment has to be repeated at certain intervals. A still further disadvantage is the pollution of the environment (the waters and their living creatures) due to the wear of the paints.

The laid open patent application JP-A-3-106487 describes a method of preventing fouling and growth of seashells, algae, etc. on submerged structures. The method is based on the experience that the adherence and growth is impeded by the presence of a magnetic flux. The structure in question is provided with a layer of magnetic powder on its outer surface. Compared to other paints'it has the potential of being less poisonous. Otherwise it has the same disadvantages of requiring treatment ashore, regular maintenance due to wear, and in addition the object needs to be treated in a magnetic field to introduce a preferred direction for the individual grains of the magnetic powder.

The object of the present invention is to provide a method to achieve an anti-fouling effect on an object exposed to a marine environment, which method is flexible in use in that it may be customized to different requirements as regards placement of the sources and the distribution and the density of the magnetic flux. It is a further object of the invention to provide a method that does not require the exposed object to be treated in a magnetic field.

In the present context, the term exposed object'or exposed surface'is taken to mean those parts of an object or those parts of a surface of an object that are in direct contact with the marine environment.

This is achieved according to the invention, as disclosed in claim 1, in that the magnetic flux is created by one or more macroscopic discrete sources carried by the object In the present context, the term macroscopic'in connection with the sources of magnetic flux is taken to

mean that the dimensions involved are in the mm range and upwards (1 mm = 10-3 meter).

In the present context, the term discrete'in connection with the macroscopic sources of magnetic flux is taken to mean that the sources may be regarded as individual devices rather than a continuum of randomly scattered objects.

In the present context, the term carried by the object' in connection with the sources of magnetic flux is taken to mean that the sources are placed on a surface of the the object, or in its interior, e. g. embedded in the material constituting the object or on or in a wall of the object.

When, as disclosed in claim 2, the sources of the magnetic flux are permanent magnets, it is ensured that a convenient and flexible means for creating a magnetic flux of suitable density is provided. The permanent magnets may be chosen from a large range of materials according to the necessary field strengths, the construction materials of the object and to cost constraints.

When, as disclosed in claim 3, the sources of the magnetic flux are current carrying electrical conductors, it is ensured that the magnetic flux density may be easily adjusted to the needs, and that the magnetic flux may be conveniently provided with an AC component.

When, as disclosed in claim 4, the sources of the magnetic flux constitute a mixture of permanent magnets and current carrying electrical conductors, it is ensured that maximum flexibility in design and performance is achieved.

When, as disclosed in claim 5, the current is a DC current, it is ensured that a static magnetic flux of varying density may be created. The possible range of flux densities will be dependent on the actual construction of the current carrying conductors, including their possible cores of flux-guiding material.

When, as disclosed in claim 6, the current has an AC component, it is ensured that the magnetic flux has an alternating component (optionally superposed on a DC component), which may be important for the disturbance' of some organic objects, and which is otherwise not easily generated.

When, as disclosed in claim 7, the sources of the magnetic flux are placed in a repetitive pattern, it is ensured that a relatively homogeneous magnetic flux density over a certain area may be created, and that a basis for mass production is provided. If the repetitive pattern is hexagonal, it is ensured that a particularly homogeneous magnetic flux density may be created.

When, as disclosed in claim 8, the sources of the magnetic flux are placed on the surface of the object being exposed to a marine environment, it is ensured that sources of the magnetic flux and the surface to be protected against fouling are in the closest possible proximity so that a maximum flux density for a given configuration of sources of magnetic flux may be achieved, because any unwanted redistribution or shielding of the magnetic flux due to intervening material between the sources and the surface to be protected may be avoided.

When, as disclosed in claim 9, the sources of the magnetic flux are placed in a recess in the surface to ensure that the surface is relatively plane, it is ensured that sources of the magnetic flux are protected against wear and mechanical damage and that the surface is less irregular and therefore presents less resistance to motion (compared to a situation where the sources are placed directly on the surface).

When, as disclosed in claim 10, the sources of the magnetic flux are placed behind a surface of the object being exposed to a marine environment, it is ensured that practically no maintenance is required, since the sources are less exposed. Further, no pollution of the marine environment due to wear is created.

In the present context'behind a surface being exposed to a marine environment'is taken to mean a) fully enclosed by the material constituting the surface of the object being exposed, or b) on the surface opposite the exposed one (e. g. the non-exposed side of a wall of the object), the latter meaning being only relevant if the object is not all solid (such as e. g. the hull of a ship, a pipe or tube, etc.).

When, as disclosed in claim 11, the sources of the magnetic flux are embedded in the material below the surface of the object being exposed to a marine environment, it is ensured that special design advantages may be obtained, e. g. that the sources of the magnetic flux, when built into the construction material of the object in question, may fulfil the combined purpose of being the source of the magnetic flux and at the same time of contributing to the mechanical stability of the resulting material.

When, as disclosed in claim 12, the object has an exposed side and a corresponding non-exposed side, and the sources of the magnetic flux are placed on the non- exposed side, it is ensured that the sources of the magnetic flux are not exposed to the rough conditions present in a marine environment and thus not subject to wear. This yields the combined benefits of less pollution of the marine environment and less maintenance (resulting in lower cost). Further, in some cases the method may be exercised without taking the object ashore (e. g. when the object is a ship). The term corresponding'in connection with an exposed side and a non-exposed side is in the present context taken to mean the side lying opposite to the side in question, both sides being part of the same functional object, such as e. g. the two sides constituting the two surfaces of a plane-wall.

In a preferred embodiment of the invention, as disclosed in claim 13, the object being exposed to a marine environment is the hull of a ship.

In a preferred embodiment of the invention, as disclosed in claim 14, the object being exposed to a marine environment is a tube or pipe. When the object is a tube or pipe, the surface being exposed to the marine environment may be the interior as well as the exterior side. The anti-fouling effect on the interior side is desirable, when the fluid flowing in the tube or pipe contains organic objects. The anti-fouling effect on the exterior side is desirable, when the tube or pipe in question is submerged in a marine environment (such as e. g. the legs or the cross bars connecting the legs of an oil rig, etc.).

In a preferred embodiment of the invention, as disclosed in claim 15, the material constituting the surface of the

object being exposed to a marine environment is a magnetic material. In this context the term a magnetic material'is taken to mean a material which, at the atomic level, possesses magnetic moments that (below a certain critical temperature) interact strongly to show a magnetic moment even in the absence of an external magnetic field. In terms of the present invention a typical magnetic material would be iron. In this context the term iron'is taken to mean iron in its various forms (including steel) when used as a construction material for ships, tubes or pipes or other objects exposed to a marine environment.

In a preferred embodiment of the invention, as disclosed in claim 16, the material constituting the surface of the object being exposed to a marine environment is fibre glass. Fibre glass is extensively used as a construction material for yachts and smaller boats.

In a preferred embodiment of the invention, as disclosed in claim 17, the object being exposed to a marine environment is the hull of a ship, the material constituting the surface of the object being exposed is iron, and the sources of the magnetic flux are current carrying electrical conductors.

In a preferred embodiment of the invention, as disclosed in claim 18, the object being exposed to a marine environment is a tube or pipe, and the sources of the magnetic flux are current carrying electrical conductors.

When, as disclosed in claim 19, the sources of the magnetic flux are located in a common carrier medium, it is ensured that a simple means for covering an area with a relatively homogeneous flux density is provided.

When, as disclosed in claim 20, said common carrier medium is laid out in modules that may conveniently be joined to cover a larger area, it is ensured that a flexible and convenient means of covering larger areas of an object and thus a basis for mass production are provided.

When, as disclosed in claim 21, the common carrier medium is fibre glass, the sources of the magnetic flux are integrated into the fibre glass, thus making the anti- fouling effect an inherent'property of the construction material.

When, as disclosed in claim 22, the object being exposed to a marine environment is the hull of a ship, the material constituting the surface of the object being exposed is fibre glass, and the sources of the magnetic flux are current carrying electrical conductors embedded in the fibre glass, it is ensured that the combined benefits of designed-in mechanical reinforcement and flexible anti-fouling effect (the magnetic flux density may be changed by changing the electrical current level (and/or amplitude in case of a present AC component)) are achieved.

In a preferred embodiment of the invention, as disclosed in claim 23, an AC component of the current is used to loosen adhered living marine organic items from the surface of the object being exposed to a marine environment.

The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings, in which:

fig. 1 shows an object that is partly submerged where certain areas of the object are provided with a magnetic flux according to the invention, fig. 2 shows various ways of placing the sources of the magnetic flux on or in the object according to the invention, fig. 3 shows sources of the magnetic flux according to the invention, fig. 4 shows some possible configurations of the sources of the magnetic flux according to the invention, fig. 5 shows a schematic illustration of a fibre glass plate provided with electric wires for the generation of a magnetic flux according to the invention, fig. 6 shows an example of a modularly structured carrier containing a repetitive pattern of sources of the magnetic flux according to the invention, fig. 7 shows a vessel whose interior side, below sea level, is provided with modularly structured carriers, each containing a repetitive pattern of sources of the magnetic flux according to the invention, fig. 8 shows a schematic perspective illustration of a pipe or tube provided with an outer current carrying electrical conductor for the generation of a magnetic flux according to the invention, fig. 9 shows a schematic top-view'illustration of a pipe or tube provided with an outer current carrying electrical conductor for the generation of a magnetic flux according to the invention, and

fig. 10 shows a vessel whose exterior side, below sea level, is provided with current carrying electric wires in a repetitive pattern for the generation of a magnetic flux, according to the invention.

Fig. 1 shows an object that is partly submerged where certain areas of the object are provided with a magnetic flux according to the invention.

The submerged object 2, e. g. the hull of a ship, is fouled with seashells, algae, etc. 1 over certain areas of its exterior side 5, below sea level 7. On the interior side 4 of the hull, sources 6 of magnetic flux are positioned to cover different areas in order to provide a magnetic flux 3 on the corresponding external area. The areas of the exterior side 5 around the sources 6 of magnetic flux 3 show a markedly less fouling.

Fig. 2 shows various ways of placing the sources of the magnetic flux on or in the object according to the invention.

In a special embodiment of the invention, as illustrated in fig. 2. a, the sources 6 of the magnetic flux are placed on the exterior, exposed side 5 of the object 2.

In another special embodiment of the invention, as illustrated in fig. 2. b, the sources 6 of the magnetic flux are placed in recesses 8 in the exterior, exposed side 5 of the object 2.

In another special embodiment of the invention, as illustrated in fig. 2. c, the sources 6 of the magnetic

flux are embedded in the material 10 below the surface of the exterior, exposed side 5 of the object 2.

In another special embodiment of the invention, as illustrated in fig. 2. d, the sources 6 of the magnetic flux are placed on the interior side 4 of the object 2, opposite the surface of the exterior side 5 being exposed to a marine environment 7.

In yet another special embodiment of the invention, as illustrated in fig. 2. e, the sources 6 of the magnetic flux are placed in the material 9 constituting the wall between the interior side 4 of the object 2 and the exterior side 5 being exposed to a marine environment 7.

In the embodiments illustrated in figs. 2. a-2. e, the objects 2 are all shown with a part above and a part below sea level. The object 2 may be fully below see level as well, i. e. be fully exposed to a marine environment 7.

Fig. 3 shows sources of the magnetic flux according to the invention. As shown in figs. 3. a and 3. b, the sources (6 in figs. 1,2) of the magnetic flux 3 may be either permanent magnets 21 or current carrying electrical conductors 22 (the latter optionally with a core of a magnetic flux-guiding medium, such as e. g. iron). Fig.

3. a. shows an example of a permanent magnet 21 and (schematically) its corresponding magnetic flux. Fig. 3. b shows a current carrying electrical conductor in the form of a coil 22. The current 23 in the conductor, provided by a current generator 24, may be either static (DC) or alternating (AC) or a combination hereof. The sources 6 of magnetic flux 3, i. e. the permanent magnets 21 and the current carrying electrical conductors 22 may be used either separately (i. e. solely permanent magnets or

solely current carrying electrical conductors) or in combination.

The necessary density of the magnetic flux (also termed the magnetic induction) to prevent adherence will depend on the construction materials of the object 2 in question and on the types of relevant sea creatures and plants 1 to which the object is exposed, etc. An initial application of a particularly strong, perhaps alternating, flux may optionally be used in order to remove or loosen organic objects already adhered to the body.

By locating the sources 6 of the magnetic flux 3 in a suitable repetitive pattern, a relatively homogeneous magnetic flux density is obtained.

Fig. 4 shows some possible configurations of the sources of the magnetic flux according to the invention.

Fig 4. a shows a repetitive pattern of the sources of the magnetic flux, where the basic repetitive cell' consisting of the 4 sources spanned by the vectors 31 and 32, as indicated by the arrows and the dotted lines, is a square providing a square lattice, cf. the square denoted by 33. In fig. 4. b, the sources of the magnetic flux form a centered rectangular lattice (cf. the rectangle denoted by 36) with a basic repetitive cell'consisting of the 4 sources spanned by the vectors 34 and 35. In fig. 4. c, the sources of the magnetic flux form a hexagonal lattice (cf. the hexagon denoted by 39) with a basic repetitive cell'consisting of the 4 sources spanned by the vectors 37 and 38. Using the hexagonal lattice configuration a particularly homogeneous magnetic flux density may be obtained.

A particularly useful embodiment of the invention is shown in fig. 5. Fig. 5 shows a schematic illustration of a fibre glass plate provided with electrical wires for the generation of a magnetic flux according to the invention. Fibre glass is a commonly used construction material for yachts and smaller boats. The physical nature of the fibre glass 81 makes it well suited for embedding electrical wires 82 inside, either as modular plates 80 to be joined for covering a larger area or formed around a skeleton or model of the object, the electrical wires optionally constituting the skeleton.

The fibre glass modules 80 with embedded electrical wires 82 may be joined by conventional techniques. The feeding terminals 84,85 for the electrical current 83 may be joined in parallel or in series or a combination thereof (e. g. some modules coupled in series constituting a group and groups of serially coupled modules coupled in parallel) to achieve a suitable resistive load and current level.

Fig. 6 shows an example of a modularly structured carrier containing a repetitive pattern of sources of the magnetic flux according to the invention Fig. 6. a shows an expedient embodiment of the invention, where a repetitive pattern (in casu the hexagonal, cf. fig. 4. c) of sources of magnetic flux is located in or on a common carrier 40, e. g. a mat or tape of a suitably elastic material, and where the mats are modularly laid out to enable seamless joining of identical units 41,42, 43,44 to cover a larger area. Fig. 6. b shows another expedient embodiment of the invention, where each module 45,46,47,48 consists of a macroscopic magnetic plate 49 of a flexible material mounted on a commen carrier 401, e. g. a tape or the like. Instead of plates, tapes of

a flexible magnetic material could be used and configured in an appropriate pattern. The modules (41,42,43,44), (45,46,47,48) may be conveniently joined using standard joining techniques such as snap fasteners, glue, adhesive tape, click-join'-techniques, etc., or combinations thereof. The fastening of the modules to the relevant parts of the interior side 4 of the hull may be performed using similar techniques. The sources may be permanent magnets (21 in fig. 3. a) or current carrying electrical conductors (22 in fig. 3. b). In the latter case a suitable lattice of conductors for the feeding of current to each individual coil or conductor may be provided as part of the common carrier medium (40,401, 80).

Fig. 7 shows a vessel whose interior-side, below sea level, is provided with modularly structured carriers, each containing a repetitive pattern of sources of the magnetic flux according to the invention. On its interior side (or optionally on selected areas thereof) the vessel 50 is covered with modularly laid out mats 51,52,53, 54,.... containing repetitive patterns of sources of magnetic flux. The standard size mats are customized 56, 57,58,...., when necessary. Fig. 7 is drawn as if the hull of the vessel were transparent to show the placement of the mats on the interior side. The sea level is indicated by 59. A suitably homogeneous magnetic flux density of a certain minimum size is created on the corresponding exterior side (5 in fig. 1) of the vessel to prevent adherence and growth of seashells and algae on the submerged exterior part of the hull.

In a special embodiment, the object exposed to a marine environment is a tube or pipe. Fig. 8 shows a schematic perspective illustration of a pipe or tube 60 provided with an outer current carrying electrical conductor for

the generation of a magnetic flux according to the invention. An electrical conductor 61 for the generation of a magnetic flux on the surface of the tube or pipe may e. g. be configured as shown in fig. 8. If the exposed surface to be protected is the interior of the tube or pipe, the electrical conductor may be conveniently provided on the exterior side, optionally in a recess or optionally embedded in the wall of the tube or pipe.

Similarly, if the exposed surface to be protected is the exterior of the tube or pipe, a configuration with the electrical conductors placed on the exterior surface, optionally in a recess or optionally in the wall of the pipe or tube is convenient. If, however, the material constituting the tube or pipe is magnetic, the electrical conductors should be provided on the exposed side, optionally in a recess to lower the resistance to flow or movement.

An example of an application needing interior protection could be a pipe or tube in which the liquid flowing therethrough contains living organic objects. An example of an application needing exterior protection could be the legs or the cross bars connecting the legs of an oil rig.

In general: If the material constituting the object to be protected conducts electricity (e. g. a metal), the electrical conductors should be insulated.

Fig. 9 shows a schematic top-view'illustration of a pipe or tube 90 provided with an outer current carrying electrical conductor 91 for the generation of a magnetic flux according to the invention. The symbols @ and0 indicate the direction of the magnetic flux following from the direction of the electrical current as shown by the arrows (@ indicating a direction coming out of the

plane and 0 indicating a direction into the plane). The distances between the individual pieces of wire may be adjusted to achieve a suitable flux density. Similarly, the electrical terminals 92,93 may be arranged so that the wires of the individual pieces of tubes or pipes connect electrically when the tubes or pipes are joined together.

Fig. 10 shows a vessel 70 whose exterior side, below sea level, is provided with current carrying electrical wires in a repetitive pattern for the generation of a magnetic flux, according to the invention. The illustration is schematic and indicates that the wires may be modularly arranged 71,72,73,74,..., and current fed from sources 77 on a group by group basis, the current sources being located preferably on the interior side of the hull. The electrical terminations 78 may preferably be located on the exterior side 75 being exposed to a marine environment 79. If convenient, each module may be current fed individually. If appropriate, the fully exposed part of the vessel 70 may be protected with current carrying electrical wires, although only parts of the exposed surface are covered in the illustration. Similarly, the electrical wires may be located on the non-exposed (interior) side of the vessel or embedded in the wall, if appropriate.

In a special embodiment of the invention, the hull of the vessel 70 is made of a ferromagnetic material, e. g. iron, whose atoms interact to provide domains having a resulting magnetic moment below a critical temperature which is higher than the normal temperatures present in marine conditions. The alignment of these magnetic moments perpendicular to the surface would require a very large magnetic flux density to be applied to the hull 70.

The magnetic flux on the exterior may instead be

generated by current carrying electrical conductors, placed on the surface or in a recess therein. A possible configuration of the wires is shown in fig. 10. However, the merits of the invention may be achieved by any configuration creating a magnetic flux of a suitable density at the surface areas that need protection.

In general, the method may be used to protect objects that are fully submerged or to the parts of a given object that is submerged, or it may alternatively be applied to certain chosen parts of the object only (e. g. parts of an oil tanker, the legs of an oil drilling rig, etc.) for which it is especially important to prevent or hamper adherence and growth of organic'layers. It may be further applied to objects that are exposed to a non- aquaous but very humid environment (such as in the tropics) to avoid adherence and growth of e. g. algae or other organic items to the object in question.

Although the invention has mainly been described in relation to the hull of a ship, the method may be used on any other submerged objects such as e. g. oil-drilling rigs, oil-producing platforms, or power plants, tubes or pipes, cooling water systems, aquaria, fish tanks, other tanks, or any other submerged objects subject to adherence of living marine creatures and plants. The method may be used in connection with any material such as wood, iron, steel, concrete, ferroconcrete, plastics materials, fibre glass, etc. independent of their inherent magnetic properties, be it diamagnetic, paramagnetic, ferromagnetic, antiferro-magnetic or more complex forms.