[0001] This invention relates to a longitudinally extensive protection apparatus for a longitudinally extensive service member located in or on an offshore structure, in particular in or on a foundation of an offshore structure. The invention also relates to method of installation of the longitudinally extensive service member in the protective apparatus. The longitudinally extensive service member can be a cable, such as an electricity transmission cable or a fibre optic cable, or a pipe for conveying fluids associated with offshore oil and gas extraction processes.

BACKGROUND

[0002] In a typical conventional arrangement a longitudinally extensive service member which is connected to an offshore structure can extend along the seabed, or can be buried under the seabed. On approach to the offshore structure the longitudinally extensive service member should be directed upwardly away from the seabed to finally reach a desired location on the offshore structure for connection to appropriate equipment located on the offshore structure. The offshore structure can typically include a foundation which can extend from the seabed to a required height above the water surface. Floating foundations are also known, which can have a portion thereof below the water surface and a portion above the water surface. The longitudinally extensive service member can be secured to the foundation on its upwardly directed path from the seabed. In commonly used arrangements, the foundation can be provided with an l-tube or a J-tube (hereinafter l/J-tube) and the longitudinally extensive service member can be routed through the l/J tube. The l/J-tube is fabricated from metal and can provide a rigid enclosure for the longitudinally extensive service member. The l/J-tube can provide support for the longitudinally extensive service member and also protection from damage after installation of the longitudinally extensive service member in the l/J-tube.

[0003] However, the use of an l/J-tube can be disadvantageous. The service life of the l/J-tube can be less than that of the longitudinally extensive service member. Thus the l/J- tube may need to be replaced before the longitudinally extensive service member reached the end of its useful working life and the same can be true of seal assemblies used with the l/J-tube. For example, because of corrosion of the l/J-tube can cause a reduction in its working life.

[0004] In some cases longitudinally extensive service members such as cables that were installed some time previously (for example 25 years ago) may not meet current higher standards and cannot be given a life extension. Therefore it can more cost effective to install another protective apparatus and cable in combination, rather than replacing the existing cable. The two can then, ultimately, be decommissioned together.

[0005] Also, problems can arise in installing the longitudinally extensive service member in the l/J tube in that the minimum bend radius of the longitudinally extensive service member can be exceeded potentially causing serious damage to the longitudinally extensive service member. Typically in this context, the longitudinally extensive service member is paid out from a cable installation vessel and forms a catenary in the water terminating at the entry of mouth at the lower end of the l/J-tube. The rigid mouth of the l/J-tube provides a pinch point for the longitudinally extensive service member and careful control of the cable is required to avoid exceeding the minimum bend radius at this point.

[0006] A further problem can occur in that the foundation of the offshore structure, with the l/J-tube mounted thereon, can be located in its position of use offshore long before the apparatus or equipment which the foundation is to support. Such apparatus can be a wind turbine generator, for example. Thus the l/J-tube can be installed in its position of use for weeks, months or even years before the longitudinally extensive member is finally installed. During this time, the l/J-tube can be damaged because, for example, of the ingress to the interior of the l/J-tube of sea water or foreign material.

[0007] A further problem has been known in which the foundation is driven, at the time of its installation, too deeply into the seabed. Consequently, bell mouths and messenger lines at the lower end of the l/J-tube can be damaged, and insufficient clearance can be provided between the l/J-tube and the seabed. Remedial work, which can involve excavation by ROVs is necessarily expensive.

BRIEF SUM MARY OF THE DISCLOSURE

[0008] In accordance with a first aspect of the present invention there is provided a foundation for an offshore structure including protective apparatus for a longitudinally extensive service member mounted to the foundation, the protective apparatus comprising: a first hollow longitudinally extensive member having a first end located proximate an upper part of the foundation, a second end located at a lower part of the foundation, and an aperture arranged proximate said lower end, and

a second hollow longitudinally extensive member which is transformable from a first condition in which at least a major portion of thereof is disposed within said first hollow longitudinally extensive member to a second condition in which said second hollow longitudinally extensive member extends through said aperture and at least a major portion thereof is disposed externally of the first member,

the first and second hollow longitudinally extensive members being configured to form, when said second hollow longitudinally extensive member is in the second condition, an internal through passage for accommodating said longitudinally extensive service member.

[0009] In some preferred embodiments said longitudinally extensive service member can be selected from one or more cables for transmission of electricity, one or more fibre optic cables and one or more pipes for conveying fluids associated with offshore oil and gas extraction.

[0010] In some preferred embodiments the first hollow longitudinally extensive member can be of substantially rigid pipe or tube construction.

[0011] In particularly preferred embodiments the second hollow longitudinally extensive member can be a flexible polymeric pipe or tube. The second hollow longitudinally extensive member can be formed from a polymeric material selected from high density polyethylene (HDPE), high density polyethylene (HDPE) reinforced with fibres, cross- linked polyethylene (XLPE), polypropylene and polyvinyl chloride or combinations thereof.

[0012] In some preferred embodiments the second hollow longitudinally extensive member can comprise a first portion and a second portion wherein the first portion has a greater axial stiffness and/or bending stiffness than the second portion.

[0013] In some preferred embodiments the flexible polymeric pipe or tube can be a single, unitary component.

[0014] In some preferred embodiments the flexible polymeric pipe or tube can comprise a plurality of telescoping sections.

[0015] In some preferred embodiments, in said first condition, said second hollow longitudinally extensive member can be substantially wholly disposed within said first member.

[0016] In some preferred embodiments said first and second hollow longitudinally extensive members can further comprise cooperating latching arrangements configured to retain the second hollow longitudinally extensive member in the second condition.

[0017] In some preferred embodiments the foundation can further comprise a tubular polymeric liner interposed between the first and second hollow longitudinally extensive members when the second longitudinally extensive member is in its first condition.

[0018] In some preferred embodiments the foundation can be of lattice type construction including at least one supporting leg extending upwardly from the seabed and wherein a said supporting leg forms a first hollow longitudinally extensive member.

[0019] In some preferred embodiments the first hollow longitudinally extensive member can be an l-tube or a J-tube mounted to the foundation. [0020] In some preferred embodiments the foundation can be a gravity foundation including a through bore or passage extending between an upper region and a lower region of the foundation, the first hollow longitudinally extensive member can be disposed in said bore or passage.

[0021] In some preferred embodiments the foundation can be a gravity foundation including a through bore or passage extending between an upper region and a lower region of the foundation wherein the passage forms the first hollow longitudinally extensive member or a portion of the first hollow longitudinally extensive member. In such embodiments, the inner surface walls of the passage effectively define an inner surface of the first hollow longitudinally extensive member. In these embodiments the gravity foundation thus includes the first hollow longitudinally extensive member.

[0022] In some preferred embodiments said second hollow longitudinally extensive member can include a pulling fixture configured for attachment of a pulling line for extending said second hollow longitudinally extensive member through the aperture.

[0023] In some preferred embodiments a messenger line can be disposed within the protective apparatus, a first end of the messenger line being accessible at an upper end portion of the first hollow longitudinally extensive member and a second end of the messenger line being accessible at a lower end portion of the second hollow longitudinally extensive member.

[0024] In some preferred embodiments the second hollow longitudinally extensive member can have a length sufficient such that, when said second hollow longitudinally extensive member is in the second condition a free end thereof can be taken on board a vessel located adjacent the foundation.

[0025] According to a second aspect of the present invention there is provided a method of installing a longitudinally extensive service member in a protective apparatus of a foundation as defined in the first aspect of the invention, the method comprising extending the second hollow longitudinally extensive member of said protective apparatus from its first condition to its second condition and pulling said longitudinally extensive service member through said protective apparatus.

[0026] In some particularly preferred embodiments of the method the second hollow longitudinally extensive member of the protective apparatus can be a flexible polymeric pipe or tube.

[0027] In some preferred embodiments the method can further comprise providing a messenger line disposed within the protective apparatus, a first end of the messenger line being accessible at an upper end portion of the first hollow longitudinally extensive member and a second end of the messenger line being accessible at a lower end portion of the second hollow longitudinally extensive member, attaching said first end of the messenger device to a pulling device and attaching a second end of said messenger line to the longitudinally extensive service member and using said pulling device to pull the longitudinally extensive service member through the protective apparatus.

[0028] In some preferred embodiments the method can include the step, with the second hollow longitudinally extensive member in the second condition, of taking the free end of the second hollow longitudinally extensive member onboard a vessel and pulling the longitudinally extensive service member into the protective apparatus through said free end.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 A is an illustration of a foundation according to the invention applied as a J-tube, with the second hollow longitudinally extensive member in a retracted condition;

Figure 1 B is an illustration of a foundation according to the invention applied as a J-tube, with the second hollow longitudinally extensive member in an extended condition;

Figure 2 is a schematic cross-section of a protective apparatus for a foundation of the invention, showings typical suitable locking or latching device;

Figure 3 is a schematic section through a portion of an apparatus according to embodiments of the invention;

Figure 4 shows a foundation according to embodiments of the invention;

Figure 5 shows schematically a foundation according to another embodiment of the invention;

Figure 6 shows schematically one example of a latching or locking arrangement suitable for use in embodiments of the present invention;

Figure 7A, 7B, 7C and 7D respectively show a first side view, second side view, plan view and a perspective view of a foundation for an offshore structure according to another embodiment of the invention;

Figure 8 is an illustration of a foundation for an offshore structure according to another embodiment of the invention showing a hollow longitudinally extensive member passing therethrough and secured to its exterior; and Figure 9 is an illustration of the second hollow longitudinally extensive member together with a pulling fixture.

DETAILED DESCRIPTION

[0030] Referring initially to Figures 1A and 1 B, a foundation 100 for an offshore structure can be of the "jacket" type comprising a plurality of upright legs 102 and a lattice of connecting spars or braces 104. The foundation 100 can support an l-tube 106 which is attached to the foundation 100 by a plurality of attachment members 108. The l-tube 106 can extend from an upper end 110 located proximate or at an uppermost part of the foundation 100, such as a platform level 100P on from which operators may from time to time work, to a lower end 112 located proximate the foot or lowermost part of the foundation 100, near the seabed 10.

[0031] The foundation 100 can be manufactured or assembled at an on-shore location and transported in assembled state to its offshore location of use. The l-tube 106 can be mounted to the foundation 100 at the time of its on shore manufacture.

[0032] l-tube 106 can typically comprise a generally cylindrical pipe construction, made from a rigid, inflexible material such as a suitable metal. In this respect, the l-tube 106 can be of conventional construction. In embodiments of the invention l-tube 106 can form a first hollow longitudinally extensive member within which a second hollow longitudinally extensive member is disposed.

[0033] l-tube 106 can terminate at its lower end in a mouth or aperture 114. A progressive bend stiffener (also terminating in a mouth or aperture) can extend from the l-tube.

[0034] Within the l-tube 106 can be disposed a second hollow longitudinally extensive member (hereinafter "second member") 116. In some preferred embodiments, second member 116 can be in the form of a longitudinally extensive pipe or tube which is formed from a flexible material. The pipe or tube 116 can in preferred embodiments be generally cylindrical. The flexible material can be selected such that the second member is self supporting and can bend when required. In some preferred embodiments, the flexible material is a polymeric material, in particular high density polyethylene (HDPE), polypropylene or polyvinyl chloride. Polymeric composite materials can also be used such as HDPE reinforced with fibres or thermoset materials such as cross-linked polyethylene (XPLE). In further embodiments the flexible pipe or tube 102 can be formed from two or more of any of the above-noted polymeric materials.

[0035] Second member 116 can adopt a first condition (Figure 1A) in which it is substantially wholly contained within the l-tube 106 and a second condition (Figure 1 B) in which it extends outwardly from the l-tube 106. [0036] In some preferred embodiments, in the first condition, second member 1 16 may be entirely contained within the l-tube 106. In other embodiments, in the first condition a minor portion of second member 116 can extend outwardly through aperture 114.

[0037] The length of the second member 116 can be selected in accordance with use requirements. One limiting factor on the length of the second member 116 can be the length of the l-tube 106. Within this possible constraint the length of the second member 116 can be selected in accordance with the length which it is desired that the second member 1 16 extends away from the foundation 100 in use. In some embodiments the length of the second member 1 16 can be at least 10m. The maximum length may not be constrained, however, in embodiments of the invention wherein the foundation is of lattice type, the maximum length of the second member 1 16 is typically up to 150m.

[0038] Where a desired length of the second member 1 16 in its second, extended, condition, is longer than the length of the first member 106 (or longer than an available portion of the first member 106 in which portion the second member 1 16 is contained in the first condition), the second member 116 can comprise a plurality of telescoping sections, the respective sections being in a retracted ("telescoped") configuration when the second member 1 16 is in its first condition and in relatively extended configuration when the second member 1 16 is in its second condition. In the extended, second condition, the length of the second member can be such as to allow a distal end of the second member to be taken aboard a vessel located near the foundation. A longitudinally extensive service member can be installed from the vessel into the second member via said distal end after said distal end has been taken aboard the vessel.

[0039] The second member 116 can have a lowermost or leading end 1 18. A pulling fixture, attachment or formation can be connected to or formed on or near the leading end 118 by means of which the leading end of the second member 1 16 can be extended from the l-tube, that is, by means of which the second member 116 can be extended from its first condition to its second condition. In a typical arrangement a line or cable can be secured to the pulling fixture and a winch or the like on a surface vessel used to draw in the line or cable and so extend the second member 1 16.

[0040] A suitable pulling fixture 150 is shown in Figure 9. The pulling fixture 150 can comprise a pulling head 152 which includes a pulling eye 153 or functionally equivalent fixture to which a line or cable can be attached. A trailing end portion of the pulling fixture 150 can have attached thereto a further pulling eye 156 or functionally equivalent component that can be connected to a messenger line extending within the interior of the second member 116. In some embodiments the pulling fixture 150 can be welded in position at the leading end 1 18 of the second member 1 16. [0041] In embodiments where the second member 116 is, in its first condition, wholly contained within the l-tube 106, the pulling fixture 150 can be located in a position whereby it is readily accessible from the exterior of the l-tube 106, such that the second member can be extended using the pulling fixture 150. In embodiments where a minor portion of second member 116 can extend outwardly through aperture 114, the pulling fixture 150 can be located externally of the l-tube 106.

[0042] The second member 116 can have trailing end 120 which is disposed within the first hollow longitudinally extensive member (hereinafter "first member"), which in Figures 1A and 1 B is the l-tube 106. As the second member 116 is extended from its first condition towards its second condition, the trailing end 120 moves with respect to the first member 106 towards the aperture 114.

[0043] In some preferred embodiments the first member (l-tube) 106 and the second member 1 16 can be provided with cooperating locking or latching devices which can serve to limit the extent of extension of the second member 116 from the first member 106 (I- tube), for example such that the trailing end 120 of the second member is prevented from passing through the aperture 1 14, so that the first and second hollow longitudinally extensive members cannot become separated.

[0044] In some preferred embodiments, cooperating locking or latching devices of the first and second members 106, 1 16 can prevent movement of the second member 1 16 from the second condition to the first condition. In particular, when the second member 116 has achieved a desired extension from the first member 106, so that the second member 1 16 is in its use condition, the locking or latching devices can prevent any return of the second member into the first member 106.

[0045] Figure 6 shows schematically one example of a locking or latching arrangement. In the illustrated embodiment, the locking or latching arrangement can include latching or locking formations 134, 136 which can be formed on an inner side of first member 106. Formations 134, 136 can be cam or wedge shaped having a tapered or inclined surface which extends inwardly (towards the longitudinal axis of first member 106) from the inner side of first member 106. Inclined surfaces meet a radial surface which extends to inner side wall of first member 106. An annular groove 140 is defined between opposed radial surfaces of the formations 134, 136. Formation 134 can be resiliently compressible, deformable or deflectable in a direction generally towards inner surface of the first member 106. Second member 1 16 can include a radially outwardly directed formation 142. As the second member 116 is moved towards its extended condition formation 142 can move (compress, deform or deflect) formation 134 until formation 142 can be received in the groove 140. Formation 134 can then return to its original condition, and can prevent return of the formation 142 in a direction opposite to arrow M. Further forward movement of the second member 116 in the direction of arrow M can be prevented by formation 136 which can be non-deformable. Reference above to a formation 134 and a formation 136 can include the possibility of having a plurality of such formations arranged circumferentially around the inner surface of fist member 106. In alternative arrangements, the formation 134, 136 can be formed in corresponding location on the second member 1 16 with for radially directed formation 142 formed at an inner surface of the first member 106.

[0046] A typical locking or latching device 122 is shown in Figure 2. Locking or latching device 122 is shown in the locked or latched condition in which relative movement of the first and second members 106, 1 16 is prevented. Locking or latching device 122 can be in the form of a snap ring which is initially seated in an annular groove 126 of the second member 1 16 near the trailing end 120 thereof. The snap ring 122 is thus held in fixed relation to the second member 1 16 and moves with the second member 116 when the second member is extended from the first to the second condition. As the snap ring 122 approaches the end 1 12 of the first member 106, the snap ring 122 can expand to seat into an annular groove 124 formed in an inner surface of the first member 106.

[0047] In its second, extended condition, the second member 1 16 provides protection for a portion of a longitudinally extensive service member located within the second member 116 which portion extends from the seabed 10 to the lower end 1 12 of the first hollow longitudinally extensive member. The first hollow longitudinally extensive member (that is, the l-tube in Figures 1A and 1 B) 106 provides protection for the longitudinally extensive service member as it rises from the seabed 10 to the upper end part of the foundation, such as platform level 100P.

[0048] In some cases, the inner surface of the first member 106 (l-tube 106 in Figures 1A and 1 B) can have surface roughness or projecting features or formations which could cause damage to a longitudinally extensive service member contained within the first member 106. In particular, when the second member 1 16 is in its second (extended) condition, a longitudinally extensive service member contained within the first member 106 can come into contact with such surface roughness or projecting features, more especially when the longitudinally extensive service member is initially being drawn into the first member 106.

[0049] To alleviate the above problem, in some embodiments of the invention the first member 106 can have a liner 128. The liner 128 can also be in the form of a longitudinally extensive member, and in preferred embodiments can be a pipe or tube. The liner 128 can in some embodiments preferably be made from a polymeric material, in particular

HDPE. The shape of the liner can generally be selected to conform with the internal shape of profile of the first member 106 and the external shape or profile of the second member 116. In typical arrangements the liner 128 can be generally cylindrical.

[0050] When the second member 116 is in its first (non-extended) condition, the liner 128 can be located between an inner surface of the first member 106 and an outer surface of the second member 1 16. When the second member 116 is in its second (extended) condition and the longitudinally extensive service member is disposed within the first member 106, the liner 128 can be located between an inner surface of the first member 106 and an outer surface of the longitudinally extensive service member.

[0051] In some embodiments the liner 128 can extend for substantially the whole length of the first member 106. In other embodiments, the liner 128 can extend for only a portion of the length of the first member 106. For example liner 128 can be selectively placed at a location where there is a known risk of damage to a longitudinally extensive service member or to the second member 116 from features on or at the inner surface of the first member 106.

[0052] The respective internal diameters of the first member 106 and the second member 116 are selected in accordance with the diameter of the longitudinally extensive service member, that is, to enable feeding of the longitudinally extensive service member through the first and second members 106, 116. In some embodiments, the internal diameter of the second member 1 16 can be at least 150mm. In further embodiments the internal diameter of the second member 116 can be not greater than 500mm.

[0053] Typically the internal diameter of the first member 106 can be greater than the internal diameter second member 1 16. In some embodiments the internal diameter of the first member 106 can be 5 to 10mm greater than the second member 116. Thus in some embodiments the internal diameter of the first member 106 can be at least 155mm. In further embodiments the internal diameter of the first member 106 can be not greater than 510mm.

[0054] In some embodiments the second member 116 can comprise walls having a thickness of from 10mm up to 100mm. The walls of the first member 106 can be thicker than the walls of the second member 1 16. In some embodiments the walls of the first member 106 can be 5 to 20mm thicker than the walls of the second member 1 16. In some embodiments the first member 106 can comprise walls having a thickness of from 15mm up to 120mm.

[0055] In some preferred embodiments, the protective apparatus (comprising the first and second members 106, 1 16, and a liner 128 if present) can further include a messenger line 130 which can be in the form of a wire or cable. In use, the messenger line can be employed to draw the longitudinally extensive service member through the first and second members 106, 1 16 so that it can be connected as required to apparatus or equipment disposed on the foundation 100.

[0056] When the second member 1 16 is in its first condition, the messenger line 130 can be disposed within the hollow interior of the second member 1 16. A first end of the messenger line can be secured to an upper portion of the foundation, or the first end can be retained within the protective apparatus at a location from which it can conveniently be retrieved and can be retained at the upper part of the foundation when the second member 116 moves to its second condition. The length of the messenger line 130 contained within the protective apparatus can be considerably longer than the total length of the protective apparatus itself (when the second member is in its second condition). A second end of the messenger line 130 can be located proximate the leading end 118 of the second member 116 such that the second end of the messenger line can be retrieved from the second member 1 16 when required.

[0057] The provision of the messenger line 130 can facilitate insertion or feeding of the longitudinally extensive service member into the second member 116 and the first member 106. Thus the second end of the messenger line 130 can be attached to a leading end of the longitudinally extensive service member. The first end of the messenger line 130 may be attached to a suitable pulling device such as a winch. The winch can conveniently be located on a cable laying vessel or the like located near to the foundation 100. Thus the pulling device can take up the messenger line causing the longitudinally extensive service member to be drawn first into the second member 1 16 (which is in its second, extended, condition) and then through the second and first members 116, 106 until the leading end of the longitudinally extensive service member reaches a location proximate the upper part of the foundation, where it can be secured and connected to such equipment or apparatus as necessary or required.

[0058] The flexible nature of the second member 116 is advantageous in avoiding the problem of exceeding the minimum bend radius of the longitudinally extensive service member at its point of entry into the l-tube. Thus, the second member 116 can provide a more progressive curvature of the longitudinally extensive service member as it approaches the l-tube aperture 114, so avoiding passing the minimum bend radius.

[0059] In some embodiments the second member 1 16 can comprise a first portion and a second portion wherein the first portion has a greater axial stiffness and/or bending stiffness than the second portion. The first portion of the second member 1 16 can include regions of the second member 1 16 at or proximate the surface wave zone (i.e. regions at or near to the water level 12 as shown in Figure 1A). In these embodiments the first portion can exhibit axial stiffness and/or bending stiffness typically 20 to 50 times the axial stiffness and/or bending stiffness of the longitudinally extensive service member. Such embodiments can provide fatigue protection over a 25 year period (a typical period for which the longitudinally service member may be in use). The second portion of the second member 1 16 can include regions of the second member 116 below the surface wave zone. Comparatively, the second portion can exhibit axial stiffness and/or bending stiffness lower than the first portion and typically in the range of 10 to 20 times the axial stiffness and/or bending stiffness of the longitudinally extensive service member. Thus, as the first portion of the second member 116 will typically be subjected to enhanced wave action and increased transverse forces when compared to the second portion, the axial stiffness and/or bending stiffness of the first portion can advantageously be increased to resist such stresses. The properties of the second portion provide suitable fatigue protection over the 25 year period and are appropriate for the ultimate limit state during the installation and operation of the longitudinally extensive service member.

[0060] The above-mentioned first portion and second portions of the second member 1 16 can thus respectively be formed from different polymeric materials to provide the requisite axial stiffness and/or bending stiffness. For example, the first portion of the second member 1 16 can be formed from a polymeric composite such as HDPE reinforced with fibres or a thermosetting material such as XLPE. The second portion of the second member 1 16 can be formed from a thermoplastic polymer such as HDPE or a material with similar properties to HDPE. In some embodiments butt welding can be used to join the first and second portions form the second member 1 16 as a continuous tube or pipe.

Alternatively, pre-determined lengths of the tube or pipe can be connected together to form the first and second portions and ultimately construct the second member 116 using mechanical fixings such as bolts and flanges.

[0061] In alternative embodiments of the invention, the first hollow longitudinally extensive member can be a J-tube rather than an l-tube. J-tubes are well known in the art and need not be described in detail. With the exception that that J-tube includes a curved lower portion, the construction and use of the foundation according to the invention with a J-tube is the same as described above in relation to an l-tube.

[0062] In further alternative embodiments, neither an l-tube nor a J-tube is used. In some such embodiments the first hollow longitudinally extensive member can be a hollow leg of the foundation. An example of such an arrangement is illustrated in Figure 4. In Figure 4 features which correspond to features of the foundation of Figures 1 A, 1 B, 2 and 3 are given the same reference numbers except for the substitution of the prefix "2" instead of "1". Thus, for example, in Figures 1A and 1 B the foundation leg is indicated by 102 and in Figure 4 the corresponding foundation leg is indicated by 202.

[0063] Referring to Figure 4, the foundation 200 has a plurality of supporting legs 202 which can be of hollow construction. A typical leg can be generally cylindrical with a diameter in excess of 0.5m, such as about 2m or more. Thus a significant hollow void is defined by the interior of the leg 202. Leg 202 can form a first hollow longitudinally extensive member of the invention. Leg 202 can extend from an uppermost part 232 proximate a platform level 200P of foundation 200 to a lowermost portion 234 at the seabed 10.

[0064] An aperture 214 can be formed in a side wall of the leg 202, proximate the lowermost portion 234 and generally near to the level of the seabed 10. Typically aperture 214 can be formed at least 2m above the seabed to allow a suitable minimum bend radius of the longitudinally extensive service member. Second hollow longitudinally extensive member 216 can be arranged within leg 202 and can be extended therefrom through the aperture 214.

[0065] The construction and use of the foundation where the protective apparatus comprises a first hollow longitudinally extensive member in the form of a foundation leg 202 and a second longitudinally extensive member in the form of a form of longitudinally extensive pipe or tube which is formed from a flexible material is in other respects generally the same as described above in relation to construction including an l-tube or J- tube.

[0066] Thus, the pipe or tube 216 can in preferred embodiments be generally cylindrical. The flexible material can be selected such that the second member is self supporting and can bend when required. In some preferred embodiments, the flexible material is a polymeric material, in particular high density polyethylene (HDPE), polypropylene or polyvinyl chloride. Polymeric composite materials can also be used such as HDPE reinforced with fibres or thermoset materials such as cross-linked polyethylene (XPLE). In further embodiments the flexible pipe or tube 102 can be formed from two or more of any of the above-noted polymeric materials.

[0067] In further embodiments, the pipe or tube/second member 216 can comprise a first portion and a second portion wherein the first portion has a greater axial stiffness and/or bending stiffness than the second portion. These embodiments can be functionally and constructional ly equivalent to those previously described with respect to second member 116 above. [0068] The leg 202 and second member 216 can be provided with cooperating locking or latching devices which have the same purpose as the above described locking or latching devices of the l-tube construction. A liner 228 (not specifically illustrated) can be provided within leg 202 which has the same function as, and a construction generally the same as, the liner 128 of Figure 3. Second member 216 and leg 202 can also contain a messenger line (not specifically illustrated) which is constructionally equivalent and equivalent in use to messenger line 130.

[0069] In further embodiments of the invention, the foundation can be a floating

foundation, such as a floating foundation for a wind turbine generator. A portion of such a foundation can be arranged in use below the water surface and a portion above the water surface. A floating foundation can also include first member such as an l-tube or J-tube or supporting leg analogous to those described above and to which the present invention can be applied by locating a second member in the first member in one or other of the ways discussed above.

[0070] In further embodiments of the invention, the foundation can be a gravity foundation. A gravity foundation typically comprises a large mass of heavy material which is stably arranged in position on the seabed by virtue of its own weight. The gravity foundation can typically comprise a mass of concrete, such as in the form of a block.

[0071] A typical arrangement of a foundation according to the invention wherein the foundation is a gravity foundation is shown in Figure 5. In Figure 5 features which correspond to features of the foundation of Figures 1 A, 1 B, 2, 3 or 4 are given the same reference numbers except for the substitution of the prefix "3" instead of "1" or "2".

[0072] In Figure 5, foundation 300 can comprise a solid, massive block of material 336 which includes a through bore or passageway shown generally at 338. An upper end 338U of the passageway 338 can communicate with equipment or apparatus 340 mounted on the foundation 300, such as a wind turbine generator to which a longitudinally extensive service member is ultimately to be connected. A lower end 338L of the passageway 338 can open at a location proximate the seabed 10. A single foundation 300 can include a plurality of passageways 338.

[0073] In Figure 5, the passageway 338 is shown for convenience as following an arc of a circle. Other configurations for the passageway 338 are possible. Foundation 300 including block 336, equipment and apparatus 340 and passageway 338 are not drawn to scale and relative sizes of these features should not be interpreted from Figure 5 alone.

[0074] In some preferred embodiments, passageway 338 can contain a first hollow longitudinally extensive member ("first member") 306. First member 306 can conveniently be in the form of a polymeric pipe or tube which is shaped at least approximately to conform to the profile of the surface of the passageway 338. First member 306 can be formed from HDPE, for example. First member 306 can extend from upper end 338U to lower end 338L of passageway 338. In one convenient arrangement, the first member 306 can be constrained at a given bend radius which is not less than a minimum bend radius and then concrete or other suitable material can be poured around the constrained first member 306 to form the foundation 300. In certain embodiments the minimum bend radius can be about 5m. The shape of the first member 306 thus becomes fixed in its desired position within the foundation.

[0075] In some other embodiments foundation 300 defining passageway 338 can itself form the first hollow longitudinally extensive member, the inner surface walls of the passageway 338 effectively then defining an inner surface of the first hollow longitudinally extensive member 306.

[0076] Foundation 300 can also include a second hollow longitudinally extensive member (second member) 316 which is functionally equivalent to the second members 116 and 216 described above. The second member 316 can adopt a first condition in which it is substantially wholly contained within the passageway 338 and a second condition in which at least a major part of the second member 316 extends outwardly from end 338L of the passageway 338, end 338L effectively forming an aperture 314 of the passageway 338. In Figure 5, second member 316 is shown in a position intermediate the first and second conditions.

[0077] Passageway 338 can also include a liner 328 which is functionally equivalent to the liner 128 or 228 described in relation to embodiments above. Thus the liner can in some preferred embodiments comprise a polymeric pipe or tube, such as of HDPE. When the second member 316 is in its first condition, the liner 328 can be arranged between the respective first and second members 306, 316. When the second member 316 is in its second condition and a longitudinally extensive service member is disposed in the passageway 338, the liner 328 can be arranged between the first member 306 and the longitudinally extensive service member.

[0078] In further preferred embodiments, the passageway 338 may include a messenger line 330 which is functionally equivalent to messenger lines 130 and 230 of the above described embodiments. Thus the messenger line 330 is arranged such that it can be used to draw a longitudinally extensive service member into the respective second and first members 316, 306 in substantially the same manner as described above in relation to messenger line 130. [0079] As noted above, foundation 300 defining passageway 338 can itself form the first hollow longitudinally extensive member or passageway 338 can contain a first member 306. Additional embodiments related to this concept are shown in Figures 7A, 7B, 7C, 7D and Figure 8. The Figures illustrate one such embodiment depicting a foundation for an offshore structure 400 wherein passageway 338 extends upwardly and internally within a portion of an apparatus 340 mounted on the gravity foundation 300. Passageway 338 can be formed from first member 306 that can conveniently be in the form of a polymeric pipe or tube which is shaped at least approximately to conform to the profile of the surface of the passageway 338. It should be noted that the aforementioned Figures illustrate two sets of passageways 338 and associated first members 306, however only one set is labelled for the sake of clarity. First member 306 can be secured in place (e.g. to the internal metalwork of the apparatus 340) and its profile then cast into the apparatus. In one convenient arrangement, first member 306 can be constrained at a given bend radius which is not less than a minimum bend radius and then concrete or other suitable material can be poured around the constrained first member 306 to form the passageway 338 extending within the apparatus 340 and gravity foundation 300. In certain embodiments the minimum bend radius can be about 5m. The shape of the first member 306 thus becomes fixed in its desired position within the foundation 400. An upper section of the first member 306A defines a portion of the passageway 338 extending above the gravity foundation 300 and a lower section of the first member 306B defines a portion of the passageway extending within the gravity foundation 300. Following the formation of the passageway 338, the first member 306 can be retained within the foundation for an offshore structure 400 or can be removed. In embodiments wherein the first member 306 is removed, passageway 338 can itself form the first hollow longitudinally extensive member 306.

[0080] The foundation for an offshore structure 400 can also include a second hollow longitudinally extensive member (second member) 316 as previously mentioned above. The second member 316 can adopt a first condition in which it is substantially wholly contained within the passageway 338 and a second condition in which at least a major part of the second member 316 extends outwardly from an end 338L of the passageway 338, end 338L effectively forming an aperture 314 of the passageway 338. Figure 8 shows second member 316 in its second condition and secured to an exterior portion of the apparatus 340.

[0081] In further embodiments the foundation for an offshore structure 400 can comprise one or more anchor assemblies to releasably secure the second member 316 to the foundation 400 when in its extended condition. In some embodiments, the gravity foundation 300 can comprise said one or more anchor assemblies. In such embodiments said one or more anchors assemblies can be located at an external surface of the gravity foundation 300. In further embodiments, said one or more anchors assemblies can be attached to an external surface of the apparatus 340 mounted on the gravity foundation 300. In some preferred embodiments of the foundation 400 for an offshore structure, the gravity foundation 300 and the apparatus 340 can comprise said one or more anchor assemblies.

[0082] The inclusion of anchor assemblies enable the second member 1 16 to conveniently be secured or tethered to one or more portions of the foundation 400 when in its extended condition prior to, during or after usage of the protective apparatus.

[0083] The Figures illustrate a first anchor assembly 380A attached to an external surface of the apparatus 340 and a second anchor assembly 380B extending from an upper surface of the gravity foundation 300. Detail D of Figure 7D depicts an enlarged image of the anchor assembly 380A attached to the apparatus 340. The anchor assembly 380B located on the gravity foundation 300 is constructionally equivalent to 380A and thus will not be described further. The assembly 380A can comprise a retaining pin 384 configured to co-operate with a receiving portion 382 attached to the foundation 400 and thereby secure the second member 116 to the foundation 400. In some embodiments the retaining pin 384 is substantially U shaped and the receiving portion 382 can comprise first and second sleeves 383A, 383B to receive the retaining pin 384. The retaining pin 384 can thus comprise first and second projections, 384A, 384B that can respectively enter and be retained within the corresponding first and second sleeves, 383A, 383B of the receiving portion 382. In some embodiments the sleeves 384A, 384B and projections of the retaining pin 384A, 384B can be cylindrical.

[0084] The receiving portion 382 can conveniently be attached to the foundation 400 by one or more connecting members. Thus in Detail D of Figure 7D, the first sleeve 383A is attached to the apparatus 340 by a first connecting member 381 A and the second sleeve 383B is attached to the apparatus 340 by a second connecting member 381 B. In some arrangements portions of the anchor assemblies 380A, and particularly the receiving portions 382, can be cast into the foundation 400 for the offshore structure. Thus anchor assembly 380A can be cast into a portion of the apparatus 340 and anchor assembly 380B can be cast into a portion of the gravity foundation 300.

[0085] The anchor assemblies 380A, 380B can comprise any material sufficiently strong to retain the second member 316 without damaging the second member 316. In some embodiments the receiving portion 382 and retaining pin 384 can be coated with polyurethane in order to reduce friction between the respective components. In other embodiments the receiving portion 382 and/or retaining pin 384 can be galvanised. In these embodiments the receiving portion 382 and/or retaining pin 384 can be subject to hot dip galvanisation. In further embodiments the receiving portion 382 and/or retaining pin 384 can be coated with a protective paint suitable for the marine environment. Appropriate coatings to meet these criteria are well known to those skilled in the art and include, for example, the NORSOK marine protection system.

[0086] Figure 8 illustrates the second member 316 secured to the foundation 400 when in its second, extended condition. The second member 316 can be secured in position by first placing the pipe or tube between the two sleeves 383A, 383B and then appropriately seating the retaining pin 384 in the sleeves 383A, 383B. As shown in Figure 8, a first, lower portion of the second member 316 is secured to the gravity foundation 300 and a second, upper portion of the second member 316 is secured to the apparatus 340.

[0087] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0088] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0089] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.