GB2534595A

GB2534595A - Apparatus for anchoring a buoyant assembly to a submerged anchorage

Info

Publication number: GB2534595A
Application number: GB1501468.1A
Authority: GB
Inventors: Campbell-Smith Gregory
Original assignee: First Subsea Ltd
Current assignee: First Subsea Ltd
Priority date: 2015-01-29
Filing date: 2015-01-29
Publication date: 2016-08-03
Anticipated expiration: 2035-01-29
Also published as: GB201501468D0; GB2534595B

Abstract

An apparatus 10 for anchoring a buoyant assembly (20, Fig 2) to a submerged anchorage (22, Fig 2) comprises a receptacle 12 adapted for mounting to the buoyant assembly, an elongate member 14 passable through the receptacle between first 12a and second 12b sides of the receptacle and a mooring line 16 attached to the elongate member. The elongate member is passable through the receptacle in first and second opposing axial directions and the mooring line is connectable to the submerged anchorage. The receptacle is operable in a first mode, in which the receptacle inhibits passage of the elongate member through the receptacle in at least one of the axial directions, and a second mode, in which the receptacle permits passage of the elongate member through the receptacle in both axial directions. The apparatus may improve the ease and/or the cost efficiency of anchoring a buoyant assembly when compared to conventional apparatus.

Description

Apparatus for anchoring a buoyant assembly to a submerged anchorage The invention relates to apparatus for anchoring a buoyant assembly to a submerged anchorage, particularly, but limited to, a buoyant assembly for supporting an offshore wind turbine.

BACKGROUND

Floating offshore wind turbines increase the potential for energy generation offshore. An engineering design study for the Energy Technologies Institute in the UK has demonstrated that the cost of UK offshore wind may fall to £85/MWh by the mid-2020s using tension leg floating platforms (TLPs). This is compared to gas power starting operation in 2021 which has been estimated to cost around £88/MWh. With continuing improvements to existing TLP technologies the cost of offshore wind may be reduced further.

A TLP creates a permanent uplift below the water, as tensioned cables tether a floating structure to the sea bed. The tensioned cables inhibit yaw, pitch and roll of the structure by absorbing energy from wind and waves. While TLP technology has been around since the 1980s, when it was first used for the offshore production of oil and gas, the existing problem is principally how to carry out the tensioning of a TLP's cables at a low enough cost so as to apply the technology to floating wind turbine structures. The approaches used for offshore oil and gas production are prohibitively expensive.

It is an object of certain embodiments of the invention to provide an improved apparatus and method for installation of a TLP, which may in certain embodiments improve the ease and/or the cost efficiency of installing TLPs used in the offshore production of wind energy. Further, it is an object of certain embodiments of the invention to mitigate at least some of the disadvantages associated with prior art arrangements.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided an apparatus for anchoring a buoyant assembly to a submerged anchorage, the apparatus comprising: a receptacle adapted for mounting to the buoyant assembly, the receptacle having a first side and a second side; an elongate member passable through the receptacle between the first side and the second side, the elongate member being passable through the receptacle in a first axial direction and an opposing second axial direction; and a mooring line attached to the elongate member, the mooring line connectable to the submerged anchorage, wherein the receptacle is operable in a first mode, in which the receptacle inhibits passage of the elongate member through the receptacle in at least one of the first and second axial directions, and a second mode, in which the receptacle permits passage of the elongate member through the receptacle in both the first and second axial directions. The apparatus may improve the ease and/or the cost efficiency of anchoring a buoyant assembly when compared to conventional apparatus.

The receptacle may be provided with means to grip the elongate member so as to inhibit passage of said elongate member in the at least one of the first and second axial directions when operated in the first mode. Further or alternatively, the receptacle may inhibit passage of the elongate member in only the first axial direction when the receptacle is operated in the first mode. The elongate member may be attachable to a pulling line, the pulling line being connectable to a tensioning device.

The means to engage the elongate member may include a plurality of ramped surfaces provided on the receptacle, a ball cage inserted within the receptacle, and a plurality of roller members each captively retained within apertures of the ball cage, the ball cage being axially moveable and biased axially in the first direction, said rolling members being capable of gripping the elongate member by wedging between the ramped surfaces and the elongate member. The plurality of roller members may be provided as balls.

The apparatus may further comprising a submergible anchorage that is anchorable to a supporting stratum. The submergible anchorage may be provide as a foundation structure, the foundation structure being anchorable to the supporting stratum.

Alternatively, the submergible anchorage may be provided on an upper end of a tether, the tether being connected to a foundation structure which is anchored to the supporting stratum.

According to another aspect of the invention, there is provided a tension leg platform having a buoyant assembly and at least one apparatus as recited above, wherein at least one receptacle is mounted to the buoyant assembly. The buoyant assembly may be attached to or includes at least part of a wind turbine structure.

According to yet another aspect of the invention, there is provided a semi-submersible platform having a buoyant assembly and at least one apparatus as recited above, wherein at least one receptacle is mounted to the buoyant assembly. The buoyant assembly may be attached to or includes at least part of a wind turbine structure.

According to a further aspect of the invention, there is provided a spar platform having a buoyant assembly and at least one apparatus as recited above, wherein at least one receptacle is mounted to the buoyant assembly. The buoyant assembly may be attached to or includes at least part of a wind turbine structure.

According to yet a further an aspect of the invention, there is provided a method for anchoring a buoyant assembly to a submerged anchorage, the method comprising the steps of: providing an apparatus as recited in any of claims 1 to 9; mounting the receptacle to the buoyant assembly; ballasting the buoyant assembly such that said buoyant assembly achieves an installation draught substantially equally to a final desired installed draught; connecting a lower end of the mooring line to the submerged anchorage; pulling the elongate member through the receptacle in the second axial direction while the receptacle is operated in the first mode so as to establish a pretension in the mooring line; and deballasting the buoyant assembly in order to fully tension the mooring line. The method may improve the ease and/or the cost efficiency of anchoring a buoyant assembly when compared to conventional methods.

The method may further comprise adjusting the tension in the mooring line by pulling the elongate member further through the receptacle in the second axial direction while the receptacle is operated in the first mode.

The method may further comprise adjusting the tension in the mooring line by lowering the elongate member back through the receptacle in the first axial direction while the receptacle is operated in the second mode.

The elongate member may be on the first side of the receptacle prior to insertion of the elongate member into the receptacle. Alternatively, the elongate is on the second side of the receptacle prior to inserting the elongate member into the receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figure 1 is a cross-sectional side view of an apparatus according to an embodiment of the invention: Figure 2 is a schematic view of the apparatus of Figure 1 in combination with a buoyant assembly, the buoyant assembly positioned in relation to a submerged anchorage; Figure 3 is a schematic view of the arrangement of Figure 2, with a mooring line connecting the buoyant assembly to the submerged anchorage; Figure 4 is a schematic view of the arrangement of Figure 3, with pre-tensioning of the mooring line; and Figure 5 is a schematic view of the arrangement of Figure 3, with full tensioning of the mooring line.

DETAILED DESCRIPTION

Figure 1 illustrates an apparatus 10 according to an embodiment of the invention. The apparatus 10 includes a receptacle 12, an elongate member 14 and a mooring line 16. The receptacle 12 and the elongate member 14 are engageable with one another by insertion of the elongate member 14 into the receptacle 12. The receptacle 12 and the elongate member 14 share a common longitudinal axis 18, i.e. a line which extends through the centre of the receptacle 12 and the elongate member 14, when the two are engaged with one another. The apparatus 10 enables anchoring of a buoyant assembly 20 to a submerged anchorage 22 (as is described below with reference to Figures 2 to 5).

Returning to Figure 1, the receptacle 12 is provided in a substantially sleeve-like configuration having a cylindrical body 24 and a continuous passageway 26 extending therethrough. The passageway 26 extends through the centre of the receptacle 12, i.e. along the longitudinal axis 18, between a first side 12a and an opposing second side 12b. The first side 12a is an upper side of the receptacle 12 and the second side 12b is a lower side of same. The receptacle 12 is adapted for mounting to the buoyant assembly 20 such that, in use, a load acting upon said receptacle 12 may be transferred therefrom to the buoyant assembly 20. For this purpose, the receptacle 12 is provided with at least one annulus or flange 28 extending radially outwardly from the cylindrical body 24. The at least one annulus or flange 28 may be provided continuously about the circumference of the cylindrical body 24 or, alternatively, multiple spaced apart flanges 28 may be provided at intervals about said circumference. The at least one annulus or flange 28 may be provided with bolt holes to assist in mounting the receptacle 12 to the buoyant assembly 20. In other embodiments, no flange 28 may be present and the receptacle 12 may be mountable to the buoyant assembly 20 by any suitable means.

The elongate member 14 is configured such it is passable through the receptacle 12 from the first side 12a to the second side 12b and vice versa. The elongate member 14 moves in a first axial direction when passing from the first side 12a to the second side 12b and in second axial direction when moving from the second side 12b to the first side 12a. The elongate member 12 has an upper end 14a, which has a chamfered edge to assist insertion of the elongate member 14 into the second side 12b of the receptacle 12, and an opposing lower end 14b. The chamfered edge gives the upper end 14a a frusto-conical configuration. Further, the upper end 14a is provided with a fixing 30 to permit connection of the elongate member 14 to a pulling line 32 (shown in Figures 2 to 4) and the lower end 14b is configured for attachment to the mooring line 16. An upper end 16a of the mooring line 16 is provided with connecting means 34 so as to enable said attachment of the elongate member 14 to the mooring line 16.

Further, the mooring line 16 is connectable at a lower end 16b of the mooring line 16 to the submerged anchorage 22. Preferably, the mooring line 16 is a flexible line and may be provided in the form of a wire rope. Alternatively, the mooring line 16 may be provided as a chain or a rope of synthetic fibres such as nylon, polypropylene, polyester, aramid fibres.

The receptacle 12 is operable in a first mode in which movement of the elongate member 14 through the receptacle 12 is inhibited in the first axial direction while movement is permitted in the second axial direction. The receptacle 12 is further operable in a second mode may be which movement in both the first and second axial directions is permitted. The first mode may be a passive mode in which the receptacle 12 operates without user interaction. The second mode is an active mode in which a user interaction is required to initiate and maintain said second mode.

Figure 1 shows the receptacle 12 further having an inner wall 40 which extends along the passageway 26. The inner wall 40 comprises a ball cage 42 which captively retains a plurality of balls 44 within multiple corresponding apertures of the ball cage 42. In other embodiments, the balls 44 may be replaced by other suitable roller members, such as cylindrical rods. Each of the apertures is sized so as to permit one of the corresponding balls 44 to project partially from each of the apertures but so to prevent the balls 44 from passing through completely. Extending about the circumference of the passageway 26 is a plurality of inclined ramped surfaces 48 which define recesses in which the balls 44 may reside. The ball cage 42 is movable in line with the longitudinal axis 18 and is biased to move downwards, i.e. biased towards the second side 12b, by a biasing means 46 which may be provided in the form of springs. As the springs 46 bias the ball cage 42 downwardly, the balls 44 engage with the ramped surfaces 48 and are consequently moved radially inwards such that the balls 44 project through the apertures. As illustrated in Figure 1, with the ball cage 42 biased downwardly, the balls 44 will engage with the elongate member 14 when the receptacle 12 and the elongate member 14 are engaged with one another. In this configuration downward movement, i.e. movement in the first direction, of the elongate member 14 is not possible.

Downward movement of the elongate member 14 will urge the balls 44 along their respective ramp surfaces 48 such that the balls 44 become wedged between the ramped surfaces 48 and the elongated member 14. This causes a radially inward force to be exerted on the elongate member 14, thus gripping the elongate member 14 and retaining it within the receptacle 12. Upward movement, i.e. movement in the second axial direction, of the elongate member 14 withdraws the balls 44 from the inclined ramp surfaces 48 so as to permit further upward movement of the elongate member 14.

The ball cage 42 is movable upwardly into a release position by an actuating means. Upward movement of the ball cage 42 withdraws the balls 44 from the inclined ramp surfaces 48 and thus permits the balls 44 to move radially outwardly such that they do not project from the apertures. With the ball cage 42 in the release position, the balls 44 do not engage with the elongate member 14 when the elongate member 14 is disposed in the receptacle 12. Therefore, with the ball cage 42 in the release position, the elongate member 14 is moveable within the receptacle 12 in both the first and second axial directions. It will be understood that the receptacle 12 of the illustrated embodiment is operated in the first mode when the ball cage 42 is biased downwardly and operated in the second mode when the actuating means is used to move the ball cage into the release position.

A method of anchoring the buoyant assembly 20 to the submerged anchorage 22 in accordance with an embodiment of the invention is now described. Figure 2 shows the buoyant assembly 20, which may be either submerged or partially submerged, in combination with the apparatus 10. The receptacle 12 is mounted to the buoyant assembly 20 such that the longitudinal axis 18 is substantially vertical and that the first side 12a of the receptacle 12 is accessible from above the buoyant assembly 20. The buoyant assembly 20 may support a superstructure (not shown), for example a wind turbine or a deck for use by an installation crew during an anchoring operation. The submerged anchorage 22 is an anchoring means provided below the surface of a body of water. In the context of the described embodiment, the body of water is typically a sea or an ocean. The submerged anchorage 22 is provided on a foundation structure 60 which is secured to a supporting stratum 62, for example a seabed. It will be understood that the submerged anchorage 22 may be alternatively provided, for example on an upper end of a tether, wherein the tether has a lower end which is secured to the supporting stratum 62. The exact design of the foundation structure 60 will depend of the properties of supporting stratum 62. The foundation structure 60 may be one or more gravity anchors, piled anchors or suction anchors.

The buoyant assembly 20 is temporarily provided with a temporary installation module 64 configured such that it is removable from the buoyant assembly 20 once the anchoring operation is complete. The temporary installation module 64 has a predetermined weight which provides an installation draught approximately equally to a desired final draught required upon successful anchoring of the buoyant assembly 20 to the submerged anchorage 22. The installation draught may be at least equal to the final draught, i.e. the installation draught may be equal to or more than the final draught. The temporary installation module 64 may be provided in the form of a ballast tank which is pumped at least partially full with water to achieve the desired weight, and thus the desired installation draught. Of course, the buoyant assembly 20 may be otherwise suitably ballasted, for example using a mass of high density material, such as concrete. It will be understood that a buoyant force acts upward on the buoyant assembly 20 and that the buoyant force is greater than the weight of the buoyant assembly 20 plus the weight of any article which the buoyant assembly 20 supports, which includes the weight of the temporary installation module 64. Partial ballasting of the buoyant assembly 20 may take place before the buoyant assembly 20 is towed to location, where ballasting is completed prior to commencing the anchoring operation. Alternatively, complete ballasting of the buoyant assembly 20 may take place either before or after the buoyant assembly is towed to location.

The buoyant assembly 20 is towed to a location relative to the submerged anchorage 22 and positioned such that the receptacle 12 is vertically aligned with the submerged anchorage 22, as shown in Figure 1. Towing and positioning of the buoyant assembly 20 is performed by at least one capable towing vessel. At least one support vessel may also be required to assist with the positioning and the anchoring operation. Prior to commencing the anchoring operation the elongate member 14 is on the first side 12a of the receptacle 12. In the illustrated embodiment, the elongate member 14 is suspended on the pulling line 32 which is engaged with a tensioning device in the form of a winch 66. The winch 66 is provided on the temporary installation module 64.

However, it will be understood that in other embodiments any suitable tensioning device may be used, for example a strand jack or linear jacking device and that the tensioning device need not be provided on the temporary installation module 64. The upper end 16a of the mooring line 16 is connected the lower end 14b of the elongate member 14 such that at least an upper length of the mooring line 16 is suspended below the elongate member 14. Prior to commencing the anchoring operation the majority of the mooring line 16 will be stored on the deck with the lower end 16b of the mooring line 16 fed through the receptacle 12. In the example shown in Figures 2 to 5, a connection between the lower end 16b of the mooring line 16 and the submerged anchorage 22 is to be made by engaging a female connector 68 and male connector 70. The female connector 68 is provided on the foundation structure 60 and the male connector 70 is provided on the lower end 16b of the mooring line 16. Therefore, prior to commencing the anchoring operation, the male connector 70 is suspended on lower end 16b of the mooring line 16 adjacent to an underside of the buoyant assembly 20.

Figure 3 shows the lower end 16b of the mooring line 16 connected to the submerged anchorage 22, i.e. Figure 3 shows the female connector 68 and the male connector 70 engaged with one another. To make the connection, the mooring line 16 is fed through the receptacle 12 from the first side 12a to the second side 12b. The mooring line 16 may be fed through the receptacle 12 by operatives working on the deck of the buoyant assembly 20. As the mooring line 16 is fed through the receptacle 12 the male connector 70 descends from the underside of the buoyant assembly 20 toward the submerged anchorage 22. The length of the mooring line 16 is predetermined such that the mooring line 16 becomes fully expended as the lower end 16b of the mooring line 16 nears the submerged anchorage 22. To lower the male connector 70 further, and thus make the connection between the lower end 16b of the mooring line 16 and the submerged anchorage 22, the elongate member 14 is inserted into the passageway 26 on the first side 12a of the receptacle 12 and passed in the first axial direction therethrough. Therefore, prior to insertion of the elongate member 14, the receptacle 12 is operable in the second mode. The winch 66 advances the pulling line 32 so as to lower the elongate member 14 through the receptacle 12 in the first direction. The passage of the elongate member 14 through the receptacle 12 permits a final decent of the male connector 70 so to engage the female connector 68 and the male connector 70 with one another. A remotely operated underwater vehicle ("ROV") 72 may be used to assist making the connection.

The mooring line 16 is then pre-tensioned by retracting the pulling line 32 once the connection is made between the mooring line 16 and the submerged anchorage 22.

Prior to pre-tensioning of the mooring line 16, the receptacle 12 is switched to operate in the first mode. In the illustrated embodiment, this results in the springs 46 biasing the ball cage 42 downwards and thus causing the balls 44 to be urged radially inwards, as described above with reference to Figure 1. With the receptacle 12 in the first mode, it is no longer possible for the elongate member 14 to move downwardly, i.e. it is not possible for the elongate member 14 to move through the receptacle 12 in the first direction. Upward movement, i.e. movement in the second direction, is still possible such that retraction of the pulling line 32 will draw the elongate member 14 through the receptacle 12 in the second direction.

Figure 4 illustrates the elongate member 14 being drawn back through the receptacle 12 in the second direction as the pulling line 32 is retracted by the winch 66. This action removes slack in the mooring line 16 until the mooring line 16 is pulled taut. Once the mooring line 16 is taut, further retraction of the pulling line 32 will result in a tensile force in both the pulling line 32 the mooring line 16. The pulling line 32 is further retracted until the desired pre-tension is applied to the mooring line 16. The pre-tension applied to the mooring line 16 does not substantially alter the draught of the buoyant assembly 20. The winch 66 advances the pulling line 32 once the desired pre-tension has been applied to the mooring line 16. This action removes tension present in the pulling line 32 and enables the installation crew to disconnect the pulling line 32 from the upper end 14a of the elongate member 14. With tension in the pulling line 32 removed, tension present in the mooring line 16 will attempt to draw the elongate member 14 through the receptacle 12 in the first axial direction. Of course, it will be understood that movement of the elongate member 14 in the first axial direction within the receptacle 12 is inhibited by engagement of the balls 44 with the elongate member 14. Consequently, the tensile force in the mooring line 16 is resisted by the buoyant force acting through the buoyant assembly 20 and receptacle 12, i.e. the buoyant force is now resisted by the tension in the mooring line 16 plus the weight of the buoyant assembly 20 and the weight of the temporary installation module 64.

Figure 5 shows the buoyant assembly 20 with the temporary installation module 64 and the winch 66 removed. Removal of the ballast fully tensions the mooring line 16 as, with the weight of the temporary installation module 64 no longer acting downwards on the buoyant assembly 20, the buoyant force acting upwards on the buoyant assembly 20 is now resisted fully by tension in the mooring line 16. Accordingly, the tension in the mooring line 16 will increase by an amount substantially equally to the weight of the ballast. With the ballast removed, the tensile force now present in the mooring line 16 is equal to the buoyant force less the self-weight of the buoyant assembly 20. This increase in the tensile force may cause the mooring line 16 to strain, i.e. the tensile force may result in elongation of the mooring line 16, e.g. due to the mooring line 16 having a finite material stiffness. The final draught may, therefore, be less that the installation draught. It will be understood by the skilled person that the elongation of the mooring line 16, and thus the reduction in draught, can be calculated as a proportion of the weight of the ballast means 64.

It will be appreciated by the skilled person that, in practice, a buoyant assembly may be provided with multiple mooring lines which anchor the buoyant assembly by virtue of connecting multiple submerged anchorages and multiple receptacles mounted about the buoyant assembly. The configuration of the apparatus in accordance with embodiments of the invention permits the tensioning of multiple mooring lines using a single tensioning means. Further, the receptacle may permit the tension in the mooring lines to be adjusted until each has achieved the desired pretension. The tension may be increased by pulling an elongate member further upwards through a respective receptacle in the second direction. Conversely, the tension may be reduced by lowering the elongate member in the first direction while the receptacle is temporarily switched to operate in the second mode. Fine adjustment of the draught and level of a buoyant assembly is therefore possible before fully tensioning the mooring lines by removing the temporary installation module.

The apparatus according to the present invention may allow for a more economical process for anchoring buoyant assemblies used to support wind turbines when compared to conventional means used to anchor floating assemblies used in the production of offshore oil and gas, which typically require multiple heavy duty tensioning means to pull the floating assembly down in a body of water to achieve the desired draught.

In any embodiment, the apparatus and method may provide a means for installing a buoyant assembly at and offshore location. It will be understood that the invention is not restricted to the details of the forgoing embodiments and other embodiments are possible. The buoyant assembly may form part a tension leg platform (TLP), a semi-submersible platform or a spar platform. Other embodiments may not require male and female connectors to establish a connection between the lower end of the mooring line and the submerged anchorage. In other embodiments the elongate member may be provided on the second side of the receptacle prior to an anchoring operation. It will also be understood that other suitable means may be used for inhibiting the passage and the engagement of the elongate member in the receptacle, for example the inner wall of the passageway may be provided with rows of teeth configured to selectively engage and grip the elongate member. Further, the receptacle may inhibit movement of the elongate member without engaging the elongate member, for example the receptacle may include a stop that axially blocks a part of the receptacle so as to inhibit movement of the elongate member.

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 components. 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.

Claims

CLAIMS1. Apparatus for anchoring a buoyant assembly to a submerged anchorage, the apparatus comprising: a receptacle adapted for mounting to the buoyant assembly, the receptacle having a first side and a second side; an elongate member passable through the receptacle between the first side and the second side, the elongate member being passable through the receptacle in a first axial direction and an opposing second axial direction; and a mooring line attached to the elongate member, the mooring line connectable to the submerged anchorage, wherein the receptacle is operable in a first mode, in which the receptacle inhibits passage of the elongate member through the receptacle in at least one of the first and second axial directions, and a second mode, in which the receptacle permits passage of the elongate member through the receptacle in both the first and second axial directions.
2. Apparatus according to any claim 1, wherein the receptacle has means to grip the elongate member so as to inhibit passage of said elongate member in the at least one of the first and second axial directions when operated in the first mode.
3. Apparatus according to claim 1 or 2, wherein the receptacle inhibits passage of the elongate member in only the first axial direction when the receptacle is operated in the first mode.
4. Apparatus according to claim 1 or 2, wherein the elongate member is attachable to a pulling line, the pulling line being connectable to a tensioning device.
5. Apparatus according to claims 2 to 4, wherein the means to engage the elongate member includes a plurality of ramped surfaces provided on the receptacle, a ball cage inserted within the receptacle, and a plurality of rolling members each captively retained within apertures of the ball cage, the ball cage being axially moveable and biased axially in the first direction, said rolling members being capable of gripping the elongate member by wedging between the ramped surfaces and the elongate member.
6. Apparatus according to claim 5, wherein the plurality of rolling members are provided as balls
7. Apparatus according to any preceding claim, further comprising a submergible anchorage that is anchorable to a supporting stratum.
8. Apparatus according to claim 7, wherein the submergible anchorage is provided as a foundation structure, the foundation structure being anchorable to the supporting stratum.
9. Apparatus according to claim 7, wherein the submergible anchorage is provided on an upper end of a tether, the tether being connected to a foundation structure which is anchored to the supporting stratum.
10. A tension leg platform having a buoyant assembly and at least one apparatus according to any preceding claim, wherein at least one receptacle is mounted to said buoyant assembly.
11. A tension leg platform according to claim 10, wherein the buoyant assembly is attached to or includes at least part of a wind turbine structure.
12. A semi-submersible platform having a buoyant assembly and at least one apparatus according to any of claims 1 to 9, wherein at least one receptacle is mounted to said buoyant assembly.
13. A semi-submersible platform according to claim 12, wherein the buoyant assembly is attached to or includes at least part of a wind turbine structure.
14. A spar platform having a buoyant assembly and at least one apparatus according to any of claims 1 to 9, wherein at least one receptacle is mounted to said buoyant assembly.
15. A spar platform according to claim 14, wherein the buoyant assembly is attached to or includes at least part of a wind turbine structure.
16. Method for anchoring a buoyant assembly to a submerged anchorage, the method comprising the steps of: providing an apparatus as recited in any of claims 1 to 9; mounting the receptacle to the buoyant assembly; ballasting the buoyant assembly such that said buoyant assembly achieves an installation draught substantially equally to a final desired installed draught; connecting a lower end of the mooring line to the submerged anchorage; pulling the elongate member through the receptacle in the second axial direction while the receptacle is operated in the first mode so as to establish a pre-tension in the mooring line; and deballasting the buoyant assembly in order to fully tension the mooring line.
17. The method of claim 16 further comprising adjusting the tension in the mooring line by pulling the elongate member further through the receptacle in the second axial direction while the receptacle is operated in the first mode.
18. The method of claims 16 to 17 further comprising adjusting the tension in the mooring line by lowering the elongate member back through the receptacle in the first axial direction while the receptacle is operated in the second mode.
19. The method of claims 16 to 18, wherein the elongate member is on the first side of the receptacle prior to insertion of the elongate member into the receptacle.
20. The method of the claim 16 to 18, where in the wherein the elongate is on the second side of the receptacle prior to inserting the elongate member into the receptacle.
21. Apparatus for anchoring a buoyant assembly to a submerged anchorage substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
22. Method for anchoring a buoyant assembly to a submerged anchorage substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.