Offshore Pillar Tension Leg Platform

Abstract

The present invention aims to improve the options available for the use and installation of structures including, for example, wind turbines. An apparatus and method for installation of an offshore platform to support installation of equipment is provided. The apparatus includes a vertical compression assembly and a counter-tensioning tendon system. The vertical compression assembly may comprise multiple compression members, column trusses, or other configurations. The fabrication, shipping, and installation methods provide for cost-effective port and installation vessel requirements.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 320,569, filed March 16, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates generally to offshore structures, and more specifically to structures for supporting offshore wind turbines, oil and gas operations, desalination operations, electrical substations, or similar facilities.

[0003] In the described embodiments, there are several types of configurations that provide a stable platform for mounting offshore equipment. Many types of equipment can be supported by the structures disclosed or installed using the steps disclosed herein, but reference is made to one such example, an offshore wind turbine installation. Those skilled in the art will appreciate that other equipment can be affixed to the structures disclosed herein, and one such example is shown and should not be read off the present disclosure. [Background technology]

[0004] For offshore installations, the arrangement of piles, submerged structures, and / or platform types generally varies based on the depth of the installation. For offshore wind developments, shallow depth installations, i.e., installations less than about 50 meters, are typically fixed to the seabed by rigid structures that are anchored by piles. Examples of structures that can be used in shallow waters may include, for example, monopiles, jacket structures, jack-up installations, and the like. Noise pollution created during the installation of non-driven piles for such fixed structures may be inconvenient in certain environmentally sensitive locations. As the water depth increases beyond approximately 50 meters, the cost of fixed structures increases rapidly. This is due to the additional material costs for the structures to withstand increased wave and current loads, as well as the significantly more expensive installation vessels required to carry out the installation. Thus, floating platforms are currently used or are planned to be used in deeper waters.

[0005] In deeper waters, typically greater than 50 meters deep for wind development, floating platforms can alternatively be used. These include, for example, barges, spar buoys, tension leg platforms, semi-submersible platforms, etc. The transition depth from fixed structures to floating platforms varies depending on the local wind, wave and current, seabed conditions, and economic considerations.

[0006] Floating platforms are subject to wave and current loads, which pose challenges that require additional costs to achieve the necessary stability to support equipment such as wind turbines, or require modifications to the equipment, or reduce the operability or uptime of the equipment, or result in additional maintenance and repairs. As a result, an increase in water depth beyond 50 meters or so significantly increases installation costs, whether using traditional fixed structures or floating platforms.

[0007] The economics of the offshore wind power market require that the cost of structures or platforms be minimized. The water depth range of 50-150 meters represents a large market opportunity because of the shortcomings of both traditional fixed and floating platform installations, and because in many locations, ideal wind farm sites, i.e., easily accessible, located near available infrastructure, and not in the public view, are located within this water depth range. Such transitional water depth sites are available for installation in many offshore wind farms around the world, such as the North Sea, Baltic Sea, Celtic Sea, Irish Sea, Mediterranean Sea, US East Coast, Gulf of Mexico, Yellow Sea, Taiwan Strait, South China Sea, and Bass Strait. Improved solutions in the 50-150 meter water depth range are needed, as traditional fixed structures are not economical in water depths greater than 50 meters, and floating platforms are also relatively expensive and do not perform as well in shallower waters. The present invention seeks to improve the use of, and the options available for installing, structures, including, for example, wind turbines, in these transitional sites around the world. Summary of the Invention

[0008] One or more embodiments of the present invention describe a structure for supporting offshore installations including, for example, wind turbines. Those skilled in the art will recognize that other similar installations, such as oil and gas operations, desalination operations, electrical substations, or similar offshore operations, may use one or more of the embodiments of the present invention.

[0009] In further embodiments, features of specific embodiments may be combined with features of other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

[0010] The accompanying drawings, which are included to provide a further understanding, and which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosed embodiments. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an offshore wind turbine installation according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a diagram of an offshore wind turbine installation from an overhead view, according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 illustrates an isometric view of an offshore wind turbine platform according to an embodiment of the present disclosure. [Figure 4] 1 illustrates an isometric view of a compression guide member according to an embodiment of the present disclosure. [Diagram 5] 1 illustrates an installation sequence for a wind turbine platform according to an embodiment of the present disclosure. [Figure 6] 1 illustrates an alternative installation procedure for a wind turbine platform according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present disclosure relates generally to offshore structures, and more specifically to structures for supporting offshore wind turbines and similar equipment. As described herein, embodiments of the offshore structures described herein improve upon conventional offshore structure configurations, particularly in transitional sites with water depths of 50 to 150 meters.

[0013] FIG. 1 provides a schematic diagram of an exemplary configuration of an offshore installation 100 for supporting offshore operations, in this example, a wind turbine 106 and a turbine tower 102, according to an embodiment of the present disclosure. In the illustrated embodiment, an upper frame structure or upper platform 101 supports a wind turbine tower 102 and a wind turbine 106. In the illustrated embodiment, the upper frame structure 101 is supported by a vertical compression assembly 110 and at least three tension legs (or tendons) 104. The vertical compression assembly 110 and tendons 104 extend to a foundation 105 located on the seabed. The vertical compression assembly supports the weight of the upper frame structure 101, the wind turbine tower 102, and the wind turbine 106 and facilitates tensioning of the tendons 104. The tendons 104 resist rotation of the upper frame structure 101 due to wind loads on the turbine, thus maintaining a stable platform, which is particularly advantageous in applications supporting wind turbines or other sensitive equipment. The upper frame structure 101 is laterally supported by taut mooring lines 103. In the illustrated embodiment, the upper frame structure 101 is supported by at least three taut mooring cables 103. In certain embodiments, three pairs of taut mooring cables 103 can be used to increase yaw stiffness. In this case, each pair of taut mooring cables 103 is oriented with an angular separation of, for example, 60 degrees. The taut mooring cables 103 resist shear forces acting on the offshore structure due to wind, waves, and currents. In the illustrated embodiment, mooring anchors 107 are used to anchor the taut mooring lines 103 to the seabed. In the illustrated embodiment, the foundation 105 is located on the seabed. As will be appreciated by those skilled in the art, many different foundations can be used based on the needs of the seabed and the prevailing wind, wave, and current loads.

[0014] 2 shows an upper portion of an offshore installation supporting a wind turbine tower 102 and a wind turbine 106 according to an embodiment of the present disclosure. In the illustrated embodiment, the offshore structure 100 is not a floating hull as vertical support is provided from below the water surface by a vertical compression assembly 110. The vertical compression assembly 110 provides a compressive force on the upper frame structure 101 according to the weight of the wind turbine 106, the turbine tower 102 and the upper frame structure 101, as well as a tensile force applied to the tendons 104 and the taut mooring cables 103, so that the structure is held rigid at its installation location to counter the effects of wind, waves and currents on the offshore structure, reducing accelerations and therefore mechanical loads on the turbine tower and wind turbine in wind turbine applications.

[0015] The illustrated embodiment minimizes the exposure of the structure to wave and current loads compared to conventional floating platforms. Advantageously, this reduces mooring and mooring anchor requirements and helps minimize environmental disturbances during installation. Additionally, the design provides a smaller footprint than conventional floating platforms due to the reduced mooring requirements, thus providing more space between offshore installations for vessel movement.

[0016] Detailed description of components A vertical compression assembly 110 is connected to the upper frame structure 101 and the foundation 105. The vertical compression assembly 110 supports the weight of the turbine 106, tower 102, and upper frame structure 101 while countering the tension of the tendons 104.

[0017] In certain embodiments, the upper and lower ends of the vertical compression assembly 110 are connected to the upper frame structure 101 and the foundation 105, respectively, with flexible connections allowing rotation in any direction. In certain embodiments, the connections between the upper and lower ends of the vertical compression assembly 110 and the upper frame structure 101 and the foundation 105 are fixed. One skilled in the art will appreciate that fixed connections allow limited rotational freedom while maintaining axial stiffness. As will be appreciated by one skilled in the art, any combination of fixed or flexible connections may be used depending on design requirements. Some embodiments use pin connections during operation, but may be beneficial to lock the connections during installation.

[0018] FIG. 3 is an isometric view of an offshore platform 100 that can be used in accordance with an embodiment of the present disclosure. In the illustrated embodiment, a vertical compression assembly 310 is connected to an upper frame structure 301 and a foundation 305. The upper frame structure 301 has a center point with multiple protruding sections 302 extending from the center point. In a particular embodiment, each protruding section 302 of the upper frame structure 301 has a truss arrangement. The upper frame structure 301 supports the installation of equipment, such as a wind turbine 106, on the structure at a connection point 315. The protruding sections 302 extend from the center point of the upper frame structure 301 to a tendon attachment pouch 309 that holds tension in tendons 304. A taut tether cable 303 used to laterally support the upper frame structure 301 can be connected to the protruding section 302 at the tendon attachment pouch 309. The tendons 304 connect the upper frame structure 301 to the foundation 305. The foundation 305 provides stability to the offshore structure. It will be appreciated that the foundation 305 can be any number of foundations. The foundation 305 includes multiple protruding sections, similar to the protruding sections 302 of the upper frame structure 301. The protruding sections of the foundation 305 connect to the tendons 304, similar to the upper frame tendon attachment pouches 309 of the upper frame structure 301 that connect to the tendons 304. In the configuration shown, each of the protruding sections from the upper frame structure and the foundation are offset by 120 degrees to be equal distances from each other. It will be appreciated that the frame structure can have any number of protruding sections 302 connected to the tendons 304 depending on the engineering requirements.

[0019] The tendons 304 are tensioned to some degree so as to maintain tension at all times during operation. The number of tendons and the degree of tension in the tendons 304 are determined based on the water depth, turbine size, and the expected wave, current, and wind patterns that will be experienced at the site. Tension is transferred to each tendon by its connection to a tendon attachment pouch 309.

[0020] In certain embodiments, the foundation 305 may be stabilized on the seabed by using weight baskets 308 on each of the overhanging sections 302. In certain embodiments, the foundation 305 is secured to the seabed by piles positioned through pile guides as an alternative to weighted baskets 308. In certain embodiments, mud mats are included to limit intrusion into the seabed.

[0021] The vertical compression assembly 310 supports the weight of the turbine 106, turbine tower 102, and upper frame structure 301 and counters tension in the tendons 304 by acting in compression. The vertical compression assembly 310 may be designed to resist global buckling by having composite sections that vary along its length. In the illustrated embodiment, the vertical compression assembly 310 includes a plurality of compression members 311 that extend from the upper frame structure 301 to the foundation 305. In the illustrated embodiment, the vertical compression assembly 310 includes at least three compression members 311. The plurality of compression members 311 are supported by compression member guides 312 that allow each compression member 311 to deflect outward from the center of the assembly, thereby increasing the moment of inertia of the composite sections, but limit the deflection and ultimately laterally constrain the compression members 311 from one another to prevent global buckling of the individual compression members 311 and therefore the composite vertical compression assembly 310. In certain embodiments, the compression member guides 312 are positioned at equidistant points between the upper frame structure 301 and the foundation 305. In the illustrated embodiment, each compression member 311 extends through the compression member guides 312. In certain embodiments, the upper and lower ends of the vertical compression assembly 310 are connected to the upper frame structure 301 and the foundation 305, respectively, with flexible connections 306 allowing rotation in any direction. In certain embodiments, the connections between the ends of the vertical compression assembly 310 and the upper frame structure 301 and the foundation 305 are rigid. As will be appreciated by one of ordinary skill in the art, any combination of fixed or flexible connections 306 may be used depending on the design requirements.

[0022] In certain embodiments, the turbine tower 102 rests on the outer ends of the protruding sections 302 which together support the turbine tower 102 against wind loads and the protruding sections 302 against loads from the tendons.

[0023] In a particular embodiment, the compression members 311 are connected to end plates on the vertical compression assembly 310 by pins perpendicular to the bending plane indicated by slots in the compression member guides 312, but may be connected in any number of ways that would be apparent to one of ordinary skill in the art.

[0024] In certain embodiments, the vertical compression assembly 310 can be a column truss. In certain embodiments, the compression members 311 are constructed with prefabricated joints and mechanical connections attached to each end of the joints so that they can be easily transported to a convenient location for final assembly of the compression members 311 prior to installation.

[0025] An umbilical for power may be installed inside one of the compression members 311, entering the compression member 311 at an insertion point 317 near the upper frame structure 301 and exiting at a bottom insertion point 318 near the foundation 305. This is advantageous as the umbilical is shielded from wave and current loads, thus reducing dynamic loads and associated fatigue damage. Alternatively, the power umbilical may be clamped to the outside of the vertical compression assemblies 110 or tendons 104.

[0026] In certain embodiments, the tendons 304 may be adjustable in accordance with embodiments of the present disclosure. The tendons 304 may include adjustable sections or adjustable connections to the upper frame structure 301.

[0027] 4 shows an isometric view of a vertical compression assembly at a compression member guide or buckle stop 512 according to an embodiment of the present disclosure. In the embodiment shown, there are three compression members 511. Each compression member 511 passes through a compression member guide 512. The compression member guide 512 includes a guide slot 520 for each compression member 511. In the embodiment shown, a guide retainer 522 is mounted to each compression member 511. When the compression members 511 are positioned within the guide slots 520, the guide retainers 522 can be mounted to the compression members 511 on both the top and bottom sides of the compression member guide 512.

[0028] In the illustrated embodiment, the guide slots 520 allow the compression member 511 to move toward an outer portion of the guide body 524 as compression increases on the compression member 511, ultimately exerting additional force on the distal end of the guide slots 520.

[0029] Those skilled in the art will appreciate that structural components between the compression members 511 to increase the composite bending strength of the column assembly, such as compression member guides 512, can be positioned at any point between the upper frame structure 101 and the foundation 105. Those skilled in the art will appreciate that it may be advantageous to position such structural components equidistant between the upper frame structure 101 and the foundation 105 to optimize buckling capacity. Those skilled in the art will also appreciate that in some cases it may be advantageous to include multiple such structural components positioned between the upper frame structure 101 and the foundation 105. In some embodiments, the structural components are made from standard structural grade steel, such as API 2H grade 50.

[0030] Compression members 511 are preloaded with tension in tendons 304. As previously described, this preloaded compression is thereby increased to an operating state by increasing the tension on tendons 304. Opposing tension and compression provides good dynamic performance similar to conventional tension leg platform installations, but with a better water depth range, including offshore wind installations.

[0031] In the illustrated embodiment, a taut tether cable is used. Taut tether cables are known to those skilled in the art, and the present disclosure is not limited to any particular type or configuration of such a tether line. In a particular embodiment, a segment of chain is used at each end of the tether.

[0032] FIG. 5 illustrates a method for installing an offshore platform according to an embodiment of the disclosure. In step 1, the upper frame structure is skidded onto an installation vessel or barge with equipment, which in the illustrated embodiment is a wind turbine, and floated to the installation site. The installation site already includes a foundation and a vertical compression assembly. Once the installation vessel or barge is positioned on the foundation, tendons are deployed from the upper frame structure to the foundation, which is positioned on the seabed at the transition site. In step 2, the tendons are used to jack the upper frame structure away from the installation vessel or barge. In the illustrated embodiment, the tendons are designed to temporarily support the upper frame structure during installation. The installation vessel or barge then departs the area leaving the upper frame structure above the transition site tethered to the foundation via the tendons. In step 3, the vertical compression assembly is lifted to connect with the upper frame structure. At this point, additional tendons can be deployed from the upper frame structure to the foundation. The tendons are then tensioned.

[0033] FIG. 6 illustrates an alternative method for installing an offshore platform according to an embodiment of the present disclosure. As shown in step 1, the installation site already includes a foundation and a vertical compression assembly. The upper frame structure is floated to the installation site on an installation vessel or barge. In the illustrated embodiment, the upper frame structure supports a wind turbine. In step 2, the foundation and vertical compression assembly are disposed below the sea surface such that the foundation is raised off the seabed, with the vertical compression assembly connected to both the upper frame structure and the foundation. Tendons are deployed from the upper frame structure to the foundation located just above the seabed at the transition site. In step 3, tension is applied to the tendons such that the vertical compression assembly is compressed. The platform is then lowered until the foundation lands on the seabed. Tension mooring anchors are pre-installed at the installation site. In step 4, tension moorings are installed, the installation vessel is removed, and the moorings are tightened. Alternatively, tension moorings can be pre-attached to the upper frame structure before the platform is lowered to the seabed. In this case, the tension moorings are initially installed with some slack and are removed once the platform is positioned on the seabed. Additional tension can be added to the tendons if necessary to offset the reduction in tension due to the weight of the turbine.

[0034] In certain embodiments, a diverless subsea connection is used to connect the vertical compression assembly 110 to the foundation 105.

[0035] In certain embodiments, the foundation 105 is secured to the seabed using piles or weights.

[0036] In certain embodiments, materials for an installation can be made from components manufactured near the installation, such as an installation in the North Sea with manufacturing in the UK. In certain embodiments, where local manufacturing capacity is limited, the installation can be made from modular components prefabricated at a low-cost location and transported to a port near the installation for assembly. With prefabricated components, the structure can be partially assembled on or near land to save installation time and labor.

[0037] Additionally, these installations can be installed with standard vessels at the transition site and the towers can be installed on land, eliminating the need for expensive heavy lift crane barges and vessels. Additionally, portions of the installation on the seabed can be pre-installed prior to installation of the turbine tower sections themselves, thereby minimizing the time required for a vessel on the sea during turbine tower installation and enhancing the ability to perform multiple turbine tower installations at once.

[0038] Thus, as the offshore wind industry seeks to provide more installations at these transitional depths, the current design is cost-competitive with fixed tower and floating solutions, and also reduces the environmental impact compared to other known solutions.

[0039] Access to the tower for maintenance personnel is provided by a ladder or walkway connection to the upper frame structure and a trellis walkway with handrails.

[0040] It is understood that modifications may be made in the above without departing from the scope of the present disclosure. In some exemplary embodiments, the elements and teachings of the various illustrative exemplary embodiments may be combined in whole or in part in some or all of the illustrative exemplary embodiments. In addition, one or more of the elements and teachings of the various illustrative exemplary embodiments may be at least partially omitted and / or at least partially combined with one or more of the other elements and teachings of the various illustrative exemplary embodiments.

[0041] For example, any spatial references such as "upper", "lower", "top", "below", "between", "bottom", "vertical", "horizontal", "angle", "upward", "downward", "side to side", "left to right", "right to left", "top to bottom", "bottom to top", "top", "bottom", "bottom up", "top down", etc. are for illustrative purposes only and are not intended to limit the particular orientation or location of the structures described above.

[0042] In some exemplary embodiments, different steps, processes, and procedures are described as appearing as separate acts, but one or more of the steps, one or more of the processes, and / or one or more of the procedures may also be performed in a different order, simultaneously and / or sequentially. In some exemplary embodiments, steps, processes, and / or procedures may be combined into one or more steps, processes, and / or procedures.

[0043] In some exemplary embodiments, one or more of the operational steps in each embodiment may be omitted. Furthermore, in some examples, some features of the present disclosure may be employed without the corresponding use of other features. Furthermore, one or more of the above-described embodiments and / or variations may be combined in whole or in part with any one or more of the other above-described embodiments and / or variations.

[0044] Although some exemplary embodiments have been described in detail above, the described embodiments are merely illustrative and not restrictive, and those skilled in the art will readily recognize that many other modifications, changes, and / or substitutions are possible in the exemplary embodiments without substantially departing from the novel teachings and advantages of the present disclosure. Therefore, all such modifications, changes, and / or substitutions are intended to be included within the scope of the present disclosure as defined in the following claims. In the claims, any means-plus-function clause is intended to encompass the structures described herein as performing the recited function, as well as structural equivalents and equivalent structures. Furthermore, it is the express intent of the applicants not to invoke the sixth paragraph of 35 U.S.C. 112 to any limitation of any of the claims herein, except where the claims expressly use the word "means" with the relevant function.

Claims

1. An offshore installation, an upper platform having a weight and including an upper surface and a lower surface; a foundation configured to be disposed on the seabed; 1. A vertical column assembly comprising: a first end fixedly connected to the upper platform; a second end connected to the foundation; a vertical column assembly comprising: a first vertical support member extending from the first end to the second end such that the vertical column assembly supports the weight of the upper platform; a plurality of tendons configured to extend from the upper platform to the foundation; a plurality of lateral supports attached to the upper platform and configured to be anchored to the seabed.

2. The offshore installation of claim 1 , wherein the vertical column assembly further comprises a second vertical support member extending from the first end of the vertical column assembly to the second end of the vertical column assembly.

3. The upper platform is center point, a first platform leg extending outwardly from said central point; a second platform leg extending outwardly from said central point; a third platform leg extending outwardly from the central point; The offshore installation of claim 1 , wherein the first platform leg, the second platform leg, and the third platform leg are all on the same plane.

4. The foundation is center point, a first base leg extending from the center point to an outer end; a second base leg extending from the center point to an outer end; a third base leg extending from the center point to an outer end; The offshore installation according to claim 3 , wherein the first foundation leg, the second foundation leg, and the third foundation leg are all on a second plane.

5. a first tendon extends from an outer end of the first platform leg to the outer end of the first foundation leg; a second tendon extends from an outer end of the second platform leg to the outer end of the second base leg; The offshore installation of claim 4 , wherein a third tendon extends from an outer end of the third platform leg to the outer end of the third foundation leg.

6. The offshore installation of claim 4 , wherein the foundation further comprises a weighted basket configured to maintain the position of the foundation on the seabed.

7. 3. The offshore installation of claim 2, wherein the vertical column assembly further comprises a third vertical support member, and the first vertical support member, the second vertical support member, and the third vertical support member are spaced equidistant from each other.

8. The offshore installation of claim 2 , wherein the first and second vertical support members comprise compression members configured to deflect outwardly from a center of the vertical column assembly.

9. The offshore installation of claim 8 , further comprising a compression member guide configured to accommodate the first and second outward deflections.

10. The offshore installation of claim 1 , wherein the vertical column assembly comprises a column truss.

11. The offshore installation of claim 1 , further comprising a wind turbine configured to be mounted to the upper surface of the upper platform.

12. A method for installing an offshore installation on a seabed, comprising the steps of: mounting an offshore installation having a first weight on an upper frame structure having a second weight and including an upper surface and a lower surface; transporting the upper frame structure and the offshore equipment to an installation site; installing a foundation and vertical column assembly on the seabed at the installation site; positioning the upper frame structure on the foundation; deploying tendons from the upper frame structure to the foundation; raising an end of the vertical column assembly into contact with the lower surface of the upper frame structure such that the vertical column assembly supports the first weight and the second weight of the upper frame structure and the offshore equipment; and applying tension to the tendon.

13. 13. The method of claim 12, further comprising lifting the upper frame structure away from the installation vessel prior to lifting the vertical column assemblies into contact with the upper frame structure.

14. attaching a plurality of lateral supports to the upper frame structure; The method of claim 12 further comprising extending the plurality of lateral supports from the upper frame structure to the seabed.

15. The method of claim 12 , wherein the vertical column assembly comprises a column truss.

16. The method of claim 12 , wherein the offshore facility comprises a wind turbine.

17. A method for installing an offshore installation on a seabed, comprising the steps of: mounting an offshore installation having a first weight on an upper frame structure having a second weight and including an upper surface and a lower surface; transporting the upper frame structure and the offshore equipment to an installation site; installing a foundation and vertical column assembly on the seabed at the installation site; positioning the upper frame structure on the foundation; raising an end of the vertical column assembly into contact with the lower surface of the upper frame structure such that the vertical column assembly supports the first weight and the second weight of the upper frame structure and the offshore equipment; elevating the foundation off the seabed using the vertical column assemblies; and deploying tendons from the upper frame structure to the foundation; lowering the foundation to the seabed via the tendons; and applying tension to the tendon.

18. attaching a plurality of lateral supports to the upper frame structure; The method of claim 17 further comprising extending the plurality of lateral supports from the upper frame structure to the seabed.

19. 20. The method of claim 18, wherein the step of attaching the plurality of lateral supports to the upper frame structure is performed before the foundation is installed at sea.

20. The method of claim 17 , wherein the vertical column assembly comprises a column truss.

21. The method of claim 17 , wherein the offshore facility comprises a wind turbine.

22. The offshore installation of claim 1 , wherein the plurality of lateral supports comprises mooring lines.

23. The offshore installation of claim 9 , wherein the compression member guide comprises a number of slots equal to the number of compression members.

24. The method of claim 14 , wherein the plurality of lateral supports comprises mooring lines, the method further comprising the step of clamping the mooring lines.

25. The method of claim 18 , wherein the plurality of lateral supports comprises mooring lines.

26. 26. The method of claim 25, further comprising tightening the mooring lines after the foundation is installed on the seabed.

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