Construction of floating wind turbine foundations

Abstract

A method of constructing a floatable foundation 100 for a wind turbine generator, the method including assembling a hull 101 for the floatable foundation at a shoreside yard (102, fig. 3). The hull h

Description

The present disclosure relates to construction of floating wind turbine foundations, including but not limited to methods of constructing floatable foundations at a shoreside location. BACKGROUND Floating wind turbine systems are under development by a number of industrial players, and provide a promising option for offshore electric power generation. Floating wind turbine systems rely on a moored, buoyant substructure base, onto which a wind turbine is mounted. Publications which may be useful to understand the field of technology include: US 2016 / 0341182 A1; US 2022 / 0348288 A1; FR 3 109 924 A1; WO 2009 / 131826 A2; WO 2021 / 148156 A1; WO 2013 / 110276 A1; WO 2020 / 167137 A1; EP4 155 538 A1; WO 2023 / 014230 A1; WO 2024 / 172662 A1; WO 2024 / 170846 A1; US 2024 / 0308630 A1; and WO 2023 / 009010 A1. Such floating wind turbine systems are in many cases not presently cost-competitive compared to bottom-fixed systems, and not yet in widespread commercial use. However it is expected that further development of floating offshore wind technology can make such systems more competitive and a viable alternative at many locations in the near future. This applies particularly to offshore sites with large water depths (typically more than 50-70 m), which may be unsuitable for bottom-fixed installations. With a projected continued increase in the need for renewable electric power generation in the future, there is a need for further improved technology in this area. The present disclosure has the objective to provide such improvements, or at least useful alternatives, to the current state of the art. SUMMARY In an example, there is provided a method of constructing a floatable foundation for a wind turbine generator, the method comprises: assembling a hull for the floatable foundation at a shoreside yard, the hull comprising a central column configured for holding a wind turbine generator tower, and three outwardly extending parts fixed to the central column and extending outwardly therefrom, each outwardly extending part comprising a column and at least one connecting structure fixed between the column and the central column; moving the hull from the shoreside yard to a floating position adjacent the shoreside yard; positioning the hull adjacent the shoreside yard with a yard floor part of the shoreside yard arranged between two of the outwardly extending parts; with the hull positioned with the yard floor part between two of the parts, mounting at least one further component onto or in the hull. In an example, there is provided a method of constructing a floatable foundation for a wind turbine generator, the method comprises: assembling a hull for the floatable foundation at a shoreside yard, the hull comprising a central column configured for holding a wind turbine generator tower, and three outwardly extending parts fixed to the central column and extending outwardly therefrom, each outwardly extending part comprising a column and at least one connecting structure fixed between the column and the central column; moving the hull to a position at least partly above a wet dock in the shoreside yard; bringing a barge into the wet dock and positioning the barge at least partly below the hull; de-ballasting the barge such as to bring the barge into engagement with the hull and lift the hull off the shoreside yard; moving the barge with the hull out of and away from the wet dock; and ballasting the barge to bring the hull into a floating position and moving the hull off the barge. In an example, there is provided a method of constructing a floatable foundation for a wind turbine generator, the method comprises: assembling a hull for the floatable foundation at a shoreside yard, the hull comprising three interconnected columns, each column having a ballast tank arranged at least partly therein and a ballast water filling interface fluidly connected to the respective ballast tank; moving the hull from the shoreside yard to a floating position adjacent or spaced from the shoreside yard; and with the hull in the floating position, filling each of the ballast tanks. In an example, there is provided a method of constructing a floatable foundation for a wind turbine generator, the method comprises: assembling a hull for the floatable foundation at a shoreside yard; moving the hull from the shoreside yard to a floating position adjacent the shoreside yard; bringing the hull into contact with a prepared foundation on a sea floor adjacent the shoreside yard such that the hull rests on the prepared foundation; and with the hull resting on the prepared foundation, mounting at least one further component onto or in the hull. The detailed description below and appended claims outline further inventive aspects and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS The above and other characteristics will become clear from the following description of illustrative, non-restrictive examples, with reference to the attached drawings, in which: Fig. 1 is a perspective view of a floatable foundation according to an example. Fig. 2 illustrates details of the floatable foundation of Fig. 1. Figs 3-8 illustrate, in top views, methods of constructing a floatable foundation for a wind turbine generator in some examples. Figs 9-15 illustrate, in top views, methods of constructing a floatable foundation for a wind turbine generator according other examples. Figs 16 and 17 illustrate perspective views of steps in methods such as those illustrated in Figs 9-15. Figs 18 and 19 illustrate top and sectional (cut) views of a floatable foundation suitable for use with methods according to some examples. Figs 20-28 illustrate, in top views, steps of methods according to various examples. Figs 29-31 illustrate top views of methods for positioning a hull adjacent a shoreside yard according to other examples. Figs 32-35 illustrate side / cut views of arrangements for positioning a hull adjacent a shoreside yard according to various examples. DETAILED DESCRIPTION Fig. 1 illustrates an example of a floatable (i.e. capable of floating or buoyant) foundation 100 for a wind turbine generator. The foundation 100 provides a base for a wind turbine generator tower 16, onto which a wind turbine generator (not shown) can be mounted. Fig. 2 illustrates details of the foundation 100 according to this example. The foundation comprises a central column 10 having an upper connection part 11 and a lower connection part 12. Three outer columns 20,21,22 are disposed about the central column 10, and fixed to the central column 10 by means of three horizontally extending lower connecting structures 30,31,32 and three horizontally extending upper connecting structures 40,41,42. In this example, the upper connecting structures 40,41,42 are beams (here illustrated as box beams). Any suitable connection member may, however, be used for this purpose, such as truss structures, tubular beams, or other types. In this example, the lower connecting structures 30,31,32 are pontoons. Any suitable connection member may, however, be used for this purpose, such as truss structures, box beams, tubular beams, or other types. In this example, each of the columns 20,21,22 has the form of a polygonal prism comprising a plurality of rectangular side wall panels, which may for example be steel plates. The columns 20,21,22 may be in the form of right prisms having a hexagonal cross-section in the horizontal plane, as illustrated in this example. Each column 20,21,22 may comprise one rectangular side wall panel onto which one lower connecting structure 30,31,32 and one upper connecting structure 40,41,42 are fixed, vertically spaced from each other. Alternatively, the columns 20,21,22 may have a different form, for example a cylindrical form or a polygonal form of a different kind, such as a prism having more than six or less than six side wall panels and / or a prism in the form of an irregular polygon. Each lower connecting structure 30,31,32 is fixed to and extend between the lower connection part 12 and a respective one of the three outer columns 20,21,22, and each upper connecting structure 40,41,42 is fixed to and extend between the upper connection part 11 and a respective one of the three outer columns 20,21,22. The columns 20,21,22 and the upper and lower connecting structures 30,31,32,40,41,42 are arranged such as to provide a generally Y-shaped foundation 100 (when viewed from above or below), wherein each column 20,21,22 and the associated connecting structures 30,31,32,40,41,42 forming one outwardly extending part 50,51,52 (or “leg”) of the foundation 100. The parts 50,51,52 may advantageously be offset by 120 degrees or about 120 degrees about the central column 10. The tower 16 may be fixed at the central column 10, for example, via a flange 15 (see Fig. 1). The tower 16 may be fixed to the central column 10 by bolting, welding or by other means. Now referring to Figs 3-8, methods of constructing a floatable foundation 100 for a wind turbine generator will be described. The foundation 100 may be a foundation 100 as illustrated in Figs 1-2 and described above, or it may be another foundation having a central column 10 configured for holding a wind turbine generator tower 16 and three outwardly extending parts 50,51,52 fixed to the central column 10 and having a column 20,21,22 and at least one connecting structure 20,21,22,30,31,32 fixed between the column 20,21,22 and the central column 10. (See, for example, the publications referenced under BACKGROUND above.) The method comprises assembling a hull 101 for the floatable foundation 100 at a shoreside yard 102, i.e. at a land-based location. Upon at least partial completion, to a construction stage wherein the hull 101 is self-buoyant, the hull 101 is moved from the shoreside yard 102 to a floating position. The hull 101 may advantageously be arranged in the floating position at a location which is directly adjacent the location at the shoreside yard 102 at which the hull 101 was assembled, but the hull 101 may optionally be moved (e.g., towed) to a different location adjacent the shoreside yard 102. The load-out of the hull 101 from the shoreside yard 102 may, for example, be done by means of a barge, a crane, a dry dock or by other means. The hull 101 is subsequently positioned with a yard floor part 103 of the shoreside yard 102 arranged between two of the outwardly extending parts 50,51,52. With the hull 101 in this position, at least one further component is mounted onto or in the hull 102. Figs 3 and 4 illustrate an example of the hull 101 arranged adjacent the shoreside yard 102 and where the shoreside yard 102 has a protrusion extending horizontally outwardly, for example from a main fabrication area 104 at the shoreside yard 102, and the yard floor part 103 is arranged on the protrusion. The protrusion is arranged with dimensions which permit the hull 101 to be positioned with two of the outwardly extending parts 50,51,52 spanning the protrusion. In one example, illustrated in Figs 5 and 6, the protrusion comprises a narrowing front part 105 configured to be positioned between a pair of outwardly extending parts 50,51,52 of the hull 101. The narrowing front part 105 may, for example, have a tapering profile defined at least partly by two sides 105’, 105” arranged at an angle that generally correspond to the angle between the respective outwardly extending parts 50,51,52, such as 120 degrees or around 120 degrees, or be equal to the angle between the respective outwardly extending parts 50,51,52 ±30 degrees. (I.e. at an angle that differs from the angle between the respective outwardly extending parts 50,51,52 by 30 degrees at most.) The angle between the sides 105’ and 105” may be between 90 and 120 degrees. In another example, illustrated in Fig. 7, the shoreside yard 102 comprises an open wet dock 106 and the method comprises positioning one outwardly extending part 50,51,52 in the open wet dock 106. In this example, the yard floor part 103 comprises two yard floor parts 103’,103” which may be arranged between different pairs of the outwardly extending parts 50,51,52. The two yard floor parts 103’, 103” are arranged at opposite sides of the open wet dock 106. With the hull 101 positioned with the yard floor part 103 arranged between two of the outwardly extending parts 50,51,52, access to the hull 101 for further construction work, installation work, or other operations may be simplified. Particularly, access to the central column 10 may be improved in that the yard floor part 103 can be positioned closer to the central column 10. This can allow easier access to the hull 101, easier transport of parts or equipment onto the hull 101, etc. The further component to be installed may, for example, be installed onto the central column 10. The further component may be a wind turbine component, for example the wind turbine generator tower 16, a part of the wind turbine generator tower 16 (for example if the tower 16 is installed in sections), a wind turbine generator nacelle to be positioned on the tower 16, or a wind turbine generator blade (or blades) to be mounted on the nacelle. Optionally, or additionally, the further component may be a hull structural part. For example, the component may be at least one further connecting structure 20,21,22,30,31,32 to be fixed between a respective column 20,21,22 and the central column 10. For example, the hull 101 may be prepared onshore having the central column 10, the outer columns 20,21,22, and the lower connecting structures 30,31,32 (in this example pontoons), while the upper connecting structures 40,41,42 (in this example beams) are installed when the hull 101 is positioned in the floating position. Optionally, or additionally, the further component may be one or more of: pipework to be installed internally in the hull 101, cabling and / or electric junction boxes to be installed internally in the hull 101 or in the tower 16, internal and / or external surface treatment to be applied on the hull 101, one or more pumps to be installed in the hull 101, and / or gangways, handrails or other structure to be installed internally or externally in or on the hull 101. Advantageously, the further component(s) can be transported onto the hull 101 via the yard floor part 103. The further component(s) may, for example, be transported onto the hull 101 via temporary gangways, driveways, or be lifted onto the hull 101 from the yard floor part 103. Illustrated in Fig. 6, but equally applicable also to the other examples, a crane 110 may be positioned at least partly on the yard floor part 103. The method may comprise lifting a further components onto the hull 101 by means of the crane 110 positioned at least partly on the yard floor part 103. The crane 110 in this example is a ring crane 110, which generally can provide advantages of very high lifting capacities. The crane 110 may, however, alternatively be of another type, such as a crawler crane, a tower crane or other types. The crane 110 may be positioned with a stationary part thereof, such as a base of the crane 110, supported on the yard floor part 103 and with the stationary part of the crane 110 located at least partly between the outwardly extending parts 50,51,52 of the hull 101, for example between two columns 20,21,22 positioned at different sides of the yard floor part 103. By positioning the crane 110 at least partly on the yard floor part 103, the crane 110 can be placed closer to the central column 10, providing advantages in relation to lifting of heavy components (such as wind turbine components like tower sections or the nacelle) onto the central column 10. This can permit the use of a lower-capacity crane 110 than what would otherwise be required. In the example illustrated in Fig. 7, the crane 110 may, for example, be positioned at one yard floor part 103’, while the other yard floor part 103” remains available for other operations, such as transport of items to / from the hull 101. Illustrated in Fig. 7, but equally applicable to the other examples, the method may include assembling the hull 101 at a main fabrication area 104 of the shoreside yard 102 which is spaced from the yard floor part 103. This can permit work operations relating to, for example, assembly of one hull 101’ to take place concurrently with work operations on another, at least partly assembled hull 101” arranged adjacent the yard floor part 103. Assembling the hull 101, may, for example, involve providing the central column 10, the three outwardly extending parts 50,51,52 and the columns 20,21,22 as individual parts at the main fabrication area 104 and fixing (e.g. by welding) the central column 10, the three outwardly extending parts 50,51,52 and the columns 20,21,22 together at the main fabrication area 104. The work operations at the main fabrication area 104 may include preparing a floatable hull 10T, i.e. such that the hull 101’ becomes ready for moving to the floating position. At the same time, work operations on a previously assembled hull 101” located arranged adjacent the yard floor part 103 can be carried out, as illustrated in Fig. 7. Illustrated in Fig. 8, the shoreside yard 102 may comprise two open wet docks 106’, 106”, where each of the open wet docks 106’, 106” has a yard floor part 103 associated with it. In this example, the crane 110 may be arranged between the two open wet docks 106’, 106” and the crane 110 may be shared between the two for the purpose of mounting further component(s) onto or in the hulls 101 ’, 101 ”. The method may optionally comprise ballasting the hull 101 and resting (“grounding”) the hull 101 on a sea floor adjacent the shoreside yard 102 when the hull 101 is positioned adjacent the yard floor part 103. (As for example in the positions illustrated in Fig. 3, 4, 5, 7 or 8.) Mounting at least one further component onto or in the hull 101 may then be carried out with the hull 101 resting on the sea floor adjacent the shoreside yard 102. Advantageously, this can permit more efficient installation operations in that the hull 101 remains stationary relative to the yard floor part 103. In any of the examples or embodiments described or claimed herein, the yard floor part 103 can be horizontally aligned and / or flush with the rest of the shoreside yard 102, including the main fabrication area 104. Referring now to Figs 9-17, a method of constructing a floatable foundation 100 for a wind turbine generator according to another example will be described. Shown in Fig. 9, a hull 101 for the floatable foundation 100 is assembled at a shoreside yard 102, where the hull 101 comprises a central column 10 configured for holding a wind turbine generator tower 16 and three outwardly extending parts 50,51,52 fixed to the central column 10 and extending outwardly therefrom, each outwardly extending part 50,51,52 comprising a column 20,21,22 and at least one connecting structure 20,21,22,30,31,32 fixed between the column 20,21,22 and the central column 10. (See Figs 1 and 2 and the associated description above for an example of a hull 101 suitable for use with the method.) The shoreside yard 102 has a main fabrication area 104 and a wet dock 106. Assembling the hull 101 is carried out at the main fabrication area 104, which is spaced from the wet dock 106. Assembling the hull 101 may, for example, comprise providing the central column 10, the three outwardly extending parts 50,51,52 and the columns 20,21,22 as individual parts at the main fabrication area 104 and fixing (e.g. by welding) the central column 10, the three outwardly extending parts 50,51,52 and the columns 20,21,22 together at the main fabrication area 104. The work operations at the main fabrication area 104 may include preparing a floatable hull 101, i.e. such that the hull 101 is ready for moving to a floating position. For load-out, i.e. to bring the hull 101 off the shoreside yard 102 and into a floating position, the hull 101 is moved to a position at least partly above the wet dock 106. This is illustrated in Figs 10-12, 16 and 17. Moving the hull 101 to the position at least partly above the wet dock 106 may be carried out using at least three vehicles 121 (see Figs 16 and 17). In this example, the vehicles 121 are self-propelled modular transporters (SMTPs). Alternatively, the hull 101 can be moved by other means, such as skidding sledges. Each of the vehicles 121 or skidding sledges can be positioned below a respective outwardly extending part 50,51,52 of the hull 101. The vehicles 121 or skidding sledges may, for example, engage the hull 101 at an underside of the columns 20,21,22 and / or at an underside of the lower connecting structures 30,31,32 (which in this example are pontoons). The hull 101 may then be lifted (such as jacked up) to lift it off the floor of the main fabrication area 104 (typically off supports on which the hull 101 is resting at the main fabrication area 104). With the hull 101 lifted and carried by the vehicles 121 or skidding sledges, it can be moved towards the wet dock 106, as illustrated. Advantageously, two of the vehicles 121 or skidding sledges may be moved to a position adjacent the wet dock 106 at opposite sides thereof. The hull 101 is advantageously moved to the position above the wet dock 106 such that the central column 10 is located entirely above the wet dock 106. In the position where the hull 101 located partly above the wet dock 106 (see Figs 12 and 17), it can remain supported at the shoreside yard 102 via the vehicles 121 or skidding sledges. Optionally, the hull 101 can be lowered and rested on supports arranged adjacent the wet dock 106, for example such that the vehicles 121 or skidding sledges can be moved away and utilised elsewhere. A barge 120 is brought into the wet dock 106 and positioned at least partly below the hull 101. The barge 120 can be brought into the wet dock 106 after the hull 101 has been located partly above the wet dock 106 (as illustrated in Figs 12 and 13), or the barge 120 can be brought into the wet dock 106 prior to the hull 101 being moved above the wet dock 106 (as illustrated in Figs 16 and 17). With the hull 101 located partly above the wet dock 106 and the barge 120 located in the wet dock 106 (as illustrated in Figs 13 and 17), the barge 120 is de-ballasted such as to bring the barge 120 into engagement with the hull 101 and lift the hull 101 off the shoreside yard 102. This may include engaging the central column 10 from below with the barge 120, such as a deck of the barge 120, and / or engaging a part of each outwardly extending part 50,51,52 from below with the barge 120. The barge 120, with the hull 101 supported thereon, is then moved out of and away from the wet dock 106, as illustrated in Fig. 14. The barge 120 may subsequently be ballasted and at least partially submerged (for example such that a deck of the barge 120 becomes submerged) such as to bring the hull 101 into a floating position. The hull 101 may then be moved off and away from the barge 120 and into a free floating position, as illustrated in Fig. 15. The hull 101 may then be transported away or moored for further construction work, for example by moving the hull 101 into a position such as those illustrated in Fig. 3, 4, 5, 7 or 8. Advantageously, load-out of a hull 101 according to methods described here avoids the need for the hull 101 to be transported (e.g. by driving or skidding) from the shoreside yard 102 onto a floating barge or the like. The vehicles 121 or skidding sledges may remain on the shoreside yard 102 at all times. This can reduce the complexity of for example load-out and / or grillage / seafastening operations. In any of the examples or embodiments described or claimed herein, the method may comprise installing, with the hull 101 located at the shoreside yard 102, at least one of: a part of the wind turbine generator tower 16 (for example if the tower 16 is installed in sections), the entire wind turbine generator tower 16, a wind turbine generator nacelle on the tower 16, or a wind turbine generator blade (or blades) on the nacelle. For example, the load-out methods described in relation to Figs 9-17 may advantageously permit one or more of these components to be installed while the hull 101 is located land-based at the shoreside yard 102, and prior to load-out. This can ease the installation and construction process. According to examples and embodiments described herein, efficient construction of a floatable foundation 100 for a wind turbine generator can be achieved. The methods can advantageously realise efficient utilisation of yard space and efficient work processes for manufacturing of parts, assembly, load-out, equipment installation, completion, and / or other work processes associated with the construction of such foundations 100. The following numbered clauses outline further inventive examples and embodiments. A1. A method of constructing a floatable foundation (100) for a wind turbine generator, the method comprises: assembling a hull (101) for the floatable foundation (100) at a shoreside yard (102), the hull (101) comprising a central column (10) configured for holding a wind turbine generator tower (16), and three outwardly extending parts (50,51,52) fixed to the central column (10) and extending outwardly therefrom, each outwardly extending part (50,51,52) comprising a column (20,21,22) and at least one connecting structure (20,21,22,30,31,32) fixed between the column (20,21,22) and the central column (10); moving the hull (101) from the shoreside yard (102) to a floating position adjacent the shoreside yard (102); positioning the hull (101) adjacent the shoreside yard (102) with a yard floor part (103) of the shoreside yard (102) arranged between two of the outwardly extending parts (50,51,52); with the hull (101) positioned with the yard floor part (103) between two of the parts (50,51,52), mounting at least one further component onto or in the hull (101). A2.The method of any preceding clause, wherein the further component is installed onto the central column (10). A3. The method of any preceding clause, wherein the further component is a wind turbine component, for example wherein the wind turbine component is the wind turbine generator tower (16), a part of the wind turbine generator tower (16), a wind turbine generator nacelle or a wind turbine generator blade. A4.The method of any preceding clause, wherein the further component is a hull structural part, for example wherein the hull structural part is at least one further connecting structure (20,21,22,30,31,32), such as a beam structure (40,41,42), and the method comprises fixing the at least one further connecting structure (20,21,22,30,31,32) between the column (20,21,22) and the central column (10), such as between an upper part of the column (20,21,22) and an upper connection part (11) of the central column (10). A5.The method of any preceding clause, wherein the further component is at least one of: internally installed pipework, internally installed cabling and / or electric junction boxes, internally and / or externally applied surface treatment, one or more internal pumps, or internally or externally installed gangways and / or handrails. A6.The method of any preceding clause comprising transporting the further component onto the hull (101) via the yard floor part (103). A7.The method of any preceding clause comprising lifting the further component onto the hull (101) by means of a crane positioned at least partly on the yard floor part (103), for example wherein the crane is a ring crane (110), optionally wherein a stationary part of the crane (110) is positioned at least partly between two of the parts (50,51,52) while supported on the yard floor part (103), such as at least partly between two columns (20,21,22). A8.The method of any preceding clause, wherein the yard floor part (103) is arranged on a protrusion extending horizontally outwardly from a main fabrication area (104) at the shoreside yard (102). A9.The method of any preceding clause, wherein the step of assembling the hull (101) for the floatable foundation (100) at the shoreside yard (102) comprises assembling the hull (101) at a main fabrication area (104) and spaced from the yard floor part (103). A10. The method of any preceding clause, wherein the step of assembling the hull (101) comprises preparing a floatable hull (101). A11. The method of any preceding clause, wherein the step of assembling the hull (101) comprises providing the central column (10), the three outwardly extending parts (50,51,52) and the columns (20,21,22) as individual parts at the main fabrication area (104) and fixing, such as welding, the central column (10), the three outwardly extending parts (50,51,52) and the columns (20,21,22) together at the main fabrication area (104). A12. The method of any preceding clause, wherein the protrusion comprises a narrowing front part (105) configured to be positioned between a pair of outwardly extending parts (50,51,52) of the hull (101). A13. The method of any preceding clause, wherein the narrowing front part (105) has a tapering profile defined at least partly by two sides (105’,105”), the two sides (105’, 105”) being arranged with an angle therebetween which is equal or substantially equal to an angle between the pair of extending parts (50,51,52), such as 120 degrees or around 120 degrees, and / or equal to an angle between the pair of extending parts (50,51,52) ±30 degrees, and / or equal to an angle of between 90 and 120 degrees. A14. The method of any preceding clause, wherein the shoreside yard (102) comprises an open wet dock (106) and the method comprises positioning one outwardly extending part (50,51,52) in the open wet dock (106). A15. The method of any preceding clause, wherein the yard floor part (103) is arranged at opposite sides of the open wet dock (106) and comprises a first yard floor part (103’) arranged between a first and a second of the parts (50,51,52) and a second yard floor part (103”) arranged between the first and a third of the parts (50,51,52). A16. The method of any preceding clause, comprising ballasting the hull (101) and resting the hull (101) on a sea floor adjacent the shoreside yard (102) with the hull (101) positioned with the yard floor part (103) between two of the parts (50,51,52), and wherein the step of mounting at least one further component onto or in the hull (101) is carried out with the hull (101) resting on the sea floor adjacent the shoreside yard (102). B1. A method of constructing a floatable foundation (100) for a wind turbine generator, the method comprises: assembling a hull (101) for the floatable foundation (100) at a shoreside yard (102), the hull (101) comprising a central column (10) configured for holding a wind turbine generator tower (16), and three outwardly extending parts (50,51,52) fixed to the central column (10) and extending outwardly therefrom, each outwardly extending part (50,51,52) comprising a column (20,21,22) and at least one connecting structure (20,21,22,30,31,32) fixed between the column (20,21,22) and the central column (10); moving the hull (101) to a position at least partly above a wet dock (106) in the shoreside yard (102); bringing a barge (120) into the wet dock (106) and positioning the barge (120) at least partly below the hull (101); de-ballasting the barge (120) such as to bring the barge (120) into engagement with the hull (101) and lift the hull (101) off the shoreside yard (102); moving the barge (120) with the hull (101) out of and away from the wet dock (106); and ballasting the barge (120) to bring the hull (101) into a floating position and moving the hull (101) off the barge (120). B2.The method of any preceding clause, wherein the step of assembling the hull (101) is carried out at a main fabrication area (104) at the shoreside yard (102) which is spaced from the wet dock (106). B3.The method of any preceding clause, wherein the step of assembling the hull (101) comprises preparing a floatable hull (101). B4.The method of any preceding clause, wherein the step of assembling the hull (101) comprises providing the central column (10), the three outwardly extending parts (50,51,52) and the columns (20,21,22) as individual parts at the main fabrication area (104) and fixing, such as welding, the central column (10), the three outwardly extending parts (50,51,52) and the columns (20,21,22) together at the main fabrication area (104). B5.The method of any preceding clause, wherein the step of moving the hull (101) to the position at least partly above the wet dock (106) comprises moving the central column (10) to a position entirely above the wet dock (106). B6.The method of any preceding clause, wherein the step of moving the hull (101) to the position at least partly above the wet dock (106) is carried out using at least three vehicles (121) or skidding sledges, each of the three vehicles (121) or skidding sledges being positioned below a respective outwardly extending part (50,51,52) of the hull (101). B7.The method of any preceding clause, comprising bringing two of the at least three vehicles (121) or skidding sledges adjacent the wet dock (106) at opposite sides thereof. B8.The method of any preceding clause, wherein the at least three vehicles (121) or skidding sledges are self-propelled modular transporters (SMTPs). B9.The method of any preceding clause, wherein bringing the barge (120) into engagement with the hull (101) comprises engaging the central column (10) from below with the barge (120), and / or engaging a part of each outwardly extending part (50,51,52) from below with the barge (120). Referring now to Figs 18-28, which illustrates various methods for ballasting a floatable foundation 100 for a wind turbine generator. Ballasting floatable foundations 100 such as those described above may require several thousand litres of ballast water and a ballasting operation may require high-capacity pumps and take several hours to complete. Efficient ballasting is therefore desirable for efficient construction of floating wind turbine foundations, hereunder the completion of the floatable foundation 100 for deployment at the operating site. A method of constructing a floatable foundation 100 for a wind turbine generator may comprise assembling a hull 101 for the floatable foundation 100 at a shoreside yard 102. The assembling of the hull 101 may, for example, be carried out according to any of the examples described above. The hull 101 may comprise three interconnected columns 20,21,22, where each column 20,21,22 has a ballast tank 140-142 arranged at least partly therein. Fig. 19 illustrates a sectional view of the hull 101, illustrating a horizontal cut at a lower level of the hull 101. As can be seen, ballast tanks 140-142 are arranged in the lower parts of the columns 20,21,22 and also extending partly into the lower connecting structures (here: pontoons) 30-32. Each column 20-22 further has a ballast water filling interface 143,144,145 fluidly connected to the respective ballast tank 140-142. The ballast water filling interfaces 143-145 are illustrated in Fig. 18, which shows a top view of the hull 101. In this example, the ballast water filling interfaces 143-145 are located at a top of the respective column 20-22. Alternatively, the ballast water filling interfaces 143-145 may be arranged at different locations, such as at a side face of the column 20-22 or inside respective upper connecting structures 40,41,42 fixed to the columns 20-22 (for example such upper connecting structures shown in Figs 1 and 2). After assembling, the hull 101 may be moved from the shoreside yard 102 to a floating position adjacent or spaced from the shoreside yard 102, and positioned at the floating position, for example similarly as described above. With the hull 101 in the floating position, for example positioned adjacent the shoreside yard 102, each of the ballast tanks 140-142 may be filled via the ballast water filling interfaces 143-145. The hull 101 may additionally comprise a ballast tank 149 in a central part of the hull 101 and a corresponding ballast water filling interface 148, similarly as described above. Illustrated in Fig. 20, the method may comprise laying out a temporary ballast water filling line 151-153 from a first column 21 of the three columns 20-22 to each ballast water filling interface 143-145, and filling each of the ballast tanks 140-142 via the temporary ballast water filling lines 151-153. A temporary ballast water filling line 159 may optionally also be provided to the ballast water filling interface 148. The temporary ballast water filling lines 151-153 may subsequently, i.e. after filling, be removed from the hull 101. Providing the temporary ballast water filling lines 151-153 allows ballast water to be filled to each ballast tank 140-142 from, or via, one of the columns 20-22, in the illustrated examples column 21. This column may be one which is positioned closest to the shoreside yard 102, for easier access to the ballast water filling lines 151-153. Advantageously, the laying out of the temporary ballast water filling lines 151-153 can be carried out with the hull 101 located at the shoreside yard 102 and prior to moving the hull 101 to the floating position. Filling each ballast tank 140-142 from the shoreside yard 102 may be carried out by means of a pump 155 located at the shoreside yard 102. Access from the shoreside yard 102 may be provided to each of the temporary ballast water filling lines 151-153, for example by a temporary ballast water supply line 150 extending from the shoreside yard 102 to the column 21. There may be several temporary ballast water supply lines 150, for example one for each ballast water filling line 151-153. Alternatively, a manifold may be provided on the column 21, whereby the temporary ballast water supply line 150 serves more than one temporary ballast water filling line 151-153. Illustrated in Figs 21 and 22, the ballast water may be provided via a treatment plant 157 at the shoreside yard 102. The treatment plant 157 may for example provide additives, such as a biocide, into the ballast water. In some examples, the treatment plant 157 may simply be a handling plant, for example comprising only the pump 155 and / or relevant piping and valve arrangements. The ballast water may be fresh water, for example from a shoreside supply, or it may be sea water. A sea water suction line 156 (see Fig. 22) may be provided for this purpose. In other examples, the ballast water may be provided from a barge 160, illustrated in Fig. 23. The barge 160 may have a pump 155, a sea water suction line 156 and / or a treatment plant 157 arranged thereon or associated therewith, similarly as described above. Alternatively, or additionally, the barge 160 may have storage tank(s) for ballast water. Optionally, as illustrated in Fig. 24, the ballast water may be provided from a barge 160 to the treatment (or handling) plant 157. A connection line 154 may be provided for this purpose. The method may comprise filling ballast in two steps. Particularly, the hull 101 may first be positioned in a floating position adjacent the shoreside yard 102 and, in a first ballasting step, the ballast tanks 140-142 may be partially filled. Then, the hull 101 may be moved away to a floating position which is spaced from the shoreside yard 102, for example farther out from shore, to a location having larger water depth. In this manner, the hull 101 may be fully ballasted, i.e. brought to the operational draft, at the second position having larger water depth. This may be beneficial if the position adjacent the shoreside yard 102 does not have sufficient water depth to accommodate for full ballasting of the hull 101 at that location. The hull 101 may optionally be ballasted such as to rest (“ground”) the hull 101 on a sea floor adjacent the shoreside yard 102 in the first ballasting step. This may, for example, be in a position such as illustrated in Fig. 3, 4, 5, 7 or 8 and described above, and / or be carried out as described below in relation to Figs 29-35. At least one further component may then be mounted onto or in the hull 101 with the hull 101 resting on the sea floor adjacent the shoreside yard 102, similarly as described above. The hull 101 may thereafter be de-ballasted to bring the hull 101 out of contact with the sea floor adjacent the shoreside yard 102, and moved away from the shoreside yard 102. The hull 101 may be moved to a second location for further ballasting and bring the hull 101 to an operational draft, or for example to a different location for further work which may be necessary. Figs 25 and 26 illustrate de-ballasting the hull 101 at the location adjacent the shoreside yard 102. This may be done in a reverse process compared to that described above, for example by pumping ballast water to the shoreside yard 102, or to a barge 160. The shoreside yard 102 (for example in conjunction with the treatment plant 157) or barge 160 may have a tank to receive ballast water for this purpose. Alternatively, ballast water may be pumped overboard and to sea from the ballast tanks 140-142. Since the required de-ballasting may only be such as to bring the hull 101 off the sea floor and into a floating state, the amount of ballast water needing to be removed for this purpose may be limited. The de-ballasting may be done via the temporary ballast water filling lines 151-153 and / or the temporary ballast water supply line(s) 150, for example by use of submergible pumps lowered into the ballast tanks 140-142. Fig. 27 illustrates adding ballast water to the hull 101 from a barge 160 at a location which is spaced from the shoreside yard 102, for example a location at which the hull 101 can be ballasted to its full operational draft. The ballast water may, for example, be sourced from the sea via a sea water suction line 156. Alternatively, as illustrated in Fig. 28, ballast water may be provided from the shoreside yard 102 (or another shoreside location). This may, for example, be advantageous if fresh water or pre-treated fresh water is to be used as ballast water. A connection line 154 may be used for this purpose. A barge 160 or other floating support member may be located adjacent the hull 101 and used for this operation, or the connection line 154 may be connected directly to the hull 101. Advantageously, the method may comprise adding a biocide to each ballast tank 140-142 with the hull 101 located at the shoreside yard 102 and prior to moving the hull 101 to the floating position. The following numbered clauses outline further inventive examples and embodiments. C1 .A method of constructing a floatable foundation (100) for a wind turbine generator, the method comprises: assembling a hull (101) for the floatable foundation (100) at a shoreside yard (102), the hull (101) comprising three interconnected columns (20,21,22), each column (20,21,22) having a ballast tank (140-142) arranged at least partly therein and a ballast water filling interface (143-145) fluidly connected to the respective ballast tank (140-142); moving the hull (101) from the shoreside yard (102) to a floating position adjacent or spaced from the shoreside yard (102); and with the hull (101) in the floating position, filling each of the ballast tanks (140-142). C2.The method according to any preceding clause, wherein the ballast water filling interface (143-145) is located at each respective column (20,21,22) and the method further comprises: laying out a temporary ballast water filling line (151-153) from a first column (21) of the three columns (20-22) to each ballast water filling interface (143-145); filling each of the ballast tanks (140-142) via the temporary ballast water filling lines (151-153); and removing the temporary ballast water filling lines (151-153). C3.The method according to any preceding clause, wherein the step of laying out the temporary ballast water filling lines (151-153) is carried out with the hull (101) located at the shoreside yard (102) and prior to moving the hull (101) to the floating position. C4.The method according to any preceding clause, further comprising laying out at least one temporary ballast water supply line (150) to the first column (21) and connecting the temporary ballast water supply line (150) to the at least one ballast water filling lines (151-153). C5.The method according to any preceding clause, comprising filling each ballast tank (140-142) from the shoreside yard (102) or from a barge (160). C6.The method according to any preceding clause, comprising filling each ballast tank (140-142) from the shoreside yard (102) by means of a pump (155) located at the shoreside yard (102), or filling each ballast tank (140-142) from a barge (160) by means of a pump (155) located at the barge (160). C7.The method according to any preceding clause, the floating position being a first floating position adjacent the shoreside yard (102), and the method comprising: in a first ballasting step, partially filling each of the ballast tanks (140-142) with the hull (101) located in the first floating position, moving the hull (101) away from the first floating position to a second floating position spaced from the shoreside yard (102), the second floating position being at a location having larger water depth than the first floating position, and in a second ballasting step, filling each of the ballast tanks (140-142) with the hull (101) located in the second floating position. C8.The method according to any preceding clause, comprising ballasting, for example in the in the first ballasting step, the hull (101) to bring the hull (101) into engagement with the sea floor adjacent the shoreside yard (102). C9.The method according to any preceding clause, comprising mounting at least one further component onto or in the hull (101) with the hull (101) resting on the sea floor adjacent the shoreside yard (102). C10. The method according to any preceding clause, comprising, for example prior to moving the hull (101) away from the first floating position, de-ballasting the hull (101) to bring the hull (101) out of contact with the sea floor adjacent the shoreside yard (102). C11. The method according to any preceding clause, wherein the first ballasting step comprises filling each ballast tank (140-142) from the shoreside yard (102) by means of a pump (155) located at the shoreside yard (102) and / or the second ballasting step comprises filling the ballast tanks (140-142) with ballast water from a shoreside location, from a barge (160), and / or from sea. C12. The method according to any preceding clause, wherein the hull (101) comprises: a central column (10) configured for holding a wind turbine generator tower (16), and three outwardly extending parts (50,51,52) fixed to the central column (10) and extending outwardly therefrom, each outwardly extending part (50,51,52) comprising a respective column (20,21,22) and at least one connecting structure (20,21,22,30,31,32) fixed between the column (20,21,22) and the central column (10). C13. The method according to any preceding clause, comprising adding a biocide to each ballast tank (140-142) with the hull (101) located at the shoreside yard (102) and prior to moving the hull (101) to the floating position. The method of any of clauses C1-C13 may optionally be carried out in conjunction or combination with a method according to any of clauses A1-A16 and / or B1-B9. Illustrated in relation to Figs 29-35, there is also provided methods of methods of constructing a floatable foundation 100 for a wind turbine generator which comprise assembling a hull 101 for the floatable foundation 100 at a shoreside yard 102, moving the hull 101 from the shoreside yard 102 to a floating position adjacent the shoreside yard 102, and bringing the hull 101 into contact with a prepared foundation 170 on a sea floor adjacent the shoreside yard 102 such that the hull 101 rests on the prepared foundation 170. With the hull 101 resting on the prepared foundation 170, at least one further component can be mounted onto or in the hull 101. The further component may be a wind turbine component, for example a wind turbine generator tower 16, a part of the wind turbine generator tower 16, a wind turbine generator nacelle or a wind turbine generator blade. Alternatively, or additionally, the further component is a hull structural part, for example at least one further connecting structure 20,21,22,30,31,32, such as a beam structure 40,41,42. The method may comprise fixing the at least one further connecting structure 20,21,22,30,31,32 between the column 20,21,22 and the central column 10, such as between an upper part of the column 20,21,22 and an upper connection part 11 of the central column 10, with the hull 101 resting on the prepared foundation 170. The further component may optionally be at least one of: internally installed pipework, internally installed cabling and / or electric junction boxes, internally and / or externally applied surface treatment, one or more internal pumps, or internally or externally installed gangways and / or handrails. The step of assembling the hull 101 may comprise providing the central column 10, the three outwardly extending parts 50,51,52 and the columns 20,21,22 as individual parts at the shoreside yard 102 and fixing, such as welding, the central column 10, the three outwardly extending parts 50,51,52 and the columns 20,21,22 together at the shoreside yard 102. The methods described here in relation to Figs 29-35 may be used independently or together with any one or any combination of the methods described above. As such, the hull 101 may comprise a central column 10 configured for holding a wind turbine generator tower 16 and three outwardly extending parts 50,51,52 fixed to the central column 10 and extending outwardly therefrom, similarly as described above. Each outwardly extending part 50,51,52 may have a column 20,21,22 and at least one connecting structure 20,21,22,30,31,32 fixed between the column 20,21,22 and the central column 10. The method may comprise installing the further component onto the central column 10. The step of bringing the hull 101 into contact with the prepared foundation 170 may comprise ballasting the hull 101, for example by filling a plurality of ballast tanks 140-142 in the hull 101 if the hull 101 is a hull such as that described above (see e.g. Fig. 19 and the associated description). Subsequent to mounting the at least one further component onto or in the hull 101, the hull 101 may be de-ballasted, for example by emptying or partially emptying the plurality of ballast tanks 140-142, to move it off the foundation 170. Similarly as described above, inter alia in relation to Fig. 7, the shoreside yard 102 may comprise an open wet dock 106 having at least a part of the prepared foundation 170 arranged therein, and the method may comprise positioning one outwardly extending part 50,51,52 of a hull 101 in the open wet dock 106. Fig. 29 illustrates a top view of the hull 101 having been positioned adjacent the shoreside yard 102. The hull 101 can be positioned against fenders 174 or other support structure at the shoreside yard 102. The fenders 174 may provide dampening and optionally also guiding or positioning support of the hull 101 in order to maintain the hull 101 in the desired position relative to the shoreside yard 102. The hull 101 may, for example, be moved to and aligned at a target position, illustratively indicated in Fig. 29 with a dashed line. Illustrated in Fig. 30, the hull 101 can be positioned above the prepared foundation 170 by means of winches 176 arranged on the shoreside yard 102. The winches 176 may act, via elongate pulling members such as wire ropes 177, to adjust the position of the hull 101 and move the hull 101 into the desired position. The winches 176 may be operated in conjunction with tugboats for moving and positioning the hull 101. Illustrated in Fig. 31, the shoreside yard 102 may comprise a yard floor part 103 which is positioned between two outwardly extending parts 50,51,52 of the hull 101, similarly as described above in relation to Figs 3-8. Fig. 32 illustrates a side view of the hull 101 being positioned adjacent the yard floor part 102, for example in the manner illustrated in Fig. 30. The prepared foundation 170 may comprises a base 171, for example a compacted gravel base, a concrete base, and / or a steel base, at which the hull 101 can be supported. The base 171 can comprise a plate or upward-facing surface configured for landing the hull 101 thereon, for example when ballasting the hull 101 to bring it into engagement with the prepared foundation 170. The prepared foundation 170 may comprise three bases 171, and the method may comprise moving each of three columns 20,21,22 of the hull 101 above a respective one of the three bases 171. The hull 101 can then be lowered into engagement with and brought to rest on the three bases 171 via each of the columns 20,21,22. The columns 20,21,22 may be designed for this purpose, whereby a bottom face and a strength of the hull 101 are prepared for being supported on the bases 171. Advantageously, if ballast tanks 140-142 (see e.g. Fig. 19 and the associated description above) are positioned in the columns 20,21,22, this provides a beneficial way of temporarily supporting the hull 101 on the foundation 170. In this example, the / each base 171 comprises at least one pile 172 driven into a sea floor 173 adjacent the shoreside yard 102. The at least one pile 172 is configured to provide support for the hull 101 when the hull 101 is resting on the base 171. The pile(s) 172 may, for example, be used in conjunction with a plate or plate structure to form the base 171. Alternatively the pile(s) 172 may make up the base 171. Fig. 33 illustrate various optional arrangements for a base 171. At the top of Fig. 33, an illustrative top view of the respective base 171 is indicated. As can be seen from the left hand side of Fig. 33, the base 171 may comprise a plurality of piles 172 (in these examples, six piles 172) integrated with a plate structure which is elevated above a sea floor. The next example illustrates a base 171 which is made up of the piles 172, with a support part of the piles 172 elevated from the sea floor. The next two examples illustrate similar arrangements but where the plate structure or support part is located at or directly adjacent the sea floor. The base 171 may optionally be adjustable, such as height-adjustable and / or pivotable. This is illustrated in Fig. 34. The adjustable base 171 may thereby be used for levelling the hull 101 when the hull 101 is arranged on the foundation 170 and / or for compensating for any height differences or uneven sea floor conditions. The adjustability of the base 171 may, for example, be provided by hydraulic cylinders or other actuators (not illustrated in detail here) arranged as part of the base 171. The base 171 may, for example, comprise piles 172 and / or a bottom plate 178 and an adjustable plate or plate structure 179 which is supported via the piles 172 and / or bottom plate and adjustable relative thereto. Illustrated in Fig. 35, the base 171 (or each base 171) may comprise one or more guide members 175 configured to guide the hull 101 in the horizontal plane and to align the hull 101 with the base 171. The guide member(s) 175 may, for example, act against one of three columns 20,21,22 of the hull 101. The guide member(s) 175 may be arranged to guide the hull 101 during horizontal positioning of the hull 101, and / or during lowering of the hull onto the base 171, for example by means of slanted guide faces. Guide member(s) 175 may be arranged partly underwater or entirely under water, whereby these for example not hinder installation operations to be carried out on the hull 101. The following numbered clauses outline further inventive examples and embodiments. D1 .A method of constructing a floatable foundation (100) for a wind turbine generator, the method comprises: assembling a hull (101) for the floatable foundation (100) at a shoreside yard (102); moving the hull (101) from the shoreside yard (102) to a floating position adjacent the shoreside yard (102); bringing the hull (101) into contact with a prepared foundation (170) on a sea floor adjacent the shoreside yard (102) such that the hull (101) rests on the prepared foundation (170); and with the hull (101) resting on the prepared foundation (170), mounting at least one further component onto or in the hull (101). D2.The method of any preceding clause, wherein the hull (101) comprises a central column (10) configured for holding a wind turbine generator tower (16), and three outwardly extending parts (50,51,52) fixed to the central column (10) and extending outwardly therefrom, each outwardly extending part (50,51,52) comprising a column (20,21,22) and at least one connecting structure (20,21,22,30,31,32) fixed between the column (20,21,22) and the central column (10), and wherein the further component is installed onto the central column (10). D3.The method of any preceding clause, wherein the step of bringing the hull (101) into contact with the prepared foundation (170) comprises ballasting the hull (101), for example by filling a plurality of ballast tanks (140-142). D4.The method of any preceding clause, comprising, subsequent to mounting the at least one further component onto or in the hull (101), de-ballasting the hull (101), for example by emptying or partially emptying the plurality of ballast tanks (140-142). D5.The method of any preceding clause, wherein the further component is a wind turbine component, for example wherein the wind turbine component is the wind turbine generator tower (16), a part of the wind turbine generator tower (16), a wind turbine generator nacelle or a wind turbine generator blade. D6.The method of any preceding clause, wherein the further component is a hull structural part, for example wherein the hull structural part is at least one further connecting structure (20,21,22,30,31,32), such as a beam structure (40,41,42), and the method comprises fixing the at least one further connecting structure (20,21,22,30,31,32) between the column (20,21,22) and the central column (10), such as between an upper part of the column (20,21,22) and an upper connection part (11) of the central column (10), with the hull (101) resting on the prepared foundation (170). D7.The method of any preceding clause, wherein the further component is at least one of: internally installed pipework, internally installed cabling and / or electric junction boxes, internally and / or externally applied surface treatment, one or more internal pumps, or internally or externally installed gangways and / or handrails. D8.The method of any preceding clause, wherein the step of assembling the hull (101) comprises preparing a floatable hull (101). D9.The method of any preceding clause, wherein the step of assembling the hull (101) comprises providing the central column (10), the three outwardly extending parts (50,51,52) and the columns (20,21,22) as individual parts at the shoreside yard (102) and fixing, such as welding, the central column (10), the three outwardly extending parts (50,51,52) and the columns (20,21,22) together at the shoreside yard (102). D10. The method of any preceding clause in conjunction with clause D2, wherein the shoreside yard (102) comprises an open wet dock (106) having at least a part of the prepared foundation (170) arranged therein, and the method comprises positioning one outwardly extending part (50,51,52) of the hull (101) in the open wet dock (106). D11. The method of any preceding clause, wherein the prepared foundation (170) comprises a base (171), for example a compacted gravel base, a concrete base, and / or a steel base, optionally wherein the base (171) comprises a plate or upward-facing surface configured for landing the hull (101) thereon. D12. The method of any preceding clause, wherein the base (171) is adjustable, such as height-adjustable and / or pivotable, and the method comprises adjusting the base (171). D13. The method of any preceding clause, comprising positioning the hull (101) above the prepared foundation (170) by means of winches (176) arranged on the shoreside yard (102). D14. The method of any preceding clause, wherein the prepared foundation (170) comprises three bases (171), and the method comprises moving each of three columns (20,21,22) of the hull (101) above a respective one of the three bases (171), and resting the hull (101) on the three bases (171). D15. The method of any preceding clause, wherein the base (171) or each base (171) comprises at least one pile (172) driven into a sea floor adjacent the shoreside yard (102), the at least one pile (172) configured to provide support for the hull (101) when the hull (101) is resting on the or each base (171). D16. The method of any preceding clause, wherein the base (171), at lease one base (171) or each base (171) comprises at least one guide member (175) configured to guide the hull (101) in the horizontal plane and to align the hull (101), such as to align one of three columns (20,21,22) of the hull (101), with the or each base (171). The method of any of clauses D1-D16 may optionally be carried out in conjunction 5 or combination with a method according to any of clauses A1-A16, B1-B9 and / or C1-C13. The hull 101 in any of the examples described in relation to Figs 18-35 may be a hull 101 similar or identical to those described above (see e.g. Figs 1 and 2 and the associated description above), or it may be a hull of different type. For example, the io methods may be used with hulls having three columns 20-22 and connection structure extending directly between pairs of columns 20-22 to form a substantially triangular-shaped hull. (See, for example, the abovementioned WO 2020 / 167137 A1.) The invention is not limited by the embodiments described above; reference should is be had to the appended claims.

Claims

1. A method of constructing a floatable foundation (100) for a wind turbine generator, the method comprises:assembling a hull (101) for the floatable foundation (100) at a shoreside yard (102), the hull (101) comprising three interconnected columns (20,21,22), each column (20,21,22) having a ballast tank (140-142) arranged at least partly therein and a ballast water filling interface (143-145) fluidly connected to the respective ballast tank (140-142);moving the hull (101) from the shoreside yard (102) to a floating position adjacent or spaced from the shoreside yard (102); andwith the hull (101) in the floating position, filling each of the ballast tanks (140-142).

2. The method according to claim 1, wherein the ballast water filling interface (143-145) is located at each respective column (20,21,22) and the method further comprises:laying out temporary ballast water filling lines (151-153) from a first column (21) of the three columns (20-22) to each ballast water filling interface (143-145);filling each of the ballast tanks (140-142) via the temporary ballast water filling lines (151-153); andremoving the temporary ballast water filling lines (151-153).

3. The method according to claim 2, wherein the step of laying out the temporary ballast water filling lines (151-153) is carried out with the hull (101) located at the shoreside yard (102) and prior to moving the hull (101) to the floating position.

4. The method according to claim 2 or 3, further comprising laying out at least one temporary ballast water supply line (150) to the first column (21) and connecting the temporary ballast water supply line (150) to the ballast water filling lines (151-153).

5. The method according to any preceding claim, comprising filling each ballast tank (140-142) from the shoreside yard (102) by means of a pump (155) located at the shoreside yard (102).

6. The method according to any preceding claim, the floating position being a first floating position adjacent the shoreside yard (102), and the method comprising:in a first ballasting step, partially filling each of the ballast tanks (140-142) with the hull (101) located in the first floating position,moving the hull (101) away from the first floating position to a second floating position spaced from the shoreside yard (102), the second floating position being at a location having larger water depth than the first floating position, andin a second ballasting step, filling each of the ballast tanks (140-142) with the hull (101) located in the second floating position.

7. The method according to claim 6, comprising ballasting in the first ballasting step, the hull (101) to bring the hull (101) into engagement with the sea floor adjacent the shoreside yard (102).

8. The method according to claim 7, comprising mounting at least one further component onto or in the hull (101) with the hull (101) resting on the sea floor adjacent the shoreside yard (102).

9. The method according to any of claims 6-8, comprising, prior to moving the hull (101) away from the first floating position, de-ballasting the hull (101) to bring the hull (101) out of contact with the sea floor adjacent the shoreside yard (102).

10. The method according to any of claims 6-8, wherein the first ballasting step comprises filling each ballast tank (140-142) from the shoreside yard (102) by means of a pump (155) located at the shoreside yard (102) and the second ballasting step comprises filling the ballast tanks (140-142) with ballast water from a barge (160) and / or from sea.

11. A method of constructing a floatable foundation (100) for a wind turbine generator, the method comprises:assembling a hull (101) for the floatable foundation (100) at a shoreside yard (102);moving the hull (101) from the shoreside yard (102) to a floating position adjacent the shoreside yard (102);bringing the hull (101) into contact with a prepared foundation (170) on a sea floor adjacent the shoreside yard (102) such that the hull (101) rests on the prepared foundation (170); andwith the hull (101) resting on the prepared foundation (170), mounting at least one further component onto or in the hull (101).

12. The method of claim 11, wherein the hull (101) comprisesa central column (10) configured for holding a wind turbine generator tower (16), andthree outwardly extending parts (50,51,52) fixed to the central column (10) and extending outwardly therefrom, each outwardly extending part (50,51,52) comprising a column (20,21,22) and at least one connecting structure (20,21,22,30,31,32) fixed between the column (20,21,22) and the central column (10),and wherein the further component is installed onto the central column (10).

13. The method of any of claims 11-12, wherein the step of bringing the hull (101) into contact with the prepared foundation (170) comprises ballasting the hull (101) by filling a plurality of ballast tanks (140-142).

14. The method of claim 13, comprising, subsequent to mounting the at least one further component onto or in the hull (101), de-ballasting the hull (101) by at least partially emptying the plurality of ballast tanks (140-142).

15. The method of claim 12, wherein the shoreside yard (102) comprises an open wet dock (106) having at least a part of the prepared foundation (170) arranged therein, and the method comprises positioning one outwardly extending part (50,51,52) of the hull (101) in the open wet dock (106).

16. The method of any of claims 11-15, wherein the prepared foundation (170) comprises a base (171) and wherein the base (171) comprises a plate or upward-facing surface configured for landing the hull (101) thereon.

17. The method of claim 16, wherein the base (171) is height-adjustable and / or pivotable and the method comprises adjusting the base (171).

18. The method of any of claims 11-17, comprising positioning the hull (101) above the prepared foundation (170) by means of winches (176) arranged on the shoreside yard (102).

19. The method of any of claims 11-18, wherein the prepared foundation (170) comprises three bases (171), and the method comprisesmoving each of three columns (20,21,22) of the hull (101) above a respective one of the three bases (171), andresting the hull (101) on the three bases (171).

20. The method of claim 19, wherein each base (171) comprises at least one pile (172) driven into a sea floor adjacent the shoreside yard (102), the at least one pile (172) configured to provide support for the hull (101) when the hull (101) is resting on the base (171).

21. The method of claim 19 or 20, wherein at least one base (171) comprises at least one guide member (175) configured to guide the hull (101) in the horizontal plane and to align the hull (101) with the base (171).s

Images