HULL STRUCTURE FOR A SEMI-SUBMERSIBLE WIND POWER TURBINE PLATFORM

Abstract

A hull structure for a semi-submersible wind power turbine platform, a method for loading a set of hull structures onto a semi-submersible cargo carrying marine vessel, and a marine vessel carrying a set of hull structures. The hull structure includes: first, second and third buoyant stabilizing columns extending in a substantially vertical direction; and first, second and third elongated submersible pontoon structures extending in a substantially horizontal direction. The hull structure has a general shape of a triangle in the horizontal plane with the first, second and third pontoon structures forming sides of the triangle. The pontoon structures extend between and connects to the columns at lower parts thereof and the third pontoon structure is arranged so that an upper side of the third pontoon structure is located at a lower level in the horizontal direction than an upper side of each of the first and second pontoon structures.

Claims

1. A hull structure for a semi-submersible wind power turbine platform, the hull structure comprising: first, second and third buoyant stabilizing columns extending in a substantially vertical direction; and first, second and third elongated submersible buoyant pontoon structures extending in a substantially horizontal direction; wherein the hull structure has a general shape of a triangle in the horizontal plane with the first, second and third pontoon structures forming sides of the triangle; wherein the first pontoon structure extends between and connects the first and the second column and wherein the first pontoon structure is connected to a lower part of each of the first and second columns; wherein the second pontoon structure extends between and connects the second and the third column and wherein the second pontoon structure is connected to a lower part of each of the second and third columns; wherein the third pontoon structure extends between and connects the first and the third column at the lower parts thereof; wherein each of the first, second and third pontoon structures has an upper side facing upwards; and wherein the third pontoon structure is arranged so that the upper side thereof is located at a lower level than the upper side of each of the first and second pontoon structures.

2. The hull structure according to claim 1, wherein each of the first, second and third pontoon structures has a lower side facing downwards and wherein the lower sides of the first, second and third pontoon structures are substantially aligned with each other in the horizontal plane.

3. The hull structure according to claim 2, wherein the lower sides of the first, second and third pontoon structures are substantially aligned with downwardly facing lower sides of each of the first, second and third buoyant stabilizing columns.

4. The hull structure according to claim 1, wherein each of the first and second pontoon structures has a lower side facing downwards and wherein the upper side of the third pontoon structure is substantially aligned with, or is located at a lower level than, the lower sides of the first and second pontoon structures.

5. The hull structure according to claim 4, wherein the lower sides of the first and second pontoon structures are substantially aligned with a downwardly facing lower side of the second buoyant stabilizing columns.

6. The hull structure according to claim 4, wherein the lower sides of the first and second pontoon structures are substantially aligned with a portion of a downwardly facing lower side of the second buoyant stabilizing column, wherein another portion of the downwardly facing lower side of the second buoyant stabilizing columns is located at a lower level.

7. The hull structure according to claim 4, wherein the lower side of the third pontoon structure is substantially aligned with downwardly facing lower sides of each of the first and third buoyant stabilizing columns.

8. The hull structure according to claim 4, wherein the lower side of the third pontoon structure is substantially aligned with a portion of each of the downwardly facing lower sides of the first and third buoyant stabilizing columns, wherein another portion of the downwardly facing lower side of each of the first and third buoyant stabilizing columns is located at a higher level.

9. The hull structure according to claim 1, wherein the third pontoon structure has a height that is less than that of each of the first and second pontoon structures.

10. The hull structure according to claim 1, wherein the height of the third pontoon structure is less than 75%, preferably less than 50%, of the height of at least one of the first and second pontoon structures.

11. The hull structure according to claim 1, wherein the height of the third pontoon structure is at least 1 m smaller, preferably at least 2 m or at least 3 m smaller, than the height of at least one of the first and second pontoon structures.

12. The hull structure according to claim 1, wherein the first, second and third pontoon structures have a substantially equal length.

13. The hull structure according to claim 1, wherein the hull structure exhibits: i) a first angle in the horizontal plane between a central longitudinal axis of the first pontoon structure and a central longitudinal axis of the second pontoon structure; and ii) a second angle in the horizontal plane between a) a first imaginary line between a central point of the first stabilizing column and a central point of the second stabilizing column and b) a second imaginary line between the central point of the second stabilizing column and a central point of the third stabilizing column, wherein the second angle is larger than the first angle.

14. The hull structure according to claim 1, wherein each of the first and the second pontoon structures has, at least along a major part of its length, a width that is less than a width of the lower part of the second stabilizing column.

15. The hull structure according to claim 1, wherein each of the first and second pontoon structures has an outer side facing away sideways from the hull structure, wherein the outer side of at least one of the first and second pontoon structures is substantially aligned with an outer side of the second stabilizing column.

16. The hull structure according to claim 1, wherein at least an outer part of a lower side of the third pontoon structure is inclined in relation to the horizontal plane so as to form an inclined surface, wherein the inclination is directed so that the outer part of the lower side of the third pontoon structure is located on a higher vertical level than an inner part of the lower side of the third pontoon structure, wherein the inner part is located closer to the second stabilizing column than the outer part.

17. The hull structure according to claim 16, wherein at least a part of a lower side of the first and third stabilizing columns is inclined in relation to the horizontal plane, wherein the inclination is arranged to correspond to the inclination of the lower side of the third pontoon structure.

18. The hull structure according to claim 1, wherein the upper side of the third pontoon structure is inclined in relation to the horizontal plane so as to form an upper inclined surface, wherein the inclination is arranged so that an outer part of the upper side of the third pontoon structure is located on a lower vertical level than an inner part of the upper side of the third pontoon structure, wherein the inner part is located closer to the second stabilizing column than the outer part.

19. The hull structure according to claim 1, wherein the hull structure comprises a supporting structure arranged at the second stabilizing column between the first and second pontoon structures.

20. The hull structure according to claim 19, wherein the supporting structure is provided with a supporting surface arranged at substantially the same vertical height as the upper side of the third pontoon structure.

21. The hull structure according to claim 1, wherein the hull structure comprises a controllable ballast system configured to allow control of an inclination of the hull structure when floating in water.

22. A method for loading a set of hull structures onto a semi-submersible cargo carrying marine vessel configured to be lowered partly below the water surface into a lower position and be raised to an upper position so as to load onto the vessel cargo that is located at the water surface above the vessel, wherein the set of hull structures comprises at least a first hull structure and a second hull structure each arranged according to the hull structure of claim 1, the method comprising: providing the set of hull structures floating in water; arranging the set of hull structures in a row above the marine vessel when the marine vessel is in its lower position; and raising the marine vessel to its upper position so as to load the row of hull structures onto the marine vessel.

23. The method according to claim 22, wherein arranging the set of hull structures in the row comprises: arranging the first and second hull structures adjacent each other and so that the second hull structure is located above the third pontoon structure of the first hull structure with the second column of the second hull structure positioned between the first and second pontoon structures of the first hull structure, wherein the second column of the second hull structure is positioned closer to the second column of the first hull structure than to the first and third columns of the first hull structure.

24. The method according to claim 23, the method comprising: setting at least one of the first and second hull structures in an inclined position so as to allow the second hull structure to float above the third pontoon structure of the first hull structure into position adjacent the first hull structure.

25. The method according to claim 23, wherein the first hull structure comprises a supporting structure arranged at the second stabilizing column between the first and second pontoon structures, and wherein the supporting structure is provided with a supporting surface arranged at substantially the same vertical height as the upper side of the third pontoon structure, the method further comprising: locating the second column of the second hull structure onto the supporting surface of the first hull structure, and/or locating the first and second pontoon structures of the second hull structure onto the upper side of the third pontoon structure of the first hull structure.

26. The method according to claim 22, wherein the upper side of the third pontoon structure is inclined in relation to the horizontal plane so as to form an upper inclined surface, wherein the inclination is arranged so that an outer part of the upper side of the third pontoon structure is located on a lower vertical level than an inner part of the upper side of the third pontoon structure, wherein the inner part is located closer to the second stabilizing column than the outer part.

27. The method according to claim 22, wherein at least an outer part of a lower side of the third pontoon structure is inclined in relation to the horizontal plane so as to form an inclined surface, wherein the inclination is directed so that the outer part of the lower side of the third pontoon structure is located on a higher vertical level than an inner part of the lower side of the third pontoon structure, wherein the inner part is located closer to the second stabilizing column than the outer part.

28. The method according to claim 22, wherein arranging the set of hull structures in the row comprises: arranging the first and second hull structures adjacent each other and so that the first and second pontoon structure of the second hull structure is located above the third pontoon structure of the first hull structure with the second column of the second hull structure positioned between the first and second pontoon structures of the first hull structure, wherein the second column of the second hull structure is positioned closer to the second column of the first hull structure than to the first and third columns of the first hull structure.

29. A marine vessel carrying a set of hull structures, wherein the set of hull structures comprises at least a first hull structure and a second hull structure each arranged according to the hull structure of claim 1.

30. The marine vessel according to claim 29, wherein the set of hull structures are arranged in a row with the first and second hull structures located adjacent each other, wherein the second hull structure is located above the third pontoon structure of the first hull structure with the second column of the second hull structure positioned between the first and second pontoon structures of the first hull structure, wherein the second column of the second hull structure is positioned closer to the second column of the first hull structure than to the first and third columns of the first hull structure.

31. The marine vessel according to claim 29, wherein the first hull structure comprises a supporting structure arranged at the second stabilizing column between the first and second pontoon structures, wherein the second column of the second hull structure is located onto the supporting surface of the first hull structure, and wherein the first and second pontoon structures of the second hull structure are located onto the upper side of the third pontoon structure of the first hull structure.

32. The marine vessel according to claim 29, wherein the upper side of the third pontoon structure is inclined in relation to the horizontal plane so as to form an upper inclined surface, wherein the inclination is arranged so that an outer part of the upper side of the third pontoon structure is located on a lower vertical level than an inner part of the upper side of the third pontoon structure, wherein the inner part is located closer to the second stabilizing column than the outer Part.

33. The marine vessel according to claim 29, wherein the second hull structure comprises a supporting structure arranged at the second stabilizing column between the first and second pontoon structures.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0066] In the description of the invention given below reference is made to the following figure, in which:

[0067] FIG. 1 shows a perspective view of a first embodiment of a hull structure according to this disclosure.

[0068] FIGS. 2A and 2B show a top view (FIG. 2A) and a longitudinal section view (FIG. 2B) of a second embodiment of a hull structure according to this disclosure.

[0069] FIGS. 3A and 3B show a top view (FIG. 3A) and a longitudinal section view (FIG. 3B) of a third embodiment of a hull structure according to this disclosure.

[0070] FIG. 4 shows a perspective view of the hull structure of FIGS. 3A and 3B, further provided with a support for a wind turbine tower.

[0071] FIG. 5 shows, in a schematic side view, a first set of hull structures stowed in a row onto a deck of a marine transportation vessel.

[0072] FIGS. 6A and 6B show, in schematic side views, a second set of hull structures stowed in a row onto a deck of a marine transportation vessel (FIG. 6B), where a first hull structure to the right has a special design (FIG. 6A).

[0073] FIGS. 7A and 7B show first and second perspective views of a set of hull structures stowed in a row onto a deck of a marine transportation vessel.

[0074] FIGS. 8A-8F show in a stepwise manner how to arrange the set of hull structures according to FIGS. 7A and 7B onto the deck of the marine transportation vessel.

[0075] FIGS. 9A-9D show a comparison of stowing efficiency between sets of hull structures with different hull structure design.

[0076] FIG. 10 shows a semi-submersible wind power turbine platform comprising a hull structure according to this disclosure.

[0077] FIG. 11 shows a perspective view of a further embodiment of a hull structure according to this disclosure.

[0078] FIG. 12 shows a side view of a further embodiment of a hull structure according to this disclosure.

[0079] FIG. 13 shows a set of hull structures according to FIG. 12 stowed in a row.

[0080] FIG. 14 shows a side view of the embodiment according to FIG. 11.

[0081] FIG. 15 shows a set of hull structures according to FIG. 14 stowed in a row.

[0082] FIG. 16 shows a perspective view of a still further embodiment of a hull structure according to this disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0083] FIG. 1 shows a first embodiment of a hull structure 10 for a semi-submersible wind power turbine platform 100. The hull structure 10 comprises first, second and third buoyant stabilizing columns 1, 2, 3 extending in a substantially vertical direction and first, second and third elongated submersible pontoon structures 11, 12, 13 extending in a substantially horizontal direction. The hull structure 10 has a general shape of a triangle in the horizontal plane with the first, second and third pontoon structures 11, 12, 13 forming sides of the triangle. In this example the first, second and third pontoon structures 11, 12, 13 have a substantially equal length and the hull structure forms, roughly described, an equilateral triangle with a column in each corner.

[0084] As an example of size, the columns 1, 2, 3 may have a height of around 30-35 m and a diameter of around 13 m. Each of the pontoon structures 11, 12, 13 may have a length of around 50-70 m and a width of 6-10 m. The height of the first and second pontoon structures 11, 12 may have a height of 6-9 m.

[0085] The first pontoon structure 11 extends between and connects the first and the second column 1, 2, and the first pontoon structure 11 is connected to a lower part 1c, 2c of each of the first and second columns 1, 2. The second pontoon structure 12 extends between and connects the second and the third column 2, 3, and the second pontoon structure 12 is connected to a lower part 2c, 3c of each of the second and third columns 2, 3. The third pontoon structure 13 extends between and connects the first and the third column 1, 3, and the third pontoon structure 13 is connected to a lower part 1c, 3c of each of the first and third columns 1, 3. The lower parts 1c, 2c, 3c of the columns 1, 2, 3 are in this case the lowest possible part of the columns. All three pontoon structures 11, 12, 13 are in this case buoyant pontoon structures.

[0086] Each of the first, second and third pontoon structures 11, 12, 13 has a lower side 11b, 12b, 13b facing downwards. These lower sides 11b, 12b, 13b are substantially aligned with each other in the horizontal plane and also with downwardly facing lower sides 1b, 2b, 3b of each of the first, second and third buoyant stabilizing columns 1, 2, 3.

[0087] Further, each of the first and the second pontoon structures 11, 12, has a width that is less than a width of the lower part 2c of the second stabilizing column 2. As shown in FIG. 1, all pontoon structures 11, 12, 13 are straight and has a non-varying width. In other embodiments, the first and the second pontoon structures 11, 12 may have another design.

[0088] As can be seen in FIG. 1, the third pontoon structure 13 has a height that is less than that of each of the first and second pontoon structures 11, 12. Since the pontoon structures in FIG. 1 are arranged on the same level, it follows that the third pontoon structure 13 is arranged so that its upper side 13a is located at a lower level in the horizontal direction than an upper side 11a, 12a of each of the first and second pontoon structures 11, 12. As will be further described below, a main purpose of the particular structure and arrangement of the third pontoon structure 13 is that it allows for a more space-efficient stowing of hull structures on a marine transportation vessel and thus allows for the vessel to carry a higher number of hull structures.

[0089] In the example shown the height of the third pontoon structure 13 is around 3 m, whereas the height of the first and second pontoon structures 11, 12 is around 7 m. The height of the third pontoon structure 13 is thus less than 50% of the first and second pontoon structures 11, 12.

[0090] The hull structure 10 is further provided with a controllable ballast system (not shown in figures) configured to allow control of an inclination of the hull structure 10 when floating in water.

[0091] The embodiments of the hull structures shown in FIGS. 2-10 are principally structured in a similar way as the hull structure 10 shown in FIG. 1, and therefore the same reference numbers have been used in all figures for similar components.

[0092] FIGS. 2A-2B show a top view (FIG. 2A) and a longitudinal section view (FIG. 2B) of a second embodiment of a hull structure 20 for a semi-submersible wind power turbine platform 100.

[0093] As shown in FIG. 2A, the hull structure 20 exhibits a first angle in the horizontal plane between a central longitudinal axis 11c of the first pontoon structure 11 and a central longitudinal axis 12c of the second pontoon structure 12 (i.e., an angle between center-line axes of the first and second pontoon structures). The hull structure 20 further exhibits a second angle 3 in the horizontal plane between a) a first imaginary line 21 between a central point of the first stabilizing column 1 and a central point of the second stabilizing column 2 and b) a second imaginary line 22 between the central point of the second stabilizing column 2 and a central point of the third stabilizing column 3. As further shown in FIG. 2A, the second angle is larger than the first angle . This further improves the space-efficiency of the stowing of hull structures, as will be described further below.

[0094] As shown in FIG. 2B, the lower side 13b of the third pontoon structure 13 is inclined in relation to the horizontal plane so as to form an inclined surface 130. The inclination has an angle in relation to the horizontal plane and it is directed so that an outer part of the lower side 13b of the third pontoon structure 13 is located on a higher vertical level than an inner part of the lower side 13b of the third pontoon structure 13, wherein the inner part is located closer to the second stabilizing column 2 than the outer part. The inclined surface 130 forms a support surface for the hull structure 20 when stowed in a slightly inclined position (at an angle ) onto a deck of a transportation vessel, which is further described below. Also a part of a lower side 1b, 3b of the first and third stabilizing columns 1, 3 is inclined at an angle in relation to the horizontal plane so as to correspond to the inclined surface 130.

[0095] The hull structure 20 is further provided with a supporting structure 5 arranged at the second stabilizing column 2 between the first and second pontoon structures 11, 12. The supporting structure 5 connects the first and second pontoon structures 11, 12 and also the entire hull structure 20. The supporting structure 5 comprises a supporting surface 6 extending between the first and second pontoon structures 11, 12 at a height corresponding to that of the upper side 13a of the third pontoon structure 13. The supporting surface 6 functions as a support for an adjacent hull structure when stowing a set of hull structures onto a transportation vessel, as will be further described below.

[0096] The hull structure 20 is further provided with braces 7 that extend between and connect the columns 1, 2, 3 in a principally similar way as the pontoon structures 11, 12, 13, but the braces are arranged between upper parts of the columns 1, 2, 3. The brace between the first and third columns 1, 3 is not mounted when the hull structure is (to be) stowed for transport since it would obstruct close stowage. End parts of that bracing might be prefixed to the first and third columns, and the remaining part can be mounted after transport. Assembling of a brace after transport is generally not too complicated.

[0097] A further difference between the hull structures of FIGS. 1 and 2A-2B is that the second column 2 of the hull structure 20 of FIGS. 2A-2B is somewhat larger (in diameter) compared to the first and third columns 1, 3. A purpose of this is to provide better support conditions for arranging a wind turbine tower onto the second column 2. A further purpose may be to adjust a longitudinal center of flotation (LCF) of the hull structure since a larger diameter of the second column means a larger cross sectional area, which in turn means that the second column will exhibit a larger waterplane area than the other columns when the hull structure/platform is in operation with the pontoon structures located beneath the water surface and the columns extending through the water surface. The position of the LCF depends on the waterplane areas of the columns and adjusting the LCF can reduce motions of the hull structure/platform during operation at open sea.

[0098] FIGS. 3A-3B shows a top view (FIG. 3A) and a longitudinal section view (FIG. 3B) of a third embodiment of a hull structure 30. The hull structure 30 of FIGS. 3A-3B is principally similar to the hull structure 20 of FIGS. 2A-2B. The difference is mainly that the first and second pontoon structures 11, 12 of the hull structure 30 are arranged so as to decrease the first angle and thus to increase the difference between the second angle and the first angle . The first angle may be further decreased by using a second column with larger diameter.

[0099] As shown in FIG. 3A, each of the first and second pontoon structures 11, 12 has an outer side 11d, 12d facing away sideways from the hull structure 30. In the embodiment of FIG. 3, the first and second pontoon structures 11, 12 are arranged so that the outer side 11d, 12d of each of the first and second pontoon structures 11, 12 is substantially aligned with an outer side 2d of the second stabilizing column 2. In addition, the opposite ends of the first and second pontoon structures 11, 12 are substantially aligned with an inner side of the first and third stabilizing column 1, 3, respectively.

[0100] This further increased difference between the second angle and the first angle further improves the capability of the hull structure 30 to be stowed in a space-efficient manner onto the marine transportation vessel.

[0101] FIG. 4 shows a perspective view of the hull structure 30 of FIG. 3, further provided with an interface/support 101 for a wind turbine tower arranged on top of the second stabilizing column 2.

[0102] FIG. 5 shows, in a schematic side view, a first set of hull structures 20, 30, in this example five hull structures, stowed in a row onto a deck 65 of a marine transportation vessel. The hull structures in FIG. 5 may be of the type shown in FIG. 2 or 3. All five hull structures occupy an inclined position with an inclination angle corresponding to the inclined surface 130 on the lower side 13b of the third pontoon structure 13. The hull structure to the far right is supported below its second column 2 by a support 66 arranged on the deck 65 of the vessel. Remaining hull structures are stowed and supported in the same way, i.e., the second column 2 is supported by the supporting surface 6 of an adjacent hull structure and the inclined support surface 130 is flush with and supported by the deck 65. Further, the first and second pontoon structures 11, 12 of all these remaining hull structures are located onto and supported by the third pontoon structure 13 of the adjacent hull structure.

[0103] FIGS. 6A-6B show, in schematic side views, a second set of hull structures 20, 30, 40, in this example five hull structures, stowed in a row onto a deck 65 of a marine transportation vessel (FIG. 6B), where a first hull structure 40 to the right has a special design (FIG. 6A). Remaining four hull structures 20, 30 may be of the type shown in FIG. 2A or 3A.

[0104] As shown in FIG. 6A, the special hull structure 40 is not provided with any inclined surface 130 on the lower side 13b of the third pontoon structure 13; instead the lower side 13b is flat. However, the upper side 13a of the third pontoon structure 13 of the hull structure 40 is inclined in relation to the horizontal plane so as to form an upper inclined surface 140. The inclination is arranged so that an outer part of the upper side 13a of the third pontoon structure 13 is located on a lower vertical level than an inner part of the upper side 13a of the third pontoon structure 13, wherein the inner part is located closer to the second stabilizing column 2 than the outer part.

[0105] This means that the special hull structure 40 can and should be placed horizontally onto the deck 65 and form an end structure (the first structure) in the row of hull structures as shown in FIG. 6B. This first hull structure 40 is thereby set in a very steady position onto the deck 65 and no additional deck support 66 is needed to set this hull structure in the inclined position. The next (second) hull structure 20, 30 adjacent the first hull structure 40 occupy the inclined position and is supported by the upper inclined surface 140 of the first hull structure 40 as well as by its own lower inclined surface 130 as in FIG. 5. An additional support 67 may be arranged under the second column 2 of the second hull structure 20, 30. Remaining three hull structures 20, 30 are stowed in the same way as in FIG. 5.

[0106] FIGS. 7A-7B show first and second perspective views of a set of hull structures stowed in a row onto a deck 65 of a marine transportation vessel 60 in the form of a semi-submersible cargo carrying marine vessel configured to be lowered partly below the water surface into a lower position and be raised to an upper position so as to load onto the vessel cargo that is located at the water surface above the vessel.

[0107] The row of hull structures in FIGS. 7A and 7B include a first hull structure 40 of the type shown in FIG. 6A and four further hull structures 30a-30d, each of the type shown in FIG. 4 (but with a mid-portion of the bracing 7 between the first and third columns 1, 3 removed). The hull structures of FIGS. 7A-7B are stowed onto the deck 65 in a principally similar manner as the hull structures in FIG. 6B.

[0108] FIGS. 8A-8F show in a stepwise manner how to arrange the set of hull structures according to FIGS. 7A-7B onto the deck 65 of the marine transportation vessel 60.

[0109] A method for loading the set of hull structures 40, 30a-30d onto the semi-submersible cargo carrying marine vessel 60 comprises in general the following steps: [0110] providing the set of hull structures 40, 30a-30d floating in water (FIGS. 8A-8D); [0111] arranging the set of hull structures 40, 30a-30d in a row above the marine vessel 60 when the marine vessel is in its lower position (FIG. 8E); and [0112] raising the marine vessel 60 to its upper position so as to load the row of hull structures 40, 30a-30d onto the marine vessel 60 (FIG. 8F).

[0113] As shown in FIG. 8B, the step of arranging the set of hull structures in the row, wherein the set of hull structures comprises at least a first 40 and a second 30a hull structure, may comprise: arranging the first and second hull structures 40, 30a adjacent each other so that the second hull structure 30a is located above the third pontoon structure 13 of the first hull structure 40 with the second column 2 of the second hull structure 30a positioned between the first and second pontoon structures 11, 12 of the first hull structure 40, wherein the second column 2 of the second hull structure 30a is positioned closer to the second column 2 of the first hull structure 40 than to the first and third columns 1, 3 of the first hull structure 40.

[0114] As shown in FIG. 8A, the method may further comprise: setting at least one of the first and second hull structures in an inclined position (in this case the second hull structure 30a, see FIG. 8A) and lowering the first hull structure 40 to a slightly larger draught so as to allow the second hull structure 30a to float above the third pontoon structure 13 of the first hull structure 40 into position adjacent the first hull structure 40 (as shown in FIG. 8B). The controllable ballast system is used for setting the second hull structure 30a in the inclined position.

[0115] As shown in FIGS. 8B-8E, and also FIGS. 6B, 7A and 7B, the method may further comprise: locating the second column 2 of the second hull structure 30a onto the supporting structure 5, 6, 67 of the first hull structure 40.

[0116] Remaining hull structures 30b, 30c, 30d are arranged in the row in principally the same way as described above for the first and second hull structures 40, 30a. For instance, the third hull structure 30b in the row is set in the inclined position and moved/towed into position at the adjacent second hull structure 30a that already is positioned in a corresponding inclined position. Since the second and third hull structures 30a, 30b are not inclined in relation to each other, there is no need for the additional support 67. As already described above, the third hull structure 30b is supported (or will be supported when the vessel 60 is raised) by the third pontoon structure 13 and the support surface 6 of the second hull structure 30a. The third hull structure 30b is also supported by its own third pontoon structure that is located onto the deck 65. The procedure for arranging the fourth and fifth hull structure 30c, 30d in the row is similar.

[0117] The hull structures 40, 30a-30d are preferably fixed to each other before raising the vessel 60. Wood elements or similar may be placed between the hull structures to prevent damages.

[0118] FIGS. 9A-9D show a comparison of stowing efficiency between sets of hull structures with different hull structure design A-D. FIGS. 9A-9C show hull structure designs A-C where the first angle equals the second angle (see FIGS. 2A and 3A for cases where >).

[0119] The difference between designs A-C is the position of the first and second pontoon structures: in design A they are positioned at the inside of the columns (FIG. 9A); in design B they are positioned at the outside of the columns (FIG. 9B); and in design C they are positioned centrally onto the columns (FIG. 9A), similar to the hull structure 10 shown in FIG. 1.

[0120] Design D forms an example of hull structures where >, similar to the hull structure 30 shown in e.g., FIG. 3A.

[0121] All designs A-D have the same column diameters and pontoon structure breadth/width.

[0122] As shown in FIGS. 9A-9D, the number of hull structures that can be stowed on a given length of the deck of the vessel 60 is 3 for design A, 4 for designs B and C, and 5 for design D. It is thus clear that arranging the hull structure so that > further improves the stowage efficiency of this type of -shaped hull structures (i.e., stowable -shaped hull structures with a lower third pontoon structure).

[0123] Thin lines in FIGS. 9A-9C indicate a fourth and fifth hull structures in FIG. 9A and a fifth hull structure in FIGS. 9B and 9C to show the corresponding length of five full structures of the different designs. These indicated additional hull structures do not fit onto the vessel 60.

[0124] FIG. 10 shows a semi-submersible wind power turbine platform 100 comprising a hull structure 30 according to FIG. 4. The platform 100 is provided with a wind turbine tower 102 in turn provided with three blades 103 (as well as a generator etc., which is not shown in the figures).

[0125] FIG. 11-16 show embodiments of hull structure 50, 51 similar to what is described above but wherein each of the first and second pontoon structures 11, 12 has a lower side 11b, 12b facing downwards and wherein the upper side 13a of the third pontoon structure 13 is substantially aligned with, or is located at a lower level than, the lower sides 11b, 12b of the first and second pontoon structures 11, 12.

[0126] In the hull structure 50 shown in FIGS. 12 and 13, the lower sides 11b, 12b of the first and second pontoon structures 11, 12 are substantially aligned with the entire downwardly facing lower side 2b of the second buoyant stabilizing columns 2.

[0127] In the hull structure 51 shown in FIGS. 11, 14 and 15, the lower sides 11b, 12b of the first and second pontoon structures 11, 12 are substantially aligned with only a portion of the downwardly facing lower side 2b of the second buoyant stabilizing column 2. Another portion 2e of the downwardly facing lower side 2b of the second buoyant stabilizing columns 2 is located at a lower level. As best shown in FIG. 14, the (second) portion 2e located at the lower level is substantially aligned with the underside 13b of the third pontoon 13 as well as the underside of each of the first and third columns 1, 3.

[0128] FIG. 13 shows a set of hull structures according to FIG. 12 stowed in a row and FIG. 15 shows a set of hull structures according to FIGS. 11 and 14 stowed in a row.

[0129] To hold a hull structure according to FIG. 12 in a substantially horizontal position when there is no supporting third pontoon available, such as when the platform is located at an end of a row of similar platforms or during assembly, it is possible to arrange a separate support structure 52 beneath the second column, see FIG. 13.

[0130] A hull structure according to FIGS. 11 and 14 is positioned substantially horizontally without any separate support structure 52 since the underside of the third pontoon 3, the underside of the first and third columns 1, 3 and the (second) portion 2e of the underside of the second column 2 are aligned with each other, see FIGS. 11, 14 and 15.

[0131] A hull structure according to FIGS. 11-16 may be positioned horizontally with a small step in or an inclination portion of the underside of the bottom of the first 11b and second 12b pontoons to allow cribbing between the first and second pontoons and the upper side 13a of neighboring hull structures.

[0132] A hull structure according to FIGS. 11-16 may be positioned with a small inclination (e.g., 1-2 degrees) to allow cribbing to be arranged between the underside of the bottom of the first 11b and second 12b pontoons and the upper side 13a of neighboring hull structures and where wedge-shaped cribbing of varying height is arranged underneath the underside third pontoon 13b.

[0133] Also in the embodiments of FIGS. 11-16, the pontoons 11, 12, 13 are connected to the lower part of the columns 1, 2, 3, i.e., the pontoons will typically be located below the surface when the wind power turbine platform is in operation.

[0134] In the hull structure shown in FIG. 16, the lower side of the first and third columns 1, 3 has one portion 1e, 3e located at a lower level and another portion (indicated as 1b and 3b in FIG. 16) located at a higher level. In this example, the lower portions 1e, 3e are aligned with the lower side 13b of third pontoon 13 and the upper portions 1b, 3b are aligned with lower sides 11b, 12b of the first and second pontoons 11, 12. The upper portions 1b, 3b provide points useful for lifting and moving a platform on land using e.g., so-called self-propelled module transporters. Any of the hull structures of this disclosure may be provided with such upper portions/lifting points.

[0135] The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims. For instance, the height of the third pontoon structure may be larger and the cross sectional shape of the columns and pontoon structures may be different than exemplified, such as polygonal columns and circular or polygonal pontoon structures.