A hull structure for a semi-submersible wind power turbine platform

Abstract

The invention concerns a hull structure (10, 100, 80, 200) for a semi- submersible wind power turbine platform (50), wherein the hull structure (10) comprises: a centre column (4) configured to support a wind power tower (20) provided with a wind turbine (30), the centre column (4) being located in a central region of the hull structure (10, 100); first, second and third buoyancy structures circumferentially distributed around the centre column (4) comprising first, second and third elongated structures (5, 6, 7) connected to the centre column (4) and extending outwards in different radial directions from the centre column (4, wherein the first elongated structure (5) is located at a higher level than the second and / or third elongated structures (6, 7) so that a lower side (5A) of the first elongated connection structure (5) is located above or is substantially aligned with an upper side (6B, 7B) of at least one of the second and third elongated connection structures (6, 7).

Description

[0001] A hull structure for a semi-submersible wind power turbine platform

[0002] TECHNICAL FIELD

[0003] This invention relates to a hull structure for a semi-submersible wind power turbine platform. The invention also relates to stowing of such hull structures onto a marine vessels.

[0004] BACKGROUND OF THE INVENTION

[0005] There is a growing interest for offshore wind power, i.e. sea-based wind power stations / turbines that produce electricity. Such a wind turbine may have a fixed underwater foundation or, in particular at water depths larger than around 50-60 m, may be arranged on a floating platform anchored to the bottom.

[0006] A floating wind power turbine platform may be of a semi-submersible type comprising a semi-submersible hull structure onto which a wind turbine tower is arranged. The hull structure is typically made up of a plurality of stabilizing buoyant columns connected by submersible buoyant pontoons or other connection members. The turbine tower is typically arranged onto one of the columns. Examples of semi-submersible wind power turbine platforms are disclosed in W02014 / 031009 and WO2021 / 148156.

[0007] Platforms of this type are large constructions. For instance, each column of a 10 MW wind power turbine platform may have a height of 30 m and the distance between the columns may be 60-80 m. The total weight of the hull structure may be more than 3000 tonnes. The turbine tower may extend up to, say, 150 m above sea level and each turbine blade may be more than 100 m long.

[0008] A challenge in the field of offshore wind power is manufacturing, transportation and installation of the semi-submersible platforms. Towing of a platform with the wind turbine tower and blades etc. installed is complicated and challenging, and to reduce the towing distance for such a complete platform it is preferably arranged so that the turbine tower and the turbine blades etc. are installed onto the hull structure in a sheltered location relatively close to the final offshore location. A particular transportation challenge arises if the hull structure is manufactured at a construction yard located far away from the sheltered location, for instance because there is no construction yard suitable for such large and heavy hull structures available at or near the sheltered location. In such a situation the hull structures need to be transported a relatively long distance.

[0009] A further challenge with regard to semi-submersible wind power turbine platforms is to design the hull structure so that the platform becomes robust and stable also under harsh offshore conditions and so that the platform withstands many years of operation under such conditions.

[0010] A still further challenge is of course that manufacturing, transportation, installation, operation, etc. of the platform or hull structure must be cost efficient for keeping and increasing the interest for offshore wind power.

[0011] SUMMARY OF THE INVENTION

[0012] The invention concerns a hull structure for a semi-submersible wind power turbine platform, wherein the hull structure comprises: a centre column configured to support a wind power tower provided with a wind turbine, the centre column being located in a central region of the hull structure as seen in a horizontal plane; and first, second and third buoyancy structures circumferentially distributed around the centre column in the horizontal plane. Each buoyancy structure comprises one or more buoyant elements configured to contribute significantly to a total buoyancy of the hull structure, and each buoyancy structure comprises an elongated structure connected to the centre column so as to form first, second and third elongated structures that are connected to the centre column and that extend outwards in different radial directions from the centre column. The first elongated structure is located at a higher level than the second and / or third elongated structures so that a lower side of the first elongated structure is located above or is substantially aligned with an upper side of at least one of the second and third elongated structures.

[0013] The elongated structures form part of corresponding buoyancy structures, each of which comprising one or more buoyant elements configured to contribute significantly to the total buoyancy of the hull structure. As further described below, the elongated structures may be pontoons and thus form buoyant elements or they may be bracings or similar with no or only weak buoyancy properties. Irrespectively of whether the elongated structures form buoyant elements, they may be connected to other buoyant elements such as buoyant stabilizing columns connected at an outer end of the elongated structures. The elongated structures are in this disclosure sometimes referred to as elongated connection structures since they are connected to the centre column and in some examples also connected to a buoyant stabilizing column.

[0014] Hull structures of the above type can be placed close to each other on e.g. a marine transportation vessel since the first elongated structure of a first hull structure can be placed on top of the second or third elongated structure of an adjacent second hull structure. Further hull structures can be placed in a similar way so as to form a row-like pattern of closely located / stowed hull structures. That is, the special design of the individual hull structures provides for efficient stowing on the vessel while the hull structures are still being oriented substantially horizontally.

[0015] It is typically an advantage to design the hull structure such that the lower side of the first elongated structure is located slightly above the upper side of at least one of the second and third elongated structures. The distance may be 10-70 cm, or 20-60 cm, or 20-40 cm, or 50-70 cm, or around 30 cm or around 60 cm. This provides for the possibility to arrange spacers made of e.g. wood (“cribbing”) between the elongated structures to prevent damages.

[0016] The terms lower side and upper side of the elongated structures do not imply that there must be a flat surface facing downwards or upwards; these terms rather refer to the side of the elongated structure that generally faces downwards or upwards when the hull structure is oriented horizontally. For instance, an elongated structure with circular or elliptical transversal cross section has a rounded underside and a rounded top side that form lower and upper sides, respectively, within the meaning of this disclosure.

[0017] As further described below, one way of loading the hull structures is to arrange a row of floating hull structures positioned closely to each other, i.e. with the first elongated structure of one hull structure placed on top of the second or third elongated structure of an adjacent hull structure, and then load the row of hull structures onto a semi-submersible cargo carrying marine vessel that is raised from a position below the row of hull structures. Another way is to skid-out the platforms onto the deck of the marine transport vessel from a quay at which the vessel is moored.

[0018] A main effect of designing the hull structure as given above is that a higher number of platforms can be loaded onto the same marine transportation vessel, e.g. for transport between the construction yard to the sheltered location where the wind turbine is to be installed, which in turn reduces the transportation costs.

[0019] The hull structure of this disclosure is typically arranged so that the first elongated structure is located at a higher level than both the second and third elongated structures and so that the second and third elongated structures, together with the centre column and possibly one or more further columns, form a steady support on a horizontal flat surface. The hull structure typically contains three, or four, main elongated structures in total so as to in general exhibit an Y-shape, or X-shape (+-shape), in the horizontal plane with the centre column located in the middle of the Y, or X (or +) with the at least three elongated structures extending out from centre column. Due to the lower number of main elongated structures, a row of Y-hulls is in principle easier to stow efficiently than a row of X-hulls, but the stowing efficiency of X- hulls (with at least one elongated structure located at a higher level) may be sufficient.

[0020] Stabilizing buoyant columns provide stability to the platform and contribute significantly to a total buoyancy of the semi-submersible wind power turbine platform. Elongated structures that connect a corresponding stabilizing buoyant column with the centre column may form buoyant pontoon structures and may thereby also contribute significantly to the total buoyancy of the platform. The centre column may or may not be a buoyant component that contribute to the total buoyancy. The centre column may have a diameter that is less, equal or larger than that of the stabilizing buoyant columns. The columns typically have a circular cross section but other shapes are possible. The elongated connection structures typically has a substantially equal length.

[0021] That the platform, and the hull structure, is semi-submersible means that the platform / hull structure can be partly located beneath the water surface when in operation. The entire elongated structures and parts of the column(s) are typically to be located beneath the surface. Anchoring / securing of the platform / hull structure to the bottom can be arranged in different ways, e.g. catenary mooring, taut-leg mooring or tendon mooring.

[0022] In an embodiment, the one or more buoyant elements comprises a buoyant stabilizing column and / or an elongated structure in the form of a buoyant pontoon structure. That is, each buoyancy structure comprises at least one buoyant element in the form of a buoyant stabilizing column and / or a buoyant elongated pontoon structure. If a buoyant stabilizing column is included it is typically connected to an outer end of a corresponding elongated structure opposite to an inner end connected to the centre column. If the buoyant stabilizing column provides a sufficient buoyancy, the elongated structure may exhibit no or only a weak buoyancy, such as a bracing structure. In the absence of any buoyant stabilizing column, or where additional buoyancy is desired, the elongated structure may be a buoyant pontoon structure. Each buoyancy structure may thus, for instance, comprise i) a buoyant stabilizing column connected to the centre column via a buoyant elongated pontoon structure, ii) a buoyant stabilizing column connected to the centre column via a non-buoyant elongated structure, or iii) a buoyant elongated pontoon structure without any buoyant stabilizing column. A hull structure of the latter type, i.e. without stabilizing buoyant columns, may be used for e.g. tensionleg platforms (TLP) where tensioned vertical tethers are used to secure the platform in place.

[0023] In an embodiment, the hull structure comprises first, second and third buoyant stabilizing columns circumferentially distributed around the centre column in the horizontal plane, wherein the first, second and third elongated structures extend outwards from the centre column to a corresponding first, second or third buoyant stabilizing column, and wherein each elongated structure is connected to the corresponding buoyant stabilizing column, preferably to a lower portion thereof. In this example, the stabilizing columns form part of the buoyant elements while the elongated structures may or may not exhibit significant buoyancy properties.

[0024] Additional buoyant stabilizing columns may be connected to the first, second and / or third elongated (connection) structures. For instance, two buoyant stabilizing columns may be connected to an outer portion of each of the elongated structures. In an example, there is only one stabilizing buoyant column connected to each elongated structure, and such a single column may be connected to an outer end portion of the elongated structure. If there are two columns they may both be connected at the outer end portion of the elongated structure and / or (partly) on opposite sides of the elongated structure. Depending on the exact design and dimensions of the hull structure, it may be an advantage to locate the column(s) at the outer end portion of the elongated structure for the purpose of improving stowing efficiency.

[0025] That the elongated structures are connected to a lower portion of the corresponding buoyant stabilizing column means that the elongated structures typically are submersed when the platform is set in operation in open water.

[0026] In an embodiment, the elongated structures do not form part of the buoyant elements. In this example, the elongated structures may be bracings that do not contribute significantly to the total buoyancy.

[0027] Additional connection structures used primarily for increasing strength etc. of the platform may be arranged in different ways, for instance between the centre column and a stabilizing buoyant column above the waterplane as well as in-between stabilizing buoyant columns. Such additional connection structures do not form part of the main elongated structures and are not considered to contribute to the general shape of the hull structure, which typically is an Y-shape or X-shape as noted above.

[0028] In an embodiment, the first, second and third elongated structures extend substantially horizontally outwards in the different radial directions from the centre column.

[0029] In an embodiment, the lower side of the first elongated structure is located above or is substantially aligned with the upper side of each of the second and third elongated connection structures. The second and third connection structures may have the same height / thickness and may be arranged in level with a lower side of the corresponding columns so as to provide a support for the hull structure when placed onto a flat surface.

[0030] In an embodiment, a lower side of each of the second and third elongated structures is substantially aligned with a lower side of each of the second and third columns, respectively.

[0031] In an embodiment, a lower side of each of the second and third elongated structures is substantially aligned with a lower side of the central column.

[0032] In an embodiment, the lower side of the first elongated structure is substantially aligned with a lower side of the first column. Thus, also the first column can be located on top of a second or third elongated structure of another hull structure.

[0033] In an embodiment, a lower side of each of the second and third elongated structures comprises one or more flat support sections parallel to the horizontal plane. Also the lower side of the first elongated structure and the upper sides of each of the second and third elongated structures may comprise flat support sections to facilitate the efficient stowing described above. The elongated structures may all have a rectangular cross section and be oriented so that the entire lower and upper sides form flat support sections parallel to the horizontal plane.

[0034] In an embodiment, the elongated structures form buoyant pontoon structures. In this embodiment, the elongated structures form part of the buoyant elements. The pontoon structures may be designed to exhibit sufficient buoyancy to form the only buoyant element of each buoyancy structure.

[0035] In an embodiment, the elongated structures extend outwards from the central column in different radial directions that are substantially evenly distributed circumferentially around the central column. For instance, if there are three elongated structures they may be separated by around 120°. If there are four connection structures they may be separated by around 90°. The length of the elongated structures may be substantially equal so as to provide a hull structure with rotational symmetry. To compensate for the fact that the first elongated structure is located at a higher level and thereby typically closer to the water surface when the platform is in operation, the length of the first elongated structure may differ from that of the other elongated structures and the diameter of the first stabilizing column may differ from that of the other stabilizing columns.

[0036] In an embodiment, the lower side of the first elongated structure is structurally connected to the upper side of at least one of the second and third elongated structures via a connection plate that is arranged at an inside of the centre column. This improves the strength of the hull structure. The connection plate may be connected to the upper side of both the second and third elongated structures as well as to the lower side of the first elongated structure. The connection may be achieved by welding.

[0037] In the case where the lower side of the first elongated structure is located slightly above the upper side of one or more other elongated structures, the connection plate may be bent. For instance, the connection plate may be bent so as to form a lower level side part for connection to the upper side of the second and / or third elongated structure and an upper level side part for connection to the lower side of the first elongated structure, where the connection plate has two bends between the two side parts, i.e. an upward- bend closer to the lower level side and a downward-bend closer to the upper level side. To strengthen the connections between the connection plate and the elongated structures, the lower and upper level side parts of the elongated structure may extend in a flat or curved plane that corresponds to the shape of the side of the elongated structure it is to be connected to. In a typical case the lower and upper sides of the elongated structures are flat and extend in the horizontal plane, and in such a case also the lower and upper level side parts of the elongated structure extend in the horizontal plane

[0038] In an embodiment, the hull structure has a general shape of an Y in the horizontal plane with the central column located in the middle of the Y and with the first, second and third elongated structures forming the straight lines that meet in the middle of the Y.

[0039] In an embodiment, the hull structure does not comprise any additional elongated structure of the type defined besides the first, second and third elongated structures already defined. That is, the hull structure contains only three elongated structures, and each of these is a buoyant pontoon structure and / or (pontoon or not) connects the centre column with (at least) one stabilizing buoyant column. .

[0040] In an embodiment, in which the elongated structures form buoyant pontoon structures, a total number of buoyant pontoon structures that are i) connected to the centre column, and ii) extending substantially horizontally outwards in different radial directions from the centre column, is three or four.

[0041] In an embodiment, each of the elongated structures is substantially straight.

[0042] The invention also concerns a hull structure for a semi-submersible wind power turbine platform, wherein the hull structure exhibits an Y-like shape in a horizontal plane and is made up of the following main components: a centre column configured to support a wind power tower provided with a wind turbine, the centre column being located in a central region of the hull structure as seen in the horizontal plane; first, second and third elongated structures in the form of buoyant pontoon structures connected to the centre column and extending substantially horizontally outwards in different radial directions from the centre column, wherein the first elongated pontoon structure is located at a higher level than the second and third elongated pontoon structures so that a lower side of the first elongated pontoon structure is located above or is substantially aligned with an upper side of each of the second and third elongated pontoon structures.

[0043] In an embodiment, the hull structure further comprises first, second and third buoyant stabilizing columns circumferentially distributed around the centre column in the horizontal plane, wherein each elongated pontoon structure extends to a corresponding first, second or third buoyant stabilizing column, and wherein each elongated pontoon structure is connected to a lower portion of the corresponding buoyant stabilizing column,

[0044] The invention also concerns a marine vessel carrying a set of hull structures, wherein the set of hull structures comprises at least a first and a second hull structure of the above type.

[0045] In an embodiment, the set of hull structures are arranged in a row-like pattern with the first and second hull structures located adjacent each other, wherein the first elongated structure of the second hull structure is located above the second or third elongated structure of the first hull structure.

[0046] Exactly how to stow the hull structures onto the marine vessel depends on, for instance, the size of the (cargo deck of the) vessel, the general size of the hull structures, the particular design of the hull structures (length and width of elongated structures, dimension of columns, relative dimension of centre column and outer columns), etc., and possibly also on the method used for loading the hull structures onto the marine vessel.

[0047] In an embodiment, the set of hull structures further comprises a third hull structure, wherein the first elongated structure of the third hull structure is located above the second or third elongated structure of at least the second hull structure. The set of hull structures may comprise more than three hull structures arranged in different row-like patterns using the raised first elongated structure to allow the hull structures to be located closer to each other than would be allowable without this feature. (Small and light hulls or other structures with high strength may in principle be stowed or placed partly on top of each other in a very space efficient manner but hull structures of the size and weight of interest here require a solid support and cannot simply be lifted in place etc.)

[0048] In an embodiment, the first elongated structure of the second hull structure extends in a direction that is substantially parallel to the direction of extension of the first elongated structure of the first hull structure.

[0049] In an embodiment, the first elongated structure of the third hull structure extends in a direction that is substantially parallel to the direction of extension of the first elongated structure of the first and second hull structures, wherein the first elongated structure of the third hull structure is located above the second or third elongated structure of at least the second hull structure.

[0050] A set of, for instance, six Y-shaped hull structures may be oriented in the same way with the first elongated structure of each hull structure extending in parallel with a longitudinal axis of the marine vessel. These six hull structures may be arranged in two or three parallel sub-rows with three or two, respectively, hull structures aligned in each sub-row, where the first elongated structure of each hull structure (besides one hull structure at the end of the row-like pattern) is located above the second or third elongated structure of at least one other hull structure. This stowing principle is possible also for four or for seven or more hull structures.

[0051] In an embodiment, the first, second and third hull structures are rotated in relation to each other in the horizontal plane so that the first elongated structure of the first, second and third hull structures extend in different directions in the horizontal plane. This may allow for an even more efficient stowing. For instance, three or four (or more) Y-shaped hull structures may be arranged in a slightly bent row (i.e. a line intersecting the centroids of the centre columns has a curved shape) where all hull structures are rotationally oriented in a similar but not identical way with each first (raised) elongated structure extending from the centre column roughly in a northeast direction (as seen from above with the row of hull structures generally extending in a left-right / west-east direction) and, consequently, with each second and third elongated structures extending in roughly south and northwest directions, respectively, and where the outer ends of the “south” elongated structures are located close to each other and where the raised “northeast” elongated structure is located above the “northwest” elongated structure of the hull structure located adjacent to the “east”. By arranging the three of four hull structures in this manner, there is space provided for some additional hull structures to be included in the row-like set of hull structures to be loaded onto the marine vessel (depending on the relative size of the hull structures and the vessel, of course). For instance, the set may include an additional subset, the “east subset”, of three or four hull structures arranged in a slightly bent row similar to the “west subset” described above but turned in the opposite direction with the first (raised) elongated structure instead extending roughly in a southwest direction. This additional “east” subset may be placed close to the first “west” subset at the “east” side thereof, below one or more “northeast” elongated structures of the “west subset” and above one or more “south” elongated structures of the “west subset” so that the slightly bent rows of subsets bend in different directions (i.e. a line intersecting the centroids of the centre columns of both the “west” and “east” subsets forms a wave-shaped curve). There is a point in letting the bending of the subsets go in different directions since if too many hull structures form part of the same subset that curves in the same direction, the width of the subset would be too large for (the cargo deck of) a marine transportation vessel that has an elongated shape. By letting the subsets bend in different direction, the resulting shape of the combined, final set of hull structures reflects the shape of (the cargo deck of) the marine transportation vessel in a better way. Besides using such combinations of bent or curved subsets, additional individual hull structures may be included in the final row-like set of hull structures if there is space left on the marine vessel.

[0052] The invention also concerns 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 and a second hull structure of the above type. The method comprises: providing the set of hull structures floating in water; arranging the set of hull structures in a row-like pattern 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-like pattern of hull structures onto the marine vessel.

[0053] In an embodiment, arranging the set of hull structures in the row-like pattern comprises: arranging the first and second hull structures adjacent each other and so that so that the first elongated structure of the second hull structure is located above the second or third elongated structure of the first hull structure.

[0054] The invention also concerns a further method for loading a set of hull structures onto a cargo carrying marine vessel, wherein the set of hull structures comprises at least a first and a second hull structure of the above type. The method comprises: skidding the first hull structure from a quay onto the marine vessel, and skidding the second hull structure onto the marine vessel so that the first elongated structure of the second hull structure is located above the second or third elongated structure of the first hull structure. The method includes skidding of the first and second hull structures onto the marine vessel simultaneously in one skidding step. In an embodiment, the method further comprises skidding additional hull structures of the above type onto the marine vessel so as to form a row-like pattern of hull structures loaded onto the marine vessel. This embodiment includes skidding the row-like pattern of hull structures onto the marine vessel simultaneously in one skidding step.

[0055] BRIEF DESCRIPTION OF DRAWINGS

[0056] In the description of the invention given below reference is made to the following figure, in which:

[0057] Figure 1 shows a side view of a first example of a hull structure of this disclosure.

[0058] Figure 2 shows a top view of the hull structure according to figure 1 .

[0059] Figure 3 shows a perspective view of the hull structure according to figure 1 .

[0060] Figure 4 shows a first example of a stowing pattern of a set of hull structures according to figure 1 .

[0061] Figure 5 shows a second example of a stowing pattern of a set of hull structures according to figure 1 .

[0062] Figure 6 shows the set of hull structures according to figure 4 loaded onto a marine transportation vessel.

[0063] Figure 7 shows the set of hull structures according to figure 5 loaded onto a marine transportation vessel.

[0064] Figure 8 shows a side view of a second example of a hull structure of this disclosure.

[0065] Figure 9 shows a top view of the hull structure according to figure 8.

[0066] Figure 10 shows a perspective view of the hull structure according to figure 8. Figure 11 shows a first example of a stowing pattern of a set of hull structures according to figure 8.

[0067] Figure 12 shows a second example of a stowing pattern of a set of hull structures according to figure 8.

[0068] Figure 13 shows the set of hull structures according to figure 11 loaded onto a marine transportation vessel. Figure 14 shows the set of hull structures according to figure 12 loaded onto a marine transportation vessel.

[0069] Figure 15 shows a first example of a wind power turbine platform including a hull structure according to this disclosure.

[0070] Figure 16 shows a perspective view of a third example of a hull structure of this disclosure.

[0071] Figure 17 shows an example of a stowing pattern of a set of hull structures according to figure 16.

[0072] Figure 18 shows the set of hull structures according to figure 17 loaded onto a marine transportation vessel.

[0073] Figure 19 shows a perspective view of a fourth example of a hull structure of this disclosure.

[0074] Figure 20 shows a set of hull structures according to figure 19 loaded onto a marine transportation vessel.

[0075] Figure 21 shows a second example of a wind power turbine platform including a hull structure according to this disclosure.

[0076] DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0077] Figures 1-3 show a first example of a hull structure 10 of this disclosure. The hull structure comprises a centre column 4 configured to support a wind power tower 20 provided with a wind turbine 30 (see figure 15). The centre column 4 is located in a central region of the hull structure 10 as seen in a horizontal plane. The hull structure 10 further comprises first, second and third buoyant stabilizing columns 1 , 2, 3 circumferentially distributed around the centre column 4 in the horizontal plane. First, second and third elongated structures (in the following frequently denoted elongated connection structures) in the form of substantially straight buoyant pontoon structures 5, 6, 7 are connected to the centre column 4 and extend substantially horizontally outwards in different circumferentially evenly distributed radial directions from the centre column 4 to a corresponding first, second or third buoyant stabilizing column 1 , 2, 3. The hull structure 10 forms in this example an Y-shaped hull structure with the buoyant stabilizing columns 1 , 2, 3 circumferentially distributed in an even manner around the centre column 4 and with the elongated connection structures / buoyant pontoon structures 5, 6, 7 extending 120° apart in the horizontal plane. Each pontoon structure 5, 6, 7 is connected to a lower portion of the corresponding buoyant stabilizing column 1 , 2, 3.

[0078] The first elongated connection structure / buoyant pontoon structure 5 is located at a higher level than the second and third elongated connection structures 6, 7 so that a lower side 5A of the first elongated connection structure 5 is located slightly above (in this example around 30 cm above) an upper side 6B, 7B of each of the second and third elongated connection structures 6, 7. This allows a plurality of hull structures of similar design to be located close to each other on a flat plane and thus to be stowed in an efficient manner on a cargo deck of a marine transportation vessel as further described below. The vertical distance of 30 cm between the lower side 5A of the first elongated connection structure 5 and the upper side 6B, 7B of the second and third elongated connection structures 6, 7 makes it possible to place cribbing (wooden spacers) between the elongated connection structures to avoid damage when loading and transporting the hull structures (see below).

[0079] A lower side 6A, 7A of each of the second and third connection structures 6, 7 is substantially aligned with a lower side 2A, 3A of each of the second and third columns (2, 3), respectively, and the lower side 6A, 7A of each of the second and third connection structures 6, 7 is also substantially aligned with a lower side 4A of the central column 4. These lower sides form a steady support for the hull structure 10 when placed onto a flat surface.

[0080] As clearly shown in e.g. figure 1 , the lower side 5A of the first elongated connection structure 5 is substantially aligned with a lower side 1 A of the first column 1. This simplifies arranging a set of hull structures 10 in a close stowing configuration before or during loading onto a marine transportation vessel, and it also simplifies separating the set of hull structures after transport.

[0081] All three elongated connection structures 5, 6, 7 have in this example a rectangular cross section with lower 5A, 6A, 7A and upper 5B, 6B, 7B sides parallel to the horizontal plane, which means there are flat support sections parallel to the horizontal plane on the lower side of all connection structures. Also the upper sides form or comprise flat support sections parallel to the horizontal plane so the upper sides of the second and third elongated connection structure 6, 7 form suitable support surfaces for the lower side 5A of the first elongated connection structure 5 and the lower side 1 A of the first column 1 .

[0082] As indicated in figures 1 and 3, the lower side 5A of the first elongated connection structure 5 is structurally connected to the upper side 6B, 7B of the second and third elongated connection structures 6, 7 via a connection plate 8 that is arranged at an inside of the centre column 4. The connection plate 8 may be slightly bent as described further above.

[0083] In the example of figures 1-3, the centre column 4 has a larger diameter than the buoyant stabilizing columns 1 , 2, 3.

[0084] Figure 4 shows a first example of a stowing pattern of a set of hull structures according to figure 1 . Figure 5 shows a second example of a stowing pattern of a set of hull structures according to figure 1 . These stowing patterns are intended to be used when transporting a set of hull structures 10 from e.g. a construction yard, that might be in Asia, to a sheltered location where the wind turbine is to be installed, which might be in Europe. An efficient stowing of the hull structures increases the number of hull structures that can be loaded on the marine vessel used for transport, which in turn reduces the transport costs and the environmental impact caused by the transports. As shown in figures 4 and 5, the set of hull structures comprises several hull structures of the type described above, including first, second, third and fourth hull structures 10a, 10b, 10c, 10d, 10x, 10y, 10z, 10w. The set of hull structures are arranged in a row-like pattern with the first and second hull structures 10a, 10b, 10x, 10y located adjacent each other, wherein the first elongated connection structure 5 of the second hull structure 10b, 10y is located above the second or third elongated connection structure 6, 7 of the first hull structure 10a, 10x. The first elongated connection structure 5 of the third hull structure 10c, 10z is located above the second or third elongated connection structure 6, 7 of both the second and first hull structures 10a, 10b, 10x, 10y.

[0085] In the stowing configuration shown in figure 4, the first elongated connection structure 5 of all six hull structures extends in the same direction. The hull structures are arranged in three parallel sub-rows with two hull structures in each sub-rows, such as the first 10a and a fourth 10d hull structure. A set of hull structures as shown in figure 4 may be arranged on a marine transportation vessel with the raised first connection structures 5 of the first and fourth hull structure 10a, 10d aligned with a longitudinal centreline of the marine vessel (see figure 6).

[0086] In the stowing configuration shown in figure 5, the set of hull structures has eight hull structures, including first, second, third and fourth hull structures 10x, 10y, 10z, 10w, which are slightly rotated in relation to each other in the horizontal plane so that the first elongated connection structure 5 of the different hull structures extend in different directions in the horizontal plane. The stowing configuration of figure 5 allows in this case for a more efficient stowing than the stowing configuration of figure 4.

[0087] The first, second, third and fourth hull structures 10x, 10y, 10z, 10w form a first subset of hull structures, which may be denoted the “west subset” with north upwards in figure 5. This “west subset” is arranged in a slightly bent row (i.e. a line intersecting the centroids of the centre columns has a curved shape) where all hull structures are rotationally oriented in a similar but not identical way with each first (raised) elongated connection structure extending from the centre column roughly in a northeast direction (as seen from above). Consequently, each second and third connection structure in this “west subset” extends in roughly south and northwest directions, respectively. The outer ends of the “south” connection structures are located close to each other and the raised “northeast” connection structure is located above the “northwest” connection structure of the hull structure located adjacent to the “east”, for instance, the raised “northeast” connection structure of the second hull structure 10y is located above the “northwest” connection structure of the first hull structure 10x.

[0088] By arranging the “west subset” of hull structures in this manner, there is in this example space provided for some additional hull structures to be included in the row-like total set of hull structures to be loaded onto the marine vessel. As shown in figure 5, this total set includes an additional subset, the “east subset”, of four hull structures (the hull structures to the right in figure 5) arranged in a slightly bent row similar to the “west subset” described above but turned in the opposite direction with the first (raised) connection structure instead extending roughly in a southwest direction. This additional “east” subset is placed close to the first “west subset” at the “eastern” side thereof, partly vertically below two “northeast” connection structures of the “west subset” (belonging to the first and second hull structures 10x, 10y) and vertically above three “south” connection structures of the “west subset” (belonging to the first , second and third hull structures 10x, 10y, 10z) so that the slightly bent rows of the “west” and “east” subsets bend in different directions (i.e. a line intersecting the centroids of the centre columns of both the “west” and “east” subsets forms a wave-shaped curve). Figure 6 shows the set of hull structures according to figure 4 loaded onto a marine transportation vessel 60, and figure 7 shows the set of hull structures according to figure 5 loaded onto a similar marine transportation vessel 60.

[0089] Figures 8-14 concerns structure and stowing configurations for a second example of a hull structure 100. The differences between the hull structure 10 of figures 1-7 and hull the structure 100 of figures 8-14 are that in the latter example, the stabilizing buoyant columns 1 , 2, 3 has a greater diameter than the centre column 4 and that the pontoon structures 5, 6, 7 are shorter and have a greater width. As can be seen from figures 8-10, the second example structure is, however, in principle the same as the first example structure so what is said previously about the individual hull structure 10 according to figures 1-3 holds also for the individual hull structure 100 according to figures 8-10. However, the differences in column diameter and pontoon shape have a significant effect on the stowing.

[0090] Figure 11 shows a first example of a stowing pattern of a set of hull structures according to figures 8-10 and figure 12 shows a second example of a stowing pattern of a set of hull structures according to figures 8-10. Similar to figures 4 and 5, these stowing patterns are intended to be used when transporting a set of hull structures 100 on a marine transportation vessel.

[0091] Figures 11 and 12 exhibit many similarities with figures 4 and 5, and the focus below is set on describing the differences from what has been said above in relation to figures 4 and 5.

[0092] As shown in figures 11 and 12, the set of hull structures comprises several hull structures of the type shown in figures 8-11 , including first, second, third and fourth hull structures 100a, 100b, 100c, 100d, 100x, 100y, 100z, 100w. In the stowing configuration shown in figure 11 , the first elongated connection structure 5 of all six hull structures extends in the same direction, similar to figure 4. However, in figure 11 the hull structures are instead arranged in two parallel sub-rows with three hull structures in each sub-rows. For instance, one row comprises the first and the third hull structure 100a, 100c (and an additional hull structure) and the other row comprises the second and the fourth hull structure 100b, 100d (and an additional hull structure).

[0093] In the stowing configuration shown in figure 12, the set of hull structures has seven hull structures, including first, second, third and fourth hull structures 100x, 100y, 100z, 100w, where at least the second, third and fourth hull structures 100y, 100z, 100w are slightly rotated in relation to each other in the horizontal plane so that the first elongated connection structure 5 of the different hull structures extend in different directions in the horizontal plane. The stowing configuration of figure 12 allows also in this case for a more efficient stowing than an “aligned” stowing configuration according to figure 11.

[0094] In this example only three hull structures form the subset discussed in relation to figure 5. The second, third and fourth hull structures 100y, 100z, 100w form a first subset of hull structures, which may be denoted the “west subset” with the terminology used in relation to figure 5, while the first hull structure 100x and the two hull structures to the right thereof form the “east subset” that is turned in the opposite direction. Similar to what is described above, each subset forms a slightly bent row and the rows of the “west” and “east” subsets bend in different directions. Because the design of the individual hull structures differ between figures 12 and 5, there are some differences in how many second or third pontoons are located below a certain first pontoon and similar, but the principle of the two subsets is the same. In the stowing configuration of figure 12, one additional hull structure, i.e. hull structure to the far left, has been included in the combined set of hull structure that thus contains seven hull structures in total.

[0095] Figure 13 shows the set of hull structures according to figure 11 loaded onto a marine transportation vessel 60, and figure 14 shows the set of hull structures according to figure 12 loaded onto a similar marine transportation vessel 60.

[0096] The hull structures may be loaded onto a marine transportation vessel by any of the methods mentioned further above, i.e. in short either by arranging the set of hull structures in any of the stowing configurations when floating in water and make use of a semi-submersible cargo carrying marine vessel for loading (when raising the vessel from a lower position below the hull structures), or by skidding the hull structures in a row (or one by one) from a quay onto the marine vessel. For unloading it is useful if the marine vessel used for skid-out loading also is of semi-submersible type.

[0097] Figure 15 shows a first example of a wind power turbine platform 50 including a hull structure 10, 100 and a wind power tower 20 provided with a wind turbine 30. An approximate location of an operating waterline 25 is indicated.

[0098] Figures 16-20 show a third and a fourth example of a hull structure 80, 200 intended for a tension-leg platform, TLP anchored to the sea bottom by means of tethers 70 (see figures 16, 19 and 21 ). The type of hull structure 80, 200 of figures 16-21 differs from the type of hull structure 10, 100 of figures 1-15 mainly in that there are no buoyant stabilizing columns included. As in the examples of figures 1-15, the elongated (connection) structures 5, 6, 7 form buoyant pontoon structures, but in the examples of figures 16-21 , the elongated structures 5, 6, 7 form the only buoyant element in each buoyancy structure. Figure 16 shows a perspective view of the third example of the hull structure 80. Similar to what has been described above, the hull structure 80 comprises a centre column 4 configured to support a wind power tower 20 provided with a wind turbine 30 (see figure 21 ) with the centre column 4 located in a central region of the hull structure 80 as seen in a horizontal plane. The first, second and third elongated structures in the form of substantially straight buoyant pontoon structures 5, 6, 7 are connected to the centre column 4 and extend substantially horizontally outwards in different circumferentially evenly distributed radial directions from the centre column 4. As indicated in figure 16, the elongated structures 5, 6, 7 are configured to be connected at their outer ends to tethers 70 to thus form a connection between the centre column 4 and a tension leg at the outer end of each elongated (connection) structure 5, 6, 7.

[0099] Similar to figures 1-15, the first elongated connection structure / buoyant pontoon structure 5 is located at a higher level than the second and third elongated connection structures 6, 7 so that a lower side of the first elongated connection structure is located slightly above (in this example around 30 cm above) an upper side of each of the second and third elongated connection structures.

[0100] Figure 17 shows an example of a stowing pattern of a set of hull structures according to figure 16. The stowing pattern of the hull structures 80a-80d in figure 17 is partly similar to the stowing pattern of the hull structures 10x-10w shown in figure 5.

[0101] Figure 18 shows the set of hull structures according to figure 17 loaded onto a marine transportation vessel 60.

[0102] Figure 19 shows a perspective view of a fourth example of a hull structure 200, which in principle is structured in the same way as the hull structure 80 shown in figure 16. A difference is that each elongated connection structure 5, 6, 7 has a circular transversal cross section in figure 19, whereas the corresponding cross section of the elongated connection structures of figure 16 is rectangular.

[0103] Figure 20 shows a set of hull structures according to figure 19 loaded onto a marine transportation vessel 60. The stowing pattern of hull structures 200a- 200d is similar to that of hull structures 80a-80d shown in figures 17 and 18.

[0104] Figure 21 shows a second example of a wind power turbine platform 50, in this case of TLP type, including a hull structure 80, 200 and a wind power tower 20 provided with a wind turbine 30. An approximate location of an operating waterline 25 is indicated. Figure 21 also indicate the connection between the elongated pontoon structures 5, 6, 7 and the tethers 70.

[0105] 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 elongated connection structures 5, 6, 7 shown in figures 1-15 do not necessarily have to be buoyant elements. Further, the cross section of the elongated connection structure may be different than exemplified in the figures and, as indicated in figures 16-18, the cross section may vary along the longitudinal axis of the elongated structure.

[0106] References in figures

[0107] 1 , 2, 3 first, second and third buoyant stabilizing column 1A, 2A, 3A lower side of first, second and third column

[0108] 4 centre column 5, 6, 7 first, second and third elongated buoyant pontoon structure

[0109] 5A, 6A, 7A lower side of first, second and third elongated structure 5B, 6B, 7B upper side of first, second and third elongated structure 8 supporting connection plate

[0110] 10, 100 hull structure (first and second example) 80, 200 hull structure (third and fourth example)

[0111] 20 wind turbine tower

[0112] 25 operating waterline

[0113] 30 wind turbine

[0114] 50 wind power turbine platform 60 marine vessel

[0115] 70 tethers

Claims

27CLAIMS1. A hull structure (10, 100, 80, 200) for a semi-submersible wind power turbine platform (50), wherein the hull structure (10, 100, 80, 20) comprises:- a centre column (4) configured to support a wind power tower (20) provided with a wind turbine (30), the centre column (4) being located in a central region of the hull structure (10, 100, 80, 200) as seen in a horizontal plane; and- first, second and third buoyancy structures circumferentially distributed around the centre column (4) in the horizontal plane; wherein each buoyancy structure comprises one or more buoyant elements (1 , 2, 3, 5, 6, 7) configured to contribute significantly to a total buoyancy of the hull structure (10, 100, 80, 200), wherein each buoyancy structure comprises an elongated structure (5, 6, 7) connected to the centre column (4) so as to form first, second and third elongated structures (5, 6, 7) that are connected to the centre column (4) and that extend outwards in different radial directions from the centre column (4), wherein the first elongated structure (5) is located at a higher level than the second and / or third elongated structures (6, 7) so that a lower side (5A) of the first elongated structure (5) is located above or is substantially aligned with an upper side (6B, 7B) of at least one of the second and third elongated structures (6, 7).

2. The hull structure (10, 100, 80, 200) of claim 1 , wherein the one or more buoyant elements comprises a buoyant stabilizing column (1 , 2, 3) and / or an elongated structure in the form of a buoyant pontoon structure (5, 6, 7).

3. The hull structure (10, 100) of claim 1 or 2, wherein the hull structure comprises first, second and third buoyant stabilizing columns (1 , 2, 3) circumferentially distributed around the centre column (4) in the horizontal plane,wherein the first, second and third elongated structures (5, 6, 7) extend outwards from the centre column (4) to a corresponding first, second or third buoyant stabilizing column (1 , 2, 3), and wherein each elongated structure (5, 6, 7) preferably is connected to a lower portion of the corresponding buoyant stabilizing column (1 , 2, 3),4. The hull structure (10, 100) of claim 3, wherein the elongated structures (5, 6, 7) do not form part of the buoyant elements.

5. The hull structure (10, 100, 80, 200) of any of the above claims, wherein the lower side (5A) of the first elongated structure (5) is located above or is substantially aligned with the upper side (6A, 7A) of each of the second and third elongated structures (6, 7).

6. The hull structure (10, 100) of claim 3 or 4, wherein a lower side (6A, 7A) of each of the second and third elongated structures (6, 7) is substantially aligned with a lower side (2A, 3A) of each of the second and third columns (2, 3), respectively.

7. The hull structure (10, 100, 80, 200) of any of the above claims, wherein a lower side (6A, 7A) of each of the second and third elongated structures (6, 7) is substantially aligned with a lower side (4A) of the central column (4).

8. The hull structure (10, 100) of claim 3 or 4, wherein the lower side (5A) of the first elongated structure (5) is substantially aligned with a lower side (1 A) of the first column (1).

9. The hull structure (10, 100, 80, 200) of any of the above claims, wherein a lower side (6A, 7A) of each of the second and third elongated structures (6, 7) comprises one or more flat support sections parallel to the horizontal plane.

10. The hull structure (10, 100, 80, 200) of any of the above claims, wherein the elongated structures (5, 6, 7) form buoyant pontoon structures.11 . The hull structure (10, 100, 80, 200) of any of the above claims, wherein the elongated structures (5, 6, 7) extend outwards from the central column (4) in different radial directions that are substantially evenly distributed circumferentially around the central column (4).

12. The hull structure (10, 100, 80, 200) of any of the above claims, wherein the lower side (5A) of the first elongated structure (5) is structurally connected to the upper side (6B, 7B) of at least one of the second and third elongated structures (6, 7) via a connection plate (8) that is arranged at an inside of the centre column (4).

13. The hull structure (10, 100, 80, 200) of any of the above claims, wherein the hull structure has a general shape of an Y in the horizontal plane with the central column (4) located in the middle of the Y and with the first, second and third elongated structures (5, 6, 7) forming the straight lines that meet in the middle of the Y.

14. The hull structure (10, 100, 80, 200) of any of the above claims, wherein the hull structure does not comprise any additional elongated structure of the type defined besides the first, second and third elongated structures (5, 6, 7) already defined.

15. The hull structure (10, 100, 80, 200) according to claim 10, wherein a total number of buoyant pontoon structures (5, 6, 7) that are i) connected to the centre column (4) and ii) extending substantially horizontally outwards in different radial directions from the centre column (4), is three or four.

16. The hull structure (10, 100, 80, 200) of any of the above claims, wherein each of the elongated structures (5, 6, 7) is substantially straight.

17. A hull structure (10, 100, 80, 200) for a semi-submersible wind power turbine platform (50), wherein the hull structure (10) exhibits an Y-like shape in a horizontal plane and is made up of the following main components:- a centre column (4) configured to support a wind power tower (20) provided with a wind turbine (30), the centre column (4) being located in a central region of the hull structure (10, 100) as seen in the horizontal plane;- first, second and third elongated structures (5, 6, 7) in the form of buoyant pontoon structures connected to the centre column (4) and extending substantially horizontally outwards in different radial directions from the centre column (4) wherein the first elongated pontoon structure (5) is located at a higher level than the second and third elongated pontoon structures (6, 7) so that a lower side (5A) of the first elongated pontoon structure (5) is located above or is substantially aligned with an upper side (6B, 7B) of each of the second and third elongated pontoon structures (6, 7).

18. The hull structure (10, 100) of claim 17, further comprising first, second and third buoyant stabilizing columns (1 , 2, 3) circumferentially distributed around the centre column (4) in the horizontal plane, wherein each elongated pontoon structure (5, 6, 7) extends to a corresponding first, second or third buoyant stabilizing column (1 , 2, 3), and wherein each elongated pontoon structure (5, 6, 7) is connected to a lower portion of the corresponding buoyant stabilizing column (1 , 2, 3).

19. Marine vessel (60) carrying a set of hull structures (10, 100, 80, 200), wherein the set of hull structures comprises at least a first and a second hull structure (10a, 10b, 10x, 10y, 100a, 100b, 100x, 100y) configured according to any of claims 1-18.

20. Marine vessel (60) according to claim 19, wherein the set of hull structures are arranged in a row-like pattern with the first and second hull31 structures (10a, 10b, 10x, 10y, 100a, 100b, 100x, 100y) located adjacent each other, wherein the first elongated structure (5) of the second hull structure (10b, 10y, 100b, 100y) is located above the second or third elongated structure (6, 7) of the first hull structure (10a, 10x, 100a, 100x).21 . Marine vessel (60) according to claim 20, wherein the set of hull structures further comprises a third hull structure (10c, 10z, 100c, 100z), and wherein the first elongated structure (5) of the third hull structure (10c, 10z, 100c, 100z) is located above the second or third elongated structure (6, 7) of at least the second hull structure (10b, 10y, 100b, 100y).

22. Marine vessel (60) according to claim 20 or 21 , wherein the first elongated structure (5) of the second hull structure (10b, 100b) extends in a direction that is substantially parallel to the direction of extension of the first elongated structure (5) of the first hull structure (10a, 100a).

23. Marine vessel (60) according to claim 21 and 22, wherein the first elongated structure (5) of the third hull structure (10c, 100c) extends in a direction that is substantially parallel to the direction of extension of the first elongated structure (5) of the first and second hull structures (10a, 10b, 100a, 100b) and wherein the first elongated structure (5) of the third hull structure (10c, 100c) is located above the second or third elongated structure (6, 7) of at least the second hull structure (10b, 100b).

24. Marine vessel (60) according to claim 21 , wherein the first, second and third hull structures (10x, 10y, 10z, 100x, 100y, 100z) are rotated in relation to each other in the horizontal plane so that the first elongated structure (5) of the first, second and third hull structures (10x, 10y, 10z, 100x, 100y, 100z) extend in different directions in the horizontal plane.

25. Method for loading a set of hull structures (10, 100, 80, 200) onto a semisubmersible cargo carrying marine vessel (60) configured to be lowered32 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 and a second hull structure (10a, 10b, 10x, 10y, 100a, 100b, 100x, 100y) configured according to any of claims 1-18, the method comprising:- providing the set of hull structures floating in water;- arranging the set of hull structures in a row-like pattern above the marine vessel (60) when the marine vessel is in its lower position; and- raising the marine vessel (60) to its upper position so as to load the row-like pattern of hull structures onto the marine vessel (60).

26. Method according to claim 25, wherein arranging the set of hull structures in the row-like pattern comprises:- arranging the first and second hull structures (10a, 10b, 10x, 10y, 100a, 100b, 100x, 100y) adjacent each other and so that so that the first elongated structure (5) of the second hull structure (10b, 10y, 100b, 100y) is located above the second or third elongated structure (6, 7) of the first hull structure (10a, 10x, 100a, 100x).

27. Method for loading a set of hull structures (10, 100, 80, 200) onto a cargo carrying marine vessel (60), wherein the set of hull structures comprises at least a first and a second hull structure (10a, 10b, 10x, 10y, 100a, 100b, 100x, 100y) arranged according to any of claims 1-18, the method comprising:- skidding the first hull structure (10a, 10x, 100a, 100x) from a quay onto the marine vessel (6),- skidding the second hull structure (10b, 10y, 100b, 100y) onto the marine vessel so that the first elongated structure (5) of the second hull structure (10b, 10y, 100b, 100y) is located above the second or third elongated structure (6, 7) of the first hull structure (10a, 10x, 100a, 100x).3328. The method of claim 27, further comprising skidding additional hull structures according to any of claims 1-18 onto the marine vessel (60) so as to form a row-like pattern of hull structures loaded onto the marine vessel

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