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FLOATING WIND SEMI-SUBMERSIBLE WITH T-SHAPED PONTOON

20230160368 · 2023-05-25

    Inventors

    Cpc classification

    International classification

    Abstract

    A moored floating offshore wind semi-submersible platform with at least three columns characterized in that columns are supported on a T-shaped underwater hull made up of two elongated pontoons, where one pontoon is perpendicular to the other pontoon and a method that allow that the semi-submersible platform is constructed in hull-assemblies and blocks at a first location, transported efficiently to a second location close to the final offshore location where the hull-assemblies and blocks may be assembled quay-side while floating in the water. The platform will support at least one wind turbine on a supporting structure (tower) but may also support two turbines and in the latter case the platform will be moored offshore with a mooring turret to allow the platform to align in a favourable direction to the wind.

    Claims

    1. A semi-submersible platform for positioning in a body of water for production of electrical energy from wind energy, the semi-submersible platform comprising: a submersible underwater hull; three or more columns supported on and interconnected by the underwater hull and protruding above the surface of the body of water when the semi-submersible platform is positioned in the body of water, wherein at least three of said columns are stabilizing buoyant columns; at least one wind energy harvesting device arranged on a supporting structure arranged at an upper end of one of the columns, characterised in that the underwater hull is made up of at least a first and a second elongated pontoon, said first pontoon is at its two outer parts supporting and interconnecting to the lower end of two of the stabilizing columns, said second pontoon is approximately perpendicular to and interconnecting to said first pontoon at approximately mid-length of said first pontoon, said second pontoon is supporting and interconnecting to the lower end of a third stabilizing column at its outer part opposite to the end interconnecting to said first pontoon said first and second pontoons in the horizontal plane resemble the letter “T” with one stabilizing column arranged close to each of the three ends of the “T”.

    2. A semi-submersible platform according to claim 1, characterised in that said first and second pontoons have substantially four-sided cross-sections and are each arranged with two sides, a bottom and a deck and that said first and second pontoons have substantially the same height at their interconnection

    3. (canceled)

    4. (canceled)

    5. (canceled)

    6. A semi-submersible platform according to claim 1, characterised in that two lower horizontal bracings are arranged to interconnect the first and second pontoons, one from the outer part of each end of the first pontoon and towards the outer part of the second pontoon.

    7. A semi-submersible platform according to claim 6, characterised in that said two lower horizontal bracings are arranged at the deck level of the first and second pontoons.

    8. (canceled)

    9. A semi-submersible platform according to claim 1, characterised in that the centre of three stabilizing buoyant columns are arranged at an approximately equilateral triangle.

    10. (canceled)

    11. (canceled)

    12. (canceled)

    13. (canceled)

    14. A semi-submersible platform according to claim 1, characterised in that added mass and dampening increasing horizontal plates are arranged at close to the pontoon bottom at the outer ends of the first pontoon.

    15. (canceled)

    16. (canceled)

    17. A semi-submersible platform according to claim 1, characterised in that added mass and dampening increasing horizontal plates are arranged at close to the pontoon bottom at the outer end of the second pontoon.

    18. A semi-submersible platform according to claim 1, characterised in that one wind energy harvesting device is arranged on a vertical supporting structure supported on one of the columns, which may be a stabilizing buoyant columns.

    19. (canceled)

    20. (canceled)

    21. (canceled)

    22. A semi-submersible platform according to claim 1, characterised in that two wind energy harvesting devices are arranged on supporting structures, one at each of the stabilizing buoyant columns arranged at each end of the first pontoon.

    23. (canceled)

    24. (canceled)

    25. (canceled)

    26. (canceled)

    27. A method for assembling of a semi-submersible platform comprising: a submersible underwater hull; three or more columns supported on and interconnected by the underwater hull and protruding above the surface of the body of water when the semi-submersible platform is positioned in the body of water, wherein at least three of said columns are stabilizing buoyant columns; at least one wind energy harvesting device arranged on a supporting structure arranged at an upper end of one of the columns characterised in that the underwater hull is made up of at least a first and a second elongated pontoon said first pontoon is at its two outer parts supporting and interconnecting to the lower end of two of the stabilizing columns said second pontoon is approximately perpendicular to and interconnecting to said first pontoon at approximately mid-length of said first pontoon said second pontoon is supporting and interconnecting to the lower end of a third stabilizing column at its outer part opposite to the end interconnecting to said first pontoon said first and second pontoons in the horizontal plane resemble the letter “T” with one stabilizing column arranged close to each of the three ends of the “T” wherein the method comprises: joining a first hull-assembly to an outer part of the second pontoon so as to form a second hull assembly, wherein the first hull-assembly comprises the first pontoon, two of the stabilizing columns and a buoyant inner part of the second pontoon that has a length that is sufficient to allow the first hull-assembly to float substantially stable and upright, and wherein the outer part of the second pontoon is of such dimension that it also floats substantially stable.

    28. The method according to claim 27, wherein the method comprises: prior to joining, positioning the first hull-assembly and the outer part of the second pontoon in a body of water so as to float substantially stable and upright and at substantially the same draught and trim so as to provide for joining.

    29. The method according to claim 27, joining the first hull-assembly to the outer part of the second pontoon by joining the outer part of the second pontoon to the buoyant inner part of the second pontoon.

    30. The method according to claim 27, wherein the first hull-assembly is joined to the outer part of the second pontoon by means of welding.

    31. The method according to claim 30, wherein welding of a lower part of the joint takes place inside a welding habitat arranged around the joint and from which the water has been evacuated.

    32. The method according to claim 27, wherein the second hull-assembly is floating stable in a body of water while the remaining parts of the semi-submersible platform is erected onto the second hull-assembly to complete the semi-submersible platform.

    33. The method according to claim 27, wherein the first hull-assembly is constructed at a first location and transported to a second location where the second hull-assembly is assembled.

    34. Method for transporting at least a first and a second underwater hull of a corresponding first and second semi-submersible platform comprising: a submersible underwater hull; three or more columns supported on and interconnected by the underwater hull and protruding above the surface of the body of water when the semi-submersible platform is positioned in the body of water, wherein at least three of said columns are stabilizing buoyant columns; at least one wind energy harvesting device arranged on a supporting structure arranged at an upper end of one of the columns characterised in that the underwater hull is made up of at least a first and a second elongated pontoon said first pontoon is at its two outer parts supporting and interconnecting to the lower end of two of the stabilizing columns said second pontoon is approximately perpendicular to and interconnecting to said first pontoon at approximately mid-length of said first pontoon said second pontoon is supporting and interconnecting to the lower end of a third stabilizing column at its outer part opposite to the end interconnecting to said first pontoon said first and second pontoons in the horizontal plane resemble the letter “T” with one stabilizing column arranged close to each of the three ends of the “T” from a first location to a second location using a marine vessel, such as a semi-submersible dry-tow vessel, wherein each of the first and second underwater hulls is arranged with its first pontoon extending in a first direction and with the second pontoon, or at least an inner part of the second pontoon connected to the first pontoon, extending in a second direction substantially perpendicular to the first direction, and wherein the first and second underwater hulls are directed towards each other so that the second pontoon, or said part thereof, of the first underwater hull extends towards the first pontoon of the second underwater hull and vice versa.

    35. Method according to claim 34, wherein the second pontoon of each of the first and second underwater hulls has its full length and is connected to its corresponding first pontoon, wherein the first and second underwater hulls are arranged in an offset manner, for instance in relation to the longitudinal axis of the marine vessel, and wherein the first and second underwater hulls are arranged so that the second pontoon of the first underwater hull extends alongside of the second pontoon of the second underwater hull.

    36. Method according to claim 34, wherein the second pontoon of each of the first and second underwater hulls forms two parts, wherein one of said two parts forms an inner part that is connected to its corresponding first pontoon and wherein the other of said two parts forms a separate outer part, wherein the first and second underwater hulls are arranged to be substantially aligned with each other so that the inner part of the second pontoon of the first underwater hull projects towards the corresponding inner part of the second pontoon of the second underwater hull, wherein the two separate outer parts of the first and second underwater hulls are arranged on opposite sides of the two inner parts of the first and second underwater hulls.

    37. Method according to claim 36, wherein the pontoons and pontoon parts of the first and second underwater hulls are joined together so as to form one transport assembly with ability to float stable and upright.

    38. Method according to claim 34, wherein the first and second underwater hulls are arranged in such a way that the first pontoons extend across a longitudinal axis of the marine vessel.

    Description

    BRIEF DESCRIPTION OF DRAWINGS

    [0057] The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not !imitative of the present invention, and wherein:

    [0058] FIG. 1 shows an embodiment of a semi-submersible platform according to the invention with three stabilizing columns and one wind energy harvesting device arranged on one of the stabilizing columns.

    [0059] FIG. 2 shows a top view of the same embodiment as shown in FIG. 1 but with the wind energy harvesting device removed.

    [0060] FIG. 3 shows an embodiment of a semi-submersible platform according to the invention with one wind energy harvesting device arranged on a separate column.

    [0061] FIG. 4 shows an embodiment of a semi-submersible platform according to the invention with three stabilizing columns and two wind energy harvesting device arranged on inclined support structures on one column each.

    [0062] FIG. 5 shows a top view of the same embodiment as shown in FIG. 4.

    [0063] FIG. 6 shows the same embodiment of a semi-submersible platform as shown in FIG. 4 but with a horizontal bracing in-between the upper end of the wind turbine supporting structures (towers).

    [0064] FIG. 7 shows the magnified view of stabilizing buoyant column where the shell plating has been removed to disclose an internal vertical bulkhead.

    [0065] FIG. 8 shows a view of the first hull-assembly and the outer part of the second pontoon, an embodiment during the preferred method for construction.

    [0066] FIG. 9 shows a view of the joining of the first hull-assembly and the outer part of the second pontoon by the use of a welding inside a welding habitat to a second hull-assembly and other blocks to be erected onto the second hull-assembly.

    [0067] FIG. 10 shows a stowage arrangement of a pair of first hull-assemblies

    [0068] FIG. 11 shows the outer part of the second pontoon stowed on top of the first pontoon of the first hull-assembly.

    [0069] FIG. 12 shows the transport of six hulls of semi-submersible platforms where the hulls are arranged two and two into transport structures where the first hull assemblies are arranged with the first pontoons parallel to each other with the inner part of the second pontoons directed towards each other and where the second hull assembly are arranged with the outer parts of the second pontoons parallel to and in-between the first pontoons, one on each side of the inner parts of the second pontoons.

    [0070] FIG. 13 shows the transport of four underwater hulls where the hulls are arranged two and two in a “head to toe” arrangement with their second pontoons side by side with their first pontoons on different ends of the second pontoons.

    DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

    [0071] Examples of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which examples of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein. Rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference signs refer to like elements throughout.

    [0072] The semi-submersible platform 1 shown in FIG. 1 is floating semi-submersed in a body of water, such as the sea, at a draft giving a waterplane 2. The platform is arranged with wind turbine 301 for harvesting energy from the wind and producing electrical energy. The wind turbine 301, which may be an azimuthing horizontal axis turbine as shown in FIG. 1 or a vertical axis wind turbine, is arranged on a support structure 302, such as a structural tower (or mast).

    [0073] The semi-submersible platform 1 has an underwater hull made up of two elongated pontoons, where one (second) pontoon 12 is arranged perpendicular to the other (first) pontoon 11. The second pontoon 12 is interconnected at its inner end to the mid-length of the first pontoon 11. This gives that the underwater hull seen from above, FIG. 2, resemble the letter “T”, where the first pontoon 11 is the “roof of the T” and the second pontoon 12 is the “pillar of the T”.

    [0074] In the following marine terms will be used to define the directions of the semi-submersible platform 1 and for example the first pontoon 11 is transversely arranged in the aft end “A” and for example the second pontoon 12 is longitudinal arranged with its outward end constituting the forward end “F” of the platform 1, or vice versa depending on definition preferences due to that the platform will be moored in an offshore location with an orientation determined by the most favourable wind direction.

    [0075] With the above pontoon configuration, the semi-submersible platform 1 will in most aspects become symmetric around the longitudinal centreline of the second pontoon 12.

    [0076] The pontoons 11 & 12 are buoyant and divided internally with bulkheads and include in a well-known manner ballast tanks and a ballast system, which makes it possible to alter the draft, trim and heel of the semi-submersible platform, as well as potential other tanks. The pontoons 11 & 12 are advantageously arranged with a rectangular cross section and may be with sharp or rounded corners/bilges and are preferable of the same depth/height to provide an effective load transfer between the bottoms and decks of the two pontoons.

    [0077] At the intersection between the two pontoons 11 & 12 there are at each side of the inward/aft end of the second pontoon 12 at the corners to the first pontoon 11 arranged a triangular buoyant structure 131, which will improve the structural load transfer between the two pontoons by acting as structural brackets. The triangular buoyant structures 131 have the same depth/height as the pontoons.

    [0078] There are three stabilizing buoyant columns 201, 202 & 203 supported on and interconnected by the underwater hull and protruding above the surface 2 of the body of water. One stabilizing buoyant columns 201 is arranged in the forward end “F” of the semi-submersible platform 1 at the outer end of the second pontoon and the other two stabilizing columns 202 & 203 are arranged at the outer ends of the first pontoon, starboard aft and port aft of the semi-submersible platform 1, respectively.

    [0079] The stabilizing buoyant columns 201, 202 & 203 are buoyant and provide the semi-submersible platform 1 the required area and moment of inertia at the waterplane and are further divided internally with watertight vertical bulkheads and/or horizontal stringers and include in a well-known manner ballast and void tanks and access to the pontoons.

    [0080] The stabilizing buoyant columns 201, 202 & 203 are advantageously arranged with a circular horizontal cross section but may also be of other cross section shapes, such as rectangular with sharp or rounded corners, triangular, etc. and are further advantageously arranged with vertical orientation but may also be inclined.

    [0081] By arranging the centres of stabilizing buoyant columns 201, 202 & 203 on an equilateral triangle 291 and having the stabilizing buoyant columns with the same cross section area/diameter “D”, the semi-submersible platform will have the same moment of inertia of the water plane 2 and metacentric height in both longitudinal and transverse direction.

    [0082] In the embodiment of the invention shown in FIG. 1 the outward shell of each of the three stabilizing buoyant columns 201, 202 & 203 is extended downwardly to the bottom of the pontoons 11, 12 to form rounded ends of the two pontoons at their outward ends.

    [0083] The stabilizing buoyant columns 201, 202 & 203 are interconnected in their upper part, either at the upper end or just below, with three horizontal bracings 241, one between each pair of stabilizing buoyant columns. These bracings 241 are shown with a circular cross-section but could also be with another type of cross section, e.g. I-beam or box beam. The bracings are advantageously extending partly into the columns to give a smooth load transfer between the bracings 241 and the stabilizing buoyant columns 201, 202 & 203.

    [0084] In the embodiment of the invention shown in FIG. 1 there are shown two lower horizontal bracings 141 arranged to interconnect the first 11 and second 12 pontoons, one from the outer end of each end of the first pontoon 11 and towards the outer end of the second pontoon 12, located substantially underneath two of the upper bracings 241. In FIG. 1 the two lower horizontal bracings 141 are located just below the deck 113, 123 of the two pontoons 11, 12. The purpose of the lower horizontal bracings 141 is to support the transverse strength of the second pontoon 12, which may be beneficial for the case that the wind is acting on the wind turbine 301 in the transverse direction of the semi-submersible platform 1. While it is beneficial from a strength and fatigue point of view to arrange the two lower horizontal bracings 141 as low as possible, they also need to be above the water during the assembly of the semi-submersible platform 1 to allow that welding can be performed, see further below. By arranging the two lower horizontal bracings 141 just below the deck 113, 123 of the two pontoons 11, 12, they will be located away from the joint between the pontoons 11, 12 and the stabilizing buoyant columns 201, 202 & 203.

    [0085] At the outer ends of the first pontoon 11 there are arranged added mass and dampening increasing horizontal plates 118 close to the pontoon bottom at the outer ends of the first pontoon. These plates are in the embodiment of the invention shown in FIG. 1 arranged at the same side of the first pontoon 11 as the second pontoon 12 and in such a way that the added mass and dampening increasing plates don't substantially increase the length of the first pontoon 11/overall breadth of the semi-submersible platform 1. To reduce the overall breadth of the semi-submersible platform 1 may be beneficial to meet the transportation requirements of some dry-tow vessels.

    [0086] In the embodiment of the invention shown in FIG. 1 there is also arranged added mass and dampening increasing horizontal plates 128 at close to the pontoon bottom at the outer end of the second pontoon 12 at the forward end “F” of the semi-submersible platform 1. While the horizontal plate 128 is shown as one continuous plate around the end of the second pontoon, the horizontal plate may be divided in plates with openings in-between, for example to allow mooring line attachments to not be disturbed by the plates.

    [0087] The wind-turbine 301 of azimuthing horizontal axis type as shown in FIG. 1 is arranged on a support structure 302, such as a structural tower (or mast) which is supported on the forward stabilizing buoyant column 201.

    [0088] The semi-submersible platform 1 is moored with, in a well-known manner, a catenary mooring system or taut-leg mooring system. In alternative embodiment the semi-submersible platform 1 may be moored with tendons and the semi-submersible platform becomes a tension leg platform (TLP). As all these three types of mooring systems are well-known from the semi-submersible oil & gas industry and are therefore not described further or shown on the drawings. There are a number of alternative manners to attach the mooring lines/tendons to the semi-submersible platform but these are not detailed here.

    [0089] In an alternative embodiment of the semi-submersible platform 1 shown in FIG. 3, wind turbine 301 with its support structure (tower) 302, is arranged on a separate column 221 which primary purpose is to support the wind turbine 301. This separate column may either be buoyant or non-buoyant. By arranging the wind turbine on a separate column 221, the structural loading of the stabilizing buoyant column 201 are reduced.

    [0090] The separate column 221 is supported on one of the two pontoons 11, 12 and may further be interconnected with the buoyant stabilizing columns with upper bracings, 241.

    [0091] In FIG. 3 there is also shown an alternative embodiment of the lower horizontal bracings 141, where the lower horizontal bracings are arranged with their centre level with the pontoons deck, 113,123. This alternative embodiment may be beneficial in case of limited displacement/larger draught during assembly of the semi-submersible platform 1. The alternative embodiment of the horizontal bracings 141 in FIG. 3 is not related to the separate column 221 disclosed in FIG. 3 and could have been combined with any other embodiment of the semi-submersible platform 1.

    [0092] In FIG. 4 an alternative embodiment of the semi-submersible platform 1 with two wind-turbines 301 with a support structure (tower) 302 each arranged on the two columns 202, 203 in the aft end “A”. These wind turbines may be of a fixed orientation parallel with the longitudinal direction of the semi-submersible platform and instead the platform is aligned with the most favourable wind direction, i.e. weather vane.

    [0093] To allow the semi-submersible platform 1 weather vane there is arranged a mooring turret 401 underneath the forward stabilizing column 201 which the mooring lines are attached to and around which the semi-submersible platform may rotate. The use of mooring turrets to allow floating units to weather vane is a well-known manner from the offshore oil & gas industry and therefore the turret and mooring are not further described herein.

    [0094] With the wind turbines orientated in a fixed direction towards the semi-submersible platform 1 that weather vane, the varying wind forces will primarily act in the longitudinal direction of the semi-submersible platform. It may therefore be beneficial to have an increased stability/metacentric height/moment of inertia in the longitudinal direction than transversely and therefore the forward buoyant stabilizing column 201 may have a larger water-plane area/diameter than the aft buoyant stabilizing columns 202, 203 and also be arranged further apart from these, resulting in that the centre of the three stabilizing buoyant columns are arranged at an isosceles triangle 292, as shown in FIG. 5.

    [0095] From FIGS. 4 and 5 it's also shown that the two wind turbine support structure (tower) 302 are inclined outwards in transverse direction, parallel to the centre-line of the first pontoon 11. This will give a larger separation of the two turbines and further increase the weather vaning moment on the semi-submersible platform 1 rotating around the mooring turret 401.

    [0096] In FIG. 5 the semi-submersible platform is shown in an underwater embodiment where there are no lower horizontal bracings and the second pontoon 12 is made narrower due to the lower transverse forces acting on the second pontoon 12 and forward stabilizing column 201.

    [0097] In FIG. 6 an identical embodiment of the semi-submersible platform 1 as in FIG. 4 but with a horizontal bracing 291 added in-between the upper ends of the wind-turbine supporting structures 302. The horizontal bracing 291 reduce the static bending moment in the wind-turbine supporting structures

    [0098] In FIG. 7 a magnified view of the starboard aft stabilizing buoyant column 202 is shown where the shell plating has been removed. Inside the columns there are a vertical bulkhead 212 aligned with the direction of the lower horizontal bracing 141 and upper bracing 241 towards the centre of the stabilizing buoyant column. This vertical bulkhead which advantageously is extended down to the pontoon bottom provide a robust structural load transfer between the two bracings, the stabilizing buoyant column and the pontoon 11. Corresponding vertical bulkheads are arranged in the other stabilizing buoyant columns 201, 203.

    [0099] FIGS. 8-11 shows the various steps of a preferred method for construction, transport and assembly of the semi-submersible platform 1.

    [0100] In FIG. 8 the first hull-assembly 10 and the outer part 14 of the second pontoon are shown. The first hull assembly is constructed of the first pontoon 11, the two aft stabilizing buoyant columns 202, 203, one upper bracing 241 between these columns, the triangular buoyant structures 131 and the inner part 13 of the second pontoon and short interface parts to the other lower horizontal 141, if available, and upper bracings 241.

    [0101] The inner part 13 of the second pontoon is of sufficient length “L”, see FIG. 10, to allow the first hull-assembly 10 to float stable and upright. The outer part 14 of the second pontoon is of such dimension that this also will float stable. There are watertight bulkhead 126 enclosing the first hull assembly 10/inner part 13 of the second pontoon and the outer part 14 of the second part (not shown) close to the area where they shall be joined.

    [0102] The first hull-assembly 10 and the outer part 14 of the second pontoon is intended to be constructed at a first location, i.e. shipyard, and thereafter transported to a second location, i.e. a port close to the final offshore location of the floating wind semi-submersible platform. The first hull-assembly 10 and the outer part 14 of the second pontoon are accordingly of such dimensions that they may be positioned in a body of water, for example at a quayside in the second location.

    [0103] FIG. 9 shows one method for assembly of the semi-submersible platform 1. The first hull-assembly 10 and the outer part 14 of the second pontoon is floating in a body of water 2, such as in the sea at a quayside. Due to the enclosed construction they will float with the pontoon deck of the second pontoon well above the surface plane of the body of water 2.

    [0104] The first hull-assembly 10 and the outer part 14 of the second pontoon will be positioned in relation to each other and ballasted as required to float at the same draught and trim. Guiding arrangement (not shown) will be used as is a well-known manner from the shipbuilding industry. Around the area “J” where the first hull-assembly 10 and the outer part 14 of the second pontoon shall be joined, there is positioned a welding habitat 50.

    [0105] The welding habitat 50 is a structure, preferable floating in the body of water, with sealing devices (not shown) that will seal towards the pontoon bottom 121 and pontoon sides 122 at both sides of the joining area “J”. Due to the sealing a watertight compartment is obtained within the welding habitat 50.

    [0106] The water is evacuated from the welding habitat and the volumes/tanks inside the second pontoon at the joining area “J” and the inside of the welding habitat will become air-filled.

    [0107] This will allow that the joint “J” can be welded in a dry area and the first hull-assembly 10 and the outer part 14 of the second pontoon will be joined to a second hull-assembly 20. After painting of the area of the joining “J” the welding habitat will be filled with water and removed from the second hull assembly, for example by splitting the welding assembly in two parts and the second hull-assembly 20 will float in the body of water as one structure.

    [0108] The remaining parts of the semi-submersible platform 1, such as the forward stabilizing buoyant column 201 and the two upper bracings 241 interconnecting the forward stabilizing buoyant column with the other stabilizing buoyant columns part of the original first hull assembly 10, are erected, preferably with a crane located on the quay. Thereafter the semi-submersible platform 1 is ready for installation of the wind turbine 301 and its supporting structure 302 (see FIGS. 1, 3 & 4).

    [0109] As mentioned above, an advantageous embodiment of the invention is that the method allow that the parts of the semi-submersible platform, including the first hull-assembly 10, are fabricated in a first location and then transported to a second location where they are assembled. The two locations may be far apart, such as in different countries, but the second location is preferable as close as possible to the final offshore installation location of the floating wind semi-submersible.

    [0110] The method therefore requires that the hull parts are transported from a first location to a second location. The cost for such transportation need to be reduced and one beneficial embodiment is to transport the parts on a semi-submersible dry-tow vessel, which allow that the first hull-assembly may be floated on and off in a well-known manner for such dry tow vessels.

    [0111] To reduce the transportation cost it is important to be able to transport as many hull as possible at a single vessel. FIG. 10 shows a beneficial embodiment of the method that reduce the required space onboard the dry tow vessel.

    [0112] Due to the favourable geometry of the first hull assembly 10, two hull assemblies may be positioned in pairs opposite to each other with their respective inner part 13 of the second pontoon pointing towards the other first hull-assembly 10 in the pair and where the inner part of the second pontoons 13 of the respective first hull-assembly 10 pair are arranged side-by-side.

    [0113] The first hull-assembly 10 is therefore arranged such that that the added mass and dampening increasing horizontal plates 128 at the first pontoon 11 are arranged at a distance “>B” from the inner part 13 of second pontoon, or the triangular buoyant structure 131 if applicable, corresponding to at least the width “B” of the second pontoon.

    [0114] Multiple first hull-assemblies are transported on the same dry-tow vessel and arranged in pairs of two, where the two first hull-assemblies making up a pair are arranged opposite to each other with their respective inner part of the second pontoon pointing towards the other first hull-assembly in the pair and where the inner part of the second pontoons of the respective first hull-assembly pair are arranged side-by-side. This will allow that multiple pairs of first hull assemblies may be transported at a single dry-tow vessel.

    [0115] In a further advantageous embodiment of the method shown in FIG. 11, the outer part 14 of the second pontoon 12 may be stowed on top of the first pontoon 11 of their respective first hull assembly 10. This will further reduce the space required on-board the dry tow vessel.

    [0116] FIGS. 12 and 13 show two different examples of how to transport several pairs of underwater hulls on a marine vessel from a first location to a second location.

    [0117] FIG. 12 shows the transport of six hulls of semi-submersible platforms 1, la where the hulls are arranged two and two into transport structures where the first hull assemblies 10, 10a are arranged with the first pontoons 11, 11a parallel to each other with the inner part of the second pontoons 13, 13a directed towards each other and where the second hull assemblies 20, 20a are arranged with the outer parts of the second pontoons 14, 14a parallel to and in-between the first pontoons 11, 11a, one on each side of the inner parts of the second pontoons 13, 13a.

    [0118] FIG. 12 relates to an example where the T-shaped underwater hulls are not fully assembled before the transport, i.e. only the inner part 13, 13a of the second pontoon 12 is connected to the first pontoon 11, 11 a during transport, and the remaining portion of the second pontoon forms a separate outer part 14, 14a.

    [0119] FIG. 13 relates to an example where the T-shaped underwater hulls are assembled before the transport and shows the transport of four underwater hulls where the hulls are arranged two and two 1, 1a in a “head to toe” arrangement with their second pontoons 12, 12a side by side with their first pontoons 11, 11a on different ends of the second pontoons.

    [0120] As shown in FIG. 12, each of the two underwater hulls 1, 1a are divided into a first 10, 10a and a second hull assembly 20, 20a, where each of the first hull-assemblies comprises the first pontoon 11, 11a and a buoyant inner part 13, 13a of the second pontoon 12, 12a that has a length L that is sufficient to allow each of the first hull-assemblies 10, 10a to float substantially stable and upright. The two first hull assemblies 10, 10a are arranged such that the two first pontoons 11, 11a are substantially parallel to each other and the two buoyant inner parts 13, 13a extend towards each other.

    [0121] The second hull assemblies 20, 20a are arranged in between the two first hull assembles 10, 10a in such a way that the outer parts 14, 14a of the second pontoons 12, 12a are substantially parallel to the two first pontoons 11, 11a, one on each side of the two buoyant inner parts 13, 13a, respectively.

    [0122] The two first hull assemblies 10, 10a and second hull assemblies 20, 20a are joined together so as to form one transport assembly 30 with ability to float stable and upright.

    [0123] As shown in FIG. 13, the first and second underwater hull are arranged so that the second pontoon 12 of the first underwater hull 1 extends alongside of the second pontoon 12a of the second first underwater hull 1a, but in opposite directions and so that the first pontoons 11, 11a are positioned on opposite ends relative to said second pontoons.

    [0124] In the examples shown in FIGS. 12-13, the first and second underwater hulls or the two first hull assemblies 10, 10a are arranged in such a way that the first pontoons 11, 11a extend in a transversal direction across a longitudinal axis of the marine vessel.

    [0125] It is to be understood that the invention is by no means limited to the embodiments described above, and may be varied freely within the scope of the claims below. For example, the upper bracings 241 and lower horizontal bracings 141 may be arranged in a different manner but still interconnect the pontoons and stabilizing buoyant columns, 201, 202, 203. Further, the stabilizing buoyant columns, 201, 202, 203 need not necessarily be extending strictly vertically from the pontoons as in the shown embodiments but may instead be inclined.

    [0126] The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

    [0127] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

    [0128] The foregoing has described the principles, preferred examples and method of assembly of the present invention. However, the invention should be regarded as illustrative rather than restrictive, and not as being limited to the particular examples discussed above. The different features of the various examples and methods of the invention can be combined in other combinations than those explicitly described.

    LIST OF REFERENCE SIGNS

    [0129] 1: Semi-submersible offshore platform

    [0130] 2: Water plane of body of water/sea

    [0131] 10: First hull-assembly

    [0132] 11: First pontoon

    [0133] 12: Second pontoon

    [0134] 13: Inner part of second pontoon

    [0135] 14: Outer part of second pontoon

    [0136] 20: Second hull assembly

    [0137] 30: Transport assembly

    [0138] 50: Welding habitat

    [0139] 111: First pontoon bottom

    [0140] 113: First pontoon deck

    [0141] 115: First pontoon shell, rounded part

    [0142] 118: Added mass and dampening increasing horizontal plates

    [0143] 121: Second pontoon bottom

    [0144] 122: Second pontoon sides

    [0145] 123: Second pontoon deck

    [0146] 125: Second pontoon shell, rounded part

    [0147] 126: Second pontoon watertight bulkhead

    [0148] 128: Added mass and dampening increasing horizontal plates

    [0149] 131: Triangular buoyant structures

    [0150] 141: Lower horizontal bracing

    [0151] 201: Stabilizing buoyant column

    [0152] 202: Stabilizing buoyant column

    [0153] 203: Stabilizing buoyant column

    [0154] 212: Vertical bulkhead inside column

    [0155] 221: Separate column(s)

    [0156] 241: Upper bracings

    [0157] 291: Equilateral triangle

    [0158] 292: Isosceles triangle

    [0159] 301: Wind turbine(s)/Wind energy harvesting device(s)

    [0160] 302: Wind turbine supporting structure(s)

    [0161] 303: Horizontal bracing

    [0162] 401: Mooring turret

    [0163] 500: Marine vessel

    [0164] A: Aft end

    [0165] B: Width of pontoons

    [0166] D: Diameter of column

    [0167] F: Forward end

    [0168] J: Joint/seem between inner and outer part of second pontoon

    [0169] L: Length of inner part of second pontoon

    [0170] T: The underwater hull/pontoon configuration

    OTHER REFERENCED DOCUMENTS

    [0171] [1] Floating Offshore Wind Foundations: Industry Consortia and Projects in the United States, Europe and Japan, An Overview, May 2013 Update, Main(e) International Consulting LLC; https://cdn.website-editor.net/073319e35fa34e6189750e64c2e99060/files/uploaded/Floating%252Boffshore%252BWind%252BPlatforms%252BConsortia%252Bfor%252Bweb.pdf [0172] [2] Experimental validation of the W2Power Hybrid Floating Platform, Pedro Mayorga, EnerOcean S. L., Paper presented at EERA DeepWind 2016, 13th Deep Sea Offshore Wind R&D Conference, Trondheim (Norway), Jan. 20-22 2016, https://www.sintef.no/globalassets/project/eera-deepwind2019/presentations/g2 mayorga.pdf [0173] [3] Development of Offshore Wind Turbine Floater that Blends into Japanese Waters—Evaluation of the Validity for Design and Applied Methods for V-shaped Semi-submersible Floating structure, Masao Komatsu et al., Mitsubishi Heavy Industries Technical Review Vol. 53 No. 2 (June 2016), https://www.mhi.com.jp/technology/review/pdf/e532/e532030.pdf [0174] [4] TRUSSFLOAT—Marketing video showing construction methodology, Dolfines SAS, November 2017, https://dolfines.fr/floater-for-offshore-wind-turbines-trussfloat/ or https://www.youtube.com/watch?v=LggyY0DLKIQ