Offshore floating intervention vessels intended to temporarily support offshore wind turbine platforms, associated assemblies and intervention methods

Abstract

The vessel is a main hull (44) having an upper deck (62) defining an upper deck surface (64) at a first height (h1); a stern (48) projecting from the main hull (44) and defining an upper receiving surface (72) extending in a plane at a second height (h2) lower than the first height (h1); a wind turbine equipment lifting tower (100) configured to lift at least one piece of equipment of a wind turbine. The volume (84) above the upper receiving surface (72) freely receives the offshore wind turbine platform on the upper receiving surface (72) at its free end and over at least 50% of the length (SL) of the stern (48) taken from the free end along the longitudinal axis (A-A'). The second height (h2) is at most equal to 40% of the first height (h1).

Description

[Technical Field]

[0001] The present invention relates to an offshore floating intervention vessel intended to temporarily support an offshore wind turbine platform in a body of water in order to carry out installation and / or maintenance interventions on the wind turbine, the offshore floating intervention vessel comprising: an elongated floating main hull defining a longitudinal axis, the main hull having an upper deck defining an upper deck surface at a first elevation, the main hull having a hull length; a stern projecting longitudinally from the main hull to a free end of the offshore floating intervention vessel, the stern defining an upper receiving surface for receiving the offshore wind turbine platform, the upper receiving surface extending in a plane at a second height lower than the first height between the floating hull and the free end of the stern; a stern having an upper receiving surface configured to engage an underside of the offshore wind turbine platform, the offshore floating intervention vessel having at least a ballast receiving volume, the offshore floating intervention vessel having a ballast controller configured to control an amount of ballast received in the ballast receiving volume to lift the upper receiving surface of the stern in contact with the underside of the offshore wind turbine platform; - a wind turbine equipment lifting tower configured to lift at least one piece of equipment of a wind turbine, the wind turbine equipment lifting tower protruding from the upper deck surface.

[0002] Such intervention vessels are particularly adapted to carry out installation and / or maintenance work on offshore wind farms located in waters deeper than 60 m.

[0003] The Earth's surface is roughly 30 percent land and 70 percent ocean, with considerable potential to harness marine areas for the production of renewable energy from solar, wave, or / and wind power.

[0004] However, 80 percent of the offshore wind potential lies in waters deeper than 60 meters, where traditional fixed bottom techniques for supporting wind towers are not economically feasible or practically possible.

[0005] To exploit this potential, floating offshore wind platforms, anchored to the seabed by anchor lines, are being developed. These floating platforms can support wind turbines with nominal power in the range of up to 15 MW or more.

[0006] Such large turbines present more difficult operating and maintenance conditions and require new maintenance and operating techniques.

[0007] Today there are few or no solutions that allow for maintaining floating wind energy generating units at sea in a safe and economical way.

[0008] A number of floating body to floating body and / or mobile lifting equipment solutions have been developed which are installed in some way in relation to the offshore wind tower.

[0009] What these systems and methods have in common is that they have still not been able to challenge the fundamental method of disconnecting offshore wind units and towing them offshore for large maintenance assignments.

[0010] Floating body solutions face the significant challenge of reducing the relative movement between the floating body units up to the height of the nacelle: a downward rotation of a few degrees by the floating body can quickly form several meters upward at the height of the nacelle.

[0011] To damp and / or synchronize the relative movements that occur, some solutions use complex lifting devices with motion damping functions in interaction with sensor technology.

[0012] These can potentially be expensive and difficult to operate and maintain in marine environments, and it is unclear whether they can damp relative movements of, say, one meter down to one millimeter quickly enough.

[0013] Also known in the offshore field are floating vessels that can be used to transport and move other vessels, such as those disclosed in WO 2014 / 133463.

[0014] Such vessels submerge beneath the floating structure and lift it out of the water. This type of vessel is not configured to perform floating offshore wind turbine maintenance, including blade replacement and / or replacement of other turbine components, where access to the wind turbine platform must be between the platform's anchor lines without disconnecting these anchor lines.

[0015] One object of the present invention is to provide an offshore intervention vessel, with simplified and very stable docking to offshore wind turbine platforms, that is particularly adapted for wind farms located in deeper waters where installation and maintenance work is difficult to carry out.

[0016] For this purpose, the subject of the present invention is an offshore floating intervention vessel of the type described above, characterized in that the volume above the upper receiving surface is adapted to freely receive, at its free end, an offshore wind turbine platform on the upper receiving surface over at least 50% of the length of the stern taken from the free end along the longitudinal axis, The second height is equal to at most 40% of the first height.

[0017] The offshore floating intervention vessel according to the invention has the following characteristics, taken alone or according to any technically feasible combination: the length of the wind turbine platform receiving area of ​​the upper receiving surface, taken along the longitudinal axis between the end of the upper deck adjacent to the stern and the free end, is more than 30% of the hull length, advantageously comprised between 30% and 70% of the hull length, preferably between 40% and 60% of the hull length; the stern is a catamaran having at least two side bodies and preferably a truss connecting the two side bodies, the upper receiving surface being defined on the two side bodies; - the stern comprises at least one receiving damping pad configured to partially project above the upper receiving surface and to contact an underside of the offshore wind turbine platform, the or each damping pad being retractable from a projecting configuration to a retracted configuration within a housing provided in the stern; the or each damping pad is buoyant and biased towards a protruding configuration, the stern comprising an actuator for controlling the configuration of the damping pad between the protruding and retracted configurations; the hull comprises a bow defining a free end of the main hull and a midship having a protruding stern, the midship having a tower support area adjacent the stern, the wind turbine equipment lifting tower protruding from the tower support area; a tower support area protruding above and away from a storage area at the aft connected to the hull, the tower support area and the storage area defining a storage space, the tower support area optionally being cantilevered above the storage area; the wind turbine equipment lifting tower comprises a plurality of tower modules assembled end to end, at least one tower module being configured to be disassembled and stored in the storage space; the bow comprises a propulsion system configured to move the offshore floating intervention vessel through the body of water.

[0018] The present invention also has as its subject matter an assembly comprising an offshore wind turbine platform and an offshore floating intervention vessel as defined above supporting the offshore wind turbine platform, the upper receiving surface of the stern being engaged with the underside of the offshore wind turbine platform, preferentially the upper receiving surface of the stern being fully immersed in the body of water and the offshore wind turbine platform being partially immersed in the body of water.

[0019] The assembly according to the invention has the following characteristics, taken alone or according to any technically feasible combination: - in projection along the longitudinal axis, the longitudinal dimension of the offshore wind turbine platform is included in the longitudinal dimension of the upper receiving surface; - the floating offshore wind turbine platform may include one or more of: a floating foundation having at least three floating struts and lower pontoons connecting the at least three floating struts, the lower pontoons defining at least a portion of the lower surface of the floating offshore wind turbine platform, and an upper receiving surface of the stern engaged under each of the three pontoons.

[0020] Another subject of the invention is a method of intervention on an offshore wind turbine platform, comprising: (i) transporting an offshore floating intervention vessel as defined above to the vicinity of an offshore wind turbine platform floating in a body of water; (ii) positioning the upper receiving surface of the stern below the underside of the offshore wind turbine platform; (iii) removing ballast from the ballast receiving volume of the offshore floating intervention vessel to lift the upper receiving surface of the stern that is in contact with the underside of the offshore wind turbine platform and secure the offshore wind turbine platform on the upper receiving surface of the stern; (iv) performing an intervention on a wind turbine of the offshore wind turbine platform; (v) ballasting the stern by introducing ballast into the ballast receiving volume to disengage the upper surface from the lower surface; (vi) transporting the offshore floating intervention vessel away from the offshore wind turbine platform; An intervention method wherein during the step, the upper receiving surface of the stern is fully immersed in the body of water and the offshore wind turbine platform remains partially immersed in the body of water.

[0021] The intervention method according to the invention comprises the following characteristics, taken alone or according to any technically feasible combination: - performing the intervention comprises removing wind turbine equipment, in particular blades, from the wind turbine using the wind turbine equipment lifting tower and / or attaching wind turbine equipment to the wind turbine using the wind turbine equipment lifting tower; The wind turbine equipment lifting tower comprises a plurality of tower modules configured to be assembled end-to-end, at least one tower module configured to be disassembled and stored in the storage space, and the method may include one or more of: during step (i), maintaining the at least one tower module in a disassembled state; and between steps (iii) and (iv), assembling the at least one disassembled tower module to another tower module to increase the height of the wind turbine equipment lifting tower. [Brief explanation of the drawings]

[0022] The invention will be better understood on reading the following description, given purely by way of example and made with reference to the following drawings, in which:

[0023] [Figure 1] FIG. 1 is a schematic perspective view of a floating offshore wind turbine platform floating in a body of water. [Figure 2] 1 is a side view of an offshore floating intervention vessel according to the present invention; FIG. [Figure 3] FIG. 1 is a top view of an intervention vessel according to the invention. [Figure 4] FIG. 1 is a perspective view of the stern of an intervention vessel according to the invention; [Figure 5] FIG. 3 is a side view of the intervention vessel of FIG. 2 during a first step of approaching the floating offshore wind turbine platform of FIG. 1; [Figure 6] FIG. 6 is a view similar to FIG. 5 showing the stern of the intervention vessel being introduced beneath the underside of the offshore wind turbine platform; [Figure 7] FIG. 7 is a view similar to FIG. 6, showing the stern of the intervention vessel during the de-ballasting step. [Figure 8] FIG. 1 is a perspective view of an intervention vessel and a floating offshore wind turbine platform, the floating offshore wind turbine platform resting on the stern of the intervention vessel during the intervention. [Figure 9] FIG. 9 is a schematic top view of FIG. 8.

[0024] A first offshore floating intervention vessel 10 according to the invention is shown in particular in FIGS.

[0025] The intervention vessel 10 floats on a body of water 12. The intervention vessel 10 according to the invention is intended to carry out installation and / or maintenance interventions on at least one floating offshore wind turbine platform 14 shown in Figures 1 and 6-8.

[0026] A wind turbine platform 14 is located on the surface of a body of water 12, for example in an offshore wind farm.

[0027] The body of water 12 in the vicinity of the offshore wind turbine platform 14 has a depth of more than 50 metres, typically comprised between 60m and 3000m.

[0028] The body of water 12 may be, for example, an ocean, a sea, a lake, and / or a river.

[0029] Referring to FIG. 1 , the wind turbine platform 14 includes a floating foundation 16, an anchor assembly 17 that anchors the floating foundation 16 to the bottom 18 of the body of water 12, and a wind turbine 20 supported by the floating foundation 16.

[0030] In this embodiment, the floating foundation 16 is a semi-submersible platform. It comprises at least three floating columns 22, frame elements 24 connecting the floating columns 22, and potentially a deck (not shown). In a variant, the floating foundation is a floating barge with or without a central through-cavity.

[0031] The frame elements 24 here comprise lower pontoons 26A connecting each pair of adjacent floating columns 22 at the bottom of the columns 22, upper pontoons 26B connecting each pair of adjacent floating columns 22 at the top of the columns 22, and potentially truss members 28 connecting the sides of each column 22 to the center of the lower pontoons 26A.

[0032] The floating columns 22 extend vertically. The floating columns 22 have a buoyancy volume that provides floating buoyancy to the floating foundation 16. The buoyancy is adapted to allow the floating foundation 16 to be partially submerged in the body of water 12.

[0033] The anchor assembly 17 comprises a number of anchor lines 30 connecting each strut 22 to the bottom 18 of the body of water 12. In the example of Figure 1, each floating strut 22 is connected to at least one anchor line 30, preferentially two to four anchor lines 30.

[0034] Thus, the wind turbine platform 14 is fixed in a horizontal position within the body of water 12 .

[0035] The wind turbine 20 classically comprises a mast 32, a nacelle 34 rotatably mounted on top of the mast 32, and a rotor 36 rotatably mounted to the nacelle 34, preferentially about a horizontal axis.

[0036] The rotor 36 includes a central hub 38 and blades 40 that project radially from the central hub 38 and are reversibly secured to the hub 38 .

[0037] The mast 32 is here fixed to the top of the floating support 22 coaxially with the axis of the floating support 22 .

[0038] The floating support 22 and advantageously the lower pontoon 26A define the underside 42 of the wind turbine platform 14 below which the intervention platform 10 can dock.

[0039] 2 to 5, the floating offshore intervention vessel 10 is configured to be moved on the surface of the body of water 12 so as to come into proximity with the wind turbine platform 14. It is configured to engage beneath the wind turbine platform 14 to support the wind turbine platform 14 and to inhibit relative movement between the floating offshore intervention vessel 10 and the wind turbine platform 14 during intervention.

[0040] The intervention may be, for example, the installation of a wind turbine equipment and / or the maintenance of a wind turbine equipment. In particular, the wind turbine equipment may be a blade 40 and the intervention may be the installation of a blade 40, the maintenance of a blade 40 or the replacement of a blade 40.

[0041] Other interventions relating to the nacelle 34 or mast 32 are also within the scope of interventions that can be performed using the intervention vessel 10. Wind turbine equipment involved in such interventions includes, for example, generators, drive shafts, bearings, pitch motors, and rotor motors.

[0042] Referring to Figure 2, the intervention vessel 10 comprises an elongated floating main hull 44, a wind turbine intervention system 46 carried by the main hull 44, and a stern 48 projecting longitudinally from the main hull 40 for receiving the wind turbine platform 14 during intervention.

[0043] The offshore floating intervention vessel 10 further comprises a ballast controller 50 configured to control the amount of ballast received in a ballast receiving volume 52 of the intervention vessel 10 .

[0044] The elongated floating main hull 44 and stern 48 define a flat bottom 54 of the intervention vessel 10 , which is permanently submerged in the body of water 12 .

[0045] The elongated floating main hull 44 extends along the longitudinal axis A-A' of the intervention vessel 10.

[0046] The main hull 44 comprises a bow 58 defining a forward end and a mid-ship 60 supporting the wind turbine intervention system 46 , with the stern 48 projecting from the mid-ship 60 opposite the bow 58 .

[0047] The main hull 44 includes an upper deck 62 extending along a bow 58 and a midship 60 .

[0048] The main hull 44 has a hull length HL along axis A-A' from the edge of the upper deck 62, ie, from the forward end of the bow 58 to the end of the midship 60.

[0049] The upper deck 62 defines an upper deck surface 64. The upper deck surface 64 is at a height h1 from the bottom 54 of the intervention vessel 10.

[0050] The bow 58 includes a propulsion system 66 configured to move the offshore floating intervention vessel 10 through the body of water 12. The propulsion system may include, for example, an adjustable-angle propeller.

[0051] The central vessel 60 comprises a tower support area 70 from which the tower of the wind turbine intervention system 46 projects.

[0052] In the example of FIG. 2, the tower support area 70 is located at a cantilevered end area of ​​the upper deck 62 that is positioned above and spaced from the connection area of ​​the stern 48 that connects the stern 48 to the hull 44.

[0053] The main hull 44 preferentially supports a control room / wheelhouse (not shown) equipped with radar, radio communications, and a navigation controller including dynamic positioning for controlling, among other things, the propulsion system 66. The control room also includes at least one control unit for monitoring and remotely controlling the functional systems of the intervention platform 10, such as the ballast controller 50 and / or the wind turbine intervention system 46.

[0054] The main hull 44 advantageously includes accommodations, a helipad, and / or a boat landing platform.

[0055] The stern 48 defines an upper receiving surface 72 at a height h2 that is lower than the height h1 of the upper deck 62, for receiving and supporting the underside 42 of the floating wind turbine platform 14. The stern 48 advantageously comprises a damping system 73 (see, e.g., Figures 3 and 4) for damping the reception of the underside 42 of the wind turbine platform 14 during its docking on the upper surface 72.

[0056] In the example of Figures 2 to 4, the stern 48 has the shape of a catamaran 74. It comprises two side hulls 86 extending parallel to the longitudinal axis A-A' and spaced apart from each other, and a truss 88 connecting the two side hulls 86 in the intermediate space between them.

[0057] Each side hull 86 is connected to the main hull 44 on a respective side of the main hull 44. The side hulls 86 and the truss 88 define the upper receiving surface 72.

[0058] The upper receiving surface 72 is located below the cantilevered area of ​​the upper deck 62 and has a storage area 76 suitable for storing part of the wind turbine intervention system 46 and an open wind turbine platform receiving area 77 extending from the storage area 76 to the free edge of the stern 48.

[0059] The wind turbine platform receiving area 77 of the upper receiving surface 72 has a length SL taken along the axis A-A', the length SL being more than 30% of the hull length HL and generally being comprised between 30% and 70% of the hull length HL, preferably between 40% and 60% of the hull length HL.

[0060] The height h2 of the upper receiving surface 72 taken perpendicularly from the bottom 54 of the intervention vessel 10 is not more than 40% of the height h1 of the main hull 44 taken perpendicularly between the bottom 54 and the upper deck surface 64 of the intervention vessel 10. The height h2 is generally comprised between 20% and 30% of the height h1.

[0061] Thus, compared to the main hull 44, the stern 48 has a lightweight structure that can be easily inserted between the mooring lines 30 under the underside 42 of the wind turbine platform 14 while providing a large upper receiving surface 72 for safely docking the wind turbine platform 14.

[0062] In the wind turbine platform receiving area 77, the space above the upper surface 72 at a height between the height h2 of the upper receiving surface 72 and the height h1 of the main hull 44 defines a free volume 84 for docking the wind turbine platform 14.

[0063] When no wind turbine platform 14 is received on the upper receiving surface 72, the volume 84 is completely free along the axis A-A' between the free edge of the upper deck 62 and the free edge of the stern 48, and completely free laterally from one side edge of the stern 48 over one side hull 86 to another side edge of the stern 48 over the other side hull 86.

[0064] Within the free volume 84 , no elements protrude beyond the upper receiving surface 72 .

[0065] Thus, the upper receiving surface 72 is large enough to receive and lift a substantial portion of the underside 42 of the wind turbine platform 14. Preferably, as shown in Figure 9, more than 50% of the area A1 defined by the outer contour of the projection of the underside 42 of the wind turbine platform 14 onto a horizontal plane is contained within the area A2 defined by the projection of the outer contour of the wind turbine platform receiving area 77 of the upper receiving surface 72 onto the same horizontal plane.

[0066] The volume above the upper receiving surface 72 freely receives the offshore wind turbine platform 14 on the upper receiving surface 72 at the free end of the stern over at least 50% of the length of the stern taken from the free end along the longitudinal axis A-A', preferably over 70% of the length of the stern.

[0067] Preferably, the longitudinal dimension LD of the wind turbine platform 14 taken along the axis A-A′ is less than the length SL of the wind turbine platform receiving area 77 of the upper receiving surface 72 .

[0068] Further, with reference to FIG. 9 , the maximum width W of the wind turbine platform receiving area 77 of the upper receiving surface 72, taken perpendicular to the longitudinal axis A-A′, is less than the minimum distance DS separating the connection points of the mooring lines 30 on two adjacent columns 22, as shown in FIG. 1 .

[0069] Thus, the wind turbine platform receiving area 77 of the upper receiving surface 72 can be freely positioned below the lower surface 42 of the wind turbine platform 14 between two adjacent columns 22 without interfering with the mooring lines 30 .

[0070] Advantageously, in the example of a wind turbine platform 14 comprising struts 22 and lower pontoons 26A connecting the struts 22, the upper receiving surface 72 is engaged beneath each of the lower pontoons 26A of the wind turbine platform 14.

[0071] Thus, when the intervention vessel 10 docks below the lower surface 42, the wind turbine platform 14 can be received in a very stable manner on the stern 48. The wind turbine platform 14 is then configured to move together with the intervention vessel 10 with very limited relative movements or bending forces.

[0072] Advantageously, the upper receiving surface 72 comprises wood or other material that prevents damage to the underside 42 of the wind turbine platform 14 when the wind turbine platform 14 is placed on the upper receiving surface 72 .

[0073] 4, the damping system 73 includes at least damping pads 78, each deployable from a housing 82 emerging from the upper receiving surface 72. The damping system 73 also includes an actuator 80 configured to control movement of each damping pad 78 from a retracted configuration within the housing 82 to a protruding configuration at least partially deployed from the housing 82.

[0074] 4, each side hull 86 receives at least one damping pad 78, and preferably several damping pads 78. The damping pads 78 are spaced apart from one another.

[0075] The damping pads 78 are preferably buoyant elements. They are made, for example, of foam and / or elastomer buoys.

[0076] Thus, in this configuration, each damping pad 78 is biased toward the extended configuration by its own buoyancy. Actuators 80 are configured to retract and maintain damping pads 78 in the retracted configuration within housings 82. Actuators 80 include, for example, a winch and cable system connected to damping pads 78.

[0077] In the storage configuration, each damping pad 78 is advantageously flush with or below the upper receiving surface 72 .

[0078] In the deployed configuration, the upper regions of the damping pads 78 protrude from the upper receiving surface 72 so as to contact the underside 42 of the wind turbine platform 14. This allows for safer and softer contact between the wind turbine platform 14 and the upper receiving surface 72.

[0079] Also, in the deployed configuration, the lower region of the damping pad 78 remains within the housing 82, maintaining the horizontal position of the damping pad 78 and preventing the damping pad 78 from being pressed into full contact between the lower surface 42 and the upper receiving surface 72.

[0080] Advantageously, the damping system 73 comprises at least one sensor capable of measuring the actual height of the damping pad 78 between the retracted and extended configurations.

[0081] 2 to 5, the wind turbine intervention system 46 comprises a wind turbine equipment lifting tower 100. Advantageously, it comprises a wind turbine equipment housing 102 and at least one crane 104 for transporting wind turbine equipment between the wind turbine equipment housing 102 and the wind turbine equipment lifting tower 100.

[0082] In this example, the lifting tower 100 comprises at least one mast 112, an elevator 114 movably mounted along the mast 112, and a lifting actuator 116 for moving the elevator 114 between a lower unloading / loading position and at least an upper intervention position.

[0083] Elevator 114 is configured to receive and move wind turbine equipment, such as blades 40 , between a lower position at upper deck surface 64 and an upper position at the level of nacelle 34 .

[0084] In the example of FIGS. 2-8, the lifting tower 100 comprises a plurality of tower modules 94 assembled end-to-end from the upper deck surface 64.

[0085] The height of the lifting tower 100 is adjustable depending on the number of assembled modules 94 above the upper deck surface 64 .

[0086] The unassembled modules 94 are advantageously stored in the storage area 76 of the upper receiving surface 72 below the tower support area 70 .

[0087] Preferably, the intervention vessel 10 is equipped with a tower jack and lifting system (not shown) configured to release the lifting tower 100 from the upper receiving surface 72, move it vertically, and lock it in place.

[0088] The intervention vessel 10 preferably includes a free module movement system (not shown) configured to move the additional unassembled module 94 below the lifting tower in the area 76 so that the tower jack and lifting system can lower the lifting tower 100 into contact with the unassembled additional module 94 for assembling the additional module 94 at the bottom of the lifting tower 100.

[0089] The ability to increase or decrease the height of the lifting tower 100 allows the lifting tower 100 to be adapted to wind turbine platforms of various sizes. The tower height can also be reduced during transport of the intervention vessel 10 in the vicinity of the floating wind turbine platform 14 to improve the stability and maneuverability of the intervention vessel 10. This also makes it easier to adapt the lifting tower 100 for other functions / tasks.

[0090] The wind equipment housing 102 can be either permanent or removable. It advantageously includes a system for moving / skidding the blades 40 in all directions.

[0091] It may also include structure for performing repairs on the blade 40, such as applying glue to cracks, gluing new segments, sanding, painting, etc. It may also include a cleaning station with wastewater collection.

[0092] The ballast receiving volume 52 is located within the main hull 44 and / or within the side hulls 86 .

[0093] At rest, the ballast receiving volume 52 is at least partially filled with a gas, such as air.

[0094] The ballast here is formed of water from the body of water 12. The ballast controller 50 comprises at least one pump configured to pump ballast into and / or out of the ballast receiving volume 52 to regulate the amount of ballast received in the ballast receiving volume.

[0095] The ballast controller 50 is therefore configured to control the draft of the intervention vessel 10 between a lower position in which the upper receiving surface 72 of the stern 48 is configured to pass below the underside 42 of the wind turbine platform 14, and a fixed position in which the upper receiving surface 72 of the stern 48 is attached below the underside 42 of the wind turbine platform 14.

[0096] In the fixed position, the upper receiving surface 72 advantageously exerts an upward force on the lower surface 42 to at least partially lift the wind turbine platform 14 while maintaining both the upper receiving surface 72 and the lower surface 42 submerged in water.

[0097] A method of intervention on a wind turbine platform 14 using an intervention vessel 10 according to the present invention will now be described.

[0098] 5 , the offshore floating intervention vessel 10 approaches the offshore floating wind turbine platform 14 using the propulsion system 66. The longitudinal axis A-A′ of the stern 48 is then oriented to pass below the underside 42 of the wind turbine platform 14 between the anchor lines 30 of the anchor assembly 17. The upper receiving surface 72 of the stern 48 is submerged and the upper deck 62 is above the surface of the body of water 12.

[0099] The actuator 80 is then actuated to deploy the receiving damping pads 78 into their protruding configuration.

[0100] As shown in FIG. 6 , the stern 48 is then moved below the wind turbine platform 14 using the propulsion system 66 to position the upper receiving surface 72 of the stern 48 below the lower surface 42 of the wind turbine platform 14.

[0101] Once the upper receiving surface 72 is positioned below the lower surface 42, the ballast controller 50 removes ballast from the ballast receiving volume 52, as shown in Figure 7. This reduces the draft of the intervention vessel 10, lifting the upper receiving surface 72 in contact with the lower surface 42 and exerting an upward force on the lower surface 42, as shown in Figure 8.

[0102] The receiving and damping pads 78 ensure smooth contact between the upper receiving surface 72 and the lower surface 42. The receiving and damping pads 78 are pressed towards their retracted configuration.

[0103] Once the wind turbine platform 14 is received and lifted by the upper receiving surface 72 of the stern 48 , the height of the equipment lifting tower 46 is potentially adjusted by adding or removing tower modules 94 .

[0104] As described above, adding a tower module 94 involves releasing the lifting tower 100 from the upper receiving surface 72 and locking the lifting tower 100 in place via a tower jack and lifting system. The free, unassembled module 94 is positioned below the lifting tower 100 in the area 76 below the lifting tower 100. The tower jack and lifting system then lowers the lifting tower 100 into contact with the unassembled additional module 94, which is assembled at the bottom of the lifting tower 100.

[0105] The lifting tower 100 containing the additional module 94 is then lifted again to add another module 94 or to lock it back onto the upper receiving surface 72 .

[0106] Intervention is then performed, which may include, for example, removing wind turbine equipment, such as blades 40, from wind turbine 20 using elevator 114 or a crane on wind turbine equipment lifting tower 100. Additionally or alternatively, intervention may include attaching wind turbine equipment to wind turbine 20 using elevator 114 or a crane on wind turbine equipment lifting tower 100.

[0107] Once the intervention is complete, the intervention vessel 10 is re-ballasted by filling the ballast receiving volume 52 with water using the ballast controller 50. The upper receiving surface of the stern 48 is lowered and disengaged from the wind turbine platform 14.

[0108] The intervention vessel 10 is then moved away from the wind turbine platform 14 using the propulsion system 16 .

[0109] The intervention platform 10 according to the present invention is therefore configured to perform self-propelled and low-emission operations, including installation and maintenance, at deepwater wind farms having floating wind turbine platforms 16. The reception and lifting of the wind turbine platform 14 on the upper receiving surface 72 of the stern 48 minimizes relative movements between the intervention vessel 10 and the wind turbine platform 14.

[0110] By establishing a perfect contact surface and load transfer between the upper receiving surface 72 of the stern 48 and the wind turbine platform 14, the wind turbine platform 14 and the intervention vessel 10 behave as one unit, resulting in a matched movement pattern. The relative movements between the nacelle 34 and the lifting tower 100 are nearly equal, which greatly simplifies the lifting operation and significantly increases the potentially operable maintenance window. This provides safer maintenance operations and reduces the levelized cost of energy.

[0111] In a variant, the intervention vessel 10 has equipment for launching remotely controlled submarines (ROVs), remotely controlled air vehicles (drones), etc.

[0112] In a variant, the intervention vessel 10 is fitted with a mobile ballast system to adjust the draft and optimise the reception of the wind turbine platform 14 on the upper receiving surface 72 so that it can be attached to the wind turbine platform 14 without a ballast system.

Claims

1. 1. An offshore floating intervention vessel (10) intended to temporarily support an offshore wind turbine platform (14) in a body of water (12) for carrying out installation and / or maintenance interventions on a wind turbine (20), said offshore floating intervention vessel (10) comprising: an elongated floating main hull (44) defining a longitudinal axis (A-A'), said main hull (44) having an upper deck (62) defining an upper deck surface (64) at a first height (h1), said main hull (44) having a hull length (HL); a stern (48) projecting longitudinally from the main hull (44) to a free end of the offshore floating intervention vessel (10), the stern (48) defining an upper receiving surface (72) for receiving an offshore wind turbine platform (14), the upper receiving surface (72) extending in a plane of a second height (h2) lower than the first height (h1) between the floating hull (44) and the free end of the stern (48); a stern (48), the upper receiving surface (72) configured to engage an underside (42) of an offshore wind turbine platform (14), the offshore floating intervention vessel (10) having at least a ballast receiving volume (52), the offshore floating intervention vessel (10) having a ballast controller (50) configured to control an amount of ballast received in the ballast receiving volume (52) to lift the upper receiving surface (72) of the stern (48) in contact with the underside (42) of the offshore wind turbine platform (14); a wind turbine equipment lifting tower (100) configured to lift at least one piece of equipment of said wind turbine (20), said wind turbine equipment lifting tower (100) protruding from said upper deck surface (64); the volume (84) above the upper receiving surface (72) is characterised in that it freely receives an offshore wind turbine platform (14) on the upper receiving surface (72) at the free end and over at least 50% of the length (SL) of the stern (48) taken from the free end along the longitudinal axis (A-A'), The offshore floating intervention vessel (10), wherein said second height (h2) is equal to at most 40% of said first height (h1).

2. 2. The offshore floating intervention vessel (10) according to claim 1, wherein the length (SL) of the wind turbine platform receiving area (77) of the upper receiving surface (72), taken along the longitudinal axis between the end of the upper deck (62) adjacent the stern (48) and the free end, exceeds 30% of the hull length (HL), advantageously is comprised between 30% and 70% of the hull length (HL), preferably between 40% and 60% of the hull length (HL).

3. 3. The offshore floating intervention vessel (10) according to claim 1 or 2, wherein the stern (48) is the stern (74) of a catamaran having at least two side hulls (86) and preferably a truss (88) connecting the two side hulls (86), and the upper receiving surface (72) is defined on the two side hulls (86).

4. 4. The offshore floating intervention vessel (10) according to any one of claims 1 to 3, wherein the stern (48) comprises at least one receiving damping pad (78) configured to partially project above the upper receiving surface (72) and to contact the underside (42) of the offshore wind turbine platform (14), the or each damping pad (78) being retractable from a projecting configuration to a retracted configuration within a housing (82) provided in the stern (48).

5. 5. The offshore floating intervention vessel (10) of claim 4, wherein the or each damping pad (78) is buoyant and biased towards the extended configuration, and the stern (48) comprises an actuator (80) for controlling the configuration of the damping pads (78) between the extended and retracted configurations.

6. 6. The offshore floating intervention vessel (10) of any one of claims 1 to 5, wherein the hull (44) comprises a bow (58) defining a free end of the main hull (44) and a mid-ship (60) from which the stern (48) projects, the mid-ship (60) having a tower support area (70) adjacent the stern (48), and the wind turbine equipment lifting tower (100) projecting from the tower support area (70).

7. 7. The offshore floating intervention vessel (10) of claim 6, wherein the tower support area (70) projects above and away from a storage area (76) of the stern (48) connected to the hull (44), the tower support area (70) and the storage area (76) defining a storage space (90), and the tower support area (70) is optionally cantilevered above the storage area (76).

8. 8. The offshore floating intervention vessel (10) of claim 7, wherein the wind turbine equipment lifting tower (100) comprises a plurality of tower modules (94) assembled end-to-end, at least one tower module (94) configured to be disassembled and stored in the storage space (90).

9. 9. The offshore floating intervention vessel (10) of any one of claims 6 to 8, wherein the bow (58) comprises a propulsion system (66) configured to move the offshore floating intervention vessel (10) within the body of water (12).

10. 10. An assembly comprising an offshore wind turbine platform (14) and an offshore floating intervention vessel (10) according to any one of claims 1 to 9 supporting the offshore wind turbine platform (14), wherein the upper receiving surface (72) of the stern (48) is engaged with the underside (42) of the offshore wind turbine platform (14), and preferentially the upper receiving surface (72) of the stern (48) is fully immersed in the body of water (12) and the offshore wind turbine platform (14) is partially immersed in the body of water (12).

11. 11. The assembly of claim 10, wherein in projection along the longitudinal axis (A-A'), a longitudinal dimension of the offshore wind turbine platform (14) is contained within a longitudinal dimension of the upper receiving surface (72).

12. 12. The assembly of claim 10 or 11, wherein the floating offshore wind turbine platform (14) comprises a floating foundation (16) having at least three floating struts (22) and lower pontoons (26A) connecting the at least three floating struts (22), the lower pontoons (26A) defining at least a portion of the lower surface (42) of the floating offshore wind turbine platform (14), and the upper receiving surface (72) of the stern (48) being engaged beneath each of the three pontoons.

13. A method of intervention on an offshore wind turbine platform (14), comprising: (i) transporting an offshore floating intervention vessel (10) according to any one of claims 1 to 9 to the vicinity of an offshore wind turbine platform (14) floating in a body of water (12); (ii) positioning the upper receiving surface (72) of the stern (48) below the underside (42) of the offshore wind turbine platform (14); (iii) removing ballast from the ballast receiving volume (52) of the offshore floating intervention vessel (10) to lift the upper receiving surface (72) of the stern (48) that is in contact with the lower surface (42) of the offshore wind turbine platform (14) and fix the offshore wind turbine platform (14) on the upper receiving surface (72) of the stern (48); (iv) performing an intervention on a wind turbine (20) of the offshore wind turbine platform (14); (v) ballasting the stern (48) by introducing ballast into the ballast receiving volume (52) to disengage the upper surface from the lower surface (42); (vi) transporting the offshore floating intervention vessel (10) away from the offshore wind turbine platform (14); 1. The method of intervention, wherein during steps (i) to (vi), the upper receiving surface (72) of the stern (48) is fully immersed in the body of water (12) and the offshore wind turbine platform (14) remains partially immersed in the body of water (12).

14. 14. The method of intervention according to claim 13, wherein performing the intervention comprises removing wind turbine equipment, in particular blades (40), from the wind turbine (20) using the wind turbine equipment lifting tower (100) and / or attaching wind turbine equipment to the wind turbine (20) using the wind turbine equipment lifting tower (100).

15. 15. The method of intervention according to claim 13 or 14, wherein the wind turbine equipment lifting tower (100) comprises a plurality of tower modules (94) configured to be assembled end-to-end, at least one tower module (94) configured to be disassembled and stored in the storage space (90), the method comprising: during step (i), maintaining the at least one tower module (94) in a disassembled state; and between steps (iii) and (iv), assembling the at least one disassembled tower module (94) to another tower module (94) to increase the height of the wind turbine equipment lifting tower (100).

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