WO2011031148A1

WO2011031148A1 - Method for installing a wind turbine

Info

Publication number: WO2011031148A1
Application number: PCT/NL2010/050575
Authority: WO
Inventors: David Christoforus Bruin; Henry Charles Van Der Pol; Kuno Johannes Alexander Van Den Berg
Original assignee: Ihc Holland Ie B.V.
Priority date: 2009-09-10
Filing date: 2010-09-10
Publication date: 2011-03-17
Also published as: NL2003465C2; EP2475574A1; CN102574566A

Abstract

The invention relates to a vessel for transporting a plurality of elongate structures, such as wind turbines, in the upright position, in which the vessel comprises a device for adjusting the stability and mass inertia of the vessel for influencing the vessel's own period of oscillation, in which the vessel is provided with a seafastening frame which extends along the elongate structure for connecting the elongate structure and the vessel at an elevated level.

Description

Method for installing a wind turbine

Background of the invention The invention relates to a method for installing upright elongate structures such as a wind turbine. The method also relates to loading a wind turbine.

The invention furthermore relates to a method for transporting upright elongate structures such as wind turbines.

The invention furthermore relates to a vessel for transporting, loading and/or installing an elongate structure such as a wind turbine in the upright position.

WO 03/066427 Al discloses a vessel for installing upright structures. The vessel has gripping and lifting means for picking up wind turbines at the coast. The fact that the wind turbines are picked up at the coast results in stringent boundary conditions for the vessel with regard to draught and/or feasible depth. In order to reach the seafloor, the vessel is lowered, as a result of which the spud piles touch the seafloor. This results in a long installation time for a wind turbine.

WO 03/093584 Al shows a vessel for handling a wind turbine with respect to a stationary support. When handling the wind turbine, the vessel rests on the seafloor by means of feet. The vessel is moved along the feet in order to position the wind turbine vertically. The use of feet is disadvantageous due to the installation time involved and the feasibility in deep water.

WO2004/038108 discloses a foundation for mounting a wind turbine thereon. The foundation has a base with an internal guide surface which interacts with guide means which are connected to the end of the wind turbine for vertical alignment of the wind turbine. Subsequently, thin mortar is applied between the end of the wind turbine and the base in order to fix the wind turbine to the base. The hardening of the mortar is disadvantageous for the installation time and, moreover, the guide means can only be removed from the turbine once the mortar has hardened. WO2007/091042 Al shows a device and method for installing a wind turbine. The wind turbine is placed on a support frame and the combination is placed on a prepared foundation. The support frame has a number of hydraulically actuated feet which gradually transfer the weight of the wind turbine from the cranes to the foundation. A drawback of this known device and method is the relatively long time during which the ship is connected to the foundation. This is disadvantageous due to the risk of damage and also disadvantageous for the workability when sea conditions are rough. Summary of the invention

It is an object of the invention to improve the installation time of a wind turbine.

It is a further object of the invention to improve the workability of a vessel for installing wind turbines in heavy swell, in particular the workability when sea conditions are rough.

To this end, the invention provides a vessel for transporting an elongate structure, such as a wind turbine, in an upright position, with the vessel comprising a device for adjusting the stability and mass inertia of the vessel in order to influence the vessel's own period of oscillation, with the vessel being provided with a seafastening frame (shortly "seafastening") which extends along the elongate structure in order to connect the elongate structure and the vessel at an elevated level. Transporting a wind turbine in an upright position is advantageous for the period of oscillation. When the period of oscillation is longer, a nacelle of the wind turbine is subjected to a slower acceleration. Acceleration of the nacelle, specifically of a nacelle of an assembled wind turbine, during transport and installation is generally a bottleneck. By using the device for adjusting the stability and mass inertia of the vessel, it is possible to adapt the acceleration of the nacelle to the specified acceptable acceleration of the nacelle. By using this device, it is also possible to transport a plurality of wind turbines in an upright position. After one wind turbine has been unloaded, the stability and mass inertia of the vessel are then adjusted, following which the period of oscillation is increased again to the desired level. By using the device for adjusting the stability and mass inertia of the vessel, it is possible to adjust the stability and mass inertia to the current state of the sea. The period of oscillation is then preferably set to be as different as possible from the wave period. As a result of the possibility of connecting a wind turbine at an elevated level by means of the seafastening frame, the forces on the deck of the vessel are reduced, as are the acceleration of the nacelle and the forces acting on the nacelle, for example due to the inherent movement of the wind turbine. In this context, connecting at an elevated level is understood to mean that the seafastening frame engages the wind turbine (the elongate structure) approximately halfway up the wind turbine. Other levels are conceivable, provided that they have a positive effect on the forces on the deck, the distribution of forces on the wind turbine and/or the acceleration of the nacelle.

In this context, a seafastening frame is understood to be a (lattice-work) structure, suitable for securing cargo on the vessel in case of rough seas.

In one embodiment of the vessel according to the invention, the seafastening frame comprises at least a part of the device for adjusting the stability and mass inertia of the vessel. At least partly incorporating the device for adjusting the stability and mass inertia of the vessel results in an advantageous installation volume. Furthermore, it is then possible to take the device to an elevated position with respect to the roll axis of the ship. In one embodiment, the seafastening frame comprises a ballast tank for adjusting the stability and mass inertia of the vessel. Preferably, the ballast tank extends on the end of the seafastening frame which faces away from the vessel, which has an advantageous effect on the action of the ballast tank. Preferably, the ballast tank extends parallel to the longitudinal axis of the vessel, which has an advantageous effect on the adjustability of the stability and mass inertia of the vessel, specifically in relation to the roll about the roll axis. Incidentally, it is conceivable for the seafastening frame comprising the part of the device for adjusting the stability and mass inertia of the vessel, and the seafastening frame which engages with the elongate structure in order to connect it to the vessel at an elevated level, to be separate seafastening frames. In one embodiment of the vessel according to the invention, the vessel is provided with a handling device for connecting the elongate structure to the vessel in such a manner that it can be handled. The handling device makes it possible to compensate for movements of the freely floating vessel during installation of a wind turbine.

In one embodiment of the vessel according to the invention, the handling device comprises an X-Y table for compensating for the movements of the vessel when the elongate structure is being placed on a base in order to direct the elongate structure to the base. By using the X-Y table, movements of the freely floating vessel can be compensated for much better.

In one embodiment of the vessel according to the invention, at least one table of the X- Y table can be moved along a curved path for simultaneous height adjustment of the wind turbine when adjusting the at least one table. By using the curved path, movements of the freely floating vessel can be compensated for much better.

To this end, the invention furthermore provides a method for vertically transporting an elongate structure, such as a wind turbine, by means of a vessel according to the invention, comprising one or more of the following steps:

- Adjusting the stability and mass inertia of the vessel for influencing the vessel's own period of oscillation,

— Measuring the displacement and/or acceleration of the elongate structure, in one embodiment of an end of the elongate structure which faces away from the vessel.

By measuring the acceleration, it is possible to control and regulate the acceleration of the wind turbine, specifically the nacelle, much better. It is conceivable for an acceleration sensor to be placed on the nacelle in order thus to measure as directly as possible. It is furthermore conceivable to also measure the speed and position of the nacelle. To this end, the invention provides a method for unloading a freely floating vessel according to the invention, the method comprising the following step:

- Adjusting the centre of gravity and mass inertia of the vessel with the elongate structure, for influencing the vessel's own period of oscillation.

As a result of this step, it becomes possible to transport a plurality of wind turbines and to install them from one vessel. After one wind turbine has been unloaded, the period of oscillation is returned to the desired level by means of the device for adjusting the stability and mass inertia of the vessel. This method can also be used for loading a wind turbine.

In one embodiment of the method for unloading, the method comprises the following steps:

- Placing the elongate structure in an outboard position by means of a handling device which is fixedly secured to the vessel,

- Compensating for movements of the vessel by means of the handling device during placement of the elongate structure on a base in order to direct the elongate structure to the base,

- Damping the movement of the elongate structure at the base.

By compensating for movements of the vessel during placement of the elongate structure, it is possible to keep the wind turbine exactly above the base before lowering the wind turbine onto the base. This shortens the contact time between the vessel and the base via the wind turbine. The term contact time is understood to mean the period of time during which the vessel and the base are in contact via the wind turbine. This reduces the risk of collisions with the base which could result in various kinds of damage and/or makes it possible to lower the wind turbine when the ship's movements are quite severe, that is to say when the seas are relatively rough. By damping the movement of the wind turbine at the base, accelerations and damage by any residual speed are limited and it becomes possible to lower the wind turbine at greater speed, thus greatly reducing the contact time between the vessel and the base via the wind turbine. In addition, damping is advantageous with regard to the acceleration of the nacelle and forces acting on the nacelle. In one embodiment of the method for unloading, the method comprises one or more of the following steps:

— Displacing or sliding the elongate structure across the deck in a vertical position,

- Engaging the elongate structure by means of the base for positioning the elongate structure about its longitudinal axis,

- After releasing the elongate structure by the vessel, lowering the elongate structure from a first position to a second position for mutually engaging mounting flanges of the elongate structure and the base,

— Measuring the displacement and/or acceleration of the elongate structure in one embodiment of an end of the elongate structure which is turned away from the vessel. By only lowering the elongate structure from a first position to a second position afterwards for mutually engaging mounting flanges of the elongate structure and the base, it is possible to use a greater fall velocity of the wind turbine, resulting in a correspondingly shorter contact time. The distance between the first and second positions is advantageous since this gives the opportunity to dampen the fall velocity of the wind turbine.

To this end, the invention furthermore provides an assembly comprising a vessel according to the invention and one or more elongate structures which are held in a vertical position on the vessel.

To this end, the invention furthermore provides an installation device for use with a method according to the invention, for placing the elongate structure on a base, the installation device comprising:

- A positioning device for positioning the elongate structure with respect to me base,

- A damping device for damping the movement of the elongate structure with respect to the base,

- A locking device for locking the elongate structure with respect to the base. By locking the elongate structure with respect to the base by means of the locking device, it becomes possible to place a turbine with an even shorter contact time which is highly advantageous in practice.

To this end, the invention furthermore provides a device provided with one or more of the characteristic features described in the attached description and/or illustrated in the attached drawings. To this end, the invention furthermore provides a method comprising one or more of the characteristic steps described in the attached description and or illustrated in the attached drawings.

It will be clear that the different aspects mentioned in this patent application can be combined and may each be considered individually for a divisional patent application.

Short description of the figures

The attached figures illustrate, inter alia, various embodiments of a vessel according to the invention and parts thereof, in which:

Fig. 1 shows a side view of a vessel which is loaded with wind turbines;

Fig. 2 shows a rear view of the vessel from Fig. 1;

Fig. 3 shows a top view of the vessel from Fig. 1;

Figs. 4a-4d successively show the steps during unloading of a wind turbine;

Fig. 5 shows a top view of a handling device for unloading and loading the wind turbines;

Fig. 6 shows a rear view of a clamping device for connecting two wind turbines to a seafastening frame;

Figs. 7a-7e show successive steps of an installation device for installing a wind turbine; Fig. 8 shows a diagrammatic view of a device for compensating for wave movements; Fig. 9a shows a front view of a wind turbine and a part of the handling device;

Fig. 9b shows a side view of a wind turbine and a part of the handling device. Description of embodiments

Fig. 1 shows a side view of a vessel 1 which is loaded with wind turbines 3. The vessel 1 is loaded with a plurality of wind turbines 3, which is advantageous for the installation time of a wind turbine park of which the wind turbine 3 forms part. The vessel 1 containing wind turbines 3 is also referred to as the assembly 2 of the vessel 1 and the wind turbines 3. The wind turbines 3 are completely assembled which is advantageous for the installation time offshore. When wind turbines are completely assembled, they are subject to stringent requirements regarding transportation, specifically regarding the maximum acceleration which the wind turbine 3 may be subjected to, more specifically the maximum acceleration which the nacelle 12 may be subjected to. The wind turbines 3 in the upright position are connected to the vessel 1 for transportation. The upright position of the wind turbines 3 is unadvantageous with regard to the static stability of the assembly 2. However, this, as such unadvantageous, stability of the assembly 2 results in a high period of oscillation of the ship with regard to roll and pitch, that is to say rotating to and fro about the longitudinal axis and rotating to and fro about the width axis. In this context, it is the period of oscillation with regard to roll which is of particular importance. A high period of oscillation of the vessel 1 containing the wind turbines 3 is advantageous for the acceleration which the nacelle 12 of the wind turbine 3 is subjected to. Thus, by reducing the static stability of the vessel 1, the stringent requirements with regard to the maximum acceleration which the nacelle 12 may be subjected to are met. The vessel 1 is furthermore provided with a device 5 for adjusting the stability and mass inertia of the vessel 1. This makes it possible to influence the static stability of the assembly 2, depending on the number of elongate structures which are still on board and thus to maintain the period of oscillation at a similar level, independent of the number of elongate structures on board. Here, the device 5 for adjusting the stability and mass inertia of the vessel 1 comprises a seafastening frame 27. The seafastening frame 27 in this case consists of a lattice and extends transversely to the vessel 1 and along the wind turbines 3. At the end which is turned away from the vessel 1 , the seafastening frame 27 is provided with a ballast tank 25. In this way, the stability and mass inertia of the vessel 1 can be influenced efficiently by filling or emptying the ballast tank 25. It is conceivable for the device 5 for adjusting mass inertia of the vessel 1 to have alternative or further ballast (not shown) for adjusting mass inertia of the vessel 1 , such as for example, a weight, specifically a concrete weight, which is adjustably connected to the seafastening frame 27. The main concern is that the device 5 displaces a mass with respect to the vessel 1 so that the own period of oscillation of the vessel 1 is increased. Preferably, the mass is displaced vertically with respect to the vessel 1. In other words, the period of oscillation of the vessel is increased by combining a reduction in the stability with an increase in the rotational inertia. In this case, the seafastening frame 27 is provided at and along the ballast tank 25 with a tooth path 26 (gear rack) with which the drive mechanism 77 from Fig. 6 engages for moving the wind turbine 3 across the deck of the vessel 1.

Here, the wind turbine 3 comprises an elongate mast 14 having an outer casing 15. The mast 14 extends along the longitudinal axis 16. At the top, the mast 14 is provided with a nacelle 12. The rotor 13 with vanes 11 is assembled together with the nacelle 12. Transportation, but also positioning or loading in a harbour, of an assembled wind turbine 3 imposes strict boundary conditions with regards to acceptable acceleration of, in particular, the nacelle 12. These boundary conditions have to be respected all the more when a wind turbine 3 is being transported in an upright position. The vessel 1 here comprises a handling device 4 for handling wind turbines 3. The handling device 4 is suitable for loading and unloading wind turbines 3 in an upright position. The handling device 4 extends along its longitudinal axis 24, transversely to the vessel 1. In this case, the handling device 4 comprises a fixed part 21 by means of which the handling device 4 is connected to the vessel 1, and an rotatable part 17 which is rotatable about the longitudinal axis 24 and is rotatably connected to the fixed part 21 by means of the bearings 82 and 83. Both the fixed part 21 and the rotatable part 17 are in this case of cylindrical design, which makes it possible to rotate the adjustable part 17 about the longitudinal axis 24. The adjustable part 17 rotates about the fixed part 21, specifically along the outer casing 22 of the fixed part 21. The handling device 4 comprises a transverse structure 18 so that the handling device 4 can reach an outboard position. By means of a rail structure 84, the transverse structure 18 can be adjusted in height and is height adjustably connected to the outer casing 23 of the adjustable part 17 of the handling device 4. The handling device 4 comprises an X-Y table 19 for positioning the wind turbine 3 with respect to the vessel 1 for compensating for movements of the vessel 1 at sea.

Fig. 2 shows a rear view of the vessel 1. Here, the wind turbines 3 are displaceably connected to the seafastening frame 27 (not shown here) by means of a clamping device 7. The wind turbine 3 is displaceably or slidably connected to the vessel 1 by means of a carriage 10 which runs or slides in a rail system 9. The wind turbines 3 are - drivably connected to the vessel 1. The wind turbine 3 is drivably connected to the vessel 1 by means of a number of drive devices 77. Here, the drive device 77 is a combination of a gear rack and driving wheel, which combination is known per se. The wind turbine 3 is driven both at the deck of the vessel 1 and at the clamping device 7, which leads to the wind turbine 3 being driven in a smooth and steady manner.

Fig. 3 shows a top view of the vessel 1. The wind turbines 3 are arranged in two rows on either side of the seafastening frame 27, so that all wind turbines 3 can be connected to one single seafastening frame 27 by means of clamping devices 7.

Figs. 4a-4d show the successive steps when unloading a wind turbine 3 from the vessel 1 by means of the handling device 4. First, a wind turbine 3 is moved in the direction of the handling device 4 by means of the drive devices 77. The handling device 4 then rotates in the direction of the wind turbine 3 and clamps the wind turbine 3, rotates the wind turbine 3 with respect to the handling device 4 by means of the rotating platform 86 from Fig. 5, and subsequently rotates the wind turbine 3 to an outboard position by rotating the transverse structure 18 in order to attach the wind turbine to a base (not shown here), such as the pile 39 from Fig. 7a-e.

Fig. 5 shows a top view of a handling device 4 for unloading and loading the wind turbines 3. The transverse structure 18 comprises two cross girders 78, 79 by which an X-Y table is connected to the rotatable part 17 of the handling device 4. The X-Y table 19 is known per se and consists of a first table 28 and a second table 29 which are movable at right angles with respect to one another. The X-Y table 19 makes it possible to translate the wind turbine 3 to the horizontal plane. In operation, the wind turbine 3 is connected to the top table 29 of the X-Y table 19 by means of a bearing girder 76. At one end, the bearing girder 76 is fixedly connected to the top table 29 and at its opposite end, it is cardanically connected to the wind turbine 3. The cardanic coupling 20, which is known per se, preferably engages exactly above the centre of gravity of the wind turbine 3. Due to the cardanic coupling 20, the wind turbine 3 is freely rotatable about the axles 30 and 31.

Fig. 6 shows a rear view of a clamping device 7 for connecting two wind turbines to the seafastening frame 27 from Figs. 1 and 3. The clamping device 7 connects the wind turbine 3 in a displaceable or slidable manner to the seafastening frame 27. At one end, the clamping device 7 comprises a clamp 32 by means of which the clamping device 7 engages with the mast 14 of the wind turbine 3, specifically the outer casing 15 of the mast 14. At the opposite end, the clamping device 7 engages with the seafastening frame 27. The clamping device 7 engages with the seafastening frame 27 by means of a drive mechanism 77 for sliding or displacing the wind turbine 3 with respect to the vessel 1. When the clamping device 7 engages with the seafastening frame 27, the seafastening frame 27 is partly received in aperture 34, 35. On the right-hand side in Fig. 6, the clamp 33 is illustrated in a position from which the clamping halves pivot to the position which is shown on the left-hand side in Fig. 6. In this position, the clamping device 7 with the drive mechanism 77 can pass a wind turbine and/or vanes of the wind turbine. This is advantageous since only one driven clamping device 7 per row of wind turbines is required in this way, as is shown in Fig. 3. The other wind turbines 3 which do not yet have to be driven are connected to the seafastening frame by means of a fixed clamp. Figs. 7a-7e show the successive steps of an installation device 6 for installing a wind turbine 3. The installation device 6 comprises two parts, a stationary part 37 and a support part 38 to which the wind turbine is attached. The stationary part 37 is connected to a pile 39 which extends along its central axis 41 and has an outer casing 40. The pile 39 is fixedly connected to the seafloor or another foundation in a manner which is not shown. Reference numeral 39 also refers to the base 39. It is clear that this is a fixed point on which the wind turbine 3 is positioned in order to operate. The support part 38 is provided with an aperture 43 for positioning the support part 38 with respect to the stationary part 37. The support part 38 comprises a stop 80 which in this case is circumferential for engaging with the stationary part 37 in a first mutual position and a flange 61 for engaging with the stationary part 37 in a second mutual position. The support part 38 comprises a number of hooks 55 for locking the support part 38 onto the stationary part 37 in the first mutual position.

The stationary part 37 comprises a cam 42 for positioning the support part 38 with respect to the stationary part 37. The stationary part 37 comprises a damping device 60 for damping the engagement of the support part 38 with the stationary part 37. The stationary part 37 comprises a number of hydraulic cylinders 58 which engage, by their cylinder rod 59, in this case by means of the damping device 60, specifically the front 81 of the damping device 60, with the support part 38 for lowering the support part 38 from the first mutual position to the second mutual position. The stationary part 37 comprises a number of further hooks 56 for locking the support part 38 to the stationary part 37 in the second mutual position.

The operation of the installation device 6 is as follows. The support part 38 and the stationary part are aligned with respect to one another by means of the handling device 4. During alignment, the handling device 4 compensates for movements of the vessel 1. The central axle 16 of the wind turbine 3 is now in line with the central axle 41 of the pile 39. The handling device 4 then lowers the wind turbine 3 so that the cam 42 engages in the aperture 43. The cam 42 and the aperture 43 are correspondingly shaped in order to determine the mutual angular position of the wind turbine 3 with respect to the pile 39 about the central axle 41. The cam 42 and the aperture 43 taper which also contributes to the positioning of the support part 38 and the stationary part 37 in the horizontal plane with respect to one another. The wind turbine 3 is then lowered, with the support part 38 landing on the stationary part 37 at some speed. By means of the stop 80, the support part 38 initially engages with the hydraulic cylinders 58, in this case via damping device 60. The support part 38 comes to a stop in the first mutual position. In the first mutual position, the hooks 55 grip behind the flange 62 of stationary part 37 in order to temporarily lock the wind turbine 3 and the pile 39. The vessel 1 with the handling device 4 subsequently detaches as quickly as possible from the wind turbine 3. The cylinder rods 59 then lower the support part 38 from the first mutual position in Fig. 7d to the second mutual position in Fig. 7e. In the second mutual position, the flanges 61, 62 engage with one another in order to mutually bolt it. The further hooks 56 now grip behind the flange 61 of the support part 38 for temporarily locking the wind turbine 3 and the pile 39 before the flanges 61 , 62 are bolted with respect to one another.

Fig. 8 shows a diagrammatic representation of a device 8 known per se for

compensating for wave movements. This device 8 here connects the fixed part 21 of the handling device 4 to the height-adjustable transverse structure 18 of the handling device 4. The roller 67 is in this case connected to the vessel 1. The cable connection 71 is connected to the transverse structure 18 by means of roller 85 from Fig. 1. The height of the transverse structure 18 can be adjusted by means of the control cylinder 70 and via the cable 68, pulley 66 and pulley system 69. This makes it possible to adjust the vertical position of the wind turbine 3 during installation and to compensate for movements of the vessel 1, in particular heaving (up and down) and pitching of the vessel 1.

Fig. 9a is a front view of a wind turbine 3 and a part of the handling device 4. In this embodiment of the handling device 4, the first table 28 has a radius of curvature 72, with the radius of curvature 72 crossing the roll axis 73 of the vessel 1 in a specific embodiment. When the first table 28 a radius of curvature 72, the height of the wind turbine 3 is also corrected during positioning along this first table 28, in which case the wind turbine 3 remains vertical. When the radius of curvature 72 crosses the roll axis 73, this height correction is all the more effective. Fig. 9b shows a side view of a wind turbine 3 and a part of the handling device 4. The cross girders 78, 79 of the transverse structure 18 have a radius of curvature 74. The first table 28 of the X-Y table 19 can be moved over these cross girders 78, 79. When the first table 28 moves over the cross girders, the height of the wind turbine 3 is corrected at the same time. When the radius of curvature 74 crosses the roll axis 75, this height correction is all the more effective. Moreover, the vertical position of the wind turbine 3 is maintained. It will be clear that the above description has been given to illustrate the operation of preferred embodiments of the invention, and not in order to limit the scope of the invention. On the basis of the above explanation, many variations which fall within the spirit and the scope of the present invention will be obvious to a person skilled in the art.

Claims

1. Vessel (1) for transporting an elongate structure, such as a wind turbine (3), in an upright position, in which the vessel comprises a device (5) for adjusting the stability and mass inertia of the vessel for influencing the vessel's own period of oscillation, in which the vessel is provided with a seafastening frame (27) which extends along the elongate structure for connecting the elongate structure and the vessel at an elevated level.

2. Vessel according to a preceding claim, in which the seafastening frame comprises at least a part of the device (5) for adjusting the stability and mass inertia of the vessel.

3. Vessel according to Claim 1 or 2, provided with a handling device (4) for

connecting the elongate structure to the vessel in such a manner that it can be handled. 4. Vessel according to Claim 3, in which the handling device comprises an X-Y table (19) for compensating for movements of the vessel when the elongate structure is being placed on a base (39) in order to direct the elongate structure to the base.

5. Vessel according to Claim 4, in which at least one table (28, 29) of the X-Y table can be moved along a curved path for simultaneous height adjustment of the wind turbine when adjusting the at least one table.

6. Method for vertically transporting an elongate structure, such as a wind turbine (3), by means of a vessel (1) according to a preceding claim, comprising one or more of the following steps:

- Adjusting the centre of gravity of the vessel for influencing the vessel's own period of oscillation, - Measuring the displacement and/or acceleration of the elongate structure, in one embodiment of an end of the elongate structure which faces away from the vessel.

Method for unloading a freely floating vessel according to a preceding claim, comprising the following step:

Method according to Claim 7, furthermore comprising the following steps:

- Placing the elongate structure in an outboard position by means of a handling device (4) which is fixedly secured to the vessel,

- Compensating for movements of the vessel by means of the handling device during placement of the elongate structure on a base (39) in order to direct the elongate structure to the base,

- Damping the movement of the elongate structure at the base.

9. Method according to Claim 7 or 8, in which the method furthermore comprises one or more of the following steps:

- Displacing or sliding the elongate structure across the deck in a vertical position,

- Measuring the displacement and/or acceleration of the elongate structure in one embodiment of an end of the elongate structure which is turned away from the vessel.

Assembly (2) comprising a vessel (1) according to a preceding claim and one or more elongate structures (3) which are held in a vertical position on the vessel.

11. Installation device (6) for use with a method according to a preceding Claim 7 or 8, for placing the elongate structure on a base (39), the installation device comprising:

- A positioning device (42, 43) for positioning the elongate structure with respect to the base,

- A damping device (58, 60) for damping the movement of the elongate structure with respect to the base,

- A locking device (55, 56, 61, 62) for locking the elongate structure with respect to the base.

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