Technical Field

The present invention relates primarily to a floating support structure for offshore wind turbines.

The support structure has a stable vertical floating position and is particularly suitable for assembly of a vertically floating support structure and tower of a wind turbine horizontally positioned on a barge or key side. Also, it is suitable for transport on heavy-lift vessels over large distances.

Background and prior art

Floating support structures for offshore wind turbines are known in the art and several methods for connecting a tower of a wind turbine to a floating support structure have been described.

For example, patent publication US 2014/0196654 A1 discloses a floating support structure for wind turbines consisting of columns having stabilizing elements mounted to their ends. The columns have an inner volume for ballasting. Another type of support structure having the possibility of stabilization and ballasting is disclosed in patent publication US 2019/0061884 Al. Yet other examples of floating support structures are disclosed in patent publications US 10,518,846 B2, WO 2014/163501 Al and JP 2005-201194 A.

A common disadvantage for any of the known floating support structures of the above-mentioned type is that the cost related to the use of large cranes are substantial. Prior art support structures all need large cranes when mounting the tower of a wind turbine and/or when mounting nacelle and rotor blades. Having people and expensive equipment suspended at high altitude also rises security issues and the delay caused by bad weather is significant.

In view of the above, it is an object of the invention to provide a floating support structure that solves or at least mitigates one or more of the aforementioned problems related to use of prior art solutions.

A particular object of the invention is to provide a floating support structure that enable mounting of the tower of the wind turbine to the support structure, with nacelle and rotor blades attached, without using a crane. Summary

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.

In one aspect, the invention concerns a floating support structure configured for connection to a tower of a wind turbine without using a crane for mounting the tower. The support structure comprises a first and second pivot line buoyancy unit having a pivot line between them. As will become clear later in the text the support structure is designed to pivot around the pivot line while floating on the two pivot line buoyancy units. The support structure further comprises a top buoyancy unit and a support structure flange for connecting the tower of a wind turbine to the support structure. The top buoyancy unit is positioned in a top corner of an isosceles triangle T with equal sides extending from the top buoyancy unit to each of the first and second pivot line buoyancy unit and the support structure flange is positioned on the lower half of a perpendicular line H from the top corner. Furthermore, the support structure comprises a binding structure binding the buoyancy units and support structure flange together in their respective positions. The binding structure can have an infinite number of forms as long as it keeps the buoyancy units and support structure flange in their respective positions in a structurally sound manner.

The support structure is characterized by having a stable vertical floating position with the first and second pivot line buoyancy units floating in a body of water and the top buoyance unit vertically above them. The support structure flange, which is vertically positioned when the support structure is floating vertically, is configured to be connected to the bottom end of a horizontally positioned wind turbine tower. The support structure is further configured to maintain sideways stability of a combined structure of the support structure and wind turbine during a 90 degrees rotation to an erected operational position of the combined structure. By sideways stability it is meant stability in a plane parallel to the pivot line.

In an exemplary configuration, the top buoyancy unit comprises at least one reinforced top connection structure for fastening of at least one rising wires for causing a combined pull in a rearward direction.

In another exemplary configuration, each of the first and second baseline buoyancy unit comprises at least one reinforced connection structure for fastening of respective restriction wires for causing a combined pull in a forward direction.

In yet another exemplary configuration, the top buoyancy unit comprises at least one reinforced support connection structure for respective at least one support wires, which are configured to transfer rotational force from the at least one rising wires onto the wind turbine tower connected to the support structure. In a second aspect, the invention concerns a method for connection a floating support structure according to claim 1 and a wind turbine tower. The method comprises the following steps: A. Positioning the wind turbine tower horizontally on a barge or quay with the bottom end by the edge of the barge or quay and mount the nacelle and the rotor blades. The wind turbine tower is supported at a height matching the position of the support structure flange

B. Positioning the support structure vertically with the support structure flange opposite of a bottom end of the tower.

C. Connecting the bottom end of the tower of the wind turbine with the support structure flange of the support structure.

D. Rotating the combined structure of support structure and wind turbine 90 degrees to an erected position by means of a method for rotation of the support structure and wind turbine to an erect position.

In an exemplary performance of the method of claim 5, the method for rotation of support structure and wind turbine to an erect position in step D comprises the wind turbine being horizontally positioned on a quay or anchored / fixed barge. The method comprises the following steps: 1. positioning, fastening and/or connecting the wires and winches as follows: a. Fastening at least one rising wire, connected to at least one rising winch positioned rearward of the combined structure, to the top buoyancy unit. b. Fastening respective at least one restriction wires, connected to respective at least one restriction winches positioned on the barge or quay, to the respective first and second pivot line buoyancy units. c. Fastening at least one counteracting wire, connected to at least one counteracting winch positioned on the barge or quay, to the upper part of the wind turbine tower.

2. Moving the wind turbine and support structure away from the barge or quay until the top end of the wind turbine tower is close to the edge of the barge or quay.

3. Tightening the restriction wires and rising wires. 4. Rotating the support structure and wind turbine by pulling the at least one rising wire in a rearward direction and / or pulling the restriction wires in a forward direction and keeping the rising wire or restriction wire taut if it is not pulling.

5. Holding the rising wires taut when passing a tipping point causes the support structure to fall into a horizontal erect position while the counteracting wire controls the movement during the free fall part of the 90 degrees rotation.

The combined pull vector from the rising wires and counteracting wires are positioned in a central plane C and the restriction wires holds the pivot line in a perpendicular position relative to the central plane C.

In an exemplary performance of the method according to claim 5, step 1 in the method for rotation of support structure and wind turbine to an erect position also includes fastening securing wires to the first and second pivot line buoyance units on the rearward side opposite of the restriction wires to prevent uncontrolled movement of the combined structure towards the quay or barge during a free fall part at the end of the rotation.

In another exemplary performance of the method according to claim 5, step 1 in the method for rotation of support structure and wind turbine to an erect position also includes fastening at least one support wires to the top buoyancy unit in one end and to the top end of the tower in the other end.

In yet another exemplary performance of the method according to claim 5, the wind turbine tower is positioned on a winchable barge.

In an exemplary performance of the method according to claim 5 and 9, the method for rotation of support structure and wind turbine to an erect position is characterized by the following steps:

1. Positioning, fastening and/or connecting the wires and winches as follows: a. Positioning the barge with the combined structure at a site for rotation with at least one barge wire and barge winch, which is able to move the barge rearward in the central plane, b. Fastening at least one rising wire, connected to at least one rising winch positioned rearward of the combined structure, to the top buoyancy unit, c. Fastening respective at least one restriction wires, connected to respective at least one restriction winches positioned on the barge, to the respective first and second pivot line buoyancy units, wherein the restriction wires are symmetrical relative to plane C. d. Fastening at least one counteracting wire, connected to at least one counteracting winch (58) positioned forward on the barge, to the upper part of the wind turbine tower,

2. Tightening the at least one rising wires and at least one barge wires by pulling the at least one barge wires,

3. Rotating the support structure and wind turbine by pulling the at least one barge wires while the at least one rising wire is held taut,

4. Holding the at least one rising wires and counteracting wires taut when passing of the tipping point causes the combined structure to fall into an erect operational position during the free fall part of the 90 degrees rotation, and

The combined pull vector from the rising wires and counteracting wires are positioned in the central plane C and the restriction wires holds the pivot line 2 in a perpendicular position relative to the central plane C.

Brief description of drawings

The following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only.

Fig. la, b and c show three embodiments of the invention seen from above.

Fig. 2a and b shows particular embodiments of the invention similar to Fig. lc seen in perspective view.

Fig 3a shows the embodiment of Fig. 2a in a side and top view and with a wind turbine mounted.

Fig. 4 shows an embodiment of the support structure in a stable vertical floating position.

Fig 5a shows a sideview of an arrangement of wires and winches for rotating the combined structure 90 degrees from resting on a quay.

Fig 5b shows a sideview of an arrangement of wires and winches for rotating the combined structure 90 degrees from resting on a movable barge.

Fig. 5c shows a top view of the arrangement in Fig. 5b Fig. 6 a-c illustrates a method for connecting a horizontal tower and vertical support structure.

Fig. 7a-e illustrates a method for rotating the combined structure of the support structure and wind turbine 90 degrees.

Fig. 8a-d illustrates another method for rotating the combined structure 90 degrees.

Detailed description

In this text we will refer to directions pertaining to the support structure as when the support structure is in its vertical position. By wind turbine 100 we mean the tower 101, nacelle 102 and rotor blades 103. The combined structure of the floating support structure 1 and the wind turbine 100 is simply called the ‘combined structure’. Forward is the direction from the vertical support structure and along the tower in its horizontal position and rearward is the opposite direction as illustrated with arrows in fig. 6

The support structure

The invention describes a floating support structure 1 configured for connection to a tower 101 of a wind turbine 100. The invention includes a method for mounting the tower 101 without use if a crane. The method is achieved by first mounting the nacelle 102 and the rotor blades 103 to the tower of the wind turbine 100 when the tower 101 is positioned horizontally and then mounting the tower 101 to the floating support structure 1 when in vertical position. When the tower and support structure are connected, the combined structure is rotated 90 degrees to an erect position.

Below we will describe a floating support structure 1 that is able to perform such an operation. Figures la-c and 2a-b show different embodiments of such a floating support structure.

The support structure according to the invention comprises a first and second pivot line buoyancy unit 3, 4 having a pivot line 2 between them and a top buoyancy unit 5 positioned in the top corner vertically above the first and second pivot line buoyancy units 3,4 when the support structure 1 is in a stable vertical floating position as seen in fig. 4. The figure shows the center of gravity (COG), marked with a crossed circle, straight above the center of buoyancy (COB), marked with an X, in a vertical floating position. In other words, the support structure 1 is configured to have a stable horizontal floating position for normal operation (figs. 2 and 3) and a stable vertical floating position for mounting of the tower 101 of the wind turbine 100 when in horizontal orientation.

As illustrated in figures la-c showing three embodiments of the support structure 1 from above, the top buoyancy unit 5 is positioned in the top corner of an isosceles triangle T with equal sides extending from the top buoyancy unit 5 to each of the first and second pivot line buoyancy unit 3, 4 and a support structure flange 15 is positioned on the lower half of a perpendicular line H from the top corner. The isosceles triangles T are marked with a dotted line in figures la-c. As explained in greater detail below, this configuration will enable an advantageous transfer of rotational forces applied to the combined structure.

The pivot line 2 is a theoretical line around which the combined structure 1,100 rotates during the mentioned 90 degrees rotation. This line will in most cases change position during the 90 degrees rotation according to which method is used for rotating the combined structure 1,100 and how the rotational forces are applied.

Furthermore, the support structure 1 comprises a support structure flange 15 for connecting the tower 101 of a wind turbine 100 to the support structure 1. The support structure flange 15 is configured to mate with the bottom end of the tower 101 of the wind turbine 100 when the tower 101 is positioned horizontally and the support structure 1 is floating vertically (figs. 4 and 5a).

The support structure 1 also comprises a binding structure binding the buoyancy units 3, 4 and 5 and the support structure flange 15 together in their respective positions. A great variety of possible binding structures are possible, where figures 1-3 shows a number of preferred embodiments.

The support structure 1 is configured to have a stable vertical floating position with the first and second pivot line buoyancy units 3, 4 floating in a body of water and the top buoyance unit 5 vertically above them. This is achieved when the support structure 1 floats in a vertical position with the center of gravity (COG) and the center of buoyancy (COB) positioned along the common vertical line such that sufficient restoring force is achieved when the support structure tilts in any direction.. This stability can be obtained through an endless variation of actual constructions and parts of the binding structure can be used for the purpose of buoyancy in the vertical position.

Figure 2a and b shows an embodiment of the invention comprising two main sections: a transvers main section 20 and an aft main section 10. In this embodiment the binding structure comprises a horizontal pipe 21, which is a part of the transvers main section 20, providing sufficient vertical floating stability for controlled movement in calm waters. The binding structure further comprises a horizontal pipe 11 in the aft main section 10 on which the support structure flange 15 is positioned and which is connected to the middle of the transverse main section 20 by means of a coupling structure 24. The binding structure may further comprise a transition cone 13 between the horizontal pipe 11 and a vertical pipe 12 in the aft main section 10, because the two sections 11 and 12 might advantageously have different diameters. The vertical pipe 12 constitutes the top buoyancy unit 5. Vertical pipes 22 on each side of the transverse main section 20 constitutes the first and second pivot line buoyancy units 3, 4. This structure provide a desired combination of characteristics: Low point of gravity and sufficient stability and buoyancy in a vertical position, low overall weight and low resistance during towing. Furthermore, the main aft section 10 provides the strength and stiffness needed to handle the rotation.

Figure 2 also shows circular damping plates 30a, 30b, 30c on the top buoyancy unit 5, the second buoyancy unit 4 and the first buoyancy unit 3, respectively. The damping plates 30 dampens movements in the support structure 1 caused by wave action and forces from the wind turbine.

As can be seen in fig. 3 the aft main section is in one embodiment provided with a fastening device for mooring line connection 16 and on each side of the transverse main section a first and second fastening device for mooring line connection 26 and 27.

For the purpose of explanation, a central plane C is defined and shown in fig. 2a containing the mentioned perpendicular line H. The central plane (C) is perpendicular to the pivot line 2. The top buoyancy unit moves in the central plane C during the rotational movement of the support structure 1.

The support structure flange 15 is vertically positioned when the floating support structure 1 is vertically positioned. The vertically positioned support structure flange 15 is configured to be connected to the bottom end of the horizontally positioned wind turbine tower 101. Using bolts and bolt holes is one way of executing the connection. Welding is also conceivable.

As seen in figure 5a, when the wind turbine 100 is fixed to the support structure 1, , the combined structure needs to be rotated 90 degrees for the wind turbine 100 to reach an erect position. The support structure 1 is therefore configured to maintain sideways stability of the combined structure of the support structure and wind turbine during a 90 degrees rotation of the combined structure to an erected position of the wind turbine. In practical terms this amounts to the two pivot line buoyancy units 3, 4 being dimensioned to avoid total submersion during the rotational movement. The two buoyancy units 3,4, and possibly buoyant parts of the binding structure, must have sufficient buoyancy to hold the weight of the combined structure 1,100 of the wind turbine 100 and support structure 1 and any vertical component of the rotational force applied to the combined structure during the 90 degree rotation. Because of the great height of the top buoyancy unit 5 in the vertical position, dynamic inertia must also be taken into account. However, this kind of considerations is within the ordinary tasks of a skilled person and will not be discussed in detail. Wires 51, 53, 55, 60 and 62 and winches 56, 57, 58, and 59 may be used for rotating the combined structure 90 degrees. Preferably the wires are connected to reinforced connection structures 50, 52 and 54, as seen in figs. 4 and 5. It is conceivable to use slings or some kind of removable equipment, but due to the high level of forces, often reaching hundreds of tons, reinforced connection structures 50, 52 and 54 are advantageous.

Mainly, the rotational forces acting on the combined structure during rotation will have a direction in the central plane C. For all types of wires 51, 53, 55, 60 and 62, the rotational forces may be set up by one wire or a combination of wires. Each type of wire set up a combined force mainly positioned in the central plane.

In one embodiment for use of wires 51, 53 and 55 and winches 56, 57 and 58, the top buoyancy unit 5 of the floating support structure 1 comprises at least one reinforced top connection structure 50 for at least one rising wires 51, preferably positioned on the top of the top buoyancy unit 5 or the damping structure 30a, as shown in fig. 4.

Each of the first and second baseline buoyancy units 3, 4 comprises at least one reinforced connection structure 54, preferably positioned on the lower part of the respective first and second baseline buoyancy unit 3,4, and symmetrically relative to the central plane C.

Preferably the top buoyancy unit 5 comprises at least one reinforced support connection structure 52, preferably positioned on the top side of the top buoyancy unit towards the tower 101. The at least one reinforced support connection structure 52 is configured for connection to at least one support wire 53, which are connected to the tower 101 of the wind turbine 100 to transfer rotational force from the at least one rising wires onto the tower 101.

Configuration of wires and winches

Figure 5a shows a sideview of a first configuration for wires and winches with the wind turbine 100 positioned on the quay side. The combined structure is pulled away from the quay 63 and the nacelle 102 is resting close to the edge of the quay. The at least one rising wire 51 is connected to a rising winch 56 positioned on a rising wire barge 65 in the rear end and to the top buoyancy unit 5 in the other end, preferably to the reinforced top connection structure 50. In one embodiment a support wire 53 is directly or indirectly connected to the top buoyancy unit 5 in one end, preferably to a reinforced support connection structure 52, and to the upper part of the tower 101 of the wind turbine in the other end. A restriction wire 55 is connected to each of the respective first and second pivot line buoyancy units 3, 4 in one end, preferably to reinforced connection structures 54, and to respective restriction winches 57 positioned on the quay side in the other end. In one embodiment a securing wire 61 is connected to the respective pivot line buoyancy units 3, 4 in one end and to a rearward fixpoint in the other end, i.e. an anchor or a fixpoint on land. Not visible is a counteracting winch 58 positioned behind one of the restriction winches 57. A counteracting wire 60 is connected to the tower 101 of the wind turbine 100 in one end and to the counteracting winch 58 positioned on the quay 64 in the other end.

Figure 5b shows sideview of a second configuration of winches 57, 58 and 59and wires 51, 53, 55, 60 and 62 with a wind turbine 100 positioned on a barge 64. The figure shows a situation where the rotation has just started. At least one barge wire 62 is connected to a fixpoint rearward of the barge 64, in one end, and to a barge winch 59 on the barge 64 in the other end. A counteracting wire 60 is connected to the tower 101 of the wind turbine 100 in one end and to a counteracting winch 58 positioned on the barge 64 in the other end. In one embodiment a support wire 53 is directly or indirectly connected to the top buoyancy unit 5 in one end, preferably to a reinforced support connection structure 52, and to the upper part of the tower 101 of the wind turbine in the other end. Restriction wires 55 are fixed to the barge and the respective first and second buoyancy units 3, 4. The rising wire 51 is connected to a rearward fixpoint, i.e. an anchor or a fixpoint on land in one end, and to the top buoyancy unit 5 in the other end, preferably to the reinforced top connection structure 50. Preferably the wires are symmetrically positioned relative to plane C.

Figure 5c shows the second configuration in 5b from above. The plane C is indicated with a dotted line. Seen from above the counteracting winch 58 is visible between the barge winches 59. Although, restriction winches are not necessary, it may be advantageous to be able to adjust the length of the restriction wires during the rotation.

Method for connecting a vertically floating support structure and a horizontally positioned wind turbine

Figure 6 illustrates a method for connecting a vertically floating support structure 1 and a horizontally positioned wind turbine 100. The method comprises the following steps:

The first step shown in fig. 6a and b is to position the wind turbine tower 101 horizontally on a barge 64 or quay with the bottom end by the edge of the barge or quay and mounting nacelle 102 and rotor blades 103 onto the tower 101 of the wind turbine 100. In fig. 6 the wind turbine is positioned on a quay. This will normally require some means for adjustment of height due to tidal variations. The tidal adjustment could be done by ballasting and deballasting the support structure or by hydraulic tools supporting the tower 101. The advantage of using a barge 64 is that adjustments of height due to tidal fluctuations is avoided. Another advantage is that the barge 64 can be towed to any location which is suitable for the rotation of the combined structure.

The second step shown in fig. 6a and b is to position the support structure 1 vertically with the support structure flange 15 opposite of a bottom end of the tower 101. It is not within the scope of the invention to describe how the support structure is positioned in a vertical position. This is described in another application.

The third step is connecting the bottom end of the tower 101 of the wind turbine 100 with the support structure flange 15 of the support structure 1. In one embodiment the support structure flange is provided with bolts and the bottom end of the tower is provided with mating bolt holes.

The fourth step is to rotate the combined structure of the support structure 1 and wind turbine 100 90 degrees to an erected position. The 90 degrees rotation of the combined structure can be done in a number of ways using bars, wires, winches, cranes, tugs, barges and ballasting / deballasting separately or in combination.

Method for rotation of the combined structure from quay or fixed barge

Below we will describe a method for rotation of the support structure 1 and wind turbine 100 to an erect, operational position from a quay side or anchored/fixed barge mainly using wires and winches. The method comprises the following steps:

First step is to position and fasten all the wires and winches. The essential wires and winches are shown in fig. 5a and 7a.

First step includes to fasten at least one rising wire 51, connected to at least one rising winch 56 positioned rearward of the combined structure, to the top buoyancy unit, preferably to the at least one reinforced top connection structure 50. The combined pull of the at least one rising wire 51 must have a significant component tangential to the circle described by the top buoyancy unit during the 90 degrees rotation. Thus, causing a rotational movement of the combined structure.

First step also includes to fasten respective at least one restriction wires 55 to the respective first and second pivot line buoyancy units 3, 4. The restriction wires 55 are connected to respective at least one restriction winches 57 positioned on the barge 64 or quay side. Preferably the restriction wires are fastened to the at least one reinforced connection structures 54 on said buoyancy units 3, 4. This configuration must be symmetric relative to the central plane C.

The first step also includes to fasten the at least one counteracting wire 60, connected to at least one counteracting winch 58 positioned on the barge or quay, to the upper part of the wind turbine tower 101. The combined pull of the at least one counteracting wire is within the central plane C and is pointing forward.

In one embodiment the first step also includes to fasten securing wires 61 to the first and second pivot line buoyance units on the rearward side opposite of the restriction wires to prevent uncontrolled movement of the combined structure towards the quay or barge during a free fall part at the end of the rotation.

Preferably, in one embodiment the first step also includes fastening at least one support wire 53 in one end to at least one reinforced support connection structure 52 on the forward side of the top buoyancy unit 5 and fastened to the upper part of the tower 101 in the other end. The purpose of the support wire is to hold the tower 101 in position relative to the support structure 1 during the 90 degrees rotation.

The second step shown in fig. 7a is moving the wind turbine and support structure away from the barge 64 or quay until the nacelle 102 at the top end of the wind turbine tower 101 is close to the edge of the barge 64 or quay 63.

The third step is tightening the restriction wires 55, the at least one rising wires 51 and the at least one support wires 53.

The fourth step shown in fig. 7b and 7c is rotating the combined structure by pulling the at least one rising wire and /or the restriction wires. At a predetermined angle at around 60 degrees the COG of the combined structure will be ‘on the hull side’ of the support structure 1 and the combined structure will pass a tipping point and start to fall towards its intended erected floating position. The 90 degrees rotation can be split in a lifting part and a free fall part. The lifting part is the part where the rising wire needs to pull on the top buoyancy unit to continue the rotational movement and the free fall part is when COG is ‘onboard’ or ‘on the hull side of’ the support structure.

The fifth step shown in fig. 7d is holding the counteracting wire taut and be prepared to counteract the free rotation before reaching the tipping point at the end of the rotational process.

The sixth step is holding the rising wires taut when the tipping point is passed and the support structure fall towards its intended erected horizontal position shown in fig. 7e while the counteracting wire controls the movement during the free fall part of the 90 degrees rotation. If securing wires 61 are present, they will prevent the lower part of the combined structure to move forward during the free fall part of the rotation.

During the rotational movement the combined pull vector form the at least one rising wires 51 and the combined pull vector from the at least one counteracting wires 58 and the wind turbine tower 101 is positioned in the central plane C and the restriction wires holds the pivot line 2 in a perpendicular position relative to the central plane C.

The problematic part of this operation is the free fall part of the rotation. If the top buoyancy unit hits the water at too great a speed, a large wave might be generated. This can be mitigated by the mentioned securing wires 61 which prevent forward movement of the pivot line buoyancy units 3, 4 and allows the securing wire 61 and counteracting wire 60 to control this part of the rotation. Alternatively, the rising winch 56 could be mounted at an altitude on a nearby hillside. This would allow the rising wire 55 and counteracting wire 60 to control the free fall part. Alternatively, a free fall is allowed to take place. If the counteracting wire 60 pulls the tower 101 forward the forward movement of the pivot line buoyance units 3, 4 is dampened by the resistance in the water and the velocity of the top buoyancy unit 5 when hitting the water would be low enough to avoid a large wave.

In another embodiment of the method the combined structure of the support structure 1 and wind turbine 100 is positioned on a barge 64. As seen in fig. 8 the wind turbine 100 is resting on a barge 64 and the support structure 1 is positioned vertically in the water.

Method for rotation of combined structure from winched barge

In this embodiment the combined structure is resting on a barge 64 as seen in fig 8a. The barge is anchored to a fixpoint in a forward position and a barge winch 59 is able to winch the barge forward by pulling the barge wire 62 connected to the fixpoint or anchor. The method for rotation of support structure 1 and wind turbine 100 to an erect position comprises the following steps:

First step is to position, connect and fasten, the barge 64 and all the wires 51, 53,

55, 60 and 62 and winches 57, 58 and 59. The essential wires and winches are shown in fig. 5b and c and fig. 8.

The first step includes to position the barge with the combined structure 1, 100 at a site for rotation with at least one barge wire 62 and barge winch 59 able to move the barge 64 forward in the central plane C. The barge winch can be positioned on the barge, at an anchor point or on shore.

The first step also includes to fasten the at least one rising wire 51 to the top buoyancy unit, preferably to the at least one reinforced top connection structure 50 in one end, and the other end to a rearward fixpoint. Preferably, but not necessarily, the rising wire 51 is connected to at least one rising winch 56 positioned on a rising wire barge 65 (see fig 5a) or on land. The rising wire 51 may also simply be fixed to a fixpoint in the form of an anchor or installation on shore The combined pull of the at least one rising wire 51 must have a significant component tangential to the circle described by the top buoyancy unit during the 90 degrees rotation. Thus, causing a rotational movement of the combined structure. It should be understood that the mentioned pull of the at least one rising wire 51 may be a resultant force originating from the barge winch 59 or restriction winch 56.

The first step also includes fastening respective at least one restriction wires 55 to the respective first and second pivot line buoyancy units 3, 4 and to the barge 64. Preferably the restriction wires 55 are fastened to the at least one reinforced connection structures 54 on said buoyancy units 3, 4. This configuration must be symmetric relative to the central plane C. Preferably, but not necessarily, the respective restriction wires 55 are connected to respective at least one restriction winches 57 positioned on the barge.

The first step also includes fastening at least one counteracting wire 60, connected to at least one counteracting winch 58 positioned on the barge, to the upper part of the wind turbine tower 101. The combined pull vector of the at least one counteracting wire 60 is within the central plane and is pointing forward.

Preferably, in one embodiment the first step also includes fastening at least one support wire 53 in one end to at least one reinforced support connection structure 52 on the forward side of the top buoyancy unit 5 and fastened to the upper part of the tower 101 in the other end. The purpose of the support wire is to hold the tower 101 in position relative to the support structure 1 during the 90 degrees rotation.

The second step comprises tightening the at least one barge wires and the at least one rising wires 51 by pulling the at least one barge wires 62.

The third step comprises rotating the support structure 1 and wind turbine 100 by pulling the at least one barge wire 62 while the rising wire 51 is also pulling or held taut.

The fourth step comprises holding the rising wires 51 and counteracting wires 60 taut when passing of the tipping point causes the combined structure to fall into an erected operational position during the free fall part of the 90 degrees rotation.

The right side of Fig.8a-d shows how the barge moves as the rotation progresses. The dotted line illustrates the same position in all the figures.

As with the previously described method with the tower 101 positioned on a quay 63 or fixed / anchored barge 64, the combined pull vector from the at least one rising wires 51 and the combined pull vector from the at least one counteracting wires 58 and the wind turbine tower 101 is positioned in the central plane C and the restriction wires 55 holds the pivot line 2 in a perpendicular position relative to the central plane C throughout the 90 degrees rotation. In the preceding description, various aspects of the system and the method according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the system and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiments, as well as other embodiments of the system and the method, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.

Reference numerals:

1 Support structure for floating wind turbine

2 Pivot line

3 First pivot line buoyancy unit

4 Second pivot line buoyancy unit

5 Top buoyancy unit

10 Aft main section

11 Horizontal pipe in aft main section 10

12 Vertical pipe in aft main section 10 constituting the top buoyance unit 5

13 Transition cone between horizontal pipe 11 and vertical pipe 12 in aft main section 10

15 Connecting flange for wind turbine tower 101

16 Dynamic fastening device for mooring line connection on aft main section

20 Transverse main section

21 Horizontal pipe in transverse main section 20

22 Vertical pipe in transverse main section 20 constituting the first and second pivot line buoyancy units 3 and 4

23 Transition cone between horizontal pipe 21 and vertical pipe 22 in transverse main section 20

24 Coupling structure connecting aft main section 10 and transverse main section 20

25 Joint (between aft main section 10 and transverse main section 20)

26 First static fastening device for mooring line connection on transverse main section 20

27 Second static fastening device for mooring line connection on transverse main section 20

30 Damping structure

30a Horizontal damping plate on aft main section 10

30b First horizontal damping plate on transverse main section 20

30c Second horizontal damping plate on transverse main section 20

50 Reinforced top connection structure on the top buoyancy unit 5 for at least one rising wire 51

51 Rising wire

52 Reinforced support connection structure on the top buoyancy unit 5 for at least one support wire 53

53 Support wire

54 Reinforced connection structure on the respective first and second pivot line buoyancy units 5 for at least one restriction wire 53

55 Restriction wire

56 Rising winch

57 Restriction winch

58 Counteracting winch

59 Barge winch

60 Counteracting wire

61 Securing wire

62 Barge wire

63 Quay side

64 Barge

65 Rising wire barge

70 Water level

100 Wind turbine

101 Wind turbine tower

102 Wind turbine nacelle

103 Wind turbine blades