WO2012007002A2

WO2012007002A2 - Offshore unloading

Info

Publication number: WO2012007002A2
Application number: PCT/DK2011/050271
Authority: WO
Inventors: Michael Kastrup; Henrik E. KJÆRGAARD; Anders Thorsager; Tobias Lidegaard Rossel; Gorm Ditlev Christensen; Torben Christensen; Michael Hemmingsen; Asger Sibuhr Nielsen
Original assignee: Vestas Wind Systems A/S
Priority date: 2010-07-12
Filing date: 2011-07-11
Publication date: 2012-01-19
Also published as: WO2012007002A3

Abstract

A system and method for movement of payloads between a service vessel and an offshore wind turbine comprising employs a ramp (14,36,80,84,101,130) engageble by means of a connection device (22,28,30,48,54,62,68,72,88) with a structure on the tower or foundation and extending between the wind turbine and vessel,and a transfer device in the form of an moving conveyor surface, or a movable loader or platform or the like, for moving the payload over the ramp to the tower, from where it can be hoisted by a crane in the turbine.

Description

Offshore unloading

Field of the invention The present invention relates to a system and method for movement of payloads such as major turbine components from a service vessel to the turbine in the offshore environment.

Background of the invention

The installation, repair and servicing of offshore wind turbines is a major technical challenge. The growth in the size of turbines and the components that make them up places severe demands on the vessels and the technology used for transferring components from service vessels to the turbines. Moreover, the constant drive to reduce the cost of energy produced places increasing demands to minimise the time of installation, and to minimise any downtime of turbine operation resulting from servicing or repair. The offshore environment also requires that one has to operate within oftentimes short windows of benign sea state and wind conditions.

The lifting of components directly off a service vessel alongside the turbine requires that the lifting crane have a rating which is significantly in excess of that required to lift the same component in an onshore environment. The movement of the component as a result of the movement of the vessel in response to the action of waves, current and wind can significantly increase the loading on the crane depending on the particular conditions.

The present invention is directed to providing apparatus and methods for facilitating the unloading of components from a vessel onto a wind turbine.

Summary of the invention

According to a first aspect of the invention there is provided a system for movement of payloads between a service vessel and a wind turbine comprising a ramp engageble with the wind turbine for extending between the wind turbine and vessel, a connection device at a distal end of the ramp which in use engages a structure on the tower or foundation; and a transfer device for moving the payload over the ramp.

With such a structure the transfer of payloads from vessel, which is necessarily moving owing to action of waves, wind and current, to turbine by crane is avoided. The transfer device may take the form of a driven conveyor surface on which the payload can be disposed, in the manner of an endless conveyor belt, or a conveyor having a surface portion which can be driven along the ramp, on which the payload can be supported. In one further form the transfer device comprises a driven platform movable over the ramp on which the payload can be supported.

Alternatively, the transfer device may comprise a driven connecting member to which the payload can be engaged, for example a connecting hook to which the payload can be connected.

As a further alternative the transfer device may include a loader onto which the payload is placed which is driven along the ramp. This may be in the form of a carriage or trolley or frame which is driven through means in the ramp, or alternatively it may be a self-powered device which is able to move along the ramp.

As a still further alternative, the transfer device may comprises a driven wire or cable or the like connectable to the payload to pull the payload over a static ramp surface. The cable or wire may be wound on a drum, winch or capstan, preferably disposed on the service vessel, and extending around a pulley or block at the turbine tower or foundation. Alternatively the drum, winch or capstan may be disposed at the tower end of the ramp. If a system is used employing a loader it is preferable to be able to in effect remove it form the ramp once it reaches the tower or foundation, and to this end the loader is preferably releasingly engageable with the tower or foundation or a structure on the tower or foundation. In one form this engagement is a pivotable connection, such as is provided by a ball and socket structure. In an alternative form the connection is provided by a hook or pair of hooks which engage over structures on the tower or foundation as the loader reaches the tower or foundation. In this case the loader is formed with legs which are able to lift it relative to the ramp once engaged with the tower or foundation, as well as assisting with the engagement process.

Alternatively, the loader may be adapted to be lifted off the ramp once it makes engagement with the tower or foundation structure, for example through the action of lifting wires between the tower/foundation and loader.

The connection device for engaging a structure on the tower or founndation may be a clamping device having opposed fingers which grip a frame structure on the tower or foundation. In an alternative form the connection device comprises a ball or socket for engaging a socket or ball arranged on the structure on the tower or foundation. In a still further alternative form the connection device comprises an inverted U-shaped locking eye for engaging a locking pin on the tower or foundation. In a still further alternative form the connection device comprises a locking hook for engaging on part of a lattice- type or similar structure on the tower or foundation, for example on a jacket- type foundation.

In a preferred form the ramp comprises a main section, and a distal section which is adapted to make a rigid connection with the tower or foundation , the main and distal sections being pivotally connected. In this manner, once a payload has been moved up the ramp to the distal section, this distal section provides a stable platform from which the payload can then be conveniently lifted. The ramp may further comprise a proximal section for connection to the vessel, with the main section and proximal sections being pivotably joined. The proximal end of the ramp or the proximal section may rest on the vessel allowing relative movement, or it may be structurally connected thereto. In one form the proximal end or section may be joined to the vessel through an automatic stabilising or motion-compensating system, whereby wave-induced motion of the vessel is not transferred to the ramp.

In a further aspect the invention resides in a wind turbine service vessel provided with a system as described above.

In a further development the vessel may be provided with at least one loading shelf disposed in the vicinity of the ramp on which payloads can be placed prior to movement to the turbine. A pair of such shelves may be provided arranged in the vicinity of the ramp, with a passage defined between the shelves leading to the ramp. In a still further aspect the invention resides in a method of unloading a payload from a service vessel employing a system as described above.

In a still further aspect the invention resides in a method of unloading a payload from a service vessel, the vessel having a ramp for connection to the turbine and a transfer device, the method comprising the steps of bringing the vessel into the vicinity of the turbine, arranging the ramp so as to engage a connection device thereof with a tower or foundation of the turbine, and moving the transfer device to move the payload along the ramp to the turbine. Brief description of the drawings

Embodiments of the present invention are now described, by way of example only, with reference to the following drawings in which:

Figure 1 shows schematically the unloading of components from a vessel by means of a ramp;

Figure 2 shows schematically a structure including a lower component- receiving platform;

Figure 3 illustrates a connection of ramp and vessel;

Figure 4 shows the structure of Figure 3 viewed from above; Figure 5(a) shows a ramp in the extended orientation prior to engaging a wind turbine tower;

Figure 5(b) shows the ramp making connection with the wind turbine tower; Figure 5(c) shows the ramp adopting a transfer configuration;

Figure 5(d) shows a payload being moved by the ramp.

Figure 6(a) shows a connection structure for the ramp in the process of being connected to the tower;

Figure 6(b) shows a clamp arrangement of the connection structure;

Figure 6(c) shows the ramp when connected;

Figure 7(a) shows an alternative connection structure for the ramp in the process of being connected to the tower;

Figure 7(b) is an enlarged view of the connection structure, with ramp removed for reasons of clarity;

Figure 7(c) shows the ramp when connected;

Figure 8(a) shows a further alternative connection structure for the ramp, in the process of being connected to the tower;

Figure 8(b) is an enlarged view of the connection structure, with ramp removed for reasons of clarity;

Figure 8(c) shows the ramp when connected;

Figure 9(a) shows a still further alternative connection structure for the ramp, in the process of being connected to a tower which has a lattice-type structure;

Figure 9(b) is an enlarged view of the connection structure;

Figure 9(c) shows the ramp when connected;

Figure 10(a) shows a still further alternative connection structure for the ramp, in the process of being connected to a tower which has a lattice-type structure;

Figure 10(b) is an enlarged view of the connection structure, with ramp removed for reasons of clarity;

Figure 10(c) shows the ramp when connected;

Figures 1 1 (a) to (e) show the use of a conveyor-type ramp having an integrated platform;

Figures 12 (a) to (e) show the use of a conveyor ramp employing a loader removable from the conveyor for lifting; Figures 13 (a) to (e) show a conveyor ramp employing an alternative form of loader;

Figures 14 (a) to (e) show the lifting of an add-on type tower crane;

Figures 15(a) to (e) show the lifting of a payload off a platform;

Figures 16 (a) to (c) show a mobile ramp on a vessel:

Figures 17(a) to (f) show a fixed type ramp;

Figure 18 shows a vessel with overhead crane:

Figures 19(a) and (b) show loading shelves to facilitate movement of payloads to the ramp; and

Figure 20 shows the disposition of a gangway for personnel used alongside a ramp.

Detailed description of the preferred embodiments Turning to the drawings, Figures 1 to 4 is illustrate schematically the use of a ramp system for the unloading of components from a vessel to a wind turbine, with the ramp making connection to the tower or its foundation. Such turbine components may comprise components of the wind turbine itself, including major components such as blades, generators, gearboxes, and a host of other internal components of the wind turbine, an add-on tower crane, as well as apparatus used in repair or servicing processes. Although it is described that the components are unloaded from the vessel, it will be appreciated that the ramp system is equally applicable to the removal of a component from the wind turbine and loading it onto the vessel. Moreover, although the connection of the ramp may be made to either the tower or a part of the turbine which is technically part the foundation, reference is generally made to the 'tower', which expression should accordingly be taken to include the foundation beneath the tower. Moreover, although described in the context of fixed tower/foundation secured to the sea bed, the invention is also applicable to a floating-type foundation

In Figure 1 there is shown a wind turbine generator in an offshore environment, with the wind turbine indicated generally by numeral 2, having a tower 4, in this version supported by a monopile-type foundation, a nacelle 6 atop the tower 4 and a rotor 8, comprising as is conventional, three blades. It is to be understood the expression Offshore' encompasses a variety of situations including a true marine environment, but also estuary, or lake environments. The tower 4 is provided with a platform 10 as is conventionally disposed a suitable distance above maximum expected wave height, at which typically there is provided access for personnel to the tower interior via a tower door. The platform 10 is adapted to be able to support the weight of a major component, for example rated up to 80 tonnes. The Figure shows a support vessel 12 in the vicinity of the turbine. Between the vessel 12 and platform 10 there is provided an unloading ramp 14. The ramp is secured at the platform 10, and at the vessel 12 in a manner to be further explained below. The Figure shows a number of payloads indicated 16 representing major turbine components. It is illustrated schematically that the payload is moved up the inclined ramp 14 to the platform 10, from where it can be lifted up, either by a nacelle internal crane, or if utilised, by an additional add-on type tower crane .

Figure 2 shows similar arrangement, noting however that the tower 4 is supported on a jacket foundation 18. Located at a relatively lower level beneath the conventional platform is an additional loading platform 20, the unloading ramp 14 being connected between the vessel 12 and this additional loading platform 20. The figure indicates the lifting by the nacelle internal crane of an 80 tonne payload directly from this additional loading platform 20. Figures 3 and 4 show the ramp 14 making a connection between vessel 12 and a hook-like structure 22 on the tower. More particularly, the vessel 12 is provided with a ball 24, whilst the lower end of the ramp 14 is formed with a socket 26, such that a connection is made allowing relative pivoting about three mutually perpendicular axes. Similarly, the upper end of the ramp 14 is formed with a socket 28 making connection with a ball 30 on the hook 22, again allowing pivoting movement about three mutually perpendicular axes.

As illustrated, payload 16 is pulled up the ramp 14 by means of cable 32 to which the payload 16 secured through the action of drum, winch, capstan or the like 34 located on the vessel, with the cable 32 passing round an appropriate pulley, block or pulley system at the tower hook 22. It will be appreciated that the winch 34 might equally be disposed on the tower. It will further be appreciated that a variety of block/pulley structures may be employed to increase the mechanical advantage. Moreover, in order to facilitate the sliding of the payload 16 up the ramp 14 it may be formed with a low-friction surface. Alternatively, the payload 16 may be loaded into a dedicated receptacle, trolley or sleigh adapted to move over the ramp surface 14.

As a further alternative, instead of using a cable/winch system, the ramp 14 may be provided with an active conveyor system which serves to propel a payload up the ramp 14, as is discussed in relation to subsequent embodiments.

During an unloading or loading operation the vessel 12 is maintained in the spaced disposition relative to the tower 4, partly through the connection of the ramp 14, but also through the action of an appropriate positioning system interactively connected to the vessels engines, such as a GPS-based positioning system such as DP2.

Figures 5(a) to (d) illustrate schematically the use of a ramp indicated 36 which is a conveyor-type ramp. Figure 5(a) shows a vessel 12 approaching the wind turbine 2 with the ramp 36 extended vertically having been moved from a stowage position on the vessel deck. The ramp 36 is lowered into position where it's far or distal end makes connection with the tower 4, in a manner as discussed further below. During this process fine positioning of the vessel 12 may be facilitated through an appropriate automatic positioning system. The ramp 36 is then moved into its operative configuration as indicated in Figure 5(c) where it's distal section 38 furthest from the vessel 12 makes a rigid connection with the tower 4 and forms a generally horizontal platform section. The proximal ramp section 40 adjacent vessel 12 makes a rigid or semi-rigid connection with the vessel. The distal ramp section 38 constitutes a rigid and stable platform on the tower from which the payload can be lifted by the nacelle crane, or other add-on type crane previously taken up the tower. The ramp 36 includes pivoting joints between end sections 38, 40 and central section 42, whereby the sections are able to pivot about axes parallel to the ramp surface, which are substantially horizontal. It may be arranged that the connection between proximal section 40 and vessel 12 is achieved through a servo-driven automatically-stabilising system, which is thereby able to accommodate at least a degree of movement of the vessel 12, without transmitting this on to the ramp 36. The ramp 36 includes a conveying surface or structure at least in its central section 42 and preferably also in end sections 38, 40. This conveying surface may be in the form of an endless belt, or may comprise a series of relatively articulated elements supported on an endless belt in the manner of an escalator or moving walkway. Alternatively, the ramp may utilise a loader as described further below. Figure 5(d) illustrates a payload 16 being moved on the conveyor ramp between the vessel 12, and the end platform-forming section 38.

Figures 6(a) to (c) illustrate a connection system for making connection between a ramp 36 and tower 4. More particularly, the tower is formed with a ladder-like structure comprising a pair of uprights 44 and a series of spaced crosspieces or rungs 46 to which selective connection can be made depending on tide height. As is visible in Figure 6(b) beneath the end ramp section 38 are a pair of opposed clamp fingers 48 movable towards and away from each other for example by hydraulic means, engageable over a selected pair of crosspieces 46. The distal end ramp section 38 is formed with a shaped protruding section 48 which fits between the uprights 44 and rests on the upper of the engaged crosspiece 46 whereby the distal ramp section 38 is rigidly and firmly secured to the tower, thereby forming a stable platform to which payloads can be moved up the conveyor, and from which they can be conveniently and safely lifted.

In Figures 7(a) to (c) connection is made between conveyor ramp 36 and structure of uprights and crosspieces 44,46 on the tower with the crosspiece(s) formed with protruding pin 50 having enlarged head 52, and with the conveyor ramp end provided with an inverted U-shaped eye 54 which engages over the pin 50 behind the enlarged head 52. It may be arranged that this eye 54 is secured to the end of the conveyor ramp 36 through a pivoting connection 55. Figure 5(b) shows the eye 54 being lowered onto the pin 50 to make the connection. An additional locking pin 56 may be provided to prevent the eye 54 from lifting off the pin 50. As indicated in Figure 7(c) the connection allows relative rotation of the ramp about its longitudinal axis, allowing some accommodation of the rolling movement of the vessel 12. It also allows a degree of pivoting about the connection 55 as the vessel rises and falls (pitches) with the waves.

In Figures 8(a) to (c) there is illustrated a connection system employing a pair of balls 58 at the ends of hooks 60 secured to a crosspiece 46. These are received within sockets 62 at the conveyor ramp end. Figure 6(b) shows the sockets fitted over the balls 58 and the insertion of locking pins 64 to lock the sockets 62 and thereby the ramp 36 in position. It may also be arranged that only a single ball/socket structure is utilised.

Figures 9(a) to (c) show a connection system for connecting the conveyor ramp 36 to a tower having a lattice-type structure at least at its foundation. The end of the conveyor ramp is formed with a double-headed hook 68 which is able to engage behind a part of the lattice to make a connection therebetween. More particularly, the lattice structure has a number of cross- shaped portions or interstices, indicated 66 in Figure 9(a), the double-headed hook 68 engaging behind one of these in the V-shaped region adjacent the interstices 66 as shown in Figure 6(b), and locking pins 70 being inserted into the lattice to lock the ramp 36 in place.

In the embodiment illustrated in Figures 10(a) to (c) there is shown a connection system which incorporates a clamping structure 72 in the form of opposed clamp fingers 74 which can grippingly engage a structure on the tower such as part of the conventional docking structure of uprights 44 and crosspieces 46, or a part of a lattice in the case of a lattice- type foundation or tower. The clamp fingers 74 may be movable towards or away form each other through the action of hydraulics. Alternatively, one of the pair of fingers may be static and the other movable, to grip the tower structure therebetween. Although the connection techniques to the tower of the embodiments of Figures 6 to 10 are illustrated in the context of a ramp having an active conveying system thereon it will be appreciated that the connection systems are equally applicable to a ramp with a system where payloads are dragged up the ramp by a lifting system, as described in relation to Figures 1 to 4.

Figures 1 1 to 13 illustrate various adaptations of a conveyor ramp in order to facilitate the movement of a payload 16 from vessel to tower onto a structure or into a position in which the payload is firmly held on the tower in a static manner, from where it can be conveniently lifted by the nacelle crane or other add-on type crane as if the lifting were being performed in an onshore environment.

The conveyor 80 illustrated in Figures 1 1 (a) to 1 1 (e) incorporates a moving shelf 82 on which the payload can be placed in a substantially horizontal orientation. Figure 1 1 (a) shows the payload 16 having been moved to a position adjacent the lower end of the conveyor 80. This is achieved by use of a crane, lifting truck or other kind of lift depending on the weight and nature of the component. As shown in Figure 1 1 (b), the conveyor 80 is activated so that the shelf 82 is moved to its lowermost position overlying the vessel deck. The payload is then moved form its support frame onto the shelf as shown in Figure 1 1 (c) and secured thereto as shown in Figure 1 1 (d). With the payload secured on the shelf 82, the conveyor is activated, moving the shelf with payload thereon up to the tower. Once the shelf 82 is at its uppermost position adjacent the tower the payload 16 can then be lifted by the internal nacelle crane (or add-on tower crane if used) , the shelf 82 forming a stable structure for lifting.

Figures 12 (a) to (e) show a conveyor structure 84 adapted to move a loader 86 which carries the payload 1 6 thereon. Figure 12 (a) shows the payload on the loader 86 moving up he conveyor 84. An upper end of the loader 86 is provided with a connecting structure whereby it can engage an adaptation on the tower such as a part of the conventional docking structure, such as a crosspiece 46 as described above. As illustrated, the loader is fornned with a ball structure 88 which engages in a socket structure 90 in the crosspiece, forming a releasable and pivotable connection therewith. The loader is also fornned with a lifting device 92 whereby it can be raised off the conveyor surface in the manner of a drawbridge once the pivotable connection has been made. To this end a pair of lifting strops 94 incorporating hydraulic structures 96 can be provided between tower and loader 86, which when activated lift the loader 86 off the conveyor as shown in Figures 12 (c) to (e). It will be appreciated that a variety of flexible lifting structures, block/tackle arrangements, winces, capstan etc might equally be used to lift the loader. Once lifted off the conveyor into the substantially horizontal orientation of Figure 12(e), the payload can be conveniently lifted off the loader 86 and up the tower by the nacelle crane or other add-on type crane.

In Figures 13(a) to (e) there is shown a loader 100 for a payload having a base 102 and a leg structure comprising a pair of articulated legs 104 supporting the base 102 and the payload 16 thereon in a substantially horizontal orientation whilst on the inclined conveyor 101 . It may be arranged that the legs 104 operatively engage with the conveyor 101 for example through a clamping engagement, or the loader 100 may simply rest on the conveyor 101 surface. The loader 100 is provided with a pair of hooks 106 which serve to engage over cross pieces of the conventional docking structure. Figure 13(a) shows the loader 100 approaching the top of the conveyor 101 . Figures 13(b) and (c) show the articulated legs 104 raising the height of the base 102 relative to the conveyor surface so that the hooks 106 can engage over the crosspiece 46. As shown in Figures 13(d) and (e) the legs 104 retract beneath the base 102, leaving the loader 100 suspended above the conveyor 101 , from where payload 16 can be readily lifted by the nacelle crane, with the loader 100 providing a stable lifting platform.

Figures 14(a) to (f) illustrate the lifting of add-on type crane 1 12 by means of a loader 1 10. The loader 1 10 may comprise either of the connection devices of the aforedescribed embodiments illustrated in Figures 12 or 13, whereby after movement up the conveyor and connection of the loader 1 10 to the tower the crane 1 12 is supported on a stable platform ready for lifting. The loader 1 10 is provided with a tack frame 1 14 which is slidably retained beneath the base, which can be slid out and then pivoted into an upright orientation is indicated in Figures 14(a) and (b). To this tack frame 1 14 is secured a tack line 1 18 which is played out as the crane is lifted, which serves to guide and constrain the crane body 1 12 as the crane is lifted up the tower shown in Figures 14(c) and (d), and in particular maintaining the tack line and crane outboard of the conventional platform 10 at the tower base. The tack frame 1 14 may be provided with a movable crosspiece 1 16 to which the tack line 1 18 is connected to further allow adjustment of the tension in the tack line 1 18 during lifting.

Figures 15 (a) to (e) illustrate the lifting of a payload by a nacelle crane.

Figures 15 (a) and (b) show the attachment of a lift hook 120 lowered from the nacelle crane, and connected to lifting wires 122 on the payload 16. Figures 15(c) and (e) show service personnel playing out a guide wire 124. Figure 15(d) shows that the nacelle crane includes a jib or arm 126 which is positioned or moved outboard so that they lifting wire 1 19 is outboard of a conventional tower platform structure 10 which is provided just above the conveyor connection point on the tower.

The connection between vessel and conveyor ramp may be fixed, subject to allowing the ramp to incline upwardly towards the tower. Figures 16(a) to (e) however show a mobile conveyor ramp 130 which can be stored on the vessel deck and moved into position at en edge of the deck as the vessel

approaches the turbine. This mobile ramp has a base section 132 provided with tracks, and a main section raisable into an inclined configuration as shown in Figures 16 (b) and (c) from where it can engage the tower.

Figures 17(a) to (f) show an alternative form of connection where the conveyor ramp 140 is permanently disposed at the edge of the vessel 12, having a base section 142 which is mounted on the vessel deck so as to allow pivoting about a vertical axis and a main section 144 connected to this base section 142 and pivoting about a horizontal axis whereby it may be raised or lowered. Figure 17(a) shows a storage position with the main conveyor part 144 extending upwardly, and where a pair of wire support arms 146 are retracted lying parallel with the deck. In Figure 17(b) the wire support arms are raised, and in Figure 17(c) the wires are released to allow the conveyor ramp to pivot downwardly against the turbine making engagement therewith utilising one of the aforedescribed techniques. As shown in Figure 17(e) the wire support arms are folded. Figure 17(f) indicates that the base may be pivoted to allow optimum positioning of the vessel relative to the waves, wind and/or current.

It will be appreciated that the vessel may carry a large number of components and these need to be moved over the deck of the vessel for optimum carrying capacity of the vessel and optimisation of handling, and including movement alongside or onto the conveyor ramp for unloading from the vessel. Figure 18 illustrates that the vessel 12 may be provided with an overhead-type crane 150 movable over the deck in order to move payloads over the deck, for example from a storage position to position adjacent the lower end of the conveyor. The vessel may also be provided with wires, winces, tackle etc to allow movement of payloads over the deck.

Figures 19(a) and (b) show the provision of a loading shelves 160 disposed adjacent the lower end of the conveyor ramp, arranged spaced so that a mobile loader or trolley 162 can move between them to the base of the conveyor ramp, and depending on the type of conveyor structure may then move up the conveyor. These shelves facilitate the loading of payloads 16 onto a mobile loader or trolley 162 in that the payload can be moved laterally onto the loader or trolley from the shelf 160 without having to vertically raise or lower it, and then moved on the loader or trolley to the conveyor ramp. It may be that the payload is stored on the shelf during transport, or it may be moved there by a crane or lift as part of the unloading process.

Figure 20 shows that alongside the conveyor ramp there may be arranged a bridge for transfer of personnel from the vessel 12 to the tower to a position at the top of the conveyor where personnel may access the payload to assist with the handling operation.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made without departing from the scope of the invention.

Claims

1 . A system for movement of payloads between a service vessel and a wind turbine having a tower and foundation comprising:

a ramp engageable with the wind turbine for extending between the wind turbine and vessel;

a connection device arranged at a distal end of the ramp for engaging a structure on the tower or foundation;

and a transfer device for moving the payload over the ramp.

2. A system according to claim 1 wherein the transfer device comprises a driven conveyor surface on which the payload can be disposed.

3. A system according to claim 1 wherein the transfer device comprises a driven platform movable over the ramp on which the payload can be supported.

4. A system according to claim 1 wherein the transfer device comprises a driven connecting member to which the payload can be engaged.

5. A system according to claim 1 wherein the transfer device comprises a driven wire or cable or the like connectable to the payload to pull the payload over the ramp surface.

6. A system according to claim 5 wherein the cable or wire is wound on a drum, winch or capstan.

7. A system according to claim 6 wherein the drum, winch or capstan is disposed on the service vessel.

8. A system according to claim 1 wherein the transfer device comprises a loader device onto which the payload is placed, and which is driven along the ramp.

9. A system according to claim 8 wherein the loader is releasingly engageable with the tower or foundation of the wind turbine.

10. A system according to claim 8 or 9 wherein the loader is adapted to be lifted off the ramp on engagement with the wind turbine tower or foundation.

1 1 . A system according to claim 8, 9 or 10 wherein the loader is formed with legs which lift it relative to the ramp once engaged with the tower or foundation.

12. A system according to claim 8, 9 or 10 wherein the loader is provided with lifting wires which lift the loader off the conveyor once engaged with the tower or foundation.

13. A system according to any one of claims 8 to 12 wherein the loader is provided with a pivoting connection for engagement with a cooperating structure on the tower or foundation.

14. A system according to claim 10 wherein the loader is provided with a hook-like connection for engagement with a cooperating structure on the tower or foundation, and which supports the loader on the tower or foundation.

15. A system according to any preceding claim wherein the connection device is a clamping device having opposed fingers which grip a structure on the tower or foundation.

16. A system according to any one of claims 1 to 14 wherein the connection device comprises a ball or socket for engaging a socket or ball arranged on a structure on the tower or foundation.

17. A system according to any one of claims 1 to 14 wherein the connection device comprises an inverted U-shaped locking eye for engaging a locking pin on the tower or foundation.

18. A system according to any one of claims 1 to 14 wherein the connection device comprises a locking hook for engaging on part of a lattice structure on the tower or foundation.

19. A system according to any preceding claim wherein the ramp comprises a main section and a distal section which is adapted to make a rigid connection with the tower or foundation, the main and distal sections being pivotally connected.

20. A system according to claim 19 wherein the ramp further comprises a proximal section for connection to the vessel, and wherein the main section and proximal sections are pivotably joined.

21 . A system according to claim 20 wherein the proximal section is joined to the vessel through an automatic stabilising or motion-compensating system.

22. A wind turbine service vessel provided with a system according to any preceding claim.

23. A wind turbine service vessel according to claim 22 further comprising at least one loading shelf disposed in the vicinity of the ramp on which payloads can be placed prior to movement to the turbine.

24. A wind turbine in combination with a system according to any one of claims 1 to 21 .

25. A method of unloading a payload from a service vessel to a wind turbine, the vessel having a ramp for connection to the turbine and a transfer device, the method comprising the steps of bringing the vessel into the vicinity of the turbine, arranging the ramp so a connection device thereon engages with a structure on a tower or foundation of the turbine, and moving the transfer device to move the payload along the ramp to the turbine.

26. A method according to claim 25 wherein the connection device is a clamping device having opposed fingers the method including the gripping of a structure on the tower or foundation by the opposed fingers.

27. A method according to claim 25 wherein the connection device comprises a ball or socket, the method including engaging the connection device with a socket or ball on a structure on the tower or foundation.

28. A method according to claim 25 wherein the connection device comprises an inverted U-shaped locking eye the method including engaging the locking eye with a locking pin on the tower or foundation.

29. A method according to claim 25 wherein the connection device comprises a locking hook, the method including engaging the connection device on part of a lattice structure on the tower or its foundation.

30. A method according to any one of claims 25 to 29 wherein the transfer device includes a loader on which the payload is supported, the method including connecting the loader to the tower or foundation when it reaches the end of the ramp.

31 . A method according to claim 30 wherein once connected the loader is lifted form the ramp.

32. A method according to claim 31 wherein the loader is lifted through the action of lifting wires.

33. A method according to claim 31 wherein the loader is lifted through the action of lifting legs beneath the loader.

34. A method of unloading a payload from a service vessel to a wind turbine utilising the system of any one of claims 1 to 21 .