Technical Field The present invention relates generally to transfer apparatus for waterborne craft. Background

Transfer of personnel and/or equipment to and from a vessel to an offshore structure, such as a wind turbine tower, can be a difficult, hazardous and time-consuming operation, especially in anything other than calm sea conditions. We seek to provide an improved transfer apparatus.

Summary

According to a first aspect of the invention there is provided a lift to enable access between a waterborne vessel and a structure, the lift mountable to the vessel and the lift comprising a platform and a lift shaft assembly, the platform is driveable along the lift shaft assembly, and the lift comprising a motion compensation arrangement arranged to compensate for movement of the vessel relative to the structure.

Preferably the motion compensation arrangement is operative to reduce movement of the platform relative to the structure when the platform is in a structure access condition.

Preferably, the lift is positionable in a stowed position and in an operative position, and when in the operative position the lift shaft assembly is substantially upright.

Preferably, the motion compensation arrangement comprises a base for supporting the lift shaft assembly, and the base comprises a basal portion and a pivot, the pivot arranged to allow pivotable movement between the lift shaft assembly and the basal portion. The base preferably comprises a first pivot connection and a second pivot connection, and an axis of rotation of the first pivot connection being substantially orthogonal to an axis of rotation of the second pivot connection. Preferably the first pivot connection is a pitch compensation pivot connection and preferably the second pivot connection is a roll compensation pivot connection.

Preferably the motion compensation arrangement comprises at least one sensor to monitor the position of the lift shaft assembly in an operative condition relative to the structure. Preferably the motion compensation arrangement comprises an actuator responsive to signals from the sensor to adjust the lift shaft assembly relative to the structure. The sensor may be configured to output a signal indicative of the distance between the lift shaft assembly and the structure.

Conveniently, the actuator may also serve to drive the lift shaft structure from a stowed position to an operative position.

The base preferably comprises a third pivot connection having an axis which is substantially orthogonal to the first and second pivot connections, to allow pivotable movement of the base relative to the vessel.

Preferably, the motion compensation arrangement arranged to adjust the position of the platform along the lift shaft structure to take account of vertical movement of the lift shaft relative to the structure, and most preferably so as to reduce relative vertical movement between the platform and the structure.

The motion compensation arrangement preferably comprises a damped roller assembly arranged to at least partially embrace a fender of the structure.

A further aspect of the invention relates to a waterborne vessel comprising a lift of the first aspect of the invention.

Brief description of the drawings

Various embodiments of the invention will now be described, by way of example only, with reference to the following drawings in which:

Figure 1 is a perspective view of a vessel provided with an access lift docked at a structure to be accessed, Figure 2 is an enlarged view of the region II,

Figure 3 is an enlarged view of the region III, Figures 4a to 4c are plan views of the docking sequence of the vessel of

Figure 1 with the structure,

Figures 5a to 5c are plan views of the vessel of Figure 1 in different orientations relative to the structure, whilst docked,

Figure 6 is a perspective view of the vessel of Figure 1 , docked to the structure, and

Figure 7 is a side elevation of the vessel of Figure 1 showing an access lift of the vessel being driven from a stowed condition to an operative condition.

Detailed Description

Reference is made initially to Figure 1 which shows a waterborne vessel 1 docked to a structure 30 in the form of a tower of a foundation of an offshore wind turbine. As will be described in more detail below, the vessel 1 comprises an access lift 2 which allows personnel and/or equipment to be transferred between the vessel 1 and an upper surface 32. The access lift 2 comprises a lift shaft assembly 3 and a lift platform 4, the lift platform 4 driveable along the lift shaft assembly by a suitable drive assembly (not illustrated). The lift shaft assembly 3 comprises an elongate framework arranged to receive the lift platform 4 therein. The access lift 2 further comprises a base 5, as shown in Figure 3, which supports the lift shaft assembly 3 (and the platform 4). The base 5 is essentially in the form of a gimballed assembly comprising a lower frame 5a and an upper sub-frame 5b, the sub- frames 5a and 5b connected by way of a pivot 6, and the sub-frame 5b fixedly attached to the foredeck 40. Two damper rams 7 (of which one is shown in Figure 3), provided at respective side regions of the base 5, connect the upper and lower frames 5a and 5b, and serve to damp motion of the frame 5b relative to the frame 5a about the axis of the pivot 6.

A further pivot 8 is provided which pivotably connects a lower end portion of the lift shaft assembly 3 to the upper sub-frame 5b. Two driveable rams 9, located at opposite sides of the lift shaft assembly 3, the rams connecting the lift shaft assembly 3 to the upper sib-frame 5a. When activated, the rams 9 serve to pivot the lift shaft assembly 3 about the axis of the pivot 8. It is to be noted that the respective axes of the pivots 6 and 8 are substantially orthogonal to one another.

Underlying the base 5, there is provided a damped roller assembly 10 located at the bow of the vessel, as best seen in Figure 6. The damped roller assembly comprises two spaced-apart rollers 1 1 and a further roller 12 associated with each of the rollers 1 1. Each of the rollers is of substantially diabolo shape. Each of the rollers 1 1 is connected to a damper (not shown) comprising a continuous rotational damping (CRD) device, which comprises a continuous rotation hydraulic system in which as the roller is forced to rotate, fluid is forced through a valve or baffle, or similar fluid constriction, so as to act against and in proportion to the force urging the roller to rotate. It will be appreciated that other forms of damper are possible.

The damped roller assembly 10 further comprises a yoke beam 15, to which the rollers 1 1 are rotatable mounted. It will be appreciated that the yoke beam 15 is not fixedly attached to the lower sub-frame 5b and can move independently of 5b. (However, it will be appreciated that in some circumstances it may be appropriate to fix the sub-frame 5b to the yoke 15. The yoke beam 15 further supports an actuated arm 16 for each of rollers 12, the angular position of each arm (and therefore the roller 12) is determined by a respective ram 17, operative to drive the arm about a respective pivot 18. The yoke beam 15 is mounted on the foredeck 40 of the vessel for pivotable movement thereto. This is achieved by way of a pivot at 19, to pivotably mount the yoke beam 15 to the foredeck 40. The yoke beam 15 is further mounted to the foredeck 40 by way of fixtures 20, and damper rams 21 , the damper rams connecting the fixtures 20 to the yoke beam 15. The damper rams 21 are connected to fixtures 20 and the yoke beam 15 by way of pivots 22 and 23, and are operative to damp the yaw. The procedure of docking the vessel 1 to the structure 30 is now described. (In relation to Figures 4a to 4c and Figures 5a to 5c it is to be noted that for the purpos e of simplicity of explanation, the views shown omit the lift shaft structure and the upper and lower sub-frames.) In Figure 4a, the vessel 1 is shown nosing-up to the structure 30. In this condition, the arms 16 of the damped roller assembly are held generally away from the rollers 1 1. In Figure 4b one of the rollers 1 1 is brought into contact with a fender 31 of the structure 30. By further driving vessel 1 towards the structure 30, the other roller 1 1 also comes into contact with and bears against the other respective fender 31. Each of the arms 16 is then caused to be driven inwardly so as to cause the rollers 12 to contact the (rearward surface of the) the respective fender, as shown in Figure 5a. With the rollers in such an engaged condition each pair of rollers embraces/grips the respective fender 31 and thus the access lift is secured to the structure 30. As is illustrated in Figures 5b and 5c, the pivotable mounting between the damper roller assembly 10 and the vessel 1 , allows the vessel to yaw about the pivot 19. A sensor may be provided to monitor the movement of the yoke 15 or the dampers 21 , and a feedback signal output from the signal operative, via a control unit, to suitably operate side thrusters of the vessel and so compensate for yaw. With the vessel now docked to the structure 30, the rams 9 are activated to raise the lift shaft assembly 3 from a stowed, substantially horizontal position, as shown in broken line in Figure 7, towards an upright position. With the lift shaft assembly in an upright position a roller assembly 25, attached to the lift shaft assembly 3, bears against the fenders 31. Specifically, the roller assembly 25 comprises two pairs of rollers, one pair for each fender.

The access lift is now ready for use to transfer personnel and/or equipment to and from the vessel 1 and the structure 30. The lift shaft assembly 3 is of extendable/retractable length by virtue of an inner portion 3a of the assembly. The inner portion 3a is translatable within the outer portion 3b, in telescopic fashion. With the lift shaft assembly in the upright position, the inner portion 3a is driven upwardly of the outer portion 3b so as to extend uppermost of the outer portion 3b, as shown in Figures 1 and 2. At a lowermost end of the lift shaft assembly there is provided an entrance 50, reached by steps 51. When the platform 4 is situated at the base of the lift shaft assembly personnel and/or equipment can be loaded onto the platform 4. The platform 4 is then driven upwardly towards the height of the upper surface 32, and simultaneously the inner portion 3a is extended upwards. On reaching the height of the upper surface 32 the personnel and/or equipment can transfer from the access lift to the structure 30 across a gangway 53. With the platform 4 in this structure access position in the lift shaft, its position can advantageously be maintained by virtue of using a signal output from a proximity sensor between the platform and the structure to monitor the distance between the same. In response to such a signal a control unit (preferably comprising a suitably configured data processor) could be arranged to drive the platform up or down, depending on the signals received from the roller sensors to ensure that the platform 4 remains at substantially the same height as the upper surface 32 of the structure 30.

Advantageously, the effect of any rolling (ie tilting side-to-side) motion of the vessel 1 is compensated for by virtue of the pivot 6 between the upper and lower sub-frames 5a and 5b, and damped by the rams 7. According the effect of any such roll motion on the lift shaft assembly 3 is inhibited, so reducing any corresponding relative movement between the lift shaft assembly and the structure 30. Further advantageously, any pitching motion (ie tilting forward and backward) of the vessel is compensated for by virtue of the pivot 8 between the lift shaft assembly and the upper sub-frame 5a. To further enhance compensation for any pitching motion, a sensor (not illustrated) could be provided to sense the spacing between the lift shaft assembly and the structure 30, and feedback signals output from the sensor could used to control the rams 9 to adjust the angle of inclination of the lift shaft assembly relative to the vessel, whilst aiming to hold the sensed distance constant. The sensor may comprise an accelerometer. It will be appreciated, however, that the motion compensation achieved by the illustrated embodiment benefits from not including an accelerometer, since this can involved complex signal processing.

The access lift described above advantageously allows personal and equipment to be safely transferred from and to a vessel, with any motion of the access lift relative to the structure being reduced, and preferably there being substantially no such relative motion. Although particular mention has been made to accessing a wind turbine structure, it will be appreciated that the access lift could also enable, or could be adapted to enable, access to other offshore structures, or to enable access from one vessel to another.