This invention relates to a platform for a watercraft. In particular, but not exclusively, this invention relates to a platform suitable for transferring crew from a watercraft to an offshore wind turbine.

In recent years, there has been increasing demand for renewable energy, such as that derived from the wind. Power generation from the wind utilizes a wind turbine, commonly part of a larger wind farm, which is a large and unsightly structure. As communities do not want their landscape encroached upon with unsightly wind farms, they are commonly located at sea. Such wind farms are known as offshore wind farms.

The wind turbines in offshore wind farms require maintenance; therefore a crew has to travel to the offshore wind farms, via watercraft, to carry out the maintenance work. Upon arrival at the wind turbine, the crew must be transferred from the watercraft to the wind turbine.

An offshore wind turbine comprises, in a simple form, a mast and a blade. For maintenance, the wind turbine also includes a ladder extending up the mast for a maintenance worker to ascend. A cross sectional view of a wind turbine 100 is shown in the illustration of the prior art in Figures 1 to 4, showing the mast 101 .

The watercraft 1 , 10 for transferring crew to the wind turbine 100 must not crash into the wind turbine 100 during the transfer, as this would cause damage to the wind turbine 100 and/or watercraft 1 , 10. Therefore, there is provided a transfer station 102 including two inner poles 103a, 103b and two outer poles 105a, 105b adjacent to the ladder 107 of the wind turbine 100.

There are two types of conventional watercraft used for transferring crew to a wind turbine: a watercraft 1 with a pointed bow/stern, and a catamaran 10.

The watercraft 1 with a pointed bow 2 docks with the transfer station 102, as shown in Figure 1 . Due to the shape of the pointed bow, the periphery of the pointed bow of the watercraft 1 abuts the ladder 107. Therefore, a crewmember can move from the watercraft 1 to the ladder 107. However, if the crewmember falls from the ladder 107, he/she will fall back onto the watercraft 1 , causing injury. Furthermore, if the watercraft 1 rises due to the motion of the water, the watercraft 1 will collide with a crewmember as the crewmember ascends the ladder 107. Still furthermore, if the watercraft 1 moves away from the ladder 107, and the crewmember descends to the level of the pointed bow 2, the crewmember may be crushed should the watercraft 1 subsequently move towards the ladder 107.

The catamaran 10 transfers the crew at the bow 12 of the catamaran 10. Figure 2 illustrates the catamaran 10 docking with the transfer station 102 at the bow 12, showing the substantially rectangular shape of the platform 13. The catamaran 10 is also not well suited for docking alongside the outer poles 105a, 105b as it leaves a large gap between the catamaran 10 and the ladder 107 due to the substantially rectangular shape of the platform 13. Furthermore, there is poor visibility of the transfer station 102 from a wheelhouse of the catamaran 10, as the wheelhouse of the catamaran 10 is commonly located at the bow 12. This makes it difficult for the helmsman to safely manage the crew transfer.

Furthermore, both conventional watercraft 1 , 10 are vulnerable to the motion of the water around the wind turbine 100. When the conventional watercraft 1 , 10 are docked with the transfer station 102, the watercraft 1 , 10 are susceptible to yaw. This can cause the watercraft 1 , 10 to rotate about the transfer station 102, which varies the distance from the conventional watercraft 1 , 10 to the ladder 107. This is dangerous when transferring crew to the ladder 107. This effect is illustrated in Figures 3 and 4, showing the watercraft 1 and the catamaran 10 rotating about the transfer station 102.

Furthermore, the watercraft 1 , 10 are susceptible to motion of the water causing the watercraft 1 , 10 to move in a direction parallel to the X axis. This can either extend the distance between the watercraft 1 , 10 and the ladder 107, or can cause the watercraft 1 , 10 to collide with the outer poles 105a, 105b. Both situations can be dangerous when transferring crew to the ladder 107.

It is therefore desirable to have a more stable and safer platform for the transfer of crew from a watercraft to a wind turbine.

According to a first aspect of the present invention, there is provided a platform, for use on a watercraft for abutting two poles, comprising a convex curved part, shaped to protrude between the two poles when in abutment with the two poles, a platform section, a watercraft section, wherein the platform section and the watercraft section are relatively moveable, and biasing means, arranged to resist relative motion of the platform section and the watercraft section.

The convex curved part is preferably shaped such that, when the watercraft abuts two poles, e.g. two outer poles of a transfer station of a water turbine, the convex curved part protrudes between the two poles.

The transfer station of the water turbine preferably includes a ladder positioned a distance behind the outer poles. The distance which the convex curved part protrudes between the two poles is preferably such that if a crewmember falls off the ladder of the transfer station, he/she will fall between the ladder and the convex curved part and not collide with the watercraft.

When the watercraft rotates in a yawing motion about the two poles, the convex curved part is preferably shaped such that the distance which the convex curved part protrudes between the two poles is substantially constant.

The skilled reader will understand that the calculation of the radius of curvature of the convex curved part is dependent on the arrangement of the outer poles, inner poles and ladder at the transfer station.

Therefore, when the watercraft docks with the transfer station, there is a gap between the platform and the ladder. Therefore, if a crewmember falls off the platform or the ladder, there is a clear gap between the platform and the ladder for the crewmember to fall through, such that the crewmember will not collide with the watercraft. Furthermore, if the crewmember descends to the level of the platform, there is no risk of being crushed should the watercraft move towards the ladder.

Furthermore, if the watercraft is subject to movement in a direction perpendicular to the bow- stern direction of the watercraft, causing the watercraft to rotate about the transfer station, the convex curved part is such that the distance between the the platform and the ladder does not vary. This makes the crew transfer safer as the crewmember can judge more accurately the distance he/she needs to move from the periphery of the platform to the ladder.

To achieve this rotation, the radius of curvature of the convex curved part is such that the origin of the circular arc is situated near the bow of the watercraft. Therefore, if the watercraft rotates about the transfer station, the watercraft should rotate in such a manner that the convex curved part remains in contact with both of the outer poles of the transfer station. Furthermore, the curve is such that the periphery of the convex curved part substantially remains a constant distance from the ladder.

When the watercraft docks with the transfer station, or there is forward movement of the watercraft due to the motion of the water, the biasing means reduces the impulse of the collision with the transfer station, which reduces the risk of damage to the watercraft and the outer poles of the transfer station.

This also decreases the rate of change of distance between the part of the platform and the ladder, which decreases the likelihood of a crewmember falling off the watercraft whilst moving from the platform to the ladder. The biasing means is preferably further arranged to bias the watercraft section and the platform section away from each other. Optionally, the shape of the convex curved part is arcuate.

The radius of the convex curved part is preferably selected to accommodate the configuration of the transfer station with which it will be used. Typically it will have a radius of curvature between 1 m and 3m. Preferably, the radius of curvature is 1 .8m.

The platform section may have one or more engagement portions for engaging complimentary portions on the watercraft section to allow relative movement.

Preferably, the one or more engagement portions and complimentary portions include any combination of one or more protrusions and complimentary channels to allow slidable engagement.

The convex curved part may substantially form a semicircle. Preferably, the watercraft section and the platform section include a layer of PTFE. This is preferably provided on the respective contacting surfaces. This reduces the friction between the two sections. The biasing means may be a spring. This may be formed from a polymer material, such as rubber. The biasing means may include a pneumatic or hydraulic ram, a gas strut, or an airbag. Preferably, the platform further comprises at least one fender extending substantially about the periphery of the convex curved part.

Therefore, the fender will further cushion any collision between the watercraft and the outer poles of the transfer station. The fender will also frictionally engage the watercraft with the outer poles of the transfer station, which increases stability.

The platform may further comprise a plurality of vertical fenders situated about the periphery of the convex curved part. Therefore, the surface area of fender in contact with the outer poles of the transfer station is increased compared to a single fender. This increases the magnitude of the frictional engagement between the fender and the outer poles of the transfer station, which will further increase stability. The platform may be embodied on a watercraft, such that the watercraft section could be an integral part of the watercraft. Alternatively, the platform further includes attachment means to attach the platform to the watercraft.

Preferably, the platform is situated or attachable to a bow or stern of the watercraft. Optionally, the watercraft further comprises a bow thruster or stern thruster.

Advantageously, the bow thruster is used to counteract yaw of the watercraft when the watercraft is docking with the transfer platform. Furthermore, when there is a movement in the water causing the watercraft to rotate about the transfer platform, the watercraft can counteract this movement by using a bow and/or stern thruster. This increases the stability of the platform during crew transfer, as it reduces the rate of change of the yaw of the watercraft. Preferably, the watercraft further comprises a controller.

Preferably, the watercraft further comprises a damping sensor for sensing relative motion of the platform section and the watercraft section, wherein the controller controls the thrust of the watercraft as a function of the detected damping of the buffer.

Advantageously, the controller can automatically control the thrust of the watercraft to ensure the part of the platform stays in position at the transfer station. For example, if the detected damping decreases, the watercraft would move away from the transfer station, therefore the controller would increase the thrust of the watercraft.

Preferably, the watercraft further comprises a rotation sensor, wherein the controller controls the thrust of the bow thruster or stern thruster as a function of the detected rotation of the watercraft. Advantageously, if there is detected rotation of the watercraft, such that the watercraft is rotating about the transfer station, the controller will automatically adjust the alignment of the watercraft with the transfer station by using the bow/stern thrusters. Optionally, the watercraft further comprises a wheelhouse, wherein the wheelhouse is situated vertically higher than the platform.

This is advantageous as the helmsman will have a clear view of the transfer station, and can therefore adjust the thrust and/or bearing of the watercraft accordingly to maximise the stability of the platform during transfer of crew to the wind turbine.

Preferably, the watercraft is a monohull watercraft for transferring crew to a wind turbine. Monohull watercrafts have less drag compared to multihull watercrafts, and therefore have reduced fuel efficiency when travelling to the wind turbine.

According to a second aspect of the present invention, there is provided a method for transferring crew from a watercraft to another structure, the watercraft including a platform, the platform including biasing means to resist relative movement of the watercraft and the platform and to bias the watercraft and platform away from each other, the another structure including two poles, the method comprising bringing the platform into abutment with the two poles, and forcing the watercraft towards the poles against the force of the biasing means such that the platform is moved towards the watercraft. Therefore, the watercraft can force the watercraft into the two poles of the another structure, which maintains the abutment of the watercraft and the two poles, but the force of the watercraft against the two poles is reduced due to the biasing means. An embodiment of the present invention will now be described, by way of example, and with reference to the drawings in which:

Figure 1 illustrates a top view of a watercraft in accordance with the prior art;

Figure 2 illustrates a top view of a catamaran in accordance with the prior art;

Figure 3 illustrates a top view of watercraft in accordance with the prior art, docking with a transfer station at a first angle;

Figure 4 illustrates a top view of catamaran in accordance with the prior art, docking with a transfer station at a first angle;

Figure 5 illustrates a top view of a watercraft in accordance with the present invention;

Figure 6 illustrates a side view of the watercraft of Figure 5;

Figure 7 illustrates a front view of the watercraft of Figure 5;

Figure 8 illustrates a top view of a front of the watercraft of Figure 5, docking with a transfer station;

Figure 9 illustrates a top view of the front of the watercraft of Figure 5, docking with a transfer station at a first angle;

Figure 10 illustrates a top view of the front of the watercraft of Figure 5, docking with a transfer station at a second angle;

Figure 1 1 illustrates a top view of the front of the watercraft of Figure 5, docking with a transfer station, showing a buffer at a width di ; Figure 12 illustrates a top view of the front of the watercraft of Figure 5, docking with a transfer station, showing a buffer at a width d ₂ ;

Figure 13 illustrates a top view of a buffer in accordance with the present invention;

Figure 14 illustrates a cross sectional view of the buffer of Figure 13; and

Figure 15 illustrates a top view of the buffer of Figure 13, the buffer being forced in a negative x direction;

A first embodiment of the present invention will now be described with reference to Figures 5 to 10. A watercraft 200 is provided comprising a platform 202. The platform 202 includes a forward portion 204.

The forward portion 204 includes part of a circular arc, such that it forms a semicircle.

The platform 202 extends from the periphery of the bow of the watercraft 200, away from the watercraft 200, forming a substantially horizontal surface.

Figures 5 and 6 show the platform 202 at the bow of the watercraft 200. The platform 202 also includes a buffer 206. Figure 8 shows the watercraft 200 docking with a transfer station 102. The transfer station comprises two inner poles 103a, 103b, a ladder 107, and two outer poles 105a, 105b. In Figure 8 the watercraft 200 is perpendicular to the ladder 107.

The curve of the front portion 204 is such that when it engages the outer poles 105a, 105b there is a distance between the periphery of the front portion 204 and the ladder 107 to provide a safety space for a crewmember to fall through should he/she fall off the ladder 107.

Figure 9 illustrates the watercraft 200 at an angle to a first axis X. The curve of front portion 204 is such that the distance from the part of the platform 204 to the ladder 107 is substantially constant when the angle of the watercraft 200 varies with respect to the first axis X. This effect is also illustrated in Figure 10, when the watercraft 200 has an opposing rotation. To counteract the rotation of the watercraft 200, the watercraft 200 includes a bow thruster and a stern thruster (not shown). The watercraft 200 can therefore exert a rotational force to counteract the rotation of the watercraft 200 about the transfer station 102, and assist in realigning the watercraft 200 with the first axis X. The watercraft 200 also includes a fender 208 at the periphery of the front portion 204. The fender 208 is made of a material that will frictionally engage with the outer poles 105a, 105b of the transfer station 102, preferably rubber.

The fender 208 takes the form of individual vertical strips of fender 208a, 208b...208N at the periphery of the front portion 204. This increases the surface area of fender engaging with the outer poles 105a, 105b. The fender is illustrated in Figure 7.

The watercraft 200 also includes a wheelhouse 210. The wheelhouse 210 is situated at such a height that the helmsman has a clear line of sight from the helm to the platform 202 and the curved part of the platform 204. Figures 1 1 -15 illustrate the buffer 206 of the watercraft 200.

In Figure 1 1 , the buffer 206 has a width of distance d _{1 ;} when the watercraft 200 is not exerting any force on the outer poles 105a, 105b of the transfer station 102.

Figure 12 illustrates the watercraft 200 when exerting a force on the outer poles 105a, 105b of the transfer station 102, such as when the thrust of the watercraft 200 drives the watercraft 200 towards the outer poles 105a, 105b, or when the motion of the water forces the watercraft 200 towards the outer poles 105a, 105b.

As illustrated, the buffer 206 reduces its width from di to d ₂ during the impact, maintaining the periphery of the front portion 204 in contact with the poles 105a, 105b. The buffer 206 also absorbs the energy of the impact. This reduces the impulse of the collision, which increases the stability of the watercraft 200, and therefore the likelihood of a safe transfer of the crewmember from the front portion 204 to the ladder 107. Furthermore, the risk of damage to the watercraft 200 and the outer poles 105a, 105b is reduced..

The buffer 206 will now be described in more detail, with reference to Figures 13 to 15. The buffer 206 comprises two sections, a platform section 206a and a watercraft section 206b.

The platform section 206a includes a protrusion 216, which extends along each side of the platform 202. The watercraft section 206b is formed on the watercraft 200. The watercraft section 206b includes opposing channels 217 extending along the inner surfaces of the watercraft section 206b. The channels 217 are complimentary to the protrusions 216 such that the protrusions 216 can slide within the channels 217. The protrusions 216 and channels 217 are constructed out of PTFE. This allows the platform 202 to slide in and out along the longitudinal axis of the watercraft 200.

As shown in Figures 13 to 15, the platform section 206a is situated within the watercraft section 206b, and is therefore able to slide within the watercraft section 206b.

The buffer 206 also includes a biasing means 206c, such as a spring, connected at a first end to the watercraft 200, and a second end to the platform 202. As shown in Figures 13 to 15, the biasing means 206c is connected to the platform section 206a. The biasing means 206c is biased to force the platform 202 away from the watercraft 200, that is, in the positive X direction. Therefore, when the platform 202 is not subject to an external force, the biasing means 206c forces the platform 202 away from the watercraft 200. The buffer 206 also includes a stop (not shown) such that the platform 202 is forced up to a maximum distance away from the watercraft 200. During a collision between the watercraft 200 and a foreign object, such as an outer pole 105a, 105b, the platform is subject to an external force in the negative X direction. If this external force is greater in magnitude than the hydraulic ram's 206c force in the positive X direction, then the platform section 206a will slide towards the watercraft 200. As the biasing means 206c is compressed, the magnitude of the force it produces on the platform 202 increases. Therefore, during the collision, the magnitude of the force of the hydraulic ram 206c in the positive X direction will exceed the magnitude of the force of the collision in the positive X direction, and the platform 202 will be forced to slide in the positive X direction.

The platform 202 will therefore return to the maximum distance away from the watercraft 200, and the impulse of the collision is reduced. In a further embodiment, the watercraft 200 also includes a controller, a damping sensor, and a rotation sensor (not shown). Therefore, the controller can control the thrust of the watercraft 200 in response to a detected damping, such as detected compression of the biasing means 206c or detected relative movement of the platform section 206a and the watercraft section 206b, or control the bow and/or stern thrusters in response to a detected rotation.

For example, if the controller's damping sensor detects a damping of the platform 202, the controller decreases the thrust of the watercraft 200. If the controller's rotation sensor detects a rotation of the watercraft 200 about the transfer station 102, then the controller uses the bow and stern thrusters to oppose the rotation of the watercraft 200 and align the watercraft 200 with the first axis X.

In the embodiment described above and illustrated in the figures, the platforms 202 extend from the periphery of the watercraft 200 away from the watercraft 200 at the level of a deck of the watercraft 200. The skilled reader will understand that the platform 202 could be at any level, for example, above or below the level of the deck of the watercraft 200. Furthermore, the platform 200 could be the deck of the watercraft 200, such that the periphery of the deck follows a curve and includes a buffer. The skilled reader will also understand that the forward portion 204 ideally only needs to be a convex curve, suitable for protruding between the two outer poles 105a, 105b of the transfer station 102.

In the embodiment described above, the watercraft buffer section 206b is formed on the watercraft 200, as a channel extending along an inner side of the watercraft 200. The skilled reader will understand that the watercraft buffer section 206b could be a separate part, further including attachment means to attach the watercraft buffer section 206b to an existing watercraft. The watercraft buffer section 206b would therefore include a channel extending along its inner side. Therefore, the watercraft buffer sections 206b can be retrofitted to a bow/stern of an existing watercraft. With the watercraft buffer section 206b attached, the platform buffer section 206a of the platform 202 can be inserted into the watercraft buffer section 206b, and the platform 202 would be fully retrofitted to the existing watercraft.

The skilled reader will understand that any combination of features is possible without departing from the scope of the invention, as claimed.