WO2020043255A1

WO2020043255A1 - A method of installing a crane on a portion of an offshore wind turbine generator and a vessel therefor

Info

Publication number: WO2020043255A1
Application number: PCT/DK2019/050251
Authority: WO
Inventors: Jens Andersen Gad; Allan Melgaard
Original assignee: Maersk Supply Service A/S
Priority date: 2018-08-31
Filing date: 2019-08-28
Publication date: 2020-03-05
Also published as: DK201800521A1

Abstract

A method of installing a crane (300) on a portion of an offshore wind turbine generator (308 ) from a vessel (100) having a crane support structure (332), the method comprises: elevating the crane (300) in the support structure (332) above the vessel (100); transferring the elevated crane (300) between the vessel and the portion of the offshore wind turbine (308); and suspending the crane (300) from a portion of the offshore wind turbine (308) with one or more cables (700, 702).

Description

A method of installing a crane on a portion of an offshore wind turbine

generator and a vessel therefor

The present invention relates to a method of installing a crane on a portion of an offshore wind turbine generator and a vessel therefor.

In order to reduce the dependence on limited fossil fuel resources around the world, there has been an increasing demand for renewable energy generation. One such source of renewable energy that has become increasingly reliable is wind energy generation.

Typically electricity is generated from the wind with wind turbine generators (WTG) installed in locations with a reliable prevailing wind. Some wind turbine generators have been installed on land in windy areas such as on hilltops. Wind turbine generators installed on land are also known as“onshore” wind turbine generators.

In recent times, the trend has been to install bigger and taller wind turbines. This increases the area that the blades of the wind turbine sweep through and increases the total potential energy production. In addition, by positioning the blades higher into the atmosphere, the wind blows more steadily, and the wind turbine blades are further from objects that may cause turbulent airflow.

The feasibility of the construction of onshore wind turbine generators can be affected by the local population objecting to the noise and other environmental impact. Accordingly, larger wind turbine generators can be installed in coastal waters. Wind turbine generators installed in coastal waters, the sea or deep ocean are also known as“offshore” wind turbine generators.

The complexity of installing offshore wind turbine generators is greatly increased with respect to installing onshore wind turbine generators. For example, the materials and structure of the offshore wind turbine generators must be transported to the installation site with a suitable vessel. Furthermore, the offshore wind turbine generator must be anchored securely in position. In this way, offshore wind turbine generator installation is typically carried out in separate stages. One current method of installation is to anchor a foundation to the seabed using a monopile foundation. This is a steel and / or concrete tube which is fixed to and protrudes from the seabed. A transition piece (TP) is fixed to the monopile foundation and the transition piece projects out of the water. The offshore wind turbine generator is then fixed to the transition piece.

WO2014/070024 discloses a method of installing an offshore wind turbine generator is using a jack-up vessel. The jack-up vessel comprises legs that extend down to and engage with the seabed. The jack-up vessel comprises a crane sufficiently tall to receive and install pre-assembled offshore wind turbine generators to the transition piece. A problem with a jack-up vessel is that not all types of seabed are suitable for receiving the extended legs which means this vessel cannot be operated in all coastal waters. Furthermore, the jack-up vessel is very sensitive to adverse weather which means operation of the jack- up vessel is restricted to calm weather windows.

W02007/091042 discloses an alternative method of installing an offshore wind turbine generator using a crane mounted on a vessel. In order to install the largest wind turbine generators, the crane must be suitably massive. Similar to a jack-up vessel, a crane mounted vessel is also sensitive to adverse weather conditions during operation. Another problem is that the vessel must not collide with the foundation or transition piece and this means that the vessel must operate at a safe distance. This means the height of the crane is increased even further so that the crane has sufficient outreach whilst the vessel is positioned at a safe distance from the transition piece.

Another alternative method of offshore wind turbine generator installation is contemplated in WO2017/055598. This discloses installing separate parts of a wind turbine generator with a crane mounted to part of the tower. The crane is initially winched onto the tower from a barge. A problem with this arrangement is that the cable must be pre-attached to the tower in order for the crane to be winched onto the tower. This means that the vessel must be in close proximity to the foundation and transition piece because otherwise the crane will be immersed in water during the winching operation.

It is undesirable for the vessel to be in immediate proximity of the foundation piece for a protracted period of time because this increases the risk of collision of the vessel with the foundation and transition piece. Furthermore, during the final stage of the winching, swing against the foundation piece. The foundation can become damaged when the crane hits the tower. Alternatively, the impact can damage the eyes or the climbing mechanism which would render the crane inoperable.

Embodiments of the present invention aim to address the aforementioned problems.

According to an aspect of the present invention, there is a method of installing a crane on a portion of an offshore wind turbine generator from a vessel having a crane support structure, the method comprising: elevating the crane in the support structure above the vessel; transferring the elevated crane between the vessel and the portion of the offshore wind turbine; and suspending the crane from a portion of the offshore wind turbine with one or more cables.

Optionally, the suspending comprises suspending the crane from a coupler removeably mounted to a portion of the offshore wind turbine generator.

Optionally, the coupler is a yoke arranged to engage the top of a tower portion of the offshore wind turbine generator.

Optionally, the coupler is a hook coupled to an open top of a tower portion of the offshore wind turbine generator.

Optionally, the coupler is configured to engage with a protrusion, bracket, eye, lip, flange, loop of the offshore wind turbine generator. Optionally, the coupler is configured to engage with at least one hole in the offshore wind turbine generator.

Optionally, the method comprises hoisting the suspended crane up the offshore wind turbine generator with the one or more cables.

Optionally, the hoisting is carried out with a winch mounted in the crane.

Optionally, the crane comprises a first winch to hoist the crane and a second winch to hoist loads.

Optionally, the winch is configured to operate in a first mode for hoisting the crane and a second mode for hoisting loads.

Optionally, the method comprises closing one or more moveable doors hinged on a body of the crane around the portion of the offshore wind turbine generator.

Optionally, the method comprises engaging at least one gripping arm mounted on the crane with a portion of the offshore wind turbine generator.

Optionally, at least one gripping arm is engageable with a protrusion, bracket, eye, lip of flange of the offshore wind turbine generator.

Optionally, the at least one gripping arm is configured to move between a disengaged position and an engaged position.

Optionally, the hoisting comprises moving the crane to a position on the offshore wind turbine generator such that the at least one gripping arm is engageable with the portion of the offshore wind turbine generator.

Optionally, the step of elevating the crane above the vessel comprises elevating the crane from a first position where the crane is adjacent to a deck of the vessel and to a second position wherein the crane is suspended above the deck of the vessel. Optionally, the step of elevating comprises elevating at least a portion of the crane above the portion of the offshore wind turbine generator.

Optionally, the step of suspending the crane on the portion of the offshore wind turbine generator comprises lowering the crane with respect to the potion of the offshore wind turbine generator until the cables are under tension.

Optionally, the step of suspending the crane on the portion of the offshore wind turbine generator comprises attaching the cables to the offshore wind turbine generator.

Optionally, the suspending the crane comprises suspending the crane with two cables on at different positions on the offshore wind turbine generator.

Optionally, the suspending the crane comprises suspending the crane with two cables on different sides of the crane.

Optionally, the method comprises attaching the one or more cables between the offshore wind turbine generator and the crane when the crane is positioned on the vessel.

Optionally, the method comprises operating the crane when crane is suspended from the portion of the offshore wind turbine with one or more cables.

In another aspect of the invention there is a crane mountable on a portion of an offshore wind turbine generator comprising: a crane body; a first coupling mounted on the crane body attaching a first cable on a first side of the crane and a portion of the offshore wind turbine generator; and a second coupling mounted on the crane body for attaching a second cable on a second side of the crane and a portion of the offshore wind turbine generator; such that the crane arranged to be suspended from the offshore wind turbine with the portion of the offshore wind turbine generator between the first and second cables. Optionally, at least a portion of the crane body surrounds the portion of the offshore wind turbine generator when suspended from the offshore wind turbine generator.

Optionally, the portion of the crane circumferentially is arranged to surround the offshore wind turbine generator.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims with reference to the accompanying drawings, in which:

Figure 1 shows a side view of a vessel in the proximity of a wind turbine generator;

Figure 2 shows a schematic perspective view of a vessel;

Figure 3 shows a side view of a vessel with a crane in a first position according to an embodiment;

Figure 4 shows a side view of a vessel with a crane in a second position according to an embodiment;

Figure 5 shows a close up perspective view of the crane in a first position according to an embodiment;

Figure 6 shows a schematic plan view a vessel with a crane according to an embodiment;

Figures 7a, 7b, 8a, 8b and 9 show a schematic cross section of the crane mounted on the offshore wind turbine generator;

Figure 10 shows a schematic view of a vessel; and

Figure 1 1 shows a flow diagram of a method of installing a crane on a portion of an offshore wind turbine generator.

Figure 1 shows a side view of a vessel 100 in the proximity of a wind turbine generator (WTG) 102. For the purposes of clarity, the WTG 102 is not drawn to scale and the broken portions of the WTG 102 represent missing portions of the WTG 102. The WTG 102 comprises a foundation 104 anchored to the seabed 106. The foundation 104 is a steel and / or concrete tube which is fixed to and protrudes from the seabed 106. Typically the foundation 104 engages with the seabed 106, but in some embodiments the foundation can be floating where the ocean is particularly deep. In other embodiments, other types of foundation 104 can be used including, but not limited to: monopile foundations, tripod foundations, jacket foundations, space-type foundations, floating foundations and / or gravity-based structure foundations.

A transition piece (TP) 108 is fixed to the monopile foundation 104 and the transition piece 108 projects out from the surface of the water 1 10. The transition piece 108 comprises access ladders (not shown) for access to the WTG 102 from a boat. The transition piece 108 further comprises a platform 1 12 and a door 1 14 for internal access to the WTG 102.

The WTG 102 comprises a tower 1 16 which is fixed to the transition piece 108. The tower 1 16 can be a unitary element or can be constructed from a plurality of tower segments. A nacelle 1 18 is rotatably mounted on the top of the tower 1 16. The nacelle 1 18 can rotate about the vertical axis A-A of the tower 1 16. The nacelle 118 houses a generator (not shown) for converting the rotation of a hub 120 and blades 122 into electrical energy. There may a plurality of blades 122 connected to the hub. The generator is connected to an electrical substation via one or more cables (not shown). Access to the nacelle 1 18 can be achieved via an internal set of stairs (not shown).

Each of the elements of the WTG 102 is installed with the vessel 100, which will be described in further detail below.

The vessel 100 as shown in Figure 1 is a subsea supply vessel. In other embodiments the vessel is another type of vessel including but not limited to an anchor handling tug supply (AHTS) vessel, a platform supply vessel (PSV), multipurpose support vessel (MSV), a tug boat, a barge or any other suitable vessel for installing WTGs 102. The vessel 100 can be used for various marine operations such as anchor handling, towing, supply of offshore installations, and fire-fighting. The vessel 100 comprises one or more winches (not shown) for handling towlines and anchors of offshore installations such as oil rigs. The vessel 100 comprises an open aft portion 124 for storing and managing anchors.

In some embodiments, the aft portion 124 is used for stowing one or more parts of the WTG 102. In some embodiments, the aft portion 124 can be used to store disassembled parts 302, 304, 306 of the tower 1 16 (as shown in Figure 3), the nacelle 1 18, the hub 120 and / or the blades 122. In other embodiments, disassembled parts of the WTG 102 can be stowed on a separate vessel (not shown) such as a barge which is positioned close to the vessel 100 when the WTG 102 is being installed.

Figure 1 shows that the open aft portion 124 is clear from anchors and towlines for the purposes of clarity. The open aft portion 124 may comprise one or more cranes (not shown) fixed to the structure of the vessel 100 for lifting and moving objects. The vessel 100 can use the winch together with a towline for towing the barge or other floating structures, if required. Alternatively, the towline can be attached to a capstan or bollard secured to the deck 334 of the vessel 100 when towing the barge. The method of towing barges with a towline and vessel is known and will not be discussed in any further detail.

The vessel 100 comprises a plurality of propulsors for moving the vessel through the water. In some embodiments, the propulsors are one or more of the following: a propeller, a thruster, or an azimuth thruster. The vessel 100 can have any number or configuration of propulsors. The vessel 100 as shown in Figure 1 comprises two propellers 1002 (schematically represented in Figure 10). The propellers 1002 are both coupled to a diesel two stoke engine 1000 (schematically shown in Figure 10) or each propeller 1002 is coupled to a separate diesel two stroke engine 1000. Alternatively, the two propellers 1002 can be driven by one or more diesel four stroke engines 1000. In other embodiments, the propulsors can be powered with a diesel electric engine with or without a direct coupling. Under normal sailing, the propellers 1002 are principally used for moving the vessel 100 in a direction towards the bow 126 of the vessel 100. When the propellers 1002 are reversed, the vessel 100 will move in a direction towards the stern 128. In some embodiments, the vessel 100 only has one propeller mounted along the centreline X-X (as shown in Figure 2) of the vessel 100.

A rudder 130 is positioned aftwards of each propeller 1002 for steering the vessel 100. The rudder 130 is used for directing a wash which is a mass of water moved by the propellers 1002. Each propeller 1002 can have a nozzle which is a hollow tube that surrounds each propeller 1002 for increasing the propulsive force of the respective propellers 1002.

The vessel 100 comprises plurality of bow thrusters 132, 134, 136 and a plurality of stern thrusters 138, 140, 142. Each of the bow thrusters 132, 134, 136 and the stern thrusters 138, 140, 142 are mounted in a tunnel 144. For the purposes of clarity, only one tunnel 144 has been labelled. The tunnel 144 is a hollow tube integral with the hull 146 of the vessel 100 and is open at both sides, e.g. port side and starboard side of the hull 146. This means a thrust force can be imparted at either side of the vessel 100. The tunnel 146 which is integral with the hull 146 of the vessel 100 maintains a compact form and reduces drag on the thrusters 132, 134, 136, 138, 140, 142 when the vessel 100 is moving forwards.

The bow thrusters 132, 134, 136 and the stern thrusters 138, 140, 142 provide a side force with respect to the vessel 100. In this way, the thrusters 132, 134, 136, 138, 140, 142 increase the manoeuvrability of the vessel 100. In some embodiments, the thrusters 132, 134, 136, 138, 140, 142 are driven by an electric motor 1004 (schematically shown in Figure 10). The electric motor 1004 is powered by a diesel engine which may be an auxiliary engine (not shown) in addition to the diesel engines 1000 driving the propellers 1002. Optionally, the electric motor 1004 can also drive the propellers 1002. Alternatively, the electric motors 1004 can be powered from the same engine 1000 which drives the propellers 1002. Additionally or alternatively, the electric motors 1004 of the thrusters 132, 134, 136, 138, 140, 142 are powered by a battery (not shown). In other embodiments, the thrusters 132, 134, 136, 138, 140, 142 are driven by a diesel engine 1000 and gearing and linkages (both not shown) couple the engine 1000 to the thrusters 132, 134, 136, 138, 140, 142. In operation, one or more thrusters 132, 134, 136, 138, 140, 142 can generate a thrust on a side of the vessel 100. All the thrusters 132, 134, 136, 138, 140, 142 can generate a thrust on the same side of the vessel 100 or on different sides of the vessel 100.

In other embodiments, one or more of the propellers 1002 or the thrusters 132, 134, 136, 138, 140, 142 are replaced with azimuth thrusters 1006 (as shown in Figure 10). The azimuth thruster 1006 is housed in a pod and is also known as an“azipod”. The azipod 1006 is rotatable by an angle (azimuth) around a horizontal plane parallel with a main horizontal plane of the vessel 100. In this way, the azipod 1006 can direct thrust in any direction. Similar to the thrusters 132, 134, 136, 138, 140, 142, the azipods 1006 can be driven by an engine 1000 or an electric motor 1004.

Turning back to Figure 1 , control of the vessel 100 is achieved by manual controls 1008 such as joysticks, helm, wheel etc. (shown schematically in Figure 10) located in the bridge 148. The bridge 148 is usually located in position such that the crew members have good visibility of the vessel 100 and the surrounding sea. The bridge 148 as shown in Figure 1 has 360 degree visibility of the sea surrounding the vessel 100. This means that crew members operating the vessel 100 can safely and easily control the vessel 100 irrespective of whether the vessel 100 is moving forwards, backwards or side to side. In other embodiments, the vessel can be autonomously controlled with a dynamic positioning module 1010 and a vessel control module 1012 (as shown in Figure 10). Use of the dynamic positioning module 1010 will be discussed in further detail together with Figure 10 below.

Motion of the vessel 100 during operation will now be discussed in reference to Figure 2. Figure 2 shows a perspective schematic view of the vessel 100. The vessel 100 has three principle axis about which it can rotate, a longitudinal axis X-X, a transverse axis Y-Y, and a vertical axis Z-Z. Rotation about the longitudinal axis or centreline X-X of the vessel 100 is called roll. Rotation about the transverse axis Y-Y which is the perpendicular to the longitudinal axis X-X, is called pitch. Rotation about the vertical axis Z-Z is called yaw. In addition to rotational motion about the axes X-X, Y-Y and Z-Z, the vessel 100 can also experience translational motion along each of the axes. Translational motion about the longitudinal axis X-X, the transverse axis Y-Y and the vertical axis Z- Z is respectively known as surge, sway and heave.

During operation of the vessel 100, motion compensation of the vessel 100 is carried out to compensate for one or more of roll, pitch, yaw, sway, surge, and heave. In order to compensate for the motion of the vessel 100, measurement of the motion of the vessel 100 is carried out by one or more sensors. Figure 2 schematically represents a pitch motion sensor, 200, a roll sensor 202, a yaw sensor 204, a surge sensor 206, a sway sensor 208 and a heave sensor 210.

In some embodiments, the sensors for detecting the motion of the vessel 100 can be accelerometers, gyroscopes, cameras, or any other suitable sensor for detecting motion of the vessel 100. In some embodiments, alternatively, or additionally the translation movement of the vessel 100 in a plane substantially parallel to the surface of the water is detected with a global positioning system (GPS) 1016 of the vessel 100. This means that the sway sensor 208 and the surge sensor 206 can optionally be omitted. The one or more sensors 200, 202, 204, 206, 208, 210 in some embodiments, can be one or more accelerometers for detecting motion in three perpendicular axes. In some embodiments, one or more sensors (not shown) can detect motion of the vessel 100 in all six degrees of freedom (roll, pitch, yaw, surge, sway, heave). The sensors 200, 202, 204, 206, 208, 210 are connected to a motion compensation module 1014. The motion compensation module 1014 determines the motion of the vessel 100 due to the wind and the waves based on the received sensor information. The compensating for the motion of the vessel 100 will be described in further detail below.

Turning to Figure 3, installation of the WTG 102 will be described in further detail. Figure 3 shows a side view of a vessel 100 with a crane 300 in a first position according to an embodiment. In the first position, the crane 300 is positioned at the aftmost part of the vessel 100. In the first position, the crane 300 is mounted on the deck 334 or positioned on a platform 324 mounted on the deck 334.

The crane 300 is mountable on a portion 308 of the WTG 102. The portion 308 of the WTG 102 is a first section 308 of the tower 1 16. The first section 308 has been installed and fixed to the transition piece 108 before the crane 300 is mounted on the WTG 102. In other embodiments, the crane 300 is mountable on other parts of the WTG 102 such as the transition piece 108 or the foundation 104.

The crane 300 comprises a crane body 310 engageable with the tower 1 16. Briefly turning to Figure 6, the crane body 310 will be described in further detail. Figure 6 shows a plan view of the crane 300. As shown in Figure 6, in some embodiments the crane body 310 optionally comprises a first door 900, and a second door 902 pivotally hinged to the crane body 310. The first and second doors 900, 902 are arranged to move between a first position in which the doors 900, 902 in an open position and a second position in which the doors 900, 902 are in a closed position. In the open position, the crane body 310 can be positioned around the tower 1 16. In the closed position, the crane body 310 envelops the tower 116 and secures the crane body 310 to the tower 1 16. In some embodiments, as discussed below one or more other mechanisms for securing the crane body 310 to the tower 1 16 are additionally or alternatively used. In some other embodiments, the doors 900, 902 do not perform a securing function but instead when the doors 900, 902 are closed, the crane body 310 guides the vertical movement of the crane 300 on the WTG 102. The doors 900, 902 are actuated with hydraulic arms (not shown for clarity). The doors 900, 902 can be held together with a locking mechanism (not shown). The hydraulic arms can be connected to the vessel hydraulic system 1022.

In some other embodiments, the crane body 310 comprises a single pivotally hinged door (not shown). In other embodiments, the doors 900, 902 slide against the crane body. In yet other embodiments, the crane body 310 does not have doors. Optionally there is a strap or other securing mechanism which secures around the tower 1 16 when there are no doors.

Optionally, the crane body 310 comprises one or more shock absorbers 904 for engaging with an external surface 906 of the tower 1 16. The shock absorbers 904 can be sprung mounted to absorb the impact of the crane body 310 abutting against the tower 1 16. In some embodiments, the shock absorbers 904 are sprung mounted wheels. The wheels reduce the friction between the inside surface 908 of the crane body 310 and the external surface 906 of the tower 1 16. Additionally or alternatively, the shock absorbers are resiliently deformable pads made from rubber or a similar material. The one or more shock absorbers 904 guide the vertical movement of the crane 300 on the WTG 102 and protect both the WTG 102 and the crane 300 from damage.

In some embodiments, when the crane body 310 surrounds the tower 1 16, a plurality of shock absorbers 904 engage the tower 1 16. Figure 6 shows three shock absorbers 904 surrounding the tower 1 16, however there can be any number of shock absorbers positioned on the inside surface 908 of the crane body 310. The position and orientation of the plurality of shock absorbers 904 can be in any suitable arrangement. In some embodiments, the shock absorbers 904 are arranged in a plurality of circles and each circle of shock absorbers 904 is positioned at a different height on the crane body 310.

Turning back to Figure 3, the crane 300 will be described in further detail. The crane 300 comprises a boom 312 which is pivotally coupled to the crane body 310 at pivot 314. The crane 300 comprises one or more cables 316 which is coupled to a winch 318. The cable 316 is connected to yoke 320 for engaging with a load, such as a tower segment 302, 304, 306 to be lifted. The boom 312 projects laterally from the crane body 310 so that the load can be lifted clear from the crane body 310. In some embodiments, the boom 312 is optionally pivotally connected to an additional jib portion (not shown). The jib portion fixed to the boom 312 or is pivotally mounted to the boom 312 and increase the lateral reach of the crane 300. In some embodiments, the crane 300 comprises a counterweight 322 positioned on the opposite side of the crane body 310 to the boom 312. In some embodiments, the counterweight 322 is a water filled container suspended from the crane body 310. In this way, the counterweight 322 is emptied of water when the crane 300 is being transferred from the vessel 100 to the WTG 102. This reduces the weight of the crane 300 during the lift operation.

As mentioned previously, the crane 300 as shown in Figure 3 is mounted in a first position on the aftmost portion of the vessel 100. The crane 300 is removeably mounted on the stern 128 of the vessel 100. In some embodiments, the crane 300 is attached to the vessel 100 with quick release fixings. This means that the crane 300 can be fixed in place when the vessel 100 sails to the location of the WTG 102. Once the vessel 100 is in the proximity of the WTG 102, the crane 300 can be released from the vessel 100 and prepared for the transfer to the WTG 102. In some embodiments, the crane 300 is mounted on a moveable platform 324. The moveable platform 324 can be mounted on wheels or rails (not shown) on the deck 334 of the vessel 100. This means that the moveable platform 324 can undergo a translational movement on the deck 334 of the vessel 100. In this way, the crane 300 can be moved from a stowed position on the aft portion 124 of the vessel 100 to a transfer position at the aftmost part of the vessel 100 (as shown in Figure 3). The parts of the WTG 102 stowed on the vessel 100 can also be mounted on moveable platforms (not shown) to move them from a stowed position to a position ready for transfer.

The crane 300 is releasably coupled to a support structure 332 arranged to suspend the crane 300 above the deck 334 of the vessel 100 as shown in Figure 4. The support structure 332 comprises a first adjustable arm 326 which is releasably engageable to a first side of the crane 300 and a second adjustable arm 500 (better viewed from Figure 5) releasably engageable to a second side of the crane 300. The first and second adjustable arms 326, 500 (as shown in Figure 5) are moveably mountable to the platform 324. In other embodiments, the adjustable arm 326 is moveably mounted on the vessel 100. In some embodiments, the adjustable arms 326, 500 are each pivotally mountable with first and second orthogonal pivoting joints 508. In other embodiments, the adjustable arms are mounted in ball and socket joints. In yet other embodiments the adjustable arms 326, 500 can be moveably mounted using any suitable mechanism for permitting multiple degrees of freedom.

The adjustable arms 326, 500 are configured to pivot with respect to the longitudinal axis X-X of the vessel 100. In this way, the adjustable arms 326, 500 can increase the outreach of the crane 300 as the adjustable arms 326, 500 tends towards the horizontal.

Similarly, the adjustable arms 326, 500 are configured to pivot with respect to the vertical axis Z-Z of the vessel 100. Accordingly, as the vessel 100 experiences roll or pitch in the X-X axis or Y axis respectively due to waves, the adjustable arms 326, 500 can be moved to remain upright.

Optionally, the crane body 310 comprises one or more crane couplings 502. Figure 5 shows a first crane coupling 502 mounted on a first side of the crane body 310. The opposite side of the crane body 310 comprises a second crane coupling (not shown). The first and second crane couplings 502 are configured to mount the crane 300 to the support structure 332 during the transfer operation. In some embodiments, the first and second crane couplings 502 permit relative movement between the crane 300 and the support structure 332. In some embodiments, the crane couplings 502 permit pivotal movement of the crane 300 about the centre axis B-B of the crane couplings 502. This means that as the angle between the adjustable arms 326, 500 and the longitudinal axis X-X varies as the adjustable arms extend, the crane 300 pivots in the plane of the longitudinal axis X-X and the vertical axis Z-Z and the crane 300 remains vertical. The difference in the angle between the adjustable arms 326 500 and the longitudinal axis X-X is visible between Figures 3 and 4. In some embodiments, the first adjustable arm 326 and the second adjustable arm 500 are independently controllable. In this way, the first adjustable arm 326 can be moved with respect to the second adjustable arm 500. The relative movement between the first and second adjustable arms 326, 500 can be due to pivotal movement or extension of the telescopic arms. This means that the crane 300 can be tilted and rotated due to the relative movement between the first and second adjustable arms 326, 500. Where the first and second adjustable arms 326, 500 are independently controllable, the crane couplings 502 permit movement in more than one degree of freedom. In this way, the crane couplings 502 can be ball and socket joints or a plurality of orthogonal pivoting joints.

In some other embodiments, the crane couplings 502 only permit pivoting movement along the X-X axis. Accordingly, the relative movement of crane 300 with respect to the adjustable arms 326, 500 is constrained. Instead, the support structure 332 is mounted on a motion compensated platform 324. This means that the roll, pitch and heave can of the vessel is compensated by the platform 324. In this way, the pivoting movement of the crane 300 about axis B-B is to compensate for the change in angle of the adjustable arms 326, 500 as the adjustable arms 326, 500 extend from the first position to the second position.

Referring back to Figure 3, in some embodiments, the platform 324 is rotatable with respect to the vessel 100 about an axis parallel with the Z-Z axis of the vessel 100. Indeed, the platform 324 comprises a rotatable bearing (not shown) mounted on the deck 334 of the vessel 100. In this way, the crane 300 can slew whilst mounted to the vessel 100.

Discussion of the method installing the crane 300 on the WTG 102 will now be discussed in reference to Figures 4, 5, 10 and 1 1. Figure 10 is a schematic view of the components and control systems of the vessel 100. Figure 11 is a flow diagram of the method installing the crane 300 on the WTG 102. In order to transfer the crane 300 to the WTG 102, the crane 300 is suspended in the support structure 332. The support structure 332 will be further described in reference to Figure 4. Figure 4 is the same as the arrangement shown in Figure 3, except that the adjustable arms 326 are extended.

The adjustable arms 326 are telescopic and have extended from the first, transfer position as shown in Figure 3 to a second position in which the crane 300 is in a suspended position in Figure 4. As the adjustable arms 326, 500 extend, the crane 300 is moved closer to the tower 1 16. In some embodiments, the telescopic arms are hydraulically actuated. In other embodiments, the extension of the telescopic arms 326, 500 is carried out with a rack and pinion mechanism (not shown) or any other suitable mechanism. In some embodiments, the extension of the telescopic arms is controllable via a hydraulic system 1022 (as shown in Figure 10). The adjustable arms 326, 500 extend along their longitudinal axis. Optionally, the adjustable arms 326, 500 can also pivot with respect to the vessel 100.

In the suspended position, the crane 300 is ready to be mounted on the tower 1 16. As shown in Figure 4, the crane body 310 is surrounding the tower 1 16. When the crane 300 is being suspended from the support structure 332, movement of the vessel 100 from the wind and the waves are exaggerated. Optionally, the boom 312 is in a horizontal position as shown in Figure 4. Placing the boom 312 in a horizontal position can protect the crane 300 during the transfer of the crane 300 from the vessel 100 to the WTG 102. Accordingly, the doors 900, 902 of the crane body 310 have been closed and secured together. Accordingly, the motion of the vessel 100 is compensated in order to keep the suspended crane stable relative to the tower 1 16. This means that the movement of the vessel due to the waves and wind does not affect the position of the crane 300 with respect to the tower 116. Instead, translational movement of the crane 300 with respect to the tower 1 16 is due to transferring the crane 300 from the vessel 100 to the tower 1 16. In this way, the translational movement of the crane 300 is with respect to the tower 1 16 is due to the extension of the support structure 332 or from a controlled thrust of the vessel itself required to move the crane 300 closer to the tower 1 16. Accordingly the crane 300 is elevated and suspended in the support structure 332 above the vessel 100 as shown in step 1 100 of Figure 1 1 .

Optional compensation for relative motion between the portion of the offshore wind turbine generator 102 and the vessel 100 is then carried out. Discussion of compensating the motion of the vessel 100 will now be discussed in reference to Figures 5 and 10.

Turning to Figure 10, the vessel 100 comprises a plurality of different modules for controlling one or more aspects of the vessel 100. The modules may be implemented on hardware, firmware or software operating on one or more processors or computers. A single processor can operate the different module functionalities or separate individual processors, or separate groups of processors can operate each module functionality.

The vessel 100 further comprises modules for determining parameter information relating the vessel 100. Figure 10 is a non-exhaustive list of the different control modules of a vessel 100. The vessel 100 comprises a vessel control module 1012 for controlling the movement, positioning and orientation of the vessel 100 by sending instructions to the propulsors e.g. the propellers 1002, the thrusters 132, 134, 136, 138, 140, 142 and / or azipods 1006. The vessel control module 1012 can control one or more other aspects of the vessel 100 such as the motion compensation module 1014.

The vessel control module 1012 receives position information from a dynamic positioning module 1010. The dynamic position module 1010 receives positioning information from one or more inputs such as a global positioning system (GPS) 1016, global navigation satellite system (GLONASS) 1018, and a compass 1020 for determining the current position and heading of the vessel 100. The dynamic positioning module 1010 can receive additional positioning input information from other input sources, if required such as a WTG distance module 1026. The dynamic position module 1010 sends target position information to vessel control module 1012. The target position information received from the dynamic positioning module 1010 is position information for moving the vessel 100 from a current position to a desired target position of the vessel 100. For example, the target position information can be position information for maintaining the vessel 100 in a static position for the vessel 100 or a maintaining the vessel on a course or heading.

Additionally or alternatively, at least one beacon or 400 is placed on a surface of the WTG 102 for measuring the distance between the WTG 102 and the vessel 100 by the WTG distance module 1026. The beacon 400 can be passive and provide a surface which is better for reflecting the measurement signals e.g. light, radio waves, sound waves. In this way the beacon 400 can be made from a reflective material such as foil. In alternative embodiments, the beacon 400 can be active and send a signal to a distance sensor 1024 for measuring the distance. The distance sensor 1024 can be a laser range finder, LIDAR, a camera, radar, sonar or any other suitable sensor for measuring distance between the vessel 100 and the WTG 102. For example, the active beacon 400 can comprises a GPS detector for determining position of the WTG 102 which is sent to the distance sensor 1024. In some embodiments, the beacon 400 can be launched from the vessel 100 to the WTG 102 using a drone, cannon or any other suitable means for delivering the beacon 400 to the WTG 102.

In some embodiments, the WTG distance module 1026 sends target position information based on the measured distance between the WTG 102 and the vessel 100. Based on the measured distance, the WTG distance module 1026 issues a command to the dynamic positioning system to move the vessel 100 to a safe operating distance. In this way, the WTG distance sensor 1024 can provide accurate distance information to the dynamic positioning module 1010 which the dynamic positioning module 1010 may not be able to determine using only information from the GPS sensor 1016.

Accordingly, the dynamic positioning module 1010 can compensate for vessel motion due to drift from the wind and the waves. That is the sway, surge and yaw motion of the vessel 100 can be compensated with use of the thrusters and propellers.

As mentioned above, the vessel 100 can also experience motion due to roll, pitch and heave from the waves. The motion compensation module 1014 moves the support structure 332 in order to compensate for the roll, pitch and heave of the vessel 100.

The support structure 332 will be discussed in more detail with reference to Figure 5. Figure 5 shows a close up perspective view of the crane 300 mounted on the vessel 100. Only the aft portion of the vessel 100 is shown for the purposes of clarity.

The support structure 332 is suspending the crane 300 above the deck 334 of the vessel 100. Indeed, the first and second adjustable arms 326, 500 are in the extended, second position. The doors 900, 902 of the crane body 310 are open so that the crane body 310 can be positioned to surround the tower 1 16. In comparison with Figure 4, the doors 900, 902 are in the closed position.

In some embodiments, the support structure 332 comprises at least one actuator for moving the suspended crane 300 with respect to the vessel 100. In the embodiment shown in Figure 5, there is a first actuator 328 and a second actuator 330 for moving the first adjustable arm 326. Similarly the second adjustable arm 500 comprises first and second actuators 504, 506 for moving the second adjustable arm 500. The actuators 328, 330, 504, 506 are configured to move the adjustable arms 326, 500 to compensate for the motion of the vessel. In some embodiments, there are any number of actuators for moving the support structure 332. The actuators 328, 330, 504, 506 are hydraulically actuated extendable pistons and are coupled to the hydraulic system 1022. In some embodiments, the actuators 328, 330, 504, 506 moved by linkages and gearing or any other suitable mechanism.

The pitch roll and heave motion of the vessel 100 is detected using the pitch motion sensor, 200, the roll sensor 202, and the heave sensor 210. The motion compensation module 1014 receives the sensor data relating to the detected motion of the vessel 100. The motion compensation module 1014 determines the deviation of the crane 300 due to the detected motion of the vessel from a stable crane position.

The stable crane position is a position whereby the movement of the vessel 100 due to the waves and wind does not affect the position of the crane 300 with respect to the tower 1 16. Instead, translational movement of the crane 300 with respect to the tower 1 16 is due to transferring the crane 300 from the vessel 100 to the tower 1 16. In this way, the translational movement of the crane 300 is with respect to the tower 1 16 is due to the extension of the support structure 332 or from a controlled thrust of the vessel 100 itself required to move the crane 300 closer to the tower 116.

In some embodiments, the motion compensation module 1014 calculates the deviation from a position of the crane suspended above the vessel at a height corresponding to the position on the WTG 102 where the crane 300 is to be transferred to. On detection of deviation from a stable crane position, the motion compensation module 1014 then sends one or more instructions to the actuators 328, 330, 504, 506 to move the crane 300 back to a stable position. In this way, the motion compensation module 1014 controls the actuators 328, 330, 504, 506 to keep the crane 300 fixed at a height with respect to the WTG 102.

Additionally or alternatively, in some embodiments, the motion compensation module 1014 generates a model of the motion of the vessel 100 over a period time based on observed vessel motion. Accordingly, the generated model is a prediction of the motion of the vessel 100 based on recent motion on the vessel. The motion compensation model sends control instructions to the actuators 328, 330, 504, 506 based on the vessel motion model.

Additionally or alternatively, the platform 324 is coupled to actuators connected to the motion compensation module 1014. Accordingly, the platform 324 can be used for loading the crane 300 and / or parts 302, 304, 306 of the WTG 102 and stabilized.

Once the crane 300 is in a suspended position adjacent to the WTG 102, the crane can be transferred to a portion of the WTG 102 as shown in step 1102 of Figure 11 .

During the transfer step 1 104, the crane 300 is positioned such that it is orientated around the tower 1 16 as shown in Figure 4. Accordingly the crane 300 can be transferred to the WTG 102.

Once the crane 300 is in position the crane 300 can be secured to any portion of the offshore wind turbine 102 by suspending the crane 300 from the portion 308 of the WTG 102 with one or more cables 700, 702 (see Figure 7). The step of suspending is shown in step 1 104 of Figure 1 1 and will be described in further detail with respect to Figures 7a, 7b, 8a, 8b and 9. Figures 7a, 7b, 8a, 8b and 9 show a schematic cross section of the crane 300 along the axis C-C as shown in Figure 4.

The crane 300 as shown in Figure 7a is a close up of the crane body 310 with a partial representation of the boom 312. The rest of the crane boom 312 above the crane body 310 is represented by the dotted lines in Figure 7a.

In Figure 7a, the support structure 332 has positioned the crane 300 around the first portion 308. In addition the crane 300 is suspended from the portion 308 of the tower by a first cable 700 and a second cable 702. The first and second cables 700, 702 are coupled to a yoke 704 via couplings 706, 708 fixed to the yoke 704. The couplings 706, 708 as shown in Figure 7a are eyes fixed to the yoke 704. The yoke 704 is positioned on the top lip 710 of the first portion 308 of the tower 116. The yoke 704 extends across the diameter of the top lip 710 of the tower 1 16. In some embodiments, the yoke 704 optionally comprises locking clamps (not shown) for clamping on to the first portion 308. The locking clamps engage against a bracket, bolts, flange, lip, overhang or any other suitable feature of the tower 1 16. In some embodiments, the first and second cables 700, 702 are positioned on different positions e.g. different sides of the WTG 102. In some embodiments, the first and second cables 700, 702 are positioned on different positions e.g. opposite sides of the WTG tower 116. This makes hoisting the crane 300 into an operation position on the WTG 102 more stable because the crane 300 is less likely to twist about the first and second cables 700, 702.

The yoke 704 as shown in Figure 7a is mounted on the first portion 308 of the tower 116. However, the yoke 704, can be mounted on any portion of the WTG 102, such as different parts of the tower 302, 304, 306 or the nacelle 118.

In other embodiments, the yoke 704 rests on the top lip 710 of the first portion 308. The yoke 704 remains in position because the weight of the crane 300 causes sufficient friction between the yoke 704 and the top lip 710 to prevent the yoke 704 from slipping off the first portion 308. Optionally, the yoke 704 can comprise one or more projections (not shown) to project into the open top of the tower 116. The yoke 704 can comprise any suitable shape for engaging with the top lip 710 of the first portion 308. As shown in Figure 7a, the yoke is a horizontal beam that extends across the top lip 710 of the first portion 308. In other embodiments the yoke can be an annulus to engage with the annular shaped flange of the first portion 308.

During the transfer operation as shown in step 1102, the crane 300 is elevated above the top lip 710 of the first tower portion 308. Accordingly the yoke 704 is positioned and aligned with the top lip 710 and the crane 300 is lowered by the support structure 332. In this way the yoke 704 engages with the top lip 710 and the crane 300 is suspended as the first and second cables 700, 702 are tensioned.

Once the crane 300 is suspended from the first portion 308 of the tower 116, the crane 300 is secure and can hoist further parts of the WTG 102 to be installed on the WTG 102. This means that the crane 300 can be quickly transferred and secured with cables 700, 702 to the WTG 102 by the vessel 100. Accordingly, the amount of time that the vessel 100 spends in close proximity to the transition piece 108, is limited because the transfer operation is one action. Indeed, the vessel 100 is not needed if the crane 300 is required to reposition itself after being suspended from the WTG 102. In this way, the crane 300 can move with respect to the WTG 102 without assistance from the vessel 100.

Figure 7a shows the crane 300 being suspended by two cables 700, 702 respectively attached on a first side 716 of the crane 300 and a second side 718 of the crane 300. The first side 716 comprises a first coupling 712 for securing the first cable 700 to the crane body 310. The second side comprises a second coupling 714 for securing the second cable 702 to the crane body. In some embodiments, the first and second cables 700, 702 are positioned on different positions e.g. different sides of the crane body 310. This makes hoisting the crane 300 into the operational position on the WTG 102 more stable. Figure 7a shows the first and second cables 700, 702 being positioned on opposite sides of the crane body 310. The first portion 308 of the tower 1 16 is positioned between the first and second cables 700, 702 when the crane 300 is suspended from the first portion 308. In some embodiments, there can be any number of cables from which the crane 300 is suspended. In some embodiments, the crane 300 is suspended from a single cable. In other embodiments, the crane is suspended from more than two cables e.g. three, four, five etc. cables. The plurality of cables are circumferentially distributed around the first portion 308 when the crane 300 is being suspended.

In some embodiments, the couplings 706, 708 are aligned with the diameter or the widest part of the first portion 308. Furthermore, the centre of gravity of the crane 300 is aligned with the plane defined by the couplings 706, 708, 712, 714. Accordingly, the crane 300 does not experience any turning moment when suspended from the first portion 308 of the tower 1 16. In some embodiments, the centre of gravity of the crane 300 is aligned with the longitudinal axis A-A of the tower 116. The first and second cables 700, 702 are coupled to the crane body 310. Optionally, the crane 300 comprises one or more winches 712, 714 mounted to the crane body 310 for winching the first and second cables 700, 702. The winches 712, 714 are arranged to reel in the first and second cables 700, 702. As the first and second cables 700, 702 are winched in, the crane 300 moves towards the top lip 710 of the first portion 308 where the first and second cables 700, 702 are attached to the first portion 308. In this way, the crane 300 climbs vertically up the first portion 308. In other embodiments, the winching can be carried out with a winch not mounted on the crane 300. For example, the yoke 704 can comprise pulleys and the winch is mounted on the transition piece 708 or on the vessel 100.

Figure 7b shows the position of the crane 300 with respect to the first portion 308 of the tower 1 16. After the crane 300 as climbed up the WTG 102, the crane 300 optionally engages the WTG 102 with one or more couplers 720, 722. Figure 7a shows a first gripping arm 720 and a second gripping arm 722 respectively mounted on the first side 716 and the second side 718 of the crane body 310. The first and second gripping arms 720, 722 are arranged to move between a disengaged position and an engaged position. The first and second gripping arms 720, 722 are hydraulically actuated, but movement between the disengaged position and the engaged position can be achieved with any suitable mechanism such as gears and linkages. The first and second gripping arms 720, 722 are in the engaged position and are in mechanical engagement with the top lip 710 of the first portion 308.

In other embodiments, the first and second gripping arms 720, 722 are configured to engage with a flange, eye, bracket or any other suitable protrusion or feature of the WTG 102. The first and second gripping arms 720, 722 are configured to engage with the exterior or the interior of the WTG 102. When the first and the second gripping arms 720, 722 are engaged with the outer surface 906 of the WTG 102, the weight of the crane 300 is supported by the gripping arms 720, 722. In some embodiments, there can be any number of couplers or gripping arms 720, 722 for engaging the WTG 102. The gripping arms 720, 722 are circumferentially distributed around the crane body 310. In further embodiments, there can be a first set of gripping arms 720, 722 positioned at a first height on the crane body 310 and one or more other sets of gripping arms (not shown) for engaging one or more different parts of the WTG 102.

Optionally, once the first and second gripping arms 720, 722 have engaged with WTG 102, the first and second cables 700, 702 are not supporting the weight of the crane 300. This means that the first and second cables 700, 702 can be detached from the first portion 308 of the tower 1 16. The yoke 704 can be removed from the top lip 710. This can provide clearance for a subsequent portion 306, 304, 302 to be placed on top of the first portion 308. In some embodiments, the yoke 704 does not have to be removed before further portions 306, 304, 302 are installed. Indeed, the subsequent portion 306, 304, 302 can be discarded and left in place, or alternatively, the position of the engaged yoke 704 means that the yoke 704 can be removed after the subsequent portion 306, 304, 302 has been installed.

Accordingly, the yoke 704 can be positioned on top of the subsequent portion 306, 304, 302 of the tower 116. The first and second cables 700, 702 can then suspend the crane 300 from the yoke 704 positioned on the freshly installed second portion of the tower 306. Optionally, the crane 300 itself can place the yoke 704 on top of the second portion 306 of the tower 1 16. Alternatively, the yoke 704 can be threaded through holes on either side of the tower 1 16.

In some embodiments, the crane 300 comprises the first and second winches 712, 714 for self-hoisting the crane 300 up the first portion 308. The first and second winches 712, 714 are separate from the winch 318 of the crane for hoisting loads e.g. the portions of the WTG 102. In other embodiments, the crane 300 comprises a single winch 318 for winching the first and second cables 712, 714 and for winching cable 316. In this way, the winch 318 can hoist loads and self-hoist. Another embodiment will now be described in reference to Figures 8a and 8b. Figures 8a and 8b are the same as Figures 7a and 7b except that the mechanisms for attaching the cables 700, 702 to the first portion are different.

In Figure 8a, the first and second cables 700, 702 are coupled to the first portion 308 by a first and second tower couplings 800, 802 which are fixed to the body of the first portion 308. The first and second tower couplings 800, 802 can be pad eyes, loops, hooks, brackets or any other suitable fixing for attaching the first and second cables 700, 702. Since the first and second tower couplings 800, 802 are fixed to the first portion 308 of the tower 116, the cables may be attached and detached as required. The other portions 306, 304, 302 of the tower 1 16 may have similar tower couplings 800. The crane 300 can crawl vertically up the first portion 308 in the same way as described in in reference to Figures 7a, 7b. Alternatively, the crane 300 can be fixed in place with respect to the WTG 102.

In some embodiments, the tower couplings 800, 802 are removeable. For example the tower couplings 800, 802 are one or more of removeable pad eyes, loops, hooks, brackets or any other suitable fixing for attaching the first and second cables. The tower couplings 800, 802 can be releasably fastened to the tower 1 16 via one or more bolts. In other embodiments, the tower couplings can be fastened to the tower 1 16 with any other suitable fastening for releasing the tower couplings 800, 802 such as magnetic fastenings. The tower couplings 800, 802 can be threaded through a hole in the tower 1 16 and fastened to the tower 1 16 on the inside of the tower 1 16. In this way, the removeable tower couplings 800, 802 can be retrofittable to any type of tower 1 16. Furthermore the tower couplings 800, 802 are reusable on subsequent WTGs 102. Since the tower couplings 800, 802 are threaded through a hole in the wall of the tower 1 16, the tower coupling 800, 802 securely fastened to the side of the tower 1 16 without compressing the sides of the hollow tower 1 16 together.

The holes in the tower 1 16 for receiving the tower couplings 800, 802 can be positioned at the top of the tower 116. Alternatively, the removeable tower couplings can be releasably mounted to any position on the WTG 102. For example, the tower couplings 800, 802 can be mounted to the nacelle 1 18.

In some embodiments, the removeable tower couplings 800, 802 can be mounted to the tower 116 with one or more cables attached to the removeable tower couplings 800, 802. In this way, when the tower couplings 800, 802 are mounted to the tower 1 16, the cables 700, 702 are ready for use. In some examples, the cables 700, 702 are not under tension when the tower couplings 800, 802 are mounted to the tower 1 16.

In Figure 8b, the first and second cables 700, 70 are coupled to the first portion 308 by hooks 804, 806 which clip over the lip 710 of the open top of the first portion 308. The hooks 804, 806 can be lifted out of engagement with the lip 710 as required. The crane 300 can crawl vertically up the first portion 308 in the same way as described in in reference to Figures 7a, 7b. Alternatively, the crane 300 can be fixed in place with respect to the WTG 102.

In another embodiment, as shown in Figure 9, there is an adaptor 808 that grips the external surface 906 of the tower 116. This means that the adaptor 808 is fixed with respect to the WTG 102. The first and second cables 700, 702 are attached to the adaptor 808. The crane 300 as shown in Figure 9 is fixed with respect to the WTG 102 because there are no winches for reeling in the first and second cables 700, 702. In other embodiments, winches can be used to move the crane 300 vertically on the WTG 102.

Optionally in some embodiments, as mentioned above the securing comprises additionally abutting shock absorbers 904 against the outer surface 906 of the WTG 102.

Once the crane 300 is secured to the WTG 102, the vessel 100 can move away from the WTG 102. The crane 300 can then hoist parts 302, 304, 306 of the WT G 102 to be installed from the vessel 100 or another vessel such as a barge (not shown). This means that the crane 300 can be transferred to the WTG 102 without endangering the vessel 100 or damaging the WTG 102 or the crane 300. Furthermore, the crane 300 is operable whilst being suspended from the first and second cables 700, 702. This means the crane 300 hoists loads whilst being suspended from the first and second cables 700, 702.

In another embodiment, which is not shown in the Figures, the first and second cables 700, 702 each comprise a loop which are threaded over a projection on the WTG 102 such as a stud, peg, pin, hook or bracket or into a hole in the WTG 102. In some embodiments, the projection comprises a mushroom cross- sectional shape so that the loop is prevented from slipping off the projection.

The method as described in reference to Figures 10 and 1 1 for transferring the crane 300 to the WTG and suspending the crane 300 from cables can be applied to any of the described embodiments in this application.

In other embodiments, the support structure 332 can be any suitable structure for suspending the crane 300 above the deck 334 of the vessel 100 and transferring the crane 300 to the WTG 102. Indeed in some embodiments, the support structure 332 is a structure fixed with respect to the vessel 100. Alternatively, instead of extendable adjustable arms as shown in Figures 3, 4 and 5, the support structure 332 comprises a pivoting frame 600 with fixed length arms which pivot with respect to the vessel 100.

In another embodiment two or more embodiments are combined. Features of one embodiment can be combined with features of other embodiments.

Embodiments of the present invention have been discussed with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the invention.

Claims

1 . A method of installing a crane on a portion of an offshore wind turbine generator from a vessel having a crane support structure, the method comprising:

elevating the crane in the support structure above the vessel;

transferring the elevated crane between the vessel and the portion of the offshore wind turbine; and

suspending the crane from a portion of the offshore wind turbine with one or more cables.

2. A method according to claim 1 wherein the suspending comprises suspending the crane from a coupler removeably mounted to a portion of the offshore wind turbine generator.

3. A method according to claim 2 wherein the coupler is a yoke arranged to engage the top of a tower portion of the offshore wind turbine generator.

4. A method according to claims 2 or 3 wherein the coupler is a hook coupled to an open top of a tower portion of the offshore wind turbine generator.

5. A method according to claim 2 wherein the coupler is configured to engage with a protrusion, bracket, eye, lip, flange, loop of the offshore wind turbine generator.

6. A method according to claim 2 wherein the coupler is configured to engage with at least one hole in the offshore wind turbine generator.

7. A method according to any of the preceding claims wherein the method comprises hoisting the suspended crane up the offshore wind turbine generator with the one or more cables.

8. A method according to claim 7 wherein the hoisting is carried out with a winch mounted in the crane.

9. A method according to claim 8 wherein the crane comprises a first winch to hoist the crane and a second winch to hoist loads.

10. A method according to claim 8 wherein the winch is configured to operate in a first mode for hoisting the crane and a second mode for hoisting loads.

11. A method according to any of the preceding claims wherein the method comprises closing one or more moveable doors hinged on a body of the crane around the portion of the offshore wind turbine generator.

12. A method according to any of the preceding claims wherein the method comprises engaging at least one gripping arm mounted on the crane with a portion of the offshore wind turbine generator.

13. A method according to any of the preceding claims wherein at least one gripping arm is engageable with a protrusion, bracket, eye, lip of flange of the offshore wind turbine generator.

14. A method according to claims 12 or 13 wherein the at least one gripping arm is configured to move between a disengaged position and an engaged position.

15. A method according to claims 12 to 14 when dependent on claims 7 to 10 wherein the hoisting comprises moving the crane to a position on the offshore wind turbine generator such that the at least one gripping arm is engageable with the portion of the offshore wind turbine generator.

16. A method according to any of the preceding claims wherein the step of elevating the crane above the vessel comprises elevating the crane from a first position where the crane is adjacent to a deck of the vessel and to a second position wherein the crane is suspended above the deck of the vessel.

17. A method according to any of the preceding claims wherein the step of elevating comprises elevating at least a portion of the crane above the portion of the offshore wind turbine generator.

18. A method according to any of the preceding claims wherein the step of suspending the crane on the portion of the offshore wind turbine generator comprises lowering the crane with respect to the potion of the offshore wind turbine generator until the cables are under tension.

19. A method according to any of the preceding claims wherein the step of suspending the crane on the portion of the offshore wind turbine generator comprises attaching the cables to the offshore wind turbine generator.

20. A method according to any of the preceding claims wherein the suspending the crane comprises suspending the crane with two cables on at different positions on the offshore wind turbine generator.

21 . A method according to any of the preceding claims wherein the suspending the crane comprises suspending the crane with two cables on different sides of the crane.

22. A method according to any of the preceding claims wherein the method comprises attaching the one or more cables between the offshore wind turbine generator and the crane when the crane is positioned on the vessel.

23. A method according to any of the preceding claims wherein the method comprises operating the crane when crane is suspended from the portion of the offshore wind turbine with one or more cables.

24. A crane mountable on a portion of an offshore wind turbine generator comprising:

a crane body;

a first coupling mounted on the crane body attaching a first cable on a first side of the crane and a portion of the offshore wind turbine generator; and a second coupling mounted on the crane body for attaching a second cable on a second side of the crane and a portion of the offshore wind turbine generator;

such that the crane is arranged to be suspended from the offshore wind turbine with the portion of the offshore wind turbine generator between the first and second cables.

25. A crane according to claim 24 wherein at least a portion of the crane body surrounds the portion of the offshore wind turbine generator when suspended from the offshore wind turbine generator.

26. A crane according to claim 25 wherein the portion of the crane is arranged to circumferentially surround the offshore wind turbine generator.