WO2021123236A1

WO2021123236A1 - Offshore vessel crane

Info

Publication number: WO2021123236A1
Application number: PCT/EP2020/087125
Authority: WO
Inventors: Joop Roodenburg; Marc Louis Brinkman
Original assignee: Itrec B.V.
Priority date: 2019-12-19
Filing date: 2020-12-18
Publication date: 2021-06-24
Also published as: EP4077197A1; NL2024512B1; EP4077197B1; CN114981200A

Abstract

An offshore vessel crane configured for mounting on an offshore vessel, for example for use in the handling of one or more offshore wind turbine components, e.g. for installation and/or maintenance of an offshore wind turbine. The crane comprises a base structure adapted to be mounted on the vessel and a revolving superstructure. The crane a boom that is pivotal up and down. The boom has an extensible boom structure that is slidably mounted between distal sections of the boom legs of a main boom structure, so as to be movable between a retracted position and an extended position in the direction of the length of the main boom section.

Description

OFFSHORE VESSEL CRANE

The invention relates to an offshore vessel crane that is configured for mounting on an offshore vessel.

In the field of offshore wind turbines, the need exists for the handling very heavy components, like the foundation, e.g. the monopile, which can have a mass of 1000 tons or more. In addition the need exists for the handling of components "at the height of the nacelle", which includes, for example, the handling of the nacelle itself and/or one or more components that are housed in a nacelle and/or mounted on the nacelle, e.g. a gearbox, an electric generator, the hub, and/or the rotor blades. Current designs propose or already have the nacelle at a height of more than 100 meters above sea level, e.g. at 120 meters or more, for example the Haliade-X 12 MW offshore wind turbine. Therefore, the handling of such components requires a both a very heavy load crane as well as a very tall crane. It is noted that also the mass of the nacelle may be several hundreds of tons, e.g. over 500 tons.

In a common approach, the offshore wind turbine is installed or serviced using a jack-up vessel that is positioned close to the wind turbine location and then the jack-up legs are extended and the vessel is lifted, at least in part but mostly entirely above the sea, to provide a stabilized situation for the crane operation.

It is noted that the invention is primarily envisaged for the field of offshore wind turbines, so for maintenance, and also for installation and/or decommission of wind turbines. However, the inventive crane may also be of use in other offshore applications, like oil & gas related operations, civil engineering operations, etc.

In the field, offshore cranes are known comprising:

- a base structure that is adapted to be mounted on the vessel, e.g. fixed to the hull of the vessel;

- a revolving superstructure that is slewable on a slew bearing about a slew axis relative to the base structure, the superstructure being provided with:

- a boom connection member comprising a left-hand connector and a right-hand hand connector arranged at a distance of each other, together defining a horizontal boom pivot axis; - a boom having a longitudinal axis, wherein the boom has an inner end connected to the left-hand connector and to the right-hand connector of the boom connection member, so that the boom is pivotal up and down about the boom pivot axis which is perpendicular to the longitudinal axis of a boom;

- a luffing device for pivoting the boom up and down, comprising a luffing winch and a variable length luffing system;

- a main hoisting system for hoisting a load, comprising a main winch and an associated main hoisting cable.

It is known to provide a boom having a single leg embodied as a latticed hollow box structure. A known alternative is a A-frame booms which has generally the shape of an A with two boom legs connected, each embodied as a latticed hollow box structure. Another known example, is a twin leg boom with two parallel legs, each embodied as a latticed hollow box structure, wherein the legs are interconnected by multiple cross members, distributed over the length thereof, interconnecting the boom legs.

The present invention aims to provide a crane having enhanced versatility and capabilities, e.g. in view of increasing demands in the field of offshore wind turbines.

The present invention provides an offshore crane according to claim 1.

The boom has a main boom structure having a left-hand boom leg and a right-hand boom leg, each of these two boom legs having a proximal end portion that is pivotally connected to the left-hand connector and to the right-hand hand connector respectively.

Each of the two boom legs has a length of at least 60 meters, e.g. between 80 and 140 meters. For example, in a practical design, the legs of the main boom structure have a length of more than 100 meter, e.g. of about 120 meters.

In an embodiment, the legs are rigid, unitary legs, e.g. welded steel unitary legs, each having a fixed length. In another embodiment, the legs are composed of leg modules that are fastened end-to-end, e.g. with one or more intermediate leg modules that are selectively mountable in the structure of a leg in order to set the length of the leg to a desired length.

Each boom leg is embodied as a hollow box structure, preferably a latticed hollow box structure. The hollow box structure has a cross section defined by an inner side face and by multiple further faces. Herein the inner side faces of the left-hand and right-hand boom legs are spaced from one another to form a clearance between the boom legs along the length of the main boom structure.

For example, each leg is over at least a major portion of the length thereof, e.g. all of the length, embodied with a rectangular cross section defined by the inner side, an outer side, a top side, and a bottom side.

In an embodiment, each leg is over a portion of the length thereof, e.g. a minor portion, embodied with a triangular cross section, defined by the inner side, a top face, and bottom face, said top face and bottom face adjoining one another at an outer apex that is remote from the inner side, e.g. forming a cross section corresponding to an equilateral triangle or an isosceles triangle.

The main boom structure comprises, distributed over the length thereof, multiple cross members interconnecting the left-hand and right-hand boom legs.

In an embodiment, the legs are straight over their entire length, e.g. parallel to one another.

The two boom legs each have a distal section with a distal end remote from the proximal end portion.

The boom of the inventive crane further comprises an extensible boom structure. This extensible boom structure is slidably mounted between the distal sections of the two boom legs of the main boom structure, so as to be movable between a retracted position and an extended position in the direction of the length of the main boom section.

The extensible boom structure is over at least a major portion of the length thereof, e.g. over at least 75% thereof, embodied as a hollow box structure, e.g. a rectangular cross section hollow box structure with a top face, a bottom face, and opposed side faces.

Preferably, the extensible boom structure is in majority embodied as a latticed hollow box structure.

The side faces of the extensible boom structure each extend adjacent an associated one of the inner side faces of the distal sections, these faces being parallel to one another and extending in longitudinal direction of the boom. For example, the inner side faces of the distal sections each have parallel upper and lower chords interconnected by lacing members in the plane of the inner side face, and the side faces of the extensible boom structure each have parallel upper and lower chords interconnected by lacing members in the plane of the inner side face of the extensible boom structure, wherein bearing members are arranged between each pair of adjacent upper chords and each pair of adjacent lower chords to allow for sliding of the extensible boom structure and for transmission of loads between the extensible boom structure and the distal sections of the two legs of the main boom structure.

The extensible boom structure is extendable and retractable over a range of at least 10 meters relative to the main boom structure, e.g. over at least 20 meters, e.g. between 20 and 40 meters.

The distal sections are interconnected by at least one of the cross members, which at least one cross member is located in proximity of the distal ends. This at least one cross member between the distal sections is configured to allow for extending and retracting motions of the extensible boom section.

The extensible boom structure is provided with a boom head at a tip end of the extensible boom structure.

In an embodiment, the variable length luffing system extends from the luffing winch to the boom head. In an alternative embodiment, the variable length luffing system extends from the luffing winch to the distal sections, e.g. to the distal ends thereof. Herein, preferably, the crane boom is further provided with a stay mechanism. This mechanism has, for each of the boom legs, a fixed length stay extending from an anchoring member on the boom leg arranged in proximity of the proximal end of the boom leg to a top end of a strut that extends from the distal section of the boom leg. A variable length stay extends from said top end of the strut to the boom head.

The main hoisting cable extends from the main winch to a main cable sheave assembly that is arranged on the boom head.

The boom head is, in an embodiment thereof, provided with an auxiliary jib member that is fixed on the boom head, and the crane is provided with an auxiliary hoisting system having an auxiliary hoisting winch, an auxiliary hoisting cable driven by said winch, and an auxiliary sheave assembly on the auxiliary jib member from which an auxiliary load connector, e.g. a crane hook, is suspended.

In an embodiment, the two boom legs each have a proximal section extending from the proximal end portion thereof and a central section adjoining the proximal section, the distal section of the boom leg adjoining the central section, wherein the proximal sections are parallel to one another, wherein the central sections converge towards one another in the direction towards the distal sections, and wherein a cross member interconnects the boom legs where the proximal section and central section adjoin, and wherein a cross member interconnects the boom legs where the central section and distal section adjoin. In a further development, an inner end of the extensible boom section, in the retracted position thereof, is located in proximity of the cross member where the central section and distal section adjoin.

In an embodiment, the distal sections are each embodied as a latticed hollow box structure, each have an inner side face with parallel upper and lower chords interconnected by lacing members in the plane of the inner side face, wherein the cross member in proximity of the distal ends comprises trusses that are arranged in a plane between the upper chords and trusses arranged in a plane between the lower chords.

In an embodiment, the extensible boom structure is over at least a major portion of the length thereof, e.g. over at least 75% thereof, embodied as a hollow box structure having a rectangular cross section of a width of at least 6 meters and a height of at least 3 meters.

In an embodiment, the superstructure is provided with a gantry thereon, on which a luffing cable sheave assembly is mounted, the luffing cable sheave assembly guiding a luffing cable extending from the luffing winch to the boom head.

In an embodiment, the luffing system comprises:

- two luffing winches on the superstructure; and

- two luffing cables, each driven by a respective luffing winch, said luffing cables extending spaced from one another, e.g. parallel to one another, from luffing cable sheave assemblies mounted on the superstructure, e.g. on a gantry thereof, to respective luffing cable connectors on the boom head, or on the distal sections, which luffing cable connectors are spaced apart from another in a width direction of the boom, e.g. arranged on opposite sides of the boom head seen in width direction. In an embodiment, the crane comprises an extension mechanism comprising an extension winch, a winch driven extension cable, and an extension cable sheave system with multiple sheaves. The extension mechanism is configured to engage on the extensible boom structure so as to provide an extension motion thereof, preferably retraction of the extensible boom structure being caused by the mass of the extensible boom structure whilst the boom is upwardly oriented. In an alternative embodiment, retraction is done by a winch or some other drive. In embodiment, extension and/or retraction is done by a rack-and-pinion mechanism.

In an embodiment, the crane comprises a locking mechanism configured to lock the extensible boom mechanically to the distal sections in at least the retracted and extended position thereof. For example, the locking mechanism comprises one or more actuated locking pins or the like.

The invention also relates to an offshore vessel comprising a crane as described herein.

The invention also relates to a jack-up type offshore vessel comprising:

- a buoyant hull with a main deck,

- at least three jack-up legs,

- a plurality of elevating units, each associated with a respective jack-up leg, adapted to move the respective jack-up leg vertically relative to the hull and to bring the vessel in an operational position wherein the legs engage the seabed and the hull is above water level,

- a crane as described herein.

In an embodiment, the crane is an around-the-leg crane, wherein a jack-up leg of the vessel extends through the revolving superstructure and the slew bearing extends about the jack-up leg.

In an embodiment, the crane is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a jack-up leg in the parking position, e.g. the vessel having a boom rest on which the boom is parked in a substantially horizontal orientation.

In an embodiment, the crane is an around-the-leg crane, wherein a jack-up leg of the vessel extends through the revolving superstructure and the slew bearing extends about the jack-up leg, and wherein the crane is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a jack-up leg in the parking position, e.g. the vessel having a boom rest on which the boom is parked in a substantially horizontal orientation.

In an embodiment, the vessel has two aft jack-up legs and two front jack-up legs, wherein a rear jack-up leg extends through the revolving superstructure and the slew bearing extends about said jack-up leg, and wherein the crane is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a front jack-up leg in the parking position, e.g. wherein a cross member arranged at the join of the proximal section and central section of each boom leg is located at a rear side of the front jack-up leg when in the parking position.

A second aspect of the invention relates to a jack-up type offshore vessel comprising:

- a buoyant hull with a main deck,

- at least three jack-up legs,

- an offshore vessel crane, for example for use in the handling of one or more offshore wind turbine components, e.g. for installation and/or maintenance of an offshore wind turbine, the crane comprising:

- a base structure fixed to the hull of the vessel;

- a revolving superstructure slewable on a slew bearing about a slew axis relative to the base structure, the superstructure being provided with:

- a boom connection member comprising a left-hand connector and a right- hand hand connector at a distance of each other, together defining a horizontal boom pivot axis;

- a boom having a longitudinal axis, wherein the boom has an inner end connected to the left-hand connector and to the right-hand connector of the boom connection member, so that the boom is pivotal up and down about the boom pivot axis which is perpendicular to the longitudinal axis of a boom;

- a main hoisting system for hoisting a load, comprising a main winch and an associated main hoisting cable; wherein the boom has a main boom structure having a left-hand boom leg and a right-hand boom leg, each of said boom legs having a proximal end portion pivotally connected to the left-hand connector and to the right-hand hand connector, respectively, wherein each boom leg has a length of at least 60 meters, e.g. between 80 and 140 meters, wherein each boom leg has a cross section defined by an inner side face and multiple further faces, wherein the inner side faces of the left-hand and right-hand boom legs are spaced from one another to form a clearance between the boom legs along the length of the main boom structure, wherein the main boom structure comprises, distributed over the length thereof, multiple cross members interconnecting the left-hand and right-hand boom legs, wherein the boom legs each have a distal section with a distal end remote from the proximal end portion, wherein the boom further comprises an extensible boom structure, said extensible boom structure being slidably mounted between the distal sections of the boom legs of the main boom structure, so as to be movable between a retracted position and an extended position in the direction of the length of the main boom section, wherein the extensible boom structure has a top face, a bottom face, and opposed side faces, said side faces of the extensible boom structure extending adjacent the inner side faces of the distal sections, which side faces are parallel to one another and extend in the longitudinal direction of the boom, wherein the extensible boom structure is extendable and retractable over a range of at least 10 meters relative to the main boom structure, e.g. over at least 20 meters, e.g. between 20 and 40 meters, wherein the distal sections are interconnected by at least one of said cross members that is located in proximity of the distal ends, said at least one cross member being configured to allow for said extending and retracting motions of the extensible boom structure, wherein the extensible boom structure is provided with a boom head at a tip end of the extensible boom structure; wherein the main hoisting cable extends from the main winch to a main cable sheave assembly on the boom head.

In embodiment the crane of the vessel of the second aspect of the invention is provided with one or more of the technical features discussed herein with reference to the offshore vessel crane of the first aspect of the invention, e.g. as described in the appended claims.

In an embodiment of the second aspect of the invention, the crane is configured for an over- the-leg parking position, wherein the two boom legs are located on opposite sides of a jack up leg in the parking position, e.g. the vessel having a boom rest on which the boom is parked in a substantially horizontal orientation.

In an embodiment of the second aspect of the invention, the crane is an around-the-leg crane, wherein a jack-up leg of the vessel extends through the revolving superstructure and the slew bearing extends about the jack-up leg.

In an embodiment of the second aspect of the invention, the crane is an around-the-leg crane, wherein a jack-up leg of the vessel extends through the revolving superstructure and the slew bearing extends about the jack-up leg, and wherein the crane is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a jack-up leg in the parking position, e.g. the vessel having a boom rest on which the boom is parked in a substantially horizontal orientation.

In an embodiment of the second aspect of the invention, the vessel has two aft jack-up legs and two front jack-up legs, wherein a rear jack-up leg extends through the revolving superstructure and the slew bearing extends about said jack-up leg, and wherein the crane is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a front jack-up leg in the parking position, e.g. wherein a cross member arranged at the join of the proximal section and central section of each boom leg is located at a rear side of the front jack-up leg when in the parking position.

The invention also relates to a method for hoisting an offshore wind turbine component, e.g. for installation and/or maintenance of an offshore wind turbine, wherein use is made of a crane and/or an offshore vessel as described herein.

The invention will now be described with reference to the figures. In the figures: Fig. 1 shows a jack-up type offshore vessel provided with an example of a crane according to the invention,

Fig. 2 shows the vessel of figure 1 in plan view with the crane boom in over-the-leg parking position,

Fig. 3a shows a part of the vessel of figure 1 with the boom raised and extended,

Figs. 3b, c show the crane of the vessel of figure 1 and the aft leg 4, with the crane in extended and retracted position, respectively,

Figs. 4a, b show the boom of the crane of figures 1 - 3 with the extensible boom structure in retracted position,

Figs. 5a, b show the boom of the crane of figures 1 - 3 with the extensible boom structure in extended position,

Fig. 6 shows a cross section of the boom of the crane of figures 1 - 3 in the region of the distal sections of the two boom legs,

Fig. 7 shows a jack-up type offshore vessel provided with another example of a crane according to the invention with the extensible boom structure retracted,

Fig. 8 shows the vessel of figure 7 with the extensible boom structure extended.

With reference to figures 1 - 6 a jack-up type offshore vessel suitable in particular for handling offshore wind turbine components will be discussed.

The vessel 1 comprises:

- a buoyant hull 2 with a main deck 3,

- two aft jack-up legs 4 and two front jack-up legs 5,

- a plurality of elevating units 6, each associated with a respective jack-up leg, adapted to move the respective jack-up leg vertically relative to the hull 2 and to bring the vessel in an operational position wherein the jack-up legs 4, 5 engage the seabed and the hull is above water level.

The vessel 1 is provided with a crane 10 for handling of offshore wind turbine components. A discussed the crane 10 can also be used for other purposes, and be installed on a different type of vessel, e.g. a semi-submersible crane vessel, etc.

The crane 10 comprises:

- a base structure 11 that is fixed to the hull 2 of the vessel 1 ;

- a revolving superstructure 12 that slewable on a slew bearing 12a about a slew axis relative to the base structure 11 , the superstructure being provided with: - a boom connection member comprising a left-hand connector 13a and a right-hand hand connector 13b at a distance of each other, together defining a horizontal boom pivot axis 14;

- a boom 20 having a longitudinal axis; wherein the boom has an inner end connected to the left-hand connector and to the right-hand connector of the boom connection member 13a, b, so that the boom is pivotal up and down about the boom pivot axis which is perpendicular to the longitudinal axis of a boom;

- a luffing device for pivoting the boom up and down, comprising a luffing winch 40 and a variable length luffing system;

- a main hoisting system for hoisting a load, comprising a main winch 50 and an associated main hoisting cable 51.

The boom 20 will be discussed in more detail below.

The crane 10 is an around-the-leg crane. It is shown, that an aft jack-up 4 leg extends through the revolving superstructure 12 and that the slew bearing extends about this jack-up leg.

The crane 10, in particular the boom 20, is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a front jack-up leg 5 in the parking position. The boom 20 is the supported on a boom rest 80 of the vessel.

The boom has a main boom structure 21 having a left-hand boom leg 22 and a right-hand boom leg 23. Each of the two boom legs 22, 23 has a proximal end portion that is pivotally connected to the left-hand connector 13a and to the right-hand hand connector 13b, respectively.

Each boom leg 22, 23 has a length of at least 60 meters, e.g. between 80 and 140 meters, here about 120 meters.

Each boom leg 22, 23 is embodied as a hollow box structure, here a latticed hollow box structure. Each leg 22, 23 has a cross section defined by an inner side face and multiple further faces.

The inner side faces of the left-hand boom leg 22 and the right-hand boom leg 23 are spaced from one another to form a clearance between the boom legs 22, 23 along the length of the main boom structure 21. The main boom structure 21 comprises, distributed over the length thereof, multiple cross members 24, 25, 26, 27 interconnecting the left-hand and right-hand boom legs 22, 23.

The two boom legs 22, 23 each have a proximal section 22a, 23a extending from the proximal end portion thereof and a central section 22b, 23b adjoining the proximal section, as well as a distal section 22c, 23c adjoining the central section.

Each of the boom legs has a distal section 22c, 23c with a distal end 22d, 23d that is remote from the proximal end portion of the boom leg.

In the depicted embodiment, the proximal sections 22a, 23a are parallel to one another.

In the depicted embodiment, the central sections 22b, 2b converge towards one another in the direction towards the distal sections 22c, 23c.

The cross member 24 interconnects the boom legs in proximity of the proximal ends.

The cross member 25 interconnects the boom legs where the proximal section 22a, 23a and central section 22b, 23b adjoin.

The cross member 26 interconnects the boom legs where the central section 22b, 23b and distal section 22c, 23c adjoin.

The boom 20 further has one extensible boom structure 30. This extensible boom structure 30 is slidably mounted between the distal sections 22c, 23c of the boom legs of the main boom structure 21, so as to be movable between a retracted position and an extended position in the direction of the length of the main boom section. This is best shown in figures 4a, b and 5a, b.

The extensible boom structure 30 is over at least a major portion of the length thereof, e.g. over at least 75% thereof, embodied as a hollow box structure, see also figure 6.

In more detail, the boom structure 30 has a rectangular cross section hollow box structure, here, as preferred, a latticed hollow box structure, with a top face 31 , a bottom face 32, and opposed side faces 33, 34. The side faces 33, 34 of the extensible boom structure each extend adjacent a corresponding inner side face of one of the two distal sections. These pairs of side faces are parallel to one another and extend in the longitudinal direction of the boom.

The extensible boom structure 30 is extendable and retractable over a range of at least 10 meters relative to the main boom structure, e.g. over at least 20 meters, e.g. between 20 and 40 meters, here over about 30 meters.

Figure 6 shows that the distal sections 22c, 23c are interconnected by the cross members 26, 27, of which member 27 is located in proximity of the distal ends 22d, 23d. These cross members in the distal region of the boom 20 are configured to allow for extending and retracting motions of the extensible boom section 30.

The extensible boom structure 30 is provided with a boom head 35 at a tip end of the extensible boom structure. In practice, this boom head 35 can be embodied as a welded structure of steel plates with reinforcements, etc.

In figures 1 - 3, it is shown that the variable length luffing system extends from the luffing winch to the boom head 35 on the extensible boom structure 30.

In figures 1 and 3, it is shown that main hoisting cable 51 extends from the main winch 50 to a main cable sheave assembly 52 on the boom head 35. An main load connector, e.g. a main crane hook 53, is suspended by means of cable 51 from the sheave assembly 52 on the boom head. If desired, multiple main hoisting winches, cables, and main load connectors, e.g. two main hoisting systems or possible three main hoisting systems, can be provided.

It is illustrated that the one or more main cables 51 extend longitudinally through the extensible boom structure 30.

The cross member 26 that is arranged at the join of the proximal section and central section of each boom leg is located at a rear side of the front jack-up leg 5 when in the parking position.

In the retracted position thereof, an inner end of the extensible boom structure 30 is located in proximity of the cross member 26 where the proximal section and central section adjoin. The distal sections 22c, 23c are each embodied as a latticed hollow box structure, each have an inner side face with parallel upper and lower chords interconnected by lacing members in the plane of the inner side face.

The cross members 26 and 27, at least cross member 27 that is located in proximity of the distal ends comprises trusses 27a that are arranged in a plane between the upper chords and trusses 27b arranged in a plane between the lower chords.

The extensible boom structure 30 is over at least a major portion of the length thereof, e.g. over at least 75% thereof, embodied as a hollow box structure having a rectangular cross section of a width of at least 6 meters and a height of at least 3 meters.

The superstructure 12 is provided with a gantry 14a thereon, on which a luffing cable sheave assembly 15 is mounted, guiding a luffing cable 41 extending from the luffing winch 40 to the boom head 35.

As preferred, the luffing system comprises:

- two luffing winches 40 on the superstructure 12; and

- two luffing cables 41, each driven by a respective luffing winch 40, said luffing cables extending spaced from one another, here parallel to one another, from luffing cable sheave assemblies 15 mounted on the superstructure, here on gantry 14a thereof, to respective luffing cable connectors 42 on the boom head 35 that are spaced apart from another in a width direction of the extensible boom structure 30, here arranged on opposite sides of the boom head seen in width direction.

The crane 10 comprises an extension mechanism comprising an extension winch 60, a winch driven extension cable 61 , and an extension cable sheave system with multiple sheaves 62, 63. The extension mechanism is configured to engage on the extensible boom structure 30 so as to provide an extension motion thereof. In embodiments, retraction of the extensible boom structure is caused by the mass of the extensible boom structure whilst the boom is upwardly oriented, so that the structure 30 sinks under its mass between the distal sections of the main structure 21.

The crane comprises a locking mechanism configured to lock the extensible boom mechanically to the distal sections in at least the retracted and extended position thereof. As will be appreciated, the vessel and crane are very suitable for the hoisting of an offshore wind turbine component, e.g. for installation and/or maintenance of an offshore wind turbine.

Figures 7 and 8 show the jack-up type offshore vessel provided with another example of a crane according to the invention. In figure 7 the extensible boom structure is retracted and in figure 8 extended.

A main difference with the crane described with reference to figures 1 - 6 lies in the design of the luffing system. Whilst the crane of figures 7, 8 still has two luffing winches 40 on the superstructure and two spaced apart luffing cables 41, each driven by a respective luffing winch, these luffing cables now do not extend to the boom head 35. Instead, these luffing cables extend to respective luffing cable connectors 42 on the distal sections 22c, 23c of the boom legs, here at the very distal end thereof.

A further difference is the provision of a stay mechanism 70, having, for each of the two boom legs 22, 23, a fixed length stay 71 extending from an anchoring member 72 on the boom leg arranged in proximity of the proximal end of the boom leg to a top end of a strut 73 that extends upward from the distal section of the boom leg. The mechanism 70 further has a variable length stay 74, that extends from the top end of the strut 73 to the boom head 35 on the extensible structure 30. As can be seen, the variable length stay 74 allows for extension and retraction of the extensible boom structure. Preferably, the variable length stay comprises two stay cable arrangements, in the same plane as the corresponding fixed length stay. In embodiments, each variable length stay comprises a stay cable, a system of sheaves, and a stay cable winch to vary the effective length of the stay between the end of the strut and the boom head.

Claims

C L A I M S

1. Offshore vessel crane (10) configured for mounting on an offshore vessel (1), for example for use in the handling of one or more offshore wind turbine components, e.g. for installation and/or maintenance of an offshore wind turbine, the crane comprising:

- a base structure (11) adapted to be mounted on the vessel, e.g. for fixation to the hull of the vessel;

- a revolving superstructure (12) slewable on a slew bearing about a slew axis relative to the base structure, the superstructure being provided with:

- a boom connection member comprising a left-hand connector (13a) and a right-hand hand connector (13b) at a distance of each other, together defining a horizontal boom pivot axis (14);

- a boom (20) having a longitudinal axis, wherein the boom has an inner end connected to the left-hand connector and to the right-hand connector of the boom connection member, so that the boom is pivotal up and down about the boom pivot axis (14) which is perpendicular to the longitudinal axis of a boom;

- a luffing device for pivoting the boom up and down, comprising a luffing winch (40) and a variable length luffing system (41);

- a main hoisting system for hoisting a load, comprising a main winch (50) and an associated main hoisting cable (51); wherein the boom has a main boom structure having a left-hand boom leg (22) and a right- hand boom leg (23), each of said boom legs having a proximal end portion pivotally connected to the left-hand connector (13a) and to the right-hand hand connector (13b), respectively, wherein each boom leg (22,23) has a length of at least 60 meters, e.g. between 80 and 140 meters, wherein each boom leg is embodied as a hollow box structure, preferably a latticed hollow box structure, having a cross section defined by an inner side face and multiple further faces, wherein the inner side faces of the left-hand and right-hand boom legs (22,23) are spaced from one another to form a clearance between the boom legs along the length of the main boom structure, wherein the main boom structure (21) comprises, distributed over the length thereof, multiple cross members (24,25,26,27) interconnecting the left-hand and right-hand boom legs

(22.23), wherein the boom legs (22,23) each have a distal section (22c, 23c) with a distal end (22d,23d) remote from the proximal end portion, wherein the boom further comprises an extensible boom structure (30), said extensible boom structure being slidably mounted between the distal sections (22c, 23c) of the boom legs

(22.23) of the main boom structure (21), so as to be movable between a retracted position and an extended position in the direction of the length of the main boom section, wherein the extensible boom structure (30) is over at least a major portion of the length thereof, e.g. over at least 75% thereof, embodied as a hollow box structure, e.g. a rectangular cross section hollow box structure, preferably a latticed hollow box structure, with a top face (31), a bottom face (32), and opposed side faces (33,34), said side faces (33,34) of the extensible boom structure extending adjacent the inner side faces of the distal sections (22c, 23c), which side faces are parallel to one another and extend in the longitudinal direction of the boom, wherein the extensible boom structure (30) is extendable and retractable (60,61,62,63) over a range of at least 10 meters relative to the main boom structure (21), e.g. over at least 20 meters, e.g. between 20 and 40 meters, wherein the distal sections (22c, 23c) are interconnected by at least one of said cross members (27) that is located in proximity of the distal ends, said at least one cross member (27)being configured to allow for said extending and retracting motions of the extensible boom structure (30), wherein the extensible boom structure (30) is provided with a boom head (35) at a tip end of the extensible boom structure; wherein the main hoisting cable (51) extends from the main winch (50) to a main cable sheave assembly (52) on the boom head (35).

2. Offshore vessel crane according to claim 1, wherein the two boom legs (22,23) each have a proximal section (22a, 23a) extending from the proximal end portion thereof and a central section (22b, 23b) adjoining the proximal section, the distal section (22c, 23c) of the boom leg adjoining the central section, wherein the proximal sections (22a, 23a) are parallel to one another, wherein the central sections (22b, 23b) converge towards one another in the direction towards the distal sections, and wherein a cross member (25) interconnects the boom legs where the proximal section and central section adjoin, and wherein a cross member (26) interconnects the boom legs where the central section and distal section adjoin.

3. Offshore vessel crane according to claim 2, wherein in the retracted position thereof, an inner end of the extensible boom structure (30) is located in proximity of the cross member (26) where the central section and the distal section adjoin.

4. Offshore vessel crane according to any one or more of claims 1 - 3, wherein the distal sections (22c, 23c) are each embodied as a latticed hollow box structure, each have an inner side face with parallel upper and lower chords interconnected by lacing members in the plane of the inner side face, wherein the cross member in proximity of the distal ends comprises trusses that are arranged in a plane between the upper chords and trusses arranged in a plane between the lower chords.

5. Offshore vessel crane according to any one or more of claims 1 - 4, wherein the extensible boom structure (30) is over at least a major portion of the length thereof, e.g. over at least 75% thereof, embodied as a hollow box structure having a rectangular cross section of a width of at least 6 meters and a height of at least 3 meters.

6. Offshore vessel crane according to any one or more of claims 1 - 5, wherein the superstructure^) is provided with a gantry (14a) thereon, on which a luffing cable sheave assembly (15) is mounted, guiding a luffing cable (41).

7. Offshore vessel crane according to any of claims 1 - 6, wherein the variable length luffing system (41) extends from the luffing winch (40) to the boom head (35).

8. Offshore vessel crane according to any one or more of claims 1 - 6, wherein the variable length luffing system (41) extends from the luffing winch (40) to the distal sections, e.g. to the distal ends (22d,23d) thereof, wherein, preferably, the boom 20 is further provided with a stay mechanism, having, for each of the boom legs, a fixed length stay (71) extending from an anchoring member (72) on the boom leg (22,23) arranged in proximity of the proximal end of the boom leg to a top end of a strut (73) that extends from the distal section (22c, 23c) of the boom leg, and with a variable length stay (74), that extends from said top end of the strut to the boom head (35).

9. Offshore vessel crane according to any one or more of claims 1 - 8, wherein the luffing system comprises:

- two luffing winches (40) on the superstructure; and

- two luffing cables (41), each driven by a respective luffing winch, said luffing cables extending spaced from one another, e.g. parallel to one another, from luffing cable sheave assemblies (15) mounted on the superstructure, e.g. on a gantry (14a) thereof, to respective luffing cable connectors (42) on the boom head or on the distal sections of the boom legs, which luffing cable connectors (42) are spaced apart from another in a width direction of the boom, e.g. arranged on opposite sides of the boom head (35) seen in width direction.

10. Offshore vessel crane according to any one or more of claims 1 - 9, wherein the crane comprises an extension mechanism for the extensible boom structure comprising an extension winch (60), a winch driven extension cable (61), and an extension cable sheave system with multiple sheaves (62,63), wherein said extension mechanism is configured to engage on the extensible boom structure (30) so as to provide an extension motion thereof, preferably retraction of the extensible boom structure being caused by the mass of the extensible boom structure whilst the boom is upwardly oriented.

11. Offshore vessel crane according to any one or more of claims 1 - 10, wherein the crane (10) comprises a locking mechanism configured to lock the extensible boom mechanically to the distal sections in at least the retracted and extended position thereof.

12. Offshore vessel comprising an offshore vessel crane (10) according to one or more of the preceding claims.

13. Jack-up type offshore vessel (1) comprising:

- a buoyant hull (2) with a main deck (3),

- at least three jack-up legs (4,5),

- a plurality of elevating units (6), each associated with a respective jack-up leg, adapted to move the respective jack-up leg vertically relative to the hull and to bring the vessel in an operational position wherein the legs engage the seabed and the hull is above water level,

- an offshore vessel crane according to one or more of the preceding claims 1 - 11.

14. Jack-up type offshore vessel according to claim 13, wherein the crane (10) is an around-the-leg crane, wherein a jack-up leg of the vessel extends through the revolving superstructure and the slew bearing extends about the jack-up leg.

15. Jack-up type offshore vessel according to claim 13 or 14, wherein the crane (10) is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a jack-up leg in the parking position, e.g. the vessel having a boom rest (80) on which the boom is parked in a substantially horizontal orientation.

16. Jack-up type offshore vessel according to claim 13, wherein the crane (10) is an around-the-leg crane, wherein a jack-up leg of the vessel extends through the revolving superstructure () and the slew bearing extends about the jack-up leg, and wherein the crane is configured for an over-the-leg parking position, wherein the two boom legs are located on opposite sides of a jack-up leg in the parking position, e.g. the vessel having a boom rest on which the boom is parked in a substantially horizontal orientation.

17. Jack-up type offshore vessel according to claim 13, wherein the vessel (1) has two aft jack-up legs and two front jack-up legs, wherein a rear jack-up leg (4) extends through the revolving superstructure (12) and the slew bearing extends about said jack-up leg, and wherein the crane (10) is configured for an over-the-leg parking position, wherein the two boom legs (22,23) are located on opposite sides of a front jack-up leg (5) in the parking position, e.g. wherein a cross member (25) arranged at the join of the proximal section and central section of each boom leg is located at a rear side of the front jack-up leg when in the parking position.

18. Method for hoisting an offshore wind turbine component, e.g. for installation and/or maintenance of an offshore wind turbine, wherein use is made of an offshore vessel crane (10) and/or an offshore vessel (1) according to any one or more of claims 1 - 17.