Vessel crane boom suspension with displaceable sheave block for different operations

Abstract

A vessel crane (1) and a method for raising and lowering a boom (3) of the vessel crane, in which a boom hoist (30) is provided for pivoting the boom about a boom pivot axis (03). The boom hoist (30) has a boom hoist winch (31) for hauling in and paying out a luffing wire (32) to and fro a boom suspension (6) being positioned between a gantry apex (43) of a gantry (4) and a head structure (302) of the boom. In the boom suspension (6), the luffing wire is configured in a multiple fall arrangement (60) in which a length of the luffing wire (32) is adjustable by displacing at least one detachable sheave block (63) from a hoist position (H) to carry out a hoisting operation to a gantry tilt position (GT) to carry out a raising or lowering of the gantry (4).

Description

[0001] P7638PCOO / KHO

[0002] Title: Vessel crane boom suspension with displaceable sheave block for different operations.

[0003] The invention relates to a vessel crane, in particular a tub mounted crane, and a method for raising and lowering a boom of a vessel crane.

[0004] EP3.825.274 in the name of Liebherr discloses an offshore crane including gantry formed by a pivotable front framework and a pivotable rear framework for elevating and lowering a boom. The gantry has a gantry apex which determines a total crane height of the crane for passing an obstacle.

[0005] The rear framework of the gantry is collapsible to reduce this height. The rear framework of the gantry is built out of a lower framework section and an upper framework section which are interconnected by a rotary joint. The rear framework is here called an erecting trestle. A relative pivotal movement of the sections is operable by a retracting mechanism. By retracting the lower framework section, the framework sections pivot and the rotary joint moves in a direction opposite the boom.

[0006] Another embodiment of a collapsible gantry of an offshore tub mounted crane is disclosed in WO 2020 / 204719 in the name of Itrec. In this embodiment, the gantry also has a collapsible rear framework out of two framework sections. Here, the rear framework is collapsible in a boom direction.

[0007] During the lowering of the gantry, the boom is maintained in a stable sailing position. The boom may be supported by a boom rest during the lowering of the gantry. The gantry apex of the vessel crane is then lowered by a payout of luffing wire from a boom hoist winch, also called a luffing winch.

[0008] The luffing winch has a large winch capacity which is determined to held a luffing wire length which is necessary for hoisting operations and for lowering the gantry to a lowered position. The total required large winch capacity of the boom hoist winch is only used in incidental situations in which the gantry has to be lowered. A total crane height might for example be reduced to pass a bridge structure, like the Great Belt Bridge of Denmark. It is a drawback that such incidental situations have a considerable impact on a total winch capacity to be implemented on board of a crane vessel. A known solution to reduce a required luffing winch capacity is to apply an extension to a multiple file arrangement of rigged luffing wire of a boom suspension between a gantry apex and a head structure of a boom.

[0009] Regarding the above-mentioned prior art, it is remarked that any discussion of documents, acts, materials, devices, articles or the like included in the present specification is for the purpose of providing a context for the present invention, and is not to be taken as an admission that any such matters form part of the prior art or were common general knowledge in the field relevant to the present invention before the priority date of each claim of this application.

[0010] The general object of the present invention is to at least partially eliminate the above mentioned drawback and / or to provide a usable alternative. More specific, it is an object of the invention to provide a vessel crane provided with a collapsible gantry for reducing a total crane height in which a required luffing wire capacity of a luffing winch may be reduced.

[0011] According to the invention, this object is achieved by a vessel crane according to claim 1.

[0012] According to the invention, a vessel crane is provided which is suitable for transferring a hoist load to and fro a marine vessel, a barge, a jacket or another structure. The vessel crane comprises a substructure on which a superstructure is mounted. The superstructure comprises operating machinery to carry out hoisting operations. In particular, the vessel crane is a tub mounted crane for elevating and rotating a hoist load, in which the tub mounted crane comprises a substructure formed by a tub on which a superstructure is mounted.

[0013] The superstructure comprises a crane house, a gantry on the crane house and a longitudinally extending boom. Here, in this application, gantry means a crane frame of the superstructure which crane frame is arranged for supporting the boom. The boom is at a proximal end pivotally connected to the crane house and has a head structure at a distal end. The crane house defines a rear region of the vessel crane and a distal end of the boom defines a front region of the vessel crane.

[0014] The crane house is rotatably connected to the substructure to allow a rotation of the superstructure about a vertical axis. In other words, the crane house is rotatably connected to the substructure for allowing a slew motion of the superstructure relative to the substructure. The crane house may include a cab where an operator manoeuvres the crane’s controls. The crane house comprises a boom connector for connecting the boom to the crane house. The boom connector defines a horizontal boom pivot axis.

[0015] The superstructure comprises a boom for supporting a hoist load. The boom has a longitudinal axis which extends from a proximal end portion to a distal end portion. The distal end portion includes a head structure. The boom is pivotally connected to the crane house via the boom connector so that the boom is pivotal about the boom pivot axis. The proximal end portion of the boom is pivotally connected to the boom connector of the crane house. Herewith, the boom is pivotable about the boom pivot axis.

[0016] The gantry, also called a luffing frame, is arranged to support the boom. The gantry is collapsible from a raised position to a lowered position for reducing a total crane height during transport. The gantry comprises a front framework and a rear framework. The gantry is mounted on the crane house. In the raised position, at a base, also called a lower end, the front framework and the rear framework are connected to the crane house. At an upper end, the front framework and rear framework are connected to each other by a top pivot. The upper ends of the front and rear framework form an apex of the gantry. Seen in a side view, the gantry may have an upside-down V-shape in which the V-legs are formed by the front framework and rear framework.

[0017] Further, the superstructure comprises a hoisting system for hoisting the hoist load. The hoisting system comprises at least one hoisting winch. In particular, the hoisting system comprises a hoisting winch assembly including a plurality of hoisting winches. An associated hoisting wire extends from the hoisting winch to the head structure of the boom. The hoisting winch may be provided at the proximal end portion of the boom, like in a Liebherr crane, or at the crane house. Preferably, the at least one hoisting winch is positioned inside the crane house.

[0018] Further, the superstructure comprises a boom hoist for raising and lowering the boom by pivoting the boom about a boom angle. The boom is pivotable in a vertical plane about the horizontal boom pivot axis to adjust a hoisting height of the crane. The boom hoist comprises at least one luffing winch for hauling in or paying out a luffing wire to respectively raise or lower the boom. Further, the boom hoist comprises a boom suspension for supporting the boom. The boom suspension extends between the gantry apex and the head structure of the boom.

[0019] The boom suspension includes a luffing wire in a multiple fall arrangement. The multiple fall arrangement is formed by a luffing wire which is reeved along sheaves being positioned at a side of the gantry apex and along sheaves being positioned at a side of the boom. The multiple fall arrangement of luffing wire may extend about a whole distance in between the gantry apex and the head structure of the boom, or about a portion of the distance.

[0020] The luffing wire has a luffing wire length which is rigged between a gantry sheave block and a boom sheave block. The gantry sheave block has a sheave frame which is provided with at least one sheave. In particular, the sheave frame is provided with multiple fixed sheaves. The gantry sheave block is positioned at a side of the gantry apex. The boom sheave block has a sheave frame which is provided with at least one sheave. In particular, the sheave frame is provided with multiple fixed sheaves. The boom sheave block is positioned at a side of the head structure of the boom. At a side of means that the gantry sheave block is not necessarily positioned at the gantry apex, but may be spaced at a distance from the gantry apex by an extension. Likewise, the boom sheave block is not necessarily positioned at the boom, but may be spaced at a distance from the boom by an extension, like pendant links or cables.

[0021] According to the invention, an improvement is provided in that the boom suspension further comprises at least one detachable sheave block. The at least one detachable sheave block allows a shortening of the luffing wire length in the multiple fall arrangement. The detachable sheave block has a sheave frame which is provided with at least one sheave. In particular, the sheave frame is provided with multiple fixed sheaves. The detachable sheave block is arranged to adapt the multiple fall arrangement of the boom suspension by displacing the at least one detachable sheave block from a hoist position to a gantry tilt position. In the hoist position, the at least one detachable sheave block is positioned to carry out a hoisting operation. In the gantry tilt position, the at least one detachable sheave block is positioned to carry out a raising or lowering of the gantry.

[0022] The at least one detachable sheave block can be positioned at the gantry tilt position to shorten a total length of luffing wire in the multiple fall arrangement. Beneficially, by displacing the at least one detachable sheave block for example away from the boom sheave block and closer to the gantry sheave block, the total length of luffing wire in the boom suspension can be shortened and wound onto the luffing winch. Subsequently a lowering operation of the gantry can be started by paying out luffing wire to let down the gantry.

[0023] In an embodiment of the vessel crane, the at least one detachable sheave block is in the hoist position connectable to the boom sheave block. In preparation of a gantry lowering operation, the at least one detachable sheave block is released from the boom sheave block and displaced to a gantry tilt position being a position situated closer to the gantry sheave block to obtain a shortened luffing wire length in the multiple fall arrangement of the boom suspension. In an embodiment of the vessel crane, the at least one detachable sheave block may be transferable along a path extending from the hoist position near or at the boom sheave block to the gantry tilt position being closer to the gantry sheave block or vice versa from a hoist position near or at the gantry sheave block to the gantry tilt position near or at the boom sheave block. Beneficially, an amount of falls of the multiple fall arrangement of the boom suspension can be reduced by transferring the at least one detachable sheave block from one side to an opposite side of the multiple fall arrangement. By reducing the amount of force, a length of luffing wire in the multiple fall arrangement is shortened.

[0024] In an embodiment of the vessel crane, the at least one detachable sheave block is transferable along a path between the gantry sheave block and the boom sheave block. In the gantry tilt position, the at least one detachable sheave block may be connectable to the gantry sheave block. The at least one detachable sheave block may be transferred along a path in an imaginary plane defined by the multiple fall arrangement. Beneficially, this path may remain free from any obstacle during a movement of the at least one detachable sheave block. By connecting the at least one detachable sheave block to the gantry sheave block in the gantry tilt position, a length of luffing wire may be shortened. In addition, the multiple fall arrangement may be adapted to a lower amount of luffing wire falls. A fall arrangement of rigged luffing wire may for example be reduced from 64 to 44 falls.

[0025] In an embodiment of the vessel crane, the at least one detachable sheave block is transferable along a path extending along the boom. In particular, the path extends in a longitudinal direction along the boom. In particular, the at least one detachable sheave block is connectable in the gantry tilt position to the boom at a boom position at a distance from the boom sheave block. The boom position may be located at the proximal end portion of the boom. An auxiliary block for connecting the at least one detachable sheave block may be positioned at the boom position between the boom pivot and the boom sheave block. In the gantry tilt position, the at least one detachable sheave block is connectable to the auxiliary block. The auxiliary block may comprise a connector member being complementary to a connector member of the at least one detachable sheaf block.

[0026] In an embodiment of the vessel crane, the at least one detachable sheave block is transferable from the hoist position along a path extending along the boom to a gantry tilt position at the crane house or the gantry. In particular, the at least one detachable sheave block is transferable to a gantry tilt position at or near the base of a front framework of the gantry. Preferably, the at least one detachable sheave block is transferable to a gantry tilt position which is substantially in alignment with a pivot axis of the front framework. The at least one detachable sheave block may be connectable to the base of the front framework. Beneficially, when tilting the front framework, a substantially stationary situation is obtained regarding a portion of the luffing wire extending along the pivot axis.

[0027] In an embodiment of the vessel crane, the at least one detachable sheave block is provided with a connector member. The connector member is configured to provide a releasable connection between parts. At least one of the gantry sheave block and the boom sheave block is provided with a complimentary connector member. The connector member and the complimentary connector member are configured to be attached to each other or to be released from each other. Herewith, the at least one detachable sheave block is connectable to one or both the gantry sheave block and the boom sheave block.

[0028] In an embodiment of the vessel crane, the at least one detachable sheave block is provided with a first connector member at one side and a second connector member at an opposite side for connecting the at least one detachable sheave block at opposite sides to an associate complimentary connector member. Beneficially, the at least one detachable sheave block may be transferable to and fro and may be connectable to both the gantry sheave block and the boom sheave block.

[0029] In an embodiment of the vessel crane, the sheave frame of the at least one detachable sheave block, gantry sheave block and boom sheave block is provided with a positioning member. The positioning member is configured to position the sheave frame to provide a proper connection with one of the at least one detachable sheave block, gantry sheave block or a boom sheave block.

[0030] In an embodiment of the vessel crane, the boom suspension comprises a transfer winch for transferring the detachable sheave block. The transfer winch is configured to pay out and haul in a transfer wire. The at least one detachable sheave block is connected to the transfer wire. The transfer winch may be positioned at the gantry sheave block, in particular at the gantry apex to lower and elevate the at least one detachable sheave block to and fro a position at a proximal end portion of the boom to shorten the luffing wire.

[0031] In an embodiment of the vessel crane, the transfer winch is positioned at the boom sheave block to provide a guidance when the at least one detachable sheave block is transferred from the boom sheave block to the gantry sheave block. By paying out the transfer wire, while keeping the transfer wire under tension, the at least one detachable sheave block can be properly transferred to a gantry tilt position.

[0032] In an embodiment of the vessel crane, the transfer winch is positioned at the distal boom end. The transfer winch is positioned at the head structure of the boom. From this position, the transfer winch may provide a guidance during a transfer of the at least one detachable sheave to a gantry tilt position closer to the gantry sheave block.

[0033] The multiple fall arrangement of the boom suspension may extend about a whole or a portion of a distance in between the gantry apex and the head structure of the boom. In an embodiment of the vessel crane, the boom suspension may comprise an extension for extending the multiple fall arrangement. The multiple fall arrangement is connected to the extension. The extension may for example include a chain or a rod structure. Preferably, the extension is positioned between the multiple fall arrangement and the gantry apex and wherein the at least one detachable sheave block is connectable to the boom sheave block. Beneficially, the at least one detachable sheave block may be displaceable away from the boom sheave block in either a direction of the gantry sheave block or a proximal end portion of the boom to shorten the luffing wire.

[0034] In an embodiment of the vessel crane, the gantry comprises a front framework and a rear framework which each have an integral rigid body. The front framework and the rear framework are each non-sectioned, i.e. a single piece framework. The framework may be an integral part for conducting forces which beneficially provides a robust structure to carry a load in a hoisting operation. A total crane height reduction may be obtained by lowering the gantry apex by lowering the rear framework after disconnecting the base of the rear framework from the crane house. Preferably, the base of the rear framework is guided during its displacement by a link framework.

[0035] In an embodiment of the vessel crane, the gantry comprises a front framework which is pivotal connected by a front base mount to the crane house and a foldable rear framework including a first rear framework section and a second rear framework section being connected to each other by a pivot joint. The front framework is tiltable about a base pivot. Preferably, the front framework is tiltable in a direction away from the boom. The rear framework may be collapsed by folding the first and second rear framework sections. The rear framework sections may be folded in a direction away from the front framework. Alternatively, the rear framework sections may be folded in a direction towards the front framework as for example disclosed in W02020 / 204719. Further, the invention relates to a crane vessel comprising at least one vessel crane, in particular at least one tub mounted crane, according to the invention.

[0036] Further, the invention relates to a method for reducing a total crane height by lowering a gantry of a crane, wherein use is made of a vessel crane according to the invention. The vessel crane comprises a boom hoist including a boom suspension having a luffing wire originating from at least one luffing winch and reeved in a multiple fall arrangement between a gantry sheave block, a boom sheave block and at least one detachable sheave block. The method comprises a step of:

[0037] - shortening a total length of luffing wire in the multiple fall arrangement of the boom suspension by detaching and displacing the at least one detachable sheave block from a hoist position wherein the at least one detachable sheave block is positioned for carrying out a hoisting operation to a gantry tilt position wherein the at least one detachable sheave block is positioned for carrying out a raising or lowering of the gantry;

[0038] - winding luffing wire onto the luffing winch; and

[0039] - paying out luffing wire for tilting the gantry of the vessel crane. Luffing wire is paid out when lowering the gantry of the vessel crane.

[0040] The luffing wire can be wound on the luffing winch while at the same time displacing the at least one detachable sheave block.

[0041] Preferably, the luffing wire is in a preparational step wound on the luffing winch and thereafter in a next step paid out for tilting the gantry of the vessel crane. Alternatively, the luffing wire may be shortened by a displacement of the at least one detachable sheave block while simultaneously tilting the gantry.

[0042] In an embodiment of the method, the method comprises a step of reducing an amount of falls of a multiple fall arrangement of a boom suspension by transferring the at least one detachable sheave block along a path extending from a hoist position to a gantry tilt position. Preferably, the at least one detachable sheave block is transferred from a gantry sheave block to a boom sheave block or vice versa. The multiple fall arrangement of luffing wire has a higher amount of falls in the hoist position than in the gantry tilt position.

[0043] Thus, a vessel crane and a method for raising and lowering a boom of the vessel crane is provided, in which a boom hoist is provided for pivoting the boom about a boom pivot axis. The boom hoist has a boom hoist winch for hauling in and paying out a luffing wire to and fro a boom suspension being positioned between a gantry apex of a gantry and a head structure of the boom. In the boom suspension, the luffing wire is configured in a multiple fall arrangement in which a length of the luffing wire is adjustable by displacing at least one detachable sheave block from a hoist position H to carry out a hoisting operation to a gantry tilt position GT to carry out a raising or lowering of the gantry.

[0044] P37003NL00 / KHG

[0045] In an aspect, the invention relates to a tub mounted crane and a method for reducing a total crane height of a tub mounted crane.

[0046] One of world’s largest crane vessels is known as the Saipem 7000. This crane vessel is configured for heavy lifting. This crane vessel has two fully revolving bow mounted cranes which are each capable of lifting 7000 tonnes. The cranes have each a substructure formed by a pedestal, a so-called tub, and a revolving superstructure provided with operating machinery.

[0047] The Saipem 7000 has a semi-submersible design which allows it to partially submerge in water. By pumping water in or out of ballast tanks, the vessel can adjust its height in the water. This height adjustment capability serves to improve stability during heavy lifting operations and in case provides an ability to pass under bridges or other obstacles during transit. In particular situations, this height adjustment is not sufficient. For example, to pass through the Panama Canal or the Bosporus Strait, it is desired to further reduce the total height of the cranes of the Saipem 7000.

[0048] Several similar crane structures are known from the prior art which allow a lowering of a gantry of a vessel crane. By lowering the gantry, a total crane height during travelling is reduced.

[0049] EP3.825.274 in the name of Liebherr discloses an offshore crane including an A-shaped gantry formed by a pivotable front framework and a pivotable rear framework for elevating and lowering a boom. The rear framework is here called an erecting trestle. The gantry has a total height which determines a maximum height of the crane for passing an obstacle.

[0050] The rear framework of the gantry is collapsible to reduce this maximum height. The rear framework of the gantry is built out of a lower framework section and an upper framework section which are interconnected by a rotary joint. A relative pivotal movement of the sections is operable by a retracting mechanism. By retracting the lower framework section, the framework sections pivot and the rotary joint moves in a direction opposite to the boom. In an erected position, the rotary joint is locked by a lockage which is formed by a hydraulic cylinder in order to fixate the upper and lower framework sections.

[0051] Another embodiment of a collapsible gantry of an offshore tub mounted crane is disclosed in WO 2020 / 204719 in the name of Itrec. In this embodiment, the gantry also has a collapsible rear framework out of two framework sections. Here, the rear framework is collapsible in a boom direction.

[0052] A drawback of these collapsible gantries is that despite the presence of the lockage, the rotary joint between the sections of the rear framework reduces a robustness of the gantry. The rotary joint forms a weakening of the gantry and should be sufficient strengthened by the lockage.

[0053] Regarding the above-mentioned prior art, it is remarked that any discussion of documents, acts, materials, devices, articles or the like included in the present specification is for the purpose of providing a context for the present invention, and is not to be taken as an admission that any such matters form part of the prior art or were common general knowledge in the field relevant to the present invention before the priority date of each clause of this application.

[0054] The general object in this aspect of the present invention is to at least partially eliminate the above mentioned drawback and / or to provide a usable alternative. More specific, it is an object of the invention to provide a reduction of a total crane height without or minimally compromising a robustness of the crane.

[0055] According to the invention, this object is achieved by a vessel crane, in particular a tub mounted crane, as defined in clause 1.

[0056] According to the invention, a vessel crane is provided which is suitable for transferring a hoist load to and fro a marine vessel, a barge, a jacket or another structure. The vessel crane comprises a substructure on which a superstructure is mounted. The superstructure comprises operating machinery to carry out hoisting operations. In particular, the vessel crane is a tub mounted crane for elevating and rotating a hoist load, in which the tub mounted crane comprises a substructure formed by a tub on which a superstructure is mounted.

[0057] The superstructure comprises a crane house, a gantry on the crane house and a longitudinally extending boom which is at a proximal end pivotally connected to the crane house. The crane house defines a rear region of the vessel crane and a distal end of the boom defines a front region of the vessel crane. The crane house is rotatably connected to the substructure to allow a rotation of the superstructure about a vertical axis. In other words, the crane house is rotatably connected to the substructure for allowing a slew motion of the superstructure relative to the substructure.

[0058] The crane house comprises a boom connector for connecting the boom to the crane house. The boom connector defines a horizontal boom pivot axis.

[0059] The crane house further comprises a gantry mount including a rear base mount and a front base mount for mounting a gantry. The crane house may include a cab where an operator manoeuvres the crane’s controls.

[0060] The superstructure comprises a boom for supporting a hoist load. The boom has a longitudinal axis which extends from a proximal end portion to a distal end portion. The distal end portion includes a head structure. The boom is pivotally connected to the crane house via the boom connector so that the boom is pivotal about the boom pivot axis. The proximal end portion of the boom is pivotally connected to the boom connector of the crane house. Herewith, the boom is pivotable about the boom pivot axis.

[0061] The gantry, also called a luffing frame, is collapsible from a raised position to a lowered position for reducing a total crane height during transport. The gantry comprises a front framework and a rear framework. The gantry is mounted on the crane house. In the raised position, at a base, also called a lower end, the front framework and the rear framework are connected to the crane house to respectively the front base mount and rear base mount of the gantry mount. At an upper end, the front framework and rear framework are connected to each other by a top pivot. The upper ends of the front and rear framework form an apex of the gantry. Seen in a side view, the gantry may have an upside down V-shape in which the V-legs are formed by the front framework and rear framework.

[0062] Further, the superstructure comprises a boom hoist for raising and lowering the boom by pivoting the boom about a boom angle. The boom is pivotable in a vertical plane about the horizontal boom pivot axis to adjust a hoisting height of the crane. The boom hoist comprises at least one luffing winch for hauling in or paying out a luffing wire and a boom suspension which extends between the gantry apex and the head structure of the boom. The boom suspension includes a multiple fall arrangement of a rigged luffing wire. The multiple fall arrangement of luffing wire may extend about a whole length in between the gantry apex and the head structure of the boom, or about a length portion, wherein the multiple fall arrangement is connected to an extension. The extension may for example include a chain or a rod structure.

[0063] Further, the superstructure comprises a hoisting system for hoisting the hoist load. The hoisting system comprises at least one hoisting winch. In particular, the hoisting system comprises a hoisting winch assembly including a plurality of hoisting winches. An associated hoisting wire extends from the hoisting winch to the head structure of the boom. The hoisting winch may be provided at the proximal end portion of the boom, like in a Liebherr crane, or at the crane house. Preferably, the at least one hoisting winch is positioned inside the crane house.

[0064] According to the invention an improvement is provided in that the superstructure further comprises a lowering mechanism for lowering the gantry. The lowering mechanism is arranged to move the gantry between the raised position and the lowered position. The lowering mechanism comprises a link framework and a lock system.

[0065] The link framework is arranged for displacing the rear framework. At one end, the link framework is pivotally connected to the base of the rear framework of the gantry. At an opposite end, the link framework is pivotally connected to the crane house. In particular, the link framework has a first link pivot coupling the link framework to the base of the rear framework and the link framework has a second link pivot coupling the link framework to the crane house.

[0066] The link framework is rotatable in a vertical plane with respect to the crane house to displace the base of the rear framework such that the gantry lowers or raises. During a displacement, the link framework provides a guidance to the base of the rear framework. Herewith, the link framework is configured to guide a displacement of the base of the rear framework when lowering the gantry to obtain a reduction of a total crane height.

[0067] The lock system is arranged for locking the rear framework in position when the gantry is in the raised position. The lock system includes at least one lock member to lock or release the base of the rear framework to the rear base mount at the crane house. In a locked state, the rear framework is configured to carry out a hoisting operation. In the locked state, the base of the rear framework is locked in position relative to the crane house. In an unlocked state, the base of the rear framework is released and a displacement relative to the crane house is enabled to carry out a crane height reduction operation. In particular, in the unlocked state, the rear framework is displaceable in a direction away from the front framework to allow a lowering of the gantry. The base of the rear framework may be lowered and guided by the link framework along a back side of the crane house to obtain a required total crane height reduction of for example about 20m to allow a bridge passage of a crane vessel. Beneficially, by reducing the total crane height in this manner, a crane vessel provided with the tub mounted crane and having a crane height of more than 70m, e.g. about 85m crane height from a water line may be suitable to sail and pass a bridge like the Great Belt Bridge (which is in Danish called: Storebaeltsbroen) which bridge has a clearance of 65 metres below the bridge.

[0068] Considering the gantry, the lowering mechanism is advantageously configured to function in reducing a total crane height during travelling while not or minimally affecting a hoisting operation of the crane at a hoisting location. From a mechanical perspective, the gantry still has a same main configuration, no matter the availability of the lowering mechanism. The gantry is formed by the front and rear framework which may each be formed by a rigid body being at the base fixated to the crane house.

[0069] In comparison with prior art solutions for reducing a total crane height, the rear framework may have a framework body which is formed by one rigid body. This one rigid body determines the robustness of the rear framework. The body of the rear framework is not sectioned by a structurally weakening rotary joint as disclosed in EP3.825.274 in the name of Liebherr.

[0070] As the total crane height reduction is -seen from a structural perspective- independent from the hoisting operation, the incorporation of the lowering mechanism for lowering the gantry does not or hardly not negatively affect the robustness of the gantry during a hoisting operation. Regarding occurring forces which act on the gantry during the hoisting operation, the robustness of the gantry remains determined by the robustness of respectively the rear framework and the front framework which may each be integral parts and which are each at a base fixated to the crane house. Exerted forces acting on the gantry via the boom suspension are conducted via the base mounts of the front framework and the rear framework to the crane house. During a hoisting operation, the lowering mechanism, in particular the link framework has no load carrying function which beneficially allows a slim configuration of the link framework.

[0071] In an embodiment of the vessel crane, the rear framework has a framework body which is formed by one rigid body. The framework body may be non-sectioned, i.e. a single piece framework. The framework may be an integral part for conducting forces which beneficially provides a robust structure to carry a load in a hoisting operation. In an embodiment of the vessel crane, an assembly of the rear base mount and the base of the rear framework is formed by a pin-hole assembly. The arrangement of the pin-hole assembly may be beneficial in installation of the gantry and alignment of the rear framework relative to the front framework.

[0072] In an embodiment of the vessel crane, the link framework is connected to the base of the rear framework by a pin-hole configuration in which the hole is slotted. Beneficially, the slotted hole may prevent an over constrained structure. The slotted hole may overcome a possible misalignment between the link framework and the rear framework during a motion of the rear framework.

[0073] In an embodiment of the vessel crane, the second link pivot of the link framework is connected to a side wall of the crane house. In particular, the second link pivot is connected to a bottom region of the crane house. Preferably, at an inner side of the side wall, the crane house has a reinforcement structure at the location of the second link pivot.

[0074] In an embodiment of the vessel crane, the link framework includes a left and right link-leg. In particular, the link framework is H-shaped or may have a rectangular shape. Each link-leg is at one end pivotally connected to the base of the rear framework and at an opposite end pivotally connected to the crane house.

[0075] In an embodiment of the vessel crane, the lowering mechanism comprises an end stop for supporting the link framework when being placed in the lowered position of the gantry. Preferably, the end stop is mounted to the substructure, in particular to the tub of a tub mounted crane. The end stop may be positioned on an outer wall of the substructure. Preferably, at the end stop, the outer wall is reinforced by a reinforcement structure. Alternatively, the end stop may be mounted to the crane house. The positioning of the end stop onto an outer side of the substructure is however beneficial in counteracting occurring forces without for example compromising a slew bearing of the crane house.

[0076] In an embodiment of the vessel crane, the lock system comprises a lock member and a lock member actuator for actuating the lock member. In particular, the lock member is pin-shaped. The pin-shaped lock member is configured to fit into a hole at the base of the rear framework and to be received into a base mount hole, such that the lock member locks the base of the rear framework to the rear base mount. A pin-hole assembly is formed by the pin-shaped lock member and the holes of the rear base mount and the base of the rear framework. The lock member actuator may be a hydraulic cylinder for moving the lock member actuator. Preferably, the lock member is linearly movable between a retracted position in which the lock system is in an unlocked state and an extended position in which the lock system is in a locked state.

[0077] In an embodiment of the vessel crane, the base of the rear framework may comprise a fork end portion having a first fork leg and second fork leg which each including a fork hole for receiving the lock member of the lock system.

[0078] In an embodiment of the vessel crane, the lowering mechanism further comprises at least one tugger winch for tensioning the base mount of the rear framework. A pull force can be exerted by the at least one tugger winch to the rear framework to control its displacement during a gantry raising or lowering operation. The tensioning force may be exerted between the rear framework and the crane house in a direct manner or indirectly via the boom and I or the front framework. To obtain a predetermined span length of a tugger wire, the at least one tugger winch is preferably positioned near the front base mount of the front framework, e.g. within a radius of 2m from the front base mount. Preferably, the at least one tugger winch is positioned at the boom connector. The boom connector beneficially provides a robust support to the tugger winch.

[0079] In an embodiment of the vessel crane, a tugger wire for tensioning the base of the rear framework may extend from the tugger winch to a tugger sheave at the boom via a tugger sheave at the front framework to the base of the rear framework. By guiding the tugger wire in such a manner, beneficially, a predetermined span length is obtained.

[0080] In an embodiment of the vessel crane, at least one guide element, in particular a guide roller is positioned at a rear edge region on top of the crane house for guiding the tugger wire across the crane house when the base of the rear frame is situated behind the crane house.

[0081] In an embodiment of the vessel crane, at least one guide element is positioned at a rear edge region on top of the crane house for conducting the tugger wire across the crane house. In particular, the at least one guide element is a guide roller. The at least one guide element allows the tugger wire to extend across the crane house and to extend downwardly behind the crane house. The at least one guide element conducts the tugger wire across the crane house when the base of the rear framework is situated behind the crane house.

[0082] In an embodiment of the vessel crane, the lowering mechanism further comprises a control unit for lowering and raising the gantry by controlling respectively a payout and hauling in of a boom hoist wire, also called a luffing wire. The boom hoist comprises at least one boom hoist winch, also called a luffing winch, and the control unit is operationally connected to the boom hoist for controlling a motion of the gantry.

[0083] In an embodiment of the vessel crane, the boom hoist for raising and lowering the boom comprises at least one boom hoist winch, also called a luffing winch, wherein the at least one luffing winch is situated inside a -seen from above- outer contour of the crane house. The at least one luffing winch may be positioned on top of the crane house on an crane house deck.

[0084] In an embodiment of the vessel crane, the hoisting system for hoisting a hoist load comprises at least one hoisting winch being situated inside a -seen from above- outer contour of the crane house. The at least one hoisting winch may be positioned on top of the crane house. Preferably, the crane house includes an inner compartment, also called a winch compartment, for housing the at least one hoisting winch inside the crane house. Preferably, the winch compartment is provided at a top region of the crane house.

[0085] In an embodiment of the vessel crane, the at least one luffing winch of the boom hoist and the at least one hoisting winch of the hoisting system may be positioned in the winch compartment. The winch compartment may comprise a winch carry frame. The winch carry frame may include a platform for supporting at least one winch. Further, winch carry frame may include a plurality of connectors at an outer circumference to connect the winch carry frame to an inner side of the substructure, in particular to an inner side wall of a tub.

[0086] Further, the invention relates to a crane vessel comprising at least one vessel crane, in particular at least one tub mounted crane, according to the invention.

[0087] Further, the invention relates to a method for reducing a total crane height by lowering a gantry of a crane, wherein use is made of a vessel crane according to the invention. The method comprises a step of unlocking a rear base mount to release a base of a rear framework from a crane house and providing a displacement of the base of the rear framework in a direction away from the front framework while guiding the displacement by a link framework of a lowering mechanism.

[0088] In an embodiment of the method, a tub mounted crane according to the invention is used. The tub mounted crane has a lowering mechanism for lowering a gantry. The lowering mechanism includes a lock system for locking a base of a rear framework of the gantry to the crane house during a hoisting operation and a link framework which is pivotally coupled to a base of the rear framework for guiding a movement of the base of the rear framework during a crane height reducing operation. In a step of the method, the base of the rear framework is displaced and guided by the link framework by paying out a luffing wire from at least one luffing winch.

[0089] In an embodiment of the method, during a displacement of the base of the rear framework, the base of the rear framework is guided by the link framework until the link framework abuts against an end stop.

[0090] In an embodiment of the method, during its displacement, the base of the rear framework is tensioned by a tugger wire. A pulling force may be applied to maintain the base of the rear framework in position to allow the lock system to be unlocked. In the unlocked state of the lock system, the base of the rear framework can be displaced. To displace the base of the rear framework, the tension of the tugger wire is reduced. The tension reduction allows the base of the rear framework and the link framework to start moving.

[0091] Thus, a method for reducing a total crane height and a vessel crane comprising a lowering mechanism for lowering a gantry to achieve a total crane height reduction is provided. The gantry is collapsible from a raised position RP to a lowered position LP. The gantry has a front framework and a rear framework. In the raised position RP, the rear framework is at a base connected to a rear base mount at the crane house. In the lowered position LP, the rear framework is disconnected and displaced. The lowering mechanism has a lock system for disconnecting the rear framework and a pivotal link framework for subsequently guiding the rear framework during its displacement.

[0092] Embodiments are described by the following clauses:

[0093] 1. A vessel crane (1), in particular a tub mounted crane (TMC; 1), for transferring a hoist load to or from a marine vessel, a barge, a jacket or another structure, which vessel crane (1) comprises a substructure (10) on which a superstructure (11) including operating machinery is mounted, in which the superstructure (11) comprises:

[0094] - a crane house (2) which is rotatably connected to the substructure (10), in particular to a tub (10), for allowing a slew motion of the superstructure (11) relative to the substructure (10) around a vertical axis (01), wherein the crane house (2) comprises a boom connector (22) defining a horizontal boom pivot axis (03) for connecting a boom to the crane house (2) and a gantry mount including a front and a rear base mount (400 and 410, resp.) for mounting a gantry (4) to the crane house (2); - a boom (3) for supporting a hoist load, in which the boom has a longitudinal axis extending from a proximal boom end portion (301) to a distal boom end portion (302) including a head structure, in which the boom (3) is pivotally connected to the crane house (2) via the boom connector (22) so that the boom (4) is pivotal about the boom pivot axis (03);

[0095] - a gantry (4) mounted on the crane house (2), which gantry (4) is collapsible from a raised position (RP) to a lowered position (LP) for reducing a total crane height during travelling, wherein the gantry (4) comprises a front framework (40) and a rear framework (41) which are each in the raised position (RP) of the gantry (4) at a base connected to the crane house (2) to respectively the front base mount (400) and the rear base mount (410) and wherein the gantry (4) has a gantry apex (43) in which the front framework (40) and the rear framework (41) are connected to each other by a top pivot (42);

[0096] - a boom hoist (30) for raising and lowering the boom (3) by pivoting the boom (3) about a boom angle, in which the boom hoist (30) comprises at least one luffing winch (31) for hauling in or paying out a luffing wire (32) and a boom suspension (6) which extends between the gantry apex (43) and the head structure (302) of the boom (3) in which the boom suspension (6) includes a multiple fall arrangement of a luffing wire;

[0097] - a hoisting system (7) for hoisting a hoist load which hoisting system (7) comprises at least one hoisting winch (70) with an associated hoisting wire (701) which extends from the hoisting winch (70) to the head structure (302) of the boom (3), characterised in that the superstructure (11) further comprises a lowering mechanism (5) for lowering the gantry (4), wherein the lowering mechanism (5) includes a link framework (50) for displacing the rear framework (41), wherein the link framework (50) is at one end pivotally connected to the base of the rear framework (41) by a first link pivot (051) and at an opposite end pivotally connected to the crane house (2) by a second link pivot (052), and a lock system (51 ) for locking the base of the rear framework (41 ) to the rear base mount (410) when the gantry (4) is in the raised position (RP) and for unlocking the base of the rear framework (41) from the rear base mount (410) to allow a displacement of the rear framework (41), wherein the lock system (51) includes at least one lock member (510) to lock or release the base of the rear framework (41) to the rear base mount (410) to allow the displacement of the rear framework (41) for a lowering of the gantry (4).

[0098] 2. Vessel crane (1) according to clause 1 , wherein the rear framework (41) has a framework body which is formed by one rigid body. 3. Vessel crane (1) according to clause 1 or 2, wherein an assembly of the rear base mount (410) and the base of the rear framework (41) is formed by a pin-hole assembly.

[0099] 4. Vessel crane (1) according to any of the preceding clauses, wherein the link framework (50) is connected to the base of the rear framework (41) by a pin-hole configuration in which the hole is slotted.

[0100] 5. Vessel crane (1) according to any of the preceding clauses, wherein the second link pivot (052) of the link framework (50) is connected to a side wall of the crane house (2), in particular at a bottom region of the crane house (2).

[0101] 6. Vessel crane (1) according to any of the preceding clauses, wherein the link framework (50) includes a left and a right link-leg being each at one end pivotally connected to the base of the rear framework (41) and at an opposite end pivotally connected to the crane house (2).

[0102] 7. Vessel crane (1) according to clause 6, wherein the link framework (50) is H-shaped.

[0103] 8. Vessel crane (1) according to any of the preceding clauses, wherein the lowering mechanism (5) comprises an end stop for supporting the link framework (50) in the lowered position (LP) of the gantry (4).

[0104] 9. Vessel crane (1) according to clause 8, wherein the end stop is mounted to the substructure (10), in particular to a reinforced outer wall of the substructure (10).

[0105] 10. Vessel crane (1) according to any of the preceding clauses, wherein the lock system (51) comprises a pin-shaped lock member (510) and a lock member actuator (511) for actuating the lock member (510).

[0106] 11. Vessel crane (1) according to any of the preceding clauses, wherein the lowering mechanism (5) further comprises at least one tugger winch (53) for tensioning the base of the rear framework (41) with respect to the crane house (2).

[0107] 12. Vessel crane (1) according to clause 11 , wherein the at least one tugger winch (53) is positioned near the front base mount (400) of the front framework (40), in particular at the boom connector (22). 13. Vessel crane (1) according to clause 12, wherein a tugger wire (530) extends from the at least one tugger winch (53) to a tugger sheave (531) at the boom (3) and wherein the tugger wire (530) returns via a tugger sheave (531) at the front framework (40) to the base of the rear framework (41).

[0108] 14. Vessel crane (1) according to any of the clauses 11-13, wherein at least one guide element, in particular a guide roller (531), is positioned at a rear edge region on top of the crane house (2) for conducting the tugger wire (530) across the crane house (2) when the base of the rear framework (41) is situated behind the crane house (2).

[0109] 15. Vessel crane (1) according to any of the preceding clauses, wherein the lowering mechanism (5) further comprises a control unit for lowering the gantry (4) by controlling a payout of luffing wire of at least one luffing winch (31).

[0110] 16. Vessel crane (1) according to any of the preceding clauses, wherein the hoisting system (7) comprises at least one hoisting winch (70) and / or the boom hoist (30) comprises at least one luffing winch (31) being situated inside a -seen from above- outer contour of the crane house (2).

[0111] 17. Vessel crane (1) according to clause 16, wherein the at least one hoisting winch (70) and / or the at least one luffing winch (31) is positioned on top of the crane house (2).

[0112] 18. Vessel crane (1) according to clause 16, wherein the at least one hoisting winch (70) and / or the at least one luffing winch (31) is positioned in a winch compartment inside the crane house (2).

[0113] 19. Crane vessel (100) comprising at least one vessel crane (1), in particular at least one tub mounted crane (TMC; 1), according to any of the preceding clauses.

[0114] 20. Method for reducing a total crane height by lowering a gantry (4) of a vessel crane (1), wherein use is made of a vessel crane (1) according to any of the clauses 1-18, wherein the method comprises a step of:

[0115] - unlocking a rear base mount (410) to release a base of a rear framework (41) from a crane house (2);

[0116] - displacing the base of the rear framework (41) in a direction away from the front framework (40) while guiding a displacement by a link framework (50). 21. Method according to clause 20, wherein during its displacement, the base of the rear framework (41) is guided by the link framework (50) until the link framework (50) abuts against an end stop.

[0117] 22. Method according to clause 20 or 21 , wherein during its displacement, the base of the rear framework (41) is tensioned by a tugger wire (530).

[0118] The invention will be explained in more detail with reference to the appended drawings. The drawings show a practical embodiment according to the invention, which may not be interpreted as limiting the scope of the invention. Specific features may also be considered apart from the shown embodiment. In a divisional application or a claim amendment, these specific features may be taken into account in a broader context as a delimiting feature, not only for the shown embodiment but as a common feature for all embodiments falling within the scope of formulated claims, in which:

[0119] Fig. 1 shows a side view of a tub mounted crane which has a tub which is mounted to a hull of a vessel, a superstructure having an upstanding gantry on top of a slewable crane house and an extending boom supported by a boom rest;

[0120] Fig. 2 shows an enlarged view of the gantry of the tub mounted crane which is provided with a lowering mechanism for raising and lowering the gantry to obtain a total crane height reduction;

[0121] Fig. 3 and 4 show a backwards tilting of a front framework of the gantry, wherein a base of a rear framework is lowered along a back side of the crane house and guided by a link framework of the lowering mechanism until the link framework abuts against an end stop at the tub;

[0122] Fig. 5 shows an enlarged view of the crane house which is provided with a boom connector defining a horizontal boom pivot axis, a front base mount for mounting the front framework and a rear base mount for mounting the rear framework to the crane house, wherein a tugger winch is provided for tensioning the base of the rear framework in case of an operation of the lowering mechanism;

[0123] Fig. 6 shows an enlarged view of the base of the rear framework being positioned in a seat forming the rear base mount and wherein the base of the rear framework is connected to a link framework of the lowering mechanism; Fig. 7 shows a side view of Fig. 6 in which the base of the rear framework has a fork end provided with a fork end hole in alignment with upstanding plates with plate holes for receiving a pin to fasten the base of the rear framework by a pin-hole assembly;

[0124] Fig. 8 is an enlarged view of Fig. 6 in which the link framework is not shown;

[0125] Fig. 9 shows a head structure on a distal portion of the boom including a jib provided with an auxiliary load suspension device and a whip line;

[0126] Fig. 10 shows a side view of a vessel crane having a boom suspension extending from a gantry apex of a gantry on top of a crane house and a distal boom end portion of a boom, wherein the boom suspension has a multiple fall arrangement of luffing wire reeved between sheaves, wherein at least one sheave is detachable to adapt the multiple fall arrangement;

[0127] Fig. 11 shows the multiple fall arrangement of the boom suspension in a frontal view including a detachable sheave block which is transferable between a gantry sheave block at the gantry apex and a boom sheave block at the distal boom end portion of the boom; Fig. 12 shows an enlarged view of the gantry sheave block of Fig. 11 being connected to the detachable sheave block;

[0128] Fig. 13 shows an enlarged view of a transfer winch for displacing the detachable sheave block being situated at the distal boom end portion.

[0129] In Figs. 1-13, a vessel crane, in particular a tub mounted crane, is shown in an embodiment according to the invention and denoted overall by reference numeral 1. Identical reference signs are used in the drawings to indicate identical or functionally similar components.

[0130] The tub mounted crane 1 is provided on board of a crane vessel 100. The tub mounted crane 1 has a pedestal, also called a tub 10, which is mounted to a hull 101 of the crane vessel. The crane vessel is configured for heavy lifting, e.g. more than 1500Mtons, in particular more than 5000Mtons. Based on a proven track record in delivering high capacity offshore cranes over the last decades, nowadays Huisman offers a range of Tub Mounted Cranes with lifting capacities up to 12,000mt. The tub mounted crane 1 is suitable to be used for transferring materials to and fro a quay, a marine vessel, a barge, a jacket, or another structure by elevating and rotating.

[0131] The shown crane vessel 100 has a semi-submersible design which allows it to partially submerge in water. By pumping water in or out of ballast tanks, the crane vessel 100 can adjust its height in the water. This height adjustment capability serve to improve stability during heavy lifting operations. In another embodiment, the crane vessel 100 may be a jack-up vessel. Such a jack-up vessel comprises a hull 101 with openings in the hull, wherein the openings extend vertically through the hull 101 to receive a respective jack-up leg. For each leg, a leg driving device may be provided to allow to move the corresponding leg up and down relative to the hull in a vertical direction to allow the hull to be lifted out of a water body. The legs are retracted for sailing with the vessel.

[0132] The top mounted crane 1 comprises a substructure formed by the tub 10 onto which a rotatable superstructure 11 is mounted. The superstructure is rotatable about a vertical axis 01 . The superstructure 11 comprises operating machinery to carry out hoisting operations.

[0133] The superstructure 11 comprises a crane house 2, a gantry 4 on top of the crane house and a boom 3 being pivotable about a horizontal boom pivot axis 03 at a proximal boom end portion 301.

[0134] In particular, in such a heavy lifting crane vessel 100, the boom pivot axis 03 is positioned at a height level of at least 20m, in particular about 30m above a deck level DL. The boom may have a boom length of at least 80m. As shown in Fig. 5, the boom 3 of the crane 1 has a latticed structure. The boom comprises an A-frame with two boom legs that are connected at one end to the crane house 2 so as to be pivotal about the boom pivot axis 03 of a boom connector 22. The latticed boom legs may adjoin another in a box structure.

[0135] The crane house 2 is rotatably connected to the tub 10 to allow a rotation of the superstructure 11 about a -practically seen- vertical axis 01 . The crane house 2 is rotatably connected to the tub 10 for allowing a slew motion of the revolving superstructure 11 relative to the substructure. The crane house comprises a boom connector 22 which defines the horizontal boom pivot axis 03. The crane house 2 may include a cab where an operator manoeuvres the crane’s controls.

[0136] The crane comprises a boom hoist 30, which may also be called a luffing assembly. The boom hoist is arranged to set an angular orientation of the boom 3 relative to the crane house 2. The boom hoist 30 is configured to raise and lower the boom by pivoting the boom 3 about a boom angle about the boom pivot axis 03 defined by the boom connector 22. The boom hoist 30 comprises at least one boom hoist winch, also called a luffing winch 31. The luffing winch 31 is arranged to wind and unwind a luffing wire 32. The at least one luffing winch 31 is positioned at the crane house. Preferably, the at least one luffing winch 31 is positioned at the rear region at an upper region of the crane house 2. The luffing wire 32 is reeved along the gantry and extends in a multiple fall arrangements between a gantry apex and a distal end portion of the boom.

[0137] The superstructure 11 comprises a hoisting system 7 for hoisting a hoist load by a load suspension device 8. Here, the load suspension device 8 includes a main load suspension device 81 provided with a main hoisting wire 810, a multi sheave main block and a hook. Further, the load suspension device 8 includes an auxiliary load suspension device 82 and a whip line 83, also called a fast line. The auxiliary load suspension device 82 and the whip line 83 are connected to a jib 38 provided at a head structure 302 of the boom 3.

[0138] The hoisting system 7 comprises at least one hoisting winch 70. The at least one hoisting winch 70 is positioned at the crane house 2. Here, a hoisting winch assembly 71 is provided including a plurality of hoisting winches 70. The hoisting winch assembly 71 is situated at the upper region of the crane house 2. Hoisting wires 701 extend from the hoisting winch assembly 71 to the head structure 302 of the boom, which is also shown in Fig. 11.

[0139] In Fig. 1 , the gantry, also called a luffing frame, is shown in a raised position RP. As shown in Fig. 2-4, the gantry 4 is collapsible from the raised position RP to a lowered position LP for reducing a total crane height during sailing of the vessel. The gantry 4 comprises a front framework 40 and a rear framework 41 which are each mounted on top of the crane house 2. The front framework 40 is positioned at a front region on top of the crane house 2. In the raised position RP, at their bases, the front framework 40 and the rear framework 41 are each connected to the crane house 2 by respectively a front and rear base mount 400, 410. The bases are connected by a pin-hole assembly.

[0140] The front base mount 400 of the front framework 40 includes a base pivot 040 which defines a front pivot axis 040. The base pivot allows the front framework 40 to tilt in a vertical plane. The base pivot 040 allows a pivotal movement of the front framework 40 relative to the crane house 2.

[0141] Here, the base pivot 040 of the front framework is positioned above the boom pivot axis 03 of the boom connector 22. Here, the front base mount is integral with the boom connector 22.

[0142] The base of the rear framework is connected to the crane house 2 by the rear base mount 410. The rear base mount 410 is positioned at a rear region on top of the crane house 2. In particular, the rear base mount 410 is provided at the crane house deck 23. The rear base mount 401 of the rear framework is here formed a pin-hole assembly, see Fig. 6 and 7. The base of the rear framework has a through hole for receiving a pin. The pin-hole assembly has a seat 411 , also called a base rest, at the crane house 2 for receiving the base of the rear framework. The seat has a seat hole 413 for receiving the pin to fixate the base of the rear framework to the seat.

[0143] Here, the seat 411 has at least one upstanding plate 412. Each plate 412 has a plate hole 413 for receiving the pin. The seat 411 is here formed by a left and right upstanding plate 412 which are each fixated to the crane house. Each plate 412 has a seat portion for supporting the base of the rear frame work.

[0144] The base of the rear framework has a plate shaped end provided with a through hole. Here, the base of the rear framework has a fork end 414 including a left and right fork leg which are each provided with a fork end hole 415. In the pin-hole assembly, the fork end holes 415 are in alignment with the left and right upstanding plate holes 413.

[0145] At an upper end, the front framework and rear framework 40, 41 are connected to each other by a top pivot 42 at a gantry apex 43. Herewith, seen in a side view, the gantry has an upside down V-shape in which the V-legs are formed by the front framework 40 and rear framework 41.

[0146] As shown in detail in Fig. 2, according to an aspect of the invention, the superstructure of the tub mounted crane 1 further comprises a lowering mechanism 5 for lowering the gantry 4. The lowering mechanism 5 includes a link framework 50 and a lock system 51 , see also Fig. 6, 7 and 8.

[0147] The link framework 50 is arranged for displacing the rear framework 41 in downwards and upwards direction to respectively lower and raise the gantry. At one end, the link framework 50 is pivotally connected by a first link pivot 051 to the base of the rear framework of the gantry for displacing the base of the rear framework. At an opposite end, the link framework 50 is pivotally connected by a second link pivot 052 to the crane house 2. During a displacement, the link framework 50 provides a guidance to the base of the rear framework. By displacing the base of the rear framework, the gantry 4 can be lowered to reduce a total crane height.

[0148] Seen from aside -in the side views of Fig. 2, 3 and 6- , the link framework 50 has an upside down L-shape. The link top 501 is provided with a first link pivot 051 at an end of a short leg of the L-shape. Here, as shown in Fig. 6, the first link pivot 051 is formed by a pin-hole coupling in which the hole has an oblong shape. The link base 501 is provided with a second link pivot 052 at an end of a long leg of the L-shape. The second link pivot 052 connects the link base 50 to the crane house 2. The second link pivot 052 has a horizontal pivot axis which allows the link framework 50 to rotate in a vertical plane with respect to the crane house 2.

[0149] The lock system 51 is arranged for locking the rear framework 41 in position when the gantry is in the raised position RP. The lock system 51 includes at least one lock member 510 to lock or release the base of the rear framework 41 , see also Fig. 7 and 8. In a locked state, the gantry 4 is fixed to the crane house 2. The fixation by the lock system 51 provides a solid and rigid connection of the gantry 4 to the crane house 2 which is required for hoisting operations. In an unlocked state, the rear framework 41 of the gantry is displaceable which allows a lowering of the gantry 4.

[0150] As shown in Fig. 3 and 4, the base of the rear framework is guided by the link framework 50 along a back side of the crane house. When lowering the base of the rear framework, the link framework 50 pivots about an angle of until about 180° along a back side of the crane house.

[0151] In Fig. 3, an initial displacement of the base of the rear framework 41 to an intermediate position 4T at a back of the crane house is shown. In Fig. 4, a further lowering of the base of the rear framework is shown, wherein the link framework 50 finally abuts against the substructure, which is here the tub of the tub mounted crane. Initially, in the raised position RP of the gantry, the link framework 50 is in an upright position. During lowering, the link framework 50 rotates in a direction away from the crane house 2 (backwards) as indicated by the references 42, 42’ and 42”.

[0152] The link framework 50 rotates until the link top 501 abuts against an end stop 52. The end stop 52 is mounted at an outer side of a tub wall of the tub 10 for stopping the link framework 50. The tub wall may be provided with a reinforcement structure. After lowering the gantry 4, the link framework 50 has rotated about an angle of about 180°.

[0153] As shown in Fig. 3 and 4 by the lowering of the gantry apex, a total crane height reduction is obtained. By using the link framework 50 for collapsing the gantry 4 of such a heavy lift crane 1 which might have a gantry height of for example about 90m from a water line WL, the gantry apex 43 can even be lowered about a distance of at least 20m. In particular, the gantry apex 43 can be lowered until a total crane height of at most 65m above a waterline to allow a crane vessel 100 to pass large bridges like the Great Belt Bridge of Denmark. Fig. 5 shows an enlarged view of the crane house 2 including a tugger winch 53 for tensioning the base of the rear framework by a tugger wire 530 during an operation of the lowering mechanism. Fig. 6 shows an enlarged view of the base portion of the rear framework 41 being positioned in the seat 411 on top of the crane house 2, wherein the tugger wire 530 is fastened to the base of the rear framework.

[0154] As shown in Fig. 4, a guide element for guiding the tugger wire is positioned at the crane house deck 23. The guide element is a guide roller 531. The guide roller is positioned at a rear edge region on top of the crane house for conducting the tugger wire across the crane house when the base of the rear framework is situated behind the crane house.

[0155] In a method for lowering a base of a rear framework, the tugger winch 53 is operated to exert a pull force when carrying out a displacement of the base of the rear framework 41 relative to the crane house 2.

[0156] The tugger winch 53 is positioned at a front region of the crane house 2. The tugger winch 53 is positioned at the base of the front framework 40. A tugger wire 530 extends from the tugger winch 53 to the base of the rear framework 41. As shown in Fig. 6, an end of the tugger wire 530 is connected to the base of the rear framework 41 . The tugger wire 530 extends along a tugger wire path which is determined by several tugger wire sheaves 531. In the illustrated embodiment, a tugger wire sheave 531 is connected to the boom 3 and another tugger wire sheave 531 is connected to the front framework 40, such that the tugger wire path extends from the tugger winch 53 via the boom 3 and the front framework 40 to the base of the rear framework 41. It is remarked that another tugger wire path is also conceivable.

[0157] Fig. 6, 7 and 8 further show the lock system 51 which is arranged for locking the rear framework 41 in position when the gantry 4 is in the raised position RP. The lock system 51 includes at least one lock member 510 to lock the base of the rear framework 41. The at least one lock member 51 fixates the base of the rear framework 41 to the crane house 2.

[0158] The lock member 510 is formed by a pin which is receivable in the through hole at the base of the rear framework 41 . The lock system 51 comprises a lock member actuator 511 for driving the lock member 510 into or out of the through hole for respectively locking or unlocking the base of the rear framework 41. Here, the lock member actuator 511 is a hydraulic actuator. The hydraulic actuator may be self-sustained and being provided with a pump unit and a battery for incidentally actuating the lock member 510. Fig. 9 shows a head structure 302 of the boom 3 in further detail. The head structure includes a jib 38. The head structure 302 is arranged to carry a main load suspension device 81 which is connected by a main hoisting wire 810 and provided with a multi-sheave main block and hook, an auxiliary load suspension device 82 and a whip line, also called a fast line 83.

[0159] According to an aspect of the invention, Fig. 10 shows a vessel crane 1 in a side view. The vessel crane 1 is suitable to be installed on board of a crane vessel 100. The vessel crane 1 is mountable to a hull 101 of a vessel. Here, the vessel crane is a tub mounted crane, a so-called a TMC. The vessel crane 1 is arranged to transfer a hoist load from one to another position. The vessel crane 1 may transfer the hoist load to or from a marine vessel, a barge, a jacket or another structure.

[0160] The vessel crane 1 comprises a substructure 10. Here, the substructure includes a pedestal, also called a tub. A superstructure 11 is mounted on top of the substructure 10. The superstructure includes operating machinery for carrying out a hoisting operation.

[0161] The superstructure 11 comprises a crane house 2. The crane house is rotatably connected to the substructure to allow a slew motion of the superstructure relative to the substructure around a vertical axis 01. The crane house comprises a boom connector 22. The boom connector 22 defines a horizontal pivot axis for connecting a boom to the crane house.

[0162] The superstructure 11 comprises a boom 3 for supporting a hoist load. The boom has a longitudinal axis which extends from a proximal end portion 301 of the boom to a distal end portion of the boom. The distal end portion of the boom is provided with a head structure 302. The boom is pivotally connected to the crane house 2 via the boom connector 22, so that the boom is pivotable about a boom pivot axis 03.

[0163] The superstructure 11 comprises a gantry 4. The gantry 4 is a crane frame which is arranged to support the boom 3 of the vessel crane 1. The gantry 4 is mounted on the crane house 2. To reduce a total crane height during travelling of the crane vessel, the gantry 4 is collapsible from a raised position RP to a lowered position LP. The gantry 4 comprises a front framework 40 and a rear frame 41. In the raised position RP, the front framework 40 and the rear framework are at their bases mounted to the crane house 2. The gantry has a gantry apex 43. The gantry apex 43 is formed by a connection of a top of the front framework to a top of the rear framework. The front framework and the rear framework are connected to each other by a top pivot 42. The superstructure 11 comprises a hoisting system 7 for hoisting the hoist load. The hoisting system 7 comprises at least one hoisting winch 70 which is provided with a hoisting wire 701 . The hoisting wire extends from the hoisting winch 70 to the head structure 302 of the boom 3. Here, the head structure 302 includes a jib 38. The jib 38 is arranged to carry an auxiliary load suspension device 82 and a fast line.

[0164] The superstructure 11 comprises a boom hoist 30 for raising and lowering the boom 3. The boom can be raised and lowered by pivoting the boom about the boom pivot axis 03 over a boom angle. The boom is depicted in fig. 10 in a substantially horizontal orientation in which the boom 3 is supported by a boom rest 39.

[0165] The boom hoist 30 is provided with at least one boom hoist winch 31 for hauling in and paying out a luffing wire 32. By hauling in the luffing wire, the boom 3 can be raised and vice versa by paying out the luffing wire, the boom 3 can be lowered.

[0166] Further, the boom hoist 30 comprises a boom suspension 6 for supporting the boom. The boom suspension 6 extends between the gantry apex 43 and the head structure 302 of the boom 3. The boom suspension contains the luffing wire which is configured in a multiple fall arrangement 60. The multiple fall arrangement 60 extends between a gantry sheave block 61 and a boom sheave block 62. The gantry sheave block 61 is positioned at a side of the gantry apex 43. The boom sheave block 62 is positioned at a side of the head structure 302 of the boom 3.

[0167] The boom suspension 6 comprises an arrangement which enables a shortening of luffing wire in the multiple fall arrangement. The shortening of luffing wire 32 in the multiple fall arrangement allows to wind up a length of luffing wire onto the boom hoist winch 31 which length of luffing wire can subsequently be used for lowering the gantry 4. The boom suspension 6 comprises at least one detachable sheave block which allows an adaptation of the luffing wire length contained by the multiple fall arrangement 60. The luffing wire length can be adapted by displacing the at least one detachable sheave block away from a hoist position. The at least one detachable sheave block is in a hoist operational status of the vessel crane positioned in the hoist position. In the vessel crane design, the hoist position of the at least one detachable sheave block is determined for a heavy lifting hoisting operation in which heavy hoist loads are to be handled. The hoist position may represent a position of the at least one detachable sheave block in which a maximum hoist load can be lifted by the vessel crane. By moving the at least one detachable sheave block away from the hoist position, the luffing wire length in the multiple fall arrangement can be shortened. During the displacement of the at least one detachable sheave block, a luffing wire may be wound onto the boom hoist winch.

[0168] When a crane vessel 100 provided with the vessel crane 1 is travelling to another location, it may occur that the crane vessel has to pass a bridge with a maximum clearance height. In incidental cases, it may then be necessary to reduce a total crane height of the vessel crane 1 on board of the crane vessel 100. A total crane height can then be reduced by lowering the gantry 4.

[0169] Depending on a particular vessel crane configuration, such a gantry 4 might be lowered in different ways. It may be possible by tilting the front framework 40 about a base pivot 040 and folding a rear framework in a backwards direction as disclosed in for example EP3.825.274 or as disclosed in for example W02020 / 204719 by folding a rear framework in a forward direction. In another method of lowering the gantry 4, the rear framework 41 may comprise an integral rigid body in which a base of the rear framework is to be demounted from a rear base mount 410 of the crane house 2 to be subsequently lowered at a back side of the crane house 2.

[0170] Generally, the gantry 4 is lowered by tilting the front framework in a backwards direction about the base pivot 040. During a tilting motion of the front framework 40, the boom is maintained stationary. Preferably, the boom 3 remains on the boom rest 39 when tilting the front framework 40. After placing the boom 3 onto the boom rest 39, the boom suspension 6 can be slackened. To allow the front framework 40 to move away from the boom, the boom suspension 6 has to be lengthened. Thus, the tilting of the front framework 40 requires a lengthening of the boom suspension 6 which can be achieved by paying out luffing wire from the boom hoist which 31. Consequently, the boom hoist winch 30 may be configured to contain an additional length of luffing wire 32 to allow this tilting of the front framework 40.

[0171] According to the invention, an improvement is provided in that the gantry 4 can be lowered without a need for the predetermined additional length of luffing wire 32. In a vessel crane, the multiple fall arrangement of luffing wire 60 of the boom suspension 6 is determined to carry out a hoisting operation in which the boom 3 and a hoisting load are to be supported. In comparison with hoisting, when lowering the gantry 4, the boom suspension 6 is subjected to lower forces. This allows the boom suspension 6 to be adapted to a less heavy configuration. The multiple fall arrangement 60 of the boom suspension 6 may contain a shorter length of luffing wire. An amount of falls of the luffing wire in the multiple fall arrangement of the boom suspension 6 may for example be reduced. For adapting the multiple fall arrangement 60, according to the aspect of the invention, the multiple fall arrangement 60 of the boom suspension 6 comprises at least one detachable sheave block 63. At one side, at a side of the gantry 4, the multiple fall arrangement 60 has a gantry sheave block 61 and at an opposite side, at a side of the boom 3, the multiple fall arrangement 60 has a boom sheave block 62. The at least one detachable sheave block 63 is detachable from at least one of the gantry sheave block 61 and boom sheave block 62. Here, in Fig. 10, the at least one detachable sheave block 63 is in the hoist position connected to the boom sheave block 62. By detaching the at least one detachable sheave block 63 and moving the at least one detachable sheave block 63 away from its hoist position H, a length of luffing wire in the multiple fall arrangement is adapted. By moving the at least one detachable sheave block 63 away, the luffing wire 32 in the multiple fall arrangement is then shortened. During the movement, the luffing wire is wound onto the boom hoist winch 31. After a predetermined displacement of the at least one detachable sheave block 63 in which the at least one detachable sheave block reaches a gantry tilt position GT, a sufficient length of luffing wire is wound onto the boom hoist winch 31 to allow a subsequent lowering of the gantry 4. Herewith, beneficially, the boom hoist winch 31 being configured for a hoisting operation needs no additional capacity to carry out an incidental operation in which the gantry 4 has to be lowered.

[0172] Here, in Fig. 10, the at least one detachable sheave block 63 is transferable along a path between the boom sheave block 62 and the gantry sheave block 61. In the gantry tilt position GT, the at least one detachable sheave block is connectable to the gantry sheave block 61 .

[0173] It is conceivable that the at least one detachable sheave block 63 is transferable along an alternative path. The alternative path may extend along the boom. Preferably, the alternative path is a linear path which extends in a longitudinal direction defined by a longitudinal axis of the boom 3. In the gantry tilt position GT, the at least one detachable sheave block 63 may be connectable to the boom at a boom position at a distance from the boom sheave block 62. An auxiliary block 621 may be positioned at the boom position for connecting the at least one detachable sheave block 63. The at least one detachable sheave block 63 is transferable to and fro the boom sheave block 62 and the auxiliary block 621. The auxiliary block 621 may be positioned between the boom pivot axis 03 and the boom sheave block 62. The boom position for connecting the at least one detachable sheave block 63 may be located at the proximal end portion 301 of the boom. In a variant, it is conceivable that in the gantry tilt position, the at least one detachable sheave block 63 is connectable to the crane house 2 or the gantry 4. In particular, the at least one detachable sheave block 63 may be connected to a base of a front framework 40 of the gantry 4. In Fig. 10, the luffing wire 32 runs from sheaves 61 in the gantry 4 directly to sheaves 62 at the distal end portion 302 of the boom which is beneficial in that it puts a less dynamic loading into the sheaves. However, this so-called continuously reeved luffing wire requires a more lengthy wire in comparison with a boom suspension including a multiple fall arrangement 60 with an extension (69: not shown) as described above. The extension may be positioned between the gantry 4 and the multiple fall arrangement 60 or alternatively between the boom 3 and the multiple fall arrangement 60. As the luffing wire is a wearing component in hoisting operations, a wire replacement in a continuously reeved arrangement is more costly. Although, the aspect of the invention is illustrated by a continuously reeved luffing wire in Fig. 10, it is conceivable that the aspect of the invention is likewise applicable in case of a boom suspension including the extension.

[0174] Fig. 11 and 12 show the multiple fall arrangement 60 of the boom suspension 6 in enlarged views. In the left-sided view of Fig. 11 , a gantry sheave block 61 is positioned at the gantry apex 43. Here, in the gantry tilt position GT, a detachable sheave block 63 is connected to the gantry sheave block 61 . In the right sided view of Fig. 11 , a boom sheave block 62 is positioned at a distal end portion 302 of the boom 3. Here, illustrated in the hoist position H, the detachable sheave block 63’ is connected to the boom sheave block 62. To reduce an amount of falls of reeved luffing wire 32 in the multiple fall arrangement 60, the detachable sheave block 63 is transferred from the hoist position H at the boom 3 to the gantry tilt position GT at the gantry apex 43. The reduction of falls results in less luffing wire contained by boom suspension which becomes available to carry out a lowering of the gantry for to reduce a total crane height.

[0175] As shown in Fig. 11 , the detachable sheave block 63 is provided with a connector member 631 and the gantry sheave block 61 and the boom sheave block 62 are each provided with a complementary connector member 611 , 621. Here, the detachable sheave block 63 is provided with a first connector member 631 at one side and a second connector member 632 at an opposite side for connecting the detachable sheave block 63 at opposite sides to an associate complementary connector member 611 , 621. To obtain a proper alignment of a detachable sheave block 63 approaching one of the gantry sheave block 61 and boom sheave block 62, the detachable sheave block 63 has a sheave frame 630 which is provided with a positioning member 65. Preferably, the positioning member is one of a male and female member, wherein a complementary counterpart is provided at at least one of the gantry sheave block 61 and boom sheave block 62.

[0176] In Fig. 10 and in the enlarged view of Fig. 13 a transfer winch 66 is shown which is configured to transfer a detachable sheave block 63. The transfer winch 66 is arranged to wind and unwind a transfer wire 660. The transfer winch 66 is positioned at the distal boom end portion 302. Here, the transfer winch 66 is positioned at the boom sheave block 62. The transfer wire 660 is connected to the detachable sheave block 63 to guide the sheave block 63 along the path from the hoist position H to the gantry tilt position GT. It is conceivable that in a variant, the transfer winch 66 is positioned at the gantry sheave block 61 . By operating the transfer winch 66, the transfer wire can be paid out to lower the detachable sheave block 63 away from the gantry sheave block 61. Subsequently, the gantry sheave block 63 may be received and connected to the boom sheave block 62 or connected at another boom position which results in a shortening of luffing wire contained by the pump suspension 6.

[0177] Fig. 4 is representing the method according to an aspect of the invention. The method for reducing a total crane height and a vessel crane 1 comprising a lowering mechanism 5 for lowering a gantry 4 to achieve a total crane height reduction. The gantry 4 is collapsible from a raised position RP to a lowered position LP. The gantry has a front framework 40 and a rear framework 41 . In the raised position RP, the rear framework 41 is at a base connected to a rear base mount 410 at the crane house. In the lowered position LP, the rear framework 41 is disconnected and displaced. The lowering mechanism 5 has a lock system 51 for disconnecting the rear framework 41 and a pivotal link framework 50 for subsequently guiding the rear framework 41 during its displacement.

[0178] Although the present invention has been described in detail, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention as hereinafter claimed. It is intended that all such changes and modifications be encompassed within the scope of the present disclosure and claims.

[0179] Reference signs list:

[0180] TMC tub mounted crane DL deck level GS ground surface

[0181] WL water line 40

[0182] 1 tub mounted crane

[0183] RP raised position 01 vertical axis

[0184] LP lowered position 100 crane vessel

[0185] 101 hull

[0186] H hoist position (of sheave) 45 102 vessel deck

[0187] GT gantry tilt position (of sheave) 10 tub; pedestal; substructure 11 superstructure 414 fork end

[0188] 12 crane subassembly 415 fork end hole

[0189] 120 assembly table 40 42 top pivot

[0190] 121 table frame 43 gantry apex

[0191] 122 crane house support

[0192] 5 lowering mechanism

[0193] 2 crane house 50 link framework

[0194] 21 circumferential wall 45 501 link top

[0195] 211 lower end 051 first link pivot

[0196] 22 boom connector 502 link base

[0197] 23 crane house deck 052 second link pivot

[0198] 212 upper end

[0199] 25 middle section 50 51 lock system

[0200] 26 lower section 510 lock member

[0201] 27 upper section 511 lock member actuator

[0202] 28 inner space

[0203] 281 carrier mount 52 end stop

[0204] 55 53 tugger winch

[0205] 3 boom 530 tugger wire

[0206] 03 boom pivot axis 531 guide roller; tugger wire sheave

[0207] 301 proximal boom end portion

[0208] 302 distal boom end portion; head structure 6 boom suspension

[0209] 30 boom hoist; luffing assembly 60 60 multiple fall arrangement

[0210] 31 boom hoist winch; luffing winch 61 gantry sheave block

[0211] 32 luffing wire 610 gantry sheave frame

[0212] 38 jib 611 complimentary connector member

[0213] 39 boom rest 62 boom sheave block

[0214] 65 620 boom sheave frame

[0215] 4 gantry; luffing frame; A-frame 621 complimentary connector member

[0216] 40 front framework 63 detachable sheave block

[0217] 400 front base mount 630 sheave frame

[0218] 040 base pivot 631 connector member

[0219] 41 rear framework 70 632 second connector member

[0220] 410 rear base mount 64 auxiliary block

[0221] 411 seat 65 positioning member

[0222] 412 upstanding plate 66 transfer winch

[0223] 413 seat hole; plate hole 660 transfer wire 69: extension (not shown) 10 712 winch seat

[0224] 781 complementary carrier mount

[0225] 7 hoisting system

[0226] 70 hoisting winch 8 load suspension device 31, 70 luffing winch, hoisting winch 81 main load suspension device

[0227] 701 hoisting wire 15 810 main hoisting wire

[0228] 71 winch carrier 811 multi sheave main block (and hook)

[0229] 710 carrier body 82 auxiliary load suspension device

[0230] 711 platform 83 whip line; fast line

Claims

- 36 -CLAIMS1. A vessel crane (1), in particular a tub mounted crane (TMC; 1), for transferring a hoist load to or from a marine vessel, a barge, a jacket or another structure, which vessel crane comprises a substructure (10) on which a superstructure (11) including operating machinery is mounted, in which the superstructure comprises:- a crane house (2), which crane house is rotatably connected to the substructure, e.g. to a tub, for allowing a slew motion of the superstructure relative to the substructure around a vertical axis, wherein the crane house comprises a boom connector (22) defining a horizontal boom pivot axis for connecting a boom to the crane house;- a boom (3) for supporting a hoist load, in which the boom has a longitudinal axis extending from a proximal end portion (301) to a distal end portion including a head structure (302), in which the boom is pivotally connected to the crane house (2) via the boom connector (22), so that the boom is pivotal about a boom pivot axis (03);- a gantry (4) for supporting the boom (3), which gantry is mounted on the crane house, which gantry is collapsible from a raised position (RP) to a lowered position (LP) for reducing a total crane height during sailing, wherein the gantry comprises a front framework (40) and a rear framework (41) which are each in the raised position of the gantry at a base connected to the crane house and wherein the gantry has a gantry apex (43) in which the front framework and the rear framework are connected to each other by a top pivot (42);- a hoisting system (7) for hoisting the hoist load which hoisting system comprises at least one hoisting winch (70) with an associated hoisting wire (701) which hoisting wire extends from the hoisting winch to the head structure (302) of the boom;- a boom hoist (30) for raising and lowering the boom by pivoting the boom about the boom pivot axis (03) over a boom angle, in which the boom hoist comprises:- at least one boom hoist winch (31) for hauling in and paying out a luffing wire to respectively raise or lower the boom; and- a boom suspension (6) for supporting the boom in which the boom suspension extends between the gantry apex (43) and the head structure (302) of the boom (3), in which the boom suspension (6) includes a luffing wire (32) being configured in a multiple fall arrangement (60) between a gantry sheave block (61) which is positioned at a side of the gantry apex and a boom sheave block (62) which is positioned at a side of the head structure; characterised in that the boom suspension (6) further comprises at least one detachable sheave block (63) for adapting a luffing wire length in the multiple fall arrangement (60) by displacing the at least one detachable sheave block (63) from a hoist position (H) wherein the at least one detachable sheave block (63) is positioned for carrying out a hoisting operation to- 37 - a gantry tilt position (GT) wherein the at least one detachable sheave block (63) is positioned for carrying out a raising or lowering of the gantry (4).

2. Vessel crane (1) according to claim 1 , wherein the at least one detachable sheave block (63) is in the hoist position connected to the boom sheave block (62).

3. Vessel crane (1) according to claim 1 or 2, wherein the at least one detachable sheave block (63) is transferable along a path between the gantry sheave block (61) and the boom sheave block (62) and wherein, in particular, in the gantry tilt position, the at least one detachable sheave block (63) is connectable to the gantry sheave block.

4. Vessel crane (1) according to claim 1 or 2, wherein the at least one detachable sheave block (63) is transferable along a path extending along the boom (3).

5. Vessel crane (1) according to claim 4, wherein in the gantry tilt position, the at least one detachable sheave block (63) is connectable to the boom (3) at a boom position at a distance from the boom sheave block (62).

6. Vessel crane (1) according to claim 5, wherein the at least one detachable sheave block (63) is transferable to and fro the boom sheave block (62) and an auxiliary block (621) positioned at the boom (3) between the boom pivot axis (03) and the boom sheave block (62).

7. Vessel crane (1) according to claim 5 or 6, wherein the boom position is located at the proximal end portion (301) of the boom.

8. Vessel crane (1) according to claim 1 or 2, wherein in the gantry tilt position, the at least one detachable sheave block (63) is connectable to the crane house (2) or the gantry (4), in particular to a base of a front framework (40) of the gantry (4).

9. Vessel crane (1) according to any of the preceding claims, wherein the at least one detachable sheave block (63) is provided with a connector member (631), wherein at least one of the gantry sheave block and the boom sheave block (61 , 62) is provided with a complementary connector member (611 , 621).

10. Vessel crane (1) according to any of the preceding claims, wherein the at least one detachable sheave block (63) is provided with a first connector member (631) at one side and a second connector member (632) at an opposite side for connecting the at least onedetachable sheave block (63) at opposite sides to an associate complementary connector member (611 , 621).

11. Vessel crane (1) according to any of the preceding claims, wherein a sheave frame (610, 620, 630) of at least one of the detachable sheave block, gantry sheave block and boom sheave block (61 , 62, 63) is provided with a positioning member (65) for aligning sheave blocks with respect to each other.

12. Vessel crane (1) according to any of the preceding claims, wherein the boom suspension (6) comprises a transfer winch (66) for transferring the detachable sheave block.

13. Vessel crane (1) according to claim 12, wherein the transfer winch (66) is positioned at the distal boom end (302), in particular at the boom sheave block (62).

14. Vessel crane (1) according to claim 12, wherein the transfer winch (66) is positioned at the gantry sheave block (61).

15. Vessel crane (1) according to any of the preceding claims, wherein the multiple fall arrangement (60) of the boom suspension extends about a whole distance between the gantry apex (43) and the head structure (302) of the boom (3).

16. Vessel crane (1) according to any of the claims 1-14, wherein the boom suspension (6) comprises an extension (69), like a chain or a rod structure, wherein the multiple fall arrangement is connected to the extension for extending the multiple fall arrangement to fit the boom suspension (6) between the gantry apex (43) and the head structure (302) of the boom.

17. Vessel crane (1) according to claim 16, wherein the extension (69) is positioned between the multiple fall arrangement (60) and the gantry apex (43).

18. Crane vessel (100) comprising at least one vessel crane (1), in particular at least one tub mounted crane (TMC), according to any of the preceding claims.

19. Method for reducing a total crane height by lowering a gantry (4) of a vessel crane (1), wherein use is made of a vessel crane (1) according to any of the claims 1-17, the vessel crane comprising a boom hoist (30) provided with a boom suspension (6) including a luffing wire (32) originating from at least one luffing winch (31) and arranged in a multiple fall arrangement (60)between a gantry sheave block (61), a boom sheave block (62) and at least one detachable sheave block (63), wherein the method comprises a step of:- shortening a total length of the luffing wire (32) in the multiple fall arrangement (60) of the boom suspension (6) by detaching and displacing the at least one detachable sheave block (63) from a hoist position (H) wherein the at least one detachable sheave block (63) is positioned for carrying out a hoisting operation to a gantry tilt position (GT) wherein the at least one detachable sheave block (63) is positioned for carrying out a raising or lowering of the gantry (4);- winding the luffing wire onto the luffing winch (31); and - paying out luffing wire when lowering the gantry (4) of the vessel crane (1).

20. Method according to claim 19, wherein the method comprises a step of:- transferring the at least one detachable sheave block (63) along a path extending from a first position to a second position, wherein the multiple fall arrangement of luffing wire has a higher fall in the first position then in the second position.

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