Heave-compensated double-lift crane

Abstract

A twin lift crane (1) is provided with a heave compensation system for both a main lift assembly and an auxiliary lift assembly (12). The heave compensation system comprises a first set (25) of sheaves for guiding the main lift cables (10), and a second set (26) of sheaves for guiding the auxiliary lift cables. The heave compensation system is configured to individually lock the first set of sheaves and the second set of sheaves to heave compensation cylinders for providing heave compensation for the main lift assembly and the auxiliary lift assembly, respectively.

Description

Technical Field

[0001] The invention relates to a double-lift crane with a heave compensation device. Background Art

[0002] A tandem lift crane, i.e., a crane comprising a main lift assembly and an auxiliary lift assembly, is generally known. Typically, the crane includes a boom supporting a main lift cable at its top end and a boom provided at the top end for supporting the auxiliary lift cable. Providing a boom with a boom enhances the crane's reach. For example, US Pat. No. 840,684 discloses a tandem lift crane.

[0003] It is known to provide offshore cranes with heave compensation systems. Such a crane is disclosed, for example, in US Pat. No. 9,290,362. If a twin-lift crane is equipped with a heave compensation system, heave compensation is often provided only for the primary lift assembly. In cases where both the primary and auxiliary lift assemblies are equipped with heave compensation, each lift assembly is typically provided with its own dedicated heave compensation system.

[0004] Providing a crane with two heave compensation systems increases the production costs of the crane. In addition, the heave compensation systems are bulky and therefore require space in the crane or on the vessel.

[0005] For example, WO2011034422 discloses a twin-lift crane in the form of a multi-purpose tower that includes a heave compensation system. The twin-lift crane comprises a main lift assembly equipped with a heave compensation system associated with the main lift cables, and a deepwater lift assembly. A releasable attachment mechanism designed to interconnect the main lift cables and the deepwater lift cables is provided. Thus, the heave compensation system associated with the main lift cables can be operated in combination with the deepwater lift cables.

[0006] A releasable attachment mechanism is located on the traveling block and tackle of the main lift assembly and is configured to engage the deepwater lift cable, interconnecting the deepwater lift cable with the main lift cable. The main lift assembly is then used to support the weight of the deepwater lift cable and the object supported by the deepwater lift cable. While the load of the deepwater lift cable and the object are supported by the main lift assembly, the heave compensation system is able to provide heave compensation, i.e., mitigate the effects of vessel movement on the object supported by the main lift cable.

[0007] It will be appreciated that since the main hoisting line must be connected to the deepwater cable, the free-hanging sections of the main hoisting line and the deepwater cable must be in the vicinity of each other or must be brought into the vicinity of each other. This requires a special arrangement of the crane.

[0008] Furthermore, shared heave compensation systems require a releasable attachment mechanism configured to directly engage the cables so that loads can be transferred to them. This releasable attachment mechanism can be complex and bulky, and must be movably supported to enable heave compensation. Furthermore, once the cables are interconnected, the deepwater winch must follow the main hoist winch to maintain parallelism and prevent slack and tension buildup in the deepwater cables. Furthermore, heave compensation can only be provided within the confines of the main hoist cables or along the trajectory of the releasable attachment mechanism. Summary of the Invention

[0009] A general object of the present invention is to provide an alternative tandem lift crane having a heave compensation system for both the main lift assembly and the auxiliary lift assembly of the tandem lift crane.

[0010] A further object of the first aspect of the present invention is to provide a tandem lift crane in which the above-mentioned disadvantages are completely eliminated or occur to a much reduced extent.

[0011] It is another object of the present invention to provide an alternative heave compensation system, in particular an improved heave compensation system configured to provide heave compensation for both the main lifting assembly and the auxiliary lifting assembly.

[0012] According to the invention, one or more of the above-mentioned objects is achieved by designing a tandem lift crane according to claim 1 .

[0013] A twin lift crane in accordance with the claimed invention includes a twin lift heave compensation system configured for use with a main lift assembly and an auxiliary lift assembly.

[0014] The dual lift heave motion compensation system includes a heave compensation cylinder, a first set of sheaves associated with the main lift cables, and a second set of sheaves associated with the auxiliary lift cables. The dual lift heave motion compensation system is configured to couple with the first set of sheaves to provide heave compensation for the main lift assembly and to couple with the second set of sheaves to provide heave compensation for the auxiliary lift assembly.

[0015] Therefore, the present invention provides a twin lift crane with an alternative heave compensation system to provide a twin lift crane with heave compensation for both the main lift assembly and the auxiliary lift assembly of the twin lift crane.

[0016] Because the twin-lift heave compensation system according to the present invention can be used with both the main and auxiliary lift assemblies, there is no longer a need for a dedicated heave compensation system for each lift assembly. Furthermore, there is no need for a releasable attachment mechanism for interconnecting the main and auxiliary lift cables. Consequently, the present invention enables a more compact and / or cost-effective configuration of a heave compensation system for a twin-lift crane, particularly for a twin-lift crane.

[0017] Furthermore, the dual lift heave compensation system does not require the free hanging sections of the main hoist cable and the free hanging sections of the auxiliary hoist cable to be near each other or to have to be brought near each other. This allows the dual lift heave compensation system to be used with many crane arrangements.

[0018] A double lift crane according to the claimed invention comprises:

[0019] - Crane structure;

[0020] a boom having an inner end, a middle section and an outer end, the boom being pivotally supported by the crane structure so that it can pivot about a substantially horizontal boom axis;

[0021] - a main lifting assembly for lifting and lowering the load, said main lifting assembly comprising a main lifting winch and associated main lifting cables, and a main load suspension device;

[0022] - an auxiliary lifting assembly for lifting and lowering a load, said auxiliary lifting assembly comprising an auxiliary lifting winch and associated auxiliary lifting cables, and auxiliary load suspension means;

[0023] -Dual lift heave motion compensation system, the heave motion compensation system comprising:

[0024] - Support frame;

[0025] - a heave compensation cylinder having a cylinder body and a cylinder rod mounted on a support frame, the heave compensation cylinder being connected to a gas buffer to achieve passive heave compensation;

[0026] - a sheave head, wherein the sheave head is supported by a ram for movement along a heave compensation track;

[0027] - a sheave dock mounted on the support frame at the end of the heave compensation track;

[0028] - a first set of sheaves, which guide the main lifting cables of the main lifting assembly;

[0029] - a second set of sheaves, which guide the auxiliary lifting cables of the auxiliary lifting assembly;

[0030] wherein the main hoisting cable extends from the main hoist winch via the first set of sheaves and via at least one main hoisting sheave at the outer end of the boom along a heave compensation trajectory to the main load suspension,

[0031] wherein the auxiliary lifting cable extends from the auxiliary lifting winch via a second set of sheaves and via at least one auxiliary lifting sheave at the outer end of the boom, preferably at the outer end of the jib, along a heave compensation trajectory to the auxiliary load suspension, and

[0032] The dual-lift heave motion compensation system is configured to lock the first set of sheaves and the second set of sheaves to the sheave head separately for providing heave compensation for the main lifting assembly and the auxiliary lifting assembly respectively, and to lock the first set of sheaves and the second set of sheaves to the sheave tail separately for not providing heave compensation for the main lifting assembly and the auxiliary lifting assembly respectively, and the dual-lift heave motion compensation system is therefore capable of providing heave compensation only for the main lifting assembly and only for the auxiliary lifting assembly.

[0033] According to the claimed invention, the lifting assembly is configured such that the main and auxiliary lift cables run along the heave-compensating trajectory of the heave-compensating assembly and are both guided via sheaves of the heave-compensating assembly. Furthermore, the heave-compensating cylinders are configured to switch between guiding the sheaves for the main lift cables and the sheaves for guiding the auxiliary lift cables. Thus, the present invention provides an efficient way to share the functionality of the heave-compensating cylinders between the main and auxiliary lift assemblies.

[0034] It will be appreciated that the heave compensation system according to the present invention may comprise a single heave compensation cylinder, or may comprise a combination of a plurality of heave compensation cylinders.

[0035] The one or more heave compensation cylinders are coupled to a gas buffer. The gas buffer may be part of the heave compensation system or may be a separate component. Preferably, the gas buffer is mounted adjacent to the heave compensation system, for example, on the heave compensation cylinders and / or to a support frame of the heave compensation system.

[0036] In one embodiment, the sheaves of the first set of sheaves and the sheaves of the second set of sheaves are configured to lock to the sheave head, such as bolted to the sheave head, or to the sheave butt, such as bolted to the sheave butt.

[0037] For example, the sheaves may each include a sheave bracket having a locking device (e.g., a hole for receiving a rod for fixing), or the sheave bracket may be configured to be bolted to the sheave head and to the sheave butt. Mounting the sheaves separately at the sheave head and the sheave butt allows for a compact configuration of the heave compensation system.

[0038] In one embodiment, each sheave is provided with a sheave bracket including a sheave bracket body in which the sheave is rotatably mounted, and a sheave head coupling section and a sheave heel coupling section on opposite sides of the sheave bracket body for engaging and coupling with the sheave head and sheave heel, respectively.

[0039] In another preferred embodiment, the sheave head coupling section and / or the sheave butt coupling section is a beak configured to engage the beam-shaped sheave head and the beam-shaped sheave butt. Preferably, the beak is shaped, for example, to be narrower in the direction toward the sheave, in order to guide the sheave bracket in the correct locking position relative to the sheave head and the sheave butt.

[0040] In a preferred embodiment, the sheave bracket is provided with locking means which are configured to cooperate with locking means provided on the sheave head and sheave butt to lock the sheave bracket and therefore the sheave held by the sheave bracket in a locked position relative to the sheave head and sheave butt.

[0041] In an alternative embodiment, the first set of sheaves and the second set of sheaves are mounted in a first sheave block and a second sheave block, respectively, and wherein the first sheave block and the second sheave block are configured to be mounted to a sheave head and to a sheave butt to lock the sheave to the sheave head and to lock the sheave to the sheave butt, respectively.

[0042] In this embodiment, a single set of sheaves can all be locked at once to either the sheave head or the sheave foot. This facilitates the locking process. It will be appreciated that it is also possible to mount a set of sheaves in multiple sheave blocks, for example, six sheaves in two sheave blocks, each including three sheaves.

[0043] In another embodiment, the tandem lift crane further comprises a locking device for locking the sheave or the sheave block in which the sheave is mounted to the sheave head and the sheave foot, wherein the locking device preferably comprises one or more locking pins movable between a locked position entered into the locking hole and an unlocked position.

[0044] In one embodiment, the locking device comprises one or more actuators, such as hydraulic cylinders or electric spindles, for semi-automatically locking the sheave or block to the sheave head or sheave foot.

[0045] The sheave or sheave block is in a locked position when locked to the sheave tail. It will be appreciated that the heave compensation trajectory preferably terminates before this locked position. Thus, the sheave supported by the sheave head will not move into the locked position when it is moved by the heave compensation cylinder during heave compensation.

[0046] Preferably, the heave compensation cylinder is configured to move the sheave head along the heave compensation trajectory. Preferably, the cylinder is configured to extend beyond the heave compensation trajectory to position the sheave locked to the sheave head in a locked position in which the sheave can be locked to the sheave heel and in which the sheave locked to the sheave heel can be locked to the sheave head.

[0047] Additionally, or alternatively, the sheave may be movably supported such that the sheave may be moved toward the sheave head when the heave compensation is in the extended position to position the sheave in a locked position in which the sheave may be locked to both the sheave head and the sheave.

[0048] In an alternative embodiment, the heave compensating assembly includes a sheave transfer device configured to transfer the sheave between a locked position relative to the sheave head for locking the sheave to the sheave head and a locked position relative to the sheave foot for locking the sheave to the sheave foot. This sheave transfer device may include a trolley to which the sheave may be mounted, the trolley being movable along a trolley track, e.g., by means of a cable and winch or by means of a hydraulic cylinder, to move the sheave between the respective locking positions.

[0049] Furthermore, the sheaves, sheave blocks and sheave heads and heels are preferably provided with cooperating guide means for guiding the sheaves or sheave blocks into the correct locking position.

[0050] It will be appreciated that the heave compensation system according to the claimed invention is preferably mounted in a crane, for example in the crane structure or, if present, to a gantry or boom of the crane.

[0051] As an alternative, the heave compensation system may be located below the crane structure, such as in the foundation of the crane, or in the hull of a vessel. In this embodiment, the lifting cables of the main and auxiliary lifting assemblies are guided from the crane to the heave compensation system and back to the crane via sheaves.

[0052] In an embodiment, the tandem lift crane further comprises a slew bearing arranged for pivoting the crane structure about the vertical crane pivot axis.

[0053] In one embodiment, the tandem lift crane according to the present invention is a mast crane or a pedestal mounted crane.

[0054] In one embodiment, a tandem lift crane includes a luffing assembly for pivoting a boom up and down, the luffing assembly comprising:

[0055] - a luffing winch and associated luffing cables; and

[0056] - a gantry supporting a luffing cable sheave for guiding the luffing cable from the luffing winch to the outer end of the boom.

[0057] In another embodiment, the platform includes a backstay and a rear frame, each pivotally mounted at a lower end to the crane structure for pivoting about a generally horizontal backstay pivot axis and a rear frame pivot axis, respectively, and each pivotally connected to each other at an upper end,

[0058] The rear frame is located between the backstay and the boom, and

[0059] The backstay comprises a lower frame section and an upper frame section, the lower frame section and the upper frame section being pivotally connected, and

[0060] The platform can be lowered by pivoting the lower frame section relative to the upper frame section.

[0061] By providing a tandem crane with such a gantry, the overall height of the crane (in particular, the crane's gantry) can be reduced, enabling it to pass under bridges. This gantry framework is particularly beneficial for large jib cranes, as for these types of cranes the gantry is particularly useful in supporting the jib and luffing cables, but it also has a disadvantage: it increases the size of the crane, thereby reducing the bridge-passing capacity of the vessel on which the crane is mounted.

[0062] In yet another embodiment, the supporting frame of the heave motion compensation system is mounted in the backstays of the platform, preferably in the upper frame section of the backstays, preferably the supporting frame is an integral part of the backstays.

[0063] Providing the dual lift heave compensation system in a gantry, rather than for example in the base of a crane or below a crane in a vessel, allows the framework of the backstays to be used as the dual lift heave compensation system framework. This allows for a compact and efficient configuration of the dual lift heave compensation system.

[0064] In another embodiment, the luffing winch is mounted to the crane structure, such as the gantry, near the rear frame pivot axis. This is particularly beneficial when the gantry is configured to fold into a lowered position, as will be described below.

[0065] In another embodiment, the pitch assembly includes a pitch cable guide arm supporting at least one pitch cable pulley, the guide arm preferably being pivotally mounted to the rear frame, the guide arm including at least one boom side pulley, the pitch cable pulley and boom side pulley being spaced relative to each other for guiding the pitch cable to the boom and keeping a portion of the pitch cable spaced a distance from the backstay.

[0066] Providing this pitch cable guide arm prevents the pitch cable from being supported too close to the frame of the gantry and provides an improved angle for the pitch cable to luff the boom out of its lowered position and thereby aids the pitching process.

[0067] In one embodiment, the tandem lift crane further comprises a towing track mounted to and extending along the boom for guiding a trolley along the length of the boom, the trolley being configured to support a cable, such as provided with a winch, for connection to a load supported by the primary or auxiliary lift assembly, thereby reducing sway of the load and preferably positioning the load relative to the boom.

[0068] A trailer equipped with towing rails provides additional support for loads being raised and lowered by a tandem crane, specifically reducing or even preventing swaying of the crane-supported load. Conventional towing cables originating from a towing device mounted on the vessel's deck are used. These towing cables need to be longer than towing cables originating from a winch mounted on a trailer supported on a boom. The relatively short towing cables improve control of the crane-supported load. Furthermore, towing rails allow for optimal positioning of the trailer relative to the crane-supported load. Depending on the load and conditions, the trailer can be positioned above, below, or flush with the load supported by the crane's lifting cables.

[0069] Furthermore, the towing track enables the trailer to be moved along the boom when the load is raised or lowered, thus maintaining an optimal position during lowering and / or lifting of the load.

[0070] In one embodiment, the boom is provided with a jib, wherein the jib is mounted at an outer end of the boom, and wherein the main lifting cables are supported at the outer end of the boom and the auxiliary lifting cables are supported at the outer end of the jib. It will be appreciated that by supporting the auxiliary lifting cables by the jib, the reach of the crane is increased without requiring a longer and therefore heavier boom.

[0071] In one embodiment, the number of sheaves of one group (e.g., a first group) is even, and wherein the sheaves of the group are divided into two subgroups, each subgroup comprising the same number of sheaves, and each subgroup having a sheave head locking position and a sheave heel locking position in which the sheaves are locked to the sheave head and the sheave heel, respectively, wherein the locking positions of the subgroups are spaced relative to each other,

[0072] wherein another set (e.g., the second set) of sheaves has a sheave head locking position and a sheave tail locking position in which the sheaves are locked to the sheave head and the sheave tail, respectively, and

[0073] The sheave head locking position and the sheave tail locking position of the another group are located between the sheave head locking position and the sheave tail locking position of the subgroup.

[0074] This configuration allows for an even load distribution, depending on which set is locked to the heave compensation cylinder or cylinders that support the sheave during heave compensation.

[0075] It will be appreciated that heave compensation cylinders, particularly in their extended position, are susceptible to load forces that are not aligned with the cylinder's working axis. Typically, cylinders with a robust design are used to compensate for suboptimal loads. The configuration disclosed above results in a less robust, and therefore more compact and lighter, heave compensation cylinder.

[0076] Preferably, the sheave head locking position and the sheave foot locking position of the other group (in the above example, the second group) are located on the central axis of the heave compensation cylinder, or the combined central axis of a plurality of heave compensation cylinders. In this embodiment, the sheave head locking position and the sheave foot locking position of the subset are located on opposite sides of the central axis.

[0077] Furthermore, the present invention provides a twin lift heave compensation system for use in a twin lift crane according to one or more of the preceding claims.

[0078] It should be understood that the dual-lift heave compensation system according to the claimed invention can also be used in other types of cranes (i.e., cranes without a jib). For example, in one embodiment, the dual-lift heave compensation system according to the present invention is installed in a multi-purpose tower. In this embodiment, the sections of the main and auxiliary lift assembly cables are parallel and run near the exterior of the tower. Furthermore, in this embodiment, the heave compensation system is preferably installed inside the tower, or in the case of a vessel, below the tower, so that it is isolated from the environment.

[0079] Furthermore, the present invention provides a ship equipped with the tandem lift crane according to the present invention.

[0080] Furthermore, the present invention provides a method for lifting a load using a tandem lift crane according to the invention, the method comprising the following steps:

[0081] - locking the first set of sheaves to the head of the sheave and the second set of sheaves to the tail of the sheave, and

[0082] - lifting the load using the main lift assembly while using the heave compensation system to provide heave compensation for the main lift cables,

[0083] and / or

[0084] - locking the second set of sheaves to the head of the sheave and the first set of sheaves to the tail of the sheave, and

[0085] The load is lifted using the auxiliary lift assembly while the heave motion compensation system is used to provide heave motion compensation for the auxiliary lift cables.

[0086] Furthermore, the present invention provides a method for changing a dual lift heave compensation system according to the present invention between providing heave compensation for a main lift assembly and providing heave compensation for an auxiliary lift assembly, the method comprising the following steps:

[0087] - moving the sheave head supporting the first set of sheaves towards the tail end supporting the second set of sheaves by extending one or more heave compensation cylinders;

[0088] - locking the first set of sheaves to the tail of the sheave and the second set of sheaves to the head of the sheave, and

[0089] - Retracting one or more heave compensation cylinders into an active position for providing heave compensation, thereby moving the sheave head away from the sheave butt.

[0090] Thus, in this method, one or more heave compensating cylinders are used to move the sheave into and out of a docked position where the sheave can be locked to the sheave head or sheave foot.

[0091] Furthermore, the present invention provides a method for lowering a platform of a tandem lift crane, wherein the platform is configured to be folded into a lowered position, the platform comprising backstays having a lower frame section hingeably connected to an upper frame section, the method comprising the following steps:

[0092] - Lowering the boom into the rest position;

[0093] - setting the hoisting cables (e.g. auxiliary hoisting cables) at a constant tension, for example by using a heave compensation system or a hoisting winch (e.g. auxiliary hoisting winch) associated with said hoisting cables, to thereby load the backstays of the gantry;

[0094] - initiating pivoting of the lower frame section of the backstay relative to the upper frame section of the backstay, for example by using an actuator (e.g. a hydraulic cylinder) or a towing cable;

[0095] - Paying out the pitch cables to lower the platform, preferably while maintaining constant tension in the lift cables, until the platform is in its lowered position.

[0096] By lowering the gantry, the height of the vessel on which the crane is mounted can be lowered and the vessel can thus pass under a lower bridge. It will be understood that the gantry and the method for lowering the gantry disclosed herein can also be used with other cranes, i.e. with single lift cranes and / or with cranes including alternative heave compensation systems or no heave compensation system.

[0097] According to a second aspect, the present invention further provides a crane having a boom, a luffing device, and a gantry, wherein the gantry is configured to be lowered by folding a portion of the gantry frame, in particular by folding the gantry's backstays. As a result, the overall height of the crane (in particular, the crane's gantry) can be reduced, enabling bridge clearance. This gantry is particularly beneficial for large boom cranes, as the gantry is particularly useful for supporting the boom and luffing cables for these types of cranes. However, it has a disadvantage: it increases the size of the crane, thereby reducing the bridge clearance capacity of the vessel on which the crane is mounted.

[0098] A crane according to a second aspect of the present invention comprises

[0099] - Crane structure;

[0100] a boom having an inner end, a middle section and an outer end, the boom being pivotally supported by the crane structure so that it can pivot about a substantially horizontal boom axis;

[0101] A pitch assembly for pivoting the boom up and down, the pitch assembly comprising:

[0102] - a luffing winch and associated luffing cables; and

[0103] - a gantry supporting a luffing cable sheave for guiding the luffing cable from the luffing winch to the outer end of the boom;

[0104] - a main lifting assembly for lifting and lowering the load, said main lifting assembly comprising a main lifting winch and associated main lifting cables, and a main load suspension device;

[0105] wherein the platform comprises a backstay and a rear frame, each of which is pivotally mounted at a lower end to the crane structure for pivoting about a substantially horizontal backstay pivot axis and a rear frame pivot axis, respectively, and each of which is pivotally connected to each other at an upper end,

[0106] The rear frame is located between the backstay and the boom, and

[0107] The backstay comprises a lower frame section and an upper frame section, the lower frame section and the upper frame section being pivotally connected, and

[0108] The platform can be lowered by pivoting the lower frame section relative to the upper frame section.

[0109] In one embodiment, the platform is provided with an actuator for pivoting the lower and upper frame sections of the backstay relative to each other and thus for lowering and raising the platform.

[0110] In one embodiment, the backstays of the platform, particularly the lower frame sections of the backstays, and the rear frame are each provided with support structures that are configured to cooperate to support the rear frame when the platform is in the folded configuration. Providing the platform with these supports provides a secure and rigid configuration for the platform when in the folded configuration.

[0111] In one embodiment, the dual-lift heave compensation system is arranged in the crane structure, preferably supported in the crane structure, such that one or more heave compensation cylinders extend in a vertical direction. In another embodiment, the dual-lift crane is further provided with a foldable platform, as discussed above. In another embodiment, the backstays, in particular the lower frame sections of the backstays, are provided with wire supports that support the main and auxiliary lift wires when the platform is in the folded configuration. In another embodiment, the wire supports are configured such that, when the platform is in the folded configuration, the lift wires are introduced into the dual-lift heave compensation system in a substantially vertical direction and, therefore, parallel to the cylinders.

[0112] In a preferred embodiment, the platform is provided with a heave compensation system according to the first aspect of the invention. In another embodiment, the platform is provided with a support frame for the heave compensation system, the support frame being mounted in the backstays of the platform, preferably in the upper frame section of the backstays, preferably the support frame being an integral part of the backstays.

[0113] In one embodiment, the luffing winch is mounted to the crane structure, for example to the gantry, near the rear frame pivot axis.

[0114] In one embodiment, the platform is a foldable platform as discussed herein, and the pitch assembly includes a pitch cable guide arm supporting at least one pitch cable pulley, the guide arm preferably being pivotally mounted to the rear frame, the guide arm including the at least one boom side pulley, the pitch cable pulley and boom side pulley being spaced relative to each other for guiding the pitch cable to the boom and spacing a portion of the pitch cable a distance from the backstay.

[0115] Preferably, the pitch cable guiding arm is arranged at the top of the rear frame, in particular at the top of the platform.Preferably, the guiding arm is pivotably supported by a guiding arm pivot axis, wherein the guiding arm pivot axis extends parallel to the boom pivot axis.

[0116] In another embodiment, the guide arm is a triangular configuration when viewed in a direction parallel to the pivot axis. In this embodiment, the triangular configuration is pivotally supported at its top, and the base of the triangular configuration supports at least one boom side pulley at one end, and the base of the triangle supports at least one gantry side pulley at an opposite end, the at least one luffing cable being routed from the crane structure through the at least one boom side pulley and through the at least one boom side pulley to the boom.

[0117] The pitch cable guide arm is configured to position the at least one boom side pulley away from the gantry, particularly the rear frame of the gantry, when the gantry is in the folded configuration. The pitch cable guide arm is configured such that, when the gantry is in the folded configuration, the at least one pitch cable does not extend from the top of the gantry to the boom, but rather extends to the boom from a position above the top of the gantry. Thus, when the boom is to be raised out of a lowered position, the guide arm provides an improved angle for at least the pitch cable relative to the boom. This is particularly beneficial when the boom is to be raised out of a lowered storage position.

[0118] Although primarily presented for illustrative purposes with reference to one or more of the accompanying drawings, any technical feature described below may be combined with any independent claim of the present application, alone or in any other technically possible combination with one or more other technical features.

[0119] Advantageous embodiments of the twin-lift crane and the twin-lift heave motion compensation system according to the invention, as well as of the method according to the invention, are disclosed in the dependent claims and in the description, wherein the invention is further described and illustrated on the basis of several exemplary embodiments, some of which are illustrated in the schematic drawings. In the figures, components with corresponding terms or construction and / or function are referenced by the same last two digits. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] In the attached figure:

[0121] Figure 1 showing a large bust perspective front view of a double lift crane according to the claimed invention;

[0122] Figure 2 exhibit Figure 1 A perspective rear view of the double-lift crane;

[0123] Figure 3 exhibit Figure 1 An enlarged view of a cross section of a double lift crane;

[0124] Figure 4 exhibit Figure 1 Another enlarged view of a cross section of a double lift crane;

[0125] Figure 5 Display with elevated platform Figure 1 Side view of a double lift crane;

[0126] Figure 6 Display with lowered stand Figure 1 Side view of a double lift crane;

[0127] Figure 7 A schematic diagram showing a double lift crane according to the present invention, wherein the platform is in a raised position;

[0128] Figure 8 A schematic diagram showing a double lift crane according to the present invention, wherein the gantry is in an intermediate position;

[0129] Figure 9 A schematic diagram showing a double lift crane according to the present invention, with the gantry in a lowered position;

[0130] Figure 10 A schematic diagram showing a heave compensation system according to the invention in a first condition;

[0131] Figure 11 A schematic diagram showing a heave compensation system according to the present invention in a second condition; and

[0132] Figure 12 A partial side view showing a partial cross section of a tandem lift crane according to the present invention; and

[0133] Figure 13 In alternative configuration Figure 12 Partial side view of a partial cross section of a double lift crane. DETAILED DESCRIPTION

[0134] Figure 1 A perspective view of a tandem lift crane 1 according to the invention is shown. The tandem lift crane 1 comprises a crane structure 2 and a boom 3 .

[0135] The boom 3 has an inner end 4, a mid-section 5 and an outer end 6. The boom 3 is pivotally supported by the crane structure 2 such that it can pivot about a substantially horizontal boom axis 7.

[0136] The tandem lift crane 1 further comprises a main lift assembly 8 for lifting and lowering a load, and an auxiliary lift assembly 12 for lifting and lowering a load.

[0137] The main lifting assembly 8 comprises a main lifting winch 9 and associated main lifting cables 10 , and a main load suspension 11 .

[0138] The auxiliary lift assembly 12 includes an auxiliary lift winch 13 , an associated auxiliary lift cable 14 and an auxiliary load suspension 15 .

[0139] In the illustrated embodiment, the tandem lift crane further includes a luffing assembly 32 for pivoting the boom 3 up and down. The luffing assembly includes a luffing winch 33 and associated luffing cables 34. The luffing assembly 32 further includes a gantry 35. The gantry supports a luffing cable sheave 36 for routing the luffing cables 34 from the luffing winch 33 to the outer end 6 of the boom 3.

[0140] It should be noted that the luffing cable 34 loops multiple times between the outer end 6 of the boom 3 and the gantry 35 to thereby enable the luffing cable 34 to support the weight of the boom 3 and potentially the weight of the load supported by the tandem lift crane 1 .

[0141] Furthermore, in the embodiment shown, the boom 3 is provided with a boom 46 mounted at the outer end 6 of the boom 3. The main lifting cables 10 are supported at the outer end of the boom 3 and the auxiliary lifting cables 14 are supported at the outer end of the boom 46.

[0142] According to the claimed invention, the tandem lift crane 1 further comprises a tandem lift heave motion compensation system 16. The heave motion compensation system 16 comprises a support frame 17, two heave compensation cylinders 18, each having a sheave head 22, a sheave foot 24, a first set of sheaves 25 and a second set of sheaves 26.

[0143] In the embodiment shown, the support frame 17 is part of a gantry 35 of the tandem crane 1. The support frame 17, and in particular the gantry 35, supports two heave compensation cylinders 18.

[0144] Each of the heave compensation cylinders 18 has a cylinder body 19 and a cylinder rod 20. The heave compensation cylinders are mounted in parallel in the support frame of the heave compensation assembly, which in the embodiment shown is mounted in the gantry of the twin-lift crane. Furthermore, the two cylinders 18 are mounted so that their cylinder bodies 19 are at the top and the cylinder rods 20 extend in a downward direction.

[0145] The heave compensation cylinders are each connected to a gas damper 21 to achieve passive heave compensation. In the embodiment shown, the gas damper is also mounted to the support frame 17, in the embodiment shown to the stage 35.

[0146] The sheave head 22 is supported by the cylinder rod 20 for movement along a heave compensation track 23. The heave compensation track extends parallel to the heave compensation cylinder 18 between the lower end of the cylinder body 19 and the sheave butt 24.

[0147] In accordance with the claimed invention, the sheave heel is mounted on the support frame of the heave compensation assembly, at the end of the heave compensation track. In the illustrated embodiment, the gantry of the tandem crane forms the heave compensation frame. Thus, in the illustrated embodiment, the sheave heel 24 is a crossbeam that is also part of the gantry 35.

[0148] The first set of sheaves 25 guides the main lift cables 10 of the main lift assembly 8 , while the second set of sheaves 26 guides the auxiliary lift cables 14 of the auxiliary lift assembly 12 .

[0149] The main hoisting cable 10 extends along a heave compensation track 23 from the main hoisting winch 9 via a first set of sheaves 25 and via at least one main hoisting sheave 27 at the outer end 6 of the boom 3 to the main load suspension 11 .

[0150] The auxiliary lift cable 14 extends along the heave compensating track 23 from the auxiliary lift winch 13 via a second set of sheaves 26 and via at least one auxiliary lift sheave 28 at the outer end 6 of the boom 3 (in the embodiment shown, at the outer end of the boom 46) to the auxiliary load suspension arrangement 15.

[0151] In accordance with the claimed invention, the dual lift heave motion compensation system 16 is configured to individually lock the first and second sets of sheaves 25, 26 to the sheave head 22 for providing heave compensation to the main lift assembly 8 and the auxiliary lift assembly 12, respectively.

[0152] The dual lift heave motion compensation system 16 is further configured to individually lock the first set of sheaves 25 and the second set of sheaves 26 to the sheave butts 24 for providing no heave compensation to the main lift assembly 8 and the auxiliary lift assembly 12, respectively.

[0153] The dual lift heave motion compensation system 16 thus provides heave compensation only for the main lift assembly 8 and only for the auxiliary lift assembly 12 .

[0154] In the illustrated embodiment, both the main lift cable 10 and the auxiliary lift cable 14 loop multiple times around the heave compensation cylinder 18 and, therefore, along the heave compensation trajectory 23. Thus, the heave compensation cylinder 18 can provide heave compensation with minimal stroke of the cylinder rod. This enables a compact configuration of the heave compensation system.

[0155] Furthermore, in the embodiment shown, for each heave compensating cylinder, the second set of sheaves 26 guiding the auxiliary lifting cables 14 is subdivided into two sub-sets 47 arranged on opposite sides of the first set of sheaves 25 guiding the main lifting cables 10 .

[0156] The number of sheaves 26 in the second group is an even number. The sheaves of the group are divided into two subgroups 47, each of which includes the same number of sheaves. In addition, each of the subgroups 47 has a sheave head locking position 48 and a sheave foot locking position 49 in which the sheave is locked to the sheave head 22 and the sheave foot 24, respectively.

[0157] The sheaves 25 of the first set also have a sheave head locking position 48 and a sheave butt locking position 49 in which the sheaves are locked to the sheave head 22 and the sheave butt 24, respectively.

[0158] exist Figure 3 and Figure 4 In the embodiment shown in FIG. 4 , a subset 47 of the second set of sheaves 26 is in a sheave tail locking position 49 , while the first set of sheaves 25 is in a sheave head locking position 48 .

[0159] The locking positions of the subset 47 are spaced relative to each other. The sheave head locking position 48 and sheave foot locking position 49 of the first set of sheaves 25 are located between the sheave head locking position 48 and sheave foot locking position 49 of the subset 47.

[0160] In the illustrated embodiment, the sheaves of the first set of sheaves 25 and the sheaves of the second set of sheaves 26 are configured to be locked to the sheave head 22, in particular to be bolted to the sheave head, and to the sheave butt 24, in particular to be bolted to the sheave butt 24.

[0161] In an alternative embodiment, the first set of sheaves and the second set of sheaves are mounted in first and second sheave blocks, respectively, and wherein the first and second sheave blocks are configured to be mounted to the sheave head and to the sheave butt to lock the sheave to the sheave head and to lock the sheave to the sheave butt, respectively.

[0162] In the embodiment shown, the tandem lift crane thus comprises a locking device for locking the sheave, or alternatively the sheave block in which the sheave is mounted, to the sheave head and the sheave butt. In the embodiment shown, the locking device comprises a nut and a bolt for locking the sheave to the sheave head and the sheave butt, and holes in the sheaves (in particular, the sheave bracket, the sheave head and the sheave butt) for receiving the bolt.

[0163] Figure 1 The double lift crane 1 depicted in the figure implements a method for lifting a load according to the present invention. The method comprises the following steps:

[0164] Lock the first set of sheaves 25 to the sheave head 22 and the second set of sheaves 26 to the sheave tail 24, as shown in FIG. Figure 3 and Figure 4 As shown in

[0165] The load is lifted and lowered using the main lift assembly 8 while providing heave motion compensation to the main lift cables 10 using the heave motion compensation system 16.

[0166] and / or

[0167] Locking the second set of sheaves 26 to the sheave head 22 and the first set of sheaves 25 to the sheave foot 24, and

[0168] The load is lifted using the auxiliary lift assembly 12 while providing heave motion compensation to the auxiliary lift cables 14 using the heave motion compensation system 16 .

[0169] In the illustrated embodiment, the tandem lift crane 1 includes a towing track 44. The towing track 44 is mounted to and extends along the boom 3 for guiding a trolley 45 along the length of the boom 3. The trolley 45 is configured to support a cable, such as provided with a winch, for connection to a load supported by the main lift assembly 8 or the auxiliary lift assembly 12, thereby reducing sway of the load and preferably positioning the load relative to the boom.

[0170] In the embodiment shown, the main hoist winch 9 and the auxiliary hoist winch 13 are secured to the crane structure 2 at the rear of the crane 1 and below the gantry 35. In the preferred embodiment shown, the main and auxiliary hoist cables extend from their respective winches to the top of the gantry 35, loop multiple times through the heave compensation system, are guided through the top of the gantry to the bottom of the boom, and run along the boom to the distal ends of the boom and jib.

[0171] In the preferred embodiment shown, the tandem lift crane 1 is mounted on a vessel 50 .

[0172] Figure 7-9 A simplified schematic diagram of a tandem lift crane 101 is shown including a luffing assembly 132 and a gantry 135. The figures depict subsequent steps in the lowering process of the gantry, which will be described below.

[0173] The platform 135 includes backstays 137 and a rear frame 138, each of which is pivotally mounted at a lower end to the crane structure 102 for pivoting about a generally horizontal backstay pivot axis 140 and a rear frame pivot axis 139, respectively, and each of which is pivotally connected to each other at an upper end. In one embodiment, the rear frame and backstays are directly coupled to each other; in alternative embodiments, they may be coupled via an intermediate body.

[0174] The rear frame 138 is located between the backstay 137 and the boom 103. The backstay 137 includes a lower frame section 141 and an upper frame section 142 that are pivotally connected to each other. The platform 135 can be lowered by pivoting the lower frame section relative to the upper frame section. Figure 9 The lowered position of the stage 135 is depicted in FIG.

[0175] In the illustrated embodiment, the luffing winch 133 is mounted to the gantry 135 , near the rear frame pivot axis 140 .

[0176] In a preferred embodiment, the supporting frame of the heave motion compensation system is mounted in the backstays of the platform, preferably in the upper frame section of the backstays, preferably the supporting frame is an integral part of the backstays.

[0177] To lower the height of the vessel, the gantry 135 can be lowered. Furthermore, the present invention provides a method for lowering the gantry 135, comprising the steps set out below. It will be appreciated that the gantry and associated method can be used with a double-lift crane equipped with a heave compensation system according to the present invention, but can also be used with a single-lift crane and / or a crane without a heave compensation system.

[0178] In order to lower the platform, first, the boom is lowered into a rest position. This preferably also includes securing the load suspension of one or more lifting assemblies in a parked position near the boom.

[0179] Subsequently, the hoisting cables 10 are set under constant tension. In the embodiment only a single hoisting assembly is depicted, but the crane may also be provided with auxiliary hoisting assemblies. This may be achieved by using a heave compensation system (if present) or by using an associated hoisting winch 109. The hoisting winch is set under constant tension thereby loading the backstay of the gantry. This step is performed in Figure 7 , where arrow 201 indicates the tensioning of the lifting cable 110 .

[0180] Subsequently, the pivoting of the lower frame section 141 of the backstay 137 relative to the upper frame section 142 of the backstay 137 is initiated. Figure 8 , arrow 202 indicates the activated articulation. This activation can be performed by means of an actuator (e.g., a hydraulic cylinder installed in the backstay) or by pulling at the articulation point using a towing cable, for example.

[0181] Once articulation of the backstays has been initiated, the platform is prevented from articulating into the lowered position by the pitch cables. Therefore, preferably the pitch cables are paid out while maintaining constant tension in the lifting cables so that the platform is lowered in a controlled manner. Thus, by paying out the pitch cables, the platform is lowered to Figure 9, wherein arrow 202 indicates the payout of the pitch cable.

[0182] Figure 7-9 The embodiment depicted in FIG. 1 also shows a schematic depiction of a pitch cable guide arm 143, which is also located in the pitch assembly. Figure 1-6 Described in more detail in .

[0183] In one embodiment, the pitch assembly 132 includes a pitch cable guide arm 143 that supports at least one pitch cable pulley 136. The guide arm 143 is pivotally mounted to the platform 135, preferably the platform's rear frame 138. The guide arm includes at least one boom side pulley 151 that is paced relative to the pitch cable pulley 136 by the arm. The purpose of the pitch cable guide arm is to guide the pitch cable to the boom while spacing a portion of the pitch cable away from the backstay. Thus, the angle between the pitch cable and the platform is optimal for lifting the boom and pulling the platform into a raised position.

[0184] Figure 10 and 11 A schematic representation of an embodiment of a dual lift heave compensation system 316 according to the present invention is depicted. FIG20 depicts a heave compensation system 316 configured to provide heave to a main lift assembly, while Figure 11 Depicted is a heave compensation system 316 configured to provide heave for the auxiliary lift assembly.

[0185] The depicted heave compensation cylinder 318 comprises a cylinder body 319 and a cylinder rod 320 , with the cylinder being mounted in a support frame 317 .

[0186] In the illustrated embodiment, a first set of sheaves 325 mounted in a first sheave block 329 guides the main lift cables 310. A second set of sheaves 326 guiding the auxiliary lift cables 314 includes sub-sets 347, each of which is mounted in a second sheave block 330.

[0187] exist Figure 10 3, the first sheave set 329 is locked to the sheave butt 324, while the second sheave set 330 is locked to the sheave head 322 supported by the heave compensation cylinder 318. Thus, the heave compensation cylinder 318 allows the first set of sheaves 325 to move along the heave compensation track 323, thereby providing heave compensation for the main lifting assembly.

[0188] Figure 11, first sheave set 329 is locked to sheave head 322, while second sheave set 330 is locked to sheave set 324. Thus, heave compensation cylinder 318 allows second set of sheaves 326 (particularly, sub-set 347 of second set of sheaves) to move along heave compensation track 323, thereby providing heave compensation for the auxiliary lifting assembly.

[0189] Figure 12 A partial side view in partial cross section of a tandem lift crane 401 according to the invention is shown. Figure 13 The same crane is shown in different configurations. Both figures provide schematic diagrams of the crane, where not all components are depicted and some components are depicted in perspective. The primary purpose of these figures is to illustrate alternative mounting locations for the dual lift heave compensation system 416.

[0190] Double lift crane 401 is similar to Figure 1 The twin lift crane 1 is shown in FIG. Both cranes are provided with a twin lift heave compensation system 16; 416 according to the invention.

[0191] The main difference between the two cranes is that Figure 12 In the twin-lift crane 401 shown in FIG, the twin-lift heave compensation system 416 is not mounted in the crane's gantry 435. Instead, the twin-lift heave compensation system 416 is mounted in the crane structure 402 of crane 401. Thus, in this embodiment of the twin-lift crane according to the present invention, the majority of the twin-lift heave compensation system is mounted low in the crane. Consequently, the center of gravity of the crane and the vessel is relatively low, which benefits the vessel's dynamic characteristics. This is particularly true when the vessel is traveling between construction sites and when the crane's boom is in a lowered position.

[0192] The tandem lift crane 401 comprises a crane structure 402 and a boom 403. The boom 403 is pivotably supported by the crane structure 402 such that it can pivot about a substantially horizontal boom axis.

[0193] The tandem lift crane 401 further includes a main lift assembly 408 for lifting and lowering a main load, and an auxiliary lift assembly 412 for lifting and lowering an auxiliary load.

[0194] The main lift assembly 408 includes a main lift winch 409 and associated main lift cables 410, as well as a main load suspension arrangement.

[0195] The auxiliary lift assembly 412 includes an auxiliary lift winch 413, associated auxiliary lift cables 414, and an auxiliary load suspension device.

[0196] Both the main and auxiliary lift cables are guided via a dual lift heave motion compensation system 416 .

[0197] Similar to Figure 3 The dual lift heave compensation system shown in FIG. 4 includes a support frame, two heave compensation cylinders 418 , each of which has a sheave head 422 , a sheave tail 424 , a first set of sheaves 425 and a second set of sheaves 426 .

[0198] Similar to Figure 3 The dual lift heave compensation system shown in FIG. 4 includes a support frame, two heave compensation cylinders 418 , each of which has a sheave head 422 , a sheave tail 424 , a first set of sheaves 425 and a second set of sheaves 426 .

[0199] It should be noted that the dual lift heave compensation system 416 is shown in side view and not all components are depicted in the drawing. Additionally, the heave compensation cylinders 418 are depicted in a retracted position, supporting a first set of sheaves 425. A second set of sheaves 426 is depicted mounted to the sheave butt 424.

[0200] In the embodiment shown, the support frame 417 is mounted in the crane structure 402 of the tandem lift crane 1 .

[0201] In the illustrated embodiment, the crane structure 402 is rotatably supported on a base via a slew bearing. A support frame 417 of a dual-lift heave compensation system 416, which supports two heave compensation cylinders 418, is supported by the crane structure 402 and extends through the slew bearing into the base supporting the dual-lift crane 401. Thus, when the crane 401 rotates, the dual-lift heave compensation system 416, or at least a portion thereof, moves through the base of the dual-lift crane.

[0202] Each of the heave compensation cylinders 418 has a cylinder body 419 and a cylinder rod 420. The heave compensation cylinders are mounted in parallel in the support frame of the heave compensation assembly. In addition, the two cylinders 418 are mounted so that their cylinder bodies 419 are at the top and the cylinder rods 420 extend in the downward direction.

[0203] The heave compensation cylinders 418 are each connected to the gas buffers 21 to achieve passive heave compensation. In the embodiment shown, the gas buffers are also mounted to the crane structure 402.

[0204] The sheave head 422 is supported by the cylinder rod 420 for movement along a heave compensation track 423. The heave compensation track extends parallel to the heave compensation cylinder 418 between the lower end of the cylinder body 419 and the sheave tail 424.

[0205] According to the claimed invention, the sheave is mounted at the end of the heave compensating track on the support frame of the heave compensating assembly.

[0206] The main hoist cable 410 extends from the main hoist winch 409 via a first set of sheaves 425 and via at least one main hoist sheave at the outer end of the boom along a heave compensation track 423 to the main load suspension.

[0207] The auxiliary lift cable 414 extends from the auxiliary lift winch 413 via a second set of sheaves 426 and via at least one auxiliary lift sheave at the outer end of the boom along a heave compensating track 423 to the auxiliary load suspension.

[0208] In accordance with the claimed invention, the dual lift heave motion compensation system 416 is configured to individually lock the first set of sheaves 425 and the second set of sheaves 426 to the sheave head 422 for providing heave compensation to the main lift assembly and the auxiliary lift assembly, respectively.

[0209] The dual lift heave motion compensation system 416 is further configured to individually lock the first set of sheaves 425 and the second set of sheaves 426 to the sheave butt 424 for providing no heave compensation to the main lift assembly and the auxiliary lift assembly, respectively.

[0210] The dual lift heave motion compensation system 16 thus provides heave compensation only for the main lift assembly and only for the auxiliary lift assembly.

[0211] Similar to the embodiment depicted in the previous figures, Figure 12 and Figure 13 The tandem lift crane 401 depicted in FIG 4 includes a gantry 435 including backstays 437 and a rear frame 438. The backstays and rear frame are each pivotally mounted at a lower end to the crane structure 402 for pivoting about generally horizontal backstay pivot axes 440 and rear frame pivot axes 439, respectively, and are each pivotally connected to one another at an upper end.

[0212] The rear frame 438 is located between the backstay 437 and the boom 403. The backstay 437 includes a lower frame section 441 and an upper frame section 442 that are pivotally connected to each other. The platform 135 can be lowered by pivoting the lower frame section relative to the upper frame section. Figure 13 The lowered position of the platform 435 is depicted in FIG.

[0213] In the illustrated embodiment, the backstays 437, and in particular the lower frame sections 441 of the backstays 437, are provided with support structures 455 that cooperate with support structures 456 provided on the rear frame 435 to support the rear frame when the stand 435 is in the folded configuration. Providing the stand with these supports provides a secure and rigid configuration for the stand when in the folded configuration.

[0214] Also, in the illustrated embodiment, the backstay 437, and in particular the lower frame section 441 of the backstay 437, is provided with a wire support 457 that supports the main lift wire 410 and the auxiliary lift wire 414 when the platform 435 is in the folded configuration. In the illustrated embodiment, the wire support is configured so that the lift wires are introduced into the dual lift heave compensation system 416 in a generally vertical direction and therefore parallel to the cylinder 418 when the platform 435 is in the folded configuration.

[0215] Reference numerals

[0216] 01 Double lift crane

[0217] 02 Crane structure;

[0218] 03 Boom

[0219] 04 Inner end boom

[0220] 05 Middle boom

[0221] 06 Outer end boom

[0222] 07 horizontal boom axis;

[0223] 08 Main lifting assembly

[0224] 09 Main lifting winch

[0225] 10 Main lift cables

[0226] 11 Main load suspension device

[0227] 12 Auxiliary lifting components

[0228] 13 Auxiliary lifting winch

[0229] 14 Auxiliary lifting cables

[0230] 15 Auxiliary load suspension device

[0231] 16 Dual lift heave motion compensation system

[0232] 17 Support frame double lifting and sinking motion compensation system

[0233] 18 Heave compensation cylinder

[0234] 19 Cylinder heave compensation cylinder

[0235] 20 Cylinder rod heave compensation cylinder

[0236] 21 Gas Buffer

[0237] 22 Pulley head

[0238] 23 heave compensation track;

[0239] 24 Pulley tail

[0240] 25 First set of pulleys

[0241] 26 Second set of pulleys

[0242] 27 Main lifting pulley

[0243] 28 Auxiliary lifting pulley

[0244] 29 First pulley block

[0245] 30 Second pulley block

[0246] 31 Locking device for locking a pulley or block

[0247] 32 Pitch assembly

[0248] 33 Luffing winch

[0249] 34 Pitch Cable

[0250] 35 racks

[0251] 36 Pitching Cable Pulley

[0252] 37 Backstay Stand

[0253] 38 rear frame stand

[0254] 39 substantially horizontal rear frame pivot axis

[0255] 40 Substantially horizontal backstay pivot axis

[0256] 41 Lower frame section rear cable

[0257] 42 Upper frame section rear cable

[0258] 43 Pitch cable guide arm

[0259] 44 towing track

[0260] 45 trailer

[0261] 46 boom

[0262] 47 Pulley subassembly

[0263] 48 Pulley head locking position

[0264] 49 Pulley tail root locking position

[0265] 50 ships

[0266] 51 Boom side pitch pulley

[0267] 55 Support structure

[0268] 56 Support structure

[0269] 57 Wire supports.

Claims

1. A double lift crane comprising: - Crane structure; - a boom having an inner end, a midsection and an outer end, the boom being pivotably supported by the crane structure such that it can pivot about a substantially horizontal boom axis; - a main lifting assembly for lifting and lowering the load, said main lifting assembly comprising a main lifting winch and associated main lifting cables, and a main load suspension device; - an auxiliary lifting assembly for lifting and lowering a load, said auxiliary lifting assembly comprising an auxiliary lifting winch and associated auxiliary lifting cables, and auxiliary load suspension means; It is characterized in that the twin-lift crane further includes a twin-lift heave motion compensation system, and the heave motion compensation system includes: - Support frame; a heave compensation cylinder having a cylinder body and a cylinder rod mounted on the support frame, the heave compensation cylinder being connected to a gas buffer to achieve passive heave compensation; - a sheave head, wherein the sheave head is supported by the ram for movement along a heave compensation track; - a sheave tail mounted on the support frame at the end of the heave compensation track; - a first set of sheaves guiding the main lifting cables of the main lifting assembly; - a second set of sheaves guiding the auxiliary lifting cables of the auxiliary lifting assembly; wherein the main hoist cable extends from the main hoist winch via the first set of sheaves and via at least one main hoist sheave at the outer end of the boom along the heave compensation trajectory to the main load suspension, wherein the auxiliary lifting cable extends from the auxiliary lifting winch via the second set of sheaves and via at least one auxiliary lifting sheave at the outer end of the boom along the heave compensation trajectory to the auxiliary load suspension, and The dual-lift heave motion compensation system is configured to individually lock the first set of sheaves and the second set of sheaves to the sheave head for providing heave compensation for the main lift assembly and the auxiliary lift assembly, respectively, and to individually lock the first set of sheaves and the second set of sheaves to the sheave tail for not providing heave compensation for the main lift assembly and the auxiliary lift assembly, respectively, and the dual-lift heave motion compensation system is thus capable of providing heave compensation only for the main lift assembly and only for the auxiliary lift assembly.

2. The tandem lift crane of claim 1 , wherein the sheaves of the first set of sheaves and the sheaves of the second set of sheaves are configured to lock to the sheave heads and to the sheave tails.

3. The tandem lift crane of claim 1 , wherein the first set of sheaves and the second set of sheaves are mounted in first and second sheave blocks, respectively, and wherein the first and second sheave blocks are configured to be mounted to the sheave head and to the sheave butt to thereby lock the sheave to the sheave head and the sheave to the sheave butt, respectively.

4. The tandem lift crane according to claim 1 , 2 or 3, wherein the tandem lift crane further comprises a locking device for locking a sheave or a sheave block in which a sheave is mounted to the sheave head and the sheave foot.

5. A tandem lift crane according to claim 1 , 2 or 3, wherein the crane comprises a luffing assembly for pivoting the boom up and down, the luffing assembly comprising: - a luffing winch and associated luffing cables; as well as - a gantry supporting a luffing cable sheave for guiding the luffing cable from the luffing winch to the outer end of the boom.

6. The tandem lift crane of claim 5 , wherein the gantry comprises backstays and a rear frame, each pivotally mounted at a lower end to the crane structure for pivoting about a generally horizontal backstay pivot axis and a rear frame pivot axis, respectively, and each pivotally connected to each other at an upper end, wherein the rear frame is located between the backstay and the boom, and The backstay comprises a lower frame section and an upper frame section, wherein the lower frame section and the upper frame section are pivotally connected, and The platform can be lowered by pivoting the lower frame section relative to the upper frame section.

7. The tandem lift crane according to claim 6, wherein the support frame of the heave motion compensation system is mounted in the backstays of the gantry.

8. The tandem lift crane of claim 6, wherein the luffing winch is mounted to the crane structure near the rear frame pivot axis.

9. The tandem lift crane of claim 5 , wherein the luffing assembly includes a luffing cable guide arm supporting at least one luffing cable sheave, the guide arm including at least one boom side pulley, the luffing cable sheave and boom side pulley being spaced relative to each other for guiding the luffing cable to the boom and spacing a portion of the luffing cable a distance from a backstay.

10. The tandem lift crane of claim 1 , 2 or 3, further comprising a towing track mounted to and extending along the boom for guiding a trolley along the length of the boom, the trolley being configured to support a cable for connecting the cable to a load supported by the main lift assembly or the auxiliary lift assembly and to reduce sway of the load.

11. The tandem lift crane according to claim 1 , 2 or 3, wherein the boom is provided with a jib, wherein the jib is mounted at the outer end of the boom, and wherein the main lift cables are supported at the outer end of the boom and the auxiliary lift cables are supported at the outer end of the jib.

12. The tandem lift crane according to claim 1 , 2 or 3 , wherein the number of sheaves of one group is an even number, and wherein the sheaves of the group are divided into two subgroups, each subgroup comprising the same number of sheaves, and each subgroup having a sheave head locking position and a sheave foot locking position in which sheaves are locked to the sheave head and the sheave foot, respectively, wherein the locking positions of the subgroups are spaced relative to each other, The sheaves of the other group have a sheave head locking position and a sheave tail locking position, in which the sheaves are locked to the sheave head and the sheave tail, respectively, and The sheave head locking position and the sheave tail root locking position of another group are located between the sheave head locking position and the sheave tail root locking position of the subgroup.

13. A twin lift heave compensation system for use in a twin lift crane, the heave compensation system comprising: - Support frame; a heave compensation cylinder having a cylinder body and a cylinder rod mounted on the support frame, the heave compensation cylinder being configured to be connected to a gas buffer to achieve passive heave compensation; - a sheave head, wherein the sheave head is supported by the ram for movement along a heave compensation track; - a sheave tail mounted on the support frame at the end of the heave compensation track; - a first set of sheaves for guiding the main lifting cables of the main lifting assembly; - a second set of sheaves for guiding the auxiliary lifting cables of the auxiliary lifting assembly; and The dual-lift heave motion compensation system is configured to individually lock the first set of sheaves and the second set of sheaves to the sheave head for providing heave compensation for the main lift assembly and the auxiliary lift assembly, respectively, and to individually lock the first set of sheaves and the second set of sheaves to the sheave tail for not providing heave compensation for the main lift assembly and the auxiliary lift assembly, respectively, and the dual-lift heave motion compensation system is thus capable of providing heave compensation only for the main lift assembly and only for the auxiliary lift assembly.

14. A ship comprising the tandem lift crane according to claim 1, 2 or 3.

15. A method for lifting a load using a twin lift crane according to claim 1, 2 or 3, the method comprising the steps of: - locking the first set of sheaves to the sheave head and the second set of sheaves to the sheave foot, and - lifting a load with the main lifting assembly while using the heave motion compensation system to provide heave motion compensation for the main lifting cables, and / or - locking the second set of sheaves to the sheave head and the first set of sheaves to the sheave foot, and - lifting a load with the auxiliary lift assembly while using the heave motion compensation system to provide heave motion compensation for the auxiliary lift cables.

16. A method for lowering a gantry of a tandem lift crane according to claim 7, wherein the gantry is configured to fold into a lowered position, the method comprising the steps of: - lowering the boom into a rest position; - setting the lifting cables at a constant tension, thereby loading the backstays of the platform; - actuating the pivoting of the lower frame section of the backstay relative to the upper frame section of the backstay; - Paying out the pitch cables to lower the platform until the platform is in its lowered position.

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