Heave compensated dual hoist crane

Abstract

A dual hoist crane is provided with a heave compensation system that can be used for both the main and for the auxiliary hoisting assembly. The heave compensation system includes a first set of sheaves for guiding the main hoisting cable and a second set of sheaves for guiding the auxiliary hoisting cable. The heave compensation system is configured to individually lock the first set of sheaves and the second set of sheaves to a heave compensation cylinder, for respectively providing the main hoisting assembly and the auxiliary hoisting assembly with heave compensation.

Claims

1. A crane, configured to be mounted on a vessel, the crane comprising: a crane structure; a boom, the boom having an inner end, a midsection, and an outer end, the boom being pivotable supported by the crane structure such that the boom can be pivoted about a substantially horizontal boom pivot axis; a main hoisting assembly, for lifting and lowering a load, the main hoisting assembly comprising a main hoisting winch and an associated main hoisting cable, and a main load suspension device; and a luffing assembly for pivoting the boom up and down, the luffing assembly comprising: a luffing winch and an associated luffing cable; and a gantry comprising a back stay and a back frame, the gantry supporting a luffing cable sheave for guiding the luffing cable from the luffing winch to the outer end of the boom, wherein the back frame is located between the back stay and the boom, and wherein the back stay and back frame are both at a lower end pivotably mounted to the crane structure, for pivoting about a substantially horizontal back stay pivot axis and back frame pivot axis respectively, and are both at an upper end pivotably connected to each other, wherein the gantry is a foldable gantry, the back stay comprising a lower frame section and an upper frame section, the lower frame section and the upper frame section being pivotably connected to each other, and wherein the gantry can be lowered by pivoting the lower frame section relative to the upper frame section, and wherein the lower frame section of the back stay and the back frame are both provided with a support structure, the support structures being configured to vertically engage one another to cooperate to support the back frame only when the gantry is in the folded configuration.

2. The crane according to claim 1, wherein the gantry is provided with actuators for pivoting the lower frame section and the upper frame section of the backstay relative to each other, and thus for lowering and raising the gantry.

3. The crane according to claim 1, wherein the luffing winch is mounted to the gantry, near the back frame pivot axis.

4. The crane according to claim 1, wherein the crane is a dual hoist crane that is provided with an auxiliary hoisting assembly for lifting and lowering a load, the auxiliary hoisting assembly comprising an auxiliary hoisting winch and an associated auxiliary hoisting cable, and an auxiliary load suspension device.

5. The crane according to claim 4, wherein the lower frame section of the back stay, is provided with a cable support, the cable support supporting the main hoisting cable and the auxiliary hoisting cable when the gantry is in the folded configuration.

6. The crane according to claim 5, wherein the gantry is provided with a dual hoist heave compensation system and wherein the cable support is configured such that the hoisting cables are led into the dual hoist heave compensation system in a vertical direction and parallel to cylinders of the dual hoist heave compensation system, when the gantry is in the folded configuration.

7. A vessel provided with the crane according to claim 1.

8. A method for lowering height of a vessel provided with a cable comprising: a crane structure; a boom, the boom having an inner end, a midsection, and an outer end, the boom being pivotable supported by the crane structure such that the boom can be pivoted about a substantially horizontal boom pivot axis; a main hoisting assembly, for lifting and lowering a load, the main hoisting assembly comprising a main hoisting winch and an associated main hoisting cable, and a main load suspension device; and a luffing assembly for pivoting the boom up and down, the luffing assembly comprising: a luffing winch and an associated luffing cable; and a gantry comprising a back stay and a back frame, the gantry supporting a luffing cable sheave for guiding the luffing cable from the luffing winch to the outer end of the boom, wherein the back frame is located between the back stay and the boom, and wherein the back stay and back frame are both at a lower end pivotably mounted to the crane structure, for pivoting about a substantially horizontal back stay pivot axis and back frame pivot axis respectively, and are both at an upper end pivotably connected to each other, and wherein the gantry is a foldable gantry, the back stay comprising a lower frame section and an upper frame section, the lower frame section and the upper frame section being pivotably connected to each other, and wherein the gantry can be lowered by pivoting the lower frame section relative to the upper frame section, the method comprising the steps of: lowering the boom in a rest position; setting the main hoisting cable under constant tension to thus load the back stay of the gantry; initiating pivoting of the lower frame section of the back stay relative to the upper frame section of the back stay; and paying out the luffing cable to lower the gantry, until the gantry is in a lowered position thereof.

9. The method according to claim 8, wherein the step of setting the main hoisting cable under constant tension comprises using a heave compensation system or the hoisting winch associated with the main hoisting cable for setting the hoisting cable under constant tension.

10. The method according to claim 8, wherein initiating pivoting of the lower frame section of the back stay relative to the upper frame section of the back stay comprises using an actuator for pivoting the lower frame section of the back stay relative to the upper frame section of the back stay.

11. The method according to claim 8, wherein paying out the luffing cable to lower the gantry comprises keeping constant tension in the hoisting cable until the gantry is in its lowered position.

12. A pedestal mounted dual hoist crane configured to be mounted on a vessel, the crane comprising: a pedestal; a slew bearing; and a crane structure which is via the slew bearing rotatable supported on the pedestal; a boom, the boom having an inner end, a midsection, and an outer end, the boom being pivotable supported by the crane structure such that the boom can be pivoted about a substantially horizontal boom pivot axis; a main hoisting assembly, for lifting and lowering a load, the main hoisting assembly comprising a main hoisting winch and an associated main hoisting cable, and a main load suspension device; and an auxiliary hoisting assembly for lifting and lowering a load, the auxiliary hoisting assembly comprising an auxiliary hoisting winch and an associated auxiliary hoisting cable, and an auxiliary load suspension device; a luffing assembly for pivoting the boom up and down, the luffing assembly comprising: a luffing winch and an associated luffing cable; and a gantry comprising a back stay and a back frame, the gantry supporting a luffing cable sheave for guiding the luffing cable from the luffing winch to the outer end of the boom, a heave motion compensation system, having one or more heave compensation cylinders that extend in a vertical direction from the crane structure, via the bearing, into the pedestal of the crane.

13. The crane according to claim 12, wherein the back frame is located between the back stay and the boom, and wherein the back stay and back frame are both at a lower end pivotably mounted to the crane structure, for pivoting about a substantially horizontal back stay pivot axis and back frame pivot axis respectively, and are both at an upper end pivotably connected to each other, and wherein the gantry is a foldable gantry, the back stay comprising a lower frame section and an upper frame section, the lower frame section and the upper frame section being pivotably connected to each other, and wherein the gantry can be lowered by pivoting the lower frame section relative to the upper frame section.

14. The crane according to claim 13, wherein the lower frame section of the back stay is provided with a cable support, which cable support supports the main hoisting wire and the auxiliary hoisting wire when the gantry is in the folded configuration, wherein the cable support is configured such that the hoisting cables are led into the heave compensation system in a substantially vertical direction, and thus parallel to the cylinders, when the gantry is in the folded configuration.

15. The crane according to claim 12, wherein the heave compensation cylinders are each connected to a gas buffer to enable passive heave compensation.

16. A vessel provided with the crane according to claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows perspective three quarter frontal view of a dual hoist crane according to the claimed invention;

(2) FIG. 2 shows a perspective three quarter rear view of the dual hoist crane of FIG. 1;

(3) FIG. 3 shows an enlarged view of a section of the dual hoist crane of FIG. 1;

(4) FIG. 4 shows a further enlarged view of a section of the dual hoist crane of FIG. 1;

(5) FIG. 5 shows a side view of the dual hoist crane of FIG. 1 with a raised gantry;

(6) FIG. 6 shows a side view of the dual hoist crane of FIG. 1 with a lowered gantry;

(7) FIG. 7 shows a schematic drawing of a dual hoist crane according to the invention, with a gantry in a raised position;

(8) FIG. 8 shows a schematic drawing of a dual hoist crane according to the invention, with a gantry in an intermediate position;

(9) FIG. 9 shows a schematic drawing of a dual hoist crane according to the invention, with a gantry in a lowered position;

(10) FIG. 10 shows a schematic drawing of a heave compensation system according to the invention in a first condition;

(11) FIG. 11 shows a schematic drawing of a heave compensation system according to the invention in a second condition; and

(12) FIG. 12 shows a partial side view, in partial cross section, of a dual hoist crane according to the invention; and

(13) FIG. 13 a partial side view, in partial cross section, of the dual hoist crane of FIG. 12 in an alternative configuration.

DETAILED DESCRIPTION OF THE DRAWINGS

(14) FIG. 1 shows a perspective view of a dual hoist crane 1 according to the invention. The dual hoist crane 1 comprises a crane structure 2 and a boom 3.

(15) The boom 3 has an inner end 4, a midsection 5, and an outer end 6. The boom 3 is pivotable supported by the crane structure 2 such that it can be pivoted about a substantially horizontal boom axis 7.

(16) The dual hoist crane 1 further comprises a main hoisting assembly 8, for lifting and lowering a load, and an auxiliary hoisting assembly 12 for lifting and lowering a load.

(17) The main hoisting assembly 8 comprises a main hoisting winch 9 and an associated main hoisting cable 10, and a main load suspension device 11.

(18) The auxiliary hoisting assembly 12 comprises an auxiliary hoisting winch 13, an associated auxiliary hoisting cable 14, and an auxiliary load suspension device 15.

(19) In the embodiment shown, the dual hoist crane further comprises a luffing assembly 32 for pivoting the boom 3 up and down. The luffing assembly comprises a luffing winch 33 and an associated luffing cable 34. The luffing assembly 32 further comprises a gantry 35. The gantry supports a luffing cable sheave 36 for guiding the luffing cable 34 from the luffing winch 33 to the outer end 6 of the boom 3.

(20) It is noted that the luffing cable 34 is looped multiple times between the outer end 6 of the boom 3 and the gantry 35, to thus enable the luffing cable 34 to support the weight of the boom 3, and potentially the weight of a load supported by the dual hoist crane 1.

(21) Furthermore, in the embodiment shown, the boom 3 is provided with a jib 46, mounted at the outer end 6 of the boom 3. The main hoisting cable 10 is supported at the outer end of the boom 3 and the auxiliary hoisting cable 14 is supported at an outer end of the jib 46.

(22) According to the claimed invention, the dual hoist crane 1 further comprises a dual hoist heave motion compensation system 16. The heave motion compensation system 16 comprises a support frame 17, two heave compensation cylinders 18, which heave compensation cylinders are each provided with a sheave head 22, a sheave dock 24, a first set of sheaves 25 and a second set of sheaves 26.

(23) In the embodiment shown, the support frame 17 is part of a gantry 35 of the dual hoist crane 1. The support frame 17, more in particular the gantry 35, supports the two heave compensation cylinders 18.

(24) Each of the heave compensation cylinders 18 has a cylinder body 19 and a cylinder rod 20. The heave compensation cylinders are mounted parallel in the support frame of the heave compensation assembly, in the embodiment shown are mounted in the gantry of the dual hoist crane. Furthermore, both cylinders 18 are mounted with their cylinder bodies 19 at the top, the cylinders rods 20 extending in a downward direction.

(25) The heave compensation cylinders are both connected to a gas buffer 21 to enable passive heave compensation. In the embodiment shown, the gas buffers are also mounted to the support frame 17, in the embodiment shown the gantry 35.

(26) The sheave heads 22 are supported by the cylinder rods 20, for movement along a heave compensation trajectory 23. The heave compensation trajectory runs parallel to the heave compensation cylinders 18, between the lower end of the cylinder bodies 19 and the sheave dock 24.

(27) According to the claimed invention, the sheave dock is mounted on the support frame of the heave compensation assembly, at an end of the heave compensation trajectory. In the embodiment shown, the gantry of the dual hoist crane forms the heave compensation frame. Thus, in the embodiment shown, the sheave dock 24 is a cross beam that is also part of the gantry 35.

(28) The first set of sheaves 25 guides the main hoisting cable 10 of the main hoisting assembly 8, while the second set of sheaves 26 guides the auxiliary hoisting cable 14 of the auxiliary hoisting assembly 12.

(29) The main hoisting cable 10 extends from the main hoisting winch 9 along the heave compensation trajectory 23, via the 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 device 11.

(30) The auxiliary hoisting cable 14 extends from the auxiliary hoisting winch 13 along the heave compensation trajectory 23, via the second set of sheaves 26, and via at least one auxiliary hoisting sheave 28 at the outer end 6 of the boom 3, in the embodiment shown at an outer end of a jib 46, to the auxiliary load suspension device 15.

(31) According to the claimed invention, the dual hoist heave motion compensation system 16 is configured to individually lock the first set of sheaves 25 and the second set of sheaves 26 to the sheave head 22, for respectively providing the main hoisting assembly 8 and the auxiliary hoisting assembly 12 with heave compensation.

(32) The dual hoist 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 dock 24, for respectively not providing the main hoisting assembly 8 and the auxiliary hoisting assembly 12 with heave compensation.

(33) The dual hoist heave motion compensation system 16 thus enables for providing only the main hoisting assembly 8 with heave compensation and for providing only the auxiliary hoisting assembly 12 with heave compensation.

(34) In the embodiment shown, both the main hoisting cable 10 and the auxiliary hoisting cable 14 are looped multiple times around the heave compensation cylinders 18, and thus are looped multiple times along the heave compensation trajectory 23. Thus, the heave compensation cylinders 18 can provide heave compensation with a minimal stroke of the cylinder rods. This allows for a compact configuration of the heave compensation system.

(35) Furthermore, in the embodiment shown, for each heave compensation cylinder, the second set of sheaves 26, guiding the auxiliary hoisting cable 14, is subdivided into two subsets 47, which subsets are provided on opposite sides of the first set of sheaves 25, guiding the main hosting cable 10.

(36) The number of sheaves of second set 26 is even. The sheaves of that set are divided into two subsets 47, each subset comprising the same number of sheaves. Furthermore, each of the subsets 47 has a sheave head locking position 48 and a sheave dock locking position 49, in which they are locked to the sheave head 22 and to the sheave dock 24 respectively.

(37) The sheaves of the first set 25 also have a sheave head locking position 48 and a sheave dock locking position 49, in which they are locked to the sheave head 22 and to the sheave dock 24 respectively.

(38) In FIG. 3 and FIG. 4, the subsets 47 of the second set of sheaves 26 are in the sheave dock locking position 49, while the first set of sheaves 25 are in the sheave head locking position 48.

(39) The locking positions of the subsets 47 are spaced relative to each other. The sheave head locking position 48 and the sheave dock locking position 49 of the first set of sheaves 25 are located between the sheave head locking position 48 and the sheave dock locking position 49 of the subsets 47.

(40) In the embodiment shown, 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, more in particular are configured to be bolted to the sheave head, and to be locked to the sheave dock 24, more in particular are configured to be bolted to the sheave dock 24.

(41) In an alternative embodiment, the sheaves of the first set and the sheaves of the second set 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 the sheave head and to be mounted to the sheave dock, to lock the sheaves to the sheave head and to lock the sheaves to the sheave dock respectively.

(42) In the embodiment shown, the dual hoist crane therefore comprises locking devices for locking the sheaves, or alternatively the sheave blocks in which the sheaves are mounted, to the sheave head and the sheave dock. In the embodiment shown, the locking devices comprise the nuts and bolts for locking the sheaves to the sheave head and the sheave dock, and the apertures in the sheaves, more in particular the sheave holders, the sheave head and the sheave dock for receiving the bolts.

(43) The dual hoist crane 1 depicted in FIG. 1 enables a method for hoisting a load according to the invention. The method comprising the steps: locking the first set of sheaves 25 to the sheave head 22 and locking the second set of sheaves 26 to the sheave dock 24, as shown in FIG. 3 and FIG. 4, and hoisting a load with the main hoisting assembly 8 while providing the main hoisting cable 10 with heave motion compensation using the heave motion compensation system 16, and/or locking the second set of sheaves 26 to the sheave head 22 and locking the first set 25 of sheaves to the sheaves dock 24, and hoisting a load with the auxiliary hoisting assembly 12 while providing the auxiliary hoisting cable 14 with heave motion compensation using the heave motion compensation system 16.

(44) In the embodiment shown, the dual hoist crane 1 comprises a tugging track 44. The which tugging track 44 is mounted to the boom 3 and extends along the boom, for guiding a tug-trolley 45 along the length of the boom 3. The tug trolley 45 is configured to support cables, e.g. is provided with winches, to be linked to a load supported by the main hoisting assembly 8 or the auxiliary hoisting assembly 12, to reduce swing of said load, and preferably position the load relative to the boom.

(45) In the embodiment shown, the main hoisting winch 9 and the auxiliary hoisting winch 13 are fixed to the crane structure 2 at the back of the crane 1 and below the gantry 35. In the preferred embodiment shown, the main hoisting cable and the auxiliary hoisting cable extend from their respective winches to the top of the gantry 35, are looped multiple times in the heave compensation system, are guided via the top of the gantry to the base of the boom, and run along the boom to the far end of the boom and the jib.

(46) In the preferred embodiment shown, the dual hoist crane 1 is mounted on a vessel 50.

(47) FIGS. 7-9 show simplified schematic drawings of a dual hoist crane 101 comprising a luffing assembly 132 and a gantry 135. The figures depict subsequent steps in the lowering of the gantry, which process will be explained below.

(48) The gantry 135 comprises a back stay 137 and a back frame 138, which back stay and back frame are both at a lower end pivotably mounted to the crane structure 102, for pivoting about a substantially horizontal back stay pivot axis 140 and back frame pivot axis 139 respectively, and are both at an upper end pivotably connected to each other. in the embodiment the back frame and the back stay are directly coupled to each other, in an alternative embodiment, they may be coupled via an intermediate body.

(49) The back frame 138 is located between the back stay 137 and the boom 103. The backstay 137 comprises a lower frame section 141 and an upper frame section 142, which lower frame section and upper frame section are pivotably connected to each other. The gantry 135 can be lowered by pivoting the lower frame section relative to the upper frame section. The lowered position of the gantry 135 is depicted in FIG. 9.

(50) In the embodiment shown, the luffing winch 133 is mounted to the gantry 135, near the back frame pivot axis 140.

(51) In a preferred embodiment, the support frame of the heave motion compensation system is mounted in the backstay of the gantry, preferably is mounted in the upper frame section of the back stay, preferably the support frame is an integral part of the back stay.

(52) To lower the height of the vessel, the gantry 135 can be lowered. The invention furthermore provides a method for lowering the gantry 135, said method comprising the steps set out below. It is submitted that the gantry, and the associated method, can be used with a dual hoist crane provided with a heave compensation system according to the invention, but can also be used with a single hoist crane, and/or with crane without the heave compensation system.

(53) To lower the gantry, first, the boom is lowered into a rest position. This preferably also includes securing the load suspension device of the hoisting assembly, or hoisting assemblies, in a parking position adjacent the boom.

(54) Subsequently, the hoisting cable 10 is set under constant tension. In the embodiment only a single hoisting assembly is depicted, but the crane can be provided with an auxiliary hoisting assembly as well. This can be done by using the heave compensation system, if present, or by using the associated hoisting winch 109. The hoisting winch is set under constant tension to thus load the back stay of the gantry. This step is depicted in FIG. 7, with an arrow 201 indicating the tensioning of the hoisting cable 110.

(55) Subsequently, pivoting of the lower frame section 141 of the back stay 137 relative to the upper frame section 142 of the back stay 137 is initiated. This is depicted in FIG. 8, arrow 202 indicating the initiated hinging. This initiating can be done by way of an actuator e.g. a hydraulic cylinder mounted in the back stay, or for example by pulling at the hinge point using a tugging cable.

(56) Once the hinging of the back stay has been initiated, the gantry is prevented from hinging into the lowered position by the luffing cable. Therefore, paying out the luffing cable, preferably while keeping constant tension in the hoisting cable, causes the gantry to be lowered in a controlled manner. Thus, by paying out the luffing cable the gantry is lowered into its lowered position, depicted in FIG. 9, in which arrow 202 indicates the pay out of the luffing cable.

(57) The embodiment depicted in FIGS. 7-9 also shows a schematic depiction of a luffing cable guide arm 143, which guide arm 43 is also depicted, in more detail, in the FIGS. 1-6, of the luffing assembly.

(58) In an embodiment, the luffing assembly 132 comprises a luffing cable guide arm 143 supporting the at least one luffing cable sheave 136. The guide arm 143 is pivotably mounted to the gantry 135, preferably the back frame 138 of the gantry. The guide arm comprises at least one boom side sheave 151, which is paced, by the arm, relative to luffing cable sheave 136. The purpose of the luffing cable guide arm is to guide the luffing cable to the boom while spacing part of the luffing cable at a distance from the back stay. Thus, the angle between luffing cable and gantry is optimal for lifting the boom, and for pulling the gantry into a lifted position.

(59) FIGS. 10 and 11 depict a schematic representation of an embodiment of a dual hoist heave compensation system 316 according to the invention. FIG. 20 depicts the heave compensation system 316 configured for providing heave to the main hoisting assembly, while FIG. 11 depicts the heave compensation system 316 configured for providing heave to the auxiliary hoisting assembly.

(60) Depicted are the heave compensation cylinder 318, comprising a cylinder body 319 and a cylinder rod 320, which cylinder is mounted in a support frame 317.

(61) In the embodiment shown, a first set of sheaves 325, mounted in a first sheave block 329, guides a main hoisting cable 310. A second set of sheaves 326, guiding an auxiliary hoisting cable 314, comprises to subsets 347, each mount in a second sheave block 330.

(62) In FIG. 10, the first sheave block 329 is locked to the sheave dock 324, while the second sheave blocks 330 are 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 trajectory 323, and thus provide the main hoisting assembly with heave compensation.

(63) In FIG. 11, the first sheave block 329 is locked to the sheave head 322, while the second sheave blocks 330 are locked to the sheave block 324. Thus, the heave compensation cylinder 318 allows the second set of sheaves 326, more in particular the subsets 347 of the second set of sheaves, to move along the heave compensation trajectory 323, and thus provide the auxiliary hoisting assembly with heave compensation.

(64) FIG. 12 shows a partial side view, in partial cross section, of a dual hoist crane 401 according to the invention. FIG. 13 shows the same crane, in a different configuration. Both figures provide a schematic view of the crane, wherein not all components are depicted and some are depicted in see through. The main purpose of the figures is to show an alternative mounting location of the dual hoist heave compensation system 416.

(65) The dual hoist crane 401 is similar to the dual hoist crane 1 shown in FIG. 1. Both cranes are provided with a dual hoist heave compensation system 16;416 according to the invention.

(66) The main differences between these two cranes is that with the dual hoist crane 401 shown in FIG. 12 the dual hoist heave compensation system 416 is not mounted in the gantry 435 of the crane. Instead, the dual hoist heave compensation system 416 is mounted in the crane structure 402 of the crane 401. Thus, in this embodiment of a dual hoist crane according to the invention, the mass of the dual hoist heave compensation system is mounted lower in the crane. Therefore, the center of gravity of the crane, and of the vessel, is relatively low, which is beneficial for the dynamic behavior of the vessel. This is in particular the case when the vessel is travelling between job sites and when the boom of the crane is in the lowered position.

(67) The dual hoist crane 401 comprises a crane structure 402 and a boom 403. The boom 403 is pivotable supported by the crane structure 402 such that it can be pivoted about a substantially horizontal boom axis.

(68) The dual hoist crane 401 further comprises a main hoisting assembly 408, for lifting and lowering a main load, and an auxiliary hoisting assembly 412 for lifting and lowering an auxiliary load.

(69) The main hoisting assembly 408 comprises a main hoisting winch 409 and an associated main hoisting cable 410, and a main load suspension device.

(70) The auxiliary hoisting assembly 412 comprises an auxiliary hoisting winch 413, an associated auxiliary hoisting cable 414, and an auxiliary load suspension device.

(71) Both the main hosting cable and the auxiliary hoisting cable are guided via the dual hoist heave motion compensation system 416.

(72) Similar to the dual hoist heave compensation system shown in FIG. 3, the system comprises a support frame, two heave compensation cylinders 418, which heave compensation cylinders are each provided with a sheave head 422, a sheave dock 424, a first set of sheaves 425 and a second set of sheaves 426.

(73) Similar to the dual hoist heave compensation system shown in FIG. 3, the system comprises a support frame, two heave compensation cylinders 418, which heave compensation cylinders are each provided with a sheave head 422, a sheave dock 424, a first set of sheaves 425 and a second set of sheaves 426.

(74) It is to be noted that the dual hoist heave compensation system 416 is shown in a side view, and that not all components are depicted in the drawing. Furthermore, the heave compensation cylinders 418 are depicted in the retracted position, supporting a first set of sheaves 425. The second set of sheaves 426 is depicted mounted to the sheave dock 424.

(75) In the embodiment shown, the support frame 417 is mounted in the crane structure 402 of the dual hoist crane 1.

(76) In the embodiment shown, the crane structure 402 is, via a slew bearing, rotatable supported on a pedestal. The support frame 417 of the dual hoist heave compensation system 416, which supports the two heave compensation cylinders 418, is supported by the crane structure 402, and extends through the slew bearing into the pedestal supporting the dual hoist crane 401. Thus, when the crane 401 is rotated, the dual hoist heave compensation system 416, or at least a part therefore, moves through the pedestal of the dual hoist crane.

(77) Each of the heave compensation cylinders 418 has a cylinder body 419 and a cylinder rod 420. The heave compensation cylinders are mounted parallel in the support frame of the heave compensation assembly. Furthermore, both cylinders 418 are mounted with their cylinder bodies 419 at the top, the cylinders rods 420 extending in a downward direction.

(78) The heave compensation cylinders 418 are both connected to a gas buffer 21 to enable passive heave compensation. In the embodiment shown, the gas buffers are also mounted to the crane structure 402.

(79) The sheave heads 422 are supported by the cylinder rods 420, for movement along a heave compensation trajectory 423. The heave compensation trajectory runs parallel to the heave compensation cylinders 418, between the lower end of the cylinder bodies 419 and the sheave dock 424.

(80) According to the claimed invention, the sheave dock is mounted on the support frame of the heave compensation assembly, at an end of the heave compensation trajectory.

(81) The main hoisting cable 410 extends from the main hoisting winch 409 along the heave compensation trajectory 423, via the first set of sheaves 425, and via at least one main hoisting sheave at the outer end of the boom to the main load suspension device.

(82) The auxiliary hoisting cable 414 extends from the auxiliary hoisting winch 413 along the heave compensation trajectory 423, via the second set of sheaves 426, and via at least one auxiliary hoisting sheave at the outer end of the boom, to the auxiliary load suspension device.

(83) According to the claimed invention, the dual hoist 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 respectively providing the main hoisting assembly and the auxiliary hoisting assembly with heave compensation.

(84) The dual hoist 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 dock 424, for respectively not providing the main hoisting assembly and the auxiliary hoisting assembly with heave compensation.

(85) The dual hoist heave motion compensation system 16 thus enables for providing only the main hoisting assembly with heave compensation and for providing only the auxiliary hoisting assembly with heave compensation.

(86) Similar to the embodiments depicted in the preceding figures, the dual hoist crane 401 depicted in FIG. 12 and FIG. 13 comprises a gantry 435 comprising a back stay 437 and a back frame 438. The back stay and back frame are both at a lower end pivotably mounted to the crane structure 402, for pivoting about a substantially horizontal back stay pivot axis 440 and back frame pivot axis 439 respectively, and are both at an upper end pivotably connected to each other.

(87) The back frame 438 is located between the back stay 437 and the boom 403. The backstay 437 comprises a lower frame section 441 and an upper frame section 442, which lower frame section and upper frame section are pivotably connected to each other. The gantry 135 can be lowered by pivoting the lower frame section relative to the upper frame section. The lowered position of the gantry 435 is depicted in FIG. 13.

(88) In the embodiment shown, the back stay 437, more in particular the lower frame section 441 of the back stay 437, is provided with a support structure 455, which support structure 455 cooperates with a support structure 456 provided on the back frame 435 to support the back frame when the gantry 435 is in the folded configuration. Providing the gantry with these supports, provides the gantry with a secure and rigid configuration when in the folded configuration.

(89) Also, in the embodiment shown, the back stay 437, more in particular the lower frame section 441 of the back stay 437, is provided with a wire support 457, which wire support 457 supports the main hoisting wire 410 and the auxiliary hoisting wire 414 when the gantry 435 is in the folded configuration. In the embodiment shown, the wire support is configured such that the hoisting wires are led into the dual hoist heave compensation system 416 in a substantially vertical direction, and thus parallel to the cylinders 418, when the gantry 435 is in the folded configuration.

REFERENCE SIGNS

(90) 01 dual hoist crane 02 crane structure; 03 boom 04 inner end boom 05 midsection boom 06 outer end boom 07 horizontal boom axis; 08 main hoisting assembly 09 main hoisting winch 10 main hoisting cable 11 main load suspension device 12 auxiliary hoisting assembly 13 auxiliary hoisting winch 14 auxiliary hoisting cable 15 auxiliary load suspension device 16 dual hoist heave motion compensation system 17 support frame dual hoist heave motion compensation system 18 heave compensation cylinder 19 cylinder body heave compensation cylinder 20 cylinder rod heave compensation cylinder 21 gas buffer 22 sheave head 23 heave compensation trajectory; 24 sheave dock 25 first set of sheaves 26 second set of sheaves 27 main hoisting sheave 28 auxiliary hoisting sheave 29 first sheave block 30 second sheave block 31 locking devices for locking the sheaves or the sheave blocks 32 luffing assembly 33 luffing winch 34 luffing cable 35 gantry 36 luffing cable sheave 37 back stay gantry 38 back frame gantry 39 substantially horizontal back frame pivot axis 40 substantially horizontal back stay pivot axis 41 lower frame section back stay 42 upper frame section back stay 43 luffing cable guide arm 44 tugging track 45 tug-trolley 46 jib 47 subsets of sheaves 48 sheave head locking position 49 sheave dock locking position 50 vessel 51 boom side luffing sheave 55 support structure 56 support structure 57 wire support