Method of upgrading a knuckle-boom crane and a heave-compensating crane

1. Method of upgrading a knuckle-boom crane to a heave-compensating crane, the method comprising:

providing a knuckle-boom crane having a crane base, a main boom pivotably mounted to the crane base, and a knuckle-boom pivotably mounted to the main boom;

removing the knuckle-boom from the main boom;

mounting a main boom extension to the main boom for increasing the length of the main boom;

mounting a heave-compensating boom at a far end of the main boom extension such that the heave-compensating boom extends in a downward vertical direction (Z) in operational use of the heave-compensating crane, wherein the heave-compensating boom is configured to be pivotable with respect to the main boom extension in both horizontal directions (X, Y) defined with respect to the downward vertical direction (Z), and

providing a heave-compensation system to the knuckle-boom crane comprising a plurality of actuators and the heave-compensating boom which is pivotable by at least one of the plurality of actuators, wherein the heave-compensation system is configured for compensating for horizontal variations by controlling the orientation of the heave-compensating boom relative to the main boom extension, and for compensating the vertical variations by means of a further vertical heave-compensation system which comprises a winch system configured for manipulating a hoisting cable to compensate the vertical variations.

2. The method according to claim 1 , wherein, in mounting the main boom extension, the main boom extension comprises a top-sheave at a far end of the main boom extension.

3. The method according to claim 2 , wherein, in mounting the heave-compensating boom, the heave-compensating boom comprises a hoisting cable guiding system for cooperating with the top-sheave.

4. The method according to claim 3 , wherein the heave-compensating boom comprises a first end coupled to the main boom extension and a second end spaced apart from the first end, and wherein, in mounting the heave-compensating boom, the hoisting cable guiding system comprises a pair of sheaves mounted on a rotatable head provided at the second end of the heave-compensating boom.

5. The method according to claim 1 , wherein, in mounting the heave-compensating boom, the heave-compensating boom comprises a first arm that is pivotably mounted to the main boom extension for allowing a rotation in a first horizontal direction (X), the heave-compensating boom further comprising a second arm that is pivotably mounted to the first arm for allowing a rotation in a second horizontal direction (Y) orthogonal to the first horizontal direction (X).

6. The method according to claim 5 , wherein, in mounting the heave-compensating boom, the first arm is mounted such that the first arm extends in a substantially horizontal direction (X) in operational use of the heave-compensating crane, and the second arm is mounted such that the second arm extends in the downward vertical direction (Z) in operational use of the heave-compensating crane.

7. The method according to claim 5 , wherein, in mounting the heave-compensating boom, said first and second arms are provided with electric or hydraulic actuators to control respective orientations of said arms.

8. The method according to claim 1 , further comprising completion steps of completing the heave-compensating crane for making the heave-compensating crane ready for operational use, wherein the completion steps comprise the installation of the hoisting cable along the main boom, the main boom extension and the heave-compensating boom.

9. A heave-compensating crane comprising:

a crane base;

a main boom having a near end pivotably mounted to the crane base and a far end spaced apart from the near end, the main boom extending in a single linear direction along the entire length of the main boom;

a heave-compensating boom pivotably mounted at a far end of the main boom and having a first end pivotably coupled to the far end of the main boom and a second end coupled to a rotatable head, the length between the far end of the main boom and the second end of the heave-compensating boom being fixed, wherein the heave-compensating boom extends in a downward vertical direction (Z) in operational use of the heave-compensating crane, wherein the heave-compensating boom is configured to be pivotable with respect to the main boom in both horizontal directions (X, Y) defined with respect to the downward vertical direction (Z),

a first heave-compensation system comprising a plurality of actuators, the rotatable head, and the heave-compensating boom which is pivotable by at least one of the plurality of actuators, and wherein the first heave-compensation system is configured for compensating for horizontal deviations by controlling the orientation of the heave-compensating boom relative to the main boom, and

a second heave-compensation system comprising a winch system configured for manipulating a hoisting cable to compensate vertical deviations.

10. The heave-compensating crane according to claim 9 , wherein the main boom comprises a top-sheave at the far end of the main boom.

11. The heave-compensating crane according to claim 10 , wherein the heave-compensating boom comprises a hoisting cable guiding system for cooperating with the top-sheave.

12. The heave-compensating crane according to claim 11 , wherein the hoisting cable guiding system comprises a pair of sheaves mounted on the rotatable head provided at the second end of the heave-compensating boom.

13. The heave-compensating crane according to claim 9 , wherein the heave-compensating boom comprises a first arm that is pivotably mounted to the main boom for allowing a rotation in a first horizontal direction (X), the heave-compensating boom further comprising a second arm that is pivotably mounted to the first arm for allowing a rotation in a second horizontal direction (Y) orthogonal to the first horizontal direction (X).

14. The heave-compensating crane according to claim 13 , wherein the first arm is mounted such that the first arm extends in a substantially horizontal direction (X) in operational use of the heave-compensating crane, and the second arm is mounted such that the second arm extends in the downward vertical direction (Z) in operational use of the heave-compensating crane.

15. The heave-compensating crane according to claim 13 , wherein said first and second arms are provided with electric or hydraulic actuators to control respective orientations of said arms.

16. The heave-compensating crane according to claim 9 wherein the main boom comprises a first boom section joined to a second boom section at a joint, wherein the first boom section comprises the near end of the main boom and the second boom section comprises the far end of the main boom, and wherein the joint is configured to maintain the first and second boom sections extending in the single linear direction.

17. The heave-compensating crane according to claim 16 , wherein the heave-compensating boom comprises a first arm that is pivotably mounted to the main boom for allowing a rotation in a first horizontal direction (X), the heave-compensating boom further comprising a second arm that is pivotably mounted to the first arm for allowing a rotation in a second horizontal direction (Y) orthogonal to the first horizontal direction (X).

18. The heave-compensating crane according to claim 17 , wherein the first arm is mounted such that the first arm extends in a substantially horizontal direction (X) in operational use of the heave-compensating crane, and the second arm is mounted such that the second arm extends in the downward vertical direction (Z) in operational use of the heave-compensating crane.

19. The heave-compensating crane according to claim 17 , wherein said first and second arms are provided with electric or hydraulic actuators to control respective orientations of said arms.

20. The heave-compensating crane according to claim 9 wherein the main boom comprises a plurality of boom sections joined together, and wherein the main boom is free of a knuckle-boom.

21. The heave-compensating crane according to claim 9 wherein the crane base comprises the second heave-compensation system.

22. The heave-compensating crane according to claim 9 , wherein the main boom comprises a first boom section joined to a second boom section by an elongate mounting bar connected between the first boom section and the second boom section such that the first boom section is prevented from pivoting relative to the second boom section.

23. The heave-compensating crane according to claim 9 , wherein the length between the first end of the heave-compensating boom and the rotatable head is fixed.

24. A heave-compensating crane comprising:

a crane base;

a main boom having a near end pivotably mounted to the crane base and a far end spaced apart from the near end, the main boom extending in a single linear direction along the entire length of the main boom; and

a first heave-compensation system comprising a plurality of actuators and a first heave-compensating boom pivotably mounted at a far end of the main boom and having a first end pivotably coupled to the far end of the main boom and a second end coupled to a rotatable head, the length between the far end of the main boom and the second end of the heave-compensating boom being fixed, wherein the first heave-compensating boom is pivotable by at least one of the plurality of actuators and extends in a downward vertical direction (Z) in operational use of the heave-compensating crane, wherein the first heave-compensating boom is configured to be pivotable with respect to the main boom in both horizontal directions (X, Y) defined with respect to the downward vertical direction (Z);

wherein the first heave-compensating boom comprises a first arm that is pivotably mounted to the main boom for allowing a rotation in a first horizontal direction (X), the first heave-compensating boom further comprising a second arm that is pivotably mounted to the first arm for allowing a rotation in a second horizontal direction (Y) orthogonal to the first horizontal direction (X);

wherein the crane base comprises a second heave-compensation system comprising a winch system configured for manipulating a hoisting cable to compensate vertical deviations.

25. The heave-compensating crane according to claim 24 wherein the first arm is mounted such that the first arm extends in a substantially horizontal direction (X) in operational use of the heave-compensating crane, and the second arm is mounted such that the second arm extends in the downward vertical direction (Z) in operational use of the heave-compensating crane.

26. The heave-compensating crane according to claim 24 , wherein the main boom comprises a first boom section joined to a second boom section by an elongate mounting bar connected between the first boom section and the second boom section such that the first boom section is prevented from pivoting relative to the second boom section.

27. The heave-compensating crane according to claim 24 , wherein the length between the first end of the heave-compensating boom and the rotatable head is fixed.