Heave compensation systems are necessary to allow offshore cranes to guarantee cargo’s soft landing on a solid surface and to manage the crane’s dynamic force in the cable. The HYDAC active heave compensation system so called HeaveCom uses a counter-rotating, hydraulically driven winch to compensate for the ship’s motions. A nitrogen-supported hydraulic accumulator is directly connected to the hydraulic winch drive. The total displacement volume of the hydraulic winch motors is regulated proportionally. This guarantees an optimised balance between the nitrogen-spring on the one hand and the load induced pressure on the other. This eliminates the necessity for a large on board nitrogen supply as the HeaveCom system uses a fixed nitrogen pressure, regardless of the work load.

A small slave cylinder, directly connected to the accumulator’s piston, compensates for the efficiency losses. Driving the slave cylinder controlled by the modified MRU-signal increases or reduces the oil flow to the winch motors and thereby counteracts the measured heave-induced position disturbance. The method results in an energy saving of up to 85%. In addition, the HeaveCom system eliminates the necessity for large compensation cylinders.

The HeaveCom system extends the area of application for hydraulic heave compensation. Accumulation not only allows the HeaveCom System to make a maximum oil volume available for position correction, it also makes a certain amount of accumulated energy available to execute this correction. Existing heave compensation systems use ‘in-line-cylinders’ with a fixed stroke, which limits the compensation of the maximum heave-induced motion. The active HeaveCom system is designed for the same maximum heave-induced motion that can be compensated for at the given work load. When the effective workloads are lower the HeaveCom system can compensate for higher heave-induced motions, by decreasing the winch motor’s stroke volumes to reach a balance in the nitrogen operating pressure.

Existing rotating hydraulically driven winch systems are easy to convert to the HeaveCom system. Parallel installation of HYDAC AHC-drive on a winch system provides redundancy to the AHC-system. Direct wear throughout the entire system is reduced, since there is no more need for additional cable disks.

The HeaveCom system saves on energy consumption, mass, nitrogen supplies, reduces wear throughout the entire system and extends the area of application.