Apparatus and method for heave compensation

A method of heave compensation for a winch or crane system, wherein the winch or crane system is provided on a vessel, the winch or crane system including a lift wire, the method comprising the steps of:

• coupling a load motion measurement device to the load and providing it on the load;
• using a control device to monitor the data output by the load motion measurement device indicative of the movement of the load suspended by the lift wire;
• and
• adjusting the pay out or recovery of the lift wire from a drum located on the vessel to compensate for the movement of the load.

A heave compensation apparatus for a winch or crane system, the winch or crane system being provided on a vessel and including a lift wire for attachment to a load, the apparatus comprising:

• a) vessel motion measurement device for measuring the motion of the vessel;
• b) a lift wire tension measuring device for measuring the tension in the lift wire;
• c) a lift wire distance measurement device which measures the length of lift wire that has been paid out;
• and
• d) a lift wire resonance calculation means comprising a computational means into which an operator can input data concerning the elasticity characteristics of the lift wire, wherein the computational means takes data output from the lift wire distance measurement device and calculates the elasticity of the lift wire from the length of wire paid out, by reference to its elasticity characteristics;
• the apparatus further comprising a control device capable of receiving an output from the vessel motion measurement device, the lift wire tension measuring device, the lift wire distance measurement device and the lift wire resonance calculation means;
• wherein the control device controls the winch or crane system, in response to the said outputs, to payout or recover lift wire from a drum located on the vessel as required to stabilise the load.

A method of heave compensation for a winch or crane system, the winch or crane system being provided on a vessel and including a lift wire, the method comprising the steps of:

• measuring the motion of the vessel and inputting data indicative of the motion into a control device;
• measuring the tension in the lift wire and inputting data indicative of the tension into the control device;
• and
• measuring the length of lift wire that has been paid out and inputting data indicative of the said length into the control device;
• and
• inputting data concerning the elasticity characteristics of the lift wire into a computational means, and further inputting data indicative of the length of lift wire that has been paid out into the computational means and using the computational means to calculate the elasticity of the lift wire and thereby provide a lift wire resonance calculation means and inputting the calculated elasticity of the lift wire into the control device;
• and
• using the control device to controlling the vessel winch or crane system in response to the said inputs, to pay out or recovery lift wire from a drum located on the vessel as required to stabilise the load.