During vessel-to-vessel cargo transfer operations, the side-by-side moored primary vessel and target vessel are moving relative to one another. Normally, the crane operator has to exercise judgment to lift and land the cargo based on experience. A judgment error may result in excessive impact on payload during landing or high rope tension when lifting. This may cause damage to the load or the crane.
When the crane is mounted on a floating vessel, the vertical movement of the floating vessel becomes critical to the crane operation. Some offshore cranes are equipped with active or passive heave compensation module, which compensates for the motion of the crane vessel. The heave compensation module is enabled when the vessel is loading/unloading cargo to onshore or to a fixed platform, or when they are performing subsea installation. However, in the scenario where cargo lifting/landing takes place between two floating bodies in motion, neither passive heave compensation (PHC) nor active heave compensation (AHC) takes into account the motion of the target vessel.
Offshore crane capacity is commonly based on Significant Wave Height. In practice, Significant Wave Height is usually provided by weather stations which uses measurements not collocated with the lifting operation. By considering the real-time motions of both crane and target vessels, the dynamics of the vessels can be more accurately assessed.
For existing vessel motion prediction, the modeling methods require environmental inputs like wave propagation model as well as sea keeping model for the specific vessel. Wave buoys and sensors are placed in the proximity of the vessel to detect the incoming waves. Anemometer is used to detect the wind parameters. The waves and wind parameters make up the environmental input parameters. The environmental input parameters are fed into the sea keeping model with vessel parameters such as hull design and weight distribution.