Dynamic positioning of ships and floaters in extreme seas

Dynamically positioned (DP) vessels with high quality control and instrumentation systems and sufficient capability on the thrust and power systems are able to keep position and heading precisely up to certain weather conditions. The operational windows are limited by various combinations of maximum wind, current and wave loads. In extreme seas performance problems may be experienced. These may be caused by off-design conditions not accounted for in the controller strategy, corrupted sensor signals, thrust losses and/or limited power capability. This paper addresses some of the aspects related to the design of a DP control strategy that is able to handle off-design conditions on extreme seas.