DYNAMIC POSITIONING OF HORIZONTAL MOTION OF A DRILLING VESSEL DURING HEADING CHANGES

A new control routine is proposed for the Dynamic Positioning System (DPS) of a drillship to act during changes of the ship's heading. The new system consists of an additional control path that works in parallel with the actual Proportional - Integral - Derivative (PID) controller, allowing higher rates of vessel heading change with minimum vessel excursions. The modification proposed here will significantly improve the restraint of the horizontal displacements of the drillship during the turning manoeuvre and it will allow the ship to operate continuously without unnecessary disconnections. A study of the stability of the proposed control system and a time domain simulation of the drillship motions are carried out for different wind, current and wave conditions. The performance of the heading change procedures with and without the aid of the new algorithm are compared. It is concluded that this proposed control system improves the turning performance of a PID controller of a DPS vessel, and that its application will be specially important for deepwater operations in hard environmental conditions.