Various modern control techniques have been applied to large ships to improve the autopilot performance over a ship’s operating envelope. The conventional techniques of autopilot design, such as those based upon PID (Proportional, Integral and Derivative) based controllers and their variants have remained in use for many years because of their simplicity, reliability and low cost. This is despite the widely held view that the steering characteristics of PID controllers are fundamentally unsatisfactory, mainly due to the necessity for user adjustment to accommodate changes in ship loading conditions and the operating environment.
A trajectory control algorithm, termed “Target Path Iteration (TPI) algorithm” is proposed for maneuvering of surface ships and its performance studied. A mathematical model for nonlinear maneuvering of cargo ships has been used in conjunction with the proposed algorithm. The TPI method works with one error measure, namely, the average mean square error, which is minimized to obtain the desired rudder angle. The proposed control scheme has been verified for a variety of straight line and curved trajectories and its performance has been found excellent.