High Performance Ship Autopilot With Wave FilterThor

This paper describes the application of Lyapunov stability theory to automatic steering of ships. The motivation for using nonlinear control theory is that nonlinearities can be compensated for in a systematic manner. For instance, this allows the designer to design the autopilot system for a ship described by the nonlinear models of Norrbin (1963) and Bech and Wagner Smith (1969) both utilizing a nonlinear maneuvering characteristic. In fact, nonlinear maneuvering properties are observed for most large tankers. Furthermore, it is emphasized on showing how the controller gains of the nonlinear autopilot can be tuned in accordance to theoretical values obtained from linear quadratic (LQ) optimal control theory. Nonlinear control system design in the context of parameter estimation and wave ltering is also discussed. The advantages of the optimal autopilot is improved performance and reduced fuel consumption. Finally, some experimental results with the Lyapunov based autopilot in combination with a parameter estimation algorithm are reported. These experiments were performed for a cargo ship in weather conditions corresponding to sea state code 2, that is smooth sea. As a consequence of this, simulation results are used exclusively to demonstrate the state estimator and wave lter design for higher sea state codes.