Energy Losses Related to Automatic Steering of Ships in Waves—Part II: Performance of Controllers Designed to a New Criterion

Minimization of energy losses associated with the steering control of modern ship types is discussed on the basis of frequency-domain sensitivity analyses and time-domain simulation studies. A high-speed containership and large tankers in the full-load condition are analyzed. A new performance criterion for minimization of steering-related propulsion losses is presented, and controllers designed to it using linear quadratic Gaussian (LQG) techniques. In the case of the containership, the resulting controller is shown to have the potential to reduce the net losses related to steering below those of the uncontrolled ship through proper use of the rudder in some conditions. While this does not seem possible for the tankers, the results indicate that a controller designed to the new criterion results in lower losses than a controller based on a form of criterion to which new autopilots for tankers are presently being designed. The implications for both autopilot and steering gear servo-design based on these results are discussed.