Turning Controller for Ships

Abstract The paper describes the design of a new type of turning controller for ships, where a feedforward model of the ship steering dynamics is introduced. The straightforward concepts of Kalman filtering and Linear-Quadratic control are used in combination with the feedforward model. The use of a ship steering model and an appropriate scaling of the parameters with respect to both ship size and ship's velocity gives a significant advantage compared to normal PID-type controllers. The total design is unified and the same ship steering model is used in all parts of the turning controller. The parameter setting is extremely simplified, since only three parameters have to be entered for a specific ship. The gain and time constant of the ship steering model are determined from a turning circle test, and then also the ship length has to be entered. The ship steering model is used in the Kalman filter, in the design of the Linear-Quadratic controller and in the feedforward model. The ship length is used in order to obtain an appropriate scaling of parameters. This means that no actual tuning of parameters is required, which results in a significant reduction of the start-up time when installing an autopilot with this type of turning controller combined with an adaptive steady-state coursekeeping regulator. The use of velocity scaling gives an excellent performance from ship speeds of about 10 knots, and quite an acceptable behaviour from 5 knots. Simulation results with a patrol boat (length 35 m) and a ferry (length 120 m) are presented in the paper.