Information on the helmsman's control behaviour is summarised in two models. One is a linear model which consists of a gain, a lag, and a lead term and describes the helmsman's behaviour in the control of a ship sailing in calm water, while the other is a nonlinear model which describes the helmsman's behaviour in the control of a ship sailing in disturbed as well as undisturbed water. The nonlinear model is based on the internal model concept, i.e., on the assumed knowledge the helmsman has about the dynamics of the ship under his control, about the disturbances acting on the ship, and about the task to be executed. The internal model as part on the nonlinear helmsman's model is a simple differential equation which is used to predict future ship states. Since the heading displayed by the compass may be disturbed by noise, e.g., due to waves, an estimator is needed to generate estimates of the undisturbed heading and heading rate, to update the internal model. The proper actions necessary to achieve the desired states are selected by the decision-making element on the basis of predictions with the internal model.
Abstract