This paper is concerned with the design of a state-space H∞ self-tuning surface ship auto-pilot. A state-space approach is employed for the on-line recursive identification which lends itself readily to the H∞ problem formulation. To improve the robustness properties of the identification scheme, vector variable forgetting factor and UD factorisation of the covariance matrix are used. Two different methods for the controller design are described and conditions are given that allow suspension of parameter estimation and controller updating. Both approaches are used to design controllers that are robust to changes in ship speed and sea-states. The benefits of an advanced control design and the advantages of self-tuning capabilities are illustrated by means of non-linear simulations.
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