The structure of the control system for a dynamically positioned ship

The article discusses functions and tasks of dynamic positioning (DP) systems for ships. The analysed issues include ship steering, in particular stabilisation of ship position and direction of motion (real course) at low manoeuvring speeds, and commonly used DP ship models. Requirements imposed by classification societies on DP ships are quoted. A multi-layer structure of the DP control system is presented, with special attention being paid to such issues as signal filtering, estimation of measured and non-measured quantities, selecting the control method and DP controller, and rudder and drive allocation. The article has a form of an overview of basic problems of DP ship control.