Design of the steering controller of a supertanker using linear quadratic control theory: A feasibility study

Linear quadratic (LQ) optimal control theory is applied to the design of the steering controller of a supertanker. A form of performance criterion commonly thought to be representative of propulsion losses related to steering is used as a basis for the design of controllers for course-keeping in the open-seas, for the ship in the full-load and ballast conditions at normal operating speed. The dynamics of the system are based on the use of locally linear models of the ship/steering system around an operating condition, deriving from hydrodynamic data from scale model tests. The effect of variation of the relative weightings in the performance criterion on controller performance when subjected to the seaway environment is examined using sensitivity analyses and simulation studies. The results suggest that it is possible to effect substantial propulsion savings without sacrifice in controllability using LQ techniques. It appears that linear regulator design offers a strong option to existing autopilots and more recently proposed adaptive control systems for ships of this type.