The problem of external disturbances rejection is considered for control systems of marine ships steered by autopilot under the action of sea wave disturbances and bias terms. The essence of the problem is to find mathematical models of adjustable corrective items for control law with a special structure, to provide desirable values of correspondent functionals, which characterize accuracy and intensity of a ship's rudders action. It is shown that minimax representation, supplied by H_∞-approach, is quite suitable to reflect multipurpose orientation of control system tuning. Specialized methods of control laws design are proposed based on the original spectral approach to SISO LTI-optimization problem. Its applicability and effectiveness are illustrated by the practical example of autopilot synthesis.