For rudder angle servo mechanism in steer-by-wire (SBW) system of pleasure boats, this paper presents a sliding mode controller with continuous control input. The sliding mode control theory is applied to the controller so as to have high robustness against the normal pressure of a rudder, which is regarded as an unknown disturbance. Designed with the twisting algorithm and the describing function method, a switching input of the proposed controller could enforce a switching function into a

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... t cycle. As a price of abandoning the perfect sliding mode, the proposed controller can bring not infinite-frequency switching input but continuous control input. As a result, the improvement of the load of the actuator in SBW system can be achieved.