In order to save energy for a ship sailing under various wave conditions, we developed an optimal-control system of propulsion power and propeller pitch. In this system, incoming irregular wave data are estimated using a wave-radar and the Fourier transformation. To respond to that wave situation, the optimal-control signals of an alternating-current induction motor and a specifically designed controllable-pitch propeller are calculated in real time using an efficient algorithm of receding horizon control. The numerical results indicate that, for a short-crested irregular seaway with a significant wave height of 3 m and a mean wave period of 12 s, the energy required to propel a 217 m bulk-carrier with 14.7 knots is reduced by about 2% in head waves and by about 7% in the following waves when the optimal-control system proposed herein is used.
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