AN EFFICIENCY OPTIMIZING PROPELLER SPEED CONTROL FOR SHIPS IN MODERATE SEAS - MODEL EXPERIMENTS AND SIMULATION

Ships in moderate sea experience time-varying thrust and torque load on the shaft of their prime mover. The reason is the varying inflow velocity to the propeller during the passage of a wave. This variation has been considered a nuisance to the main engine control where the induced fluctuations in torque, shaft speed and power have been suppressed by some control schemes and ignored in others. This paper shows how the fluctuation in inflow velocity can be utilized to increase the average efficiency of propulsion in waves without reducing the vessel speed. A nonlinear controller is proposed that is shown to theoretically enhance the propulsion efficiency. Model tests determine dynamic characteristics of propellers in waves and a simulation is employed to validate the novel control scheme.