Statistical consideration of propeller load fluctuation at racing condition in irregular waves

Propeller load fluctuation in rough sea conditions is caused by two components: one is the fluctuating inflow velocity and the other is the emergence of the propeller disk from the water. Such disturbances cause large fluctuations in engine power and revolutions, and can lead to the failure of the propulsion plant, which is unacceptable in extreme seas. However, due to strong nonlinearity in the effect of propeller emergence and nonlinear interactions with the inflow velocity in the propeller torque fluctuation, the procedure for obtaining the statistical properties of the propeller torque in extreme sea conditions is not clear. If the statistical properties of propeller torque fluctuation—such as the variance and the probability density function—are known, the corresponding statistics of the response of the engine can be obtained, allowing the safe operation of ship propulsion plants in extreme irregular seas to be assessed.