Abstract: An AC marine propulsion system which provides a constant continuous rated horsepower availability at the standard rated engine RPM, over the full useful operating range of the propeller. A prime mover diesel engine is operated at its continuous rated speed to provide for maximum fuel efficiency. An alternator connected to the prime mover is driven at a speed which is higher than the standard rated alternator speed, thus producing higher than standard rated voltage and frequency. The combination of prime mover and alternator provides for an optimum system mass to power ratio. An AC motor is coupled through a gearbox to a fixed pitch propeller system. A frequency converter is dispsoed between the alternator and AC motor. Propeller RPM is controlled by changing the frequency of the voltage supplied to the AC motor.