Power take-off (PTO)

Power take-off (PTO) is a mode where a generator coupled to the main propulsion shaft extracts mechanical power from the main engine to produce electricity, replacing the auxiliary diesel generators while the ship is at sea. Because the main engine runs on cheaper heavy fuel oil at high thermal efficiency, a shaft generator in PTO cuts running hours on the auxiliary engines and lowers fuel cost. A frequency converter keeps output at constant 50 or 60 Hz as shaft speed varies. PTO is paired with PTI in PTO/PTI/PTH systems, where the same machine can also motor the shaft.