Controllable Pitch Propeller

A controllable pitch propeller allows the angle of attack of each blade to be varied remotely while the shaft continues to rotate at a steady speed, enabling the vessel to change speed ahead, stop, and go astern without reversing the main engine. The pitch is adjusted through a hydraulic servomotor inside the propeller hub, controlled from the engine control room or bridge. CPP installations are common on ferry and ro-ro vessels where frequent direction changes and precise berthing manoeuvres require rapid thrust response, and on vessels where a constant shaft speed is needed to drive a shaft generator efficiently. The pitch control system is one of the most maintenance-intensive elements of the propulsion train: hydraulic oil pressure, pitch feedback transmitter calibration, and the condition of the hub seals must all be maintained to classification society standards. SOLAS II-1 and class rules require a mechanical emergency pitch stop device so that full pitch ahead can be achieved even on failure of the control system. Engineers regularly verify that the pitch indicator on bridge and engine control room are consistent with actual blade position, and class surveyors inspect pitch-control actuator overhaul records as part of the shaft and propeller survey.