Folding Propeller

A propeller whose blades fold towards the shaft when not driving the vessel, reducing drag under sail.

When the shaft turns, the blades open into their working position through centrifugal force and hydrodynamic loading. When rotation stops, water flow folds them aft. The design is common on sailing yachts where the resistance of a fixed propeller would reduce sailing performance.

Folding propellers vary in their ahead and astern efficiency, opening behaviour and compatibility with a particular engine and gearbox. Blade pivots, gears where fitted, anodes and fouling require maintenance because restricted movement can prevent the blades opening or closing correctly.