Fixed, controllable-pitch, and folding propeller tradeoffs

A fixed-pitch, cast propeller with roughly three to five blades is inexpensive, strong, and suitable for most ordinary requirements. Controllable- or variable-pitch machinery changes blade angle to give finer control of thrust and maneuvering, but its cost and complexity are difficult to justify for steady cruising alone. Folding propellers reduce drag for sailing craft and deploy when powered, yet their moving parts are more vulnerable to damage and obstruction than a solid screw. Canal craft illustrate the durability side of the tradeoff, because debris and grounding risks often favor a rugged fixed propeller.