Bureaucrat, staff, administrator
4,335
edits
Changes
m
→How Propellers Work
Arbitrarily increasing the speed of the propeller or making it larger without changing the design of the screw will not make the boat go faster. Indeed, at some faster rotational speed, the water around the blades cavitates excessively, and the boat will go slower.
Cavitation is the formation of a vacuum along parts of the blade. This lowers the vapour pressure of the water, causing air bubbles to form, just like in boiling water. This causes slip, loss of efficiency and pitting of the metal. Increasing the pitch of a propeller also increases its propensity for cavitation.
Consistency (accuracy) in pitch and camber are important to reduce the potential for cavitation. This also reduces vibration: as much as 80% of hull vibration can be caused by a propeller. Propellers should be balanced both statically and dynamically.
Fixed propellers are the most efficient, strongest and least expensive. But they are at their most efficient only at their designed rpm and hull speed. At other speeds, their efficiency falls off. A fixed propeller is ideal for a boat that cruises long distances at a constant speed. Boats that stop and start a lot or change speed frequently are better with a controllable-pitch propeller.
[[Category:PropulsionSystems]]
