The propeller is the most common propulsive device on motorboats and ships. It consists of a rotating piece made up of several blades similar to those of a fan and mounted on the end of a drive shaft. Propellers differ in their materials (bronze, aluminum, etc.) and functional details (fixed or variable pitch, surface-piercing propeller, etc.).
The propeller transforms the engine's rotary power into thrust as it turns. It is the most common propulsive device on motor-driven vessels.
Boat propellers work in the same way as airplane propellers. Each blade is shaped like an airfoil. Rotation creates a pressure difference between the forward and aft surfaces due to blade profile and angle of attack.
Propeller size must be adapted to the power of the engine, since undersized blades cannot handle all the engine's power. Material is also a factor. Titanium is probably the best, but it is costly and difficult to work. Large propellers often are custom-built. Manufacturers have software and special equipment to aid in selection.
