A propeller is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral, that, when rotated, exerts linear thrust upon a working fluid, such as water or air.[1] Propellers are used to pump fluid through a pipe or duct, or to create thrust to propel a boat through water or an aircraft through air. The blades are specially shaped so that their rotational motion through the fluid causes a pressure difference between the two surfaces of the blade by Bernoulli's principle which exerts force on the fluid.[2] Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis.[3]

A right-handed propeller on a merchant vessel which (when viewed from astern) rotates clockwise to propel the ship forward. The man's hand rests on the blade's trailing edge.
Propeller of Pratt & Whitney Canada PW100 mounted on Bombardier Q400