Rundquist Propeller Tools, Inc.

How a Propeller Works

The propeller is the final link in a boat's power train. Its job is to take the torque created by a marine engine and convert this torque to thrust.  A propeller is designed to control the engine's RPM and hold it at wide open throttle to the recommended RPM range specified by the manufacturer of a motor. This preferably should meet the crest of the power curve of the motor.
The power curve is the RPM range where the motor is developing its maximum horsepower and efficiently. If the motor revs beyond this point, it is over revving, and if the motor is not able to reach this point it is loaded down. Either way, this causes poor performance and unnecessary wear and strain of the drive train.