Enter the RPM of the motor and the reduction ratio of the box into the calculator to determine the prop speed.

Airboat Prop Speed Formula

The following formula is used to calculate an airboat prop speed.


  • Where PS is the prop speed (RPM)
  • RPM is the engine RPM
  • GR is the gear reduction of the box

What is a prop speed?

A prop speed is defined as the total rotations per minute an airboat propeller is spinning at given an engine RPM and a gear reduction.

How to calculate airboat propeller speed?

The following example outlines the steps needed to calculate the speed of an airboat propeller.

First, determine the RPM of the engine. This is typically provided somewhere on the side of the engine. In this example, the engine RPM is found to be 2000.

Next, determine the gearbox reduction ratio. In this example, the reduction ratio is 2.5:1.

Finally, calculate the airboat prop speed by dividing the RPM by the gear body reduction ratio.


PS = 2000/ 2.5

PS = 800 RPM