How to Size Boat Propellers

Large or small, all propellers are sized the same way.

Sizing your boat's propeller requires only that you know two dimensions: the diameter--two times the distance from the center of the hub to the tip of the blade--and the pitch, the number of inches forward the propeller moves the boat with each full turn of the propeller. While advances in propeller technology have given us propellers which give quick acceleration (called the "hole shot") as well as a high top speed, none of these advances are included in the size of the propeller.

Instructions

1. If the boat motor is an outboard motor, remove the plug wires from the spark plugs. If it is an inboard motor, be sure that you have the keys in your pocket to prevent anyone from starting the motor inadvertently.

2. Turn the propeller until you see a series of numbers embossed on the side of the propeller housing.

3. Record the numbers--there will be two digits, an "X," and two more digits, like "14X18". The first number is the diameter of the propeller. The second number is the "pitch" of the propeller. Together, these five characters are your propeller size.

Tips & Warnings

• Before sizing your propeller, be sure there is no way the engine can start. Propeller-related injuries can be serious or fatal.

References

• Olds Engineering: Boat Propeller and Propulsion Terminology