How to Compute a Boat Propeller Pitch

Boat propeller pitch is the forward movement the boat propeller travels during a revolution. The distance traveled can be 10 to 20 percent less than the pitch that was designed for the propeller. This 10 to 20 percent variance is known as slip. The weight of the boat and blade surface of the propeller determine how much slip will occur.

Instructions

Difficulty: Moderate

1. Determine the distance the propeller covers per second. This number is the designed pitch for the propeller; 10 to 20 percent of that number is more likely the actual pitch of the propeller.
2. Changing the pitch of your propeller is possible. Aluminum propellers can be changed an inch or two up or down to increase or decrease rpms. Lowering the pitch by an inch increases the motor speed by 200 rpms. Increasing the pitch by an inch decreases the motor speed by 200 rpms.
3. Prevent slippage of the pitch by adding a propeller cup to the end of the propeller blade if your propeller does not already have one. The cup allows the propeller to have better contact with the water.
4. Determine if you need to completely change the propeller in the boat to achieve your desired results. If you use your boat for fishing, waterskiing and cruising, you need at least two propellers to carry the weight required and achieve the speeds needed by each of these activities.
5. Remember the pressure, humidity and elevation can change the performance of the engine day to day. Test your boat in several different conditions before making changes to the pitch or propeller.