How to Measure the Pitch of a Prop

Use a propeller with the proper pitch for the best performance.

Boating is an age-old pastime that continues to grow in popularity. In 2009, the number of registered watercraft reached an all-time high. Maximum performance is foremost in the desires of all boat owners, and using a propeller with the proper pitch is critical to achieve this goal. Normally, a propeller's pitch is stamped on the hub by the manufacturer. Occasionally, due to wear or oversight, the number indicating that pitch cannot be located or read easily. You can calculate the pitch of your propeller manually by following a few basic steps.

Things You'll Need

• Paper
• Pencil
• Compass (drafting)
• Ruler
• Protractor
• Calculator (optional)

Instructions

1. Lay the paper on a hard flat surface. The paper must be large enough to center the propeller and extend beyond the widest potion of the blade on each side. Light-colored paper will make lines more visible and easier to work with. Construction paper works well with smaller propellers, while poster or butcher paper may be needed for larger props.

2. Place the propeller pitch side up on the paper and mark the center point. Make a second mark at a point on the paper near the widest part of the blade. Remove the propeller from the paper.

3. Place the point of the compass at the center point and adjust the distance to match the second mark in the above step and draw a circle around the center point.

4. Replace the propeller on the paper. Measure the height in inches of the upper and lower edges of one of the blades at the point at which it crosses the circle and mark the circle where you measured. If one edge is touching the paper, use zero for that measurement. Subtract the lower height from the upper height.

5. Draw lines from the center point to each of the two points marked along the circle. Use the protractor to measure the angle between the two lines.

6. Multiply the result from Step 3 by 360. Divide this number by the angle measured in Step 4. The result is the pitch of your propeller.

Tips & Warnings

• To increase the accuracy of your calculations, measure in millimeters and convert the result to inches by multiplying by 0.03937.

References

• The Propeller Pages; Manual Procedure for Propeller Pitch Measurement; Ramses Herrera