How to Calculate Boat Propeller Size

Written by will charpentier
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How to Calculate Boat Propeller Size
(Jupiterimages/ Images)

If you look at a 12-inch boat propeller, you might be surprised to see that the propeller blades aren't even 6 inches long. That's because a 12-inch propeller isn't a propeller with 12-inch blades. The size of a boat's propeller is the diameter of the circle the blades make when the propeller turns. Since most "stock" boat propellers have three blades, measuring the diameter of that circle isn't simply a matter of measuring from one blade tip to another--it takes an extra step.

Skill level:

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Things you need

  • Measuring tape
  • Calculator

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  1. 1

    Measure the outside diameter of the outside of the hub of the propeller, and divide by 2. This is the radius of the hub.

  2. 2

    Measure from the outside of the hub of the propeller to the end of one of the propeller blades to determine its length.

  3. 3

    Add the length of the propeller blade to the radius of the hub. Multiply the result by 2. The result is the diameter of the propeller.

Tips and warnings

  • Remember that the edges of a plastic propeller might be sharp, so be careful.

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