Materials
Propellers are made from various different materials. Most outboard props are made from stainless steel, aluminum, or composite (plastic). Most inboard props are bronze, nibral, or stainless steel.
Common Terms
Diameter- Is the distance from the center of the hub to the tip of a blade multipled by 2.
Pitch- Is the theoretical distance the propeller travels forward through the water during one revolution.
Cup- Is a curved lip on the trailing edge that allows the prop to get a better bite on the water by holding the water on the blade longer. It will typically reduce the amount of slippage and ventilation that occurs.
Ventilation- Occurs when air or exhaust gasses are pulled into the propeller blades causing high RPM's and lost of speed. Possible causes are an over trimmed engine, an engine mounted too high on the transom, or very tight cornering.
Cavitation- Is caused by tiny microscopic bubbles collapsing due to a reduction of pressure on the back of the propeller blade. It can cause damage to the blade surface. Some causes are: damaged blades, wrong pitch, incorrect propeller, etc.
How to Determine the Correct Size Prop
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Determine the RPM range your engine is rated for. This should be found in your owners manual or give our service team a call to assist you.
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Test run your engine at wide open throttle with an existing prop being careful not to exceed your manufacturer's recommendation. If your RPM's are too high, you need to go up in pitch. If they are too low, you need to go down in pitch. For every 1" decrease or increase will result in a change of 150-200 rpm's. | 