The RPM your engine runs at wide open throttle (WOT* click to learn more) is determined by the pitch of your propeller. With too much pitch, the engine won't be able to turn the propeller in the proper RPM range. Too little pitch and you could over-rev and possibly harm your motor.
Using a propeller that gives you the correct WOT RPM range will give you a better hole shot, better acceleration and top end, and improved fuel economy. You will get the best performance out of your boat when you are running your engine in the correct RPM range.
How do you select the correct pitch for your boat and motor combination? First, ensure you have a working and accurate tachometer. You will need to run your boat with your current prop at full throttle (without exceeding your engines recommended max rpm) and best trim angle with a normal load (see upcoming article about engine mount and trim angles). At full throttle, note the RPM on your tachometer. Compare this number to the WOT number for your engine.
For example: If your engine WOT range is 4400 to 4800 RPM, and your test run shows you are turning 4100 RPM at max throttle, your engine is running outside of the manufacturers RPM range. 1 inch of pitch usually equals 200 RPM, so for this instance installing a propeller with 2 inches less pitch would increase your RPM to 4500 (200X2=400), which is now inside your WOT range. Remember, adding pitch reduces RPM, subtracting pitch adds RPM.
As another example: If your engine WOT range as specified by your manufacturer is 4400 to 4800 RPM, and your test run shows you are turning 5000 RPM (do not run the engine higher than your manufacturer's maximum RPM for more than a few seconds), you need to add pitch to decrease your WOT RPM. If you install a propeller with two inches more pitch, you may reduce your WOT RPM by 400 RPM (200X2=400). With this new propeller installed, your boat test should now result in a WOT of 4600 RPM, which is now inside your recommended range.
Take note of your current propeller diameter and pitch. From the examples above, you will need to purchase a new propeller that has a different pitch based on your test findings. If you are currently running a 17” pitch propeller, and need to add 400 RPM, then you will need to purchase a 15” pitch propeller. If you need to subtract 400 rpm, then you would purchase a 19” propeller. Different blade numbers, material and brands may affect the WOT RPM.
Your local Turning Point dealer has stock of a variety of propeller diameters, pitches, blade designs, and materials that will meet your needs. For help determining the correct propeller for your boat and engine combination or locate your local dealer, consult the online Prop Wizard by Turning Point at www.turningpointpropellers.com. Prop Wizard is the only pitch calculating tool in the industry, and can help you get the most out of your boat's performance.
Selecting the Right Pitch
By: TP. Engineering
Turning Point Propellers, Inc.Published: 2012-07-18
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