The Wide Open Throttle Test – an Important Step in Selecting the Right Boat Prop
Before You Test Your Boat Prop
Your engine’s manufacturer will have published a recommended operating range of RPMs that will allow your engine to perform efficiently and safely. Your boat prop will play the major role in determining whether your engine can operate in this safe and efficient range. The Wide Open Throttle Test will give you the information you need to determine if you are using an optimal boat prop, or what to look for to select a boat prop that will give you optimal performance if you are not squarely in the recommended operating range for your engine.
Your boat prop should allow you to run your boat with a wide open throttle and reach the mid to upper end of your recommended operating RPMs for your motor. The first step in running this test is to check your engine’s owner's manual and find the recommended operating range figures. If you can’t find the figures, check with your engine dealer or the manufacturer to get the proper specifications. Once you have those figures in hand, you are ready to hit the water and start testing.
On The Water Boat Prop Testing
Find a location where you can safely run your boat at full throttle. With the boat prop you are testing mounted on your outboard or outdrive, increase your speed to full throttle. If it looks like you are going to exceed the maximum operating RPMs, back off and do not exceed the limit. Estimate how much throttle you have left and where you think that would take you in terms of RPMs. Log your results. If you do not exceed the maximum recommended operating RPMs for your engine, make several runs, optimizing the trim for maximum performance. Again log the results.
Using the Test Results to Evaluate Your Boat Prop
If you are able to reach, but not exceed the upper end of your recommended operating range, then the boat prop you are testing is appropriate for your engine.
If you reached your maximum operating RPMs before you reached full throttle, then you will have to estimate how many RPMs you need to drop to max out in the upper range. For example, if the top end of your recommended operating range was 6,000 RPMs, but you estimate that you would have reached 6,400 RPMs with the boat prop you were testing, then you will want to reduce the maximum RPMs by about 400 RPMs. A general rule of thumb is that RPMs will drop by about 200 RPMs for every inch of increased pitch on your boat prop. If your boat prop has a 19" pitch, then you should try a 21" pitch to reduce your top end RPMs to the published 6,000.
If you were unable to reach the upper end of your recommended operating range, then you will want to select a boat prop with less pitch. Plan to decrease the pitch of your boat prop by about an inch for every 200 RPMs you would like to gain. For example, if your recommended operating range tops out at 6,000 RPMs but you were only able to reach 5,400 RPMs going flat out, then you’ll want to gain 600 RPMs. If your boat prop has a 19" pitch, then you’ll want to try a boat prop with about a 16" pitch which should allow you to gain roughly 600 RPMs.
Remember that boat prop pitch works like gearing. Moving to a higher pitch boat prop is like being in a higher gear. It will reduce the RPMs you are turning at any given speed, and it will help with reaching higher top end speeds, but it will be less effective getting out of the hole. Lower pitch is like a lower gear and should improve your hole shot, and allow you to reach higher RPMs. However, it may reduce your top end speeds.
After you’ve run the Wide Open Throttle Test, you’ll have a good idea of whether your boat prop is appropriate for your engine and boat combination, or whether you should make adjustments to improve performance. Knowing how your current boat prop performs in the Wide Open Throttle Test is one of
Three Questions You Should Answer Before You Shop For a Boat Prop.
Visit our
Boat Propeller section or use our
Boat Propeller Finder to identify the boat prop that will fit your motor, then use the results of your Wide Open Throttle test to narrow your selection to the boat prop that will give you the best performance.
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