How Do I Choose A Boat Propeller?

How do you choose the right boat propeller?

First of all, let’s go over some propeller terminology.

• Diameter - the width of the circle carved by the rotating blades.
• Pitch - the distance a propeller moves forward in one revolution. The idea is to select a prop with a pitch that allows the engine to reach the maximum RPM suggested by the manufacturer without going over. If the prop selected doesn’t reach the recommended RPM, the boat will sacrifice speed and lift.
• Propeller Cup - some propellers incorporate a cup at the trailing edge of the prop blade. This results in reduced ventilation, slipping, and allows for a better hole shot. A cupped propeller also works very well where the motor can be trimmed so that the propeller is near the surface of the water. A cupped propeller of the same pitch and diameter will reduce your RPM by about 200.

Selecting Your Propeller
The best propeller size for your boat and engine combination is based on the recommended operating range at wide open throttle for your engine, which you will find in your engine operator’s manual. The goal in prop selection is to determine what propeller style and size will maximize performance, while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum RPM. Run the boat/motor at under normal operating load to determine the maximum RPM you are able to obtain. Adjust the motor trim angle for the optimum performance. If during this test, you begin to exceed the maximum rated RPM, reduce throttle setting to a position where maximum RPM is not exceeded. If your test results in your being able to over-rev the engine, you need to increase the pitch of the propeller. Increasing the pitch increment by 1″ will result in about a 200 RPM drop. If your testing shows, however, that you are only able to obtain a RPM somewhat lower than the maximum rating given by your engine manufacturer, you would need to decrease pitch. Decreasing pitch would increase your RPM. Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM. If you use your boat for fishing, cruising and skiing, one prop probably won’t do all three things equally well. It is best in circumstances like this to have two propellers; One to accommodate one set of circumstances and the other to perform best under the different load. It is imperative, however, that the wide open throttle RPM fall within the range specified by your engine manufacturer.

Do you have a question that you want answered? So do we! But we’re at a loss for the answer to our question. So why don’t you just ask us your question at How Do I? and see if either we can or one of our many viewers can answer it? Maybe…

[tags]propeller, boat, boating[/tags]