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Selecting the Right Propeller
by Peter Dean

Choosing the correct propeller for a boat may seem complicated, however, it's not really as difficult as many boaters may think. We at Propco Marine Propellers would like to pass along some simple guidelines that will allow anyone to select the correct propeller quickly and easily.

The "correct" propeller is one that provides the desired performance with the engine being within the manufacturer's recommended rpm operating range. The first step in finding the right propeller is looking in the boat or engine operator's manual to find the recommended full-throttle rpm range. Then, using the propeller currently on the boat, determine the maximum rpm that can be obtained on the water.

If the engine is able to exceed the recommended full-throttle rpm range, changes to the propeller's pitch or cupping are needed to reduce rpms. A 2" increase in pitch will result in roughly a 300-400 rpm drop. Changing from an uncupped to a cupped propeller, while maintaining pitch and diameter, will typically reduce rpm by about 200.

If, instead, the engine does not reach the proper full throttle rpm range, propeller pitch must be decreased or cupping must be eliminated. Again, the same principles hold: decreasing - more pitch by 2" results in roughly a 300-400 rpm increase, and switching from a cupped to an uncupped prop will boost rpms by about 200.

Once the full-throttle rpms fall within the recommended range, the propeller is correctly matched with respect to rpms. However, some aspect of performance, such as holeshot or top-end speed, may not yet be as desired. This can be corrected by switching propeller models or styles and again matching the size to meet the proper full-throttle rpms. Propeller manufacturers, marine dealers and propeller shops can provide guidance in choosing the right propeller style to achieve the desired results.

Often, a single propeller will not meet all of a boater's performance demands. In such cases, he may want to carry 2 or more propellers, each providing a different type of performance or meeting different load requirements.

From Propco Marine Propellers, P.O. Box 662, Hwy. 11 South, Monroe, GA 30655. Phone: 770-267-9425.

Note to Readers: Peter Dean is president and owner of Propco Marine Propellers of Monroe, GA. He has been involved in the propeller business for more than 35 years and has been a successful offshore boat racer.