Modular propeller

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The purpose of a modular propeller is to provide more control over a boats performance. The most common modular propeller is comprised of 3 main parts: the center hub with an integrated front cap, a set of replaceable blades, and a rear cap. Assembly of the propeller is completed by sliding the base of the blades into the corresponding slots of the center hub, and then placing the rear cap onto the assembly. A nylock nut, prop nut, and cotter pin of another prop nut will be added to keep the assembly together.

Modular propellers offer boaters several advantages a fixed pitch propeller. The ability to change blades allows boaters to make adjustments in pitch for various performance needs or a change in altitude. Carrying spare blades for this purpose takes up considerably less space then carrying a complete spare propeller. The ability to replace blades also offers the advantage of replacing damaged blades while still on the water, and saves long term repair costs. Other options include adjusting pitch for altitue, watersports, cruising, and quick turnover time.

An applicable way to view pitch is through car gears. A pitch of 13 is similar to 1st gear: less speed, more power and acceleration. The 3rd gear of a car would be in comparison to a propeller with a pitch of 17. Good acceleration and top end speed is offered with a 17 pitch. A higher pitch of 21 is similar to 5th gear, which is more speed for given rpm, but has less acceleration capabilities.

When changing a props pitch, it is important to know the specified range of diameter and pitch options from the boat manufacturer. If a diameter is too low, the engine can “over rev.” In contrast, if the diameter is too high, the engine may lug at wide-open throttle. The best estimate is that for every 2 inch pitch change will result in approximately 400 RPM change at wide-open throttle. An increase in pitch will cause the RPM to drop, and a decrease in pitch will increase the RPM

Patent

• Stahl, B. patent 2006