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FAQ: Why would I change my OBSD propeller?

The stock propeller with which most outboards are equipped is a compromise. Since it has fixed diameter and fixed pitch, it is really limited in its use and it does not provide satisfactory performance for all the combination of hulls and loads that will be encountered once it is installed.

One important fact to note is that the propeller moves the boat through the water at a specific engine RPM, and horsepower (HP) is directly related to the developed RPM. The engine cover is marked with a certain HP rating but in most instances the full benefit of the possible HP is never realized. Along with the HP rating equal emphasis should be placed on the RPM at which the rated HP is developed. This, of course, is where the propeller comes into the picture. Outboard engines are designed to run at peak RPM for full efficiency. Excessive RPM with its increased friction and wear is obviously harmful.

It is equally harmful to run the engine so overloaded that it cannot achieve its rated RPM since this results in excessive carbon buildup in the cylinder with subsequent problems of poor fuel economy, pre-ignition, frequent spark plug failure, scoring of the cylinder walls and even burned pistons.

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