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A: |
The
stock propeller with which most outboards are equipped is a compromise.
Since it has fixed diameter and pitch, it is really limited in its
use and it does not provide satisfactory performance for all the
combinations 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 h.p. is
directly related to the developed rpm. The engine cover is marked
with a certain h.p. rating but in most instances the full benefit
of the possible h.p. is never realized. Along with the h.p. rating
equal emphasis should be placed on the rpm at which the rated h.p.
is developed. This, of course, is where the propeller comes into
the picture. Outboard engines are designed to be 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. |
