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CA9
CAVITATION
Cavitation occurs when water flow cannot follow the contour of a
fast-moving underwater object, such as a gear housing or propeller.
Cavitation permits the propeller to speed up, but the boat speed to
reduce. Cavitation can seriously erode the surface of the gear hous-
ing or propeller. Common causes of cavitation are:
A. Weeds or other debris snagged on propeller or gear housing.
B. Bent propeller blade or damaged gear housing skeg.
C. Raised burrs or sharp edges on propeller or gear housing.
CA10
VENTILATION
Ventilation is caused by surface air or exhaust gases which are intro-
duced around the propeller resulting in propeller speedup and a re-
duction in boat speed. Excessive ventilation is annoying and usually
caused by:
A. Drive unit trimmed out too far.
B. A missing propeller diffuser ring.
C. A damaged propeller or gear housing, which allows exhaust
gases to escape between propeller and gear housing.
D. Drive unit installed too high on transom.
CA250
PROPELLER SELECTION
Select a propeller that will allow the power package to operate at or
near the top of the recommender full throttle RPM range with a nor-
mal load. Maximum engine speed (RPM) for propeller selection ex-
ists when boat speed is maximum, and trim is minimum for the
speed. (High RPM, caused by an excessive trim angle, should not
be used in determining correct propeller.) Normally, there is a 300 to
500 RPM change between propeller pitches. Full throttle RPM range
is listed in SPECIFICATIONS.
If full throttle operation is below the recommended range shown in
SPECIFICATIONS, the propeller must be changed to prevent loss of
performance and possible engine damage.
10
Alpha V8
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