Cavitation; Ventilation; Propeller Selection - Mercury Bravo Three Operation & Maintenance Manual

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.
CA294

Propeller Selection

IMPORTANT: Installed propeller must allow engine to run at
its specified maximum wide-open-throttle revolutions per
minute (RPM). Use an accurate service tachometer to verify
engine operating RPM.
It is the responsibility of the boat manufacturer and/or the selling
dealer to equip the power package with the correct propeller(s). Spe-
cified engine wide-open-throttle (WOT) and operating RPM range
are listed in "SPECIFICATIONS".
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