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CONDITIONS AFFECTING OPERATION
Ventilation
Ventilation occurs when surface air or exhaust gases surround the
propeller, causing propeller speed‑up (slippage) and a decrease
in boat speed. Excessive ventilation is annoying and usually
caused by:
•
A drive unit trimmed out too far.
•
A damaged propeller or gear housing, allowing exhaust gases
to escape between propeller and gear housing.
•
A drive unit installed too high on the transom.
Propeller Selection
IMPORTANT: Choosing the correct propeller allows the engine to
run at its specified maximum wide‑open‑throttle RPM. Use an
accurate service tachometer to verify engine operating RPM.
It is the boat manufacturer and/or the selling dealer's responsibility
to equip the power package with the correct propeller(s). Specified
engine wide‑open‑throttle (WOT) and operating RPM range are
listed in Specifications.
IMPORTANT: All Mercury Racing engines have a RPM rev‑limiter
that is set to an upper (or limited) RPM. This limit is slightly above
the normal operating range of the engine and is designed to help
prevent damage from excessive engine RPM. Once the RPM
drops into the recommended operating RPM range, normal engine
operation resumes.
Select a propeller that allows the engine to operate in the upper
half of the recommended full throttle RPM range with the boat
normally loaded (refer to Specifications).
If full throttle operation is below the recommended range, change
the propeller to prevent loss of performance and possible engine
damage. On the other hand, operating an engine above the
recommended operating RPM range causes higher than normal
wear or damage. Generally, there is a 200 ‑ 300 RPM change
between propeller pitches.
RPM loss may require changing to a lower pitch propeller due
to the following conditions:
•
Operating in warmer weather and greater humidity.
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