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5 - C
A
O
ONDITIONS
FFECTING
PERATION
W
D
EIGHT
ISTRIBUTION
Positioning of weight (passengers and gear) inside the boat has the
following effects:
Shifting weight to rear (stern) may:
•
Increase speed and engine RPM.
•
Cause the boat to porpoise.
•
Cause the bow to bounce in choppy water.
•
Increase the danger of a following wave splashing into the
boat when coming off plane.
Shifting weight to front (bow) may:
•
Improve ease of planing.
•
Improve rough water ride.
•
Cause the boat to veer back and forth (bow steer).
B
O
B
OTTOM
F
OAT
To maintain maximum speed, ensure that the bottom of the boat is:
•
Clean and free of barnacles and marine growth.
•
Free of distortion and nearly flat where it contacts the water.
•
Straight and smooth both fore and aft.
Marine vegetation may accumulate when the boat is docked,
clogging water inlets and causing the engine to overheat. This
growth must be removed before operation.
C
AVITATION
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
34
reduce. Cavitation can seriously erode the surface of the gear
housing or propeller. Common causes of cavitation are:
•
Weeds or other debris snagged on propeller or gear housing.
•
Bent propeller blade or damaged gear housing skeg.
•
Raised burrs or sharp edges on propeller or gear housing.
V
ENTILATION
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.
P
S
ROPELLER
ELECTION
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 propellers. Specified
engine wide‑open throttle (WOT) and operating RPM range are
listed in Specifications.
IMPORTANT: All Mercury Racing engines have an 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.
90-8M0098854 MARCH 2015
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