Section 3 - On The Water
90-8M0070851
eng
AUGUST 2012
Page 39
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Improves rough water ride
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At extremes, can cause the boat to veer back and forth (bow steer)
Bottom of Boat
To maintain maximum speed, ensure that the boat bottom is:
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Clean, free of barnacles and marine growth.
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Free of distortion, nearly flat where it contacts water.
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Straight and smooth, fore and aft.
Marine vegetation may accumulate when the boat is docked. This growth must be removed before operation; it may clog water
inlets and cause the engine to overheat.
Cavitation
Cavitation occurs when water flow cannot follow the contour of a fast‑moving underwater object, such as a gear housing or a
propeller. Cavitation increases propeller speed while reducing boat speed. Cavitation can seriously erode the surface of the
gear housing or the propeller. Common causes of cavitation are:
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Weeds or other debris snagged on the propeller
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Bent propeller blade
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Raised burrs or sharp edges on the propeller
Ventilation
Ventilation is caused by surface air or exhaust gases that are introduced around the propeller resulting in propeller speed‑up
and a reduction in boat speed. Air bubbles strike the propeller blade and cause erosion of the blade surface. If allowed to
continue, eventual blade failure (breakage) will occur. Excessive ventilation is usually caused by:
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Drive unit trimmed out too far
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A missing propeller diffuser ring
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A damaged propeller or gear housing, which allows exhaust gases to escape between propeller and gear housing
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Drive unit installed too high on transom
Elevation and Climate
NOTE: Engines equipped with an Engine Control Module (ECM) reduce the effects of changes in elevation and climate by
automatically adjusting fuel flow for weather conditions and elevation. ECM controlled engines, however, do not compensate for
increased loading or hull conditions.
Elevation and climate changes affect the performance of your power package. Loss of performance can be caused by:
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High elevations
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High temperatures
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Low barometric pressures
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High humidity
For you to have optimum engine performance under changing weather conditions, it is essential that the engine be propped to
allow the engine to operate at or near the top end of the specified maximum RPM range with a normal boat load during your
normal boating weather conditions.
In most cases, the recommended RPM can be achieved by changing to a lower pitch propeller.
Propeller Selection
NOTICE
Operating the engine with the wrong propeller installed can limit power, increase fuel consumption, overheat the engine, or
cause internal powerhead damage. Choose a propeller that allows the engine to operate at the specified wide open throttle
RPM.
It is the responsibility of the boat manufacturer and the selling dealer to equip the power package with the correct propellers.
IMPORTANT: The engines covered in this manual are equipped with an ECM that limits engine RPM. Be sure that the propeller
being used does not allow the engine to run against the limiter, as a significant loss in performance will result.
NOTE: Use an accurate service tachometer to verify RPM.
Select a propeller that will allow the engine power package to operate at the rated engine RPM with a full load.