Conditions Affecting Operation; Weight Distribution; Bottom Of Boat; Cavitation - Mercury 540 Bravo Manual

CONDITIONS AFFECTING OPERATION

Weight Distribution

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).

Bottom Of Boat

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.

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 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.

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.
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