Mercury 565 Manual page 54

CONDITIONS AFFECTING OPERATION
EXAMPLE: An engine running at an elevation of 2,438 m (8,000 ft) will have
over a 30% power loss while engine power on a hot and humid day can be
reduced by as much as 14%. These losses apply to both normally aspirated
and supercharged engines.
Compensating for power robbing conditions:
• Switch to a lower pitch propeller.
• Change the gear ratio.
Some boat performance can be regained by dropping to a lower pitch propeller,
but engine performance will remain lower. In some cases, a gear ratio
reduction may be more beneficial. To optimize engine performance, prop the
engine to allow operation at or near the top end of the recommended maximum
RPM range at wide‑open throttle with a normal boat load.
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