Water Testing New Engines; Boat And Engine Performance; Boat Bottom - MerCruiser 305 CID (5.0L) Service Manual

GENERAL INFORMATION
To test for correct propeller, operate boat (with an average load onboard) at WOT and check
rpm with an accurate tachometer. Engine rpm should be near top of the specified range so
that, under heavy load, engine speed will not fall below specifications.
If engine exceeds the specified rpm, an increase in pitch and/or diameter is required.
If engine is below rated rpm, a decrease in pitch and/or diameter is required.
Normally, a change of approximately 150 rpm will be achieved for each single inch of pitch
change of a propeller.
If a propeller is installed that does not allow engine rpm to reach the specified
full-throttle rpm range, the engine will "labor" and will not produce full power.
Operation under this condition will cause excessive fuel consumption, engine
overheating and possible piston damage (due to detonation). Conversely, installing
a propeller, allowing engine to run above the specified rpm limit, will cause
excessive wear on internal engine parts which will lead to premature engine failure.

Water Testing New Engines

Use care during the first 20 hours of operation on new Mercury MerCruiser engines or
possible engine failure may occur. If a new engine has to be water-tested at full throttle
before the break-in period is complete, follow this procedure.
1. Start engine and run at idle rpm until normal operating temperature is reached.
2. Run boat up on plane.
3. Advance engine rpm (in 200 rpm increments) until engine reaches its maximum rated
rpm.
IMPORTANT: Do not run at maximum rpm for more than 2 minutes.

Boat and Engine Performance

Boat Bottom

For maximum speed, a boat bottom should be as flat as possible in a fore-aft direction (longi-
tudinally) for approximately the last 5 ft (1.5 m).
Index Index
Page 1A-6
a
a - Critical Bottom Area
CAUTION
SERVICE MANUAL NUMBER 24
72002
90-861327--1 OCTOBER 1999