Adjusting Boat Trim - Yamaha F15C Owner's Manual

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NOTE:
Stay within the trim operating angle when
trimming the outboard motor using the power
tilt system.
To raise the bow ("trim-out"), tilt the engine
up.
To lower the bow ("trim-in"), tilt the engine
down.
Make test runs with the trim set to different
angles to find the position that works best for
your boat and operating conditions.
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Adjusting boat trim

When the boat is on plane, a bow-up attitude
results in less drag, greater stability and effi-
ciency. This is generally when the keel line of
the boat is up about 3 to 5 degrees. With the
bow up, the boat may have a greater tenden-
cy to steer to one side or the other. Compen-
sate for this as you steer. The trim tab can
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also be adjusted to help offset this effect.
When the bow of the boat is down, it is easier
to accelerate from a standing start onto
plane.
Bow Up
Too much trim-out puts the bow of the boat
too high in the water. Performance and econ-
omy are decreased because the hull of the
boat is pushing the water and there is more
air drag. Excessive trim-out can also cause
the propeller to ventilate, which reduces per-
formance further, and the boat may "por-
poise" (hop in the water), which could throw
the operator and passengers overboard.
Bow Down
Too much trim-in causes the boat to "plow"
through the water, decreasing fuel economy
and making it hard to increase speed. Oper-
ating with excessive trim-in at higher speeds
also makes the boat unstable. Resistance at
the bow is greatly increased, heightening the
Operation
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