Yamaha F2.5B Owner's Manual page 53

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Bow Up
When the boat is on plane, a bow-up atti-
tude results in less drag, greater stability
and efficiency. This is generally when the
keel line of the boat is up about 3 to 5
degrees. When trimmed out, the boat may
have more tendency to steer to one side or
the other. Compensate for this as you steer.
Too much trim-out puts the bow of the boat
too high in the water. Performance and
economy are decreased because the hull of
the boat is pushing the water and there is
more air drag.
Excessive trim-up can cause the propeller to
ventilate, which reduces performance fur-
ther. When trimmed-out too much, a boat
may "porpoise" (hop in the water), which
could throw the operator and passengers
overboard.
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Bow Down
When the bow of the boat is down, it is eas-
ier to accelerate from a standing start onto
plane.
Too much trim-in causes the boat to "plow"
through the water, decreasing fuel economy
and making it hard to increase speed.
Operating with excessive trim-in at higher
speeds also makes the boat unstable.
Resistance at the bow is greatly increased,
heightening the danger of "bow steering"
and making operation difficult and danger-
ous.
1 Bow up
2 Bow down
3 Optimum angle
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