Yamaha F4A Manuel D'utilisation page 78

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EMU00282
Bow Up
When the boat is on plane, a bow-up atti-
tude result 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. The trim tab can also be adjust-
ed to help offset this effect.
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
further. When trimmed-out too much, a
105011
boat may "porpoise" (hop in the water),
which could throw the operator and pas-
sengers overboard.
EMU00283
Bow Down
When the bow of the boat is down, it is
easier to accelerate from a standing start
onto plane.
Too much trim-in causes the boat to
"plow" through the water, decreasing
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fuel economy and making in hard to
increase speed.
Operating with excessive trim-in at higher
speeds also makes the boat unstable.
Resistance
increased, heightening the danger of
"bow steering" and making operation dif-
ficult and dangerous.
1 Bow up
2 Bow down
105015
3 Optimum angle
3-17
at the bow is
GB
greatly