Yamaha F50A Manuel D'utilisation page 96

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Trim angle settings and boat handling
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. With the bow up, the boat may
have a greater tendency to steer to one
side or the other. Compensate for this as
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you steer. The trim tab can also be adjust-
ed to help offset this effect.
1 Optimum angle (level keel line)
2 Bow up
3 Bow down
Bow Up
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
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there is more air drag. Excessive trim-out
can also cause the propeller to ventilate,
which reduces performance further, and
the boat may "porpoise" (hop in the
water), which could throw the operator
and passengers overboard.
Bow Down
When the bow of the boat is down, it is
easier to accelerate from a standing start
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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 dangerous.
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