Boat; Trim - Mercury 225 EFI Service Manual

Boat

WEIGHT DISTRIBUTION
1. Proper positioning of the weight inside the boat (persons and gear) has a significant
effect on the boat's performance, for example:
a. Shifting weight to the rear (stern)
b. Shifting weight to the front (bow)
BOTTOM
1. Boat Bottom: For maximum speed, a boat bottom should be nearly a flat plane where
it contacts the water and particularly straight and smooth in fore-and-aft direction.
a. Hook: Exists when bottom is concave in fore-and-aft direction when viewed from
b. Rocker: The reverse of hook and much less common. "Rocker" exists if bottom
c. Surface Roughness: Moss, barnacles, etc., on boat or corrosion of motor's gear
d. Gear Housing: If unit is left in the water, marine vegetation may accumulate over

Trim

TRIMMING OUTBOARD "OUT" ("UP")
Excessive trim "out" also may reduce the stability of some high speed hulls. To
correct instability at high speed, reduce the power GRADUALLY and trim the out-
board "in" slightly before resuming high speed operation. (Rapid reduction in
power will cause a sudden change of steering torque and may cause additional
momentary boat instability.)
1. Will lift bow of boat, generally increasing top speed.
2. Transfers steering torque harder to left on single outboard installations below 23 in.
(584mm) transom height.
90-884294 OCTOBER 2001
(1.) Generally increases top speed.
(2.) If in excess, can cause the boat to porpoise.
(3.) Can make the bow bounce excessively in choppy water.
(4.) Will increase the danger of the following wave splashing into the boat when
coming off plane.
(1.) Improves ease of planing off.
(2.) Generally improves rough water ride.
(3.) If excessive, can make the boat veer back-and-forth (bow steer).
the side. When boat is planing, "hook" causes more lift on bottom near transom
and allows bow to drop, thus greatly increasing wetted surface and reducing boat
speed. "Hook" frequently is caused by supporting boat too far ahead of transom
while hauling on a trailer or during storage.
is convex in fore-and-aft direction when viewed from the side, and boat has strong
tendency to porpoise.
housing increase skin friction and cause speed loss. Clean surfaces when neces-
sary.
a period of time. This growth MUST be removed from unit before operation, as it
may clog the water inlet holes in the gear housing and cause the engine to over-
heat.
WARNING
GENERAL INFORMATION
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