Boat - Mercury 40 Service Manual

Boat

WEIGHT DISTRIBUTION
Proper positioning of the weight inside the boat
1.
(persons and gear) has a significant effect on the
boat's performance, for example:
Shifting weight to the rear (stern)
a.
(1.) Generally increases top speed.
If in excess, can cause the boat to por-
(2.)
poise.
Can make the bow bounce excessively in
(3.)
choppy water.
Will increase the danger of waves splash-
(4.)
ing into the boat when coming off plane.
Shifting weight to the front (bow)
b.
Improves ease of planing off.
(1.)
Generally improves rough water ride.
(2.)
If excessive, can make the boat veer left
(3.)
and right (bow steer).
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 di-
rection.
1. Hook: Exists when bottom is concave in fore-
and-aft direction when viewed from 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 re-
ducing boat speed. "Hook" frequently is caused
by supporting boat too far ahead of transom while
hauling on a trailer or during storage.
2. Rocker: The reverse of hook and much less
common. "Rocker" exists if bottom is convex in
fore-and-aft direction when viewed from the side,
and boat has strong tendency to porpoise.
3. Surface Roughness: Moss, barnacles, etc., on
boat or corrosion of outboard's gear housing in-
crease skin friction and causes speed loss. Clean
surfaces when necessary.
1C-2 - IMPORTANT INFORMATION
TRIM
TRIMMING OUTBOARD "OUT" ("UP")
WARNING
Excessive trim "out" also may reduce the stabil-
ity of some high speed hulls. To correct instabili-
ty at high speed, reduce the power GRADUALLY
and trim the outboard "in" slightly before resum-
ing 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) tran-
som height.
3. Increases clearance over submerged objects.
4. In excess, can cause porpoising and/or ventila-
tion.
5. If trimmed out beyond the water pickup, reduced
water supply can cause overheating resulting in
engine damage.
TRIMMING OUTBOARD "IN" ("DOWN")
WARNING
Excessive speed at minimum trim "in" may
cause undesirable and/or unsafe steering condi-
tions. Each boat should be tested for handling
characteristics after any adjustment is made to
the angle (trim adjustment bolt relocation.)
1. Will help planing off, particularly with a heavy
load.
2. Usually improves ride in choppy water.
3. In excess, can cause boat to veer to the left or
right (bow steer).
4. Transfers steering torque harder to right (or less
to the left) on single outboard installations.
5. Improves planing speed acceleration (by moving
trim adjustment bolt one hole closer to transom).
WATER ABSORPTION
It is imperative that all through hull fasteners be
coated with a quality marine sealer at time of installa-
tion. Water intrusion into the transom core and/or in-
ner hull will result in additional boat weight (reduced
boat performance), hull decay and eventual structur-
al failure.
90-852572R1 JANUARY 1998