Mercury Optimax 115 Service Manual page 26

TRIMMING OUTBOARD "IN" ("DOWN") CHARACTERISTICS
Excessive speed at minimum trim "in" may cause undesirable and/or unsafe
steering conditions. 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 installa-
tions.
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 installation. Water intrusion into the transom core and/or inner hull will result in addition-
al boat weight (reduced boat performance), hull decay and eventual structural failure.
CAVITATION
Cavitation is caused by water vapor bubbles forming either from a sharp edge or angle
on the gear case or from an irregularity in the propeller blade itself. These vapor bubbles
flow back and collapse when striking the surface of the propeller blade resulting in the ero-
sion of the propeller blade surface. If allowed to continue, eventual blade failure (break-
age) will occur.
VENTILATION
Ventilation occurs when air is drawn from the water's surface (excessive trim out angle)
or from the engine exhaust flow (wrong propeller/propeller hardware installed or gear
case labyrinth seal worn) into the propeller blades. These air bubbles strike the propeller
blade surface and cause erosion of the blade surface. If allowed to continue, eventual
blade failure (breakage) will occur.
90-855347R1 JANUARY 1999
WARNING
GENERAL INFORMATION
Page 1C-5