Mariner 100, Service Manual, Page: 16 / 391

1-11 90-13645--2 495 GENERAL INFORMATION AND SPECIFICATIONS
For boaters to realize optimum engine performance
under changing weather conditions, it is essential that
the engine have the proper propeller to allow it to op-
erate at or near the top end of the recommended max-
imum RPM range at wide-open-throttle with a normal
boat load.
Not only does this allow the engine to develop full
power, but equally important is the fact that the engine
also will be operating in an RPM range that discour-
ages damaging detonation. This, of course, en-
hances overall reliability and durability of the engine.
Conditions Affecting Operation
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)
(1.) Generally increases top speed.
(2.) If in excess, can cause the boat to por-
poise.
(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.
b. Shifting weight to the front (bow)
(1.) Improves ease of planing off.
(2.) Generally improves rough water ride.
(3.) If excessive, can make the boat veer left
and right (bow steer).
2. Boat Bottom: For maximum speed, a boat bot-
tom 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 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 stor-
age.
b. 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.
c. Surface Roughness: Moss, barnacles, etc.,
on boat or corrosion of outboard’s gear housing
increase skin friction and cause speed loss.
Clean surfaces when necessary.
3. Gear Housing: If unit is left in the water, marine
vegetation may accumulate over a period of time
in certain types of water. This growth must be re-
moved from unit before operation, as it may clog
the water inlet holes in the gear housing and
cause the engine to overheat.