Yamaha F15 Owner's Manual page 44

Installation
line (keel line) of the boat, and ensure
that the boat itself is well balanced. Oth-
erwise the boat will be hard to steer. For
boats without a keel or which are asym-
metrical, consult your dealer.
1. Center line (keel line)
EMU26925
Mounting height
To run your boat at optimum efficiency, the
water resistance (drag) of the boat and out-
board motor must be made as little as possi-
ble. The mounting height of the outboard
motor greatly affects the water resistance. If
the mounting height is too high, cavitation
tends to occur, thus reducing the propulsion;
and if the propeller tips cut the air, the engine
speed will rise abnormally and cause the en-
gine to overheat. If the mounting height is too
low, the water resistance will increase and
thereby reduce engine efficiency. Mount the
outboard motor so that the anti-cavitation
plate is between the bottom of the boat and
a level 25 mm (1 in) below it.
38
1
ZMU01760
ECM01634
NOTICE
Make sure that the idle hole is high

enough to prevent water from entering
the engine even if the boat is stationary
with the maximum load.
Incorrect engine height or obstructions

to the smooth flow of water (such as the
design or condition of the boat, or ac-
cessories, such as transom ladders or
depth finder transducers) can create
airborne water spray while the boat is
cruising. If the outboard motor is oper-
ated continuously in the presence of
airborne water spray, enough water
could enter the engine through the air
intake opening in the top cowling to
cause severe engine damage. Remove
the cause of the airborne water spray.
TIP:
The optimum mounting height of the out-

board motor is affected by the boat and
motor combination and the desired use.
Test runs at different heights can help de-
termine the optimum mounting height.
Consult your Yamaha dealer or boat man-
ufacturer for further information on deter-
mining the proper mounting height.
For instructions on setting the trim angle of

the outboard motor, see page 56.