Mercury 25 Jet FourStroke Operation, Maintenance And Installation Manual page 109

INSTALLATION
IMPORTANT: If the angle of the boat transom does not allow the driveshaft
housing to be positioned vertical, a wedge kit should be installed behind the
transom brackets to increase the tilt‑in angle.
NOTE: Slight cavitation in sharp turns and rough water is acceptable, but
excessive cavitation is harmful to the outboard and should be avoided.
Test run the boat. If cavitation occurs (air enters the pump), the first thing to try
is lowering the outboard mounting height.
If cavitation still exists after lowering the outboard, it may be helpful to seek
advice from the boat manufacturer.
Another option to further reduce cavitation is a rough water plate.
A rough water plate may be helpful in reducing cavitation when running in
windy, rough water conditions where air is sucked into the water intake when
jumping waves. Install a 0.8 mm (1/32 in.) metal plate that extends from the hull
bottom to the top of the water intake housing. This plate tends to reduce air
intake as well as reduce spray.
a
24906
a - Rough water plate
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eng