75/90/115 OPTIMAX
Page 6 of 18
Determining Recommended Outboard Mounting Height
20 in.
21 in.
22 in.
23 in.
24 in.
25 in.
26 in.
19 in.
10
20
30
40
50
60
70
80
Outboard
Mounting
Height (See
NOTE Below)
Maximum Boat Speed Anticipated
NOTE: Add 5 in. (127mm) for XL mod-
els to the listed outboard mounting
height.
(660mm)
(635mm)
(609mm)
(584mm)
(560mm)
(533mm)
(508mm)
(482mm)
This solid line is recommended to determine the out-
board mounting height.
IMPORTANT: Increasing the height of outboard gener-
ally will provide the following: 1) Less steering torque,
2) more top speed, 3) greater boat stability, but, 4) will
cause more prop “break loose” which may be particu-
larly noticeable when planing off or with heavy load.
These broken lines represent the extremes of known
successful outboard mounting height dimensions.
This line may be preferred to determine outboard
mounting height dimension, if maximum speed is the
only objective.
This line may be preferred to determine outboard
mounting height dimension for dual outboard installa-
tion.
Outboard mounting height (height of outboard transom
brackets from bottom of boat transom). For heights over
22 in. (560mm), a propeller, that is designed for surfac-
ing operation is usually preferred.
1. The outboard should be mounted high enough on the transom so that the exhaust
relief hole will stay at least 1 in. (25.4 mm) above the water line when the engine is
running at idle speed. Having the exhaust relief hole above the water line will prevent
exhaust restriction. Exhaust restriction will result in poor performance at idle.
2. However, keep in mind that the mounting height (e) of the outboard must not exceed
25 in. (635 mm) for L models, 30 in. (762 mm) for XL models. Mounting the outboard
higher may cause damage to the gear case components.
NOTICE TO INSTALLER
IMPORTANT
(e)
e
a.
b.
a
c
b
d
c.
d.
e.