Installing Outboard; Determining Recommended Outboard Mounting Height - Mercury 75 HP Installation Manual

Installing Outboard

Determining Recommended Outboard Mounting Height

Outboard
Mounting
Height
(See NOTE
e
Below)
NOTE: Add 5 in. (127mm) for XL mod-
els to the listed outboard mounting
height.
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.
a.
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.
b.
26 in.
(660mm)
25 in.
(635mm)
24 in.
(609mm)
(e)
23 in.
(584mm)
22 in.
(560mm)
21 in.
(533mm)
20 in.
(508mm)
19 in.
(482mm)
10
IMPORTANT
NOTICE TO INSTALLER
75, 90 and 115 (4-STROKE) INSTALLATION MANUAL
a
20 30 40 50
Maximum Boat Speed Anticipated
c.
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
d.
mounting height dimension for dual outboard installa-
tion.
Outboard mounting height (height of outboard transom
e.
brackets from bottom of boat transom). For heights over
22 in. (560mm), a propeller, that is designed for surfac-
ing operation is usually preferred.
c
d
60 70 80
Page 5 of 18
b