Yamaha Helm Master Operation Manual page 19

Function and operation of components
Triple engine applications
The two levers provide control of gear shifting and throttle operation for all three engines. The
PORT engine is controlled by the PORT control lever. The STBD engine is controlled by the
STBD control lever.
The center engine will be controlled to obtain a throttle setting midway between the PORT
and STBD engines.
When either the PORT or STBD engine's control lever is in the neutral (N) position the center
engine will also move into the neutral (N) position with the throttle fully closed.
Note the center engine will remain in neutral (N), with the throttle fully closed, if the levers for
the PORT and STBD engines are in different (forward/reverse) gearshift positions
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