Volvo Penta D4 Series Operator's Manual page 50

Operation
48
Maneuvering
Shifting between forward and reverse should be done
at idling. Shifting at higher engine speeds can be
uncomfortable for passengers and cause unnecessary
stress on the transmission or cause the engine to stop.
If you attempt to shift gear at an excessive engine
speed, a safety function cuts in automatically, and
delays shifting until engine speed has fallen to 1500
rpm.
Always do a forwards/reverse operation as
follows:
1 Reduce engine speed to idle and let the boat more
or less lose way.
WARNING!
Never shift to reverse when the boat is planing.
2 Move the control lever to neutral with a rapid, dis-
tinct movement. Make a brief pause.
3 Then move the control lever to reverse with a rapid,
distinct movement and increase engine speed.
IMPORTANT!
It is important all engines are running during reversing
maneuvers, to avoid the risk of water entry via the
exhaust pipe into the stationary engine.
47702599 12-2011