Volvo Penta D4 Series Operator's Manual page 52

Operation
50
Cruising Speed
For best fuel economy operations at full must be
avoided. We recommend a cruising speed that is at
least 10% below the maximum engine revolutions at
top speed (full throttle).
Depending on hull type, the choice of propeller, the
load and sea state etc., the maximum revolutions at
top speed may vary, but they should be within the full
throttle range; refer to section Engines.
If the engine does not reach its maximum throttle ran-
geit can depend on a number of factors mentioned in
the Fault Handling page 57 section.
Select a propeller with greater pitch if actual enginer-
evolutions exceed the full throttle range. Contact your
Volvo Penta dealer for advice.
Synchronizing Engine Speed
When driving with twin engines, both the operating
economy and comfort will be increased when the
engines are operating at the same engine speed (rpm).
When the synchronization function is activated, the
engine speed (rpm) of the starboard engine is auto-
matically adjusted to that of the port engine. The syn-
chronization function is activated automatically if the
following conditions are met.
1 The engine speed levers for both engines are in
(approximately) the same position.
2 The engine speed on both engines exceeds 800
rpm.
The synchronizer is disengaged as soon as the con-
ditions are no longer met.
47702599 12-2011