Propellers; E - 4 Propellers; Diameter; Pitch - Four winns V Series Owner's Manual

Avoid run ning aground or striking a (submerged)
object. Serious damage to the engine(s) or
inboard/IPS underwater gear can result and the
boat can take on water. In the event of such an
occurrence, proceed at low speed to the nearest
service facility and have an immediate inspection
made of the under- water gear before further use
of the craft. Keep all life saving devices at hand
while driving to a dock area. If the boat cannot be
immediately removed from the water, thoroughly
inspect the bilge area for leaks so that the boat
does not sink while moored.
E - 4

PROPELLERS

Knowledge of the propeller is most easily gained
through better understanding of the terminology
used to refer to the aspects of propeller size and
performance.
A. Diameter
Diameter is twice the distance from the center of
the prop shaft to the extreme tip of a propeller blade.
Increasing or decreasing propeller size will have a
direct bearing on the RPM's an engine will develop.
This is due to the greater amount of propeller blade
surface in contact with the water. See Figure E4.
Figure E4: Propeller Pitch & Diameter
Engines, Drives and Instrumentation - Section E
B. Pitch
Pitch is a measure of helix angle, or angle of attack,
of the rotating blade. Pitch is easily under stood if one
imagines the propeller rotating through a semisolid
such as butter or gelatin. The distance the propeller
will travel in one revolu t ion is called "Pitch." Increasing
or decreasing pitch will also have a direct bearing on
engine RPM's because of the greater bite taken by
the blade with each rotation. See Figure E4.
C. Prop Slip
When traveling through water a propeller is unable to
get a complete bite because of the fluidity of water.
"Prop slip" is usually expressed as a per c ent of the
computed theoretical speed. Twenty - five to thirty-five
percent prop slip is com mon for a cruiser-type boat
operating at cruising speed.
Changing either diameter or pitch will have an effect
on engine speed and prop slip, and in turn, directly
effect the performance of a boat. The propellers
included with each Four Winns
general performance based on data obtained from
on-the-water testing of that model. Variations in load,
operating conditions, environment, the individual
engine and hull perfor mance may necessitate the
purchase and use of another propeller(s).
Under your normal load conditions, the engines
should turn within the maximum RPM range when at
full throttle. If the engines exceed the recom mended
RPM, an increase in pitch or diameter is required.
If the engine RPM is too low, a de crease in pitch or
diameter is required.
The load carried in a boat will directly affect perfor-
mance of the engine. If an engine that is not develop-
ing full power, be sure the engine is properly tuned
and load conditions are those normally experienced,
before changing propellers.
For shipping reasons, the propellers are not factory
installed. Initial installation of the propel lers will be
performed by the dealer during pre-delivery ser vice.
Consult your specific engine manufacturer's owner's
manual for propeller installation instructions.
See Figure E4.
boat provide the best
®
Owner's Manual Page 58