Parker 2014 - Propulsion and Trim; Propeller; Outboard Propulsion System

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performance
PROPELLER
The propeller (“prop”) converts the engine’s power into thrust to propel the boat. The right prop for any boat in a specic application is one that
allows the engine to turn up to its full rated RPM, but no more. It is necessary for the engine to turn to full rated rpm in order to develop full
rated power. If the boat is used for more than one type of activity, shing and water skiing for example, the prop can only be optimized for one
situation. Since a spare prop is an excellent safety item, the purchase of a second propeller which is more ecient for another application is not
all “added expense”.
PROPELLER TERMS
Propellers are identied by two numbers such as 14 x 17, and a material
identication, such as aluminum or stainless steel. The rst number is the
diameter and the second is the pitch. The diameter is the distance across the
circle swept by the extreme tips of the propeller blades. The term pitch comes
from the old screw analogy used to approximate propeller action. This analogy
says that a propeller screws itself through the water much as a wood screw
works itself into soft pine. The pitch is the angle of the blades expressed in the
theoretical distance a propeller would travel in each revolution. In the above
example the propeller would advance 17” on each revolution. In reality, the
propeller actually pushes the boat forward less distance than its pitch. The
dierence between the pitch and the actual distance traveled is called “slip”.
OUTBOARD PROPULSION SYSTEM
The engine manufacturer supplies all vital information concerning your engines in the operation and maintenance manuals. Details of
important engine maintenance schedules, lubrication system, cooling system and engine alert systems are outlined in these manuals. Your
familiarization with this engine reference material will result in the proper usage and service that is essential for safe and enduring engine
performance. These manuals are included with the Owner’s Packet.
CAUTION
Stay within the engine manufacturer’s maximum and minimum
RPM ranges when replacing props. This information is located in
your engine manuals. If your boat does not have a tachometer
consult your dealer for propeller changes.