Boat Propeller Terminology
Boat Propeller Size-
The size of a boat propeller is usually described by two numbers. These two
numbers indicate the sizes of diameter and the pitch respectively. Hence, we
express the size of a propeller by (DxP).
Boat Propeller Diameter-
Boat Propeller diameter is twice the distance from the center of the hub to the
tip of the blade as a propeller rotates.
Boat Propeller Pitch-
Pitch is the theoretical forward movement that a boat propeller travels during
one revolution. The actual distance a propeller travels is about 10 to 20
percent less than the design pitch. Slip is the difference between actual and
theoretical movement. It varies from boat to boat, depending on the weight of
the boat and blade surface of the propeller.
Boat Propeller Cupping-
It is said to have a cup if the trailing edge of the blades formed or cast with
the edge curled. Cupped blades improve the grip of the boat propeller into the
water, reduce cavitation and allow the boat to reach higher top speed. Cupping
benefits are so desirable that almost all modern recreational, high performance
boat propellers have some degree of cup. Compared with an uncupped boat
propeller with the same pitch, the cupped one will reduce full-throttle engine
speed. Single cup/100-200rpm. Double cup/300-400rpm.
Boat Propeller Ventilation-
Ventilation is the introduction of exhaust gases into the propeller. Ventilation
can be useful in the bottom end acceleration by allowing the propeller to slip a
regulated amount, allowing the engine to rev higher during initial acceleration.
Usually achieved by ventilation holes at the base of each blade, or over-hub
design. Ventilation is for thru-hub exhaust propellers only.
Boat Propeller Rake-
Blade rake is the angle of attachment of the blade to the hub of the propeller.
Higher rake can improve performance in higher engine elevation and/or
ventilating or cavitating situations. Lower rake is typically used in heavier
boats with fully submerged boat propellers. Rake is not to be confused with
Boat Propeller Advantages/Disadvantages
Aluminum Boat Propellers:
Disadvantage- blade flex and poor durability.
3 blade propeller vs. 4 blade aluminum propeller:
4 blade Advantage- better hole shot and increased stability.
4 blade Disadvantage- Top end speed.
Stainless Boat Propellers:
Advantage- overall performance, no blade flex, durability.
3 blade propeller vs. 4 blade stainless propeller:
3 blade Advantage- performance, good acceleration, best top end.
4 blade Advantage- best hole shot, increased stability and fuel economy.
5 blade stainless propeller:
Advantage- good hole shot.
Disadvantage- mid-range, top end and fuel economy.
This website was produced by MARINE PROP
510 West 1700 South
Clearfield, Utah 84015
Phone: 801 825-1352