Propeller Rake
Propellers are all variations of helical forms, the
pitch being the helix or distance that a blade would advance through a solid
medium in one revolution. Thus a three bladed propeller can be thought of as
three similar profiles each cut from the flight of a triple thread screw.
Rake in a propeller is the inclination of the blade
forward or aft of the conventional position of 90 degrees or square with the
propeller shaft.
A propeller can be thought of as an infinite number
of radial sections in helical or spiral arrangement. In the basic type of
propeller, one which has no rake, each of these lines on the pushing face of the
propeller radiate directly outward from the shaft center and square or
perpendicular to the p-propeller shaft. This is called 0 degree rake. A
propeller can also have a forward (negative) rake or an aft (positive) rake.
Typical Rakes
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Forward Rake - This design is used on outboard
motors by various manufacturers.
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0 degree Rake - Used on outboard, I/O's and inboards by all
manufacturers.
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15/16 degree Aft Rake - Used on outboards and I/O's by
various manufacturers.
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Parabolic Rake - Various rakes - 3 degree Forward through 35
degree Aft. Used for performance propellers by various manufacturers.
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