Updated
02/07/08
Updated
02/07/08
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Pitch & Rake |
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Your
propeller is the only source for getting available horsepower to the water.
Without the correct prop and pitch you could have a 500 horsepower motor but
go nowhere.
Pitch in a prop is a lot like gears in a car or truck. Higher pitch equals
higher top end but terrible low end. Pitch
is the theoretical travel a prop makes in one revolution. Example: A 20 pitch
prop will travel 20 inches per revolution if there is no slip.
Props come in a variety of configurations known as flat pitch, regressive pitch
and progressive pitch. Props with a flat or straight pitch have the same pitch
on the leading edge as on the trailing edge and are usually considered the fastest.
Props with regressive pitch are somewhat rarer because they have a higher
pitch on the leading edge than on the trailing edge, this configuration utilizes
the higher pitch to create drag to enhance the hole shot.
Props with a progressive pitch are the most common and are the best for
overall performance, these have a lower pitch on the leading edge for hole shot
purposes and a higher pitch on the trailing edge for speed.
These props are generally stamped with a median number, an example being
a prop stamped 25 pitch will more likely read 27 to 28 pitch under the cup when
measured on a pitch gauge.
Rake of the blades is the next consideration, a low rake prop has the most power
and a high rake has the most speed and lift.
Rake is the angle of the blade in relation to the hub, 0 rake being 90
degrees.
The better running props are usually in the 20 through 30 degree rake
angles.
Cup
added to a prop blade controls what the prop does for the boat.
Cup on the trailing edge controls stern lift and aids to some degree
hole shot.
Cup on the blade tips controls bow lift and speed.
Cup is not a generic item, it has to be designed to the application and
what works for boat and
motor X will not necessarily work for boat and motor Y.
Porting
a prop aids hole shot, these are the holes found in most props behind the leading
edge of the blades on the barrel of through hub exhaust and over and through
applications.
In the through hub configuration the porting allows extra exhaust into
the prop blades so the prop can spin up faster to help the hole shot.
On over and through hub configurations, the porting actually creates
a vacuum pulling water back into the prop blades which aids hole shot.
Selecting which combinations of the above that will work the best for your
application is usually best left up to someone who has a good working knowledge
and a lot of experience in the field.