Speedmaster prop question
08-29-2013, 03:25 PM
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Speedmaster prop question
Given the same power which prop would spin more rpm a 15 3/8 X 26 4 blade 6" hub or a 16.5 X 27 3 blade with a 6" hub? How much does each inch of diameter affect rpm and how much does each inch of pitch affect rpm?
08-29-2013, 04:01 PM
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It sort of matters the drive ratio too. If your running (lets use for example) a 1.400:1
Try to think of it like a screw every revolution of the propeller it moves in the foward direction 16.500" the more foward motion the needed increase for horsepower.
about 1 1/8" per REVOLUTION the 16.500 is going to travel....
:CHIP:
Try to think of it like a screw every revolution of the propeller it moves in the foward direction 16.500" the more foward motion the needed increase for horsepower.
about 1 1/8" per REVOLUTION the 16.500 is going to travel....
:CHIP:
08-29-2013, 04:10 PM
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the 4 blade will spin more rpm it is a lower pitch and smaller diameter, as for how much of a difference way to many variables to guess, but my guess is 500 rpm. What kind of power, what is the max RPM, what is the gear ratio, what is the x-dim, single or twin, if twin spinning in or out, what kind of boat, ect ect.
Also Chip you have the numbers confused the first number is the diameter, so one prop is 1 1/8" bigger than the other, the pitch is the second number the 4 blade moves 26" per rotation and the 3 blade 27" per rotation.
Also Chip you have the numbers confused the first number is the diameter, so one prop is 1 1/8" bigger than the other, the pitch is the second number the 4 blade moves 26" per rotation and the 3 blade 27" per rotation.
Last edited by pstorti; 08-29-2013 at 04:12 PM.
08-29-2013, 05:18 PM
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It will be close.... All things being equal the reduced slip factor of a 4 blade is usually equal to 1" of pitch size compared to a 3 blade. That being said, I speculate that given the added diameter of the 3 blade will help with slip thus the 3 blade would run slightly lower RPM.
08-29-2013, 05:30 PM
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the 4 blade will spin more rpm it is a lower pitch and smaller diameter, as for how much of a difference way to many variables to guess, but my guess is 500 rpm. What kind of power, what is the max RPM, what is the gear ratio, what is the x-dim, single or twin, if twin spinning in or out, what kind of boat, ect ect.
Also Chip you have the numbers confused the first number is the diameter, so one prop is 1 1/8" bigger than the other, the pitch is the second number the 4 blade moves 26" per rotation and the 3 blade 27" per rotation.
Also Chip you have the numbers confused the first number is the diameter, so one prop is 1 1/8" bigger than the other, the pitch is the second number the 4 blade moves 26" per rotation and the 3 blade 27" per rotation.
:CHIP:
P.S. Search this site for "propellers" and "in or out". guys have different luck with different applications..
08-29-2013, 07:31 PM
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I didn't mean to give you incorrect info. Your question would look like this.....
The smaller diameter and the lower pitch would probably put the thing right on the rev limiter and quick...
Larger diameter more surface area.... You get the idea! I actually have solid models somewhere...
:CHIP:
The smaller diameter and the lower pitch would probably put the thing right on the rev limiter and quick...
Larger diameter more surface area.... You get the idea! I actually have solid models somewhere...
:CHIP:
