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Prop Rule of thumb to raise rpm by 500 rpm ?

Old 07-29-2021, 08:17 PM
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Default Prop Rule of thumb to raise rpm by 500 rpm ?

Whats the rule of thumb to raise rpm by 500 rpm ?
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Old 07-29-2021, 08:37 PM
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I thought it was generally 300 rpm per pitch number
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Old 07-29-2021, 09:07 PM
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I thought it was 200 RPM per-pitch. To raise the RPM is to lower the pitch. Example : 28P to 26P theoretically would raise the RPM by 400 of a same prop. Different diameter propellers/ Geometry will affect the rpm
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Old 07-29-2021, 09:49 PM
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Play with the prop speed calculatirs here:
https://www.go-fast.com/Knowledge-ba...lip-calculator
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Old 07-29-2021, 11:01 PM
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It would roughly change the rpm by 28 / 26 = 1.077 x the rpm you were running with the 28P. So if you were running 4400 x 1.077= 4739. If you were running 4900 x 1.077 = 5277. That is approximate and assumes the exact same prop type and the exact same prop slip. If you were running 300 rpm below the HP peak you might gain a bit more than the calculation. I think the prop slip calculators will more or less tell you the same thing.
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Old 07-30-2021, 01:04 PM
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I changed my drive from a 1.62 running a bravo 1 26 pitch at 5000 rpm at 62 mph. Now I changed my drive to a 1.47 and the 26 is to big a wheel.
I only get 3800 and 52 mph.
With the 1.47 I need to re prop to get back up to 5000. I need to gain 1200 rpms. Ideas ?
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Old 07-30-2021, 01:09 PM
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Originally Posted by Donzi Z22 View Post
I changed my drive from a 1.62 running a bravo 1 26 pitch at 5000 rpm at 62 mph. Now I changed my drive to a 1.47 and the 26 is to big a wheel.
I only get 3800 and 52 mph.
With the 1.47 I need to re prop to get back up to 5000. I need to gain 1200 rpms. Ideas ?
Yes, see post #4. Enter what you had with moh it ran. It will give you slip. Then change gear ratio, keep slip,, keep mph, keep rpm, clear pitch and it will give you pitch
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Old 07-30-2021, 02:17 PM
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Originally Posted by SB View Post
Yes, see post #4. Enter what you had with moh it ran. It will give you slip. Then change gear ratio, keep slip,, keep mph, keep rpm, clear pitch and it will give you pitch
It says a 24, thanks
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Old 07-30-2021, 02:46 PM
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Originally Posted by SB View Post
Play with the prop speed calculatirs here:
https://www.go-fast.com/Knowledge-ba...lip-calculator
I cant seem to get this to work for my boat, do you populate the first 4 entries then click calculate ??
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Old 07-30-2021, 03:23 PM
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Originally Posted by F-2 Speedy View Post
I cant seem to get this to work for my boat, do you populate the first 4 entries then click calculate ??
You populate gear ratio, pitch and rpm and click calculate for theoretical speed. Then you put in your actual speed and click calculate for prop slip and it will give you a %
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