Prop size F40/40

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danjohns
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Joined: Tue Aug 28, 2012 5:34 am

Prop size F40/40

Post by danjohns »

I'm trying to replace my max prop on my F40/40 (needs referb) with a 3 blade MP3 prop. My owners book says the original prop was a 20-13 but doesn't say 2 or 3 blade. Does any 40/40 owners know the original size prop and would 20-13 three blade be correct? Any recommendations?

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GeoffSchultz
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Re: Prop size F40/40

Post by GeoffSchultz »

Based upon my calculations, it should be an 18" prop as you don't want to exceed 95 ft/sec at the prop tip. An 18" prop develops 95 ft/sec at 2800 RPM using a KBW10-E transmission with a 2.33:1 reduction. This is also right at the prime part of the curve for power & fuel consumption, so I'd bet that's the right size.

-- Geoff
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1997 Freedom 40/40
http://www.GeoffSchultz.org

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GeoffSchultz
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Re: Prop size F40/40

Post by GeoffSchultz »

According to the manual the original prop was a 2-blade 20x13 rh. However, based upon my research that's too large as you don't want to exceed 95 ft/sec at the blade tip. The Yanmar 3jh2-tbe that my 40/40 comes with has a sweet spot for fuel consumption and torque at about 2800 RPM, which equates to 105 ft/sec, which is too fast. Thus I believe that a smaller, higher pitched prop would be better.
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1997 Freedom 40/40
http://www.GeoffSchultz.org

danjohns
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Re: Prop size F40/40

Post by danjohns »

I just had my F 40/40's, 3 blade 20 inch max prop refirbed by PYI. What pitch do you use? 16 or 18 degrees?

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