different numbers of ratios

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fieromx3

Petty Officer 2nd Class
Joined
Nov 28, 2011
Messages
131
so i know how gear ratios work and all the science. like when i see a gear ratio for a car say like 4.10:1 i know what that means lol

but in my workshop manual for my evinrude the propeller gear ratio is 12:29??

whats this one mean?

just wondering because i found out the previous owner put a small gearcase from a 1980 60hp size onto my 1973 50.

both gearcases have different ratios and just trying to match up a correct propeller size that would have originally came with it
 
Silvertip

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,762
Re: different numbers of ratios

Divide the 12 into 39 and you have a 2.42:1 ratio. The engine turns 2.42 times to make the prop turn once. Just as with a 4.10:1 means the drive shaft (not the engine) turns 4.10 times to make the wheels turn once. Outboards don't have a transmission -- only a lower unit.
 
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fieromx3

Petty Officer 2nd Class
Joined
Nov 28, 2011
Messages
131
Re: different numbers of ratios

i actually did divide it just like you said i thought i was righ but wasnt sure lol thanks for clearing it up!! :)

BTW is that an r/c airplane as your sig. picture?? is it yours? i love r/c and aviation in general
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: different numbers of ratios

Assuming an evinrude or Johnson;
The 60 uses a signifigantly smaller prop. a 17" pitch the max here at iboats.
The 50 uses props up to 23". a 2.66 gear ratio.
 
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