What is gear ratio for most outboards 10 to 30 hp ?

[preventec47]

Somewhere in the lower end I expect some gear reduction is taking place as most of these outboards redline rev
in the 5000 to 6000 rpm range. I have visited several outboard mfg websites and read through their manuals
but I cannot find the info that will tell me actually how fast the prop is spinning.
I need this info to match available props to a direct drive inboard I want to build.

 

[gm280]

preventec47, That all depends on the individual manufacture and engine. Usually the factory engine specific, HP, Model and year shop manual specifies those numbers for that engine.

 

[Sea Rider]

You have to match a prop that revs inside IB's min-max wot rpm range, preferably towards max wot range as usually loaded. Seems will need a intense water testing under trial and error..

Happy Boating

 

[Scott Danforth]

This is in regards to you hope to use a lawn and garden air cooled motor in your other thread?

Your funeral when it ( not if) blows up

Most small outboards are about 2:1, however some are 1:1. You have to do your research. Your lawn and garden motor is a low rpm (under 3000) motor with a block temp of 400 and exhaust temp well over 1600

You would be better suited to use a PWC motor