My Honda CBR1000F has a primary drive reduction rate 1.786:1 and gear ratios from 2.75:1
to 1.045:1 and final drive (chain sprockets) 2.47:1 so I think it is no problem to find a
suitable ratio somewhere along the line. If you take out moderate horsepower (say 50-70)
by sticking to lower revs, the engine should not overload.
I would be more concerned about sufficient cooling. Perhaps a larger automotive-type
cooler would be appropriate. These engines should last about 100000 miles without overhaul
which translates to about 3000 engine hours. Check
http://www.timothypilgrim.com/bike/japengines.jpg for details :-)

BTW, everything above except the first line to "2.47:1" is pure amateur speculation.

Heikki

ewan wrote:

this is more of a theoretical question more than anything else but a
couple of mates and i were chatting about boat building and engines in
general.

basicly ive heard a lot of engines are based upon marinised car
engine based but i got to thinking how simple it would be to use a shaft
drive bike engine {1} since theres a wide range of shaft drive engines
from 550s to 1100cc especialy the 900cc yamaha diversion engine which is
dirt cheap. i know the engines wouldnt last as long but sing they start at
£80 from breakers{2} means it could be treated as disposable item like
petrol.

im just posting to see if there is any serious flaws in the idea such as
not enough torque or other variables



{1} i guess i would have to work out the forces and calculate propeller
assuming the revs arent to high

{2} breakers tend to sell all the stuff that breaks in a crash like
plastic and bits that rust leaving them with the engine which most folk
dont want to replace