I think the Yamaha engines are the same that are in snowmobiles. The snow
version would be closed loop.
Jerry

"Morgans" wrote in message
...

"Anthony W" wrote in message
news:gQPcf.7191$vC6.670@trnddc05...
Check out the Honda four stroke personal watercraft engines. They're
powerful and designed to run at full load for extended lengths of time.
However, you'd have to use a reduction unit to get the RPM down low
enough to drive a prop.

I think I am correct in saying that others have tried using a boat type
powerplant before, and have found problems, especially with keeping them
cool.

With a closed loop (most engines not on the water) water cooled engine,
the
engine sees cooling water at a pretty low temperature. They usually have
unregulated flow, and unlimited water, so the cooling passages don't have
to
be very large, or move the water very fast to be effective in keeping the
engine cool. Closed loop systems see water coming in at around 180
degrees,
so the flow has to pass through quickly and soak up as much heat as they
can, but are not able to take on much more heat. (because of it's already
high temperature) The passages have to be larger, and contact more of the
hot parts to remove enough heat to keep the engine cool.
--
Jim in NC