"Robin" wrote in message
...
I had a brainwave the other day about putting a small (300cc)
aircooled two stroke as an inboard in a small wooden boat. With
adequate air circulation can anyone see any potential issues here? I
would build the boat with this purpose in mind so adapting something
to fit would not be a problem.

Robin

Until the early '60s, lawnmower conversions, both 2-stroke and 4-stroke,
were used in small boats. I fished from one here in Barnegat Bay in the
mid-'50s.

Vertical-shaft motors were used with a commercial conversion unit that was
like the bottom end of an outboard. That provided the gearing for
shaft-speed reduction and it turned the drive axis around. Motors were
typically mounted on a small platform six inches or so off of the boat's
hull so cooling air could get out from under them.

Horizontal-shaft motors used a regular shaft log and packing. They leaked if
you looked at them sideways. Better packing is available now.

These motors, of course, have built-in flywheel cooling fans. They were
noisy; the boats were slow and the two-strokes would gag you if you didn't
use a high exhaust pipe, which was hard to support. Rigging an underwater
exhaust would be a problem. Because you had to leave them fairly open to
cool, their ignition wiring was vulnerable to water splashing in the boat.
(This is one reason that the Acadia and other make-and-break inboards used
low-tension ignition).

All in all, they weren't very satisfactory. But they were cheap. The last ad
I saw for the vertical-shaft lower units would have been around 1962 or so,
but maybe someone still makes them in a dark corner somewhere. There were
some conversions that used scrapped bottom ends from outboards, but I don't
know how successful they were.

Back in the mid-'60s one of the mechanic's magazines had plans for a nifty
little three-point hydro (about the size of a C hydro) with two go-cart
motors powering it through direct shaft drives. There were no fans on the
motors. I don't know how well they worked out, but they were said to do 60
mph.

Good luck. You're not likely to do much better than those old lawnmower
conversions, but it could be fun trying.

--
Ed Huntress