Hmmmmm, well. I think a nice slow turning Sabb 10 hp might satisfy his
needs.

http://home.no.net/sabb1/

They are hand-crankable, virtually indistructable, and can often be
found cheap because sailors don't want the terrible horsepower to
weight ratio of slow turning diesels(10 hp is 440lbs, but then 220lbs
is flywheel). The Sabb top rpm is only 1600 and pushes my 16K pound
hull along at 5-6 knots at 1200 rpm. They can sometimes be found in
back lots of boatyards, junk shops, etc. I found one in Marathon,
Florida, that had been literally laying in a guys backyard for two
years. We spirted some oil in the valve cover oiler, stuck the fuel
pump hose in a mason jar of diesel and she cranked on the second try.
Bought it for $300.

Mine is a '78 and if it ever needs parts they are still available.
Actually I did buy a spare raw water pump disphram in '85 but haven't
had to use it yet. And someday I might have to buy a starter motor for
it, but as of now, the mate says she is fine with hand cranking it.

Good luck to your friend and his 'power' boat.

pm