Daniel,
Captain Kittredge had a couple of slick mods to convert a standard
motor to an extended shaft unit (which he had built originally to use
as direct drive units). However, it's a ton of not fun to build them,
and you'd be better off, I'm certain, using the Minn-Kota 36vdc 102 #
thrust trolling motors. They produce, in reality, about 70# of thrust
at full power, which is substantial, and considerably more than
George's 1/2 horsepower side motors.
The 3 hp 36 vdc permanent magnet motors are no longer available (or
so I am told). They had a nasty habit of overheating and welding the
brushes. Drop all that and use three of the Minn Kota's in place of the
as-drawn units, and you'll have more than enough.
The conversion is pretty easy if you are a machinist, or know one.
Break the motor can down and cut proper o-ring grooves in the mating
surfaces. The shaft socket is used for garter seals or the like in
stock form. Punch that out for a ceramic rotary seal to match, and you
got it. You ought to be able to do the whole deal for a couple of
grand, give or take. Build a spare or two while you're at it and stick
it in the tool box. You never know when something will get wet.
I'll get one of these together for next year's psub meet, all
things being equal, and maybe some sketches. It'll give us something to
argue about.
Vance