On Friday, March 11, 2016 at 11:26:26 AM UTC-5, wrote:
If you could plumb steam to the engine you might be able to do this, but
there's likely no way to put reasomable power in an outboard engine with
the boiler requirements.

There have been a number of successful designs that have accomplished
this goal. You won't get 150hp out of it, but certainly enough power
to move a small skiff at a decent speed- 8hp or so. Traditional boiler
designs are too heavy, but the Serpollet monotube works quite well.
Check out Wally Mounster and Terry William's designs.

Nuclear powered naval vessels use steam turbine technology (for steam to mechanical). Is that what the OP meant back in 1996 or so? Even then, maybe that's too big of a system.