In many boats, weight matters less than fuel range and that is where a
Sterling should excel. However, many Sterlings use Helium as the gas
that expands and He is known to leak out of anything with time.
Sterlings need a good heat sink and a boat has one all around. I also
think that a Sterling powered generator would be good for places where
you really need silence.They can burn just about anything.
One of my many techie schemes was to produce arrays of tiny Sterling
Engines on a chip to be used to cool circuits. Put power in and they
cool stuff. Instead of pistons, they'd have flexible membranes made by
various micro-machining methods. I never really pursued it and the
market was taken by electronic Peltier coolers with no moving parts.