Thanks for the replies, I hadn't considered the maneuverability issue
at 2 knots.

Interesting that the two replies differ so much from each other :-) I
don't understand the need for 25 horse for slow speeds (2 knots); and I
also don't understand how a planing hull could be more efficient than a
displacement hull at slow speeds. I think I'll be looking at
displacement hulls with keel as first option.

Planing hull, outboards, direct injected E-TEC as the main engine and
a kicker 25 horse for slow speed maneuvering.

Efficient, miserly on fuel and ton's of power when you need it if you
go with a four blade prop.