When people say the new outboards have good fuel
economy they are verses two stroke outboards or maybe a bad diesel
set up. A displacement
vessel is set up on the amount of torque the engine
produces to push a certain amount of water
(hulls do differ and can be calculated) using the least amount of HP as possible to save fuel
usage, propped somewhere near maximum torque which is nowhere near max HP. A good example of this is the light plane industry where some diesel
set ups can fly nearly twice the distance.
When you take out the engines the volume can be used for the extra fuel tanks
that you will need, plus the problems Stumble ect. mentioned.
A Cat with long waterlines and kept light and full bow and stern to alleviate the pitching to keep the props deep and not cavitate, work with outboards, some I have seen with large outboards can really get mobile, but as they are fly past my brain starts to try and calculate the $$$$$
Different strokes for different folk.
I must be getting old and senile!