Re: Open electric displacement boat 16-18'
Have you studied the electric boat systems -your mention of "a couple of batteries" makes me wonder. What sort of range / distance / time on the water are you looking for? Will it live mostly in the water, or do you plan on trailering it every time you use it? I've moved too many marine batteries in and out of boats to ever want to do it on a regular basis!
If you plan to trailer it with batteries in place, you may need a design and trailer supports that can handle that. Can't imagine anything of the size and capacity you describe with fewer than 4 batteries, quite possibly more. And if you'll be going out daily, you'll need to be able to either recharge the banks at the dock, or swap charged batteries in & out of the boat.
"The enemies of reason have a certain blind look."
Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.