What is the best way to make a boat hull made of foil?

I assume the boat is a toy, and not a full size sailing boat?

Make a boat's hull out of a block of solid wood. Cover the outside of the hull with foil, and carefully press smooth with a soft pad of cloth (to avoid tearing the foil). I would fold a large sheet of foil to form several layers for strength. Carefully remove the shaped foil from the wooden hull - and you will have a boat make of foil.