Like Joecb said, you are asking for trouble – bad connections, galvanic action corrosion, etc it you use an aluminum boat hull as a ground return. It’s just as easy to run two wire instead of one and not much added cost.
Dave
FYI: If you don’t already know, there is a good message board like this one and a lot of other info for old Crestliner restoration at http://retrocrestliner.com/
