Hi Joe.Paul wrote...."What we need is a clever trick like that used in water ballasted sailboats - just fill the tanks before sailing to increase your displacement. But of course that doesn't help a sub, unless you look at flooding most of your crew compartment while diving. Maybe you need a sand ballast keel system. :-) Run along in shallow water scooping up sand until you've got the two tons or so that you need.".How do you run in shallow water scooping up sand in a trolling motor ambient sub? How would that be accomplished without the friction of some kind of scoop attached to the sub stopping the sub dead? It would be like running into a sandbar wouldn't it?