duncan

Water ballast tanks have to be baffled to prevent surge etc. make them in say eight separate sealed units for trimming,fore and aft and beam-wise, but with egg-crate style boxes in each compartment. A drain plug in each tank and let gravity empty them when back on trailer. If it is stable enough when launched just open the cocks/plugs to flood the tanks, if not half fill them before going in and do final trim on water. Be sure to flash them out with tap water every time as they will stink with the bacteria and algea from seawater and even worse with canal water. Weiles ( rat pee ) disease can be contracted from river and canal water. A touch of household bleach will kill the algea. Have a look at some of the wooden boatbuilder pages for canoes, stitch and glue ie Mirror dinghy etc methods. Your painter friend might be redundant, the last thing you want is a glass-like finish.