I've just finished sanding and varnishing the wood trim on a 1955 Old Town Canoe. It's time now to flip it over on its sawhorses and pay attention to the painted hull. I've been under it and flicked off the loose paint (thin layer). In places there is a white substance exposed which sheds some dust when touched. Most of the bottom of the hull is covered with large sections of intact paint but with ridges. I'm attaching a couple of photos taken while lying under the boat, so color may be a bit off. The brown showing is actually white. First question is what kind of sanding/scraping needs to go on. Then, sealer? or what? and what kind of paint. This canoe is use in salt or mixed river/sea at the mouth of our river, and can be 6-8 hours at a time. The sides are looking good except for a couple of small wounds, but the bottom is a mess. I'll appreciate any suggestions. This is a beautiful canoe, and my friend is only the 2nd owner.