The Grady Express models that are kept outdoors sometimes get black streaks down the side of the hull mid-ships where the "gutter" from the forward deck ran back and drained overboard. Every time it rains I would get the very hard to remove streaks from the rub rail to the water line just below the drain cutout. I found a very simple and very effective fix. I took 2 pieces of fairly stiff clear plastic about 11" long and 6" wide. (I used the cover of a report folder, the kind that has a clear cover and you insert the pages of a report.) I taped the plastic to the rub rail with removable-residue free 3M duck tape. I can take the tape off when I am cruising and it leaves no residue at all.
Dan Clark Tarpon Coast Grady-White Boat Club