I spent the majority of 1999 in Corpus Christi and I had a great downwind slip at the Marina. We had a floating dock, great and Old tires for bumpers, yeck. I had black marks on the port side and was getting awfully tired of the appearance. I tried the reccomended 1200 to 1600 grit but it leaves the hull with that sandpapered look. Well guess what I found today while discussing the problem with a friendly cleark at Ace of all places. Very Fine Pumice. Using a bucket of clear water, a plate stolen from my wife's kitchen and an old piece of felt. The black marks come off and darned if it isn't polished too. Now a tad of wax and wow, it is pretty as new. O fcourse their is the elbow grease but I was wondering if a buffer might work(toolman?).