Last summer I tried Meguiar's multi stage compounds on the four dull spot where the bumbers had rubbed for three years wiith little success. It did polish nice and improve the shine but the scratches were still visible. Gel Coat is harder than modern auto paint so I went to the old school 3M Hd rubbing compound and wool pad at about 1500-2000 RPMs. It has grit in it and is pretty much equal to wet sanding with 600 grit paper. I used a generous amount of compound a couple of times, cleaning pad between buffs, and the scratches drastically disappeared. They were not totally gone but the areas looked great compared to before the buffing. Then I switched to a finishing pad and used an old school polishing compound that we used to use to remove swirl marks. A quick rub on both sides and then went to a dark blue liquid wax (forget the brand). After a hand wax and hand polish with a clean soft Shammy, it looked great and drew many positive comments.
Try to determine if your hull is scratched or hopefully a transfer of material that scraped against it. Use fingernail to test. If a deep scratch, still try the buffing first. It will not hurt and is easily removed with a prepsol cleaner if it needs a spot repair.
