I am a fairly skilled amateur furniture and auto paint refinisher. Strictly amatuer so take my ideas with a grain of salt. But anyway, couple ideas. I have very successfully used plastic scratch remover on all sorts of scuffs. One brand name is PlastiX, or something similar. You can use it on milky headlights. Seems to have just enough super fine grit to clean and polish to a gloss. A bit softer is Bar Keepers Friend, maybe off a bit on the name. But that stuff I use on windshields and its abrasive enough to give a good cleaning and polish. If those ideas don't work, you can wet sand to any finish you want. I'd say to start with nothing more abrasive than 320, better to go with 400 first and see what it does. Keep things wet and you will get good results. The 400 will leave a bit of a matte surface, no biggie, go to 600 grit, then 800, 1200. All wet. You can go crazy and go to 2000 or even finer but I think that would not be needed. When it looks like the gloss you almost want, use some polishing compound. Not a heavy cutting compound but something that is for polish. You will be able to bring up whatever luster you want. Problem it might look so good you will want to do the whole deck/hull. Anyway, some ideas. If there is a gouge through a gel/clear coast, I'd clean it well and get a rattle can of clear coat for auto use and spry the area, then use the suggested sanding approach. You ought to be able to blend that in with not a lot of effort. I have used this approach on cars paint as well as furniture finishes.