Are you doing it by hand? If you have the tools I would suggest an electric or air orbital sander. Light to no pressure just gliding it across... although I tilted the electric on a bit of an edge and, for lack of a better word, lightly scored the hull and the sanded the scores out... does that make any sense? I can take some pictures this morning.... I'm by no means a a pro but I know there like 5-6mm of gel coat on it. Just have to remember No pressure when scoring, kind of just touching the surface. It's seems to be the only way to get the hull one color and get rid of the stripes.

I agree after reading all the posts on wet sanding I thought this was going to be a cake walk..... Wrong. Oh well just thinking of the results.