I'm correcting my not-too-skillful fiberglass job on the bottom with sanding, lots of sanding. Its like I didn't know how much I would have to do until I started. I made a padded sanding block big enough for a full sheet of paper for the flat areas, and one half the size for the curved areas. Here you can see how the ripples sand out (with difficulty). I always use Norton 3X paper. The dust falls off, rather than packing into the paper, and it really does cut faster & last longer.
This is how a wrinkle looks after sanding flat. I have clearly cut into the fiberglass, and will have to recoat, this time with as many thin coats as necessary. I am determined on a "fair" hull.