Dan has some good suggestions. But one thing you should know - Hobies are not like most other fiberglass boats. It is not standard for one to be painted at all, because they are not meant to be left in the water. So if you are right and it was in water for 10 years, you probably have other issues besides staining to deal with. You need to be concerned about hull delamination. Where on this board we talk about hulls blistering, a Hobie will likely delaminate. A Hobie hull is a sandwich of two thin layers of fiberglass separated by a foam core. This sandwich gives the hull its rigidity and strength - kind of like plywood. Osmosis will delaminate the layers and cause 'soft' hulls. You should test your hulls for this (all over - but especially the stained areas) by manually pushing firmly all over the hulls. Any springiness indicates delam. A little bit isn't a death sentence and can be repaired. A lot over a large area isn't worth fixing. There is a lot more info on the Hobie company forum. Good luck!Any suggestions? Short of repainting?