If your hulls are not bad enough to need repainting, give a go at the 3M gelcoat restoration products. I've restored a badly oxidized Nacra 5.2 and a slightly oxidized Nacra 6.0 using this stuff in combination with a power buffer (strong grinder style). They both came out excellent! You will definitely need the buffer to do an effective job - do not confuse the buffer with a 'random orbit polisher'. The polisher doesn't have near enough ooomf. There are two or three different strengths of the 3m compound based on degree of oxidation.

Catsailor 3m stuff