Buy one of these from Harbor Freight.
Wash your boat with TSP(TriSodiumPhosphate, get it at Lowe's and mix according to directions).
After it dries to a wipe down with acetone keeping a clean rag.
Then get some of this...
and Use the polisher to apply but don't stay in one spot too long and don't press down too hard. You'll get the hand of it after a while. This will take the oxidation off and get you down to good gelcoat. Change your wool buffing pad often.
Give her another bath with TSP and Acetone.
Then get some of this...
Use a Clean Wool buffing pad, apply liberally and buff to shine.
She'll look like new but...It will take time, and a lot of "Elbow Grease" to bring her back to her Bee - U - Tee- Ful self. Seasonal maintenance will ensure you won't have to go thru all this work again.