hey tom,
trust me on this one ;D if the gelcoat is not too far gone or even if it is this will make it shine. after you used the 600 you have to wet sand with 1200 then 1500 it will shine........try just a 2by 2ft section. if you want, also after the wet sanding buff it out with rubbing compond then wax............no one said it would be easy.......but it will shine. ken