I redid the bottom of my Shark last spring too! I took of the old soft antifouling paint (not sure what it was but it was reddish). I used a scraper and the palm sander with 80 moving to 180 grit (no other sanders needed - definitely keep the belt sander away!)
I used a layer interlux interprotect before adding the vc17 (mostly because I went through the gel coat in a couple of places), it might have been over kill but after a year in fresh water, the vc17 still looked great!
Maybe you could the Interprotect as a primer over the hard paint on your hull. I also used the Interlux 202 thinner to clean after sanding.
I bough four cans of vc17 put 3 on for the fist 2 coats, and saved the 4th for the haulout this year and it seemed unneccessary.
Good luck to you.
Last edited by GreatWhite; 11-02-2008 at 10:48 PM.