Bottom only or Topsides?
You didn't say if you were painting the bottom only or the whole vessel. This past spring , I redid my entire 1980 H-27. First, new Interprotect bottom after sand blasting, dry-out and fairing.Then, new Imron top sides (3 finish coats of dark green) spray applied, after de- waxing, ding repairs, sanding, solvent washing, more sanding and dusting, more solvent washing, tack raging and then applying 2 coats of 2-part primer (spray applied) with 600 grit sanding and tack raging before spraying the 3 finish coats. The final product is very beautiful and well worth the effort. I also hand painted the decks with interthane two- part white epoxy paint.( I had to do all of the same steps to prepare.) I also had to remove all deck and top side hardware and teak before I got started. This was a lot of work also but the finish is great. If all you want to do is paint the bottom with anti-fouling paint, I suggest you follow the steps suggerted by Interlux or whatever paint you use. Finally, Interlux has a great web site which explains all step-by-step instructions with full pictures. Let me know what your plans are. Good luck.