Re: Prepping for paint....
"It depends..."
Edit: Typed all this up then re-read the original post... yep, 320 grit to rough the hull. Ah, well, that's what I get for going off half cocked
Assuming a more or less standard, shiny surface is desired, then you need to take prep in a few steps:
1) Repair - fix any problems with the hull, including major dents, dings, gouges, holes, etc.
2) Fair - Use a long board or other leveling sanding system to level the surface... you're not going for shiny here, you're going for level, smooth curves, and even transitions from surface to surface. Check fair with a guide coat.
3) Finish - Prime, then check for lack of fair and missed dings... you'll find some, guaranteed. Fix 'em by fairing again, fill when necessary. Hopefully filling should only need to be done with another coat of primer.
Note that when painting with paint or primer you will have to fix any problems caused by painting before going on... sags, drips, etc.
Then prime again and check again for problems. At this point there should be very few remaining issues, and how many times you want to sand, prime, level is up to you. When you're happy with the way it looks (when the remaining dings or level problems don't bother you) then you can move on. For really accurate/picky detailing, check the hull with the lights off and a flashlight at a low angle. You'll see every detail. Keep in mind if you decide later to fix a ding you didn't think was a problem, it's hard to do so, so be sure you're ok with the look.
If you've got significant sections of glass or repairs uncoated, prime them and lightly sand with about 180 grit. Just enough to rough the primer up.
Obviously through all this make sure the surface is clean... if you get wax, grease, or dust on the hull, remove it before you do anything more, otherwise it'll be part of the coating.
Put on a light first coat of paint. Sand with 180-240 grit, then apply a second coat. Sand again and repeat until the color is as intense as you want it. Some people can get this with one coat, others take five. Once that's done you can either start finish sanding or put on a clear coat for even more shine.
If you clear coat, one or two coats ought to do it.
Finally, finish sand. Start with 200 or so grit, then when you're sure it's evenly smooth all over move to 320. Same thing, sand until the scratches from the 200 are gone. Then move to 400. At this point you'll probably have to wet sand to keep the fine paper unclogged. Finally you can go to 600 and wet sand. At this point you should have a very fine, shiny surface. Check for any final defects or problems to correct (hopefully none) and then use a polishing compound with cutting grit to finish the hull. Then wipe it down to clean the cutting grit off and wax with a good boat wax and rub until shiny.
More info than you wanted, eh?
Erik
