Re: painting the the hull of a fiberglass boat
Use marine paints, you will be happier with the result. Prep is more than just scuffing. First dewax the surface by cleaning it with a good solvent. Lacquer thinner or Acetone will work but there are solvents made for this also. Be thorough, its a real pain to get to the painting part just to have it fisheye or fail and come off altogether because of surface contaminates. Do this first before sanding. Gelcoat is porous, sanding can drive wax and contaminates into the surface causing problems.
While you are doing that you are going to find damage. (cracks, chips, dings) The paint will not cover this and cracks (surface crazing) will worsen and come through the paint. If the surface is ok, your lucky, now you can sand. (after you have removed any non-painted items first of course)
After getting the surface clean scuff sand with 220-320 grit. No need to get too ambitious here you just want to get the surface dull. After scuff sanding wipe down the surface again with solvent. I do not recommend acetone for this cleaning. It dries too quick and will leave sanding residue on the surface.
If your paint recommends primer use it. If primer is optional use it anyway. Sand the primer smooth with the recommended grit set by the primer. (400) Sand lightly just enough to get the primer smooth. Good primer will be hard to sand through.
Now you can think about painting. First go back and recheck for damage you missed before. Then paint.
I left allot out of the process here. How involved you get with the prep process will dictate how good the finish coat looks. Most folks like to spend about 10% of the time prepping. The reality is that a good paint job is about 90% prep work. It all depends how good you want it too look and how long you want it to last.
Oh, and how much $$$ you want to spend. You can paint a boat with house paint and make it look, well,..... like house paint. It is all in what you want.
