I really appreciate the fact that you have bought this wherry and you want to fix it up and make it your own. I worry, however, that if you try to sand all the bottom paint off, it will be very hard not to sand right through the resin and into the fiberglass. Then you've got a whole new set of issues.

I would lightly sand your current paint and repaint. I'm not sure you need Pre-Kote over the existing paint, but it will probably help achieving a smooth finish and it probably won't hurt anything.

Interlux has an "Ask The Expert" section on their web site and it might be worth your time to send them this question. I asked them a question a few months ago and they got right back to me.

Thanks careybob.  I'll try contacting Interlux.  So far my sanding has been pretty light pressure and I've only broken through the paint to the resin in a few place, primary along the keel line at the bow behind the brass keel strip that the prior owner installed. I'm trying the give the hull that dull wax paper look everywhere before painting. There are some imperfections in the hull that I was hoping to fill in with a couple coats of Pre-Kote, then sand again prior to two coats of Brightsides. I probably should switch to 320 grit for sanding the Pre-Kote.  Would 400 grit on the first coat of Brightsides provide a deep enough profile for paint adherence?

I don't know about the 400 grit, as I usually get tired of sanding by the time I get to 320 and quit. Perhaps someone else know...

I have been using Brightside for over 40 years with great success.

As paint ages (cures) it get brittle.  Sand the old paint with no more than 320 for the first coat.  I personally would sand with 220 for your first reapplication.

Tooth is important especially when coating old paints.

If you have low spots I would use a 2 part  filler. Prekote will not adhere to previously painted surfaces. The 2 part surface prep. will cure hard and will sand well. Prekote is only designed to fill small imperfections and small scratches. It is basicly talcum powder and has no strength.

After our first coat of Brightside you can move up to 320 then 400 between coats.

This works becuase the paint is still very soft and the solvents will allow bonding of the additional coats.

barkkeydave

Here is the Interlux data sheet for Pre-Kote:

http://www.yachtpaint.com/MPYACMDatasheets/Pre-Kote__+eng-usa+A4+Y+20110217.pdf

Here are the sections on preparing previously painted surfaces and fiberglass:

PREVIOUSLY PAINTED SURFACES Sand old surfaces with 120 grade (grit) paper. Remove sanding residue. Wipe with Brushing Liquid 333. Repair surface defects with Surfacing Putty 257. Sand surface, wipe clean.

BARE FIBERGLASS Wipe a small area with a clean rag that has been wetted with Fiberglass Solvent Wash 202. While the surface is still wet, wipe with a clean, dry rag. Continue this process until the entire surface has been cleaned. Sand with 80 grade (grit) paper. Wipe with Fiberglass Solvent Wash 202. Repair surface defects with Watertite Filler. Sand surface, wipe clean.

Thanks everyone.  After reading all the suggestions and Pre-Kote data sheet, I think I am going to skip the Pre-Kote and just keeping adding thin layers of Brightsides. I really don't want to sand the existing Brightsides with 120 grit for fear of getting into the resin and opening up a new can of worms.  I have it all sanded now with 220 grit, so my plan will be to apply 1 coat of Brightsides, sand it with 220 grit, apply a 2nd coat, sand it with 320 grit, apply a 3rd coat and wet sand it with 400 or 600 grit.  I'll use 333 brushing liquid as cleaner between coats instead of the 216 solvent that I mentioned in my initial email.  My arms and shoulders feel sore already!  Thanks again everyone.  I really appreciate the dialogue and advice.