Have seen that. The bad news is that it's not a defect in the paint or application. It's in the layup
and the boat builder's fault, and your boat is probably long out of warranty. I spoke with 2 pros who paint boats all the time and they both said it's rare but it happens and they don't know how to detect it in advance.
The problem is small air bubbles or voids beneath the underlying gelcoat
, at the gelcoat/layup interface. If you were to sand the gelcoat
nearly all the way through the gelcoat to the fiberglass layup
you'd see small voids or pinhole gaps. The cracks are there from soon after the time the boat was built -- but they were very fine and not detected (and they were probably filled with compound/wax residue and any other coatings applied to the gelcoat).
The paint is a much smoother non-porous surface and is more flexible than gelcoat, and as it cures it shrinks to a high surface tension. The cracks in paint form when small defects of the underlying substrate expand/contract out of proportion to the rest of the surface.
If you went back to the boat builder
with photos of the defect they'd likely take a position something like: "It's long out of warranty and the finish wore out, and it was fine for X years longer than our warranty."
The gelcoat must be removed (about 99%) until the voids are exposed, then if you follow the Awlgrip "textbook" -- use Hullguard Extra epoxy
filler, then High Build Primer, then 545 Epoxy
Primer, then color coat(s). Unfortunately that's more work than your original paint job.
You can live with it, or talk with your paint contractor and get Awlgrip involved. Awlgrip has seen this before, although they might pretend they haven't and tell you they need to investigate by "destructive tests" (sanding through to the bottom of the gelcoat). Chances are your painting contractor can get Awlgrip to supply free replacement materials and the painting contractor might cut you a break on the labor.
The deal you want to cut before any destructive testing is:
1) If it's a defect in the underlying gelcoat, prove it and give me your best reduced rate fixed-price to fix it forever, with a 3 year 100% warranty against cracking (other than wear/collision and abuse).
2) If the tests show it's in the paint or prep then you fix it for free.
If you don't cut one of the deals above you might just want to live with it, or get competitive bids, or consult an attorney. Unfortunately an attorney gets paid in most situations no matter what the outcome.