So watching this thread makes me have a question. What's the difference between a gel coat and an epoxy barrier coat, functionally speaking for an underwater application?
Epoxy barrier coats have lower permeabity than polyester. The OP asked about doing this on a center board. What's the concern about UV resistance? The center board is going to be in the water, not in the sun. Just a question?
dj
All resins are porous to a greater or less degree. Plain old epoxy is less porous than polyester resin which is more porous than vinyl ester resins. Gelcoat is basically a polyester resin.
Barrier coats are typically epoxy and have added fillers to make it less porous and harder than standard epoxy. Take a look at Interlux Interprotect 2000. West System has their own method as do the other major paint manufacturers.
In what is becoming ancient history in the world of fiberglass boats is underwater blistering. The early gelcoats and polyester resins were susceptible to water infiltration which caused blisters to form on hull under the waterline. Barrier coats and vinyl ester resins were the solution.
In this particular application, UV resistance is perhaps not as important as it is in some other applications. Some epoxies are more tolerant of UV resistance than others. The issue with a centerboard is getting a very smooth surface so the board is more efficient and has less drag. Gelcoat can be polished out to a very smooth finish and is a good choice. Interlux VC Performance is an epoxy that has some UV resistance and can be polished out to an exceptionally hard and smooth surface. Smother surface, less friction, better laminar flow, faster boat.
