Osmosis in integral FG water tanks
Thanks for your detailed and thought-provoking reply.
I have owned this "classic" for 22 years, am happy with her and hope to keep her for another 10 years of sailing. Twelve years ago, it became clear that the hull was high in water-content. Small "weeps" of white would show up on the hull after haul-out. A surveyor checked the hull and advised that there were no structural blisterings or delaminations, that the thick layup of the HR would probably last as long as I wanted to keep the boat, and that I should just do minor epoxy "cosmetic" repairs of the "weep" spots each year -- keeping an eye out for bigger problems developing. That''s what I have done for the last 12 years -- with no structural problems becoming apparent. As you say, it is just a boat.
This last year, I decided to start on a semi-major refit, starting with the epoxy barrier coat. Over the years, I have done all the work on the boat myself (except for the engine overhaul done in 1993) and enjoy working on her as well as sailing her.
When I took the bottom paint completely off (changing to a different bottom paint system), it became clear the gel coat was shot and the resin in the laminate was being washed out.
Again, no major blisters or delaminations -- just resin-starved fiberglass mat. So I removed the gel coat and rebuilt the whole bottom: dremeled out the larger voids, sealed and filled them, then two coats of epoxy sealer on the entire bottom, two coats of epoxy filling/fairing on the entire bottom, six coats of epoxy barrier coat, many new thru-hulls and seacocks, three coats of bottom paint. It was only about $3000 in materials but 5 weeks of hard and satisfying work.
I had hoped someone out there might have a "magic bullet" for shutting the door on that last part of the 80/20 rule! I appreciate your thoughts, though. Maybe I''m being a bit too concerned with the ingress of water from the fresh-water tank. As you say, it is a small part of the hull surface and I probably can effectively reduce that by nearly half if I repair the starboard side of the tank as best as possible. If I cut an access hole under the settee area and build a fiberglass cover similar to the starboard ones, I could probably repair 60 to 70% of the tank surfaces.
Probably good enough for another 10 years!
Again, thanks for the sanity check!!