The layers are visible where a thru-hull has been removed. The layer between the two fiberglass skins is some type of rigid closed cell foam. The blueprints for the boat specify an Airex core for the hull below the waterline, which is why I assume that is what the foam is.
I'll try to take some pictures of the cross-section of the coring when I am down at the boat this weekend. More than half of the thickness is the external skin, which is thicker than the entire hull on many similarly sized boats. Having read a bit more on the design of this particular boat, it seems the foam layer may have been added by the designer (Stan Huntingford) not for structural purposes but to provide an insulating layer that would prevent condensation from forming inside the hull.
I was able to use a shop-vac to get some water out of an access hole cut through the internal skin and foam from inside the boat. Given that it should not be possible to suck water through closed cell foam, I realize this means there is water between the layers (i.e., delamination). I am thinking no delamination showed up on the survey because the external layer is so thick and rigid that the surveyor was unable to detect anything on the other side of it.
In theory, the best repair would be to replace this foam layer altogether, by cutting out the interior skin, removing the foam, and then laminating in a new foam layer and skin. In reality, significant portions of the interior of the hull are inaccessible (under the fuel or water tanks, under the sole in the galley or nav station, under the built-in cooler, etc.) and removing the foam layer from those areas would require gutting the boat, including removal of a great deal of hand-crafted teak joinery. The cost of such a project (in dollars, labor hours, and damage to the rest of the boat) makes proceeding with it prohibitive.
I have no reason to think that the moisture in between the layers is a new development. I suspect we just saw no signs of it before because the prior barrier coat was somewhat permeable. While having water in the foam layer is bad, the hull is otherwise in excellent shape and does not seem to have been adversely affected by this issue, aside from the surface blistering between the old permeable barrier coat and the new non-permeable barrier coat. Given that and the cost of removing the foam layer, I am leaning toward removing as much of the water as possible, preventing new water from getting in (around thru-hulls, e.g.), and then using access plates to periodically vent any moisture that does get in there.
