Chris,
1) This heat and vacuum drying process is taking time, but it really isn't that much effort. I do think you could make a good case that just wasting the skin and replacing the core would be faster and possibly end up with a stronger end result, particularly if the core is well on its way to mush. But the fairing process would be exponentially more difficult, unless a fair hull is not your requirement.
2) As to scarfing and repairs of the saw kerfs that is minor compared to maintaining the 95+% of the exterior hull shape to start the fairing process with. Removing the exterior skin, replacing the core and then replacing the exterior skin followed by some serious fairing does not even come close to the amount of work that I am now seeing as required with this process. Keep in mind that the problem with my boat is not delamination, it is wet core. The "nailing" technique might make sense for a local repair of delamination when the core itself is sound. But if the core is essentially sound, only wet, I do not see how nailing it adds anything to strength, particularly in shear. What makes balsa core such a good core material from an engineering point of view is its compressive and shear strength. When it is wet and the fibers are pliable it has lost some of both of these qualities, but not all strength is lost as evidenced by the many J30's still sailing around with saturated hulls. The nailing process does little to repair the shear strength of this matrix. To regain that shear strength somehow you would need to reestablish the bond across the surfaces of the core and the skins. Replacing the core and reskinning would accomplish that.
I have already demonstrated to myself how to remove the outer skin without too much effort simply by prying it off after cutting 4" wide strips and then using some sharpened pry bars. The bond between the skin and the balsa is not all that substantial as to require any extraordinary techniques. I am also quite certain that the process I am using isn't doing anything that would damage the existing lamination because that would require the moisture to expand in a confined space. That expansion can not happen in a reduced atmosphere environment, nor can it happen if that space isn't 'confined' (so far this hull leaks like a sieve). If there were no vacuum then the expansion would be a problem and may cause delamination. I am in no position to test what the thresholds for minimum vacuum are to prevent steam expansion, but my empirical impression is that even when the vacuum level was in the 7" of Hg. the moisture wants to move to the lowest pressure, which is the pump. The plan is to
add heavy biaxial cloth laminate using epoxy resin once this drying adventure is completed. There will be no means for water to intrude through this very heavy epoxy laminate skin, this is not a thin barrier coat it will be much thicker coating than that, but it will also ultimately get epoxy barrier coating applied to it. If I were using a polyester resin for the lamination then maybe there could be moisture move back into the core, but epoxy is impervious unless there were an imperfection in the laminate and I don't plan on leaving too many of those.
The overall heat levels I am applying to the skin also do not concern me for delamination. So far the skin is getting into the 200° range, which is not much higher than the deck temperatures can achieve on a hot sunny day in a southern lattitude.
So to sum up, I am very satisfied with how this is working overall and with what I perceive the entire repair process is going to be using heat and vacuum. The area I am working right now does concern me that it is possible that the balsa has deteriorated too far, so I will remove a small patch to inspect it. If that little inspection patch is not black mush I will rebond the skin and move on. I am not opposed to removing balsa where it is necessary, but I am really sure that getting an area that the skin has been removed, the balsa replaced, back into to a fair condition is a lot of overhead work.
So I appreciate your paying attention to this project and commenting. I also understand that I am using a somewhat unconventional process, but so far I think this is better than any of the many alternatives I've studied so far. If at some point I think this process sucks and is not going to get me a a sound and fair hull I will be the first to say so.
