Our original plan was to re-caulk the leaking keel joint, get the engine running, and go sailing. On closer inspection, it was clear that a good bit more work was going to be needed. As we removed the various layers of fiberglass "bandages" that had been applied to the keel, we found that the keel had never been fitted properly and that the compound used to "bed" it was so soft as to be useless in supporting it. No wonder it leaked. It could be moved side to side and was hanging a few degrees out of plumb. We would have to drop the keel, clean out the old compound, and re-bed it with something a lot stronger.
To complicate matters a bit more, the bilge was filled to the top of the keel bolts with some sort of hard (but brittle) resin. The resin was riddled with cracks and stank of the residue of accumulated bilge spills. All of it would have to be chipped out before we could even begin to loosen the keel bolts. Also, the plywood floor supports (embedded in the resin) had completely de-laminated. They would come out as the bilge was opened up. All it needed was time, patience, eye goggles, a couple of cold chisels and a 4 pound sledge hammer.
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We then glassed over the joint and re-faired the whole keel. Unfortunately, I did not discover the NACA formula until after we were done, so our shape is not quite correct. We'll leave that for another day. As part of this project, we also built a new glass aft section for the keel. The original (?) was fat and strangely shaped (see picture). When we removed it, we also found it was full of voids and, consequently, full of water. The new one is solid glass and epoxy, looks a lot better, and almost matches the published factory drawings.
We started with West Systems products for the fairing job, but found that we had so much to do that it would quickly become prohibitively expensive. Since the 'marine' Bondo at our local ship chandler looked identical to the fiber-filled Bondo we could get at NAPA for half the cost, we did most of the fairing with the NAPA product - almost 10 gallons of it. (A good bit of that was sanded off - we used a 4" belt sander for most of the rough shaping and a 7" disk sander for most of the rest.) Since we later coated the finished bottom with several coats of epoxy, I don't expect any blistering or adhesion problem. (I had used the same Bondo on our Tartan after repairing its centerboard with no problem.) It has now survived several seasons in good shape.
UPDATE: There have been no problems with the NAPA Bondo after over 20 years.