The keel boats didn't fail -- it was the embedment to the "top" (Inside) of the grid. What was left was the lower side of the skin which was attached to the grid.

I think what happened was that the keel came loose from the inside "top" of the grid) and pulled-out -- not the normal shearing of the bolts or failure of the rods.

Then they "peeled" the bottom of the grid and the skin of the hull with it as it "withdrew".

What ever happened to "blocking" the top of the keel with a backing plate that makes sure it won't get pulled-out?