I guess there are two options:
1) SHe hit something and knocked it loose.
2) She had a mechanical failure.
Most boats can see their keel boats from the bilge. You would expect some VERY serious crazing around the bolts had it been a glass failure. I cannot iagine any captain that would not check his bilge before taking off. THat a bolt would just sheer or the glass just suddenly snap seems very unlikely to me. Also, if it was a bolt failure, It seems unlikely they would all sheer at the same time.
On the other side, you would REALLY have to nail something hard to knock off a keel. I have grounded my 380 REALLY hard and it had no effect other than sitting for hours waiting for the tide (should I have told you that???)
I realize that I am hypotesizing here, but the only thing that makes sense to me is that they hit something. My guess is a underwater rig. I think a container might give enough so as to not take off a keel.
Here is a look at the keel. Look how vertical she is. That does not give much room wanting to slide up a underwater object (for those who have run aground hard, you go horizontal AND vertical):
Here is a terrible pic of a Catalina 400. Look how much more swept back thge keel is (esp on the wing):
Anyone know how many keel boats she has?
What are others thoughts?
Is a swept back keel safer offshore (or inshore) than a vertical keel?
I realize this is a hypothetical - but worth discussing.