Evidently, hard pounding --whether from a whale or a grounding, etc.-- would rupture such a tube at the hull. Not surprising.

I guess belt and suspenders (tube and watertight bulkhead) would be ideal, but not possible on all boats. Me, I have rudder tube that goes well above the waterline, and the rudder is protected by a skeg --but I don't have a watertight bulkhead. However, reading about the sinking has made me realize just how easy it would be (and it wouldn't detract from/inconvenience any interior fittings/furnishings) for me to build in a watertight bulkhead in my lazarette to seal the rest of the boat off from water ingress should I somehow lose the rudder.

The story has definitely made me think a bit more closely about holes in my boat --belt and suspenders for something like the rudder post probably is a good idea, even though my rudder is protected by a skeg.