NAB,
That explanation helps explain the usage of the words "Cast Iron Failure" when big things break bringing things to a stop.
So with that explanation and the report the Ship's Rudder was damaged in the process....can one assume the female section of the shaft backed off the male section ahead of it and the attached Prop made contact with the Rudder damaging it?
Just yesterday I had a small demonstration of Rudder/Prop failure on my 20 foot outboard when it managed to pickup a length of Ski Tow Rope with attached handle....wrapping the rope about the prop until the handle conveniently grabbed the Skeg of the outboard motor....bringing them to an instant halt.
Thank goodness for a trolling motor that got me to the shoreline where a wet dock repair was done.