Mike:

Perhaps I missed something, but why would the 10-15 feet of water break a mast that extends 30 feet above the water's surface? I see the mast breaking when the boat is upright (See image 8). I have been in water shallower than 10-15 feet many times, and done a jibe, unfortunately, but never been concerned with my mast breaking because of the water depth. I do understand your concept once the boat rolled.