Being pretty new to maintaining my own boat and in the interest of keeping it safe, I'm kind of wondering about the different failure modes of a through hull valve. If the hose connected to it broke or popped off (maybe the host clamp failed), I could see how you would get a lot of water coming in. So, checking hoses is a good thing. How does the valve itself fail and let that much let water in ? If the fitting to the hull is tight, you could get a trickle but it's not going to be a gusher of water if there is a leak. Maybe around the handle ? I guess we will never know in this particular case, but something to think about in terms of our own boats.