About the time
you start taking water over the rail and into the cockpit, your self-preservation instinct will kick in (if it hasn't before then), and you will start taking steps to make the boat sail more upright. In other words, for most of us the boat can stand more heel than we can. The more it heels, the more wind is spilled from the sails, and the greater the leverage of its ballast, so it actually becomes more resistant to further heeling, all other factors being equal. Many boats are sailed "rail under" much of the time, and I recall seeing a photo taken early in the century of the royal yacht "Britannia"'s captain with one foot in the water rushing along the deck, holding the wheel, and steering her quite comfortably.