I recall a story told to me by Alan Thompson. He capsized and got snagged under the tramp as she went turtle. He recalled not being able to inhale a full breath before being dragged under. He had a knife and tried first to saw through the mainsheet his leg or arm was tangled in. He mentioned getting to the knife was tough as one arm was tied up...luckily he had put the kife where he could access with either hand. Quickly realized he could not cut enough of the rope wraps fast enough, so tore into the tramp to get his head above water.
Things he told me to remember: 1. You likely will not have the chance to take a full breath of air as you go under, so you'll have less time than you might otherwise believe. 2. Knife needs to be as long as you can easily carry...shorties make line/tramp cutting much slower. 3. Knife needs to be accessible from either hand.