It's like Jetset lady mentioned, it's to do with the length of the tapes.
It's easier to tie a bow than a knot, given of the length of the tapes you have to feed through tying the knot. Also bear in mind it will probably be dark with panic setting in so you don't want to be struggling with 6 feet of tapes, a double bow is unlikely to slip therefore allowing your life jacket to ride up when floating in the water or worst still come off over your head.
Last edited by Above The Clouds; 9th November 2012 at 16:47.