A personal flotation device ( P.F.D ) gives you more buoyancy to help you stay afloat in water. The most important thing is to remember to wear one when boating as unexpected immersion can lead to a serious accident that can even be life threatening. Even experienced swimmers have succumbed to the shock of immersion at times. A P.F.D, as the name suggests, is a floating device that is designed to keep a person’s head above water in the case of a mishap