A few minutes in cold water makes it very difficult to swim, even to keep yourself afloat. Drowning can be almost instantaneous. Your body can cool down 25 times faster in cold water than in air. If you examine the chart below you will see that survival time can be as short as 15 minutes. Water temperature, body size, amount of body fat, and movement in the water all play a part in cold water survival.
Small people cool faster than large people and children cool faster than adults.
PFDs can help you stay alive longer in cold water. You can float without using energy and they cover part of your body thereby providing some protection from the cold water. They cover more of your body and provide even more protection. Hypothermia does not only occur in extremely cold water. It can, and does, occur even in the warmer waters of Florida and the Bahamas.