Hypothermia is subnormal temperature within the central core of your body. When a person is immersed in cold water, the skin and nearby tissues cool very fast. However, it may take 10 to 15 minutes before the temperature of the heart and brain begin to drop.
When the core temperature drops below 90 degrees Farenheit, serious complications begin to develop. Death may occur at about 80 degrees, however a person may not last that long. You can drown at a higher temperature due to loss of conciousness or the inability to use your arms and/or legs.
The water doesn't have to be very cold for you to get hypothermia. You can get hypothermia even in the middle of summer in fairly warm water and outside temperatures.
Survival in cold water depends on many factors. The temperature of the water or air is only one. Others include your body size, percentage of body fat, and type of activity on the water. Small people cool faster than larger people.
Swimming, or treading water, will cool your body about 35 percent faster than remaining still. Water conducts heat much faster than air, so the more of your body you can get above water (especially the head and neck, which contribute to over 50 percent of body heat loss), the slower you will lose heat. Getting into or onto anything that floats may save your life.
The following table describes a couple different scenarios and the predicted survival time (in hours) for the average person.
|Situation||Predicted Surival Time|
|Treading water||2.0 hours|
|Holding still||2.7 hours|
* Drown-proofing is a energy-saving technique where you float on your
stomach face down, lifting your head for breaths every 10-15 secons. It
causes heat loss to accelerate due to the head and neck being underwater.
** HELP stands for Heat Escape Lessening Posture (basically sitting in the fetal position to conserve heat)
*** Huddle is where several people huddle close together to conserve heat. Children can be placed in the middle so they can benefit from heat generated by the adults.
This depends on many things. An experienced swimmer may be able to swim .8 miles in 50 degree water before hypothermia overcomes them. Others may be able to swim only 100 yards. Plus, distances on the water can be very deceptive. What may look like a short swim can be out of reach and attempting to swim to it can mean the difference between rescue and death.
Generally, it's best to stay with your boat if it capsizes. You'll be spotted more easily by rescuers. Do not swim unless there is aboslutely no chance of rescue and you are certain you can make it. If you do swim make sure you're wearing a PFD or other flotation aid.
Because most boaters who die in water-related accidents had no intention of going in the water, the obvious answer is to avoid those things that cause you to go overboard.