Championship cold-water swimmer Lynne Cox can freestyle and breaststroke for as long as two hours in the Bering Strait, where the water temperature can hover around the mid-30-degree Fahrenheit mark.

Boaters who fall overboard into 60-degree seas and drown within minutes are often said to have succumbed to hypothermia.

How can both of these statements be true?

"The reality for boaters is that you can last a lot longer than you think if you get thrown into the drink, even in cold-water cruising places like Maine and the Pacific Northwest," says Dr. Eric Johnson, a Staff Physician at Teton Valley Hospital, in Driggs, Idaho; past president of the Wilderness Medical Society; a NAUI diving instructor; and a Mount Everest base camp physician.

The more you remain calm, the better your chances for surviving an overboard situation.

A lot of deaths following sudden cold water immersion are incorrectly classified as drowning due to hypothermia, according to Johnson and other experts. Often, these victims drown because of effects of the initial Cold-shock Response.

The Cold-shock Response is initiated the minute your skin touches the water, usually in water below 60 degrees. Your Cold-shock Response kicks in faster than you can blink – causing you to gasp uncontrollably and breathe rapidly, as your body tries to acclimate itself to the water temperature around you. Though these reflexes do eventually subside, they can be extremely detrimental in an overboard situation.

"It lasts one to three minutes," says Johnson, who spoke at the week-long "Medicine for Mariners and Safety at Sea" conference at The Bitter End Yacht Club on Virgin Gorda in January. "This is actually when most people drown, not from hypothermia, but from the gasping from Cold-shock Response. They suck in water while they are hyperventilating and trying to get air."

If they're not wearing a floatation device and their head goes underwater in the first minutes, they can easily inhale seawater and drown, Johnson said. If you can get through that initial first few minutes alive, with your head above water, then you have a good chance of surviving before hypothermia actually sets in.

A MATTER OF TIME

In truly icy cold water – say, if you've fallen overboard off the coast of Juneau, Alaska – you will have five to 10 minutes of what doctors call "meaningful movement" after your breathing settles down from the initial Cold-shock Response. This is certainly enough time to grab a life ring that has been tossed to you, call for help on a handheld VHF, reboard a capsized craft, or consider swimming to a nearby shore. After that 10 minutes has passed, your muscles, joints, and nerves will become so cold that movement is very limited – but even at this point, you will not be hypothermic.

"As long as you are wearing a PFD that keeps your head above water, you can still widen your window of opportunity for rescue," Johnson says. "Conserve the heat you have. Don't thrash around. If you're near floating ice, put your arms on top of it so that if you go unconscious, your head will stay above water until rescuers can arrive. People have been saved because they literally froze their arms to the ice and kept their head above water while they were unconscious, so they didn't drown."

True hypothermia doesn't occur until your body's core temperature drops below 95 degrees Fahrenheit – which, by the way, can happen even in 80-degree Bahamian or Caribbean waters given enough time, be it hours or days of immersion. A core body temperature below 95 degrees Fahrenheit is mild hypothermia, and the definition doesn't change to moderate hypothermia until your core temperature drops to 90 degrees.

Just as rescue crews regularly train to aid drowning victims, you should educate yourself on how to prevent it from happening.

Now, you can't determine a person's core temperature with an oral thermometer. Unless you carry a rectal probe on your boat to measure people's core temperatures (and who would go boating with you if you did that?), the best way to tell whether someone is still in the mild to moderate stages of hypothermia is to ask them questions and see whether they are shivering. Anyone who can answer questions has probably not begun to enter the later stages of hypothermia that are characterized by neurological changes and unconsciousness, and anyone who is shivering still has a body working to re-warm itself by generating metabolic heat (just as we generate heat through voluntary exercise).

"If you have stopped shivering and need to have heat applied, you're in trouble. You can't warm yourself," Johnson says. "But if you're still shivering, usually all you need are calories and time."

TREATING IMMERSION

A lot of boaters who rescue a person and see him shivering uncontrollably try to re-warm him as quickly as possible, perhaps by placing him into a hot shower. This is actually the opposite of what you want to do, because hot water hitting the skin can dilate the person's blood vessels and cause a drastic drop in blood pressure.

Instead, get the person out of his wet clothes, wrap him in a blanket near a heater and out of the wind, and let him shiver until his body corrects its own temperature. Study after study shows that the speed with which a person is re-warmed has little to no effect on survival rates, Johnson says. Shivering in this case is good, even if it goes on for an hour or two. It means the body is still working properly and just needs more time.

You can give the person a mug of tea or coffee to ease his mind, but the fact that a liquid is hot has little effect on core body temperature. Liquids high in calories are a better choice, since they give the body the fuel it needs to continue the re-warming process. Hot chocolate is an excellent option, since it is both high in calories and psychologically reassuring.

"All of these things are passive re-warming," Johnson says. "The body is doing all the work itself. If the person has stopped shivering, you need active re-warming, which means applying heat bottles, warm IV fluids and things that are likely to require a medical evacuation. Just remember that for longer than most people think, you have time to correct the problem. Panic is the enemy with Cold-shock Response and hypothermia."