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Brighton Swimming Team
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pool t-shirt freezing cold
"It's freeeeezing cold!"

Strategies for Preserving Body Heat
    Above the water our body does not use much energy to regulate its temperature. In the water we spend a considerable amount of energy to keep warm which leads to tiredness and dehydration. Add windchill and you'll see the challenge.

    Your body loses body heat in water at a rate that is 25 times the rate of body heat loss in air. If the water is moving around the body the heat loss is much higher. In other words, if the water is not perfectly calm but is moving by even small amounts of current or small waves you'll chill out faster. Also, the top thermal layer of "warm" water, even in the hottest days of Summer, does not extend far into waters that are deeper than one's own height.

 Law of Heat Conduction 

Dressing to stay warm is all about slowing the transfer of heat from your body to the outside. This can be described quantitatively using the physical Law of Heat Conduction:

 H = A k dT / dx 

H is the amount of heat energy per time unit that moves from your body to the outside.

A is the surface area of your body.

dT is the difference in temperature between your body and the outside.

dx is the distance from your skin to the outside.

k is a constant determined by the insulating material.

The k, or thermal conductivity, of water is 0.6 and the thermal conductivity of air is 0.023. From this (0.6/0.023) you can see that the conductivity of heat through water is about 26 times greater than through air.

Dry fleece is mostly trapped air and has a thermal conductivity of about 0.08 whilst cotton saturated in water is mostly water and will have a thermal conductivity close to that of water.

Warm Swimwear
Windproof waterwear
keeps you warmer even when wet.

Keep Warm
    For a more comfortable and ultimately safer swim follow these tips for conserving body heat:

  1. Stay warm before the swim. Heat loss is gradual and can start long before you get to the swim site.

  2. Reduce windchill. Wear windproof outer layers to keep you warm. Use unlined clothes as they won't get waterlogged if you enter the water.

  3. Stay warm between repetitive swims. Standing around in wet gear between swims can add to your body's deprivation of warmth through evaporative heat loss. Windproof outer layers reduce this heat loss.

  4. You can develop hypothermia without immediately recognising it. When choosing your swimming clothes, err on the side of thermal protection.

  5. Get warmed up as soon as possible after a swim. You can start on the beach by toweling off and getting into dry clothes. If you want to jump in again later have extra sets of dry clothes handy as it is uncomfortable to put the wet and cold clothes back on.

  6. Become an educated consumer. Visit your local sports shop and have them show you the different styles of protective garments and accessories. Don't be afraid to ask questions.

Cold Water
    Water doesn't have to be extremely cold to cause hypothermia. Any water that is colder than body temperature causes heat loss. Water that is colder than 20°C can quickly begin to cause hypothermia. The following tips may increase your survival time in cold water, if you accidentally fall in:

  • Wear a life jacket. If you plan to ride in a watercraft, wear a life jacket. A life jacket can help you stay alive longer in cold water by allowing you to float without using energy and providing some insulation.

  • Don't panic. If you're unable to swim to safety, stay calm. Unnecessary movements require you to exert extra energy and lose body heat.

  • Don't remove your clothing. Buckle, button and zip up your clothes. Cover your head if you have a hood. The layer of water between your clothing and your body will be warmed and helps insulate you.

  • Position your body to minimize heat loss. Use a body position known as the heat escape lessening position (HELP) to reduce heat loss while you wait for assistance. Hold your knees to your chest to protect the trunk of your body. If you're wearing a life jacket that turns your face down in this position, bring your legs tightly together, your arms to your sides and your head back.

  • Huddle with others. If you've fallen into cold water with other people, keep warm by facing each other in a tight circle.

  • Don't attempt to swim unless you're close to safety. Unless a boat, another person or a life jacket is close by, stay put. Swimming expends extra energy, lowers body temperature and can shorten survival time.

  • Avoid excessive alcohol consumption and the use of illegal substances, because these may increase your risk of hypothermia. Also, don't drink alcohol and operate a boat or other watercraft. Alcohol can impair your ability to navigate the waters, increasing your risk of an accident and of falling into cold water.