Marine Glossary

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wind chill factor

A factor which describes a human being's response to temperature in the presence of wind. Wind increases evaporation by removing the insulating surface layer of air, which in turn cools the body. Hence in wind, the body cools faster in response to a particular ambient temperature than it would otherwise.

The factor is expressed several ways, but is based on heat loss per hour per square foot of skin surface for a nude human body in the shade. The values are approximate in any case due to variations in human shape, size, and metabolic rate.

One way they are expressed is as the equivalent ambient temperature that might lead to the same degree of cooling. For a given body in calm air, cooling should be just proportional to the air temperature. G200 lists these temperatures. In 50° F air with a wind of 20 miles per hour, a nude human would cool at the same rate as they would in calm air at 32° F. Clearly, 50° F is too cool to be nude in a breeze.

These wind chill temperatures have limited application as they are affected by clothing. Another approach is to categorize the regions where the cooling affects work at sea when properly dressed. These are presented in G199. The data are adapted from the Mariner's Handbook (see Source Book).

Note that wind chill factors do not apply to inanimate objects. A pan of water will not freeze in 40° F, even if the wind blows 40 knots and the "wind chill temperature" is some 20° below freezing. Likewise metal objects to not get cooler in a dry breeze.