The Beaufort Scale

This scale for describing the wind speed was developed by Sir Francis Beaufort in 1806. While commanding the H.M.S. Woolwich, he observed the effect on the sails and ship. He defined twelve different classes for the power of the wind. Since this time the unit for the wind strength is called "Beaufort" [Bft]. In 1835, at the First International Meteorological Conference in Brussels, the Beaufort scale was established as international standard.

In 1949 the scale was extended by the International Meteorological Organization up to 17 classes. However, since 1970 the old 12-part scale is applied again.

Every water sports knows how to use tables for converting a value of the Beaufort scala. However, clever mathematicians have determined a regression curve (nonlinear) through these scale values. By the aid of the regressions curve the wind strength can be converted merely by means of the following formulae:

equation one

The following form is applied for converting the wind speed. Bft stands for the wind force in Beaufort; v [m/s] is the wind speed in meters per second; v [km/h] the wind speed in kilometers per hour and v [kt] is the wind speed in knots, i.e. nautical miles per hour.

Bft Bft v [m/s] v [km/h] v [kt]

You can make entries in all fields. The other fields are calculated accordingly. In fact, there are no values with decimals defined in Beaufort. The entire Beaufort-values are formed by rounding. The Bft value from 0.5 to 1.4 is rounded to 1 Bft. A Bft a value between 1.5 and 2.4 is rounded to 2 Bft and so on. Besides, as mentioned above, since 1970, the Beaufort scale is defined only up to 12 Bft, wind speeds with more than 36.5 meters per second are defined as 12 Bft.

The 12-level scale has also further deficiencies. The dynamic effect of wind does not only depend on the wind speed, but also on the air pressure. Thus, a storm of 11 Beaufort on a 6000 meter high mountain has only half of the power compared to sea level. Fortunately, at these heights water activities are rather seldom ...