The Beaufort wind scale is a measure of the speed or force of a wind and is widely used on land and at sea. Knowing the strength of approaching winds is obviously important for many reasons. Advance warning of oncoming storms allows for preparation, but some standardization is necessary so people know what they are preparing for.
Measures of wind scale have probably existed long before the formal system that is used today, the strength of the wind having long been important for sailors. It is very likely that the Arabs had a scale in the Middle Ages as by 1500 they had classifications for most other meteorological effects. Earlier civilizations on the Mediterranean and in China probably had their own scales as well, but no written records exist.
Early in the sixteenth century in the United Kingdom a twelve-point scale was in use, varying from stark clam to a tempest, Daniel Defoe refers this to in 1703. The problem with this was that the measure was subjective and one man’s tempest could be another man’s storm or gale.
From this time onwards different people tried various quantitative scales. In the 1780’s one of the first meteorological societies, the Palantine society of Mannheim, published a four-point scale based on the appearance of trees and likely damage. In 1801 Colonel Capper of the east India Company used wind speed observations to devise a nine-point scale along with a Mr Rous.
Francis Beaufort was one of many people that devised a private wind speed recording system around this time. Beaufort went to sea at the age of 13 in 1787, and gained command of the Woolwich in 1805. He devised and began using his private system in his personal logs on board the Woolwich in 1806.
Initially this was a scale from zero to thirteen with no wind speeds associated with it. He modified this in 1807 by combining categories one and two leaving a system of measurement from zero (dead calm) to twelve (storm). The system was based on the ability of a ship to make headway under certain conditions, and the amount of sail that could be shown to the wind.
In 1812 his sea going career was ended by injury until in 1829 he was appointed as hydrographer to the Royal Navy. It was Beaufort that commissioned Darwin’s celebrated voyage of the Beagle in 1831. Robert Fitzroy, the captain of the voyage used Beaufort’s scale to record the weather. Fitzroy was a close friend of Beaufort, and became the chief of the meteorological office in 1854.
The first public mention of Beaufort’s scale was in a letter in 1832. The Royal Navy used the scale that was published in this letter in a memo to all ships on 28th December 1838, which required all ships to keep a note of wind speed every hour in their logs.
The scale was continuously modified over time to reflect the changes in the rigging of warships; until in 1903 a mathematical formula was introduced that required the measurement of wind speed across the water.
V=1.87 x the square root of B cubed, V being the speed of the wind thirty feet above the sea and B is the Beaufort number.
This scale was impractical for many vessels, especially with the dawn of the steam era. In 1906 George Simpson modified the Beaufort scale using the appearance of the sea as an additional reference. He included in this scale references suitable for land-based observers.
In 1955 the Beaufort scale was extended by forces thirteen to seventeen, these speeds cannot be judges from the appearance of the sea alone but are intended for hurricanes and cyclones. Forces zero to twelve are adequate for most measurements.
Force Zero: Dead calm,(0-1 mph or 0-1 knots), smoke rises vertically and wind cannot be felt.
Force1: Light Air, (1-3 mph or 1-3 knots), smoke drift shows wind direction but wind vanes do not move.
Force 2: Light breeze, (4-7 mph, 4-6 knots), wind can be felt on the face, leaves rustle and wind vanes move to sow direction.
Force 3: Gentle Breeze, (8-12 mph, 7-10 knots), leaves and twigs move, a light flag is extended.
Force 4: Moderate breeze, (13-18 mph, 11-16 knots), raises dust and paper, moves small branches.
Force 5: Fresh Breeze, (19-24 mph, 17-21 knots), small trees sway, inland waterways show crests.
Force 6: Strong breeze, (25-31 mph, 22-27 knots), whistling is heard in telegraph wires, difficulty with umbrellas, large branches move.
Force 7: Near gale, (32-38 mph, 28-33 knots), difficulty walking against wind, whole trees sway.
Force 8: Gale, (39-46 mph, 34-40 knots), small twigs broken from trees.
Force 9: Severe gale, (47-54 mph, 41-47 knots), slight structural damage such as slates and roof tiles moved.
Force 10: Storm, (55-63 mph, 48-55 knots), trees are uprooted, extensive structural damage. (Seldom occur inland)
Force 11: Violent storm, (64-72 mph, 56-63), widespread damage to trees and property.
Force 12: Hurricane, (73-83mph, 64-71 knots), devastating damage to property and trees.
Today the Beaufort scale is less commonly used by meteorologists; exact wind speed measurements are more commonly used except when issuing warnings to the public.
