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The Beaufort Scale
Links to Meteorological sites Rear-Admiral, Sir Francis Beaufort, Knight Commander of the Bath, was born in
Ireland in 1774. He entered the Royal Navy at the age of 13 and was a midshipman
aboard the Aquilon. Beaufort is said to have had an illustrious career on the
seas and by 1800 had risen to the rank of Commander. In the summer of 1805
Commander Beaufort was appointed to the command of the Woolwich, a 44 gun
man-of-war. It was at this time that he devised his wind force scale. By 1838
the Beaufort wind force scale was made mandatory for log entries in all ships of
the Royal Navy. Beaufort last served as Hydrographer to the Admiralty. He died
in 1857 two years after his retirement.
 Beaufort's
specification is essentially an association of a set of integers (0 to 12) with
a description of the state and behaviour of a "well-conditioned man-of-war."
While the choice of numbers is quite arbitrary, as a sailor Beaufort apparently
felt there were 13 levels of behaviour that he could recognize in a man-of-war.
Although he describes them in terms that may be vague to a modern sailor, his
descriptions would certainly convey the full meaning of the force of the wind to
men who shared years of sailing in ships with characteristics similar to the
Woolwich. The effect of the wind on an 18th-century fighting ship is at the
heart of Beaufort's scale. Note that Beaufort intends that you look at the ship
not at the wind! The scale was devised for a group of men who shared the same
experience - years of unremitting blockade of Europe in sailing ships which were
all quite similar in characteristics. His descriptions are couched in terms of
the ship's characteristics under sail. The descriptions for Beaufort numbers 0
through 4 described the wind in terms of the speed that it may propel the ship;
those for 5 through 9 in terms of her mission and her sail carrying ability; and
those for 10 through 12 in terms of her survival. So how then did Beaufort's
wind force scale ever make the jump to a wind speed scale? Special wind scales
had been routinely suggested through the years but their lives were usually as
short as mayflies'. What happened after 1838, when the Royal Navy made
Beaufort's scale mandatory, helps to explain its incredible longevity. In one
sense the story is a tale of the triumph of technology over rational thought. It
begins with a couple of gadgets - in 1837 Samuel Morse demonstrated the first
practical telegraph and in 1846 T. R. Robinson invented the cup anemometer.
Neither of these inventions would have saved Beaufort's scale, however, if it
weren't for a catastrophe. In 1854 the English and French were entrenched in fighting at
Sevastopool. The fleets carrying almost all their winter supplies was struck by
an intense, early winter storm on the morning of November 14. In 12 hours the
English and French suffered losses (no less than 21 supply ships by the British
alone) that exceeded the most savage fleet action that had ever been fought. In
response to the losses and with the hope that there might be some way to
forecast future storms, the British Admiralty and the French Marine jointly
sponsored a weather network - the ancestor of the World Meteorological
Organization - to provide storm warnings. And here then is when Sir Beaufort's
scale begins its protean growth. Since the task of forecasting
storms was commissioned partly by the Royal Navy for use by mariners and
they had made the use of Beaufort numbers mandatory, it naturally developed
that Beaufort numbers would be used for a meteorological purpose. At the
same time, meteorologists of the time were excited about the possibilities
of the new weather net and the deployment of anemometers everywhere. And how
better to code and telegraph this wealth of new wind information than
Beaufort numbers! Ah, but here the trouble begins. In central
Europe a peasant who had never seen the ocean, let alone an 1805 man-of-war,
observed 37 revolutions of his anemometer and, after looking up the
equivalent in his conversion table, sent a Beaufort 7; his cohort in Kansas,
who had never seen the ocean either, looked up the same 37 revolutions in
his table and sent it as a Beaufort 5. The confusion only increased with the
proliferation of more than 30 sets of wind speed equivalents by 1900 - some
disagreeing by more than 100 percent. It was no longer clear just what the
old force scale meant (and few men survived who were competent to judge what
the behaviour of an 1805 man-of-war would be!). In 1912 the International Commission for Weather Telegraphy sought some
agreement on velocity equivalents for the Beaufort scale. A uniform set of
equivalents was accepted in 1926 and revised slightly in 1946. By 1955, wind
velocities in knots replaced Beaufort numbers on weather maps. But there were
still a need for eyeball estimates by seamen to fill the gaps in the global
observing network. Thus it became imperative to relate the seaman's guess logged
in Beaufort numbers to the wind speed in knots. And so Beaufort's scale had
transformed itself from a tool of the mariner to a means for the meteorologist!
Meteorologists set in motion the search to define a set of wind velocity
equivalents for the Beaufort force numbers. That the numbers were ever used to
transmit anemometer readings may well be one of those minor stories of history
that has a much more significant affect than warranted. If 100 years ago there
had been a way to extend weather observations across the oceans using only the
science of meteorology, perhaps Admiral Beaufort's scale and numbers might have
been buried long ago - preferably at sea!
|
Beaufort Number |
Wind Speed (Knots) |
WMO Description |
|
|
0 |
<1 |
Calm |
|
|
1 |
1 - 3 |
Light air |
|
|
2 |
4 - 6 |
Light breeze |
|
|
3 |
7 - 10 |
Gentle breeze |
|
|
4 |
11 - 16 |
Moderate breeze |
|
|
5 |
17 - 21 |
Fresh breeze |
|
|
6 |
22 - 27 |
Strong breeze |
|
|
7 |
28 - 33 |
Near gale |
|
|
8 |
34 - 40 |
Gale |
|
|
9 |
41 - 47 |
Strong gale |
|
|
10 |
48 - 55 |
Storm |
|
|
11 |
56 - 63 |
Violent storm |
|
|
12 |
> 63 |
Hurricane |
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