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The Beaufort Scale

The son of a cartographer, Sir Francis Beaufort was born in Ireland, despite the French last name, in 1774. His father instilled attention to the accuracy of charts and information, but his grasp on the value of these accuracies sunk in with literal meaning when he was shipwrecked due to erroneous graphs at age 15.

Undeterred by the disaster, Beaufort thrust himself into a career on the sea. As a member of the Royal Navy, he fought during the French Revolutionary Wars and the Napoleonic Wars. In peacetime, he explored the world, from the Mediterranean to the East Indies to South America. Though an accomplished sailor, his greatest gifts to humanity came from his role as a hydrographer, a scientist studying the physical features of the sea.

Perhaps due to his experience with calamity, Beaufort strove to make the life of a mariner more manageable. The scale that bears his name deals with one of the ocean’s most significant attributes and dangers: wind. Without modern technology, how could one measure wind speed empirically? After all, one human’s “moderate breeze” is another’s “harsh gust.” Wind speed can be notoriously difficult to gauge without proper equipment.

Sir Francis Beaufort portrait by Stephen Pearce

Others had dabbled with wind scales before Beaufort lived. Daniel Defoe, of Robinson Crusoe fame, whipped up a “table of degrees” after a major storm hit the British Isles in 1703. His hierarchy included “bald terms used by sailors,” including “start calm,” a fine breeze,” “a fret of wind,” and “a tempest.”

In 1805, Beaufort hoped to standardize wind speed in a way that nearly every ship could grok, based on non-subjective terms. His 12-point system included descriptions of wind speeds, but also tangible effects those speeds had on the sails of a frigate. Beaufort added criteria to match a designation.

Zero denoted calm winds.

1 = Light Air, which is “just sufficient to give steerage way.”

2 is a Light Breeze, “with which a well-conditioned man of war, under all sail, and ‘clean full’, would go in smooth water from 1 to 2 knots.” In other words, he tied the speed of the boat to the speed of the wind. 3’s Gentle Breeze and 4’s Moderate Breeze replicated this description, replacing the boat speeds with 3 to 4 knots and 5 to 6 knots, respectively.

Beaufort grouped 5 through 9 together: Fresh Breeze, Strong Breeze, Moderate Gale, Fresh Gale, and Strong Gale. Number five, for example, is a speed in “which a well-conditioned man of war, under all sail, and ‘clean full’, could just carry close hauled royals.” Different types of sails replace “royals” as the numbering increases: single-reefs and top-gallant sails; double-reefs, jibs, etc.; triple-reefs, courses, etc.; close-reefs and courses. The differences between these sails sound like a foreign language to my ear, but the seasoned wayfarer would understand.

Once we hit 10, things start to get gnarly. A Whole Gale is a speed with “which she could only bear close-reefed maintop-sail and reefed fore-sail.” 11 corresponds to Storm, with “which she would be reduced to storm staysails.” Hurricane was the highest designation, “to which she could show no canvas.”

The early Beaufort scale - graphic by MetOffice

Beaufort’s original scale is obviously an empirical upgrade to previous incarnations. It became the standard for ship log entries by the 1830s and was adopted by the First International Meteorological Conference in 1853. However, it’s still a limited grouping. Though it was designed for a small subsection of people, no one outside of that group would ever derive practical benefit from it.

Thankfully, enterprising scientists recognized the raw talent of the Beaufort Scale. Since the original iteration, improvements were implemented, first to accommodate steam-powered ships and then to translate the concept to land-based winds.

For steamboats, the wind’s effect on sails obviously wouldn’t work, so they instead described the wind’s influence on the sea. The 0 designation, which was simply “Calm,” was extended to describe the sea as “like a mirror.” At a 1, the water has “ripples with appearance of scales are formed, without foam crests.” At 5’s Fresh Breeze level, “moderate waves” have formed with “many white horses.” High waves take over by Level 9. At Hurricane force, “the air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected.”

Differences in the ocean on the Beaufort Scale - graphic from delta-s

This description of the ocean is something more people can intuitively comprehend than the original scale.

Perhaps even better, though, is the adaptation to land conditions. The descriptions are such that most people can visualize what they mean without seeing them happening.

0 – Calm – Smoke rises vertically
1 – Light Air – Direction shown by smoke drift but not by wind vanes
2 – Light Breeze – Wind felt on face; leaves rustle; wind vane moved
3 – Gentle Breeze – Leaves and small twigs in constant motion; light flags extended
4 – Moderate Breeze – Raises dust and loose paper; small branches moved
5 – Fresh Breeze – Small trees in leaf begin to sway; crested wavelets form on inland water
6 – Strong Breeze – Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty
7 – High Wind – Whole trees in motion; inconvenience felt when walking against the wind
8 – Gale – Twigs break off trees; generally impedes progress
9 – Strong Gale – Slight structural damage (chimney pots and slates removed)
10 – Storm – Seldom experienced inland; trees uprooted; considerable structural damage
11 – Violent Storm – Very rarely experienced; accompanied by widespread damage
12 – Hurricane – Devastation

The good part about separating wind into effects is that we can map speeds onto them. Waves tend to form uniformly based on wind velocity; trees tend to sway, bend, and break in relatively consistent manners. The interesting part is that we get to a decently high portion of the scale while winds are rather “mild” by miles-per-hour standards. Level 6, which sends large branches moving, occurs between a range of 25 and 31 miles per hour. Compared to hurricanes, this rate is quite low, but it still packs a wallop. Winds that reach a 6 or 7 on the Beaufort Scale prompt small craft advisories in the United States. Gale warnings transpire at 8s and 9s, while a 10 or 11 prompts a storm warning.

Click to view a larger version of this Howtoon

The Beaufort Scale is a surprisingly useful non-precise method for measuring wind. It allows an easy universality, which is why it’s still used in quite a few meteorological settings in the 21st century.

Sir Francis Beaufort was a bit of a renaissance human, too. In addition to his contributions to windiness, cartography, and exploration, he boasted a few rather eclectic achievements. He developed a variation of the famous Vigenere cipher, which bears his name. Though the Beaufort Cipher is easily cracked by today’s technology, it was surprisingly sophisticated for its time. Beaufort is credited with rediscovering Hadrian’s Wall, an artifact in Turkey from the time of Ancient Rome. Further, as a Rear Admiral and official Hydrographer of the Navy, he oversaw the deployment of HMS Beagle. When Beaufort’s chosen captain, Robert FitzRoy, asked for a “well-educated and scientific gentleman be sought” for the ship’s expedition, Beaufort eventually unearthed a person named Charles Darwin. FitzRoy escorted Darwin to the Galapagos and the rest is evolutionary history.

Beaufort’s curriculum vitae certainly merits a 12 on the Resume Scale, a hurricane force of the 18th and 19th centuries.

Further Reading and Exploration

Beaufort Wind Scale – National Oceanic and Atmospheric Administration

Beaufort – National Meteorological Library and Archive


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