Show No Canvas
By Margaret Graham Neeson, 91 Years Young, Marine Parts Express
It’s a mistake to assume, as the erudite Edmund Wilson once pointed out, that everyone is necessarily familiar with a well-known subject. Mr. Wilson went on to discuss the Old Testament, and we’re gong to talk about the Beaufort Scale. But maybe the two subjects are not so far apart, for the originator of the scale was the son, grandson and brother of clergymen; and it can be safely assumed that he knew his Bible well.
Admiral Sir Francis Beaufort was born in 1774 in Navan, County Meath, Ireland. The family name had been de Beaufort, but the “de” was dropped when, staunch Protestants, they left France first for England, then Ireland. Francis’ father, Daniel Augustus Beaufort, was not only a prominent cleric, but also, a geographer and topographer.
Following the custom of the day, the young Beaufort entered the Royal Navy at the early age of thirteen, and served, as the “Dictionary of National Biography” puts it, “under a number of gallant captains” during the wars with France and Spain that then occupied Britain. He gradually reached post rank, but in 1800 after “seeing much active and splendid service,” he was invalided home with “nineteen wounds in the head, arms and body, three sword cuts and sixteen musket shots.” He was promoted to commander and given a wound pension of forty-five pounds, but was not sent to sea again until 1805. In the interim years he helped his brother-in-law, Richard Edgeworth, establish a line of telegraphs from Dublin to Galway.
On returning to sea duty, he served first in South America, then in the Mediterranean and along the coast of Asia Minor. Here he was attacked by Turkish pirates in 1812 and was badly wounded. He was retired on his return to England, but kept himself fruitfully busy publishing his surveys of the Rio de La Plata and of the Karamania Coast, doing them so expertly that the Hydrographic Office engraved its charts directly from his drawings. He refused any remuneration for this work, since the “material had been gathered while in His Majesty’s Service.”
In 1829, he was appointed hydrographer to the British Navy, a post which he held for twenty-six years, and which “rendered his name almost a synonym in the Navy for hydrography and nautical science.”
He was elected a member of several learned and scientific societies, and served on two Royal Commissions which investigated the pay of pilots and the state of harbors. He was promoted to rear admiral in 1846 and made a knight commander of the Bath in 1848. He retired as hydrographer in 1855 and died two years later.
Tradition tells us that the admiral devised his scale of wind force while captain of the armed frigate Woolwich in the port of Buenos Aires. His aim was not only to give seamen a workable method of figuring what the sea and wind were up to, but also a way of rendering their logs “more concise and comprehensive.”
To do this he gave a force number, from one to twelve, to a succession of estimated wind forces. To the number he added the then current seaman’s description of the wind. And, as a third point, included an analysis of what canvas, under each force should be carried by a “well-conditioned man-of-war,” with, for the lighter winds, an estimate of her speed.
“Force Four; moderate breeze; under all sail and clean full, would go from five to six knots.”
“Force Ten; whole gale; with which she could only bear close-reefed main topsail and reefed foresail.”
The admiral’s scale was adopted by the British Navy in 1838 and was gradually accepted by the other navies and mercantile fleets of the world. A fourth factor, that of the effect of the wind on the sea, was soon added to the first three.
To Force Four; “small waves, becoming longer; fairly frequent whitecaps.”
To Force Ten; “very high waves with long, overhanging crests . . . foam, in great patches, is blown in dense white streaks . . . white appearance . . . rolling . . . heavy and shocklike. Visibility affected.”
(For use on land, the effect of the wind on smoke, branches, telegraph wires and trees was given.)
In 1874, when the International Meteorologic Committee adopted the Beaufort Scale for telegraphic transmission of weather data, it took notice of the fact that the scale dealt in wind results, not in actual wind speed or velocity. Therefore, a correlative scale was developed, matching each Beaufort point with a wind velocity within certain limits, from one to three knots for the lesser winds, on up to a differential of from seven to nine knots for the stronger. Later the Beaufort Scale was extended five more force numbers, up to seventeen, with a top velocity of one hundred eighteen knots.
Force Four has a wind velocity from eleven to sixteen knots; Force Ten, from forty-eight to fifty-five knots.
These speeds are presumably read from an anemometer set up in an unobstructed area six meters (around twenty feet) from the ground.
In its search for better weather forecasting, the United States Weather Bureau has raised its anemometer height to eleven meters (approximately thirty-six feet) above the ground, and has systemized its velocity increases into an orderly progression, in all but five instances, of five miles an hour. It is this reading that most weather broadcasts give (abroad, this may be read in kilometers per hour or meters per second), but weather maps, somewhat confusingly, record the wind speed to the nearest five knots. Arrows are drawn, plotted as flying with the wind, and velocity is shown by half feathers for five knots (one point Beaufort), full feathers for ten knots (two pints Beaufort), and flags for fifty knots.
Not that the admiral is completely forgotten. As he felt, a good seaman can always observe. For ships and boats at sea, as well as for interested persons on shore, with no anemometer available, observation can result in a very good estimate of the speed and force of the wind.
For when “the air is filled with foam and spray,” the wind is described as “hurricane” and has a probable speed of over sixty-five knots. It’s Force Twelve on the Beaufort, and it’s time for our ship “to show no canvas.”
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March 3, 2010 / JD Neeson / 0
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Margaret Graham Neeeson
Margaret Graham Neeson
Marine Parts Express