Beaufort Scale - sea state, not wind speed

7:24 AM Mon 12 Apr 2010 GMT

'There we were...' .

'..so there we were in a Force 8..'
'A what?'
'..a Force 8, and the winch jammed...'
'What's a Force 8 mate?'
'It's a bloody big wind - where do you come from?'
'Australia.'
'I see old chap - that explains it. Now can I get on with my story?'

What the sailor telling the story said was wrong, because the Beaufort Scale is NOT a measure of the wind at all. It's a measure of the sea state, and, as any half way experienced sailor will tell you, it's the sea state that matters on the ocean, not the wind speed. Imagine sailing in a 50 knot wind on a perfectly calm sea...

heavy weather sailing - .. .

However, usually (not always) the sea state can be associated with certain wind strengths, particularly in an open ocean, and particularly when the sea is well developed by the present wind, so the Beaufort scale numbers are traditionally associated with a certain range of wind speed.

The Beaufort scale has long been a bit of a mystery to those who don't have occasion use it very often, and, as many forecasts from certain parts of the world are given using the Beaufort Scale, if you're not familiar with it, it's a good idea to have the translation pasted up above the chart table.

The scale was created in 1805 by, surprise surprise, Sir Francis Beaufort, an Irishman who became a British admiral. He created the scale to attempt to standardise the descriptions that naval officers made to each other, and eliminate subjectivity. This was so successful that by the 1830's the standard was accepted throughout the Royal Navy.

Here's a brief summary of the scale, with accompanying wind speed:

Beaufort number	Description		Wave height		Sea conditions
		Knots	Metres	Feet
0	Calm	< 1	0	0	Flat.
1	Light air	1 - 2	0 - 0.2	0 - 1	Ripples without crests.
2	Light breeze	3 - 6	0.2 - 0.5	1 - 2	Small wavelets. Crests of glassy appearance, not breaking
3	Gentle breeze	7 - 10	0.5 - 1	2 - 3.5	Large wavelets. Crests begin to break; scattered whitecaps
4	Moderate breeze	11 - 15	1 - 2	3.5 - 6	Small waves with breaking crests. Fairly frequent white horses.
5	Fresh breeze	16 - 20	2 - 3	6 - 9	Moderate waves of some length. Many white horses. Small amounts of spray.
6	Strong breeze	21 - 26	3 - 4	9 - 13	Long waves begin to form. White foam crests are very frequent. Some airborne spray is present.
7	High wind, Moderate gale, Near gale	27 - 33	4 - 5.5	13 - 19	Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray.
8	Gale, Fresh gale	34 - 40	5.5 - 7.5	18 - 25	Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray.
9	Strong gale	41 - 47	7 - 10	23 - 32	High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility.
10	Storm, Whole gale	48 - 55	9 - 12.5	29 - 41	Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility.
11	Violent storm	56 - 63	11.5 - 16	37 - 52	Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility.
12	Hurricane	= 64	= 14	= 46	Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.

by Nancy Knudsen

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