UK Sailing and Yachting - Cruising Guide
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The Beaufort Scale for use at sea
Beaufort Force
Description
Sea State
Speed
knots km/h mph
0 Calm Sea like a mirror Less than 1 Less than 1 Less than
1
1 Very Light Ripples with appearance of scales, no foam crests 1 - 3 1 - 5 1 - 3
2 Light breeze Wavelets, small but pronounced. Crests with glassy appearance, but do not break. 4 -6 6 - 11 4 -7
3 Gentle breeze Large wavelets, crests begin to break. Glassy looking foam, occasional white horses. 7 - 10 12 - 19 8 - 12
4 Moderate breeze Small waves becoming longer, frequent white horses. 11 - 16 20 - 29 13 - 18
5 Fresh breeze Moderate waves of pronounced long form. Many white horses, some spray. 17 - 21 30 - 39 19 - 24
6 Strong breeze Some large waves, extensive white foam crests, some spray. 22 - 27 40 - 50 25 - 31
7 Near gale Sea heaped up, white foam from breaking waves blowing in streaks with the wind. 28 - 33 51 - 61 32 - 38
8 Gale Moderately high and long waves. Crests break into spin drift, blowing foam in well marked streaks. 34 - 40 62 - 74 39 - 46
9 Strong gale High waves, dense foam streaks in wind, wave crests topple, tumble and roll over. Spray reduces visibility. 41 - 47 75 - 87 47 - 54
10 Storm Very high waves with long overhanging crests. Dense blowing foam, sea surface appears white. Heavy tumbling of sea, shock-like, poor visibility. 48 - 55 88 - 101 55 - 63
11 Violent storm Exceptionally high waves, sometimes concealing small and medium sized ships. Sea completely covered with long white patches of foam. Edges of wave crests blown into froth . Poor visibility. 56 - 63 102 - 117 64 - 73
12 Hurricane Air filled with foam and spray, sea white with driving spray, poor visibility. >64 >119 >74