Beaufort Scales Sea
The scale was created in 1805 by Sir Francis Beaufort, an Irish-born British admiral and hydrographer while serving on HMS Woolwich. The scale that carries Beaufort's name had a long and complex evolution, from the previous work of others, including Daniel Defoe the century before, to when Beaufort was a top administrator in the Royal Navy in the 1830s when it was adopted officially and first used during Darwin's voyage on HMS Beagle.
In the early 19th Century, naval officers made regular weather observations, but there was no standard scale and so they could be very subjective - one man's "stiff breeze" might be another's "soft breeze". Beaufort succeeded in standardizing the scale (source: wikipedia.org)
PS: We also have a page for Beaufort scales land.
Beaufort specifications and equivalent speeds for use on seamiles/h km/h knots description 0 0-1 0-1 0-1 Calm Sea like a mirror 1 1-3 1-5 1-3 Light air Ripples with the appearance of scales are formed, but without foam crests 2 4-7 6-11 4-6 Light Breeze Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break 3 8-12 12-19 7-10 Gentle Breeze Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses 4 13-18 20-28 11-16 Moderate Breeze Small waves, becoming larger, fairly frequent white horses 5 19-24 29-38 17-21 Fresh Breeze Moderate waves, taking a more pronounced long form, many white horses are formed. Chance of some spray 6 25-31 39-49 22-27 Strong Breeze Large waves begin to form, the white foam crests are more extensive everywhere. Probably some spray 7 32-38 50-61 28-33 Near Gale Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind 8 39-46 62-74 34-40 Gale Moderately high waves of greater length, edges of crests begin to breakinto spindrift. The foam is blown in well-marked streaks along the direction of the wind 9 47-54 75-88 41-47 Severe Gale High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility 10 55-63 89-102 48-55 Storm Very high waves with long overhanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected 11 64-72 103-117 56-63 Violent Storm Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected 12 73-83 >117 64-71 Hurricane The air is filled with foam and spray. Sea completely white with driving spray, visibility very seriously affected