http://www.rya.org.uk/regions/eastern/Pages/default.aspx
Measuring the wind – The Beaufort Scale
In 1805, a British Naval officer called Francis Beaufort introduced a scale from 0 -12 for measuring the speed of the wind at sea. Admiral Beaufort developed the scale based on his observations of the wind and waves and used everyday terms for each level of his scale.
The Beaufort Scale is still used today to describe the speed of wind at sea and the effect of wind on the surface of the water. Wind speed is measured in knots, with one knot equal to one nautical mile per hour. A nautical mile is just a bit longer than a land mile.
Today we also use wind instruments to measure the exact speed of the wind.
So lets’ take a look at the Beaufort Scale – the force, the speed of the wind in knots, how you would describe the wind and how you would describe the state of the sea…
| Force | Knots | Description | Sea Description |
|---|---|---|---|
| 0 | 1 knot | Calm | Calm (glassy) |
| 1 | 1 – 3 knots | Light air | Calm (rippled) |
| 2 | 4 – 6 knots | Light breeze | Smooth (wavelets) |
| 3 | 7 – 10 knots | Gentle breeze | Slight |
| 4 | 11 – 16 knots | Moderate breeze | Slight – Moderate |
| 5 | 17 – 21 knots | Fresh breeze | Moderate |
| 6 | 22 – 27 knots | Strong breeze | Rough |
| 7 | 28 – 33 knots | Near gale | Rough – Very Rough |
| 8 | 34 – 40 knots | Gale | Very rough – High |
| 9 | 41 – 47 knots | Severe gale | High |
| 10 | 48 – 55 knots | Storm | Very High |
| 11 | 56 – 63 knots | Violent storm | Very High |
| 12 | Over 64 knots | Hurricane | Phenomenal |