Beaufort Wind Scale. At sea the wind speed is expressed in numbers according to the Beaufort scale. The Beaufort Number (BF) is estimated from the sea surface appearance.
Beaufort/ Description of wind /Speed in Knots
0 /Calm Less than/ 1
1 /Light air /1-3
2/ Light breeze /4-6
3/ Gentle breeze /7-10
4/ Moderate breeze /11-16
5/ Fresh breeze /17-21
6 /Strong breeze/ 22-27
7 /Moderate gale /28-33
8 /Fresh gale /34-40
9/ Strong gale /41-47
10/ Whole gale /48-55
11 /Storm /56-63
12/ Hurricane /64-71
The Beaufort wind force scale extends to Force 17 (up to 118) knots but Force 12 is the highest which can be identified from the appearance of the sea.
