Beaufort Wind Force Scale

Learning Goal 8e: Explain the change in wind speeds and sea state as you move along the Beaufort Wind Force Scale, and which Beaufort-force values are best for recreational sailing.

The Beaufort wind force scale was developed in 1805 by British Naval admiral Francis Beaufort. His system to estimate and report wind speeds was based on the amount of canvas sail that a full-rigged frigate (a large military sailing ship) could carry. The scale ranges from 0-12, with 12 being for the strongest winds.  In the table below, we apply this scale to small sailboats (dinghies).

[Definition: A dinghy is a small open-cockpit sailboat, typically 2 to 6 m long, used for recreation.]

In the "Extra Info" box at the end of this web page is a video demonstrating the effects of different wind speeds to structures and trees on land near the coast.  Also in that info box is the original description of winds on large frigates.

Beaufort Force	Wind (Knots)	Description	Dinghy Sailing	Image
0	< 1	Calm. Sea surface smooth and mirror-like.	Cannot sail due to absence of wind
1	1-3	Light air. Scaly ripples, no foam crests	Very slow, barely sailing
2	4-6	Light breeze. Small wavelets, no breaking waves	Slow sailing
3	7-10	Gentle breeze. Large wavelets, crests begin to break, scattered whitecaps	Good dinghy sailing
4	11-16	Moderate breeze. Small waves (1-4 ft) becoming longer, numerous whitecaps	Good dinghy sailing, most dinghies will get up on plane, good for larger sailing boats
5	17-21	Fresh breeze. Moderate waves (4-8 ft) taking longer form, many whitecaps, some spray	Advanced dinghy sailing. Have to be careful of gusts. Good for larger sailing boats	Source: Public Domain, https://commons.wikimedia.org/w/index.php?curid=2557081
6	22-27	Strong breeze. Larger waves (8-13 ft), whitecaps common, more spray	Advanced dinghy sailing, advanced sailing, sail with reefed main sail and small jib	Source: Public Domain, https://commons.wikimedia.org/w/index.php?curid=2557083
7	28-33	Near gale. Sea heaps up, large waves (13-19 ft), white foam streaks off breakers	Not suitable for dinghies. Advanced sailing, difficult
8	34-40	Gale. Moderately high waves (18-25 ft) of greater length, foam blown in streaks	Very difficult to sail, head to safe haven immediately
9	41-47	Strong gale. High waves (23-32 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility	Dangerous, take refuge, take all safety measures	Source: Public Domain, https://commons.wikimedia.org/w/index.php?curid=2557088
10	48-55	Storm. Very high waves (29-41 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility	Extremely dangerous, inform the authorities if you are on the water unable to make it to safe haven	Source: Public Domain, https://commons.wikimedia.org/w/index.php?curid=2557090
11	56-63	Violent storm. Exceptionally high (37-52 ft) waves, foam patches cover sea, visibility more reduced	Extremely dangerous, inform authorities, survival mode	Source: Public Domain, https://commons.wikimedia.org/w/index.php?curid=2557093
12	64+	Hurricane. Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced	Extremely dangerous, inform authorities, survival mode. Even at anchor or in harbour, boat should be abandoned, look for hurricane shelters	Source: United States National Weather Service - http://www.crh.noaa.gov/mkx/marinefcst.php Public Domain, https://commons.wikimedia.org/w/index.php?curid=2557094

 

Extra Info, including Videos: (non-required material)

• Beaufort Scale: https://www.youtube.com/watch?v=WwDNWm6IEVw
  
• Big waves: https://www.youtube.com/watch?v=Le-tHm3OLMo
  

from Stull 2017 "Practical Meteorology", used with permission.
https://www.eoas.ubc.ca/books/Practical_Meteorology/