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Beaufort Scale

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One of the first scales to estimate wind speeds and the effects was created by Britain's Admiral Sir Francis Beaufort (1774-1857). He developed the scale in 1805 to help sailors estimate the winds via visual observations. The scale starts with 0 and goes to a force of 12. The Beaufort scale is still used today to estimate wind strengths.


FORCE
SPEED MPH
SPEED KNOTS
DESCRIPTION
SPECIFICATIONS FOR USE ON LAND
IMAGE
AT IBRSC
FORCE
FORCE
0
MPH
MPH
0-1
KNOTS
KNOTS
0-1
Calm
Calm; smoke rises vertically.
Beaufort Scale Force 0
Sailors stand around drinking tea.
FORCE
1
MPH
1-3
KNOTS
1-3
Light Air
Direction of wind shown by smoke drift, but not by wind vanes.
Beaufort Scale Force 1
Very light and patchy: a Solo wins the race!
FORCE
2
MPH
4-7
KNOTS
4-6
Light Breeze
Wind felt on face; leaves rustle; ordinary vanes moved by wind.
Beaufort Scale Force 2
A nice gentle racing wind. 
FORCE
3
MPH
8-12
KNOTS
7-10
Gentle Breeze
Leaves and small twigs in constant motion; wind extends light flag.
Beaufort Scale Force 3
 A decent racing breeze: things are getting lively.
FORCE
4
MPH
13-18
KNOTS
11-16
Moderate Breeze
Raises dust and loose paper; small branches are moved.
 Beaufort Scale Force 4
Very lively, some capsizes. 
FORCE
5
MPH
19-24
KNOTS
17-21
Fresh Breeze
Small trees in leaf begin to sway; crested wavelets form on inland waters.
 Beaufort Scale Force 5
Probably too much wind for novices unless using reefed Toppers. Much capsizing. 
FORCE
6
MPH
 25-31
KNOTS
22-27
Strong Breeze
Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
 beaufort scale force 6
 Many sailors stay ashore and watch the fun
FORCE
7
MPH
 32-38
KNOTS
28-33 
Near Gale
Whole trees in motion; direction of wind shown by smoke drift, but not by wind vanes.
 beaufort scale force 7
Only a few Lasers go out sailing 
FORCE
8
MPH
 39-46
KNOTS
34-40
Gale
Breaks twigs off trees; generally impedes progress.
 beaufort scale force 8
Only for the very experienced and foolhardy, and they soon regret it.
FORCE
9
MPH
 47-54
KNOTS
41-47
Severe Gale
Slight structural damage occurs (chimney-pots and slates removed).
 beaufort scaleforce 9
Sailors go and check that their boats and those next to them are well tied down. 
FORCE
10
MPH
 55-63
KNOTS
48-55
Storm
Seldom experienced inland; trees uprooted; considerable structural damage occurs.
 beaufort scale force 10
Sailors stay at home 
FORCE
11
MPH
 64-72
KNOTS
56-63
Violent Storm
Very rarely experienced; accompanied by wide-spread damage.
 beaufort scale force 11
Club Committee organise emergency meeting to discuss new clubhouse roof. Boats blown over fences, rescue boats blown ashore.
FORCE
12
MPH
 73-83
KNOTS
64-71
Hurricane

 beaufort scale force 12
 Michael Fish was right: fortunately we don't get these in the UK.

Images courtesy of Howtoons


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