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Beaufort Scale or Beaufort Wind Force Scale
is a system for estimating wind strengths without
the use of instruments, based on the effects wind
has on the physical environment. The behaviour of
smoke, waves, trees, etc., is rated on a 13 point
scale of 0 (calm) to 12 (hurricane). The scale was
devised in 1805 by the British naval Commander, later
Admiral, Sir Francis Beaufort (1774-1875). A further
set of numbers (13-17) for very strong winds were
added by the US Weather Bureau in 1955.
The
Beaufort Scale, as originally drawn up, made
no reference to the speed of the wind and various
attempts have been made to correlate the two.
Specially
when sailing in high latitudes, wind gains additional
strength due to cold and related higher air density.
Also the effect of windchill on bare skin make cold
water sailing more dangerous.
Information
on related windchill. |
|
Conversion
table
Table de conversion
Umrechnungstafel
Wind
Force / force vent (Bft):
0,
1, 2, 3,
4, 5, 6,
7, 8, 9,
10, 11, 12+
Wind speed / vitesse vent (kts):
0, 5, 10,
15, 20, 25,
30, 35, 40,
45, 50, 55,
60, 65, 70
Wind speed / vitesse vent (km/h):
0, 10, 20,
30, 40, 50,
60, 70, 80,
90, 100, 110,
120
Sea Disturbance Number / état
de la mer:
0, 1, 2,
3, 4, 5,
6, 7, 8,
9
Average wave height / hauteur de vague (m):
0, 0.5, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
12, 14, 16
Average wave height / hauteur de vague (ft):
0, 1, 2,
4, 10, 15,
20, 25, 30,
35, 40, 45,
50 |
0
Bft
Calm
Calme
Winstille |
Wind speeds:
less than 1 knot (<1 mph; <1 kph; <0.3
m/s)
At
sea:
Sea like a mirror, calm
La
fumée s'élève verticalement ; la mer est comme un
miroir
Spiegelglatte See
Sea disturbance number: 0
Probable wave height: flat (0 ft; 0 m)
On land: Smoke rises vertically
Notes: Boring, boring, boring...
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
1
Bft
Light Air
Très légère brise
Leiser Zug |
Wind speeds:
1-3 knots (1-3 mph; 1-5 kph; 0.3-1.5 m/s)
At
sea:
Ripples with the appearance of scales are formed
but without foam crests
Il
se forme des rides, mais il n'y a pas d'écume
Kleine schuppenförmig aussehende Kräuselwellen ohne
Schaumkämme
Sea disturbance number: 0
Probable wave height: 5-10 cm (2-4 in) (0
ft; 0 m)
On land: Direction of wind shown by smoke
drift, but not by vanes
Notes: Yachts just have steerage way
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
2
Bft
Light Breeze
Légère brise
Leichte Brise |
Wind speeds:
4-6 knots (4-7 mph; 6-11 kph; 1.6-3.3 m/s)
At sea:
Small wavelets, still short but more pronounced;
crests have a glassy appearance and do not break
Vaguelettes
courtes ; leurs crêtes ne déferlent pas
Kleine Wellen, noch kurz, aber ausgeprägter. Die
Kämme sehen
glasig aus und brechen sich nicht
Sea disturbance number: 1
Probable wave height: 10-15 cm (4-6 in);
(0-1 ft; 0-0.3 m)
On land: Wind felt on face; leaves rustle;
ordinary vane moved by wind
Notes: Wind fills sails of yacht, which then
may move at 1-2 knots
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
3
Bft
Gentle Breeze
Petite brise
Schwache Brise |
Wind speeds:
7-10 knots (8-12 mph; 12-19 kph; 3.4-5.4 m/s)
At sea:
Large wavelets; crests begin to break; foam of glassy
appearance; perhaps scattered white horses
Très
petites vagues ; écume d'aspect vitreux
Die Kämme beginnen sich zu brechen. Schaum überwiegend
glasig, ganz vereinzelt können weisse Schaumköpfe
auftreten
Sea disturbance number: 2
Probable wave height: 60 cm (2 ft); (1-2
ft; 0.3-0.6 m)
On land: Leaves and small twigs in constant
motion; wind extends light flag
Notes: Yachts start to careen and travel
at 3-4 knots
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
4
Bft
Moderate Breeze
Jolie brise
Mässige Brise |
Wind speeds:
11-16 knots (13-18 mph; 20-28 kph; 5.5-7.9 m/s)
At
sea:
Small
waves, becoming longer; fairly frequent white horses
Petites
vagues devenant plus longues ; moutons nombreux
Wellen
sind noch klein, werden aber länger. Weisse Schaumköpfe
treten schon ziemlich verbreitet auf
Sea disturbance number: 3
Probable wave height: 1 m (3.5 ft); (2-4
ft; 0.6-1.2 m)
On land: Raises dust and loose paper; small
branches are moved
Notes: Good working breeze for yachts; carry
all sail with good list
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
5
Bft
Fresh Breeze
Bonne brise
Frische Bise |
Wind speeds:
17-21 knots (19-24 mph; 29-38 kph; 8.0-10.7 m/s)
At sea:
Moderate waves taking a more pronounced long form;
many white hourses are formed; chance of some spray
Vagues
modérées, allongées ; moutons nombreux
Mässige
Wellen, die eine ausgeprägtere lange Form annehmen.
Überall weisse Schaumkämme. Ganz vereinzelt kann
schon Gischt vorkommen
Sea disturbance number: 4
Probable wave height: 2 m (6-7 ft); (4-8
ft; 1.2-2.4 m)
On land: Small trees in leaf begin to sway;
crested wavelets form on inland waters
Notes: Yachts shorten sail
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
6
Bft
Strong Breeze
Vent frais
Starker Wind |
Wind speeds:
22-27 knots (25-31 mph; 39-49 kph; 10.8-13.8 m/s)
At
sea:
Large waves begin to form; the white foan crests
are more extensive everywhere; probably some spray
Des
lames se forment ; crêtes d'écume blanche plus étendues
Die
Bildung grosser Wellen beginnt; Kämme brechen und
hinterlassen grössere weisse Schaumflächen; etwas
Gischt
Sea disturbance number: 5
Probable wave height: 3 m (9-10 ft); (8-13
ft; 2.4-4 m)
On land: Large branches in motion; whistling
heard in telegraph wires; umbrellas used with dificulty
Notes: Yachts with double reef in mainsail;
cared required when fishing
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
7
Bft
Near Gale /
Moderate Gale
Grand frais
Steifer Wind |
Wind speeds:
28-33 knots (32-38 mph; 50-61 kph; 13.9-17.1 m/s)
At
sea:
Sea heaps up and white foam from the breaking waves
begins to be blown in streaks along the direction
of the wind
La
mer grossit ; l'écume est soufflée en trainées ;
lames déferlantes
See
türmt sich; der beim Brechen entstehende weisse
Schaum beginnt sich in die Windrichtung zu legen
Sea disturbance number: 6
Probable wave height: 4 m (13-14 ft); (13-20
ft; 4-6 m)
On land: Whole trees in motion; inconvenience
felt when walking against wind
Notes: Yachts remain in harbour, those at
sea lie to
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
8
Bft
Gale / Fresh
Gale
Coup de vent
Stürmischer Wind |
Wind speeds:
34-40 knots (39-46 mph; 62-74 kph; 17.2-20.7 m/s)
At
sea:
Moderately high waves of greater length; edges crests
begin to break into spindrift; the foam is blown
in well-marked streaks along the direction of the
wind
Lames
de hauteur moyenne ; de leurs crêtes se détachent
des tourbillons d'embruns
Mässig
hohe Wellenberge mit Kämmen von beträchtlicher Länge.
Von den Kanten der Kämme beginnt Gischt abzuwehen.
Der Schaum legt sich in gut ausgeprägten Streifen
in die Windrichtung
Sea disturbance number: 6
Probable wave height: 5.5 m (18 ft); (13-20
ft; 4-6 m)
On land: Breaks twigs off trees; generally
impedes progress
Notes: All yachts make for harbour if possible
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
9
Bft
Strong Gale
Fort coup de vent
Sturm |
Wind speeds:
41-47 knots (47-54 mph; 75-88 kph; 20.8-24.4 m/s)
At
sea:
High waves; dense streaks of foam along the direction
of wind; crests of waves begin to topple, tumble
and roll over; spray may affect visibility
grosses lames ; leur crête s'écroule et déferle
en rouleaux
Hohe Wellenberge; Dichte Schaumstreifen in Windrichtung;
"Rollen" der See beginnt. Der Gischt kann die Sicht
schon beeinträchtigen
Sea disturbance number: 6
Probable wave height: 7 m (23 ft); (13-20
ft; 4-6 m)
On land: Slight structural damage occurs
(chimney post and slates removed)
Notes:
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
10
Bft
Whole Gale /
Storm
Tempête
Schwerer Sturm |
Wind speeds:
48-55 knots (55-63 mph; 89-102 kph; 24.5-28.4 m/s)
At sea:
Very high waves with long overhanging crests; 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 a white appearance; tumbling
of the sea becomes heavy and shock-like; visibility
affected
Très
grosses lames à longues crêtes en panache ; déferlement
en rouleaux intense et brutal
Sehr hohe Wellenberge mit langen überbrechenden
Kämmen. See weiss durch Schaum. Rollen der See schwer
und stossartig. Sicht durch Gischt beeinträchtigt
Sea disturbance number: 7
Probable wave height: 9 m (29 ft); (20-30
ft; 6-9 m)
On land: Seldom experienced inland; trees
uprooted; considerable structural damage occurs
Notes:
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
11
Bft
Storm / Violent
storm
Violente tempête
Orkanartiger Sturm |
Wind speeds:
56-63 knots (64-75 mph; 103-117 kph; 28.5-32.6 m/s)
At
sea:
Exceptionally high waves (small and medium size
ships might be for a time lost from view behind
waves); sea is completely covered with long white
patches of foam lying along the direction of wind;
everywhere the edges are blown into froth; visibility
afected
Lames
exceptionnellement hautes ; mer recouverte de bancs
d'écume blanche
Aussergewöhnlich
hohe Wellenberge. Die Kanten der Wellenkämme werden
überall zu Gischt zerblasen. Die Sicht ist herabgesetzt
Sea disturbance number: 8
Probable wave height: 11 m (37 ft); (30-45
ft; 9-14 m)
On land: Very rarely experienced; accompanied
by widespread damage
Notes:
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+
|
12-17
Bft
Hurricane
Ouragan
Orkan |
Wind speeds:
64 knots and greater (> 75 mph; >117 kph; >32.7
m/s)
At sea:
The air is filled with foam and spray; sea completely
white with driving spray; visibility very seriously
affected
Air
plein d'écume et d'embruns ; mer entièrement blanche
; visibilité très réduite
Luft
mit Schaum und Gischt angefüllt. See vollständig
weiss. Die Sicht ist sehr stark herabgesetzt; jede
Fernsicht hört auf
Sea disturbance number: 9
Probable wave height: 11 m and more (> 37
ft); (>45 ft; >14 m)
On land: Very rarely experienced; accompanied
by widespread damage
Notes:
13 Bft > 72-80 kts
14 Bft > 81-89 kts
15 Bft > 90-99 kts
16 Bft > 100- 108 kts
17 Bft > 109- 118 kts
Go
to Beaufort number: 0, 1,
2, 3, 4,
5, 6, 7,
8, 9, 10,
11, 12+ |
|
Windchill
index - refroidissement éolien
L'association
du froid et du vent entraine un refroidissement important de la
peau exposée et peut provoquer
de graves engelures. Les liens ci-dessous donnent des informations
au sujet du refroidissement éolien.
Explications
du calcul du facteur de refroidissement éolien (nouvelle
formule):
Information
on windchill calculation (new formula versus old):
http://meteo.lcd.lu/papers/windchill/newwindchill.html
The
'Imram' logbook
The
'Nanuq' logbook
Sources description: http://www.anbg.gov.au/jrc/kayak/beaufort.html
(2001)
Sources
images: http://www.crh.noaa.gov/lot/webpage/beaufort/ (2001)
Adaptation (c) peter gallinelli 08/2001
last
update pg 12/2019 |
