How To: Understand the Beaufort Wind Scale – An essential observational skill for the OW Swimmer

One thing I’ve really noticed a lot this year is the inability of many swimmers to accurately gauge wind speed and water conditions.

The way to do this is the Beaufort Scale, which measures wind speed based on empirical observed conditions. (It is, by the way, named after an Irish explorer and British Navy Admiral.)

I’m just pasting the Wikipedia chart in here. I first used a version of this when I was learning to parachute, although that scale used the leaf and tree movement. When I started surfing, I starting using the modern Beaufort scale of sea conditions.

When I was crewing for Gábor, it was how I was able to give current wind conditions during the swim. It’s very easy with just a bit of practice. Sailors will also use the description in the second column. At one point I described that we had moved to Force Three for about 45 minutes. This was based on observation that the waves had just started to break. For my own swim, it had moved to Force Five by the end, disorganised larger waves, lots of whitecaps, and water washing unpredictably across my face.

For sea swimming, the critical noticeable tipping point (for me anyway) is between Force Two and Force Three. At Force Three it becomes more work and at this point the chance of aspirating water increases with the unpredicability of the water surface conditions.

Also remember, that these conditions can occur On Top Of Groundswell, which I’ve previously described. The combination of Force Four to Five wind and groundswell leads to conditions that should only be swum by experienced open water swimmers, and who have a defined water exit point.

For the much mentioned “lumpy” day outside Sandycove, it’s either Force Three or Force Four. By Force Five we rarely go outside the island, though those who can recall the Champion of Champions race in 2008, and who made it to the eight mile, will recall how tough that was, which I estimated at Force Five headwind (South Easterly).

Beaufort number Description Wind speed Wave height Sea conditions Land conditions Sea state photo
0 Calm < 1 km/h 0 m Flat. Calm. Smoke rises vertically.

< 1 mph
< 1 kn 0 ft
< 0.3 m/s
1 Light air 1.1–5.5 km/h 0–0.2 m Ripples without crests. Smoke drift indicates wind direction, still wind vanes.

1–3 mph
1–2 kn 0–1 ft
0.3–1.5 m/s
2 Light breeze 5.6–11 km/h 0.2–0.5 m Small wavelets. Crests of glassy appearance, not breaking Wind felt on exposed skin. Leaves rustle, vanes begin to move.

4–7 mph
3–6 kn 1–2 ft
1.6–3.4 m/s
3 Gentle breeze 12–19 km/h 0.5–1 m Large wavelets. Crests begin to break; scattered whitecaps Leaves and small twigs constantly moving, light flags extended.

8–12 mph
7–10 kn 2–3.5 ft
3.4–5.4 m/s
4 Moderate breeze 20–28 km/h 1–2 m Small waves with breaking crests. Fairly frequent white horses. Dust and loose paper raised. Small branches begin to move.

13–17 mph
11–15 kn 3.5–6 ft
5.5–7.9 m/s
5 Fresh breeze 29–38 km/h 2–3 m Moderate waves of some length. Many white horses. Small amounts of spray. Branches of a moderate size move. Small trees in leaf begin to sway.

18–24 mph
16–20 kn 6–9 ft
8.0–10.7 m/s
6 Strong breeze 39–49 km/h 3–4 m Long waves begin to form. White foam crests are very frequent. Some airborne spray is present. Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.

25–30 mph
21–26 kn 9–13 ft
10.8–13.8 m/s
7 High wind,
Moderate gale,
Near gale
50–61 km/h 4–5.5 m Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray. Whole trees in motion. Effort needed to walk against the wind.

31–38 mph
27–33 kn 13–19 ft
13.9–17.1 m/s
8 Gale,
Fresh gale
62–74 km/h 5.5–7.5 m Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray. Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.

39–46 mph
34–40 kn 18–25 ft
17.2–20.7 m/s
9 Strong gale 75–88 km/h 7–10 m High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility. Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.

47–54 mph
41–47 kn 23–32 ft
20.8–24.4 m/s
10 Storm,[6]
Whole gale
89–102 km/h 9–12.5 m Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility. Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.

55–63 mph
48–55 kn 29–41 ft
24.5–28.4 m/s
11 Violent storm 103–117 km/h 11.5–16 m Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility. Widespread damage to vegetation. Many roofing surfaces are damaged; asphalt tiles that have curled up and/or fractured due to age may break away completely.

64–72 mph
56–63 kn 37–52 ft
28.5–32.6 m/s
12 Hurricane-force[6] ≥ 118 km/h ≥ 14 m Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility. Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.

≥ 73 mph
≥ 64 kn ≥ 46 ft
≥ 32.7 m/s

4 thoughts on “How To: Understand the Beaufort Wind Scale – An essential observational skill for the OW Swimmer

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