You hear it referred to all the time. Author John Rousmaniere even used it in the title of his book on the 1979 Fastnet Race, Fastnet Force 7. It’s the Beaufort Scale—technically the Beaufort Wind Force Scale—but let’s not stand on formalities. We’ve all heard about the Beaufort (BOH-fərt) Scale and we probably understand only that the bigger the number, the stronger the winds. However, there’s more to the story than just a numerical scale.
The 18th century found officers in various navies creating their own terms to describe wind strength: stiff, howling, light, etc. Not at all quantified. Then, in the early 1800s, a British Rear Admiral named Francis Beaufort changed all that.
Here’s an interesting factoid. Originally, the Beaufort Scale’s numbering system wasn’t tied to wind speed. Rather, it reflected the effect of the wind on the sails of a frigate, the common denominator ship of the then British Navy. Initial readings ranged from “just sufficient to give steerage” to “that which no canvas sails could withstand.” Adding to this soft database, in 1906, to accommodate the expansion of steam-powered fleets, these descriptions were changed from sails only to also reflect sea state. At the time, that was probably better than nothing; but it’s a long way from the data we receive and use today.
Throughout this time, the original Beaufort Scale was comprised of 13 Force classifications: 0–12. One can only imagine the forces on a frigate’s sails or a side-wheeler’s sea state that would qualify as Force 12. Remember, the famous Fastnet Race was only a Force 7.
It wasn’t until the 1920s that anemometer rotation frequency was standardized, which eventually led to meteorologists expressing wind speeds in terms of kilometers or miles per hour. That, along with quantifying wave height, gave way to today’s Beaufort Scale. The following chart from the Royal Meteorological Society (RMetS.org) lays out each Force’s wind strength and probable sea state—from Force 0, “sea like a mirror,” to Force 12, “Devastation.”
| Force | Name | km/h | mph | knots | Wave m (typ/max) | Sea state | Conditions |
|---|---|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | — / — | 0 | Smoke rises vertically. Sea like a mirror. |
| 1 | Light air | 1–5 | 1–3 | 1–3 | 0.1 / 0.1 | 1 | Smoke drift shows direction; wind vanes unaffected. Sea rippled. |
| 2 | Light breeze | 6–11 | 4–7 | 4–6 | 0.2 / 0.3 | 2 | Wind felt on face; leaves rustle; vanes move. Small wavelets. |
| 3 | Gentle breeze | 12–19 | 8–12 | 7–10 | 0.6 / 1.0 | 3 | Leaves and twigs in constant motion; light flags extended. Large wavelets. |
| 4 | Moderate breeze | 20–28 | 13–18 | 11–16 | 1.0 / 1.5 | 3–4 | Dust and loose paper raised; small branches move. Small waves, frequent white horses. |
| 5 | Fresh breeze | 29–38 | 19–24 | 17–21 | 2.0 / 2.5 | 4 | Small leafy trees sway; crested wavelets on inland waters. Moderate waves, many white horses. |
| 6 | Strong breeze | 38–49 | 25–31 | 22–27 | 3.0 / 4.0 | 5 | Large branches in motion; umbrellas difficult. Large waves, extensive foam crests. |
| 7 | Near gale | 50–61 | 32–38 | 28–33 | 4.0 / 5.5 | 5–6 | Whole trees in motion; walking into wind inconvenient. Foam blown in streaks. |
| 8 | Gale | 62–74 | 39–46 | 34–40 | 5.5 / 7.5 | 6–7 | Twigs break off trees; progress generally impeded. Wave crests break into spindrift. |
| 9 | Strong gale | 75–88 | 47–54 | 41–47 | 7.0 / 10.0 | 7 | Slight structural damage; chimney pots and slates removed. Crests topple; spray affects visibility. |
| 10 | Storm | 89–102 | 55–63 | 48–55 | 9.0 / 12.5 | 8 | Trees uprooted; considerable structural damage. Sea surface largely white. |
| 11 | Violent storm | 103–117 | 64–72 | 56–63 | 11.5 / 16.0 | 8 | Widespread damage. Medium ships lost to view behind waves. Sea covered in white foam. |
| 12 | Hurricane | 118+ | 73+ | 64+ | 14+ / — | 9 | Devastation. Air filled with foam and spray; very poor visibility. |
It should also be noted that these scale breaks were largely based on visual or subjective observations—again, not the precise wind data we use today to determine when to change sails. However, one can impress others at the bar after sailing by noting, “That was a real Force 5 we sailed in today!”
According to Mayday! Mayday! Heroic Air-Sea Rescues in Irish Waters by Lorna Siggins, recounting the 1979 Fastnet Race: “The 1979 race started on 11 August. The BBC Radio Shipping Forecast, broadcast at 13:55 that day, predicted ‘south-westerly winds, force four to five increasing to force six to seven for a time.’ By 13 August, winds were reported at Force 6 with gusts of Force 7, and forecasters were predicting winds of Force 8.” Today, one would not expect to hear wind forecasts in anything other than knots, miles, or kilometres per hour—but in 1979 the BBC was reaching back to the British Navy’s roots using the Beaufort Scale.
As weather recording became more and more accurate, it became apparent that certain storms could well exceed the designated Force 12. Currently, the US National Oceanic and Atmospheric Administration (NOAA) publishes an extended Beaufort Scale going up to Force 17: more than 108 knots, 125 mph, or 200 km/h. Reportedly there was a junior meteorologist dispatched to record Force 18 winds—we’ll let you know what he has to say, if we ever find him!
