22 Oct The Beaufort Scale: How to Measure Wind Force at Sea

Welcome back to the Marina Puerto Sherry logbook! If there is one element that dictates the rules of the game in sailing, it is the wind. In this guide, we are going to explore the fundamental tool to understand its behavior: the Beaufort Scale.

Knowing how to interpret this wind scale is not just maritime culture, but a vital safety matter. We will explain what it is, what it is used for, its relationship with the Douglas Scale, and answer the eternal question of novice sailors: when is it considered a strong wind?

What is the Beaufort Scale and what is it used for?

The Beaufort Scale is an empirical system used internationally to measure wind force, based on the state of the sea (its waves and foam) and its effects on land surfaces.

Unlike an anemometer that gives you an exact number, this wind scale provides a practical, visual, and standardized way to describe wind speed and its impact. It is primarily used so that sailors, meteorologists, and rescue services speak the same language. By categorizing the winds (the famous BFT wind), it facilitates the interpretation of VHF radio weather reports and allows the crew to anticipate dangers.

The Origin: Sir Francis Beaufort

This Beaufort scale was devised in 1805 by the hydrographer and British Royal Navy officer, Sir Francis Beaufort. At that time, sailors used very subjective terms to describe the weather (“stiff wind”, “gentle breeze”). Beaufort standardized this by relating the wind force to the behavior of a frigate’s sails, creating a tool that today, over two centuries later, we still use.

Key Difference: Beaufort Scale vs. Douglas Scale

One of the most common mistakes is confusing the wind with the swell. While the Beaufort Scale measures the speed and force of the wind, the Douglas Scale is used exclusively to measure the state of the sea, that is, the height of the waves.

Although they usually go hand in hand (a lot of wind usually generates large waves), this is not always the case. You can have a Force 6 wind on the Beaufort scale in a protected bay, but the sea might only be rippled (low Douglas). Knowing both scales makes you a much more prepared sailor.

Beaufort Scale Table: Categories and Effects

Below is the complete Beaufort table (from 0 to 12). You can save this page or export it as a Beaufort scale PDF to always carry it in your boat’s logbook. It shows the equivalence of the Beaufort scale in knots and kilometers per hour.

BFT	Description	Speed (Knots)	Speed (km/h)	Effects at Sea (Beaufort Sea Scale)	Effects on Land (Beaufort Wind Scale on Land)
0	Calm	< 1 knot	< 2 km/h	Sea like a mirror.	Smoke rises vertically.
1	Light Air	1 – 3 knots	2 – 5 km/h	Ripples with the appearance of scales, no foam.	Direction of wind shown by smoke drift.
2	Light Breeze	4 – 6 knots	6 – 11 km/h	Small wavelets, crests have a glassy appearance.	Leaves and small twigs in constant motion.
3	Gentle Breeze	7 – 10 knots	12 – 19 km/h	Large wavelets, crests begin to break.	Leaves and light flags flutter.
4	Moderate Breeze	11 – 16 knots	20 – 28 km/h	Small waves, becoming longer; fairly frequent white horses.	Raises dust and loose paper; small branches are moved.
5	Fresh Breeze	17 – 21 knots	29 – 38 km/h	Moderate waves, many white horses are formed.	Small trees in leaf begin to sway.
6	Strong Breeze	22 – 27 knots	39 – 49 km/h	Large waves begin to form; the white foam crests are more extensive.	Large branches in motion.
7	Near Gale	28 – 33 knots	50 – 61 km/h	Sea heaps up and white foam from breaking waves begins to be blown in streaks.	Whole trees in motion; inconvenience felt when walking.
8	Gale	34 – 40 knots	62 – 74 km/h	Moderately high waves of greater length; edges of crests begin to break into spindrift.	Twigs break off trees; generally impedes progress.
9	Strong Gale	41 – 47 knots	75 – 88 km/h	High waves; dense streaks of foam along the direction of the wind.	Slight structural damage occurs.
10	Storm	48 – 55 knots	89 – 102 km/h	Very high waves with long overhanging crests.	Trees uprooted; considerable structural damage.
11	Violent Storm	56 – 63 knots	103 – 117 km/h	Exceptionally high waves; sea is completely covered with long white patches of foam.	Widespread damage.
12	Hurricane	> 64 knots	> 118 km/h	The air is filled with foam and spray; sea completely white with driving spray.	Catastrophic destruction.

How much is too much wind and when is it considered a strong wind?

One of the most frequent doubts among novice sailors is: “How much wind is too much to go sailing?” or “Is a 38 km/h wind a lot?”

The answer depends on the crew’s experience and the type of vessel, but based on the Beaufort Scale, we can establish these general rules:

1. Moderate Wind (Force 4 – up to 28 km/h): This is the ideal condition to enjoy sporty and fun sailing. The boat heels, moves at a good speed, and maneuvers are controllable.
2. The Caution Limit (Force 5 – about 30 to 38 km/h): To the question of whether a 38 km/h wind is a lot, the answer is yes, it is starting to become considerable. In a recreational sailboat, this requires reefing (reducing sail) and keeping the crew alert. The sea will have abundant whitecaps.
3. When is it considered a strong wind? (Force 6 or higher – over 39 km/h): From Force 6 (Strong Breeze) onwards, we enter strong wind territory. Navigation becomes demanding and exhausting. If you don’t have much experience, it is time to return to a safe port.

Importance of the Wind Scale in Modern Sailing

Even though today we have digital anemometers and sophisticated satellite weather stations, the Beaufort scale remains irreplaceable.

Weather bulletins broadcasted by Maritime Rescue via VHF radio always use the wind force in Beaufort degrees and the Douglas Scale for the state of the sea. If the radio operator announces: “Attention all stations, forecast for the Bay of Cadiz: Southwest wind force 6 to 7, rough sea increasing to very rough”, you must instantly know what to expect.

Knowing this table will allow you to adapt your vessel, ensure the safety of your crew, and above all, enjoy your passion for the sea with total responsibility.

The best home port, no matter how hard the wind blows

At sea, a good sailor doesn’t fight the wind: they simply adjust their sails and choose the right mooring. Whatever force the Beaufort Scale shows today in the Bay of Cadiz, your vessel deserves to be in the best hands.

If the forecast announces an ideal breeze (Force 3 or 4), our facilities are the perfect starting point to cast off and give it your all in our vibrant regattas and competition calendar.

On the contrary, if the weather reports announce a storm and you need a safe haven, Marina Puerto Sherry offers you maximum protection. We are much more than a marina; we are a comprehensive nautical ecosystem prepared for any scenario.

Take advantage of the days when the wind is not favorable to pamper your boat in our technical boatyard, or disconnect in our exclusive hotel and dining area while you wait for the sea to calm down.

Don’t leave your peace of mind at the mercy of the weather. Make sure you always have the best facilities to return to and book your berth in El Puerto de Santa Maria today.

Frequently Asked Questions (FAQ)