Module 13 - Meteorology
The Beaufort Scale
The Beaufort Scale describes wind force from 0 (calm) to 12 (hurricane). It links wind speed to observed sea and land conditions. For coastal and offshore passage planning, pay particular attention to: Force 4–5 (moderate to fresh breeze, building seas), Force 6 (strong breeze, reef early), and Force 7+ (near gale and above — most cruising yachts should avoid being underway unless very well prepared and shelter is unavailable).
F3
7-10 ktGentle breeze
F4
11-16 ktModerate breeze
F5
17-21 ktFresh breeze
F6
22-27 ktStrong breeze
- Force 0: Calm (< 1 knot), sea like a mirror
- Force 3: Gentle breeze (7–10 kn), large wavelets
- Force 4: Moderate breeze (11–16 kn), small waves, whitecaps
- Force 5: Fresh breeze (17–21 kn), moderate waves, many whitecaps
- Force 6: Strong breeze (22–27 kn), large waves, spray. Reef sails.
- Force 7: Near gale (28–33 kn), sea heaps up. Seek shelter.
- Force 8+: Gale and above. Dangerous for small craft.
Beaufort force lookup
| Force | Name | Knots | mph | km/h | Sailing meaning |
|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | Sea like a mirror. |
| 1 | Light air | 1-3 | 1-3 | 1-5 | Ripples; little drive under sail. |
| 2 | Light breeze | 4-6 | 4-7 | 6-11 | Small wavelets and gentle sailing. |
| 3 | Gentle breeze | 7-10 | 8-12 | 12-19 | Large wavelets; comfortable for many crews. |
| 4 | Moderate breeze | 11-16 | 13-18 | 20-28 | Small waves and whitecaps; good sailing. |
| 5 | Fresh breeze | 17-21 | 19-24 | 29-38 | More demanding; many yachts prepare to reef. |
| 6 | Strong breeze | 22-27 | 25-31 | 39-49 | Large waves and spray; reef early on many cruising yachts. |
| 7 | Near gale | 28-33 | 32-38 | 50-61 | Sea heaps up; most training and family cruising plans should seek shelter. |
| 8 | Gale | 34-40 | 39-46 | 62-74 | Dangerous for small craft. |
| 9 | Strong gale | 41-47 | 47-54 | 75-88 | Severe conditions. |
| 10 | Storm | 48-55 | 55-63 | 89-102 | Very high waves; avoid being at sea. |
| 11 | Violent storm | 56-63 | 64-72 | 103-117 | Exceptional waves and dangerous survival conditions. |
| 12 | Hurricane force | 64+ | 73+ | 118+ | Extreme danger. |
Practice weather decisions
The meteorology module connects wind force, forecasts, pressure systems, fronts, and practical passage decisions.