Wind force
Beaufort scale
Slide the wind speed to see the force, the sea state, and a plain-language note for a 17-foot open boat, a 23-foot boat, and a 40-foot boat.
Moderate breeze. Small waves. Frequent whitecaps. A 17-ft open boat feels this wind. Many 23-ft boats are still fine. A 40-ft boat usually has margin. Boat or Nope's default 23-ft profile uses a 15-knot wind limit, inside this band.
| Force | Knots | Name | Sea | On a recreational boat |
|---|---|---|---|---|
| 0 | Under 1 | Calm | Sea like a mirror. | Comfortable for almost any recreational boat. |
| 1 | 1–3 | Light air | Ripples without crests. | Comfortable for almost any recreational boat. |
| 2 | 4–6 | Light breeze | Small wavelets. Crests do not break. | Comfortable for almost any recreational boat. |
| 3 | 7–10 | Gentle breeze | Large wavelets. Scattered whitecaps. | A normal day for most open boats. |
| 4 | 11–16 | Moderate breeze | Small waves. Frequent whitecaps. | A 17-ft open boat feels this wind. Many 23-ft boats are still fine. A 40-ft boat usually has margin. Boat or Nope's default 23-ft profile uses a 15-knot wind limit, inside this band. |
| 5 | 17–21 | Fresh breeze | Moderate waves, many whitecaps, and some spray. | Many 17-ft boats stay in sheltered water. A 23-ft boat is often a caution day. A 40-ft boat may still go, depending on sea and direction. |
| 6 | 22–27 | Strong breeze | Large waves, foam crests, and spray. | Small-craft-advisory weather on many coasts. Most recreational boats treat this as a stay-in day. |
| 7 | 28–33 | Near gale | Sea heaps up and foam streaks. | Gale-force planning weather. A No-Go for the boats this site is built around. |
| 8 | 34–40 | Gale | Moderately high waves with breaking crests. | Gale. Stay in harbor. |
| 9 | 41–47 | Strong gale | High waves and dense foam. | Stay in harbor. |
| 10 | 48–55 | Storm | Very high waves. Overhanging crests. | Stay in harbor. |
| 11 | 56–63 | Violent storm | Exceptionally high waves. | Stay in harbor. |
| 12 | 64 or more | Hurricane | Air filled with foam and spray. | Stay in harbor. |
A force is not the harbor call
The same force 4 can be a pleasant reach on a 40-foot boat and a wet ride in a 17-foot skiff, depending on fetch and whether the wind is against the tide. Boat or Nope's harbor page applies your wind, gust, and sea limits to the forecast for that water.
Beaufort questions
What is the Beaufort scale?
The Beaufort scale is a 0 to 12 wind scale. Each force has a wind-speed band and a sea-state description. NOAA and the National Weather Service use it as a reference for how the wind looks on the water.
What Beaufort force is 15 knots?
15 knots is force 4, a moderate breeze. That is the wind limit on Boat or Nope's default 23-foot boat profile. Gusts and wave period can make the same force feel very different.
Is a Beaufort number a go or no-go decision?
No single force fits every boat. The notes here are context for a 17-ft open boat, a 23-ft boat, and a 40-ft boat. The harbor page applies your own wind, gust, and sea limits to the forecast.