Wind Speeds and Required Sails
Beaufort scale        Speed  knots         mph, km/h        sail lore
0  calm            <1                <1            no steering way
1 light air            1-3                1-3, 1-5        just steering way
2 light breeze        4-6                4-7, 6-11        full sail, 1-2 knots
3 gentle breeze        7-10                8-12, 12-19    full sail, 3-4 knots
4 moderate breeze    11-16            13-17, 20-28    full sail, 5-6 knots
5 fresh breeze        17-21            18-24, 29-38    + royals
6 strong breeze        22-27            25-30, 39-49    + full topgallants
7 high wind                28-33            31-38, 50-61    + reefed topgallants
8 gale                     34-40            39-46, 62-74    + topsails
9 strong gale        41-47            47-54, 75-88    + reefed topsails, courses
10 storm            48-55            55-63, 89-102    + double reefed topsails and reefed courses
11 violent storm        55-63            64-73, 103-117         storm sails only
12 hurricane        => 64            => 74, => 118    no sails