Beaufort Scale
of Wind Speeds
Before electronic instruments, the British Navy developed a means of estimating wind speed by its effect on the water. It became known as the Beaufort Scale for its author.
Portsmouth Handicaps are wind-strength dependent; in Sailwave it is necessary to input wind strength here is a brief explanation of the Beaufort Scale
| Beaufort Scale | ||||
| BN | Knots | MPH | Term | Sea Conditions * |
| Light Air | ||||
| 0 | 0-1 | 0.0-1.7 | Calm | Glassy |
| 1 | 2-3 | 1.8-4.0 | Light Air | Small Ripples |
| 2 | 4-6 | 4.1-7.4 | Light Breeze | Small, short waves, glassy crests |
| Moderate Air | ||||
| 3 | 7-10 | 7.5-12.0 | Gentle Breeze | Large wavelets, crests start to break, occ. foam |
| 4 | 11-16 | 12.1-18.9 | Moderate Breeze | Small waves, some whitecaps, |
| 5 | 17-21 | 19.0-24.7 | Fresh Breeze | Better formed waves, many whitecaps, some spray |
| Heavy Air | ||||
| 6 | 22-27 | 24.8-31.6 | Strong Breeze | Large waves, many whitecaps, more spray |
| 7 | 28-33 | 31.7-38.5 | Moderate Gale | Sea heaps up, streaks of foam, spindrift begins |
| 8 | 34-40 | 38.6-46.6 | Fresh Gale | Mod. high long waves, streaks of foam |
| 9 | 41-47 | 46.7-53.9 | Strong Gale | High waves, sea rolls, spray affects visibility |
* The table above gives the standard scale. Conditions on small lakes at altitude are usually less severe for the wind strengths indicated. Two factors explain this:
(1) The air is less dense than at sea level, so contains less mass & thus energy. (9% less at 5,000 ft.; 17% less at 9,000 ft.)
(2) "Fetch" (the distance the wind travels over the water, creating disturbance) is less.
But for Portsmouth handicapping, these differences between sea & lake are technical and can be ignored without difficulty. Use the Beaufort number indicated by the water conditions.