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, Sir Francis Beaufort, an Irish admiral and hydrographer.
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, occasional 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 much 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.