Sail Plan
Beaufort Scale, Wind Speed and Pressure
| Force | Wind Speed mph | Wind Pressure g/cm.sq | Description | Specification |
|---|---|---|---|---|
| 0 | 0 - 1 | Calm | Sea like a mirror. Calm; Smoke rises vertically. |
|
| 1 | 1 - 3 | 0.01 (2) | Light Air | Scale like ripples, no foam crests. Wind direction shown by smoke drift. |
| 2 | 4 - 7 | 0.06 (5) | Light Breeze | Small wavelets, no breaking crests. Wind felt on face, leaves rustle, wind vanes moved by the wind. |
| 3 | 8 - 12 | 0.24 (10) | Gentle Breeze | Large wavelets, foamy crests begin to break, some white horses. Leaves in motion, light flag extends. |
| 4 | 13 - 18 | 0.54 (15) | Moderate Breeze | Small waves, frequent white horses. Raises dust and loose paper, small branches move. |
| 5 | 19 - 24 | 0.98 (20) | Fresh Breeze | Long moderate waves with many white horses, small trees sway. Crested wavelets on inland water. |
| at 30 m | (at mph) |
Sail and Winch Loads in a Force 4
| Sail | Area cm.sq | Sail Force (1) | C of E A | Tack B | M.A. (3) | Winch kg (4) |
|---|---|---|---|---|---|---|
| Main - Full | 2640 | 1.32 | 26 | 50 (2) | 1.9 | 0.69 |
| Main - 1 Reef | 2070 | 1.04 | 25 | 50 (2) | 2.0 | 0.52 |
| Main - 2 Reefs | 1510 | 0.76 | 23 | 50 (2) | 2.2 | 0.32 |
| Topsail | 670 | 0.34 | 11 | 25 | 2.4 | 0.14 |
| Jib | 770 | 0.39 | 7 | 21 | 3.0 | 0.13 |
| Staysail | 613 | 0.31 | 6 | 25 | 4.2 | 0.07 |
| Yankee | 620 | 0.31 | 9 | 20 | 2.2 | 0.14 |
C of E = Centre of Effort of the sail shown by the +. Distance from luff or mast centre.
Tack = Distance of Tack from luff.
Winch = Sheet load on Winch in kg at Clew E. Double for force 5 and halve for force 3.
(1) - Sail Force in Kg calculated for a Force 4 wind using 0.5g/cm.sq.
(2) - Distance of main sheet E from mast centre.
(3) - M.A. - Mechanical Advantage = B/A
(4) - Sail Force / M.A. = (1)/(3)