## If this sail is too deep the fastflowing air will not be able to remainattached after the deepest parr of the sail and itwillseparpte

Different chord depths are important for different wind conditions in order to keep the flow of the wind attached to the sail. As a general rule of thumb, full sails (read lower chord-depth ratios) work better in light winds, and flatter sails (read higher chord-depth ratios) work better in medium to heavy winds. Using a full sail in a lot of wind will cause the fast-flowing air to separate from the sail (Figure 6.2). Flat sails can also work well in extremely light winds since they make it easier for the air to remain attached to the sail. If you try to make the sail too full there is simply not enough wind for the flow to even get around the corner, let alone to the leech.

The chart below gives you some idea of optimum chord-depth ratios for both mainsails and headsails. These are general estimates and should not be cast in stone. There are so many variables among boats of different designs that the numbers need to be manipulated to suit the conditions, but as a jumping-off point, these wind strengths and numbers are a good start.

 Apparent Wind in Knots Headsail Chord Depth 0-2 15-16 percent 3-12 18-19 percent 10-18 16-17 percent 16-23 15-16 percent 20-26 14-15 percent 24 + 12-13 percent Apparent Wind in Knots Mainsail Chord Depth 3-6 15-16 percent 6-12 14 -15 percent 12-18 12-13 percent 18-24 11 percent 24 10 percent

* Courtesy of North Sails

* Courtesy of North Sails

Figure 6.2.

With a chord-depth ratio too high, the flow of the wind cannot remain attached to the sail.

### Figure 6.3

When the wind blows across a body of water the surface friction slows the molecules closest to the surface, which in turn have an effect on those molecules closest to them.

### Figure 6.3

When the wind blows across a body of water the surface friction slows the molecules closest to the surface, which in turn have an effect on those molecules closest to them.