Leading Edge Angle

The very front of a sail, called the leading edge, is the part of the sail that first comes into contact with the wind and therefore is vital to overall aerodynamic shape. It is here, especially with headsails, that the sail generates its power since it is the first place that the wind comes into contact with the sailplan. The obvious goal of the sail designer is to create a sail with an angle of entry that facilitates a smooth introduction of the flow of air over the sails, i.e., the front of the sail should be directly in line with the wind. But as is so often the case with sails, this is not quite as easy as it sounds and involves a number of trade-offs.

For example, if a sail has a fine entry then the boat should be able to sail closer to the wind, so why would anyone choose anything else when the basic goal of sailing to windward is to steer a course as close to the wind as possible? Actually there are a number of reasons, including the fact that the angle at which the sail starts out will have an effect on the rest of the camber of the sail (Figure 6.8), which can result in a number of unintended consequences. Take, for example, two sails with an identical chord length. If the designer wants to keep the area of maximum draft in the same place in both sails, then a sail with a fine entry will end up being flatter (higher chord-depth ratio) than one with a rounder entry (Figure 6.9 on next page). Along these same lines, if he wants to keep the chord-depth ratios the same, the sail with the fine entry will end up having the area of maximum draft further aft while the draft will be forward with

Figure 6.7

The sail designer's job is to create a perfect sail with smooth transitions in the right place - from flat down low to full toward the top.

VERTICAL DISTRIBUTION OF DEPTH

Sailsare full up high

Figure 6.7

The sail designer's job is to create a perfect sail with smooth transitions in the right place - from flat down low to full toward the top.

Sailsare full up high

Figure 6.8

The angle at which the sail starts out will have an effect on the rest of the camber of the sail.

DRAFT FORWARD SAIL

Point of Maximum Draft

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