North Sails Tuning guides- How do sails work?

Rod Davis, drives to windward on Day 1 of the 2008 New Zealand Match Racing Championships Richard Gladwell www.photosport.co.nz

Pressure vectors and flow over a cambered section © North Sails http://www.northsails.com/

Sails are Flexible Wings
It is useful to recognize what a typical sail is. They are normally built from a flexible material in order to allow the sail to work with the wind on either side to allow tacking. This is a significant restriction that prevents many shapes from being built because they would not be able to support themselves in the wind. This leads to the traditional triangular planform of sails, since the material below has to hang from the material above, which eventually is reduced to a point at the top of the mast. So, the problem becomes how to build and operate a flexible sail in the wind to produce a substantial force component to move the boat.

As the restriction that sails support themselves is diminished (full battens and stiffer materials for example), sails can evolve to be more efficient. Their appearance then becomes more wing-like and less sail-like. Analyzing how a sail works as a wing is useful, not just for modern sails that look more like wings, but also for very traditional sails that, while they look like sails, operate very much like wings.

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