Bernoulli's principle is that the air moving past a foil, an object that has one curved side and one flat side, will take longer to move past the curved side than the flat side of the foil. This will cause the flat side to have higher air pressure and to exert a force on the object. The force cause a planes wing to lift and a sail to push a boat. "With the wind pushing on one side of the sails and the water pushing on the other side of the centerboard, the boat moves forward." (p. 35, Dellenbaugh)

The angle at which sailing is important. A 45 degree angle to the wind is the most effective angle.

photo taken by Susan Underbakke