Sailing Theory

In a sailboat you play an extremely active role in harnessing the energy that propels you through the water. It is easy to see how a boat can sail when it is going in the same direction as the wind: the sails catch the wind and push the boat forward. But how does a boat make progress sailing across the wind or even towards the wind? Why doesn't a sailboat always get blown with the wind?

Very simply, the forces of the wind on the sails and the water on the underwater parts of the boat combine to propel the boat throught the water. The wind blows across the sails, creating aerodynamic lift - similar to that of an airplane wing. The lift contains a sideways force and a small forward force. Adjusting the sails to the most wind efficient posistion produces the most forward force and the least resistance.

A sailboat would slide sideways with the wind if it did not have any appendages underneath it that prevented it from sliding. These appendages, the keel or centerboard, and the rudder, create an offset of the sideways movement which transmits the energy into a forward movement of the boat.