How a Sail Works ?
When set at the correct angle to the wind, a sail converts the winds energy into forces,
sideways force, which cause the boat to heel or tip sideways and also a forwards force
Which propels the boat forwards. If the wind splits around the sail, the sail becomes curved like an airplane wing and areas of high and low pressure are created. The area of high pressure moves toward (pushes) the area of low pressure (pulls) and the boat moves forward.
To stop the boat going sideways we use the centreboard.
A boat moves in a windward direction (towards the wind) by forces which are created on both sides of the sail. The forces create a pushing force on the windward side (the positive force) and a pulling force on the leeward side (the negative force), both combined work in the same direction. The negative, pulling is the more stronger of the two forces.