And even though the leeward pressure is negative and the windward is positive, they both work in the same direction. So now we have a total of 6 pounds per square foot. Each point of the sail has different pressures working on it. The strongest force is at chord depth, where the curve of the sail is the deepest. This is where air flows fastest and pressure drops most.
Force weakens as it moves to the rear and separates.
The direction of these forces changes also. At every point in the sail the force is perpendicular to the sail's surface. The strong forces in the forward part of the sail are also in the most forward direction. In the middle of the sail the force changes to a sideways, or heeling, direction. In the rear part of the sail the force grows still weaker as wind speed decreases, and causes backward or drag direction.