How does a sailing boat work?

Answer 1

Most sail boats use a fore & aft rigged triangular sail, also known as a Bermudan rig.

Assuming this as a normal rig:-

When running before the wind (pointing the same way as the wind is blowing) the sails simply catch the wind like a bag and transfers this pressure to the mast. The pressure on the mast pushes the boat along.

Where Burmudan rig vessels are cleverer than a square rig vessel, is the ability to sail nearly into the wind. Intuition would predict that the wind would push the boat backwards.

Having the wind fine on the bow, will cause the sail to fill with wind on one side and form an aerofoil shape, much like an aeroplane wing.

The wind flows faster around the curved surface causing a drop in pressure.

This imbalance in pressure causes pressure on the mast, drawing the vessel forward.

The wind being on one side like this will also have the effect of pushing the boat sideways. To prevent this happening too much and preserving forward motion an effective keel is needed.

The keel is a blade that sticks out under the boat in a fore and aft plane. Forward motion is alllowed by presenting the thin edge to the direction of travel and sideways movement is prevented by the broad sides of the keel causing resistance.

Sailing across the wind, with the wind on the beam, either side, the sail is set like a wedge. The wind fills the sail and slides off the rear, pushing the mast (and the vessel)forward in the opposite direction.

Answer 2

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