If the wind is blowing in one direction, wouldn’t your sails just propel you in that direction? What if you want to go parallel to the wind direction?
I understand sails can move, but wouldnt that just speed up or slow down how fast you go in the direction of the wind?
In: Technology
Sailboats have something called [a centreboard or a keel](https://boatingforbeginners.com/wp-content/uploads/2019/01/keel.jpg). The keel resists the lateral force created by the wind, helping the boat go forward instead of sideways. That being said, boats at certain points of sails do move sideways quite a bit, even with a keel. This is called leeway.
In addition to the keel, sails work more like an airplane wing than a simple pushing object. As you can see in this [image](https://guernseydonkey.com/wp-content/uploads/2019/12/how-sails-work.jpg), wind pass around the sail creating low pressure on one side, and high on the other. This interaction between high and low pressures creates lift in the sail. The yellow arrow in the image represents to sum of the forces, the red arrow is the forward component, and the green arrow is the lateral component. As discussed above, the keel prevent lateral force, which shrinks that green arrow, allowing the boat to mostly travel forward.
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