I tried to google it and it left me very confused.
In: 306
A boat angles its sails depending on the direction of the wind. When a boat is travelling *downwind* (away from the wind), the wind is *blowing* on the sails to push the boat.
When a boat is travelling *upwind* the air is *sucked* between the mainsail and foresail, like air around an airplane wing, pulling the boat forward. (Well, technically, pulling the boat sideways but it has a keel underwater to resist lateral movement, so the boat moves in the direction of the pointy end, the bow, because that’s the course of least resistance).
Note, a boat cannot sail directly into the wind (a position called “irons” in which the sails flap, or “luff”), but must instead attack the wind from a slight angle, tacking or zig-zagging back and forth to move along the desired trajectory.
Well, they don’t sail upwind. What they do is adjust their sails so the ship moves at an angle of less than 90 degrees to where the wind is blowing from. They commonly sail in a zig zag pattern , slowly movin “upwind”, but always sailing at an angle.
*Edit for typos
Sail ships have a [big fin](https://keyassets.timeincuk.net/inspirewp/live/wp-content/uploads/sites/21/2015/01/Keel-safety-tips-Keels-Sep14.jpg) underneath called a keel, and the purpose of it is to prevent the ship from being pushed sideways by the wind.
So then, the sails aren’t [like this](https://cdn.boatinternational.com/files/2021/06/dd062130-d346-11eb-922c-a95d91958631-Maltese-Falcon-Superyachts-Monaco-3.jpg) where the wind pushes the ship from behind, they are [like this](https://photo-assets.superyachttimes.com/photo/183202/image/large-19e53079b60be7d27fbca4b11c064372.jpg), where the wind “bounces off” the sail and gets redirected. The effect is that the total force pushing on the boat has a different direction than the wind direction.
So [here’s an image](https://www.kavas.com/media/wysiwyg/sailorsguide/how-sails-work.jpg), the wind is blowing straight down from the top, but as you can see it gets deflected by the sail, so the force on the sail is the yellow arrow towards the lower LEFT corner of the screen. And then the KEEL completely prevents the downward portion of that force from moving the ship, so the only “portion” of the force that’s left is the red force moving the ship forward.
So because ships can [angle their sails](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/Points_of_sail–English.jpg/300px-Points_of_sail–English.jpg) to deflect the wind as it suits them, they can pretty much go even at relatively steep angles against the wind. Not DIRECTLY against the wind though, for that they actually have to zig-zag left and right so that their angle vs. the wind is outside that red cone. This zig-zag maneuver is called tacking.
There are a few different explanations which are all looking at it a different way so let me try one of the less common ones. When wind hits a flat surface it pushes on that surface. If the surface is angled then it will not only push in the direction of the wind but rather push the surface at its angle. You may have experienced this when holding your hand out the open window of a moving car, angling the hand may generate lift upward or downwards. For a sailing boat this means that they can change the angle at which the wind pushes the sail by angling the sail in the direction they want to be pushed, it is however still limited to 90 degrees of the angle of the wind so you can still not sail upwind, only cross wind.
But a sailing ship have two “sails”, there is also the keel. It acts as a kind of sail in the water instead of the air. And you can angle the keel using the rudder. The same way that the angle of the sail determines the angle of the forces from the wind the angle of the keel does the same with the force of drag from the water. This gives another 90 degree change in force direction. When a sailboat is sailing upwind they are therefore angling the sails so the force of the wind push them mostly cross wind but also a bit downwind and then the keel is angled further so that the crosswind forces from the sail is converted to upwind forces. If the upwind forces created by the keel is larger then the downwind forces from the sail the boat will end up sailing upwind.
Press an olive bone between your thumb and index; which direction where you pressing, and which direction did it go flying?
It’s the combination of the angle of the sale and the fact that the keel forces the boat to mostly move in line with the keel. Basically already covered by others, but it’s the combination of both that allow sailboats to tack into the direction of the wind.
Think about squeezing a bar of soap in your hand in the shower. The soap shoots out to the side which is a different direction than you are squeezing.
A sailboat works similarly to sail against the wind. It’s getting squeezed by the wind against the sail on one side and the water on the other. By changing the angle of the sail and the rudder, it can control how it gets squeezed out and angle into the wind.
Okay, imagine you have a sailboat. The sail is like a giant piece of cloth that catches the wind and makes the boat move forward. When the wind is blowing in the same direction as the boat is moving, it’s called a “tailwind” and the sailboat can go very fast. But when the wind is blowing in the opposite direction of the boat, it’s called a “headwind” and the sailboat has a hard time moving forward.
To sail upwind, the sailor has to do something called “tacking.” This means that the sail is not pointed straight into the wind, but at an angle. The sailboat then zig-zags back and forth, going from one side of the wind to the other, to make its way forward. Each time the sailboat changes direction, the sailor has to carefully adjust the sail to catch the wind just right. It’s kind of like how a kite flies when it’s being pulled back and forth by the wind.
So even though it’s hard to sail directly into the wind, sailors can use their skills and the shape of the sail to move their boat forward. It just takes a little more effort and finesse than sailing with the wind.
[It’s called tacking](https://www.safe-skipper.com/tacking-a-sailing-boat/)
Basically it’s just turn the boat at an angle so that you get some wind in your sail.
Let’s start first with an airplane moving forward. An airplane wing is horizontal and its top surface is curved more than the bottom surface. As the air (wind) moves over the wings, because of the curved top the air moves faster over the top surface of the wing than it does over the bottom. The curved top means the air has further to travel. That further distance makes the air move faster. A principal called Bernoulli’s theorem tells us that as the speed of air increases the pressure decreases. So that curved surface of the wing is giving us less pressure on the top of the wing. Less pressure on the top means more pressure on the bottom. This is what creates lift and the plane flies.
Now take that horizontal wing and move it vertically. You now have the same shape as the sail. One side is curved more than the other. As the boat moves into the wind, air moves, faster on one side of the sail than the other, and this creates lift. The wind is essentially pulling the boat forward.
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