The only way I can think that this would be possible is if the wind was blowing directly onshore?
Edit: thanks for all the well thought out replies. I think I’ve got it figured out know, I’ve always Been a bit confused about ships tacking into to wind and I think the key thing I was missing was the sail being using like as an airfoil creating pull, used in tandem with with the fins/keel .
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when trying to sail towards the direction of the wind you leverage the pressure of the wind against the keel in the water at an angle that will push/pull it sideways to the wind but also slightly into the wind. you’re now making slow progress into the wind but you’re also moving sideways to where you want to go, so you zigzag left and right to negate this sideways movement. much like when you’re hiking up a mountain zigzagging up switch backs, the progress is slow but you get there eventually.
In general, windsurfers sail across the wind – if the wind is from the east, a windsurfer will first travel north, then turn and travel south. The hold their sail at an angle, so it deflects the wind one way, and the wind pushes them the other.
They can tack into the wind if need be, but with a surfboard’s flat shape an no real keel, they aren’t built for it.
I’ve seen a lot of mostly or almost correct answers so I wanted to clarify some things:
First, to answer the original question: windsurfers use lift to sail into the wind. However, you can’t sail directly into the wind. Instead you can only sail about 45° off the wind. If your destination is directly upwind you must zig-zag your way into the wind, called tacking or beating upwind.
This is the same principle of most modern sail powered vessels & vehicles to sail into the wind.
How do you use lift to sail upwind?
There are two different wings using lift to make you go forward.
The first is the sail. As the wind blows over the sail it creates lift, but this lift is mostly pulling sideways on the sail and a little forward.
In the water a fin, such as a keel or daggerboard, is used to generate lift to resist the sideways force from the sails and translate it into more of a forward force.
These forces are in opposite directions but one is above the water and the other is below the water. That makes the boat want to lean towards the direction the sail is pulling. This is why you often see sailboats heeling to one side. Keelboats use a weighted keel to resist heeling. On windsurfers, the sailor provides the weight to counteract heeling.
So why ~45° off the wind?
The exact angle depends on the shape of the sail, but as you make that angle smaller and smaller two things happen. First, with flexible sails, the wind no longer fills the sail so it can’t generate lift. Second, even with a rigid wing sail, the lift force pushes less and less forward, and more and more sideways, and eventually backward.
How do sails and fins generate lift?
What you’ve been told about lift is wrong. The air traveling over the top of the wing doesn’t need to go faster so it can catch up to the air on the bottom; it doesn’t care about the air on the bottom.
Instead, a wing turns the air. Air comes in at one angle and goes out at a different angle. The difference between air in and air out is what gives you lift. The wing shape we are familiar with is just the most efficient at turning the wind.
If you think of lift like this, a sail making lift makes more sense. Wind comes in the front of the sail and is turned by the curve of the sail, making lift.
The fins work the same way, turning water instead of air.
Sooo…no one here got blown into open ocean when windsurfing during offshore winds and can’t get back to shore when the wind suddenly started gusting and you didn’t wear your harness? No one?
You can not go directly into the wind but you can go 45 degrees in to the wind.
Have you ever held the back of a spoon against a running water faucet? It holds it in place even though logic tells you it should not stick the spoon to the water because the water is running away from it. This is called the Bernoulli effect and it’s the same principle why aircrafts fly and sails works.
For a windsurfer, there’s a fin in the water, the air tugs the sail one way while the speed through the water creates an opposite force on the fin.those two balance each other out into forward motion.
People assume you can only sail if the wind is pushing you. Actually, the sail can function as a “wing” with its curve allowing you to sail against the wind. Low pressure on the curve side pulls the ship in the same way a wing provides lift.
Sort of… Basically… Hey its Eli5…
These explanations have some merit, but I think they miss the visual that really made this feel intuitive when I finally got it.
Key point: if the boat was floating on top of the water and didn’t break the surface, it couldn’t go into the wind at all.
With a rudder or fin in the water, you can use the wind coming at you from one side and the water pushing against you on the other to shoot out from between them like a seed that shoots out from being squeezed between fingers.
This way, you can cut a little towards the wind. Not directly towards it, but at an angle, you can aim your sail and rudder so the ship gets squeezed and shoots a little into the wind.
Then you zig zag.
Sailing downwind is rarely done by windsurfers as you would have to stretch the sail out to catch the wind and pretty much only go as fast as the wind is blowing…
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