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 .
In: 341
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.
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