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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Sailing ships, and windsurfers, can make progress upwind by tacking.
Say the wind is coming from the north. The ship can sail as close to the wind as northeast or northwest. So if it alternates, first going this way and then that, the *net* movement will be north.
well, luckily the majority of the time the wind IS blowing generally perpendicular to the shoreline due to a phenomena called the land-sea breeze.
but, even if that isn’t the case wind surfers CAN “sail” into the wind by zig zagging back and forth at 45 degree angles from the wind.
When they do this, they use the wind to push them left or right, so the kite/sail is still getting blown by the wind. But then they angle the rudder of the board at a 45 degrees angle, so as the wind blows their sail to the right, the rudder is directing the surfer both to the right AND forward into the wind.
Mostly windsurfers sail across the wind, not down-wind (or up-wind). Going across the wind you can still head fairly high to windward to overcome the wind pushing you downwind.
When sailing toward the wind, you are being **pulled** by it instead of pushed.
A windsurfer, like all modern sailboats, can ”sail into the wind” because the shape of the bent sail works like an **airplane wing** (except its turned vertically). When the wind flows faster on the outside of the sail than the inside, it creates “**lift**” (like an airplane) except the lift is pulling the boat forward instead of up. The keel on the bottom of the boat, which is like a upside down shark fin, works kinda like the tail of an airplane, and keeps the boat from being pushed sideways.
Windsurfers (and sailboats) cannot sail directly towards the wind, they have to **zigzag**, because there is no lift from the sail unless it is angled somewhat. I know this sounds unbelievable, but so does the flight of an airplane until you understand how a wing works.
Modern sails don’t push you along, they pull the same way a wing creates lift. As long as the sail is full, you can head almost directly into the wind.
The other answers are all correct, but windsurfers generally don’t sail in offshore winds for safety reasons in case of a breakdown.
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Windsurfers generally start out with their backs to the wind and then sail 90degrees or 270 degrees (perpendicular direction) to the oncoming wind. To come back they just do a 180° turn (called a tack or gybe) and come back .more or less from where they started (assumes the wind direction doesn’t change radically in the mean time)
They can streer close to the wind if they want to go upwind or away from the.wind to goote downwind, but most of the time they’re sailing back and force relative to their beach starting location.
Sails are never fully flat, but slightly curved. Turning the sail sideways to the wind the wind then flows over both sides of the sail. It has a long path on the outside of the curved sail, and a short path on the inside of the sail. The “faster” bit of air leaves underpreasure where new air is sucked into.
Imagine standing on a skateboard with a massive vacuum cleaner pulling you forward.
As others have said, the sail acts like an airfoil or wing that interacts with the “apparent wind” (true wind plus relative motion of the boat) to create a pressure differential between the two surfaces of the sail. Which generates a force.
The keel on a sailboat or sailboard is absolutely essential, as it *also* acts like a wing down in the water, which works to mostly “cancel” the force that would push the boat sideways as well as a righting moment to keep it from just tipping over, so that only the forward force remains to push the boat forward.
Remove the keel, and the boat/board will just blow mostly downwind!
But with the keel and the forward momentum of the boat, the forces on the sail allow you to sail across the wind, and even at an upwind angle. Some well designed racing boats can sail as close to 20-25 degrees off of directly upwind!
The “apparent” wind speed/direction due to the motion of the boat allowing it to sail perpendicular to the wind at faster than the “true” wind speed sort of seems like it should violate physics, but there *is* a mathematical solution that shows momentum and energy are still conserved. The key is to realize you are balancing wind forces, not wind speeds.
It is however, a surprisingly devious and non-intuitive physics problem! It starts to make sense when you realize an airplane operates on the same principle, generating lift by interacting with the “wind” from its own forward motion, even in dead calm weather.
To give you an idea of the complexity, my college physics class normally had a problem set each week with 5-10 problems to solve, but one week during the term, we were instead given a single physics problem – the infamous “sailboat problem” to solve, open collaboration with other students in the class, and It was *by far* the hardest problem “set” of the entire year, at least until we started into quantum physics!
Here’s a decent explanation if you want to get into the weeds.
https://www.real-world-physics-problems.com/physics-of-sailing.html
Also, if you want your mind blown by another nautical aerodynamics problem, look up “Magnus Sail” and the “Magnus effect”
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