I realize a sailboat can’t go directly at the wind (or maybe it can🤷🏽♂️) but for the life of me I can’t picture it going anywhere but where the wind is bowing.
Also, lets say you were in a round pond, could you sail to any point you wanted to in the pond with the wind blowing steady in one direction?
In: 34
A boat sails into the wind by using the sail as a wing. Normally, a sail works by being hit with wind and making a push force, but if you orient the sail *into* the window, like edge-on, it creates a lift force, a force side-to-side and not front-back.
So now the boat would want to skitter sideways, so you have to play some angles, you use the rudder and keel to minimize sideways motion. This bit is a little hard to explain without high-school level math and geometry, but you do all of this right, you can angle the sail, the wind, and the boat in such a way that you end up with the boat wanting to be pushed side-to-side *and* get pulled forward *into* the wind. The keel/rudder minimize the side-to-side motion and moving forward into the wind is what you wanted.
You can’t fully minimize the side-to-side skating so after a while the boat will be blown off course, so they basically do the opposite angles and stuff for a while floating the boat back the other way. This process of moving into the wind while being blown back and forth side-to-side is called ~~”tacking~~”.
EDIT – Multiple people have corrected that tacking is something else, the proper term is ‘beating’. Fun fact, I grew up on an island and am an extremely strong ~ semi-competitive open swimmer ~ and sailing terrifies me. Kudos to y’all, I’ll stay over here on my beach chair thank you very much.
The answer is you can’t go directly into the wind but you can to an angle to the wind.
If the angle is more than 45 degrees to the wind you can sail [https://qph.cf2.quoracdn.net/main-qimg-b516ce2f092bcecb0c4db380163c8df8-lq](https://qph.cf2.quoracdn.net/main-qimg-b516ce2f092bcecb0c4db380163c8df8-lq) To go in the direction of the wind you first to 45 degrees to the right on the wind and then turn to 45 degrees to the left of the wind and the net result is you go towards the wind but the distant you need to travel is longer [https://hatterassailing.org/wp-content/uploads/2021/04/download-64.jpg](https://hatterassailing.org/wp-content/uploads/2021/04/download-64.jpg)
You can demonstrate that you can do this at home. Take a toy car or anything else with wheels that can roll in one direction. Put a vertical flat surface on top of it that you can push on. The surface should not be parallel to the car but at an angle. To simulate the wind by moving your finger vertically and moving it in a straight line. Change the direction of the car relative to the direction you move the finger and you will notice when the angle is more than 45 degrees the car will start to move in forward again the direction you move the finger.
There is friction between the toy car and the ground just as it is between the boat and the water so it can only move in one line. It is the combination of the direction of that friction and the force from the wind/finger that determines the direction it moves and it will be forward if the angle is above 45 degrees.
You can compare it to if you push down on a wedge with low friction to what supports it and to your hand. It will move in the direction of the thickest part. If you push down it on an inclined surface it will still move along the surface, if you put the thick part of the wedge pointing up it will move up. This is the same as sailing into the wind, your hand is the wind, and the surface is the friction from the ground/water that stops sideways motion.
They can’t go directly into the wind, but angles of around 40-50 degrees to the wind are achievable for most sailing boats. Sails aren’t just flat sheets, they have a bit of a curved shape to them, thus they deflect the wind a bit. There’s a resultant force on the sail (i.e., sail pushes wind one way, wind pushes back on the sail the opposite way), some component of which is in the forward direction. There’s also a big sideways component, but sailing boats have deep keels / centreboards that create a big amount of sideways drag while minimising forward drag in order to ensure the sideways force doesn’t result in too much sideways movement but the forward component does push make the boat move forward.
In a round pond you can get to any point, but not in a straight line – to go directly upwind you have to set off at 45 degrees to it going left, then change direction and go 45 degrees to it heading right, zig-zagging your way there. If you watch for a few minutes from 1:49 there are several aerial shots showing this (also the curvature of the sail) [https://www.youtube.com/watch?v=BNk7k0f3tPg](https://www.youtube.com/watch?v=BNk7k0f3tPg)
I want to add that there’s a cool effect of *apparent wind* direction, that lets sailboat move even closer to straight into the wind. As the boat accelerates, it generates its own relative wind as it moves through the air. A very fast wind-powered vehicle, like an ice-boat or wheeled wind-cart can shift the apparent wind direction so that it can move within 10 or 15 degrees of straight into the wind. And as it accelerates, the wind speed over the sail increases, the vehicle accelerated even more, generating more apparent wind . . .
It’s exciting.
To sail into the wind, sailboard do something called tacking. This means angling the sail to catch some of the wind, alternating the side of the boat the sale is angled over, and having to sail in a zig-zag path to stay on course. In each case, 1/2 the wind power is sending ship in correct direction and 1/2 is sending it off course, hence the need to flip the sail and zig-zag to stay on course.
in a typical ”Marconi” or “Bermuda” [you would recognize as a triangular shape sail] rig (not an old fashion square sail) the sail acts like an airplane wing and generates lift but pointing sideways (not up like an airplane) that force propels the boat forward.
often the shape of the hull helps, the deep keel (fin on the bottom of the hull) helps stop the boat from sliding [sometimes called skating] sideways across the water and moves it forward instead
a ”triangle type sail boat” {not square sails} can come to or point to about 30 degrees off the wind. this happens because the sails help channel the wind across the other sails.
square sail ships use some of the same physics but not as efficiently, they typically can point to about 70 degrees from the wind
OP, lots of good answers here. If you want to look more into it, look up “points of sail” and how they relate with the movement of the ship.
Also fun fact, the sideways movement you get when going into the wind is called “Leeway” as it is pushing you to the leeward side of the vessel. Since you have a little drift and don’t maneuver exactly on the bow, this is where the term “giving leeway” comes from.
Off topic, but I find it amazing that there are also wind powered wheeled vehicles that can drive upwind and down wind faster than the wind speed!
[https://www.youtube.com/watch?v=u5InZ6iknUM&t=573s](https://www.youtube.com/watch?v=u5InZ6iknUM&t=573s)
This video has a really cool visual explanation.
Modern sailboats can do this to a much greater extent than old sailing ships with the square sails. But essentially the sail creates a wing and creates a “lifting” force. An important part of this mechanism is that the sailboat needs a “keel” which is a solid vertical piece that sticks down in the water to keep it from moving sideways. Not only can it sail at an angle towards the wind, it can actually go faster than the wind.
Imagine a circle around the sailboat, and for the sake of simplicity let’s say the wind is blowing from the top of this circle, and that point is 0 degrees. In a clock face it would be 12. Take two 45 degree slices of that circle, left and right from 0 degrees, which gives us a total slice of 90 degrees, or a quarter of the circle, or to more easily visualise, in a clock face with the wind blowing from 12 o clock the slice would be from 10 to 2. That slice is the area where you cannot point your boat to since it’s either blowing directly opposite to the boat or close to that.
Sailboat sails move the boat through two means. One is that they act as a foil, which is the scientific term for a wing, and the other is that they work through drag, which is what you and most people are familiar with when they’re thinking of sails. When the boat is pointing as close to the wind as possible, the sail acts as a foil. This means that it redirects the wind coming over it and deflects it, which creates a force on the sailboat that’s trying to push the boat diagonally. Underneath the sailboat is a large fin, the keel, which also acts as a foil but it’s much smaller since water is denser so it doesn’t have to be as big as a sail to have an effect. The keel resists the sideways drift of the boat and creates a force that’s perpendicular to that of the sails. So basically it resists the tendency of the boat to drift diagonally. Since the sails produce a force that’s diagonal in relation to the bow of the boat, and the keel produces a force equal to it and diagonal from the other side, the resultant force pushes the boat straight down the middle of those two, so forward.
This effect is dominant when the boat is pointing towards the wind, up until the wind is perpendicular to the boat, so coming from the side. Once the boats steers past that, and starts pointing in a direction closer to the direction of the wind, up until 180 degrees, or 6 on a clock face, the main component of the propulsion the sails create comes from drag, which is that they basically catch wind coming from behind and use the wind’s kinetic energy to move the boat.
Both of these forces are at play in varying degrees depending on the heading of the boat relative to the wind. To sail upwind a maneuver called tacking has to be performed, which is when a sailboat zigzags from left to right and always keeping the wind either 45 degrees to their right or 45 degrees to their left. This means they’re sailing in the general direction the wind is blowing from but not literally.
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