How Does A Sailboat Actually Work?

[@OJsY]

"What could make a ship go forward if the wind's coming from the side?" "An engine" clever.

[@kinga1925]

bro where tf is all of your replies

[@theflamekeeper6670]

Lol

[@mogasesegopotje8483]

​@@kinga1925looool, good question. 😂😂😂

[@joemamaligmaballs7737]

let that dude think about his life 10 years ago

[@madcat97]

What about in the past when they had no engines

[@TheShoreman1]

This is the first episode of Veritasium that I have watched where I feel like I did not really learn anything. I love the channel and this is a great subject. Lots of physics involved. I wish that you would revisit this subject in the future some time.

[@idle3719]

Ccccccccc

[@prisminc158]

Yeah me too.

[@industrialdonut7681]

Oh, he used to have a lot of shitty videos lol.

[@immanuellasker4273]

well, the base is the "Bernoulli law" that is true for any modern boat sailing with an orientation of the sails included between "close-hauled" to "broad reach", depending on the direction of the wind. In all these directions the sail, due to its shape, reacts exactly like a wing, having low pressure on the outer side and high pressure on the inner side (as Bernoulli predicted). No way that any boat can go faster than the wind!... unless the hull gets completely out of the water, like in more recent boats, thanks to particular shapes of the hull and to the introduction of foils. (this is what they missed to explain in the video). What happens, in this particular modern and marvelous boats, is that the sum of the real wind with the relative wind generates a sum of vectors that increases the pressure on the sails BUT, at the same time, modifies the angle of the wind compared with boat's direction. The boat then, in order to use this additional power, must progressively tighten the sails to adjust them to the new wind direction. As a final result, the boat keeps accelerating until it reaches the "close-hauled" orientation (about 30° compared with the direction of the relative wind) that is the limit over which the boat cannot tighten the sails anymore without loosing power (stall). Finally when the boat is running "downwind", with the wind exactly behind, the sail stops acting like a wing and becomes more similar to a sack or to a round parachute: in this position the maximum possible velocity is equal to the wind speed (not considering the resistance of water on the hull). So, contrary to the popular belief, wind in the stern is the worse solution possible for a sailing boat.

[@syrrysaver2775]

TheShoreman1 I don't disagree but, he linked to videos that explain the physics. This seems to be aimed sort of at being a landing vid for new viewers vs really adding content for those already indoctrinated

[@willgordge6003]

The modern sailboat is one of the purest most beautiful applications of mechanics. The video failed to describe this very well. As the wind provides a pressure gradient between both sides of the sail, the force exerted generated by the lift is somewhat parallel to the of the boats boom. Why does this not cause the boat to drift off in that direction? The center board that protrudes the bottom of the hull causes an opposite effect to take place. The force with the wind opposes the force in the water, which is stationary. The two forces can be visualized as vectors on a vector diagram. These two forces create a resultant vector, in the direction in which the boat moves, which is a single component representing the effect of all other present vectors. For those of you who know sailing, you might know now why a broad reach (135° from oncoming wind) is the fastest point of sail, not because of the wind behind generally behind the sail, but because the vectors point nearer to the direction of motion (increasing the value of the resultant) than at any other point of sail.

[@my-days-co]

thank you. but that leads me to a question, it seems that vector also has a degree point upward, let assume it is 20 degree, would it change the acceleration rate or how do we value that speed?

[@shananagans5]

My dad was an Air Force engineer when I was a kid & he fully explained how wings work etc. When we took up sailing, I was about 12. We took a beginning sailing course to learn all the knots & rules of the road etc. Anyways, my dad had already explained wings to me & he showed me how the sails work like wings. As far as that aspect of sailing, we were way ahead of the rest of the class. I thought it was really cool because the teacher would draw a boat on the board & indicate the direction of the wind & then ask the class who knew how to set your sails. I got up every time & drew the sails in & explained how the boat moved on the point of sail. lol I was 12 & up there explaining it to a class full of adults. I thought that was really cool. Once you understand the basics, it's not really complicated but it made me feel smart & was a big boost to my confidence.

[@JulienNeel]

Very interesting and intriguing video! I love it when physics get counter-intuitive like this, yet with a little effort, you can understand what's really going on. I think you could have spent a little more time in your video explaining how it all works. The segment was a little short and quick on that point.

[@JulienNeel]

I don't find the question obvious at all. I never learned the physics of sailing in school, and I have some background in math & physics.

[@jean-alexandreamat4038]

It would be nice if you remade this video, you make them much better than you used to! Big fan, I look forward to all your new videos!

[@veritasium]

OK, I recognise the last vid may have been confusing. Bernoulli is fine if you don't make simplifications like 'air meets up at the trailing edge,' and 'air does not need to be deflected by its interaction with the air foil.' This is what I was trying to say. And the reason I made that vid was so there would be backup for this vid because I knew we didn't have time to go into lift in detail in this vid.

[@alainbellemare2168]

Wake me up when the survey is over and he actually get to the point

[@simon4043]

My aerospace engineer son tells me that the "convex wind speed higher leading to lower pressure" theory is incorrect. He says that no lift occurs without deflection of the airstream. A helicopter blade can spin as fast as it likes, but goes nowhere unless the blades are angled to generate downdraft. The traditional theory always bothered me as, unlike a planes wing, the concave surface of a sail is actually the same length as the convex, so the airstream velocities should be the same

[@keiyakins]

I hadn't internalized the physics, but it really doesn't take long to learn how to sail a small boat. Like, a week is enough if you have a good teacher. And then for the rest of your life you curse at Nintendo for getting it wrong in The Wind Waker.

[@TheUglyGnome]

+Keiya Bachhuber You don't need a teacher. I learned by myself in one afternoon when I was something like 10 years old. All you need is a sailing dinghy and desire to understand how the things work. Of course it didn't make me a top class racing sailor ... but my passion on sailing (created in that one afternoon) helped other guys to win an olympic gold medal on sailing years later.

[@jasexavier]

I used to teach sailing at a summer camp to kids mostly 11-13 years old. They would usually be sailing within an hour, and sailing well enough to go out by themselves in small craft and get where they wanted to go within a couple of days with 90 minute classes each day. You are correct, it's not that difficult to learn the basics.

[@jasexavier]

Oh, and yeah, I really wanted to love Wind Waker, but just couldn't stand the wrongness of the sailing.

[@jeremystanger1711]

Ironically, there's a decent chance Nintendo did that intentionally to avoid confusing players. (And of course being able to travel in any direction no matter the wind direction would kind of weaken the central game mechanic, but let's not worry about that :P)

[@iwillwatchyourbacknooneels7850]

You can learn it in a day but you the more difficult part is getting ur boat ready alone bc if im not wrong sometimes camps do it for the kids but learning how and where all the cables and how to put on the sail can be difficult depending on the boat but yeah in the end when ur on the water its pretty easy u just have to tell them some safety things bc of the metal pole they might get hit in the head with

[@spacepirateivynova]

My father had me on a sailboat from an early age, and one thing i learned more than anything else is that you use the sails to push the keel against the water in different ways to create the pressure to 'go faster than the wind'. Water currents also come into play. Moving into the wind requires 'tacking' back and forth sometimes depending on the wind conditions.

[@FlyntofRWBY]

4:03 That was the most uninterested response I've ever heard xD

[@prashanthshyamala9713]

Unsolved Paradox Thats called EGO!

[@prashanthshyamala9713]

Unsolved Paradox Thats called EGO!

[@noaha8915]

+Prashanth Shyamala That doesn't really have much to do with ego... He simply wasn't interested in the topic, but wasn't trying to appear rude.

[@prashanthshyamala9713]

Noah A That uninterested-ness came out of his ego and for you-- its uninterested to you bcoz of your mind-makeup man. I wonder if its so uninterested why do you take interest in responding-- interesting! Anyways,

[@noaha8915]

Prashanth Shyamala What are you talking about? "I wonder if its so uninterested why do you take interest in responding-- interesting!" I never said I found it uninteresting... I said he wasn't interested. I found the thread interesting, so I contributed to it. Simple. Forgive me if I'm misunderstanding something here, but your grammar does confuse me somewhat. And I think it's wrong for you to make assumptions about him like that... It seems very judgmental of you. It doesn't necessarily come from his ego; sometimes it's hard to give enthusiastic responses when you aren't interested. At the very least, it's apparent he was trying to be polite, which suggests he doesn't have a large ego. If he did, he'd have said something more along the lines of "Yeah, whatever, I really don't care."

[@veritasium]

Thank you! It was clear in my head but I know it was fast.

[@thtkk]

How is that comment still not liked or replied by a single person for 7 years lol i am the first one

[@theshocktart]

@@thtkk Then I am the second ^_^

[@gaijingojira3601]

@@theshocktart Then I am the third

[@B5Scheuert]

​@@gaijingojira3601then I am the sixth

[@lhabubu]

@@gaijingojira360110 years later and I’m the 7th

[@daanbos5918]

Whit the wind is actually one of the slowest Because the sail is only pushing the boat forward instead of pulling it forward

[@tmrossello]

Hi Derek, I think you got the last one wrong. The boat is fastest not at 45 or 90 degrees but somewhere around 135 degrees. Sailing in this direction and thanks to the position of your sails you still have a laminar flow of wind on both sides of the sail, which generates lift (which doesn't happen when sailing at 180°) and in addition more lift gets generated underneath the hull, which causes it to raise higher from under the water, grateful reducing drag on the hull. Therefore 135° would be the fastest direction to sail.

[@moaerdo1357]

Derek’s idea works In a theoretical world where you have enough ballast or counter weight to overcome the lateral force on a course 90° to the wind. Some boats like the international canoe or the amac moth mk2 sail fastest around 95° to 100° relative to the wind.

[@BobElHat]

I'm not sure if you'd call it sailing as such, but you can link a propellor via a gearbox to the wheels of a land yacht and go directly downwind faster than the wind, powered only by the wind. It's counter-intuitive but it's theoretically sound and has been practically demonstrated. In theory you could do the same with a boat by linking your "sail" propellor to a "drive" propellor in the water, but in practice I expect you'd have too much drag from the hull in the water.

[@scythedd7]

As a sailor, I'd have to disagree with his conclusion of 90-45 degrees off the wind being the fastest point of sail, at least with most boats. The fastest most boats goes is when they're broad reaching, or about 110-160 degrees or so off the wind. I don't know the physics behind it, but I know it's enabled partially with a combination of using wave action, being able to put up large, parachute-like sails called spinnakers which can't be used sailing upwind, and the all important ability to plane, which greatly reduces drag. Also, since the centerboard is less necessary when headed in that direction, some boats allow it to be retracted, thus reducing drag even more. Some super high performance boats may act differently, but with most traditional boats, it simply isn't true. For example, a boat I typically sail on, the Melges 24, can, in let's say 20 knots of breeze, go about 6-8 knots beating upwind, but can get up to speeds of 12-15 knots while reaching back down wind with it's chute up,

[@MrJeanelgato]

thank god some actual know how!!! the reason you sail faster as you come off the wind from a fetch to the reach and finally broad reach is because of the fatt that the boat lift generated by the sail and keel starts to move from a right angle to the wind when close hauled to more in line with the direction of course as when you are broad reaching the lift angle is almost the same direction as the direction of travel. have a look at your polars on your white sails and you will see it beautifully illustrated

[@edwardlittle9362]

Depends on the boat, depends on the wind, depends--as you pointed out--on the sail plan. On a typical 10-12 knot day in San Diego my Ghost 13's optimal point of sail is just below a close reach. As the breeze freshens, the optimal point of sail works its way down. At around 18 knots, that boat flat hauls the mail on a broad reach. All that's a bit nuanced for a four-minute video intended for a mostly non-sailing audience. He could have said a boat's fastest on a broad reach and left it at that.

[@Sugarsail1]

Depends on the boat, the sails it's using AND the true wind speed. Most catamarans sail fastest on a beam reach (90 degrees) but only in light to medium winds, as the true wind speed increases, sailing lower is faster (130-135).

[@Naarden4ever]

I've done some race sailing myself as well on various sizes of boats (catamaran up to 42 feet) and I can tell you that your explanation is partly true, but it really depends on the boat, the size, the shape of the hull, the depth of the keel and the weight. The story told in the video is true for a very lightweight boat with low friction (such as a catamaran). The lift generated is easily able to lift almost all of the hull out of the water, especially when the keel is designed to create lift in the water as well (like the curved keels you see in top level catamaran racing nowadays). In extreme cases and high speeds, these boats can actually plane on their keels alone. These boats easily exceed the speed of the wind. Watch some Olympic Catamaran or Finn racing to see an example. Bigger boats can still go pretty fast upwind, but they will definitely not exceed it; the weight of the keel pulls down a lot of the hull which in order creates a lot of friction with the water, in which case hoisting a spinnaker and going downwind is definitely faster, especially if you can plane (but for big/heavy boats that requires seriously heavy wind). For the biggest boats, making a surf (which means having downwind and riding a wave) is the best way to win time. Going downwind with a spinnaker with the 35 footer I sail right now in 20 knots will take me up to maybe 9-10 knots, but when I make a surf that can jump up to 13-14 knots easily.

[@miniberserker]

that guy actually did not explain anything at all... wtf.

[@thepussygrabbingfamilyvalu557]

+Clark Eom totally. the sail guy repeats the bernouilli stuff we all learnt in middle school. he should know better.

[@RForReversal]

+Clark Eom it made sense to me...

[@monsieurbernoulli8101]

+Carl Coppens u wat mate

[@Paulo_Dirac]

asking question is at least as valuable as answering them ;) it rises awareness

[@philipfahy3589]

Essentially a sail works as a sideways wing.

[@andrea7mares]

who’s here from the Blackbird (wind car) video?

[@teletesselator]

Oops, this is the first video where you are mistaken. I've watched about 70 of your videos so far. The sail does not act like a ridged wing structure. Instead it has more to do with fluidics where the wind is essentially redirected by "spilling" it in a common direction. The redirection of course provides the equal and opposite force which propels the boat. A parachute operates with the same principles but spillage is limited to a down vector and the decent of the parachuter is slowed.

[@gingersteve]

I have a fluid dynamics exam next week and my lecturer is a sailing fanatic and explains nearly everything to do with lift through sailing. This helped, thanks!

[@ninodoko]

I used to be a member of a sailing club, and the mentors there actually taught us that going upwind is the fastest way to go. I always thought that didn't hold water.

[@HerraTohtori]

Agh, again with this nonsense about the air having to "travel different distances". Lift is caused when the sail (aerofoil) turns the direction of the flow. The sail applies a force to the airflow, and the airflow has to exert equal and opposite force on the sail. That force is the lift. That is the kinematic basis for aerodynamic lift - trying to explain it by high and low pressures is technically correct but unnecessarily complicated. The pressure zones just kind of have to happen that way for any interaction with flowing fluid. When you push something with your hand, you're not thinking that you're creating a high pressure zone on your palm which pushes the object away, even though that is essentially what you're doing by applying a force on the surface area of your palm. You're just applying a total force on the object.

[@tjbvver231]

HerraTohtori The guy giving the explanation was a sailor, not a physicist. Pretty silly that he had a competitive sailor as the expert. Thats like having a cook as an expert on what happens when you boil meat. He might have some knowledge but more accurate answer is from a biologist or chemist. jep jep

The longer/shorter way explanation is especially embarrassing when transferred from airfoils to sails. It is very obvious that the way on both sides of a cloth is equally long. This is an interesting demonstration of how we tend to mask out obvious contradictions in explanations if they are presented by teachers/authorities/gurus.

[@sterhax]

Jörg Wagner yeah I can't believe they left in the already false long/short ways explanation that becomes completely nonsensical with a sail! ugh

[@sterhax]

Jörg Wagner Similarly, lindybeige once asked a british tank commander at a public demonstration a question about the tank cannon's muzzle brake and the tanker had no idea what he was talking about. You need not know physics details to be an expert or champion machine operator. You shouldn't be tasked with explaining the physics, though.

[@xilefx]

I actually think the pressure zone explanation is clearer to me. what changes the direction of force? right: the air pushing to fill the pressure hole inside the airfoil (or under)

[@jamalmahdavian2200]

I believe the fastest point of sail is a Beam Reach (~ 90' to the wind). In this direction the sails are always powered (unlike downwind). The angle of attack needs to be adjusted as you speed up. This will still be 90' to the apparent wind but pointing slightly away from the true wind.

[@rcgldr]

Although a sail could be considered to generate lift, a simpler explanation is that similar to a wing that diverts the relative air flow (relative to the wing) downwards (when in level flight), a sail diverts the relative air flow. (relative to the sail). A sailboat takes advantage of the difference in the speed of the wind versus the speed of the water, which assuming a steady wind, is independent of the sail boat's speed. The key component of the sails diversion of flow is that it diverts a relative crosswind (relative to the sail boat) backwards, which coexists with a forwards force exerted onto the sail (which in turn exerts a forward force to the sail boat). For a given true wind speed relative to the water, then the crosswind relative to a sail boat is the sin of the angle between the path of the sail boat and the path of the true wind, and this crosswind is independent of the sailboats speed. For sailing upwind, the more efficient the sail boat, the smaller the angle between the boats path and the wind's path, and the smallest angle for a specific sail boat is called "beta". The fastest speed (with respect to the water) occurs when the sail boat travels at 90 degrees across the wind and "beta" degrees downwind. Remember the crosswind (relative to the boat) is independent of the sail boats speed and only depends on the sail boat's heading with respect to the wind. Very efficient sail boats like catamarans can "outrun" the wind, meaning their net downwind component of speed can be faster than the true wind speed. The Americas cup catamarans can achieve net downwind speed faster than 1.5 x true wind speed both downwind and upwind. Although the sail boat "outruns" the wind it's currently in, the wind ahead of the boat has a head start and the boat continues to sail into a continuous supply of crosswind, again regardless of the sail boats speed. Somewhat related, what is known as a directly downwind faster than the wind (DDWFTTW) land craft, drives a propeller with it's wheels and can go faster than the wind that propels it. In the case of the "Blackbird", it could go directly downwind about 2.5 times the speed of the true wind. en.wikipedia.org/wiki/Blackbird_(land_yacht) kzbin.info/www/bejne/a3TGmKCmd6yGeas

[@samunro01]

You can also explain the ability of a boat to move upwind using the principle of a wedge (or triangle) placing pressure on two sides of the wedge will make it move perpendicular to side 3. The two sides are A. boats sail and B. boats centre board + rudder, where the confusion occurs is that side A and B are in different locations respective to a wedge, though with the same angles they produce the same effect as a wedge. This also nicely explains how a boat can go faster than the wind.

[@blayman92]

Usually when I watch these videos I can't believe people don't know the answers to what you're asking them, like in the "What makes a tree grow," but in this one I was just as stumped as everyone else. Learned something, thank you!

[@ShlomoOvadya]

Your videos are excellent man, thanks for giving so often!

[@pickledavis]

four minutes of ignorant people and 30 seconds of information. fantastic!

[@krappa]

I dont think many people know how sailboats work, no. I certainly didn't and there are even sailsmen who dont know it. So yeah, this is really interesting, even if you belong to the small minority that knows how sailboats work

[@krappa]

***** But how did you get them to be ignorant? I don't get it at all.

[@Kidrock87]

+erikharfager I guess he meant the actual definition of ignorance to be "lack of knowledge". I agree it is its true academic meaning. I believe most of us refer "ignorance" to be the noun of "to ignore", as in "disregard", which is not correct. Ignore is not the root of ignorance. I've been researched about this matter for a few, so at least I know I am correct :) Saying that, I do not condole his (stupidfacefaceface) to criticize this video to have full of ignorance. This video aims to educate, and the correct information is pretty straightforward. The point of this video is show the supply and demand of knowledge as to how sailboats work. I myself do not know how they work prior to this video and I am not embarrassed to say so. I am glad to stumble upon this video to be educated. Videos like this should be encouraged to show that people actually needs to be supplied with knowledge of various aspect. Wow, this is a long message

[@Kidrock87]

***** I think I do. He/she means "You said they are ignorant. Why?"

[@mariacovasneanu1517]

I burst out laughing. The engine bit starting at 1:52 was insanely funny.

[@icedragon769]

I always assumed, and was taught as a child sailing with my parents, that when you're running (nautical term for moving in the direction of the wind with full sails) it feels like you're not going very fast because the wind is behind you. There is no wind in your face, which is what people usually associate with speed. If you were to put your finger in the water, however, you'll notice that you're really moving fast. I don't quite understand the premise laid out in the video for that reason.

[@pauljdowney]

Wow! I was amazed how little most people know about how a sailboat works. Maybe other people want to jump in on my explanation but I explain it simply my saying that a sailboat can do more than just go downwind because it has a keel. With a keel the boat is like it is on railroad tracks and does not move sideways. The sail can be used to blow the boat down wind and obviously more and more degrees off of directly downwind because it has a keel. As the wind is 90 degrees off one side the sail can be used as a wing and make lift 90 degrees off the wing surface and move the boat forward and the keel prevents the boat from sliding sideways. Now you could see that this technique could be used to go a few degrees upwind and may a few more degrees and a few more degrees... You can keep doing this to about roughly 45 degrees into the wind. You can not go directly up wind. I hope this helps and is a very simplified explanation of how a sailboat works.

[@tsmwebb]

It is probably possible by linking a wind rotor to a water rotor to get a boat to go *directly* downwind faster than the wind. The key is that the difference in speed between the water and the air is what provides the potential. Some sail boats can get to point downwind faster than a packet of wind would get there but they need to tack back and forth to do it. The mechanism is very similar to the linked propellers but it is unwound.

[@sincerelyjerry244]

3:47 is why the Olympian hesitated to answer. trying to explain it like I'm 5. the other dude still blanked out! Awesome!

[@gingerfeest]

I get it, although you may have more initial acceleration with a tail wind, the acceleration decreases proportionally as velocity increases. But at a 40 degree angle, although most of the acceleration is perpendicular to the boat, the component that is parallel to the boat will more or less remain constant, and will be less affected by the velocity of the boat increasing. Pretty neat!

[@Michellesalot]

Oh something I didn't really need an explanation for, now I want to go sailing though just a bit of the summer left to do it. On a side note I think every so often you need to put a video up with people who actually know the answers to your questions, just as a little behind the scenes. It would make me feel like the world isn't quite so stupid.

[@veritasium]

please refer to the vid I did before this one "How a wing actually works". I intentionally posted in this order to hopefully make it clear. What he says is not wrong, but as you say it could be misinterpreted.

[@njsification]

Agreed, it's not about distance. It's simply the sail diverting the air from a path it was going previously. This diversion causes some backup in the molecules of air, leading to higher pressure on the interior of the sail. The diversion towards the inside leaves a void on molecules of air (low pressure) on the outside.

[@AlanKey86]

Can you explain why air travels faster over the upper surface of a wing?

[@thejonjon5000]

Soon as I heard the word 'lift' I finally understood the answer to this question I've been asking myself for a little while now

[@isaaclove1144]

Would this work in another frame such as the bottom of a long swimming pool that also has a current flowing? Of course the question is would a propeller Contraption like this be able to move faster than the current?

[@fshihab]

You're coming from the latest veritasium video, aren't you?

[@a.y.102]

Yes. In conclusion, as stated in Derek's most recent video, if you have 2 mediums moving relatively to each other, you can theoretically build a vehicle that go faster than the relative velocity of the 2 mediums.

[@turkeyphant]

Wow are there really so many people who have never thought about this?!

[@alphazero924]

The reason the videos don't contradict each other is because the last one was why a plane (which is powered) stays in the air whereas this one is why a sailboat (which is unpowered) moves.

[@hasta228]

Hey mate, close hauled isn't actually the fastest way to sail in general on a modern boat. It's usually on a beam or broad reach (perpendicular to the wind)

[@MrAtaguas]

Its funny how the Canadian guy gives such an elaborate explanation of how fluid dynamics works in reference to a sailboat...while he forgets that in Canada the wind just goes,"Oh, Soary" and gets out of your way so that you go wherever you want...

[@flapjackattack4]

i had no idea a sail worked like a wing... and i took a physics class last year.... thanks so much

[@od107]

Looking at the polar plots of several recreational sailboats, it seems that for most boats the maximal hull speed is achieved at a true wind angle of around 145 degrees, so diagonally from behind. The peak you described at 40 degrees due to the Bernoulli effect is only present in sport sailing vessels it seems. I guess because of the light high-performance materials reducing friction. I am not a sailer so correct me if I'm wrong.

[@clayz1]

Conclusion: most people don’t know, or at least are short on words to explain it. Because it is intuitive how to sail across the wind, or downwind. Tacking to go upwind is just a variation on sailing across the wind.

[@rivercarson5763]

to my knowledge the center board doesn't actually generate any force it just prevents the boat from moving sideways because of the large mass of water it would have to move so then the boat has to move forward. I imagine it like a ball on a hill gravity is pulling the ball strait down but the ground underneath it is preventing that so it goes down at an angle.

[@horizob]

Good video, but lacking in physical explanation. You should explain it using the ice skating analogy: the ice skater pushes his legs laterally with a force directed 60-90° to the direction of motion. The ice skates bite into the ice and transform this force into forward acceleration (that is why the ice skates need to be sharp, otherwise they would not transform this force and just slide all over the ice). That is why the centerboard and the rudder are so important: they bite into the water and propel the ship.

[@agnieszkasekula2954]

its not about being dishonest, its about making an attempt to understand and explain a phenomena, with facts known to you at a given moment, without previously having it explained to you by someone else. it is about the one and only way to creatively inquire and push people to use their brains. I dare say this is what Derek tries to do by making these videos. With all the answers available behind the keyboard one easily forgets how to question anything. Thanks Veritasium!

[@Hixie101]

I'd just like to point out where the majority of the 'lift' actually comes from. When the wind hits the sail, the curvature of the sail cause a very small difference in wind speed. However, the air on the far side of the sail 'likes' to carry on moving in the direction it was originally going even when the surface of the sail ends. This cause the previously on top air to curve around the sail and 'push back' the air on the inside of the sail.

[@lincolndutcher1360]

But here's another fun question, how is the sail pulling on the boat? Where is the force being transferred from the sails on the model into the boat to make it go forward?

[@svamour4574]

I enjoyed the Calculus, Geometry and Physics lecture. I have found most of the information on the internet is like getting a weather forecast. Everyone repeats what they have heard; no one verifies the facts or even knows what the facts are. Allow me to ask you a simple physics question; take two round objects the same length and size, both have the same nose cone similar to a jet aircraft. Object A; starts the gradual curve to the end (tail/stern) point at 50% of the length. Object B; starts the gradual curve to the end (tail/stern) point at 75% of the length. Simple Question: which object is faster given everything else is constant; Object A or Object B. Last question what is making Object A or B slower given everything else is the same (constant)?

[@sachmophoclies]

Thank you for bringing in an expert, explaining the physics, and showing that your interviewees might learn something.

[@tsmwebb]

I understand. Sorry about the confusion. FWIW, in ideal conditions some of the fastest more or less "conventional" sailboats can get DDW faster than the wind in "velocity made good" terms. I think Tornado cats with the spinnaker rig can just about do it and 18 foot skiffs are also on the cusp. The last America's cup boats were faster than the wind both upwind and down. All of those "tack" (jibe) downwind.

[@Bluemann]

DEREK!!! I love how you let people figure things out. You are the best and nicest guy EVER.

[@atomgonuclear]

They left out an important explanation of the actual forces that occur on the boat while sailing up wind. The rudder, keel, and hull actually absorb almost all of the horizontal forces. The reason that you can re-direct all of that wind energy into a favorable vector is because the rudder and keel transfer opposing energy to the water. To accelerate the wind you need something to push against. You aren't just moving forward. You are actually moving sideways too, just very slowly.

[@jeremystanger1711]

This video is pretty inaccurate, even though the explanations are the accepted ones. Anyone can see that sails aren't shaped like wings, and there's no significant difference in distance the air needs to go on each side (they're just sheets of canvas!). The sails work simply because the wind hitting them is deflected by a certain amount. This means the wind experiences a force, and so the sails get the same force by Newton's third law. Because the sail is effectively a 'reflector' of wind, the net force on the sail is normal to the sail (ignoring drag; drag brings the direction of the net force backwards a bit). The normal to the sail always points at least slightly forwards so there is always a component of force from the sails that points forwards. The keel and rudder are there to react to as much of the sideways component as possible. The difference in pressure is an equivalent explanation, but it makes no attempt to explain the origin of the pressure difference. Which direction is fastest is actually is far more nuanced than just a single number. For an average cruising boat, the best angle is probably around 110-130 degrees to the wind, but for a racing boat this angle is larger. For an ice yacht (these experience almost no forwards drag from the ground, but don't slip sideways like boats do on water), this angle will approach 180 degrees. This is because any wind the boat makes (called apparent wind) will tend to decrease the relative wind angle, because any apparent wind must come from 0 degrees. The most efficient relative wind angle (including apparent wind) is probably around 90 degrees, but the exact number is unimportant. If you start sailing from stationary with the wind at 90 degrees, you'll pick up speed, but now because of your apparent wind, the wind angle is probably closer to 70 degrees now, so you should turn away from the wind again to bring the apparent wind angle back to 90 degrees. But now because your efficiency has increased you'll accelerate, meaning the apparent wind will decrease the wind angle again, so you must turn away from the wind again. This is obviously a positive feedback loop that in principle will allow you to accelerate indefinitely. The limiting factor is obviously drag, but if drag is small enough, one can sail faster than the wind. Normal cruisers have a lot of drag so their most efficient angle is relatively low, whereas an ice yacht will have an ideal angle of around 170 degrees once they're up to speed.

[@J3zzaG]

Ironically the model of sailing that you stated was actually the old accepted model, and works decently well up to a point. Frank Bethwaite sums up why this model is inaccurate and why the airfoil model is more accurate in his 1992 book “high performance sailing”. It goes extensively into how he and his son developed more efficient sailing rigs by using the airfoil model. You will see that all modern racing sails nearly perfectly resemble a wing shape when viewed from above. That being said I agree with your assessment of the fastest sailing direction

[@PTomB]

A couple of points, Jeremy - "..The normal to the sail always points at least slightly forwards..", but why? To derive forward motion, that's essential, but to simply assert 'forwardness' leaves a gap in the explanation. "..The keel and rudder are there to react to as much of the sideways component.." - the keel, or fin underbody, yes, but pressure on the rudder? If it had a central axis, perhaps, but for rudders hung off a forward hinge, as most rudders are, pressure is the last thing you'd want ..until you want to steer somewhere else. You're likely familiar with 'weather helm' whereby you have to use the rudder to counteract the boat's effort to round up to windward. That rudder resistance is highly undesirable, simply because it's drag; a well-balanced boat will go where it's pointed. And finally, as apparent wind increases (as boatspeed increases) the direction the wind comes from moves forward, as seen from the boat, so why "..any apparent wind must come from 0 degrees."? Ah, I think I see an expression new to me: in a windless sea, any movement of the boat through the air will yield a 'wind' from directly in front. Apparent wind plus actual wind sum to a resultant wind further forward than it would be with wind alone. Fair enough. Thanks.

[@Statek63]

I think Bernoulli's Law and Fluid Mechanics would be a better model for airflow forces explanations, don't you think ?

[@jeremystanger1711]

​@@J3zzaG I think ultimately I was just trying to get at the fact that there's nothing 'magic' about how sails work, fundamentally, because I feel jumping straight to fluid dynamics leaves a lot of gaps. There's a difference between explaining why sails work (Newton's third law, everyone can understand) and explaining why an optimised sail is more efficient than a simple one (fluid dynamic magic, only wizards can understand). As a side note, there is a video linked in the description that pretty much says what I'm saying. I don't know if it was there when I posted.

[@jeremystanger1711]

@@PTomB "That rudder resistance is highly undesirable..." Yes and no I think. In my experience, a balanced rig should still have a touch of weather helm. I'm not quite sure why this is the case, but one advantage is that the boat naturally wants to turn into wind and therefore slow down, which is preferable from a safety perspective if you lose your rudder/steering at any point. The other aspect is leeway; if the boat is moving sideways through the water (which it always is when sailing), then any rudder will experience pressure (causing weather helm again if hung from a forward hinge), whether you like or not. Obviously, too much weather helm is a bad thing! Oh, and the normal to the sail always points a bit forwards because the angle the sail makes with the centre-line of the boat is more than zero!

[@666devilknight]

air traveling behind the sail fills the sail to create the air foil shape and add a little push. air traveling over in front of the sail is what causes life. this happens because of a few things: first is the boundary layer. air is, basically, a fluid. it follows the same laws of motion. any fluid maintains a boundary layer around objects, in that fluid. this layer of fluid 'sticks' to the surface of the object. as you move away from the object, subsequent layers of the fluid become less and...

[@dlakodlak]

I am a sailor and I used similar word attempting to explain the principles of sailing to my crew. I hit a wall when it turned out most of them had no idea how wings work.

[@FlunkTVGaming]

The fastest position is called close hauled; it is the closest you can face toward the wind without going into irons. However if it is a rather windy day, there's a very big chance that you'll capsize.

[@joopie99aa]

The fastest direction is not between 45 degrees and 90 degrees. It's between 90 and 135 degrees. You start of at 90 degrees, then when you gain speed, the headwind makes it so that the relative wind is coming more and more from the front. To counteract that, you turn downwind. Eventually you'll probably end up at about 110-120 degrees. Also, if the boat has a gennaker, the fastest course will be even further downwind, because that's where it's the most effective.

[@TheLostSorcerer]

Canadian for the win. Even while I knew I did not know the right answer, I was aware sail boats moved in a counter intuitive way.

[@snower13]

Understood. Just felt like we were going backwards :-). Keep up the good work.

[@jpchevron]

By asking people first how they *think* it works, they actually learn more. Much better than if you were just told how it works from the beginning. Which makes sense. By giving an answer you invest yourself in the question and obviously would rather not be wrong, so you give more of your attention.

[@exon901]

Loved your last two videos explaining lift and how sailboats operate. Always learn something new from you Derek. Love how you question people as to how things work and even when the answer is incorrect, you have this amazing way of encouraging further discussion without ever making them feel stupid. I know this formed a major part of your thesis. Well done!

[@DanGoodShotHD]

Think of flinging watermelon seeds by squeezing them between your fingers. Which way does the seed go? Well, the sail boat is the seed, the wind is one finger squeezing in one direction and the water against the keel is the other finger squeezing in the other direction. What direction is the sail boat going to go? That's the best way I've heard it explained.

[@MMICKELS1]

I belong to a radio controlled sailing club. Nearly every time we race our boats we get asked about "the motor". The general public doesn't understand how sailboats work.

[@nicthmsn]

This is helping with my Science Fair project! THANKS! :)

[@mrfail330]

Sailing down wind is actually one of the fastest point of sail a boat can travel due to the boat will plane on the surface of the water if light enough and water current. If the hull of the boat is flat enough and is light enough it is able to surf on the waves also. Reaching or sailing perpendicular to the wind is fast but is not faster than straight downwind. Sailing perpendicular requires lots of leverage to keep the boat flat, so that the boat can travel at maximum speed on that point of sail. Many boats are equipped with spinnakers which allow the boat to travel even faster downwind. Now some boats like the AC72s and Moths are using hydrofoils which reduce friction from the water on their hulls.

[@MichaelChanCY]

A boat doesn't depend on the wind to blow it forward, but depends on the lift created by the sail, that's why sailors have to adjust the sail to direction for maximum lift, and that's why a boat can sail upwind. The lift generated has a side way direction, so a dagger board is needed to cancel the side force. The boat would tend to turn over, and the sailors need to use his body weight to balance the boat.

[@camelCaseFTW]

Usually I would know the answers to the questions you usually ask people, and it is almost sad that most people don't know some of the answers, but you got me this time. I always wondered how sails work against the wind.

[@GaudioWind]

I think I have a better explanation for that. The sail with the boat act like a peace of soap squeezed by a hand against a wall. The water plays the role of the wall and the hand that pushes the soap is like the wind. If the wind goes in a certain direction and the boat and water are at rest initially, then it may not cause movement as a whole to the opposite direction, given the conservation of linear momentum law. So, actually, the water (or the wall) is pushed in the same direction of the wind (the hand), but the boat squeezed against the water (the soap against the wall) is pushed by the water and the wind (the wall) in a transversal direction or even, to some extent, possibly against the wind. Never in the exact opposite direction, though. So, I think the answer to the main question, that is, how can the wind push a boat in its opposite direction, is “the wind is actually pushing the water, the boat is just being squeezed in the process”.

[@GaudioWind]

***** Thanks, Barney.We can also see that the boat without a keel to pressure the water can't go against the wind. Another example is the kitesurfer. He can go against the wind pressing the water with the board, but he goes always in the wind direction when he jumps off the water.

[@gingerfeest]

In order to prevent motion that would other wise happen, force must be present. In order to prevent the boat from moving sideways, the center board must generate a force. So the board does generate a force, just not in the direction that the boat is moving.

[@tristanmoller9498]

I already was to happy because I thought he would give a better explanation than what I found through research

[@veritasium]

the sailing thing is counterintuitive. Lift is not as obvious as drag.

[@henrywiltcher]

My guess: The sail is curved, so the wind currents on each side have to travel unequal distances. Although the sail is thin, the average speed of the air particles either side will not be the same. It's not just the air that directly touches the sail that counts, so there is a fair difference.

[@porgy29]

From experience I knew the correct way to position the boat, but I had no idea why and always wondered why it seemed like the boat moved faster at about 45 degrees from the wind with trimmed sails, than fully with the with the wind with open sails, if it was the wind that was pushing it.

[@samunro01]

I could attempt to talk about the dynamics of a sail, but the sail is just a wing and you already did that... plus I'd probably stuff it up! :) Fun stuff!!

[@MathewCosgrove]

Here in 2021, wow, look at this young guy!

[@ianvanarsdel4342]

Goosewinging (or flying with the wind) is more effective than going on a beam reach (perpendicular) when you have a sheet sail or are on a galleon that uses square sails, but if you have the modern triangular main sail paired with a Jib you will get more out of the wind if you maintain a beam reach.

[@Hixie101]

This further reduces the 'speed' of the air on the inside of the sail, creating a pressure difference and the sail pushed outwards. Most sails have 2 inch long pieces of sting on the surface as visual markers as to how the air is flowing around the sails. Planes during landing also need to produce the extra lift due to their slower speed, so they deploy 'flaps' which cause air on top to curve around and 'push back' the air under the wing to produce the extra lift during landing.

[@gradytoback4356]

As a sailor, this was really funny to watch people say how they think it works lol

[@StanleyFlinn]

"which way would you point this boat to sail?" Me: a who has put hours and hours into Sid Meiers' Pirates! "my moment has come."

[@stephenconnors2111]

I love the guy at the end saying "thank you very much" aka "I didn't ask for this and it is in no way useful to me"

[@666devilknight]

yes. that is bartolli's principle. that is not how lift is generated. lift is caused by the air, closest to the sail, following the airfoil shape of the sail, while the air, further from the sail, keeps going straight, after being 'deflected' by the leading edge of the sail . this causes a negative pressure area between these two airflows and, since nature abhors a vacuum, it sucks the sail forwards. the underwater foil (keel, centerboard, etc) changes the sideways lift into forward drive.

[@rivercarson5763]

true that is the idea of what I was trying to say my point was that the center board is not pushing forwards if anything it is pushing backwards

[@JonasRosenven]

I would like to see what would happen if you removed the sail and put the wing from a plane in its place. Would the wind still tip the boat?

[@343jonny]

I like these science related videos! Keep doing more of these Derek!

[@Statek63]

My windsurfing board can go more than twice of the wind speed, on certain courses it will approach three times the local wind speed. These concepts are quite easy to understand. Are they not teaching any physics in these countries where you did your interviews ? ;-)

[@Statek63]

The most counter-intuitive course is deep downwind. You start running with the wind, at some angle from dead downwind - and then as you accelerate the apparent wind causes that you feel the wind blowing from your front-side. ;-) This is only possible on certain high performance sailboats or windsurfing boards. I can feel it clearly on a Formula board with a very large sail and a long fin. It's fun but it's rather counter-intuitive to a lay person :-)

[@kaboomspot]

Many expected an explanation from Derik but the reason he didn't do that was that guy himself exlplained all and most of them was correct

[@alwick1234]

The theory is not incorrect just the assumption that the air reaches the back at the same time from both sides. The pressure gradient is still created. The exact reason as to why it is created is not definitively known. The sail of a sailboat actually only creates a minimal amount of lift through this effect, the main power come from the fact that it is changing the direction of the wind, just as your son said.

[@mignik01]

You can explain how lift is produced by bernaulli's theorem fully. Newtons explanation concerns with the conservation of momentum while bernaulli's equations are derived using the concept of conservation of energy. Both theories explain. Fluid flows have to conserve mass, momentum and energy at the same time.

[@PeterRockClausen]

I knew this beforehand :D But my dad sails, so he taught me when I was younger, now I know (some of) the physics behind it, thank you :)

[@veritasium]

Soon, but for now it's science of sport since I'm hanging out at the Olympics with friends I grew up with who are now competing!

[@axemen77]

how many people got it right ?? and do you keep any of them videos ??

[@12zecharia]

just because you love aeroplanes and you put a lot of focus and concentration into learning about them doesn't mean everyone has.

[@ChrisDruif]

Just a small tip: try to lead the microphone wire with the expert through his shirt. I think most wouldn't mind, probably most of the random people you ask also wouldn't mind. But great video all in all.