Sailing Faster Than The Wind - How Is That Even Possible?
čas přidán 24. 09. 2023
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It's possible to sail a yacht faster than the wind that powers it! Although it happens all the time, it's really counterintuitive. Can it be explained with Bernoulli or Newton? Or both?
Here's Derek's video on Veritasium: • Risking My Life To Set...
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It's possible to sail a yacht faster than the wind that powers it! Although it happens all the time, it's really counterintuitive. Can it be explained with Bernoulli or Newton? Or both?
Here's Derek's video on Veritasium: • Risking My Life To Set...
Subscribe to Matt Parker here: / standupmaths
You can buy my books here:
stevemould.com/books
You can support me on Patreon here:
www.patreon.com/stevemould
just like these amazing people:
Glenn Watson
Peter Turner
Joël van der Loo
Matthew Cocke
Mark Brouwer
Deneb
Twitter: moulds
Instagram: stevemoulds...
Facebook: stevemouldsc...
Buy nerdy maths things: mathsgear.co.uk
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The sponsor is Brilliant: The first 200 people to sign up at brilliant.org/stevemould will get 20% off an annual subscription. The alternative explanation goes something like this (I'm simplifying!) - Lift is generated when air is moving relative the sail. As the boat speeds up, the relative speed of the air should increase and so the lift should increase! This explanation doesn't work for when you're sailing somewhat with the wind though. In that scenario, as the boat begins to speed up, the relative speed of the wind actually goes down.
I love you, Mr Mould 🌈
If you are sailing into the wind, and speed up, doesn't the relative wind speed increase?
I though the sponsor was brilliant as they might have done something brilliant in this video. But it was only Brilliant.
This isn't really correct. The term you are looking for is "apparent wind." As you speed up the angle that you feel the wind coming at you from shifts to in front of you, similar to how it always feels like the wind is coming from straight ahead when you stick your hand out a car window on the highway. This means that if you are sailing faster than the wind, you are also always sailing into the wind. When you sailing into the wind the relative wind speed goes UP, not down. When you are sailing away from the wind, you are moving with it, and the relative wind speed goes down. This is what the streamer on the front of the car in the veritasium video was showing.
Isn't it the other way around? Relative wind should increase with the speed of the boat when sailing into the wind and vice versa.
Delighted that I can wave my hands and a Steve Mould video appears
It's so cool when the same topic is explained by my two favourite science communicators.
Can you make a hand-propeller to improve this process?
A Wild Steve Appears!
In my experience: the novelty wears off after a while.
@Stand-up Maths kinda feels like christmas ❤️
Just as an aside, in practice sailors can rely on tactile and visual feedback to "feel" their way to approximately optimal angles. It quickly becomes largely intuitive, like learning to riding a bike. Forms of this feedback include the relative direction of small weather vanes, boat tilt or the sail floppiness.
Don't forget the telltails, they're little bits of yarn taped to the sail in various locations to help visualize airflow over the sail.
@Lex Band Aye And don't forget the nose. A good sailor can smell a fart and tell you exactly whence it came, and who the likely culprit.
We had a family boat when I was young that was not what would be called handy and even though a sloop was a pain to tack and just wanted to sit in irons and go nowhere. The sails and hull were not well balanced and apparently the hull was also used to produce a power boat version! We had to go off the wind in to a broad reach to accelerate the boat and then slam the always heavy feeling tiller over and hold the windward jib sheet to pull the bow round. This lazy boat really made you think of the relative speeds at angles to the wind. In some ways it made it more fun to sail. Happy memories.
For anyone wondering, there is also the really fun phenomenon of generating your own wind. Which occurs because as you gain speed, you are now experiencing wind equal to your speed(essentially) in the opposite direction of your travel. So as you speed up, you start having more wind, in a more bow(front of boat) position. So you can then capitalize on that and go faster, which is why many sailboats nowadays are optimized for more upwind sailing. The most dramatic example I have seen was America's Cup World series boats(which has all sorts of optimizations like wings and foils) and traveling downwind, they had their sails in close as if they were going upwind, and their windex's read that the wind was about 4x faster than we experienced elsewhere. Really good video, thank you for making. I did not know about the whole missing thing with the wind, and you could certainly make a hundred videos about the physics of sailing.
7:08 this is why in sailing, changing the angle of the sail is similar to changing to a higher gear in a car. you start at a steep angle because that gives the most perpendicular force, but after accellerating for a bit you reach the maximum speed for that angle and have to pull the sail into a shallower angle to get any more speed. until you reach the maximum speed the boat is capable of when the sail is almost perpendicular to the wind. so the best angle for the sail depends on where the boat is pointing, where the wind is coming from, the speed of the wind AND the speed of the boat.
Not true, the true wind angle stays the same. The relative wind angle shift forward due to the speed of the boat. That is why the sails need adjustments.
As a semi pro sailor we have gears in the sense of different mast angles for different breezes and different sail depth and camber to affect the CL. the pulling sail in bit is more like a rocket thruster in space.
@Jude M you've never trimmed the sails?
I was wondering how the NZ land yacht broke the land speed record recently by doing 222kmh with only 40.7kmh winds.
Pretty spot on video. I’ve been sailing most of my life and this gives a pretty good intro to what’s happening above the water. Obviously, one can’t squeeze the entire theory of sailing into one 12 min video. I hope someday you’ll look into the hydrodynamic effects of the hull/keel as they’re as, if not more, important than the sails when it comes to speed.
What’s even more interesting is dinghy’s below the waterline, because they don’t need standard elements like a keel you get way more variance, from displacement to semi planing, skiffs, cats, foilers, planing cats, foiling cats, etc you see way more variance than in keelboats
Not sure if I missed this in the video, but need to also consider that Derek was using a wind turbine as a sail. A turbine can act like a flywheel, storing energy. A good question to ask is “what happens when the wind stops?”. A sail boat will no longer generate lift, but the inertia of the boat will keep it going. A wind turbine however will continue rotating and continue providing lift, so it’s possible to build more speed thanks to the energy storage element. At least, that’s my assumption, haven’t thought all that hard about it.
@eyytee You are right, but the point here isn't that it will speed up when the wind stops. The point is that the turbine can store energy from past wind, which is added on top of the wind in the present. It's essentially a mechanical battery.
@Real Engineering My point was that the cart in Derek's video goes faster than the wind in steady state. It stays above windspeed, as long there is true wind. It doesn't rely on stored energy that would eventually run out.
When the wind stops, from the frame of reference of the rickety turbine machine, there's still wind as it continues moving for a bit. But now it's moving into the wind. Wouldn't this negate any gains made from the flywheel effect?
I'd like to point out that unfortunately this video doesn't demonstrate how a sailboat can travel faster than the wind in the downwind direction. That being said, the model used can explain it perfectly! You just need to angle the hull away from the direction of the wind more than the sail. A turbine is analogous to a screw in the same way a sail is analogous to a wedge, so if you treat the sail car as a mechanical advantage problem it all checks out.
I think about it like gearing the difference in velocity between the wind and the ground. Like gearing between a pair of pinions attached to a pair of racks Imagine the wind and ground are racks and the sail and wheels are pinions. The two pinions are geared so that the wheel pinions move faster along the ground rack than the turbine pinion is moving along the wind rack. This seemed to work when I modeled it in on shape
Matt's been on CS-tv for so long, done so many things, and I can't believe his channel doesn't have 1 million subscribers 🤔 that's the definition of underrated
Everyone gets there, eventually. 2.18 millions when I left this comment.
@Supremax67 I was talking about the guest on the video, Matt, whose channel did finally get to a million 🥳
Congrats on the 1 million subs Steve. I love this channel, I hope it continues to grow.
Your graphics actually are very good. No need for a bunch of visual noise for gratuitous reasons. Simple shapes to explain the concept in a simple manner is exactly what is called for in a video like this. Good job.
As a sailor I find it funny that this is even a topic of discussion, as we know we can go faster than the wind and we've known it for thousands of years.
I guess it's just a different source of learning. I grew up inland so I'm not familiar with sailing intuition but this video helped. Ironically I used to think some sailing games had bugs and now I realise they were realistic.
Its different in this case because sailboats can sail against wind but travel at a certain angle relative to it. Whats trying to be proven here is going faster but, in the exact same direction that the wind is going, which sailboats can’t do.
Of course we know that from experience, but this video is about how it does it, which will be counter-intuitive to many people. I'm going to bet there are other things we know work from experience, but you don't know how. That's quite normal.
I first heard about this years ago when someone claimed that his unpowered cart with a big fan on the back could travel directly downwind faster than the wind. Someone mentioned sailboats traveling faster than the wind but most people assumed this meant traveling with the wind but diagonally. Some guy who did ice sailing showed that he could arrive at a point directly downwind much earlier than a balloon floating with the wind. To me, this proved it could be done. Just left the question of explaining the physics. I was surprised that many people continued to deny it was possible based on their theoretical calculations.
but different direction
Steve, to me you are like the mid life dad who started documenting random experiments in his back yard out of curiosity for how things work. Really enjoy watching you explore and explain stuff you learned.
Bernoulli's Principle and the Coanda Effect are two sides of the same coin as I understand it. The Coanda Effect describes how flow clings to a convex surface resulting in a change in the flow's direction of travel, and Bernoulli's Principle describes how the force required to change that direction of travel is reacted against the curved surface via a change in pressure. You don't get one without the other.
Good insight. I think I might end up using your glass cutting techniques for an upcoming video by the way!
@Steve Mould Good stuff! If you use my mini sandblaster design and find it shreds right through electrical tape it's probably because the sandblaster barrel is too long. It's a balance between cutting the glass quickly without destroying the stencil.
Thanks for the tip!
I more or less agree until you say "You don't get one without the other." For example, Bernoulli's equation can be used to describe the flow in a pipe that has a reduction in diameter (no increase). With no increase in diameter (as one travels downstream), I don't think the Coanda Effect applies anywhere.
@Andrew Snow I think the coanda effect is still present in that situation unless the reduction never levels out (a closed cone shape, which would have no flow anyway), as is the reacted force on the wall of the pipe. Because of the coanda effect you can assume the fluid will fill the volume of the pipe and follow the curves of the wall (because bernoulli's principle tells you that a vacuum would form otherwise) so it's not necessary to think about both principles simultaneously.
Very nice explanation, I’ve done a couple years of sailing and this is pretty accurate. Only thing is for the perpendicular trajectory, on a sailboat when you go perpendicular you will bring your sail near completely in and counter balance your boat with your own weight on a small boat like a laser.
This reminds me of the fact that you can in theory make the point where a pair of scissors intersect move faster than light if you had a very long pair of scissors or close them very fast.
Congrats on a Million, Steve! It is well deserved and long overdue!
CONGRATS STEVE! Been watching you for years and always felt that you were an undiscovered or hidden gem. I was always shocked that more people hadn’t found you and subscribed…..well, now they have and it’s well deserved! Looking forward to seeing how long it takes to get you to 2 million subs! And worry not Matt Parker…we’ll get you to that magic 1 million soon (here’s an idea….just plaster more images of Steve’s face on your video thumbnails and you’ll reach a million subs in no time at all!)
Steve’s explanation is basically the explanation for why propeller pitch needs to be changed at higher speeds. I had always analogized it to gears on a car, but seeing the reason why gives a whole new perspective.
I don't say this lightly, but this might be my favourite video of yours. Something complicated and counter-intuitive explained with such elegance and ease that I'm half convinced that its entirely obvious and I always knew it. Worthy of being the first one after the million barrier
One thing I'd really like to see, a plot where the velocity of the ship is one axis, the angle of the sail relative to the wind on the other, and coloured according to the magnitude of the force on the ship. My new found intuition is that, the sharper angle the lower the force (wind gets deflected less) up to when you approach the "maximum speed" for that angle. But that maximum speed itself increases with that angle. Would be good to see how that would look graphed out, if there's a clear optimum trade off for a given speed, and what that optimum looks like.
@QuantumHistorian You might be interested in explanations of the tip speed ratio of a wind turbine. It covers this concept. Blades angled close to the wind have a high speed but as you say the lift force going in the direction you want is low so low torque. Used on rotors with 1 or 2 blades. What complicates things and wasn't covered in this video is that when something moves through air it has it's own headwind. This adds to the existing wind and changes it speed and direction as experienced by the moving object.
@Ed R Actually, while it's not discussed, the model presented covers these forces. It can thus explain how a boat can travel in the downwind direction faster than the wind, which unfortunately was not demonstrated because that is the true analog to Veritasium's video.
The "power cord knot" 12:10 is called HMS (Halbmastwurfsicherung), Munter hitch in English, or half clove hitch. Used commonly in rock climbing as a belay knot on a carabiner (the carabiner is also called HMS, name from this knot). It is great to see how the knot "flips" the other way when you pull the other strand. Try it! It seemed like magic for me first time I learned how to belay using HMS, and then you start to understand how it works. Try it with a rope on a carbiner!
Sails never fail to amaze me, they are so simple, het so complex
It's a lot of fun too. If you're looking for a hobby and are an extrovert you can crew for someone for fun and experience. If you're an introvert and rich you can buy your own. Bit of a joke, but I did find a boat for $2k for my own fun.
"Let's assume it worked perfectly" - Oh, yes, physics
Assume resistance is 0
Assume that a spherical cow in a vacuum...
Assume I did. Assumptions are free to take; just like mistakes! 🤷
Yeah also because when the wind pushing the boat in a reach will also rotate it a little it will carve up winward negating the force of wind pushing it leeward
You took complicated subjects and made them so accesible for people. Congratulations you're making great videos
I always wondered how sailboats can travel in a direction against the wind, but I never considered the hull shape. Great video!
Solid collaboration. Funny that I sign up for a sailing class this summer, and boom, Steve Mould makes a video about sailing. The universe is calling mate.
good decision
Algorithm*
Solid or non newtonian fluid? You may have tapped it, and it felt solid, now you need to wait to see if it oozes all over the floor. In a temperature controlled environment, to rule out melting of course
what are the chances, you must be THE ONE and the rest of us are nothing but npcs! you should buy a gun and start cleaning us up!
The universe is always calling. We only need to tap in and listen 🤙
This is a weird puzzel I've been thinking about. How would an airship navigate without propellers, as in a fantasy airship with just a balloon and sails. Thanks for this video!
Adding friction into the equation is fascinating. Because one of those slightly counter intuitive things about classes of boat, like the AC75, designed to sail faster than wind is that less sail area is often better. You need a certain amount of sail area to accelerate but then as you pick up speed the effect of dragging the sail through the air starts to reduce your top speed. This means teams have to carefully pick their sail plan for the conditions they expect. If you're at the lower end of the wind range, like six to eight knots, then your top speed might only be thirty knots so a larger sail isn't going to generate as much drag. Plus, you need to accelerate quicker out of tacks and gybes to keep yourself up on the foils (and falling off the foils will almost certainly lose you the race). But when you're up at the top end and going fifty knots, then your need to accelerate is less important than top end speed so less sail area is better in order to reduce drag.
Sails and sailing vessels come in countless variations and different configurations, of course. The most common sails these days - seen on that Bermuda-styled pleasure boat at 8:12 - are actually shaped more like wings than like triangles. They look like triangles curved out of shape by the wind but they are more like three-point _pockets_ carefully designed to catch more wind.
I don’t know if you’ve come across it, but a brilliant example of sailing faster than the wind is the Vestas Sailrocket. The gentleman who worked on it and piloted it gives a terrific explanation of how they managed to achieve that.
That also explains why you have to change the angle of your propeller's blades in an aircraft, between takeoff and cruise speed =)
Congrats on 1M subscribers. I have a query about force ?vectors? that I am very curious about , it concerns wonky shopping carts/trolleys. When I accidentally get a wonky shopping trolley, I tend to push the handle from one corner with the trolley angled about 30-50° in the opposite direction in an attempt to stop my knees blowing out while keeping it straight. How is it that I am applying force to one side but the front end of the trolley pulls TOWARD that direction even though the sources of friction/drag (wheels) are on the opposite side (for reference, where I live has steel wire mesh trolleys where all four wheels can rotate freely on castors - also the push handle is wider than, and behind all the wheels).
As a dinghy racer and yacht sailer for decades, it's good to know the exact science behind why I knew the "optimum angle" for sail setting and direction to get the best speed possible in the direction I wanted. It's kind of like I already knew this was why, but didn't have the exact terms to state it explicitly.
Incredibly well explained. I went land sailing on a Blokart - it's a lot of fun. Looks like an M number on your subs. Nice work!
Damn you guys. This video was EXCELLENT. The graphics were fantastic. I too was suffering from a lack of explanation in that other video, despite it also being very inspiring. Good combination here. That was honestly some of the best explaining of anything ever I've seen, and I watch a ton of these videos. Great job! I'd also like to posit that this phenomenon is FAR MORE important than we realize. It's not just lift in wings and sails I think but a whole host of other similar things in the universe and future technologies for space travel, or even as an alternative to the failed vacuum tube idea for hyperloops.
I have always wanted to understand this concept in an intuitive way and this video accomplishes that perfectly, thank you!
”I am the wind” -Steve Mould 2021
Someone tell Kvothe
Someone please make a Tshirt of that.
@cillian williamson why don’t u
@Aaron I C what you did there...
An analogy I use is Skating on ice where legs move slower (wind) than the skater (boat). If trains on rails had sails, it would be easier to explain. Sail angle works a bit like the gear ratio in a car transmission or propeller pitch of an aircraft. There is always a sweetspot. Given the dynamic nature of water/wind/friction/bearing, finding that sweetspot makes the best sailor.
The handle thing is about topology. I only know about it because of my String Theory reading, but essentially, if the cord is not connected, it technically has "no holes," which means you can utilize various different "knot methods" to "decompose" the manifold into an "untangled" plane. Essentially, you're performing a series of geometric transformations to modify the upper-dimensional shape of a manifold without altering anything in relation to the properties that define it in its defined dimensionality.
That hand on the plank brought tears of joy to my eyes. So simple and yet explains so much.
This made me appreciate how great Wind Waker's sail mechanic was
Such an excellent breakdown and explanation of physics that trips sooo many people up! Congrats on a cool Million!
I love watching 3 or 4 of my favorite CS-tvrs all give their "take" on a physics project/thought experiment. I learn something new from each
It helps that normally there is a LOT of stuff going on at once and reducing it down to a narrative bite size chunk leaves plenty behind for further discussion
Hey Steve congrats so much on 1 million subscribers hope to see many more interesting videos to come!
6:02 a very similar effect is happening in asynchronous induction motors (squirrel cage motors) when operated without a load. The rotating magnetic field around the rotor accelerates the rotor until it matches speed and phase with the magnetic field. By that point, no more force is generated and it slows down. The motor reaches an equillibrium state where there is just enough force generated to overcome friction and air resistance inside the motor.
The optimal angle of sail can also be adjusted by tilting the sailboat, letting some wind (and sideways force) roll over the sail.
The reason the sailboat isn't pushed sideways is not just due to the thin hull shape. There will also be some rudder input to correct the course of the boat.
also the "fin"/keel
Not if the boat is set up right, you can actually let go though most boats are designed to point up wind for stability reasons
It is good to mention that if we speak of Bermuda type rig (Genoa/Jin and main sail) that there is a possibility to not use rudder at all if we find so-called balance of the sails. Wind rotates the boat in different direction around the mast/keel depending on what sail you tighten and ease. So, if you find balance of sails, boat can go upwind with no rudder input.
@Whatswrong Withyarik Yep, we sailed a couple weekends back and found ourselves with perfectly balanced sails close hauled (with a slight inclination to a close reach) and I showed my son how we could adjust our course just but adjusting the Jib or Mainsail having the rudder locked amidship. I would be curious the efficacy if we could remove the rudder from the boat/equation.
A good sailor balace the boat, so the rudder is straigh forward without breaking. I sail on a 3 mast schooner gaff rigg. If you put up sails in the front, you have to put up sails in the back. The jib in the very front is in pair with the top sail on the mizzen mast. Whith good riggers, you never have to fight the boat and the wind at the helm.
I think what's the most difficult to accept is not that the magnitude of the boat speed can be bigger than the wind, but that the downwind component of the speed can be bigger than the wind. Or, as stated in the Veritasium video, that the boat can beat the balloon when going downwind. I'd love to see a simple explanation of this.
Congratulations on 1 mil subscribers! I know it happened a few days ago now but it's still so great to see a CS-tvr I love reach such an incredible milestone! Just to point out on this video-at the time of writing this-the captions at 7:22 say the drag force cancels out the "mega" component of the lift force, instead of "meagre". Anyway, as a subscriber to your and Veritasium's channels, this was such a great video to watch and the explanation was very clear with the models. Thank you! And congrats once again!
Fixed! Thanks for the heads up :)
Congrats on 1mil subs! I love seeing collaborations between favorite CS-tvrs. :)
I love this. I used to sail with my dad when I was a teenager and it's some of my favorite memories.
Congrats on 1M subs mate! You guys are great and answered the exact questions I had from the V video
4:27 The blue/sideways force does have an affect! Because it and the ‚resisting force on the hull‘ are offset, the boat gets tilted. Thats why big boats have weights in the keel and small boats relie on the bodyweight of the sailors to counteract it.
Yes, but "tilting against the natural vertical" is just a change in _potential_ energy, and once the tilt is achieved, no more _work_ is done, at least as far as tilting is concerned. Also, it's effect, not affect.
I really like these challenges between Matt Parker and you. Could you please continue it until 2 millions subscribers? :)
7:00 The angle of the sail is kind of like a gearbox... The steeper the angle is like a higher gear ratio with more speed but less torque, and vice versa.
How about an inclined plane?
Thats exactly how we use it, you can also control the depth of the sail to get the same effect
Not really the angle changes the efficiency when sailing at different angles to the wind
@VeggyKing so does changing gear when driving a car.
If that's accurate, then thanks that makes a lot of sense
I would love to see the rotary sail design applied to the back of a powered-paraglider. or even just a standard sail.
Brilliant work, gents. There's something quite right about this dynamic duo of daring demonstrations.
I hope these vids dont stop, was both happy and sad to see 1M subs. You deserve every last sub and more, both of you.
Loved getting this refresher. I knew it before since I got a wind surfing license, but it's been a while. Now I wanna get back on a board... Also I hate tacking. Biggest reason I haven't been on one in years.
Excellent video, but I do think it’s really important to take into account the multiple different types of sails, which you touch on a little bit in your defense, but the square rigged style of sail is just really inefficient. The better type to use as far as aquatic vessels goes is the Marconi (right-ish triangle) rig. I sailed all throughout highschool on one of the fastest boats made in 1918, and it was all thanks to the the Marconi sail design (and the long and VERY deep keel). It allows you to catch the wind at much better angles and gives a better foil effect. I’m no scientist/mathematician etc, so I don’t know all the math and physics lmao. Great video though! I enjoy watching :)
I'd like to add that sailing is only possible when you've got two mediums with different velocities (different direction and/or magnitude), that's what lets you continuously extract energy from the medium. Edited for clarity.
Probably the most important point for understanding how the car in the Veritasium video works. I think very few people appreciate this and it's the reason so many people call hoax.
Specifically, you need to have much higher resistance, at least to lateral motion, in one medium than in the other. "Sailing" on a water-oil interface likely would not work.
Is there any reason you can't extract energy from the medium you're travelling in?
Sure you can, but not in any other direction than the one where said medium is going - you've got no "leverage" to pull/push in any other direction. Imagine yourself floating in a vacuum, if someone pokes you with a stick you will extract energy off that stick but then flailing away you go.
This is much more intuitive in the boat case than the car from veritasiums video. In the boat case the water simply provides the resistance you need to hold at the right angle
As a sailor, I love to see this kind of stuff. Another addition to this is that when a sailboat is moving at a certain speed, let's say five knots in 10 knots of wind then the sailboat is experiencing another 5 knots of wind against it because of the speed it's going. This is called apparent wind. So now that boat has 15knots of wind against it. When a sailboat does this and it happens on every sail on a boat if the boat is moving, then you have to pull the sail in to counter the apparent wind. This is because the apparent wind is coming from the direction that your boat is moving or the front of the boat while the real wind on a boat's preferred angle is usually about 120 degrees from the wind. Now your boat has its sail pulled in its wind angle is around 80 degrees even though the boat is pointing in the same direction. This can be repeated for a long while when you have the right sea conditions. This is also why you don't see the GP boats or the AC75s letting their sails out very far. They are trying to capture the apparent wind.
I was expecting you to explain the way the propeller on the Blackbird is designed and how the force of the wind is being transformed into a drag force. Guess I was overly optimistic this time 😅
you should make a part 2 lol. People are debating whether this explanation works for different scenarios.
Really cool video further developing Dereck's recent video. I feel the next video on this topic will explain how to make the ship go faster than the speed of light :o Congrats on 1M!
Your channel's amazing, I learn so much, keep up the great work
Great explanation of how to sail faster than the wind but what I spent a while trying to work out after the Veritasium video was how you can sail such that the component of your velocity in the direction of the wind is faster than the wind. With this explanation that requires angling your sail in the opposite direction to the conventional way so I’m not sure how you do it in practice.
^^This^^
This is the part that is actually confusing, and the part that Steve seemed to totally skip over...
The angling of the sail shouldn't be important. It's the fact that the wind pushes the machine, which allows the wheels to turn the propeller. It seems odd that the wind can be slower, but the slower wind does reduce drag, which makes it easier for the machine to overcome friction and maintain its momentum.
I think a explanation could be: (its my explanation) When the wind speeds up the vehicle it doesnt speed it up due to it turning the blade, but due to pushing on the vehicle. Then the wheels will turn also and this causes the blade to spin. Now when the vehicle is at the speed of the wind it will get faster, cause actually if you imagine a horizontal line through the rotors blade there will be a crossing point between the imaginary line and the blade. This dot actually moves backwards while the blade is spinning, because of the blade is tilted. Now you have a point on the vehicle that is moving slower than the boat, cause this point is moving backwards relative to the boat (it could even really move backwards, but lets assume it doesnt) So then the air can push on this point, since its slower than the air and thus push on the whole boat. Of course this backwards moving point doesnt really exist. But you can also think about it this way: The rotor is spinning, and thus it will blow air against the actual wind. This will cause some swirls and this will cause the vehicle to kind if push itsselve from the wind. Now you could argue that pushing from the wind takes at least as much energy as it takes to turn the wheels. But thats not true, since the vehicle is moving faster relative to the ground than to the air. And thus its easier to push from the moving air than to turn the wheels to be able to push the air backwards. (Have you ever been in a pool with circle motion and just floated in the water while pushing yourselve activly from the fast water jet at the edge tonbe faster than the others? did you notice that gaining speed by this was easier than gaining the same amount of speed difference due to pushing off the non moving water? ) this is because the kinetic energy increases quadratic with speed. So lets say you want to gain a ∆v of 1m/s relative to non moving ground while you've got no speed in the first place. The energy reqiered would be 0.5(m^2/s^2)*M with M being your mass. But if you try to gain 1m/s when you are at 20m/s to get to 21m/s you will need a energy of 20.5(m^2/s^2)*M. So much more. So if you push from a object that isnt moving to gain 1m/s while you are at 20m/s you will have ro use a energy of 20.5(m^2/s^2)*M But if you are pushing from a object being as fast as you, you will have to use only 0.5(m^2/s^2)*M. This is because you will push the other object backwards by doing this and thus you will decreas its veilosity and thus its energy and thus you will gain energy without having to do that much of a work. (of course this 0.5(m^2/s^2)* M does only hold, if you assume that the mass of the object you are pushing from is infinity, cause else it will get slower while you are pushing from it like i already said, and this will make calculations complicated) So you can actually divide this process into steps: Step one: Pushing from the wind using a energy of 0.5(m^2/s^2)*M and increasing with speed of 1m/s Step two: using your energy relative to the ground to push from the air. So if you calculate that you will loose 0.024m/s. (cause you will get a energy of 0.5(m^2/s^2)*M if speeding down from 21m/s to 20.976m/s) . So over all you are gaining 0.976m/s without blaming the law of thermodynamics.
Steve only shows a beam reach which is 90 degrees to the wind so on the direction of the wind you do not travel any distance. the veritasium video shows a broad reach (about 45 degrees away from the direction of the wind) going faster in the down wind direction than the wind itself. on the broad reach you will travel downwind. I would like to see the Steve's model on this broad reach and see if it can out run the air molecule in the down wind direction. I think the boat will still go faster than the wind on the 45 degree course but will it go faster in the down wind direction ? my head can not picture it doing this I need to see the model doing it.
Those ridiculous models actually really made this explanation really easy to understand. I hope you guys decide that now that you're at 1 million the next goal is just 10 million and you keep challenging each other.
Physical illustrations brilliantly describe the unintuitive physics of sailing. Excellent.
That is the best explanation of this I've ever heard. Please do more
4:05 indeed, the slight sideways drift away from the wind, or to leeward (the opposite of windward) is why you should always leave yourself some _leeway_ when trying to clear an obstacle. Especially if for some reason you don't make very good _headway_ I'm always amazed by how deeply sailing has worked its way into our language!
Modern day boats can actually generate net zero leeway by canting their foils to windward as to generate windward lift as well as vertical lift which is why most moths and foiling boats cant to windward
Fun fact you’re minorly incorrect. It’s true that you can have net 0 leeway or even positive leeway but rigorous testing, a very small part of which I’ve been involved with as part of my uni program and sailing team, has shown that while it’s possible to achieve 0 or positive leeway it’s optimal to have between 1-2 degrees of leeway angle because the drag required to generate the extra hydrodynamic lift and resulting speed penalty is greater than the vmg improvements from better point, outside of niche tactical situations like pinching an opponent off a start line in a sailboat race
Steve you should include some talk about iceboat sailing. They can reach speeds several times the ambient wind speed
Friggin awesome explanation and congrats on 1 million subscribers! I can tell which parts you filmed before and after lunch from the stain on your shirt :P
I was hoping no one would notice! It was worth it for the ethiopian injera
Cool vid
@Steve Mould Ooh... now I want Ethiopian. There's a good place near my house but I'm at uni. :(
Sad to see how quick internet fame got to poor old Steve… The moment he hits a million subscribers out goes the unnecessary detail of wearing clean shirts for video shoots. Next he'll grow some ridiculous face-beast like some crazed stand-up mathematician. Or worse, move somewhere is doesn't rain all the time.
I watched the whole video again to see any stainless shot but the stain was there during the whole video, can you help me see where his shirt was clean?
Great video as always Steve. Myself and some friends recently started sailing and spent a fair bit of time pondering the physics as well. It might be worth noting that as the boat speeds up it's advantageous to reduce the angle between the sail and the direction of travel, I think this is because the 'resultant' angle of wind on the sail changes with the speed of the boat.
Sailors use what's known as an apparent wind to sail their boat and say your heading angle is 090 @ 20 knts and the wind comes from 000 @ 30 knts your apparent would be 030 at 37 knots which would be a close hauled course when you are actually on a reaching course
I really liked the "packets of air" explanation, and also the dig at the Bernoulli fans (I never felt like "It's Bernoulli OK?!?" is a good explanation for anything). I do wish you would talk a bit more about sailing into the wind and what that does to the air packets model; or indeed to the flow-direction-deflection model (since the deflection is actually a lot less when you're going upwind and keeping the sail mostly in a similar direction to the wind). I think it also would have been more intuitive if you kept the wind direction constant, rather than the boat travel direction. "If the wind is like this, how fast can I travel in direction Y?"
Also, maybe to explain why it's *possible* to sail faster than the wind, you could have started by exploring why it feels like it should be *impossible* (and then frame it as what that intuition misses)
It seems to me that a sail acts like car transmissions: the varying of the angle transforms the ratio between speed and force
As usual, an excellent explanation!
The explanation kind of works for slow sailing boats, for very light racing boats (catamarans, trimarans, hydrofoils, etc) the airplane wing concept takes over since as the boats sail fast they generate their "own" wind and the sails generate lift
Actually, the boat moves away from Steve Mould due to the awkward encounter they had at the Christmas party last year.
I like your explanation for taging or cross sailing and going faster then the wind in lengthening the axis of travel or how you name it. To understand how you can go faster then the wind in the same direktion is a whole different thing to me, because it seems to include a different mechanic of taking a tailwind and extracting more energy then it should. Amazing and Salut to the People proving that that is possible!
Not really, the applied physics are exactly identical it’s just much less intuitive. The same principles are at play!
There's a thing in the middle of most sailboats (kind of like a deployable stabilizer and i forgot the name of), which helps prevent sideways motion from near perpendicular wind. I'm not sure what size boats have that feature, but i do know having it retractable. This also neglects the flexibility of sails, so it can curve winds while transferring forces
You could try it on rails/grooves so it doesn't get displaced sideways.
I wanted this too! That was the part I wanted more of in the Veritasium video! I was so thrilled to see this come out.
I touch on that here, but not in as much detail as it deserves... cs-tv.org/tv/video-X6oJpnSJyV8.html
Steve Mould´s videos are always beautiful. I look forward to each one. Once again it is obvious that a lot of work has gone into this one. There are a number of very nice concepts and explanations presented and packed into just 9 minutes! I wish it could have been longer. Here are a couple things that I noticed that might be of general interest, or perhaps I will be corrected on and thus learn more about the subject. And though this video provides some wonderful intuition on sailing mechanics, I explain in detail here as to why it does not give us an intuition about faster than wind travel. At the end of this post I suggest something that might be a missing piece that I think would complete the explanation. Steve did not mention, but as a boat travels faster, the wind appears to change direction. Say we start sailing downwind at an angle. Initially the wind will be at our backs. As the boat speeds up we will notice that the wind appears to come more and more from the front, even though the true wind has never changed. People on motor boats and motorcycles just expect wind from the front no matter which way things are really blowing without even thinking about it. Consequently, the 'sailing upwind' part of this video also applies to fast downwind sailing. Consider sailing downwind at a 45 degrees angle when the boat is traveling equally down wind and perpendicular to it. At this angle the wind will appear to be coming over the starboard bow. (x, y) a vector (0, 1) velocity of wind blowing in the y direction (1, 1) velocity of boat at 45 degree angle traveling the same speed as the wind (-1, 0) velocity of the apparent wind (over starboard bow due to boat traveling at an angle) Thus the upwind sailing scenario that Steve shows at time 8:24 is also the downwind at the speed of the air scenario. Hence, this little demonstration is key for this video. Steve makes use of a stick and cart model for sailing. The stick has a wheel attached to the end of it. An interesting aspect of having the wheel there is that force will always be perpendicular to the surface of the board being used as a sail. This would be the case for real if air reflected upon striking a sail and had equal incident and reflection angles. Because the force is always perpendicular to the surface of the board acting as the sail, the stick may be rotated around so the shaft is perpendicular with the surface of the sail. When this is done no sideways force need be applied to hold the stick when pushing. The travel would then be scaled by cos(theta) of the angle of rotation. Hence the actual angle that we see for the stick in the video is only symbolic of wind direction. He pretty much could have used any stick angle. A sailboat has a keel, so it travels in local straight lines. Sail powered land vehicles and those with ice skates also travel on local straight lines. So we can think about these vehicles as though they are on a fixed track. With the stick and cart model, the little cart will always move on its track in such a way as to create a gap between it and the wheel attached to the stick. In other words the vehicle will always move on the track so that the wheel on the stick will roll down hill. Given a stick perpendicular to the surface of the sail, the travel of the vehicle on its track will be greater than the travel of the stick when the sail is at less than a 45 degree angle to the track. Steve shows this at 6:25. If the stick was also rotated, then another cos(theta) must be overcome to cause the cart to travel faster than the travel of the wind. For the upwind case given at time 8:24 this calls for a small angle between the sail and the track. Just look how far the stick would have to be rotated to make it perpendicular to the sail. That will make for a very small cos(theta) also. Steve himself discusses the problem with such small angles between the sail and the track at 6:47 while showing the stick rotated around. The stick and cart model is of course an approximation of what happens when sailing, so this model loses its predictive power just when it is needed, when we approach the speed of the wind. Steve presents another model, that of air displacement, at 2:51. With this model he shows the air clinging to the sail and then turning and following its surface. This is a different assumption about air behavior than that built into the stick and cart model. In the example at 2:51 the angles are not quite right for the faster than the downwind case we are interested in, and for this model we do need correct angles. The correct angles are given in the 8:24 example. However if air clings to a sail, then it takes some effort to remove it. This removal effort is known as drag and it pulls the vehicle backwards. When we use the correct angles we find that the displacement is small so the drag component question becomes critical. So like the stick and cart model, the displacement model stops being predictive just when we reach the point of interest, when the vehicle reaches the speed of the wind. I am not sure why, but Steve avoided discussing the Bernoulli Effect. Due to the Bernoulli Effect a shaped wing, such as presented at 7:56 can generate high lift force with little drag force when wind flows over it. This will cause air flow to be of a bigger concern than other variables, so the angles we see in the faster than wind travel cases actually become an advantage instead of a difficulty. With the Bernoulli Effect lift appears at about 90 degrees to the flow, without large drag. It is kind of magical. I wish the video had been longer. I would be happy to listen to Mould go on for hours. Steve, how about making a second video including the Bernoulli Effect?
"Thus the upwind sailing scenario that Steve shows at time 8:24 is equivalent to traveling downwind at about the speed of the wind." The scenarios are symmetrical, not identical: the roles of sail and keel are swapped.
@eyytee Interesting observation about the keel physics, which was not touched on in the video other than to say that the keel provides a conservative force that is just big enough to cancel off track forces. Which it is doing in both cases. In both the fast down wind case and the upwind case the sail provides the same lift, so the keel is providing the same lift. In both cases the water travels over the keel from fore to aft. However, I do see a difference in that the speed of water over the keel (or the speed of the land vehicles wheels are turning) will be higher in the downwind case because the boat will be moving over the water faster. So I don't see a symmetry, I see a difference in speed of the water over the keel, or the speed the wheels are turning. The sailing mechanics are identical. eyytee, did you not like the comment? It is well done no?
@Thomas Walker Lynch By symmetry I mean the forces vs. motion parallel and orthogonal to the wind: TACKING UPWIND: - sail drives the boat across the wind - keel drives the boat upwind TACKING DOWNWIND WITH VMG > WINDSPEED: - keel drives the boat across the wind - sail drives the boat downwind This also explains why to go directly upwind, the rotor cart would have to reverse the transmission, and turn the wheels with the propeller.
@eyytee I reworded that to say that the demo applies to both scenarios. Did you not like my post? Is it not well done?
@Thomas Walker Lynch It's true that you could hold he stick anyway you want, and push sideways with it. But the convention in the demo is that you move the stick only parallel to the stick, which indicates the true wind direction. In that sense I don't think the demo as shown applies to both scenarios. In a more general sense, there are similarities/symmetries, but it would haven been better if he had explicitly shown the downwind case.
I feel like that’s not the only framed photo of Steve he owns
The day a stumbled on his shrine was an awkward day
@Steve Mould Yeah, that’s it. “Shrine.”
@Stand-up Maths Isn't a voodoo work station a type of shrine?
@Stand-up Maths could temple be more accurate?
You are correct. There is another effect. when you sail slightly with the wind, then sail foreword, the apparent wind angle changes. Thus instead of sailing with the wind you are now sailing slightly against the wind. This happens because your vector combines with the wind vector and the wind angle the sailboat feels changes.
At 8:34 your sails are on the wrong side of the boat, you would be backwinding and actually end up traveling backwards not upwind. You would just need to switch the sides that the sail is on.
Fantastic explanation to something that has been at the back of my mind for many years.
Great explanation, with an excellent physical example!!
This is the first Brilliant-sponsored video I've seen that actually made me go "wow, I want that". Countless other "sponsored" videos talk about brilliant and what it does, but *seeing* that little graphic of the interactive coding lessons... that sold me. I wish child me had access to this kind of stuff.
Good explanation of how the boat itself can go faster than the wind. What confused me in the Veratasium video is how the boat can end up further down wind than the wind speed. Would be great with an explanation of that too 🤓
Agree! I still don’t understand that part after watching this video.
As BSc graduate and a competitive sailor (Canadian Championship), I'd like to point out that this is HIGHLY simplified. The curvature of the sail is like 90% of what makes one sailboat sail faster than the next. We spend a lot of time and brain power tweaking the sail's curvature. Championship sailing is truly the battle of the brains.
I have learned so much about sailing, and aerodynamics in 1 video. Thank you
@8:51 I could be mistaken about this, but my understanding of "tacking" is that it's the maneuver of bringing the bow of the ship across the wind, i.e., one turn in your zig-zag pattern, whereas the process of tacking repeatedly as to maintain a coarse that is overall directly into the wind is called "beating." This may be archaic usage, however, as all my sailing knowledge comes from Patrick O'Brian's book series.
Would be useful to introduce the concept of relative wind in this explanation! That's what the sail on a moving boat experiences.
Yes, aka “apparent wind”
In veritaseums video, they used the example of the poats traveling at angle, around a cylinder. That was intuitive as it gets.
Turns out it’s a mechanical advantage problem. The sail is a wedge.
Lol
In the model, the board is acting as a wedge. In a real sailboat, that's not quite the case, since as he says, the direction of the force is not the same as the direction of the wind.
Yeah, I was disappointed with that also. He only made passing reference to airfoils even though he was responding to a video that featured airfoils. I'm guessing he never learned to sail himself... A priori knowledge.
@EebstertheGreat that is correct, with a wedge the input and output forces are perpendicular, so the sail is acting as a wedge.
You have your flat sail acting like a wedge with the “sail” being pushed and not like a curved wing, which would be creating lift from the low pressure created by the air passing more quickly across the front rather than the way you are representing it... a common misconception made by non-sailors...
This was much clearer to me when I was on a frozen lake watching ice boats -- those suckers really move!
As a sailor and studing engineer, this actually made me geek out
Congrats on your 1mil! You deserve it, freaking love your videos, thanx!!!