The Physics of Sailing | KQED QUEST
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- Опубликовано: 30 сен 2024
- Northern California has a storied, 500-year history of sailing. But despite this rich heritage, scientists and boat designers continue to learn more each day about what makes a sail boat move.
Join KQED's QUEST to investigate the physics of sailing - a topic which still presents mysteries to modern sailors.
For more award-winning science and environment coverage from the Bay Area and beyond, visit www.kqed.org/s....
The physics explanation was half baked. I want to know exactly what each part of the sailboat is doing in a free body diagram.
You'll find everything you will ever need to know about sailing in the book Aero-hydrodynamics of Sailing : by Czesław Marchaj
Very detailed about every aspect of the subject.
With diagrams, illustrations and photographic images.
@@dogzebra2708 Do you know if there is any where to read it online for free?
@@latetron You're asking for a free book but you're not even willing to put in the effort to search for it?
At some point you don't deserve knowledge if you're barely even willing to lift a finger for it.
@@DrummerJacob I respect that, I didn’t mean for it to come off in a lazy way, I have searched for it, I have a paper on it and I was simply wondering any free recommendations for books on the topic.
@@DrummerJacob what a prickish response and a ridiculous thing to bite someone’s head off over. He IS searching for it. Asking people who might know where to find something is a very obvious and efficient way to sear h for something. Maybe someone has a link handily available, saving time and effort, and if not, there’s no harm done. Besides, the internet is supposed to be about sharing knowledge with others. Is knowledge only valid if you acquire it entirely by yourself?
Watching this video before sailing alone around the world
Good luck to you! What a fun adventure.
Tell us if you encounter the kraken lol
Rip
💀
Sounds rough. I imagine it'll get old after 30 days.
Was produced in high definition "360" max...
I will never choose to be with the physicists on a boat. They are too nitpicky about sail trim. Like comments about video quality, they suck the fun out of the whole experience.
@@Orcinus1967 ok boomer
@@michal5642 Actually I was born in '67. That makes me Gen-X kiddo.
@@Orcinus1967 boomer doesn't refer to age. ever heard of le 30 year old boomer sipping on monster energy
@@Orcinus1967 "actually i was born in 67'" ok boomer
Ok this will be a informative video!
“Square rigged sailboats can only go one basic direction.”
Nevermind.
xD
@@mamneo2 xD
@Ninja DIY xD
@A l xD
@@buckeye2300 xD
I came in confused about Sailing and left even more confused. Bad video.
same
Seemed pretty clear to me. Then again I had 2 semesters of physics and one of fluid dynamics.
Hard to take this seriously when the first thing they say is completely wrong. Square-rigged ships can most certainly sail into the wind. It's true that they can't lie as close to the wind as a fore-and-aft rigged ship, but they can tack.There's no way Magellan, Drake etc. could have made it around the world in ships that only sailed with the wind. Getting around Cape Horn from east to west is impossible if you can't sail your ship into the wind.
I think the reason is , under the force of wind, a square shape sail would attain a small degree of FOIL FORM. The wind hitting the leading edge of the square sail would be decelerated along the sail & exit the sail at a lesser force, & hence creating a foil form, I think.
Also, while square rig ships couldn't lie as close to the wind, not all ships of the day were square rigged. The premise that "modern" sail boats are an advancement from square rigged ships (and not an iteration on a configuration that has existed for centuries) shows they did almost no research on the subject.
interestingly, there is a line called a prior/prier known across northern Europe (since at least the middle ages) and depicted in various forms that 'alters the foil shape' of the sail as it passes from the mid part of the 'bellow' of the sail to the mast and on to the deck to be serviced. There are variants such as high prier and low prier (though named in Old High German, Danish etc) that are used to alter the upper and lower parts of the sail body. They were depicted and named in Danish, Dutch and German ships, but are never depicted/named in any British ships (as far as I have found), though there is something similar known as a slab-line on some UK square rigged barges (Humber barge IIRC). As far as I know its use(s) has not yet been analysed. I suspect they may have been for tacking, but also could be used to spill wind in increments, or stall the sail totally, or just to reinforce the sail body. Something similar appears in carvings/etchings of Viking ships and other early ships. Anyone who knows anything about them... please let me know, I've been looking for more info on them for years.
Gilbert Pilz, on day one of the zombie apocalypse I extend a hearty welcome to you and your village ... we could use someone with Magellan's good common sense!
With all them sails something else is happening. One should be put in a wind tunnel.
a luffing sail and a stall on an airplane wing are not aerodynamically equivalent.
Daniel Bernoulli (1700 - 1782) was not Swiss as this lady says on the video...he was a Dutch-born scientist who studied in Italy and eventually settled in Switzerland. Just because it is best to know the truth.
I learned nothing from this
TitanConceptss If you are into the physics of things...For those interested, much more detail, An EXCELLENT sail boat explanation site:
www.real-world-physics-problems.com/physics-of-sailing.html
Me either...
How? It's all about wind velocity and pressure.... Higher velocity = less pressure, which makes the other, high pressure (inward curved side of the sail) side, PUSH towards the lower pressure side because air is always moving to lower pressure. Sooo basically, the boat is pushed by the higher presuure side pushing towards the lower pressure side.
Did you pay attention?
Watch it again in half speed
8:50 "A sailor ... doesn't really need to understand the detailed physics"
Just 2 Chads out sailing on their boat with absolute disregard for physics like a total Chad
Average sailor W
And THIS my fellow sailors, is WHY we NEVER confuse facts with Television.
What does that mean?
@@JamesD2957 The video is an oversimplification to the point of being wrong.
@J The fact that they act like ancient sailors didn't use physics lol. Uptacking and uplift were concepts old sailors knew well. Of course a carbon fiber boat weighing a few thousand pounds is not the same as a 1500 ton frigate.
@@peterisawesomeplease In what sense?
@@Vrig See my reply to James. But in a nut shell both lift itself and turning lift from a sail into forward momentum are very difficult to explain without math. There isn't a great intuitive explanation of either that can be described in this short of a video.
Remember that time when wind was like, "Bruh, the ships changed. Guess we gotta change the way we work too."
I have 3 years of studies left then I'm buying a used sailboat and taken sometime off. For me it's the best thing in the world.
taken is past tense, study harder!
Steven Bryant Haven't you ever made a typo. Not sure why you need to be ignorant about it, web warrior.
I'm buying a Hobie Mirage sailing kayak and going to spend my days off exploring and camping puget sound where I live. and night fishing!
Audfile that sounds wicked fun
Mojo522 I read what have written. I believe that if you take the time to read what I have written that it I can take the time to look at it also. Like the difference between then and than.... It isn't that hard!
2:12 Fluid Mechanics Laboratory
aka F.M.L.
it's simpler to just figure out a workable route and let the sail dictate the angle of approach, turn away from the wind until the sail starts catching and let the wind push/pull you along. always look to your sail for information, it'll tell you how it wants to work.
hellsyeah, or point as high as you can till it starts to luff, then cinch the vang down, pull the sheet in a little, then fall off the wind a tiny bit. My shitty little boat will point hella high in a strong wind.
I'm disappointed by the fuzzy physics and the perpetuation of a series of myths kept alive by High School teachers who feel the need to oversimplify Bernoulli to explain lift. And total confusion between a sail that STALLS and a sail that LUFFS! They are not the same, they are essentially opposites. A sail presented to the wind at too close an angle becomes like a flag. That's call LUFFing. A sail presented to the wind at too great an angle loses the laminar flow of air around both sides (especially the "outside"), loses its lift, and STALLS.
It's funny to see the "water tunnel" demonstration of High School Bernoulli, because it demonstrates that the simplified theory is nonsense! The simplified theory says that the two flows -- over the straight side and the curved side of the old-fashioned asymmetrical airfoil -- arrive at the trailing edge simultaneously, predicting the higher speed over the curved side. In real life -- and in the underwater demo in the video -- that doesn't happen. And in real life, symmetrical airfoils work just fine, thanks, and airplanes fly upside-down pretty well, too! Disappointing presentation of "science"!
Fortunately, Newton's laws of motion facilitate a simple AND accurate explanation of lift, including symmetrical foils and inverted flight. Why not find some physicists who can talk about THAT on camera?
And finally, the famous curved piece of paper has NO flow over its bottom side, so it only proves that there is a pressure drop with increased flow, not that we need asymmetrically curved wings to get airborne.
Shame on KQED for this! Fortunately, the Internet has a number of accurate explanations of BOTH how airplines REALLY fly AND how sailboats sail. But not here.
Norm Rubin Norm, I agree it's quite weak and poor, but, hey! It's US TV after all. I'd be interested in a summary of how you use Newton. I've probably heard them all, so a summary of the salient phenomena is enough.
Also, which internet sources *you* recommend.
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Cheers
@109830174706736765037 US Public Broadcasting is often impressive. The only website I recall offhand that explains lift accurately is called something like How Airplanes REALLY Fly. But I have seen some that get lift right in the context of sailboats. There was a Q&A on one of the Q&A sites (Quora?) that asked something like "How could I explain upwind sailing to a scientifically literate friend?" A bunch of us responded and engaged in a useful discussion too. (That was my first introduction to the fact that a wind-turbine-driven-propeller boat can sail straight upwind!)
The simple Newtonian explanation of lift involves his 2nd [sic: really 3rd!] Law of Motion: For every action there's an equal and opposite reaction. So, in order to push a sailboat forwards, the sails have to "throw" an equivalent amount of air backwards. Specifically (and way more complex than necessarily), the forward momentum (mv) imparted to the boat equals the net (resultant) momentum (mv) imparted to the air that's deflected "aft".
And an airplane wing has to deflect enough air DOWN to hold the airplane UP. And a centerboard or keel has to deflect enough water to leeward (downwind) to hold the boat on track, pushing to windward (upwind).
There is one semi-complex part of what a sail does, which invokes the Coanda effect. Basically, through that effect, a sail can not only deflect or "curve" the airflow that HITS the sail (on the INside of the sail's curvature), but it can also deflect or "curve" the airflow that MISSES the sail and curves around the OUTside of the curve.
When the sail is too in-line with the wind, we first lose the force from the inside of the curve as the sail transforms into a flag. That's luffing. When the sail is too perpendicular to the wind, we first lose the force from deflecting the wind along the OUTside of the curve, because the Coanda effect has limits, and the wind will not curve around a sail that's perpendicular to the wind. That's stalling, and it happens similarly with airplane wings, keels, centerboards, and rudders.
Both of those airflows leave the leach (TE) of the sail at a much more "aft" or "rearwards" angle than they come at the luff (LE) of the sail. The resultant of that change in direction is partly sideways (downwind) and partly forward, and the keel or centerboard resolves that force into an effective forward force, and a sideways force that's mostly converted to heel (tipping). The forward force is conceptually identical (to Newton) to the forward force we'd get from throwing sandbags overboard, over the back of the boat. Except instead of throwing sand aft, we're throwing air aft.
The ratio of sideways force to forward force is not constant, but changes with the angle of the boat to the wind -- the Point of Sail. When cutting across the wind (Beam Reach), the sails are quite far out, so the sideways force is modest compared to the forward force.
When we sail upwind, we do several things that create bad effects (more heel and slower speed), in return for being able to point higher, i.e., closer to the wind. It's a compromise, trying to maximize our Velocity Made Good to Windward. E.g., we have to use a flatter sail shape than the high-power shape we use on a reach, and we trim in tight, with the boom more-or-less on the centerline. None of that is fast, but it lets most boats sail at a decent speed around 45 degrees off the true wind, which we couldn't do without those adjustments. And when we sail that way, the sails are probably pushing us sideways around 10 times harder than they're pushing us forwards -- but it's worth it.
Norm Rubin OK Norm. US *Public* Broadcasting is ok, but it also talks to a more general audience. Wisconsin Public Radio does an even better job.
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Now, I appologize. You went much further after your Newton summary than I intended. I wasn't looking for sailing instructions.
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I was holding back the way I asked about your Newton explanation. I understand lift well, but wanted to see how you framed it.
What you say is correct, but doesn't explain the pressure difference that causes the "lift" force in the first place, which, then causes the air to be "thrown" rearward. That explanation is sort of backwards --- or "If "A" always causes "B" and we can see "B" happening, then "A" *must* be happening even though we can't see or explain why it is happening". See what I mean?
It says that since air is thrust rearward, there must be an equal and opposite force forward that is accompanying it, but doesn't explain what causes what (or even talks about the forward force in reality). This, "what" is, of cource, the pressure difference that actually is the "lift" force that is transferred to the mast and movers the boat --- not the reward moving air as you know.
That version of the "Newton Explanation" is only half the complete story of "HOW".
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Your reference to Coanda is technically incorrect. Many mistakenly call the effect Coanda for normal airflow over the convex side of a sail/wing, but Coanda Effect is reserved for the narrowly defined effect seen by a high velocity jet, or sheet of air directed (forced) along one side of a curved surface (it is not defined [by Coanda himself] as any air moving past due to the ordinary motion of the surface through the air). The normal airflow around a moving sail or wing is not the Coanda Effect proper, although it obviously occurs for similar reasons. This is a common misconception, though I admit perhaps a bit of a nit to pick.
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BTW it's Newton's THIRD Law (equal and opposite) that you refer to.
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The web site posted in another comment
www.real-world-physics-problems.com/physics-of-sailing.html
is excelent at describing all the sailboat forces, though it glosses over the fine detail of the cause of the pressure differences resulting in lift. That's ok with me. The vast majority of discussions/disagreements about what causes lift is only among amateurs...
I also have my own set of authoritative on-line sources and wanted to see if you have any others.
--
Cheers, ScienceAdvisorSteve
www.challengerillinois.org/
Observ45er Sorry if I went too far, but maybe it'll be useful for somebody else. You had a much longer response here, then deleted most of it?
In that response, you attributed all the lift effect (and presumably the heeling effect, too) to the difference in pressure between the two sides of the sail. I've read that people who've measured those pressures found them significantly inadequate to explain the lift that's experienced -- e.g., the pressure difference between top and bottom of a plane's wing wouldn't suffice to keep the plane in the air. I haven't worked hard to reconcile every conflicting statement, and I've also taken "the Coanda effect" on faith.
Norm Rubin Hi Norm,
The 61 lines I see is what I posted. There was a glitch and I re posted it, then deleted a short portion that was the error.
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I understand and I see you have fallen prey to the many amateur discussions.
No, the pressure difference on the wing or sail *IS* the lift and causes the heel. Think carefully about it. In air (or any fluid) the only thing you have at your disposal to create a force is the fluid itself and the only way to get a force is by pressure differences. This must be understood first. There can be no other cause for forces (except for more detail when explaining just how that pressure difference comes about).
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People (pros) who have actually MEASURED the pressures have proved this is lift. People who tried to CALCULATE the pressure difference using long-standing bad assumptions got the wrong answer. This proved their assumptions were in error, not the correct concept of lift.
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What Bernoulli revealed to us is that in a classical flow, say along a pipe (where no energy is either added or extracted), there is a relationship between velocity and pressure. This is easily understood if you realize that a higher pressure region will push (accelerate) fluid toward a lower pressure region. Fast air doesn't create the lower pressure; it is being pushed toward it by a higher pressure elsewhere.
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Bernoulli's EQUATION only applies in a single stream, called a streamline. He revealed that as a bit of air moves along A PATH, pressure differences ALONG THAT PATH affect its speed (velocity) IN THAT PATH as you would expect.
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The error comes when you extend that to the two DIFFERENT paths AND also assume that the air on both sides of the foil arrive at the trailing edge at the same time (the equal transit-time theory). Using those two incorrect assumptions gives the wrong result -- EVEN THOUGH there are videos on-line showing this method today! Sigh! Two wrong assumptions don't make a right. In addition, the wing is indeed doing work on the fluid and, therefore adding energy...bad assumption abound.
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*IF* you use the Bernoulli concepts correctly in CALCULATIONS you do get the correct result, but the math is complex and completely unnecessary for understanding the phenomena happening.
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For sail boats, this is a darn good reference, though it doesn't get into the nitty-gritty of how pressures are changed:
www.real-world-physics-problems.com/physics-of-sailing.html
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. If you want authoritative sources, try any one, or all of these for a good understanding. While each author will emphasize different things or use slightly different ways to describe some things, the basic story is the same:
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An example of someone who started by doing his homework:
Peter Eastwell - teacher
www.scienceeducationreview.com/open_access/eastwell-bernoulli.pdf
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Weltner in PDF - "Misinterpretations of Bernoulli's Law":
user.uni-frankfurt.de/~weltner/Misinterpretations%20of%20Bernoullis%20Law%202011%20internet.pdf
Weltner as a web page:
www-stud.rbi.informatik.uni-frankfurt.de/~plass/MIS/mis6.html
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Anderson & Eberhardt AAPT paper: The Newtonian Description of Lift of a Wing-Revised 2009:
home.comcast.net/~clipper-108/Lift_AAPT.pdf
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NASA Glenn Research Center. This is a series of pages you move through:
www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html
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Or, AllStar is another good source:
www.allstar.fiu.edu/aero/airflylvl3.htm
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If you prefer videos...
Video lecture explaining the Bernoulli Principle. If you understand Newton, you'll clearly understand Bernoiulli after this video.
Dr Holger Babinsky, Cambridge University Engineering Department
ruclips.net/video/XWdNEGr53Gw/видео.html
His missing slides HERE (Click the Download Icon for the complete set of slides):
docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit?usp=sharing
This is the 2003 article he mentions in the video:
www3.eng.cam.ac.uk/outreach/Project-resources/Senior-glider/howwingswork.pdf
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Doug McLean Boeing Technical Fellow, retired; gets rather esoteric later in the video, but starts simply for the most part. (I've talked with him): Common Misconceptions in Aerodynamics.
ruclips.net/video/QKCK4lJLQHU/видео.html
For the "Newton" part of lift, watch the result of the pressure difference, in the GREEN VIDEO:
... amasci.com/wing/lasrWing.gif Quite impressive!
For the setup used to get that green video, watch part this 2 of 5 from 10:20 to 12:59
ruclips.net/video/H-qyrqxuH4Y/видео.html
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David Bentley Australian Air Force Cadets:
219sqn.aafc.org.au/Flight/Principles%20of%20Flight%20-%20web.pdf
Dave Bentley shows slowing of upper air & other misconseptions:
219sqn.aafc.org.au/Flight/Simple%20Aerodynamics-How%20planes%20fly.pdf
Dave Bentley Wings Don't Suck
219sqn.aafc.org.au/Flight/Wings%20don't%20suck-How%20planes%20really%20fly.pdf
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Cheers, ScienceAdvisorSteve
www.challengerillinois.org/
I love the anti-intellectual overtones of the narrator and the narration. Let's not go crazy and learn something too thoroughly!
1:52 I was dying that that jib sheet wasn't being pulled!
Me, too! :)
OMG IK
@mrpinks It's pretty clear that they haven't sailed before. Thanks for the sexist remark.
😂😂😂
Lmaooo fr
Yes all the pilgrims knew it was a one way trip because ships were only used to go there, not back. God, I have to stop watching now.
The emphasis that that's how "modern" sailing works is a bit stupid. Fore-and-aft rigs have been around for hundreds of years. Old vessels, even square riggers, could be fast and sail upwind. Replica tall ships have been know to outrun modern yachts fairly often.
***** I'm sorry but you're relying on trite misconceptions. I've been on a square rigger making headway upwind many dozens of times. Not as much headway as something fore-and-aft rigged but it's enough to make it upwind. The quoted number is about 66 degrees off the wind, but a good tops'l schooner or virginia-built brig or hermaphrodite brig (or something of the sort) could probably make more like 50-55 degrees if well-handled. The hulls on most of these vessels were deep enough to provide plenty of resistance to leeway. A squares'l will create an aerofoil, but not as efficiently as a fore-and-aft sail cut for the purpose of creating an efficient aerofoil.
If you want verifiable examples of tall ships outrunning modern yachts, Pride of Baltimore I outran several racing yachts the first time she went out according to the crew that was onboard. It's very easy to believe given her hull, rig, and size if you're familiar with sailing vessels. The crew in the documentary Pride: Legacy of the Baltimore Clipper talk about that briefly. Another example is HMS Rose sailing into Boston shortly after her construction. That's mentioned in detail in an article written for a publication of the San Diego maritime museum written by her designer who was on board at the time. You''re welcome to go find it if you like, that's the verifiable stuff that comes to mind.
But it's quite easy to see how an authentic replica of a fast sailing tall ship like a Baltimore clipper can outrun a modern yacht in many conditions. Vessels like this were very sharp with massively powerful hulls and huge rigs. They're also over twice the size of your average modern sailing yacht. Add a decent breeze and you can outstrip an average yacht, even an average racing yacht, in a variety of conditions, especially when you have stronger breezes and rougher seas which favor bigger heavier boats. This stops applying, of course, with hardcore racing yachts like volvo 70s or anything that's on foils. This is coming from a student of naval architecture who races yachts inshore and offshore and an experienced tall ship sailor.
And I should mention, no need to distinguish between modern sailing and historic sailing in that context. On a fore-and-aft rigged vessel from 2015 (excluding solid wing sails) the sails still work literally exactly the same as the sails on a fore-and-aft rigged vessel from 1890. Or 1800. The only thing that's changed is the equipment, material, and the loss of the gaff in some cases. Again, I'm experienced sailing modern and traditional craft.
ACAhmann r u high
+Tommy "Johny" Wiseau What, can't read more than four sentences? Words too long? I can give you a dumbed down version if you're interested.
+GrandOldPuba lol obviously you know nothing of sailing and sailing ships .....
generally a modern sail boats main sail can be let out to approximately 45 degrees give or take a few....
a square rigger can generally turn it's sails 45 degrees give or take .... now back when the Nina pinta and Santa Maria came to America those had round tub like hulls and we're literally some of the worst ships available. ..... viking ships were long canoe like ships with square sails
in posting here a link to viking replica square sailers and if you have ender addled you will know that these are sailing up wind ... yes they are beating into the wind and are capable of what a fore aft rig is. ....
just imagine a Lug Sail..... it's square and it can point into the wind. .... any good sailor knows how to point with any rig.....
One day am going to be a pirate. I want to learn to sail a boat, this is great for me
Hahaha
@@EdwardJamesKenway... For Real bro no joke
@@frpboy2562 gonna sail with the going merry or thousand sunny?
@@Moayad56 I like sunny but no I'll get a new boat
Nice production.
Not all pre-modern sailing ships were slow and could only be dragged along with the wind.
Airfoil shaped sails and boats that can sail into the wind have existed since the middle ages.
Even a square sail can move a ship in a vector 90 degrees to the wind.
Most tall ships had special sails to move into the wind.
Most long journeys follwed the trade winds, but if your ship can't be rowed, it has to sail into the wind at some point.
Lies, we all know sailboats sucked until it became an upper middle class hobby.
@@Name-ot3xwdude im just trying to live one piece
@@julianorozco5201 same here, but in Waterworld.
Was just about to say that, not even two minutes in and there’s a pretty common myth being introduced.
This is still a good description of the physics behind sailing, irrespective if the ‘into the wind’ debate.
4:15 is an incorrect demonstration of Bernoulli's Law. Try hanging the paper vertically and blowing on it...it will not move in the direction of the blown air.
Correctly analyzed, lift is caused by streamline curvature, which is not taken into account for by Bernoulli's equation, which only analyzes velocity and pressure gradients ALONG the streamline (from mouth to far end of paper), not PERPENDICULAR to it (from paper surface outward).
It did move in the direction of the blown wind for me, from the vertical. The paper will not move into compression on the blown side very much; and past a flat plane shape you are, as they mentioned correctly, are introducing a concave shape to the former low pressure side, thus equalising the system. Maybe you just don't blow as hard as you think! LOL Quote real evidence from a reliable source to counter me.
You are right, it's actually the Conandă effect. (The same thing that makes ping pong balls float in hair dryers.)
Haven't seen it in the comments yet, but square riggers were NOT parachutes. Using the braces, they caught the wind just like the Bermuda rig. The ship was "square rigged" to build a much larger virtual wing. SV Peking's mast stood 170 feet. It wouldn't be until the advent of carbon fiber that triangular masts would approach that size.
With all due respect, there is a scientific error in the explanation of the keel and rudder part, as per the end of the text immediately below.
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The starting point to understand how it is possible for a sailboat to sail against the wind is to understand how an airplane sustains itself (by Bernoulli's Principle and by action and reaction) and how an F1 "sticks" to the ground (essentially by action and reaction, and not by Bernoulli).
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When an airplane is cruising and flying completely horizontal, it is lifted almost exclusively by Bernoulli: the difference in geometry at the top and bottom of the wings creates lift. This force is perpendicular to the motion of the plane, and drag (drag, or air resistance) is minimal.
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As a curiosity, the aerodynamic drag of an Airbus A380 in cruise, for example, is 0.0265 (against 0.001 of a laminar fluid on a plate, and 0.005 of a turbulent fluid on a plate); even so, it consumes a huge amount of fuel, something like an average of 5 liters per second in a flight.
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An airplane can also fly based on action and reaction; the most obvious example is that of a paper airplane, whose wings are straight and could not be supported by Bernoulli. In its flight, however, its beak must be slightly tilted upwards, so that the air enters underneath and sustains it. The main characteristic of a flight by action and reaction is the high drag: a study with two types of paper airplanes showed that they have a drag coefficient between 0.8 ("Stunt Plane") and 1 (" The Glider").
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Note that even an airplane like the A380 will face enormous drag both in the climb and in the descent, due to the air that enters either below or above and will tend to brake it.
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Another situation in which there will be enormous fuel consumption is if it were to fly upside down: in this case it would be like a paper airplane, and its beak, in order to sustain itself, must be kept slightly tilted upwards. . To close this part, an F1 car "sticks" to the ground due to the forces generated by the wings (two front and one rear), which are basically inverted wedges: the airfoils of an F1 do not work like an inverted wing of an airplane ( they perhaps more closely resemble the elevators of this one). They are just wedges in which the natural downforce is generated at the cost of drag (this is sometimes positive, because it helps the car to brake. It can contribute up to 1g of braking), that is, based exclusively on the principle of action and reaction. .
As a consequence, the drag coefficient of an F1 is very high, reaching values as high as 1.1! A driver once commented that driving an F1 is like trying to accelerate a car with an open parachute behind it. . .
Having made this introduction, it became much easier to understand how a sailboat sails against the wind. That experiment where you blow on the side of a sheet of paper and it rises, almost like magic, is a clear demonstration of Bernoulli's Principle! Due to the greater air velocity in the upper part of the paper, there is a lower pressure (to understand, imagine a hose connected to a faucet, and this one is open: with the faucet open, but the nozzle of the hose locked, the force against the walls is huge, but when we unlock the nozzle and the water acquires enormous speed it may be that, even with a hole in the hose, it does not leak through it, but continues to flow), and with that the leaf rises!
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Note that blowing in one direction generated a lift force, in a perpendicular direction, which is amazing!
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Returning to the sailboat, it cannot face the wind head-on and walk against it in this situation, but it can be placed on its side, in such a position that the wind generates lift in the sails from the difference in inclination of its material (the sail is with a more rounded side, like an airplane wing); note that one of the components of lift is in the opposite direction to the force of the winds (and will obviously have a much lower intensity than this one) and the other in a perpendicular direction to this one (also lower intensity).
The tendency is for the sailboat to walk inclined in the direction of the wind (for example, either northwest or northeast, if we are talking about a north-south wind), that is, going sideways.
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And here comes the mistake.
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In a common boat, not a sailboat, the rudder is largely responsible for steering it (the helm changes the position of the rudder). On a sailboat, it also serves to counterbalance the force to one side generated by the sails, but this does not occur as an "inverted lift", or the same lift in the perpendicular but to the other side; in other words, they say that the Bernoulli Principle is at work there, when it is not. What happens inside the water is just action and reaction (that is, something more similar to the wings of an F1, and not to those of a cruising plane): if the boat tends, for example, to the northeast, just turn the rudder to the left, so that the course is corrected, so that the sailboat has the final tendency to walk into the wind. . As we are not talking about an active force, that is, in the end, it is the wind that is setting the tone (note: I am ignoring possible sea currents and proximity to surf zones), the tendency is that, even with the rudder positioned in such a way as to counterbalance the force of the sail in the opposite direction, it will still be displaced in an inclined manner, either to the northwest or to the northeast (in the case of a north-south wind), however the solution is simple: after a while, just invert the position the sails, as well as the rudder, so that the vessel zigzags around the main straight path into the wind.
I've always been so fascinated on how sailing ship works!!
@ 6:00 "In physics, they said you have a vector this way and a vector that way, and a result in vector - tricky stuffs", she didn't know what the heck he was talking about and has zero idea. LOL!
I learned to sail at 16 in San Diego, we stayed at a resort that had sailboats for rent, we went down and said we don't know how to sail, the guy renting the boats said it's simple, if you catch the wind and move forward, you are sailing, if your not moving, your not sailing, it's that simple, that was 55 years ago, nothing has changed
Do you still sail? I live in San Diego and would love to learn a thing or two.
"square" is an interesting word, i heard just yesterday.
"i stand squarely behind my decision " . come on , man ...............
Best analogy about how a boat sails when wind is forward of the beam is "squeezing the seed". The person in this video did mention this, not many know this, most think its only the lift, like aeroplane wings that move the boat.
+bethells86 but small sport sail boats have large keels, but what about large sail ships with square sails? how do they keep balance and move forward? ...a stupid question because I'm lazy to do some research
The web has made many lazy :) Watch a movie called idiocracy, shows what happens to human race in a few decades from now, all dumbed down, its all part of A21 :)
All sailing boats use same principles to sail, Older ones would have used lots of ballast instead of deep keels.
Why does the air/liquid accelerates going around the curve surface? The reason given thus far is that it needs to catch up with the flow on the other side. Why?
By the way when you blow on one side of the paper, the paper doesn't have to be curved to move across the direction of the flowing air. A flat piece of paper will do. A curved paper first wants to straighten out.
Correct me if I'm wrong, but I'm quite sure sailing against the wind with triangular sails is nothing new, been used for Millenia. Viking ships, and several mediterranian ones used those principles, albeit without a keel so I'm not entirely sure how those particular sails worked, but they did not work like the square sails where its merely pushed by the wind.
Also those square sails are needed in such huge ships, you cant quite easily correct weight by shifting passengers in a boat of that size.
Large sailing ships had a large amount of ballast in their lowest deck, acting the same as a yacht's keel.
Square sails do in fact work fine for going to windward, they're just a little less efficient at it than a small sailing yacht with Bermuda rig.
You MUST have a keel to sail upwind. So those triangular sails didn't do any good (regarding sailing upwind) and in principle the same as square sails.
Vikings didnt use triangular sails, however in the mediterainian these did exist. Also vikings have been around for (a) millenia.
You don't have to have a keel to sail upwind, you just need a hull where the submerged part is capable of inducing the water to flow around it rathher than under it, ie. any reasonably deep hull.
not so - a boat itself acts as a resistance to lateral movement in water and therefore is per-se a keel. However a deeper or heavier keel, dutch boards etc etc makes the keel effect more efficient.
Very disappointing - no mention of magic and the rituals necessary to invoke the sail gods
Everything in this Universe has its own laws (physics, maths, etc.). Those laws run the Universe beautifully, and those laws didn't even have to evolve either. They were born the moment Big Bang happened. I refuse to believe this Universe just happened by accident. Man! Everything is perfectly engineered down to Planck level.
Laws are just explanation of how things exist/happen in this universe.
It's not that everything in the universe obeys the laws
So where do I learn about "circulation flow field," "viscosity theory," and "starting vortices?" (On RUclips) . 8m05s
I think you're exaggerating a bit... but yes, this explanation is very shallow, if not on some points even inaccurate.
It was produced in high definition but you can't see it.
Components of lift are far too complex to be explained with one principal such as Bernoulli's. There is no law that states that flow must "join" together at the termination of a lifting surface with the same particles it entered the surface (in fact, it does not). However, some of the lift is created with this pressure difference. People use that principle because it is easy for most to understand but that is only partially how a wing or sail generates lift.
Correct! Most of the force of a sail comes from Newton's Second Law of Motion (for every action, there is an opposite and equal reaction). It is the deflection of the wind in one direction that causes the force of effort in the opposite direction.
This documentary completely misses the mark: It's the KEEL, not the sail, that allows "modern" sailboats (invented at least as early as the 14th century AD) to sail into the wind. Square riggers' best performance is when the window is off the beam or a little forward of it, not off the stern, so the idea that they could sail only downwind again shows a lack of understanding of the physics they are supposedly talking about as well as the history of sailing.The deep keel is made possible by two key factors: (1) smaller boats with smaller cargoes after the introduction of steam, and (2) stronger materials for masts, spars, and hulls. The key advantage of the triangular "modern" sail is that it can be handled by a much smaller crew.
+Moon Sims centerboards are useless when sailing with the wind.
Gonna go and practice this activity... looks fun . Thank you.
I'm kind of baffled by the intro, "before there were airplanes, before there were trains, there were sailboats." I mean, yeah, it is not wrong, but why not "before there were internal combustion ships, before there were steamboats?" This is like saying, "before there were pencils, before there were teapots, there were shoes." Yeah, you are not wrong, but I still question your thought process.
+Dan DCC91 ...your dealing with nasanazi...like talking to a group of bankers about baseball.
+Dan DCC91 It's related more than your examples because they were all mass transit methods.
The candle was right for 1840...the rocket engine was right for 1970...we need to move on to nuclear or electro magnetic...the metal ships might not work in high radiation areas....the human race will never leave Earth with the current NASANAZI administration...they are anachronisms!
John Rogan what the hell are you talking about?
Dan DCC91 I straight up blocked them; they are some old crazy american dude going on about NASA-NAZI's.
No clue what he is on.
The two are closely related. The reason that the angle of attack causes lift to generate is that, by keeping the foil/wing/sail at an angle to the flow, you are in fact forcing the air to accelerate around the suction side (leeward side) of the foil, reducing the pressure on that side and sucking the foil in that direction. The angle of attack is essentially another means of controlling the shape of the air foil as seen by the air flow. Too large an angle = too much curvature = stall = drag.
Note that a wing will also loose it's force vector perpendicular to the chord if the angle of attack is decreased too far, and when sailing a boat in any direction with a component into the wind, the sail is best used with the chord nearly parallel with the apparent wind. Increasing this angle will result in loss of laminar flow and reduced performance of the sail. So, yes, I think that makes them essentially the same (see hang-glider and PlaneSail).
This video contains old misinformation.
this video keeled me
I was watching Guardians Of The Galaxy 2 when all of the sudden I had an intrusive thought about how ships sail, so here I am.
Is this Groot's burner account? We're suspicious. Glad you found us.
"A luffing sail is not the equivalent of stall on an aircraft", per minute 7:40, it would be an over-trimmed sail.
And when I criticize an over-trimmed sail, I say it is STALLing (because it is). As John Wilson says, it is most definitely NOT LUFFing, quite the opposite. That statement is just embarrassing.
Right, that would exceed the critical angle of attack of the foil, detach the laminar flow of air, and cause the telltails to spin.
0:45 "(...) they were slow" - compared to what? Steam ships? Ctrl+w.
@@InForTheLonghaul modern boats are slow as well then
1:40 Lift from the sail is *_perpendicular_* to the wind. It tries to make the boat plow through the water across the wind, but the keel can only slice through the water edgewise.
The water prevents the boat from drifting sideways by pushing on the side of the keel, and *_that_* force is partially upwind.
5:40 The force from the keel has no forward component. Only the sail pushes the boat forward.
End: You need to explain torques and ballast, heeling and righting moments.
I am watching this video so when i build a ship for fictional couple, it"ll sail.
"Square rigged ships only went in one basic direction - with the wind" PARDON?! Clearly, this statement is false. What did they do if the wind changed, or if they had to return home against the trade winds?
In fact, square riggers, while not as efficient to wind as a modern sailing boat, could sail at a reasonably close angle to the wind.
Ugh. Its people like you that make me wish I had cancer. I want you to think about your question, think about the phrase "trade winds", contemplate your question. Then get back to me
Don Adamms I guess I wouldn't be as offended by the sheer ignorance of your comment if you didn't make it such a wildly offensive manner. Yes, a square-rigged ship's best point of sail is downwind. This made the trade winds useful for quickly crossing oceans. But people have been sailing into the wind in square rigged ships since at least the 12th century and probably well before that. Don't be such a putz.
If you consider 70 degrees "close to the wind" they could.
Despite Don Adamms obnoxious response, square rigged ships were quite capable of sailing on a beam reach, and smaller brig rigged ships could even manage a close reach.
Calling on my experience as a tophand on a tallship, squares are set in two ways, baggy and perpendicular to the wind when the wind is aft the beam this is the best time to sail these vessels, and on the slowness that the video states champion of the seas set a 130 year record of an average of 19 knot over 24 hours in 1854 that is just under the speed of the faster range of cargo ship today.
The second way to set squares is to achieve the airfoil like a modern sloop does but instead of haveing the mast as the leading edge of the sail they are projected out by the yards and then the luff (leading edge) is twerked (actual term for over tensioning a line) then the trailing edge is slacked a touch, this makes your wing shape. The major problem to going high upwind is the fact of the shrouds prevent the yards from achieving the same angle you can apply to a boom when closed hauled.
On the 60' Brigintine I sail in we have got 8 knots at 35º off the wind in under 20 knots of wind
And 9 knots with 12 knot of wind while running, and for a cargo style sailing ship of it's size and at about 30 ton with less than 1000 sq. ft of sail.
Modern sailing is just using a simpler rig and boats designed for sailing not trading
Being a sailor I'd very much love to delve into the detailed physics of sailing. I watched this video and didn't learn anything.
yes
This video wasn't pitched towards people incapable of learning anything from it, as you so clearly described your inability. It's designed more for the open minded person such as myself, who is ready to embrace such information contained therein. Perhaps you should ask someone to explain some of the basics of sailing to you. It's unusual for a sailor to admit their inability in this regard, but there you go.
"produced in high definition" only plays in 360p
So many people with sailing experience are griping about the specifics of what this video said. Get the hell out of here you clearly know how to sail.
For a laymen like me, who has no idea how a boat can sail upwind, this was sufficient. I learned a thing or 2
They're saying that the techniques listed are wrong, meaning you're learning incorrect information, are you stupid?
@@smittywerbenjagermanjensen1051 im not in the interest of learning about square sail ships so the controversy is beyond my interest
I think it would be more helpful if there were diagram showing wind direction and airflow around the sail. Thanks for the effort.
There is, its called points of sail
Black Ninja149 cf
I would comment as a life long Square Rig sailor and Master of Sail, that square sail rigged vessels DID NOT just get pushed by the wind. The China Clippers, the epitome of the class, could point between 35-40 degrees off the wind, and square sails operate in the same manner as fore and aft sails as the weather edge of the sail it stretched tightly down to the yard below and angled so the wind passes along its surface from side to side but UNLIKE fore and aft sails ONLY, square sails also have a downward wind flow also causing LIFT. The big cargo square riggers of the late 19th and early 20th centuries were massive but NOT SLOW as you implied. These ships could reach speeds of 20 plus knots or about 23 miles an hour.
The big Clipper ships held oceanic route records from the mid 1800's until the 1990's. Much of the speed was born of the hull designs, very much ballast balanced by as much sail as they could put up. They also plied the trade winds and ocean streams as much as possible. The ships often paid for their construction after a one way trip, like to S.F., Cal.
Sometimes they were even broken up for their valuable lumber. This preferable to losing the ships to Teredo worms. This was inevitable as copper plating wasn't mounted on the bottom of the hulls to save money, speed construction, keep the cargo weight high and keep the the hull speed high. If someone reads a script that is pertaining to a subject that they don't know well, is it fair to ridicule the orator? It depends on how well they were paid!
For me it depends on if they are trying to pass it off as if they actually do know and understand what they are reading
I dont get how it works, but a brother told me...he just got into the Sailboat & went into the water & learned by himself how to move with the combination of 1st...what direction he wanted to go + the wind, the sails , the keel
In other words....start w/a small Sailboat & work your way up. It's that sounds credible ??
dynamical my new favorite word
Right? Credibility sort of becomes suspect at this point...
P]]9p
Well, no. Luff ≠ stall. Luff is eased - too little angle of attack. Stall is over-trimmed, too much angle of attack.
Good intro vid for noobs though. 😏
Informative video. Don’t be deterred by the negative comments. Worth a watch.
For anyone out there who doesn't know, the old sailing ships they show in the video were NOT only able to sail in the direction of the wind.
Thanks for a great video, that I enjoyed a lot.
About lift: it is due to the air(and water) viscosity.
Whatever foils/sails you put in the flow of a superfluid with zero-viscosity will NOT generate lift. But air and water are not superfluids, so they obey The Kutta-Joukowsky condition: when the flowing air/water leaves the sharp trailing edge of a foil, it will continue flowing in the direction of that sharp edge instead of making a sharp turn around it (like a true superfluid would).
The following production is produced in high definition. RUclips quality menu: 144/240/360p. Great content, brought here by 37th America Cup.
4:03 and here I thought it was the midi-chlorians that leads to the force
Down wind,just bag the wind, upwind,pull the sails in till they just stop fluttering on the leach,, YOUR SAILING!!!!!!!!!!
I don't think it was the sail technology that was the major limiting factor in holding ships back from sailing upwind. They had jibs and spankers even on the old ships. It was rather the heavy, bulky hulls that created the limitation: too much water-resistance going forward compared to the side-ways resistance. Also, the sail area per weight was much higher (and weight translates to more forward water resistance).
Scientists are terrible at explaining things lol
That's why there are professional technical writers. They translate what engineers and scientists say to language most people can understand.
Yes, I was a tech writer for 30 years when I wasn't teaching sailing.
That's why technical writing is such an important profession (I did that for 30 years) Tech writers translate the things scientists, engineer, and programmers write into something the intended reader can understand.
Nothing at all wrong with being a scientist, engineer, or programmer. Some of my best friends are. Of course, I wouldn't want my sister to marry one ;)
ppplll000999
That is an excellent point. It's all the more reason why good tech writers are important.
Engineers and most programmers DO understand how things work. So much so that it is nearly incomprehensible to them that there are people who do not.
take a landsurfer,the wheels stop the thing from sliding sideways as a boat does without a keel?
The wheels do not generate lift?
... Not sure it's called as such, but it's very comparable: when too much side force is present they "stall" much the same way, and you can "re-attach flow" by turning your wheels to match the direction and/or speed of the "flow". Driving on dirt /gravel /icy roads this is an important concept to understand.
I was confused as to why a keel would generate lift, but I think I understand now. The keel typically has a teardrop shape but the shape is symmetrical and the keel does not *seem* to be upturned into the oncoming water like an airplane wing needs to be. You have to have one or other. Either you have to have an asymmetrical wing so that fluid travels faster over one surface, or you have to upturn the wing. A keel leans in the water but its leading edge is not upturned. However, the reason the keel does generate lateral lift is due to the 'angle of attack' of the boat. A sailboat does not travel 'head on' through the water. It travels at a slightly skewed angle off center (think moving forward while the hull is turned slightly to port or starboard). It's this skewing that 'upturns' the keel wing and causes lift.
No. Not really.
But it's not you misunderstanding, it's that their description of the keel is very misleading. A keel's purpose is less to generate force and more to ensure unidirectional movement. Think of it this way, go grab a credit card, driver's license, library card, etc, and fill up a sink with water. Slide the card through it so that the skinny part is "cutting" through the water. Moves pretty easy right? Now try to move it side-to-side. Doesn't work so well. It takes a much greater force to do it. That's the principle of a keel. It doesn't *add* another vector, it simply cancels out anything but the desired one so that the only motion is in the forward/backward direction.
Without a keel a sailboat would still go forward, only you will notice the boat will also shift and hop sideways, which is bad for navigation and the boat and also is incredibly dangerous.
decidiousrex Keels, dagger boards and centerboards actually do generate lift. But I agree that the lift they generate is fairly insignificant and their main purpose is to stop the boat from sliding laterally. I've sailed dagger board boats without the dagger board. It can be a bit squirrely but it's still doable.
Hans Zarkov Well, of course based on their design they might, but they don't need to. I'm sure there's benefits to it, but generally any design which would incorporate lift will inevitably have some degree of drag, which in water is BAD. Very bad. Hence most keels are as thin and simple as possible.
decidiousrex Nearly all keels, dagger boards and centerboards do generate lateral lift, not because they have exotic designs but because a sailboat's hull travels though the water at a slight angle off center. See: Physics of Sailing
www.real-world-physics-problems.com/physics-of-sailing.html
Hans Zarkov Yeah, I guess it's a kind of weird thing to call lift, though yes it technically is, but it's still just the keel resisting sideways motion.
Announcer: “The following KQED production was produced in HIGH DEFINITION.”
Actual RUclips video: 360p max
I laughed that it said "in high definition" and it's in 360p max!
Gold content
sailing seems like it would be fun to do but it looks uncomfortable when the boat is leaned right over
+Rick Pelland It is fun, especially when the boat is leaning to one side! :D
That is why I sold my mono and bought a catamaran.
It depends what kind of sailboat you're on.
I've sailed Norfolk Broads yachts and they're pretty stable, quite wide so don't lean much and the rig is optimised for that style of sailing.
Modern racing yachts are designed for high speed over comfort so lean, unless you sail a catamaran for stability.
Dude heeling when you are in a sailboat is one of the most amazing feelings ever. It might look uncomfortable but it is so fun especially when you are in the side closest to the water.
Same, you get a feel for what the wind is doing so although it makes you nervous the first time it happens, you enjoy it from then on out.
Best thing if you're nervous is to try sailing a little dinghy with the simplest kind of sail, then you're directly holding the main sheet and can feel the power of the wind, you can let out the sail to reduce heel but soon get a rate for getting as much speed as possible and at the same time learn all the important basics of how the wind interacts with the sail.
Among His* Signs is this, that He sends the Winds, as heralds of Glad Tidings, giving you a taste of His ( Grace and) Mercy,- that the ships may sail ( majestically) by His command and that ye may seek of His Bounty: in order that ye may be grateful!
Holy Quran; chapter 30; Al Rum (The Roman Empire) verse 46.
* Allah Subhana Wat'ala; Most Gracious, Most Merciful.
wow there some sceptics out there...I learned something so thanks!
The analogy is always “a sail is like an airplane wing…”, but in fairness, an airplane wing is like a sail because sails predate airplanes by a lot.
Just sayin’.
I learnd a lot from this,Thank you so much!
"the following was produced in high definition" - best availability... 360p....
I was already familiar with sailing when one of my physics professors explained that a triangle sail when properly set "sucks" a boat forward as air moves across the sail and creates lower pressure on the outside of the curve not unlike the wing of an aircraft pulls an aircraft from the ground with lower pressure on the top of the wing.
We all knew that he was talking about pressure differential but apparently liked using the pull or suck analogy.
What do you think a 1600's pirate would think if someone time-traveled with a modern yacht, and sailed circles around him... literally... ??
He'd probably tweet mind equals blown... cuz ya know ... twitter was definitely a thing back then ^‿--
That's too much damn work, on my motor boat I just need one hand on the throttle to go forward and on the other hand I can hold a beer
pretty much gotta use sails if you wanna go transoceanic, unless you're in a massive boat. fuel limitations
about treefiddy sailing is more laid back because with a motor boat you have to always have to hold the motor. But with a sailboat you can just make a knot in the sail and walk away. Unless the wind changes. They say bullshit like “Like any novice sailor will tell you, it’s harder then it sounds.” If you enthusiastic with sailing, you can sign up to a lesson and learn the basics within 1 week. Of course bigger sailboats are harder to use then like a pretty small one.
Now you sir, have the right attitude! You can come sailing with me any day. The rest of these nitpickers can stay onshore and argue.
why do stream lien HAVE TO ACCELERATE when encountering the curved part of the wing? What information they have about the geometry? in fact if you exaggerate the wing you could picture the lower line simply stopping? Case of a half wall
"Was produced in HD" ... Then I see 360p
WTF mate ?
My Grandpa taught me sailing the same way he taught me driving manual cars and motorcycles:
Step 1: Learn the Controls.
Step 2: Get used to it!
Step 3: Don't be stupid!
Step 4: Get used to the scolding..
Step 5: Naah you'll learn better by doing.
360p = high definition
that expression was when coffee was cheap. today, it would go something like this...
"that and $7 will get you a cup of coffee"
Do you have an explanation as to why the air wants to rush round the outside of the sail? I guess it is something like - as the air reaches an oblique sail and passes the leading edge, low pressure is created as this air has to turn a corner. ie the very act of putting an obstacle against the wind will tend to cause a vacuum in the lee.
Yeah, I guess that hitting something head on like that redirects the energy and creates an inward spiral that follows the curve. It's a fight of the higher pressure vs low pressure, so the side with least resistance will take the hit.
The air on the top (side) curve has to cover a longer distance than the air on bottom flat side. The air on the top side has to go faster to meet the air on the bottom side. See Bernoulli's Law. Good video, I just now learned this about sailing.
The explanation for lift is wrong. There is no reason why the air taking the longer way should reach the end of the profile at the same time as the air taking the shorter way.
"The following KQED production was produced in high definition" -> check quality setting and found 360p XD
Hey guys, just a note about why lift happens, this guy is chatting bull. Bernoullis law doesnt apply in the case of a wing (or sail). For his law to apply, certain assumptions must be made. firstly that the fluid has zero viscosity, but as we can see, the fluid 'sticks' to the shape of the wing, which is a viscous effect. secondly, that it is a steady flow. which as said in the video, it is not. Finally, Bernoullis theorem only applies to a single flow, once you talk about flows above and below a wing, its moot.
While Bernoullis can describe some of what is happening, the fundamental law behind lift is newtons 3rd. watch the flow as it comes off the wing, its at a different angle, meaning a force was imparted on the air by the wing, and thus vice versa
(im an aerospace engineering student and even people in the aero business get this wrong (including the most of the internet), and this isnt coming from me, this is coming from Dr Iain Dupere at Manchester University)
***** Don't be precipitated. The guy there above is half right. Newton's 3rd law actually explains the main forces in wings and sails (look at NASA's recent researchs). Bernoulli's principle "does" exist, but it's too weak; thats why in close-hauled the speed is very slow; much less if compared to air speed in plane's wings. There is more: en.wikipedia.org/wiki/Kutta%E2%80%93Joukowski_theorem. Also, one cannot test Bernoulli in fluids, because it supposes gas flow and pressure; in fluids (thus not compressible (not as much as air to this case)), you will be actually testing only Newton's 3rd. Even scientists have some outdated beliefs.
www.grc.nasa.gov/WWW/k-12/airplane/lift1.html
***** Wow that is a strong response. Unfortunately it is also completely wrong. Bernoulli himself would not subscribe to this. A few things to note:
1) Bernoulli's equation is a description of the momentum equation under three very specific conditions: inviscid (all viscous forces are ignored), steady (i.e. time invariant) and incompressible (actually not too bad here although interestingly ***** also comments that fluids are all slightly compressible). In fact it is easily understood, if the only two forces acting on a fluid are pressure-area and gravity, then for the flow to accelerate it must either see a drop in pressure (i.e. it accelerates from high to low pressure) or a drop in height or both. Far from causing low pressure with high speed, in fact the low pressure creates the high speed.
2) Bernoulli's equation comes from consideration of a stream tube and so only applies along a streamline and not to more than one streamline.
Bernoulli then, definitely falls down in this application, on two counts (inviscid and more than one streamline (the flow either side of the sail is on two different streamlines).
Someone else refers to Potential flow and, in particular, the Kutta condition. This is a common approximation, in which the flow is assumed inviscid apart from the generation of vorticity. This is a fudge since Kelvin's law shows that vorticity cannot be created in inviscid, incompressible flow. To have the same constant on either side of the sail requires uniform horizontal flow which has no vorticity.
All this leads to the well documented result that, in the event that Bernoull's equation is correctly applied to a wing (or sail) the actual lift will be zero!!
The Kutta condition does give a crude estimate of the lift (and was used before the days of CFD) and does give some indication of why the viscous effects are important in this case, however, Bernoulli does not strictly apply (the flow violates one of the conditions) and certainly is a poor explanation without some reference to the Kutta condition. As pointed out, it is better to say that the flow leaving the sail follows the path of the sail due to a subtle but important viscous effect (this could also be described crudely Mathematically as Kutta's condition) and the turning of the flow gives rise to the lift force through Newton's second law (force causing a rate of change of momentum) and third law (equal and opposite reaction - flow is pushed in one direction by the sail causing a force on the sail in the opposite direction).
If ***** wishes to come along to the University of Manchester I will happily not only teach him this, but show him how this works.
PS Application of Multivariable calculus leads to zero lift! precisely because Bernoulli does not apply in the strict sense of the term to this case.
blowing over the top of a sheet of paper lifted it up...good demo.
The laws of physics are so perfect... almost like they were... designed by someone...
Yeah bro science
+Andrew McKay science discovers not designs.
they are perfect. kind of like DNA...
+Rusty Shackleford Science and laws of physics is how humans interpret things that happen naturally. Sailing has been around for thousands of years in South of India and the Pacific, no science or physics developed it. It was discovered and then explained through physics by curious beings called humans :)
+bethells86 Science is "how humans interpret" things around them. :)
This is outdated. The Bernoulli Effect is a minor player in lift. There's no "deadline" for the streams on the curved side to meet up with their counterpart on the flat side at the trailing edge (so they don't need to accelerate). In fact if anything, hitting a curved surface would slow down the stream because it's an obstacle.
They've discovered that something called the "Coanda Effect" plays a bigger role. This is the tendency for molecules near a surface to stick to the surface and the molecules next to them stick to those molecules. This accelerates the stream away from the direction of lift (90° to the direction of the stream). This acceleration produces an equal and opposite force in the "lift direction" causing the lift. This is a simple example of Newton's famous equation F=MA.
That's why you can make a wing create lift upside down by just adjusting the angle of attack (watch an air show). The Bernoulli Effect can't explain that.
- Warren - BSc (Physics)
Anyone ever notice the "models" in these videos never use a "wing" shape that is only a few millimeters in thickness from front to back like real sails? These demos use sails that are apparently made of cloth several feet thick on the luff. The models also show the wing directly facing the wind, instead of properly trimmed. The sail would be luffing horribly if it was trimmed like this video shows. SERIOUSLY, watch this video again at 3:26 seconds. The wind would push the sail cloth flat from front to back since it is only sail cloth! There would be nothing to hold the curved shape against the forward wind.
Square-rigged ships COULD sail
into the wind! Just not very well.
Channel 9, maybe a wee bit of
research would be handy.
steve
Woah 12 years ago!!!
The terminology is confusing from the get-go, and no....liquids do not follow gases in wind tunnel testing.....water (liquid...) is a LOT heavier than a gas (the air...) so it reacts much slower.
I saw an MIT video from an aeronautics class and the professor was saying that the Bernoulli Effect is not what cause lift on an airplane wing. I’d love to know the engineers in this video have to say about that?
Square sails only sail in one direction? Nope. Bernoulli's principle? Nope. At normal wind speeds, Newton's law is the primary reason how the sail generates force. Horribly misleading. Are they really aerospace engineers at Ames? Huge fail.
337 people know square rigged sailboats could not only sail across the wind, they could sail slightly INTO the wind. What a horrible lie to begin a documentary.