How Does A Sailboat Actually Work?
Sailing 12 years ago 674,117 views
How lift actually works: http://www.youtube.com/watch?v=aFO4PBolwFg More with Canadian Olympian Hunter Lowden: http://www.youtube.com/watch?v=6YVOPUkbu6g How does a sailboat work? The standard idea is that the wind pushes the sails from behind, causing the boat to move forward. Although this technique is used at times, it is not the most efficient way to sail a boat (and it means the boat can never go faster than the wind). Lift is the key mechanism driving a boat forwards. As air flows over the sails, it moves faster over the outer side, creating lower pressure than on the inner side. This produces a force which is mostly to the side and a bit forwards. Lift on the centerboard pushes to the opposite side, cancelling the sideways force and adding a forward component of force to the boat. numberphile http://bit.ly/numberphile efit30 http://bit.ly/O4CMme appchat http://bit.ly/NxAMlX erikaanear http://bit.ly/MdyUzQ whoisjimmy http://bit.ly/LtFzpW minutephysics http://bit.ly/Muh6CC 1veritasium http://bit.ly/MrupzL
The key component of the sails diversion of flow is that it diverts a relative crosswind (relative to the sail boat) backwards, which coexists with a forwards force exerted onto the sail (which in turn exerts a forward force to the sail boat). For a given true wind speed relative to the water, then the crosswind relative to a sail boat is the sin of the angle between the path of the sail boat and the path of the true wind, and this crosswind is independent of the sailboats speed.
For sailing upwind, the more efficient the sail boat, the smaller the angle between the boats path and the wind's path, and the smallest angle for a specific sail boat is called "beta". The fastest speed (with respect to the water) occurs when the sail boat travels at 90 degrees across the wind and "beta" degrees downwind. Remember the crosswind (relative to the boat) is independent of the sail boats speed and only depends on the sail boat's heading with respect to the wind.
Very efficient sail boats like catamarans can "outrun" the wind, meaning their net downwind component of speed can be faster than the true wind speed. The Americas cup catamarans can achieve net downwind speed faster than 1.5 x true wind speed both downwind and upwind. Although the sail boat "outruns" the wind it's currently in, the wind ahead of the boat has a head start and the boat continues to sail into a continuous supply of crosswind, again regardless of the sail boats speed.
Somewhat related, what is known as a directly downwind faster than the wind (DDWFTTW) land craft, drives a propeller with it's wheels and can go faster than the wind that propels it. In the case of the "Blackbird", it could go directly downwind about 2.5 times the speed of the true wind.
https://en.wikipedia.org/wiki/Blackbird_(land_yacht)
https://www.youtube.com/watch?v=5CcgmpBGSCI
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sorry, I know you have your reasons, but there might be more effective ways to get to your goal.
The algorithm is A LOT smarter than I thought if it can do this kind of connections.
Warning, long explanation:
but because of "vmg" or velocity made good, It is actually more like 95°. VMG is the speed that the boat is travelling in the direction the boat is pointing because all boats slip to the side a little because the centerboard can't be 100% efficient. The more downwind one turns, the less sideslip there is (because the sideslip is in the direction of travel). Anyways, turning 5° more downwind helps eliminate sideslip and therefore 92-98° is the fastest point of sail.
To windward, 'good' is towards the top point you're ultimately tacking to. A boat at 10 knots on a tack may be progressing towards the 'top point' at only 5, depending upon direction. In racing, it's a measure of the speed of the 'perpendicular progress' towards the top mark, irrespective of what your zig-zag course is, where you're pointing, or where you are sideways on the course.
Invert similarly for the leeward mark. HTH
Which direction is fastest is actually is far more nuanced than just a single number. For an average cruising boat, the best angle is probably around 110-130 degrees to the wind, but for a racing boat this angle is larger. For an ice yacht (these experience almost no forwards drag from the ground, but don't slip sideways like boats do on water), this angle will approach 180 degrees. This is because any wind the boat makes (called apparent wind) will tend to decrease the relative wind angle, because any apparent wind must come from 0 degrees. The most efficient relative wind angle (including apparent wind) is probably around 90 degrees, but the exact number is unimportant. If you start sailing from stationary with the wind at 90 degrees, you'll pick up speed, but now because of your apparent wind, the wind angle is probably closer to 70 degrees now, so you should turn away from the wind again to bring the apparent wind angle back to 90 degrees. But now because your efficiency has increased you'll accelerate, meaning the apparent wind will decrease the wind angle again, so you must turn away from the wind again. This is obviously a positive feedback loop that in principle will allow you to accelerate indefinitely. The limiting factor is obviously drag, but if drag is small enough, one can sail faster than the wind. Normal cruisers have a lot of drag so their most efficient angle is relatively low, whereas an ice yacht will have an ideal angle of around 170 degrees once they're up to speed.
"..The keel and rudder are there to react to as much of the sideways component.." - the keel, or fin underbody, yes, but pressure on the rudder? If it had a central axis, perhaps, but for rudders hung off a forward hinge, as most rudders are, pressure is the last thing you'd want ..until you want to steer somewhere else. You're likely familiar with 'weather helm' whereby you have to use the rudder to counteract the boat's effort to round up to windward. That rudder resistance is highly undesirable, simply because it's drag; a well-balanced boat will go where it's pointed.
And finally, as apparent wind increases (as boatspeed increases) the direction the wind comes from moves forward, as seen from the boat, so why "..any apparent wind must come from 0 degrees."? Ah, I think I see an expression new to me: in a windless sea, any movement of the boat through the air will yield a 'wind' from directly in front. Apparent wind plus actual wind sum to a resultant wind further forward than it would be with wind alone. Fair enough.
Thanks.
I think you got the last one wrong. The boat is fastest not at 45 or 90 degrees but somewhere around 135 degrees. Sailing in this direction and thanks to the position of your sails you still have a laminar flow of wind on both sides of the sail, which generates lift (which doesn't happen when sailing at 180°) and in addition more lift gets generated underneath the hull, which causes it to raise higher from under the water, grateful reducing drag on the hull. Therefore 135° would be the fastest direction to sail.
About faster than the wind sailing - you kind of hinted at the forces involved, but it's quite simple. Terminal velocity is where all forces balance out, and that can happen at higher than wind speed if drag is low. The new AC foiling cats are doing about 3x windspeed in 15 knots in Bermuda right now, but at about 120deg off the true wind. Ice boats can do more than that, at much deeper angles again (apparent wind is quite forward at those speeds)
"I dont have all the answers"
Sarcastically "okay. Thank you very much"
Idk why, I feel something similar now. Happiness all over the place \o/
Wind actually pushes the sail and this generates torque which is constrained by the keel. This creates vectorial speed and now the system is developing power. That's basically the actual and real concept behind a sail boat going faster than wind: the resultant power prescinds from wind speed.
Secondarily, the outer part of sail generates lift as soon as any speed exists (just as an airfoil in every wing), and this helps to achieve higher efficiencies in some sailing assets.
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As for the terms I can't comment on this for my sailing language is not English.
Step up your education sistem!
I respectfully suggest that there's a combination explanation.
https://www.youtube.com/watch?v=PF22LM8AbII
This seems to be aimed sort of at being a landing vid for new viewers vs really adding content for those already indoctrinated
No way that any boat can go faster than the wind!... unless the hull gets completely out of the water, like in more recent boats, thanks to particular shapes of the hull and to the introduction of foils. (this is what they missed to explain in the video).
What happens, in this particular modern and marvelous boats, is that the sum of the real wind with the relative wind generates a sum of vectors that increases the pressure on the sails BUT, at the same time, modifies the angle of the wind compared with boat's direction. The boat then, in order to use this additional power, must progressively tighten the sails to adjust them to the new wind direction. As a final result, the boat keeps accelerating until it reaches the "close-hauled" orientation (about 30° compared with the direction of the relative wind) that is the limit over which the boat cannot tighten the sails anymore without loosing power (stall).
Finally when the boat is running "downwind", with the wind exactly behind, the sail stops acting like a wing and becomes more similar to a sack or to a round parachute: in this position the maximum possible velocity is equal to the wind speed (not considering the resistance of water on the hull). So, contrary to the popular belief, wind in the stern is the worse solution possible for a sailing boat.
I assume as some point they were trimming the square sail to catch more wind and discovered the wing effect.
Besides, the question was very disingenuous as it asked them how to position a triangular sail to best catch the wind, when in reality you should change the rotation of your boat if you are using that kind of sail or you will just end up going very slowly and/or probably tipping over.
It's basically like asking someone how hard they should press down with a bread knife to cut the bread quickly, when in reality the sawing motion is what does the cutting.
Not absulutley. With square sail you can go in about 50 degrees to the wind direction (about 40-30 in modern sailboats).
By triming the sails very spesificley, you can make a "wing" shape with a square sail
The thing is, Bernoulli's principle doesn't apply to planes because there is nothing telling the air where it's "counterpart" is and how to meet again at the other side of the wing. In the experiments - which you mentioned one of - they showed that the air really doesn't align. It's the same thing with sailing, Bernoulli's principle doesn't apply.
For reference, the Wikipedia entry of "Bernoulli's principle":
https://en.wikipedia.org/wiki/Bernoulli%27s_principle
I believe you are saying the same thing about sailboats but I know nothing about them so maybe they are different than planes and really do use Bernoulli without any deflection?
It is caused by a low pressure created on the front side of the blade and high pressure on the back
If the wind goes in a certain direction and the boat and water are at rest initially, then it may not cause movement as a whole to the opposite direction, given the conservation of linear momentum law. So, actually, the water (or the wall) is pushed in the same direction of the wind (the hand), but the boat squeezed against the water (the soap against the wall) is pushed by the water and the wind (the wall) in a transversal direction or even, to some extent, possibly against the wind. Never in the exact opposite direction, though.
So, I think the answer to the main question, that is, how can the wind push a boat in its opposite direction, is “the wind is actually pushing the water, the boat is just being squeezed in the process”.
Thanks, Barney.We can also see that the boat without a keel to pressure the water can't go against the wind. Another example is the kitesurfer. He can go against the wind pressing the water with the board, but he goes always in the wind direction when he jumps off the water.
And then for the rest of your life you curse at Nintendo for getting it wrong in The Wind Waker.
When you push something with your hand, you're not thinking that you're creating a high pressure zone on your palm which pushes the object away, even though that is essentially what you're doing by applying a force on the surface area of your palm. You're just applying a total force on the object.
At least, that's what I understand from your point. Maybe I misunderstood.
2) turning of flow is important but its not everything (I'm taking abt airplanes now I dont know anything about boats) there is Bernoullis principle but its bc of the area and shape of the wing that causes higher velocities on top. the angle of attack or AOA is one way Newtons 3rd law comes in by hitting the bottom. and the coanda effect also uses newtons third law by "throwing" air down off the top.
You need not know physics details to be an expert or champion machine operator. You shouldn't be tasked with explaining the physics, though.
Thats like having a cook as an expert on what happens when you boil meat. He might have some knowledge but more accurate answer is from a biologist or chemist.
jep jep
What do you think the sailor was for? He explained everything.
Edit: Plus, noting that few people actually understand such an everyday thing we are all familiar with is useful in and of itself.
So yes, you can have a ship that works without lateral lift but it must be light enough not to break surface tension.
My advice is to take lessons and don't rush into buying a boat because there are so many different types of sailboats you are likely to change your mind about what kind of sailboat is right for you. I'd take lessons each Summer for a few years and then maybe join a boat club where you pay monthly dues and a small fee each time you want to take one of their sailboats out for the day. Most clubs have a variety of boats you can try out. Then maybe crew on a race boat. You can do a LOT of sailing without buying a boat. Biggest mistake I made was to take a few lessons then immediately buy a boat I thought I'd like.
That's really cool man. Thanks for sharing.
Usually they'd sail 'over there' in the ocean and days later find a breeze that would let them sail elsewhere, closer to 'home'. They'd learn wind patterns.
The story told in the video is true for a very lightweight boat with low friction (such as a catamaran). The lift generated is easily able to lift almost all of the hull out of the water, especially when the keel is designed to create lift in the water as well (like the curved keels you see in top level catamaran racing nowadays). In extreme cases and high speeds, these boats can actually plane on their keels alone. These boats easily exceed the speed of the wind. Watch some Olympic Catamaran or Finn racing to see an example.
Bigger boats can still go pretty fast upwind, but they will definitely not exceed it; the weight of the keel pulls down a lot of the hull which in order creates a lot of friction with the water, in which case hoisting a spinnaker and going downwind is definitely faster, especially if you can plane (but for big/heavy boats that requires seriously heavy wind). For the biggest boats, making a surf (which means having downwind and riding a wave) is the best way to win time. Going downwind with a spinnaker with the 35 footer I sail right now in 20 knots will take me up to maybe 9-10 knots, but when I make a surf that can jump up to 13-14 knots easily.
All that's a bit nuanced for a four-minute video intended for a mostly non-sailing audience. He could have said a boat's fastest on a broad reach and left it at that.
Saying that, I do not condole his (stupidfacefaceface) to criticize this video to have full of ignorance. This video aims to educate, and the correct information is pretty straightforward. The point of this video is show the supply and demand of knowledge as to how sailboats work. I myself do not know how they work prior to this video and I am not embarrassed to say so. I am glad to stumble upon this video to be educated. Videos like this should be encouraged to show that people actually needs to be supplied with knowledge of various aspect.
Wow, this is a long message
But how did you get them to be ignorant? I don't get it at all.
This knowledge will keep you alive in EVERY situation you can imagine. :D