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HowarthSailing
Добавлен 10 ноя 2008
Physics of Sailing - Steering with CE and CLR
This video is a screen recording of part of a webinar delivered in Spring 2020 to a class of new sailing instructors.
Topics covered in this video include:
- Forces, and the centre (location) where forces act
- Steering moments and the effect of multiple forces on the boat
- The effect of sail trim and boat heel, and other actions on the location of the Centre of Effort and Centre of Lateral Resistance (and associated steering effects)
Topics covered in this video include:
- Forces, and the centre (location) where forces act
- Steering moments and the effect of multiple forces on the boat
- The effect of sail trim and boat heel, and other actions on the location of the Centre of Effort and Centre of Lateral Resistance (and associated steering effects)
Просмотров: 7 306
Видео
Sail Trim and Sail Controls
Просмотров 8 тыс.3 года назад
This video is a screen recording of part of a webinar delivered in Spring 2020 to a class of new sailing instructors. Topics covered in this video include: - Sail Ticklers and Telltales - Sail Fullness and Sail Twist - The effects of the Cunningham on sail fullness and draft Position - The effects of the outhaul on sail fullness - The effects of the mainsheet and boom Vang on sail twist - The e...
Physics of Sailing - Wind Velocity Vectors
Просмотров 2,6 тыс.3 года назад
This video is a screen recording of part of a webinar delivered in Spring 2020 to a class of new sailing instructors. Topics covered in this video include: - Introduction to vectors and vector addition - Define True Wind, Boat Wind, and Apparent Wind - Diagrams and exercises in understanding velocity lifts and knocks as a result of changes in true wind and boat wind speed.
Racing Rules of Sailing - When Boats Meet
Просмотров 6 тыс.3 года назад
This video covers a slide deck that I made for an online course delivered to sailing instructors. Topics Include: - Background introduction to the Racing Rules of Sailing - Definitions that are critical to the RRS part 2 - Rule 10 - On Opposite Tacks - Rule 11 - On The Same Tack, Overlapped - Rule 12 - On The Same Tack, Not Overlapped- Rule 13 - While Tacking- Rule 17 - On the same tack, proper...
Sailing Theory Tutorials - Sail Construction and Care
Просмотров 26 тыс.6 лет назад
This video cover the following topics: How a sail-maker uses edge and seam curvature to put shape into a sail. As well as, an introduction to sail materials and some general information on what can damage a sail or cause it to wear out.
Sailing Theory Tutorials - Introduction to Sail Shape
Просмотров 39 тыс.6 лет назад
In this video the general shape of a sail is discussed and reasons are presented for why it is beneficial to introduce curvature into the shape of a sail. More formally, key points including: the Leading Edge, Trailing Edge, and Point of Maximum Draft are located on a section-view of a sail. A number of parameters which define the shape of a sail are also presented including: Chord Length, Draf...
Sailing Theory Tutorials - Sailing In Current
Просмотров 6 тыс.6 лет назад
In this video a simple model of relative motion is presented to illustrate how the motion of a sailboat will be affected by current. A closer look is taken to the flows that are experienced by the foils below the water line, and the sails above the waterline when current is at play.
Sailing Theory Tutorials - Introduction to Tides
Просмотров 8 тыс.6 лет назад
In this video, the following terms are defined: Tides, High-Tide, Low-Tide, Spring-Tide, Neap-Tide, Ebbing, Flooding, and Slack-Tide. A brief explanation of the relationship between the position of the sun and the moon, and the height of the tides is presented, along with an explanation of why we experience two tide-cycles per day. Finally, local tide tables are shown for an example day and loc...
Sailing Theory Tutorials - Introduction to Current
Просмотров 3,5 тыс.6 лет назад
In this video, the idea of currents is introduced and explained. The interaction of depth of water on the speed/strength of current as well as some directional current effects are also discussed.
Sailing Theory Tutorials - Location of CE CLR and Helm Feel
Просмотров 30 тыс.7 лет назад
In this video, the idea that a distributed pressure force can be simplified to a single force vector acting on a force centre is introduced. It is also discussed, that two forces separated by a distance will generate a moment or torque, which causes an object to rotate. The locations of the centres of effort, and lateral resistance are discussed in 3 dimensions on a model sailboat. And an ortho...
Sailing Theory Tutorials - Forces on Sails and Foils
Просмотров 13 тыс.7 лет назад
In this video, the lift and drag forces on the sail of a boat are combined to form a resultant "Effort" Force vector. The forces on foils below the water are discussed and the idea of leeway is introduced to explain how the foils experience flow at and angle of attack and generate lift just like the sails. The effort and resistance forces are combined on a simplified 2D model of a sailboat to s...
Sailing Theory Tutorials - Sail Trim, Separation, and Stall
Просмотров 39 тыс.7 лет назад
This video introduces the concepts of angle of attack, flow attachment and separation, and the stall condition. Trimming the sail in is related to increasing the angle of attack, and it is mentioned how angle of attack can affect the lift and drag forces generated by the sail. Trailing edge separation and stall are treated with reference to the leech telltale, and laminar separation bubbles are...
Sailing Theory Tutorials - Airflow Over a Sail
Просмотров 16 тыс.7 лет назад
This video introduces the concept of streamlines and how to sketch an airflow diagram that represents both flow direction and velocity magnitude changes with streamlines. The topics of stagnation and Bernoulli's principle are introduced to explain how areas of locally high and low pressure develop over the surface of the sail. The approximate pressure distribution is then linked to the lift and...
Sailing Theory Tutorials - True, Boat, and Apparent Wind Examples
Просмотров 7 тыс.7 лет назад
This video presents 2 word problems that ask about the changes in apparent wind speed and direction as it relates to changes in boat speed and true wind speed.
Sailing Theory Tutorials - True, Boat, and Apparent Wind
Просмотров 17 тыс.7 лет назад
This video defines wind velocity vectors called True, Boat, and Apparent Wind. It also demonstrates the conventional wind vector diagram for a boat on each of the points of sail.
Sailing Theory Tutorials - Introduction To Vectors
Просмотров 11 тыс.7 лет назад
Sailing Theory Tutorials - Introduction To Vectors
Good morning. Do you know somewhere where I could download the project to sew a size 5.7 sail in the classic windsurfing style one design windsurfer
We learned a lot! Thank you, Julian! 🙏
Thanks for your valuable help.
I want to know what it is called when you lower the sail and tie it. It's called trim. That's not what you are saying.
When you lower the sail part of the way and tie it, it's called "Reefing". Not covered in my presentation here but definitely a valid strategy for depowering your sail.
@@howarthsailing Thank you my Dad and I did it a lot but I couldn't remember what he called it. Thank you for reading my comment and answering. Hats off to you Sir!
I kept looking up trimming but I knew that wasn't it. I knew that wasn't what it was called. Thank you for understanding what I meant. So cool and Happy Sailing!
The only part I disagree with is the depowering. It's the short shift and the extra trim to go even faster. But safer.
Thank you for sharing your knowledge. One day, I hope to circumnavigate the globe, and this is precisely the type of information I am looking for. As a commercially rated pilot, much of the information in this video is similar to what I have learned in aviation. Of course, some of the terminology is specific to sailing, but the physics principles of an airfoil remain constant. I'm really looking forward to watching more of your videos.
“Sailing Theory” means they’re not going to give you the facts about how a sail boat works.
Thank you for your video! I learned quite a lot and refined some of my knowledge. I don't quite agree with "Boats Experience just Enough Leeway", though. My students often try to accelerate the boat sailing close hauled with no speed after setting sails or a bad tack. What this leads to if that the boat is actually going sideways a lot. As I understand it, the first second that the wind fills sails in such a situation and the water starts flowing, the direction of it's flow should be opposite to the direction of "E", combined forces of the sail. And even if the sail is trimmed perfectly, the angle of attack on foils is to big, so they stall. A lot of drag is generated, which results in either the boat heeling a lot, or drifting sideways if hiked. Also, the rudder is useless in this situation, so the boat usually can't be controlled. It can head up or bear away, but it's not relevant in my question. What happens underwater, when sails seem to be trimmed perfectly and the boat points very well, but drifts sideways? Of corse, as you gain any speed angle of attack changes drastically and foils lift starts to help in acceleration, and then the boat flies as you said - easy in going forward and really bad in going sideways. But I don't like seeing my students crashing into each other on a start line because of this misunderstanding :) I would be really greateful if you could clarify. Thank you!
Hi Ivan. I think you're spot on. I'd add a couple of points to clarify this aging video and its explanations: 1. My use of the expression "Just enough leeway" doesn't imply that the amount of leeway your boat experiences is desirable or even beneficial, just that it is this missing piece of the vector equation. Maybe I could have used different language for that part. 2. My description really only applies once the boat is moving and once the sails are trimmed within a reasonable range for the direction of the wind. Starting from a stop is sort-of outside the scope of this video. You might want to give this article a read: gentrysailing.com/pdf-theory/Origins-of-Lift.pdf
Awesome
Hi JH, I believe the impact of current to a sailboat speed and direction is not absolute, or 1 to 1. In otherwords, I don't think you can just add up the combined speed and directions to determine a new vessel speed and direction, like you can in a powerboat. When making these calculations in a powerboat we assume a constant amount of power is being applied at the throttle, rpms. But in a sailboat the "rpms" from the wind increase and decrease relative to current, but are constant relative to the ground. Assuming for a second the sailboat is attached only to the wind and not to the water, the boats speed and direction overground would not change at all regardless of the current. The best example I can give is a sailboat sailing directly down wind at 5 knots in 8 knots of wind, that suddenly comes upon 5 knots of current going in the same direction of the boat is not going to being going 10 knots over ground. It's going to struggle getting over 5 knots overground because it's going to run out of power, "rpms" from the wind. Exaggerate the numbers and it becomes more obvious. Like 5 knots of wind and 20 knots of current. Please help me with this, because you're the only sailor I've found online that really understands this stuff and can explain it in a way that is digestible. Thanks!
You're onto something here, but it's more complicated than that because the direction the boat is travelling relative to the wind will really influence how fast it can travel. In fact, the speed of the current will be a part of a velocity vector addition to determine the apparent wind speed and direction as well. I think the examples in this video will hold true for a boat that travels at approximately its hull speed, in a situation where the wind strength is much greater than the current. Otherwise, you're right, more analysis is necessary.
Great Video to explain sailboat balance!
Very, very good.
Thank you, excellent demonstration.
That was absolutely fantastic, thank you!
It seems like CLR should point forward not aft. It appears CE and CLR are exact opposites at 18:09 which means the boat would not move if CE and CLR were at same spot fore and aft or the boat would just turn in circles if they were separated.
15:00 You can't do experiments on simulations, they simply regurgitate the ideas of the designer. Develop a hypothesis and then test it in reality. Testing on a model that incorporates the hypothesis is the ultimate circular argument.
8:59 No, it doesn't. It either goes over or under. Check Babinsky's video. Sometimes the smoke arriving at the so-called stagnation point flicks over the top and sometimes it flicks under the bottom. It never stops.
As I understand it, there's an infinitesimaly small amount that does stagnate but it really doesn't matter though, the dashed line helps us understand where the air divides to pass on each side of the sail. We are not analyzing a sail design here, we are just developing a visualization of how the air is moving over a sail and being careful to avoid the commonly used, incorrect explanations of longer and shorter distances.
@@howarthsailing If it "really doesn't matter", then why introduce it at all? You are just confusing your readers by harping on about it. Why don't you just say that: "It is the point where the air divides...." and save yourself and your readers the hassle of struggling with the myth of the stagnation point. It was introduced by misguided mathematicians who needed to seed their PDEs in order to get some sort of correlation with nature.
@Alan Smith Hardly harping, you're commenting on a video I made in 2018 where I explain as clearly as I can, the flow over a sail, visualized. There's plenty of literature to support the stagnation streamline, and stagnation point, I am not the author of those works. Feel free to link to the content you prefer. Please take your argument somewhere else.
that´s gold my man
Thanks for the informative videos! Any chance you could share what drawing app you are using?
The old videos were recorded on my Samsung Galaxy Note 10.4 tablet and the stock SNote app was what I used. I haven't found anything that I like for annotation on my newer Microsoft surface pro.
@@howarthsailing Thanks!!!
You have a new follower bud
Excellent ! Love the combination of theory and practice explained visually in simple terms.
Hi Julian, I'm trying to solve a weather helm issue in a Flying Fifteen, which is an early Classic fleet boat so doesn't have a particular set of dimensions, the Classic boats all seem to be dimensioned and rig a little differently. The mast foot has 3 positions, the forward and aft positions being about +/-40mm from the central position. I currently have the mast foot in the forward most position and I'm still experiencing weather helm. Previously I extended the shrouds to get the mast rake as far forward as possible. This did produce a neutral helm, however other aspects of the rig were stupid, the boat looked awful with the boom climbing to aft and the gib clew way above the deck. So I have now reverted to a more normal geometry. I believe I cannot sensibly get the CE further forward than the current set up. Neither is it an easy task to move the keel on a Flying Fifteen, well pretty much impossible! I am wondering whether the rudder itself may not balanced. I'm not sure this is a thing in sailboats (but I believe it is in power boats). The Flying Fifteen rudder is very raked backward with the pivot point close to the top leading corner. This suggests to me there is potential that the rudder itself could have a CLR to aft of the rudder pivot point. If so, this would effectively make the rudder bear down and produce a weather helm effect on the tiller, the tiller being on the opposite side of the rudder pivot point. Does this make any theoretical sense?
Kind of a complex issue but here are some thoughts. 1. When you move the mast step backwards, does this rake the rig forward? Usually the mast but adjustment is for inducing some pretend, or for changing g the rake, not for actually moving the whole.rige forward or backwards. 2. Sure it's difficult to move the keel, but this is some thing that high performance keel keelboat sailors do. They have a boat shop 'fair' the keel and at the same time, build up material at the front and shave off material at the back. Probably not your go-to solution, but a possibility. 3. How bad is the weather helm? It's typical to have some weather helm with the sails trimmed in hard, especially when it's windy, when the boat is heeling, etc. The trick then is to use sail controls to depower or ease the main to keep the boat "on its feet".
Great video
Julian, I have just discovered your tutorials on Utube. I am reasonably new to sailing so on a big learning curve. Your video on Sail Trimming Separation and stall is excellent. Really starting to understand what is happening with tell tales, why and what corrective action you need to take. Really appreciated thanks so much.
Pure excellent these explanations. I've been sailing for almost 20 years and I've never received this information as clearly as I have looking at your videos.
This is excellent!
It would be helpful to go over the when boats meet scenarios in a way that specifically focuses on upwind boats meeting downwind boats. I know it's "the same", but it sure doesn't feel the same.
Could you explain how the underwater slipstream affects how the boat holds it's course? For instance, on the Lee side of the hull/fin the water is experiencing high pressure and naturally the windward underwater side of the hull and fin are experiencing low pressure. The opposite of what is happening to the mast and sails.
I think that the other video I have called "Sailing Theory Tutorials - Forces on Sails and Foils" goes through this. Basically, the hull, keel (or centerboard as the case may be) and rudder have a flow over them, and because the boat makes a small amount of leeway as it travels through the water, there is a small angle of attack between the foils and the flow, this results in lift being generated in a direction that opposes the force of the sails.
@@howarthsailing what effect will that have on the rudder?
@@mikecritchlow1114 I don't think of it as having an effect on the rudder, more that the rudder takes some of the resistance forces, which should factor into where you consider the CLR to be. An interesting point though, is that you can stall your rudder by steering too hard, essentially, creating too large of an angle of attack at the rudder and causing flow to detach.
@@howarthsailing HS... as I see it, the streamline from the hull and fin will have a sideways effect on the rudder inducing a turn downstream... hope that makes sense. i.e. if the boat is heeling to port, the slip stream will curve up and push against the port side of the rudder causing the boat to turn to port, or lee helm. This in turn will require the helmsman to have to keep adjusting to starboard if he/she wants to stay close hauled.
@@mikecritchlow1114 I'd say that's possible. Most often the helm is out of balance in the other direction though, because the mainsail is often overpowering and the CE is roo far aft, so I think you'll find most helms people are used to having to fight to bear off.
How does mast rake affect the C/E?
If you rake the mast forward, the CE moves forward. If you rake the mast aft, the CE moves aft.
The centre of lateral resistance is also affected be the underwater profile of the hull, not just the keel. The underwater profile of the hull changes as the boat heels.
Absolutely, we discussed this at length is some of the deleted comments years ago. The shape of different hulls affects the location of the CLR and heeling (side to side) or even pitching the boat (fore and aft) can also move the CLR around.
Very nicely done.
Exceptionally good explanations.
Try adding shorter telltales that are much closer to the jib's luff, like shown in Photo 2 here: gentrysailing.com/pdf-magazines/9-Achieving-Proper-Balance.pdf Also Figures #2 and #3 here: gentrysailing.com/pdf-magazines/10-Sailing-to-Windward.pdf These telltales are much better because they warn of impending luff and stall rather than signal that luff and stall has happened.
I am a fan of the Gentry articles.
Can we measure the force created by the sail by measuring the tension on the sheet with say a force meter or a simple digital scale.? Could this single measurement assist triming of the sail. Much like a the resulting speed increase or decrease with triming the sail for max speed?
You can certainly get a sense of how much load there is on the sheets, and relate it to the force on the sails, but you have to remember that as you sheet in and out the magnitude and the direction of the forces on the sails changes. The farther you sheet in, the greater the sideways, heeling, component of the force will be, so you can't say that more load in the sheet will equate directly to more thrust force driving you forward.
Great examples and explanations. Thank you!
Excessive healing
I do have a problem with understanding your conclusion. Perhaps you can clarify it for me and others, please! The problem is that you are referring to Lee Helm and Weather Helm on your drawings without considering that both of the boats are on opposite tacks! Therefore your conclusion on the right drawing is wrong as it is Leeward heel as the boat is on port tack and the heel is to Leeward; therefore, it is Weather Helm also! Well, I hope I explained it clearly, but need to add that scientifically, you explained this fairly clearly, but CE and its relations to the CLR while sailing is not about the boat's heel instead, it is about the position of CE versus CLR in Forward or Aft position, which will establish whether it is beneficial or not beneficial for sailing!
Hi Chris, I think you are mistaken, both ot the boats are on the same tack in the renderings (notice the direction that the sail is filled by the wind. The boat that is heeled yo windward is not being tipped by the wind, but rather by the crew weight, which might be placed on the windward side, either on purpose or by accident. CE and CLR can move fore and aft, and side to side, and both dimensions will have effects on the helm of the boat.
@@howarthsailing Then it is not clearly stated so, and that creates confusion. Also, heel of the boat if the sails are set properly has no effect on the helm as it becomes automatically a part of the steering due to necessary and beneficial heel associated with theory of sailing in general (5-12 degrees on monohull). There is more to it but I don’t want to create debate (example; luck of CG in the presentation). Anyway, I like the animations in your presentation! 😏
@@chriskaminski4642 this was all discussed in a series of comments that got purged in 2020 by youtube. I think that the whole CE/CLR topic is re-treated in a more recent video with clearer diagrams. Thanks for watching.
Might I please ask a very ignorant, amateurish question? For the sake of some medieval research I'm doing ... for example, I'm sailing from a port on a tidal river to the open sea, and assuming a boat where hitting bottom is not a concern .... would I want to leave for the sea with a low tide, since it's going OUT and would not fight me? And conversely, when I want to come back into the river from the sea, enter at high tide, which presumably helps push me in? Apologize for this terribly uneducated question.
3 considerations come to mind. First is water depth, but you said that's not an issue. The second is speed, the boat will move faster if it is going with the tide (i.e. coming into a bay while the tide is flooding, between low tide and high tide, coming in, or leaving a bay when the tide id ebbing, between high tide and low tide, going out. The third is manoeuvrability. If you have to dock on a pier, depending on the direction and speed of the tidal flow it could help you, or it could make the task harder/more risky.
@@howarthsailing That is precisely the kind of information I was looking for. Greatly greatly appreciate the reply. Take care.
Why does the stagnation line curves like this? What force is dragging the air towards the sail?
Streamlines are PUSHED by higher pressure towards lower pressure. In this case, the relatively higher pressure on the windward side of the sail pushes the stagnation streamline to leeward before it contacts the front of the sail or mast.
Fantastic explanation of vectors and I have found all your videos very clear and concise. Just one issue here. Nautical miles should be read off the parallels of latitude scale (vertical scale) and never meridians of longitude (horizontal scale) when using a chart. Meridians of longitude converge towards the poles as you travel from the equator.
You're right, that is an error at 12:45, although there is no scale available on the screen where I could have taken kts from, thank you for pointing this out. This is definitely not a chartwork tutorial, just an illustration of a practical use for vectors in sailing.
Wow
This is super helpful, thanks! I'm getting ready to learn to sail, and my math brain insists I understand the physics, too. It is surprisingly tricky to find a video diving into the physics and "why" of sails, there's just so much practical content out there that it swamps the algorithm and theoretical content like this gets hidden.
you're lucky you have a math brain... my brain freezes when i hear the word "angle" lol but i've been practicing sailing and need to learn theory too
The current does not affect the performance of the foil. I don't think what this video says it is right
What's the timestamp for the part of the video you think is incorrect?
Minute 16:00 The current moves respect the land and it doesn't matter if it was 1000km/h it would not affect how the boat eprforms
excellent description with very accurate illustrations of sail boat physics..would be extremely useful if these information are compiled in a booklet
how did you do it can you share with me , thank you
Really good go at a thorough explanation of it. Even if I think you may have time to think some things through.
I pronounce you Sir as "Best Physics/Math Teacher" on RUclips!!
how did you do it can you share with me , thank you
Hi Julian, I do read and see a lot of sailing tutorials and books....your vids are one of the best sources of information.Very well made ! Easy to understand and of great value for beginners and professional sailers. Thank you for your time and effort and for sharing it, you did a great job ! Franz Vienna
Great video on sail trim
My physics teacher is making me watch this, I hate her stupid class but this video does a fantastic job of explaining this topic and making it easy to understand, much better than my teacher. Good job.