I think you would find the leech is moving less than you think. It is the leading edge / mast that is shaking around. The leech staying still helps reduce / smooths out the drag. Now if there only some way we could lift the board out of the chop to reduce the shaking of the whole rig.
Select to expand quoteolskool said..
Mathew, sails n fins are only trying to mimic what is found in nature. Sail designers mustve looked at a birds wing for inspiration. Twist n looseness of leech is required bcoz we need to control the power produced. The sail is not part of the human body. We cannot control its shape or power as a bird infinately controls its wing in flight. We are stuck with a lifeless man made substitute.
Sure lets do the tests n refine the design. But until we have say, 97 sensors n servos which can infinately change the shape n power at will for performance, we are stuck with what we have. A design which has come a long way in the past 40years. But still has a LONG way to go to be equal with what is found in nature.
Just no. No bird has infinite power and shape. And the SR-71 Blackbird is proof alone that humans understand aerodynamics.
Select to expand quoteDarrylG said..
I think you would find the leech is moving less than you think. It is the leading edge / mast that is shaking around. The leech staying still helps reduce / smooths out the drag.
That is a very good point, if the leech stays still and the mast oscillates back and forth, you effectively have a flapping wing and you would be getting lift (or at least a reduction in drag) for both directions of the oscillation. Much like small rig pumps, but the chop is doing it for you.
When downhalled properly, the twist is already in the sail. It doesn't need a gust to open up.
Select to expand quotemathew said..olskool said..
Mathew, sails n fins are only trying to mimic what is found in nature. Sail designers mustve looked at a birds wing for inspiration. Twist n looseness of leech is required bcoz we need to control the power produced. The sail is not part of the human body. We cannot control its shape or power as a bird infinately controls its wing in flight. We are stuck with a lifeless man made substitute.
Sure lets do the tests n refine the design. But until we have say, 97 sensors n servos which can infinately change the shape n power at will for performance, we are stuck with what we have. A design which has come a long way in the past 40years. But still has a LONG way to go to be equal with what is found in nature.
Just no. No bird has infinite power and shape. And the SR-71 Blackbird is proof alone that humans understand aerodynamics.
Ohhhh yeah, here we go. Just how much electronics n wiring n sensors are reqd to fly the mighty SR71?
SAILBOARDING IS ABOUT SIMPLICITY........ try dismantling an SR71 n putting it in the back of your van!! Cmon Matthew.. Really? Totally different set of rules involved there. Its not making propulsion from the wing. Its only making lift n uses serious amounts of thrust to keep it airbourne.
The streamlines on the sail below are unlikely be right, but illustrate the general point that the flow is 3D. Without twist the flow on the upper sail is horrible - streamlines are way too long for the small camber on this part of the sail, very draggy. Twist allows more exhaust from just above the boom and corrects the airflow. The designed-in tension in the sail from the clew to the Neil Pryde "N" allows this twist-off of the upper sail, avoiding the old-school tight leach. Speed is a bit both about thrust but more importantly about reducing drag, especially at higher speeds. Shame about the overly floppy bits of leach, a bit hard to have twist mid-sail and a not prevent over-twist up the top.
Select to expand quoteolskool said..mathew said..
Just no. No bird has infinite power and shape. And the SR-71 Blackbird is proof alone that humans understand aerodynamics.
Ohhhh yeah, here we go. Just how much electronics n wiring n sensors are reqd to fly the mighty SR71?
SAILBOARDING IS ABOUT SIMPLICITY........ try dismantling an SR71 n putting it in the back of your van!! Cmon Matthew.. Really? Totally different set of rules involved there. Its not making propulsion from the wing. Its only making lift n uses serious amounts of thrust to keep it airbourne.
Fine. Highest souring no-thrust plane is +70k feet vs 37k for birds. And that plane didn't need sensors - it is completely mechanical. This is not a pissing-contest - humans very much understand aerodynamics.
Which implies -> windsurf foils/fins dont mimic what is in nature - the laws of physics are pretty well understood at the macroscopic level, quite a lot at the microscopic and even a bit at the atomic level. The reason birds have foiled wings is because flight through air, needs that kind of shape. Which is why your own statement is accurate for fish to have a different shape.
What is not well understood, is why twist gives windsurf-sails the performance benefits that we are very confident of.... And thus the various hypothesis that it is likely to be a number of factors.
BTW: The whole tall-poppy / anti-intelligence movement is just tiring. If windsurfing is about simplicity, do feel free to *not* comment on a thread that is discussing the performance merits of sail twist.
Select to expand quotemathew said.. >>>> BTW: The whole tall-poppy / anti-intelligence movement is just tiring. If windsurfing is about simplicity, do feel free to *not* comment on a thread that is discussing the performance merits of sail twist.
Yep!!!!!!!!!!!!!
It's great to enjoy the simplicity of just blasting around.
But it's rather stupid to think that you'd enjoy it just as much, without people doing the extremely complicated stuff of trying to understand, how to do it.
Andrew, an hour of testing rigged with and without downhaul in your "local" university wind tunnel should shed some light on it:
OK, as we're getting personal and you choose to set-up a pissing contest yourself if someone like oldskool or yourstruly mention something that doesn't fall into the equation you are trying to set up, while failing miserably yourself on trying to find an explanation -and I explain later why- first the following.
I will beat most of you guys sailing with my head in my arse when it comes to a competition. And no, I won't keep it there, I stick it out to discuss, as I thought this was meant as an open discussion, not as a self centered science club that is basing themselves purely on physics.
Again...where does inspiration come from? There is something before physics. Physics responds, physics doesn't create, at least not in an organic form. For that you need cell bioligy. Are you starting to catch my drift?
Call me a tall puppy or anti intelligent creature whenever you want -just like you do with hyper intelligent people who dare to step out of the box again and...my dear God...dare to use metaphores as our language simply doesn't have the right words for that which cannot be seen...hey?...my whole point-, but yesterday I was standing in only a slight breeze. My back against the wind, shirt put of, arms spread to notice directions and fluctuations in direction, like a bird can do. I tried to feel as good as humanly possible and noticed my back was getting a massage from the wind and there were lots of pressure points. It was as if tenthousand fingers were pushing my back, nearly all at a different force.
Now, the point oldskool tries to make is that a bird can adjust the tiniest parts of it's Wings and we as humans cannot.
We are forced to seek answers in the mechanical world and have to do so by applying the laws of physics on the models with which we are creating for sailing.
What I tried to point out is the following: can we as humans trust our own calculations for being right and what do we base our theory on? Hence my suggestion to see the human, board, fin and sail like one organism within the equation to calculate the optimum amount of twist in relation to all parametres involved. The human being holding the set to the water being the most important, and this is very important...LIMITING...factor.
And I am not even going to say sorry for the fact that I got the refugees and bombs in as I knew this was coming. Before even starting out to try and understand where these tall puppies are coming from that in the now are rising in vast numbers spread over the earth, you have to start to at least try and understand where physics got us in the here and now. This is why I showed this very simple lecture of Bruce Lipton who does sound weird and like an old hippie to most, but does that make him wrong and doesn't it have to do with twist? If you don't understand what I am trying to say, I won't say the same like you are saying so I won't request you to leave the discussion, but I WILL keep on adding my comments as this is an open forum.
Twist cannot be seen apart from the response needed within the whole set consisting of the weight, length, strength, response time etc. etc. of the rider, the board, the fin and the sail.
First of all the industry is putting us up with stuff that only can be sailed effectively by giants and proves simply because of this fact, it's moving the wrong way. If I, as light rider, follow in the footsteps of the giants, I will loose upfront whenever I would want to enter a competition.
So the first challenge is to rethink and realize we're all bound by our size, but not by the size of our brain, which is sometimes better organized than some of you think as ridiculing seems to be the accepted norm by at least two people.
Select to expand quotechoco said..
Did this thing have any twist?
I dont think so - the sail is largely a semi-solid wing. It does appear to have something going on with the top of the wing which allows for the tip-air-flow to be different from the rest of the foil. I''m not privy to the design, so no sure what it does.
It also had a rudder and vertical stabiliser.
^^^ and Sailrocket's sail doesn't rake backwards - our windsurfer rig rake is one of the reasons we need twist to be efficient. They also don't need twist to quickly reduce the height of the center of effort on sheeting out so as to reduce overturning moment when powered up and hit by a gust - their thrust line goes through their hook foil so they can basically just absorb a gust and just go faster 
.
Matthew, no pissing comp going on here mate. You are well above my level at pissing in the wind.
So what do the actual sail designers use to support their designs n ideas? Surely they have the $$$ to investigate n test their designs n actually find out what works n why? Is it a SECRET SOCIETY SCIENCE that they dont want us to know?
Or are you telling me they just whip up a sketch n go 'wow that sure looks great, lets make it n market it for all to use'??? Tell em its the best yet n theyll believe it!
Surely someone on planet earth has done these tests before n found out why twist is needed to control the power n thrust of a windsurf sail???
Please excuse my naievity.. but,
40 years of windsurf sail design n NO ONE has done testing??
Select to expand quoteTGale said..
^^^ and Sailrocket's sail doesn't rake backwards - our windsurfer rig rake is one of the reasons we need twist to be efficient. They also don't need twist to quickly reduce the height of the center of effort on sheeting out so as to reduce overturning moment when powered up and hit by a gust - their thrust line goes through their hook foil so they can basically just absorb a gust and just go faster .
I like this post and especially the following tiny part, metaphorically and physically speaking.
..their thrust line goes through their hook foil..
We are bound by our size. We need as much power per sqmtr to keep the Centre of Effort down and use our thrust line -which goes through the fin- in the most optimum way.
We also need to cope with the tiniest of gusts and the sail needs to absorb those gusts within a gust. That's why twist, or better a total breathing rig is needed.
Power per sqmtr. and gust absorbtion.
Follow that route and you get close to making (much) better sails than now available to us mortals riding those silly vessels.
Effectively we need to make masts softer and adjust the total foil in a way that it pulls us forward, not sideways as that's what I feel when holding 90% of the sails in my hands. ****loads of sideways pressure and I can FEEL.....this is not good as it's simply energy lost.
That's why the largest are fastest. Combine this with the way the PWA is set-up, like gybing in the windhole (what you never do when freesailing, or GPS racing going for the alpha) and you've got your modern day **** for brains sails that we now have to cope with.
We can go much, much faster if we rethink the whole concept, not just the twist alone. Twist is dependent on way more variables than all physicists within this discussion seem to think. You are all forgetting the bigger equation and that's feeling. A top rider feels the wind better than a mediocre rider. That's why a top rider could give worthful comments from a deeper insight seen through the eyes and shared based on the feeling this rider has. I dig it that sailmakers listen to top riders. The main problem being that most top riders think they don't suffer from a lack of strength as they are mostly larger than your average rider, when in reality even they do suffer from their very limited amount of force and leverage
If you don't start at A, you will never get to understand the whole alphabet. And this is exactly what we have been doing for ages. This is why I got in Descartes and the movie about Bruce Lipton.
In the now we are all wired. Because of the massive amounts of information that connected computers on a world wide scale are interpreting, in the end computers can predict your cultural and even personal behaviour.
What makes us stand out from those computers is feeling and connected love. This is the deeper meaning totally connected to the Hippie movement that made our sport come alive. A free thinking world without boundaries was temporarily created. We hit the wall as we are simply not far enough in the evolution just yet to understand our true potential as species, but that makes this fight for freedom in the sixties to get rid of all standing barriers holding back progress, no less interesting or important.
And how is this important for the question on Twist? Computers are better at calculating than we are and will come up with the deisgn solutions sailmakers are choosing.
However, what computers cannot do, at least in the now within our sport that simply lacks the funding for massive tests with lots and lots of sensors, is to decide where A, B, C, are starting. A computer could start at F and that's what actually IS happening now. We're not teaching computers the whole aplhabet as first of all we're forgetting the most important variable: humans.
We as riders need to express what we FEEL in order for the sailmakers and thus, in our day and age, ideally software designers understanding the needs, to implement the right parametres to create the best possible sail.
Yeahhh...now we're moving!
Lets step out of the box and get phylosophical. It's high time. And I mean that with all due respect to physics and the physicists.
Select to expand quoteolskool said..
Mathew, sails n fins are only trying to mimic what is found in nature. Sail designers mustve looked at a birds wing for inspiration. Twist n looseness of leech is required bcoz we need to control the power produced. The sail is not part of the human body. We cannot control its shape or power as a bird infinately controls its wing in flight. We are stuck with a lifeless man made substitute.
Sure lets do the tests n refine the design. But until we have say, 97 sensors n servos which can infinately change the shape n power at will for performance, we are stuck with what we have. A design which has come a long way in the past 40years. But still has a LONG way to go to be equal with what is found in nature.
Ahh, it's a nice warm and fuzzy notion that sail designers have taken inspiration from bird wings. 
And it is often repeated.
Oh, I am sure they do, and from all sorts of other things as well. Such is the nature of the enquiring mind,
But really, lets face it. Birds winds (and of course birds) have many more extreme variations than windsurfing sails in all their specialist disciplines. Which particular bird wing looks like a racing or speed windsurfing sail?
And although some sailors kind of flap their sails a bit (pumping), most birds wings are designed more for the flapping, I dont think we are trying to equal what is found in nature. We are after something much better and more specific for US. 
I understand what you are saying, but we should never thing we are stuck with what we have, or all innovation would cease.
Select to expand quoteolskool said..
So what do the actual sail designers use to support their designs n ideas? Surely they have the $$$ to investigate n test their designs n actually find out what works n why? Is it a SECRET SOCIETY SCIENCE that they dont want us to know?
Or are you telling me they just whip up a sketch n go 'wow that sure looks great, lets make it n market it for all to use'??? Tell em its the best yet n theyll believe it!
Surely someone on planet earth has done these tests before n found out why twist is needed to control the power n thrust of a windsurf sail???
Please excuse my naievity.. but,
40 years of windsurf sail design n NO ONE has done testing??
It's called trial and error. Lots of testing of ideas and seeing which ones work for them. They don't really know why it works either, just that what they test works in the certain situations. That is why development has been so slow. Lots of dead ends and contradictory ideas.
This seems pretty good.
Mast: soft in the middle, stiffer higher and low.
Low aspect ratio.
Top raked back enough. Powersection easy to control for us humans.
I'd show this as a nice example to any sailmaker in the world. Obviously translation is needed, but I'm sure it gets close to the optimum for us as riders.
Oh, and put the head of the boom just below the transition point from power section to release section, or better breathing section as you need to have a breathing sail from top to bottom. Same goes for draft depth. It needs to be deep from bottom to top with the top being able to release enough by creating sidebend and creating low enough tension in the top to ensure autonomous and free thinking twist and sailbody movement responding to waterstate, rider- ,board-, fin-, rigbalance and gusts fired at the overall constellation at speed.
That my friends comes close to the optimum sail for us humans on windsurfboards at speed. For low wind, high efficiency planing I'd take another, higher aspect example. Now it's up to the sailmakers or better, software engineers. I chose the one who understands best.
Select to expand quoteTGale said..
The streamlines on the sail below are unlikely be right, but illustrate the general point that the flow is 3D. Without twist the flow on the upper sail is horrible - streamlines are way too long for the small camber on this part of the sail, very draggy. Twist allows more exhaust from just above the boom and corrects the airflow. The designed-in tension in the sail from the clew to the Neil Pryde "N" allows this twist-off of the upper sail, avoiding the old-school tight leach. Speed is a bit both about thrust but more importantly about reducing drag, especially at higher speeds. Shame about the overly floppy bits of leach, a bit hard to have twist mid-sail and a not prevent over-twist up the top.
Thanks for you theories TGale, but this just sound likepure supposition on your part.
Define: 'the flow on the upper sail is horrible'
Explain why'streamlines are way too long for the small camber on this part of the sail',and why this is 'very draggy'
Explian why the twist would line the streamlines up more acrosss the chord of the sail?
Explain what is'exhaust'and why it'corrects the airflow'
Explain why tight leech is 'old school' when it is designed into many modern sails - even windsurfing sails which win course races.
So is the twist up top correct, or is it 'over twist'. If it is 'over twist', what is it doing and why is it correct?
And then how about some eveidence to back your theories as you explain them?
I am temped to say your spiel sounds like 'Marketing Crap' but I'll give you the benefit of the doubt awaiting you dissertation.
Sailquik Dictionary definition: Marketing Crap - What the sales people tell you when they have no freaking idea, but they think it sounds plausible enough for you the believe it and be impressed
Kwibai.
Define: 'Top raked back enough' i.e.. What is the rake for and why is it enough. enough for what?
What is the release section? What is being released and more importantly why?
define 'breathing'. Is this a technical term in physics or aerodynamics? I thought it was something that animals do the get air in and out of lungs?
explain: 'autonomous and free thinking twist' is the sail now sentient??
This sounds like the ultimate sail. now explain to me how and why it works in terms of physics and science, not pretty marketing words.
Perhaps some of this is due to a language barrier. If it really is as good as you say. I will have one for sure.
Who is this'one' who seems to know all? Is he human? I hope it's not the guy in the video. 
My point is, all these meaningless, or out of context words and phrases have been thrown around at us for so long that we start to actually believe it all without any real evidence. We put whatever interpretation we have in our mind on what it means, and we think that they, and us, understand it.
My theory is that the reason why none of the top sailmakers will come out and explain their designs with physics, is that they just don't know the 'WHY'. Sure, they know that what they are doing is working, and it is taking them forward, albeit, slowly. Sure, they have their theories, just like many of us, but they also know that they have very, very little to really explain how and why it works, so they do not want to expose themselves to embarrasment. I can't blame them for that. I would be the same in their shoes.
Select to expand quoteIan K said..
An excellent example of low twist, dare I say 'tight leech' windsurfing type sails that appear to work really well. 
.
so we disagree on the wisdom shared within the video. By the way, I don't support all of his views but find his view refreshing, not in the least because he dares to speak out in a way we don't feel comfortable about as lots of our knowledge seemingly contradicts with what he says.
As for the picture....I am waiting for the right sailmaker who understands and translate. As said, physics is for the physicists, and I know my limitations. I am looking at this discussion from the other side of the room, remember :-). I am in awe of what's expressed here and really think this is a very valuable topic, so thanks for that!!!
The description to the picture is pretty vivid though and could be implemented pretty easily in a software program by someone skillful enough to translate the needs as expressed by me. I know I would want one if it could be made :-).
Sorry, I just saw your additions. I didn't need to quote just yet. It seems we're both on fire :-). I couldn't agree more on your judgement on many sailmakers. What could be more important though, is building the right 3D software program, calculate all variables (so far we can't as forces on/from...man, board, fin, waterstate, windflow, rotal rig can't be measured properly) and as a follow up the implementation of the right variables.
And no...we don't need floppy twist. We need controlled twist, functioning as a whole. But so far there seems to be no better when windspeeds are catching up with boardspeeds. Proof is with the pudding, in this case raceresults.
What I do know is that we need to go lower aspect and we need to get self balancing rigs that can be steered by the fingertips. I've got my preferences in the now and I simply feel who is on track for me (my personal sailingstyle, weight and length) and who is not. No marketingtalk in the world could convince me otherwise.
