Select to expand quoteImax1 said..sheddweller said..Phromsky said..
The way I figure it is this 
:
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
No, he would not. Not even close.
What a dumb conversation.
Silverback Gorillas are notorious for wobbly windsurfing. There is no way of getting one to go in straight line. They just won't.
Thats nonsense.
just the other day i saw a south african maned gibbon with a sawn off f35 wing flying down the street on his wind skate. He was holding a perfectly straight line.
a gorilla has a much greater mass than south african maned gibbon, so a little less stable, i'll give you that. But im sure if you gave a gorilla a sawn off cessna wing the drastically shorter chord length would allow the gorilla to maintain a much straighter line than the gibbon was capable of, and therefore obtain a much higher speed.
Select to expand quoteSubsonic said..Imax1 said..sheddweller said..Phromsky said..
The way I figure it is this :
If I could afford to trash a light aircraft. As in saw off the starboard wing at the wing root (which would likely be around 7 to 8 square metres) and then attach a windsurf boom and a board to it. Meanwhile also teach a Silverback Gorilla to windsurf in a straight line. ..Then I could send him off sailing down that strip in Namibia with my aircraft wing and he just might beat Albeau.
No, he would not. Not even close.
What a dumb conversation.
Silverback Gorillas are notorious for wobbly windsurfing. There is no way of getting one to go in straight line. They just won't.
Thats nonsense.
just the other day i saw a south african maned gibbon with a sawn off f35 wing flying down the street on his wind skate. He was holding a perfectly straight line.
a gorilla has a much greater mass than south african maned gibbon, so a little less stable, i'll give you that. But im sure if you gave a gorilla a sawn off cessna wing the drastically shorter chord length would allow the gorilla to maintain a much straighter line than the gibbon was capable of, and therefore obtain a much higher speed.
You can't use Gibbons in the argument. Gibbons are different. Everyone knows how good they hold lines .
Every sawn off Cessna wing wielding Gorilla I come across use them foiling . They all do it now. There's only one that still windsurfs and is so wobbly . Bit of an odd character. I understand you can't compare windsurfing with foiling . It would be silly of me to comment on that .
I'm worried you could be right.
Good to see this thread has become a far more productive and informative discussion than it was
Finally some sensible discussion. I'm surprised that it took 3 pages of crap and poor acceptance of good advice to get to the heart of the matter.. there's just no wind anywhere . Luckily there's snowboarding
Select to expand quotesheddweller said..aeroegnr said..Phromsky said..MHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
There's a pretty strong surface gradient in windsurfing because the sail is right next to the water, so the wind speed (and thus apparent wind direction) changes rapidly up the mast.
The larger sail craft don't have their masts start right on the water where this effect is large...
Have you measured it?
Can judge by eye alone in this photo of the Sail GP fleet racing on a broad reach to the bottom mark. ..Can see approx. 90 degrees between the wakes of the four cats on starboard and the two leading cats on port, and so its reasonable to surmise that all six are established approximately 135 degrees off the breeze. They have some washout/twist going on as you would expect, but they're certainly not flopping around allover the show with it.
That's a supported rig, different to an unsupported rig, for the sailor hanging on to it.
Not sure if you're just trolling now but I'll play.
First off these are the one design wings from the gp series and not the cup. But anyway
in this pic of the gp series they are vmg running in like 8 knots of breeze. Max power, Max camber, less twist mode. And look, they still have the boom way up and the top blading off going way below boom height.
Now get a photo of the reaching first leg of the course in 15 knots. They are twisting those solid ribs as much as they dare within the limits of the design.
I remember some articles about the teams in the cup actually using the leeward side of the top of the wing super twisted to actually add righting moment.
Now in the meantime, have you rigged your sail properly yet? Go on, Post some pics.
Here, I'll help by copying from the severne site what everyone here has already told you 50 times.
'WHY DON'T MY CAMBERS ROTATE PROPERLY?
If your cambers don't rotate properly, it could be a sign that the sail has too little downhaul. Other possible issues might be the use of the wrong mast, too much batten tension, or the wrong spacer setting.'
I think I can see that gorilla hanging off the wing 2nd from the right. See Imax? Perfectly straight line.
I rest my case.
^^^^
Hang on a minute , he's foiling , that's why he's going in a straight line.
Whats wrong with you for Gods sake ?
At the considerable risk of getting serious for a moment
:
Being a born sceptic, I have always been wondering if sooooo much twist in some of the race sails is really an advantage, and why it seems to work in some situations, for all the reasons mentioned here and more. Just because something gets popular doesn't not mean it is 'truth'. and there is often no ONE 'truth' anyhow. (This applies to a lot of things that are not a well studied and well defined science - and windsurfing sails certainly fall into that bucket).
First problem is to define' advantage'.
The core of that problem is that there are an abundance of use cases - legitimate uses that are very different. Was is the advantage to YOU?
Be careful what you choose. How do you want to fly?
I will just give one example that has always kept the above scepticism ticking over for me.
In the early 80's, I saw a little old man wandering down the spit at Sandy Point holding a a very tall pole. Every now and than he would stop and hold it vertically and consult some gauge in his other hand. He would drop the pole down and write down some numbers.
My curiosity naturally fully aroused, I asked him what he was studying. He replied that we was designing a sail, and was trying to determine the twist (washout) required tomatchwith the wind velocity gradient. (or words to that effect).
The man turned out to be Lindsay Cunningham, one of my childhood idols, on account of him designing many of the sailing cats that I grew up lusting after (and later in my teens, had the privilege to sail some
). He was of course, designing Yellow Pages, Endevour, which went of to hold the Outright World Speed Sailing 500m World Record, for many, many years.
That wing sail didn't have a great deal of twist! neither did the later, lower aspect wing he later designed for Macquarrie Innovation, which I also had the privilege of watchingdoingmany runs (and have a few interesting incidents!
) on the Sandy Point Speed Strip.
So when people say, "Oh, we have twist in the windsurfing race sails to compensate for the wind gradient" I say BS! There is no way that stacks up. It's not just this example that shows this, just look at all the high speed watercraft like the AC and sailGP foilers! None have more than low teens degrees twist, many have less.
It must be for different reasons.
And therein lies the conundrum. There are lots of theories (I have a few myself ) for so much twist in some windsurfing sails, but I still have not seen any really compelling explanation of any of those theories backed up with any actual hard data. There is no doubt that many sails with a great deal of twist do 'work' in th e situation's they are specifically designed and tested for. But there is not of lot of clear explanations about how and why they work, and what situations exactly that applies too. No really well backed up data to explain and define what degree of twist works where, and for who, in what situations. Most of us recreational sailors are flying blind in that respect. It's back to trail and error, to find out what works for us in our situations. Sure, we can see what is working for our peers, and especially champions in various aspects of our sport in what situations and disciplines, but do we mere mortals really sail in the same situations and in the same way as those champions? (check your ego here!)
Ludwig Prandtl's Theories and studies come closest to what I have found. Papers on the subject abound on the WWW, but very, very few directly mention, or seem to directly apply to windsurfing Slalom/Race sails.
If you find any, please share them. 
All I can suggest, is to keep experimenting with sail models, shapes and settings to see what actually works for you in your particular situation. Seek advice and wisdom, and respect it, but don't abandon scepticism, and certainly not curiosity.
Oh, and sail to put a smile on your dial. Thats the only really meaningful measure of things.
The twist question is indeed an interesting one. I also have been skeptical howbig thechange in the wind direction really is for a windsurfing rig. There is no doubt in my mind that the twist has other functions, and those other functions may be more important in certain instances (and perhaps even most of the time).
The minimal twist in the picture of theYellow Pages Endeavourabove seems to be based on actual measurements of the wind gradient at Sandy Point. One has to remember that this was purpose-built for speed runs on very flat water. The YPE's top speed was 46 knots in 20 knot winds -2.3 times the speed of the wind. Both of these facts are highly relevant with respect to the twist - wind direction question. The twist is supposed to compensate for the change inapparentwind direction over the height of the sail. For the YPE record runs, the apparent wind was dominated by the headwind, which was more than 2x stronger than the true wind. Compared to the windsurfing records in Luderitz, where the board speed was much closer to the wind speeds, that means that the change in apparent wind angle was a lot less.
How large the wind gradient is in the first place depends a lot on "surface roughness", which is minimal on flat water. But typical slalom raceare held inconsiderable chop, even when held at offshore places like Fuerteventura. The wind gradientin the chopis a lot bigger than, for example, on Lake George. Anyone who sailed spots like Lake George, and tried to water start in 4 foot waves or chop, will know exactly what I mean.
So if you compare the wind gradient when doing light wind speed runs on Lake George, at > 2x the wind speed and very laminar wind, with a slalom race held in 2 foot chop in 30 knots, there's definitely a huge difference.If the main function of twist was indeed to adapt to wind direction change over the height of the rig, then sails with a lot less twist should work a lot better on flat water speed spots. I did not see that at the flat water spots in Oz, though. As I said above, I think other aspects of how twist works in slalom sails may often be more important.
As I said, and other correspondents have agreed, I think a good part of the answers lay in the work of Prandtl and much more recently, and experimentally, Al Bowers.
If some very smart PhD student, with lots of tools at their disposal, were to try to design a windsurfing (speed)sail on these principles, I wonder what it might end up looking like? 
Here is something of a glimpse from Al Bowers for those who are interested.
Select to expand quotePhromsky said..sheddweller said..aeroegnr said..Phromsky said..MHSA said..
Fortunately the aerodynamicists that worked on the americas cup winning solid wings knew the importance of trailing egde twist to enable a water craft to smash top speed.
And I thought this was the speed forum.
In windsurfing not enough downhaul to match the designed luff curve and twist is so slow.
Its often over done in windsurfing. ..If the top cam looks flat and not producing any curve at all, what's the point of putting it there? ..Neither the America's Cup yachts nor any other speed focused sail craft exhibit anything like the amount of washout some windsurfers are using.
There's a pretty strong surface gradient in windsurfing because the sail is right next to the water, so the wind speed (and thus apparent wind direction) changes rapidly up the mast.
The larger sail craft don't have their masts start right on the water where this effect is large...
Have you measured it?
Can judge by eye alone in this photo of the Sail GP fleet racing on a broad reach to the bottom mark. ..Can see approx. 90 degrees between the wakes of the four cats on starboard and the two leading cats on port, and so its reasonable to surmise that all six are established approximately 135 degrees off the breeze. They have some washout/twist going on as you would expect, but they're certainly not flopping around allover the show with it.
Eh but that's not a sail its a ridged wing rig either 28,24 or 18M tall with rams ribs membrane tensioners rotator bearings standing and running rigging and all manner of other technical gizmos. Nothing like a windsurfing sail, no healing moment for a start....
here we go again Oh Ohh Ohh the funky Gibbon.
Select to expand quotepeterowensbabs said..Phromsky said..
Can judge by eye alone in this photo of the Sail GP fleet racing on a broad reach to the bottom mark. ..Can see approx. 90 degrees between the wakes of the four cats on starboard and the two leading cats on port, and so its reasonable to surmise that all six are established approximately 135 degrees off the breeze. They have some washout/twist going on as you would expect, but they're certainly not flopping around allover the show with it.
Eh but that's not a sail its a ridged wing rig either 28,24 or 18M tall with rams ribs membrane tensioners rotator bearings standing and running rigging and all manner of other technical gizmos. Nothing like a windsurfing sail, no healing moment for a start....
here we go again Oh Ohh Ohh the funky Gibbon.
No healing moment??
Really, it may be a wing, but the biggest difference is that the crew are not holding onto it with a wishbone, and yes, that can make some big differences.
I'd love to know if they were designed with Prandtl's principles along the lines Al Bowers and his research associates worked on?
The way I see it is , newer stuff generally goes better than older stuff , wether your a beginner or pro. Less and less so as time goes by. But we have to presume we're going in the right direction. So be it , if we're using oversized , over twisting easier to use sails. If that is what it takes . I love new ideas . If we can get a smaller more powerful tighter leeched sail that works better , we will all buy that .
My only whinge is the accepted poor life expectancies of new gear.
Select to expand quoteImax1 said..
The way I see it is , newer stuff generally goes better than older stuff , wether your a beginner or pro. Less and less so as time goes by. But we have to presume we're going in the right direction. So be it , if we're using oversized , over twisting easier to use sails. If that is what it takes . I love new ideas . If we can get a smaller more powerful tighter leeched sail that works better , we will all buy that .
My only whinge is the accepted poor life expectancies of new gear.
Seconded. The reality is almost no one can describe whether a new feature is providing any benefit or not. Most people can barely say what they like or dont like - often a change to something, causes the gear to feel a little different, so most people tend to assume "its worse than before".
We dont have to presume. Wavesailors can do bigger tricks than ever - clearly they are highly skilled... but as important is the quality of the gear -> take for example a Severne Gorilla mast, they are quite strong which encourages you to sail harder. Similarly for the other end of the spectrum, you can use a gps to run your metrics for changes to your kit. And the other end with beginner gear going through an era of brittle gear, but now there are blow-up-rigs. Gear is getting better - it really isn't a debate.
Some professionals are convinced that there is way too much twist in modern racesails, so they take their brandnew sails to the sailmaker for some "minor" adjustments.....
Select to expand quotesailquik said..peterowensbabs said..Phromsky said..
Can judge by eye alone in this photo of the Sail GP fleet racing on a broad reach to the bottom mark. ..Can see approx. 90 degrees between the wakes of the four cats on starboard and the two leading cats on port, and so its reasonable to surmise that all six are established approximately 135 degrees off the breeze. They have some washout/twist going on as you would expect, but they're certainly not flopping around allover the show with it.
Eh but that's not a sail its a ridged wing rig either 28,24 or 18M tall with rams ribs membrane tensioners rotator bearings standing and running rigging and all manner of other technical gizmos. Nothing like a windsurfing sail, no healing moment for a start....
here we go again Oh Ohh Ohh the funky Gibbon.
No healing moment??
Really, it may be a wing, but the biggest difference is that the crew are not holding onto it with a wishbone, and yes, that can make some big differences.
I'd love to know if they were designed with Prandtl's principles along the lines Al Bowers and his research associates worked on?
No - the vessel is a Proa and by definition they sail upright/flat. So that the healing moment is converted into forward moment. Their rig does not dip and the COE does not lower. The same way sail GP vessels strive to remain up right or foiling moths etc etc they are fastest upright . By reducing that one variable they help max out. Keep expounding those wonderful theories they amuse us!
Select to expand quotepeterowensbabs said..sailquik said..peterowensbabs said..Phromsky said..
Can judge by eye alone in this photo of the Sail GP fleet racing on a broad reach to the bottom mark. ..Can see approx. 90 degrees between the wakes of the four cats on starboard and the two leading cats on port, and so its reasonable to surmise that all six are established approximately 135 degrees off the breeze. They have some washout/twist going on as you would expect, but they're certainly not flopping around allover the show with it.
Eh but that's not a sail its a ridged wing rig either 28,24 or 18M tall with rams ribs membrane tensioners rotator bearings standing and running rigging and all manner of other technical gizmos. Nothing like a windsurfing sail, no healing moment for a start....
here we go again Oh Ohh Ohh the funky Gibbon.
No healing moment??
Really, it may be a wing, but the biggest difference is that the crew are not holding onto it with a wishbone, and yes, that can make some big differences.
I'd love to know if they were designed with Prandtl's principles along the lines Al Bowers and his research associates worked on?
No - the vessel is a Proa and by definition they sail upright/flat. So that the healing moment is converted into forward moment. Their rig does not dip and the COE does not lower. The same way sail GP vessels strive to remain up right or foiling moths etc etc they are fastest upright . By reducing that one variable they help max out. Keep expounding those wonderful theories they amuse us!
So moths sail upright? Or do they sail canted to windward?
Select to expand quotesheddweller said..
So moths sail upright? Or do they sail canted to windward?
To windward
Select to expand quotepeterowensbabs said..sailquik said..peterowensbabs said..Phromsky said..
Can judge by eye alone in this photo of the Sail GP fleet racing on a broad reach to the bottom mark. ..Can see approx. 90 degrees between the wakes of the four cats on starboard and the two leading cats on port, and so its reasonable to surmise that all six are established approximately 135 degrees off the breeze. They have some washout/twist going on as you would expect, but they're certainly not flopping around allover the show with it.
Eh but that's not a sail its a ridged wing rig either 28,24 or 18M tall with rams ribs membrane tensioners rotator bearings standing and running rigging and all manner of other technical gizmos. Nothing like a windsurfing sail, no healing moment for a start....
here we go again Oh Ohh Ohh the funky Gibbon.
No healing moment??
Really, it may be a wing, but the biggest difference is that the crew are not holding onto it with a wishbone, and yes, that can make some big differences.
I'd love to know if they were designed with Prandtl's principles along the lines Al Bowers and his research associates worked on?
No - the vessel is a Proa and by definition they sail upright/flat. So that the healing moment is converted into forward moment. Their rig does not dip and the COE does not lower. The same way sail GP vessels strive to remain up right or foiling moths etc etc they are fastest upright . By reducing that one variable they help max out. Keep expounding those wonderful theories they amuse us!
But..... What?
First there was "no healing moment"
and now,
There is healing moment, but "the healing moment is converted into forward moment"
Also, almost all the foiling craft I have observed, especially the foiling Moths, but including the large rigid wing foilers, are best sailed heeled to windward.
I am at loss to know what 'wonderful theories" I have 'expounded' that amuse you so.
..Ah well, looks like I won't be able to make that race we arranged Sailquik ..I bust the main batten in my favourite 5.0 yesterday. Only sailed 4kms, didn't fall into it or anything, have never fallen into it. I just turned it over and it bust. ..Had to sail back about 700 metres with it broken, and rather curiously my 2 sec high of 31.7 knots was actually with the batten broken as seen below - It had plenty of belly going on!
..
By the way, thanks for posting that great photo above of Yellow Pages Endeavour. I think at the very least it shows that in order to sail significantly faster than the wind (as in twice wind speed or more), washout/twist-off probably needs to be limited to similar values as seen in aircraft wings and also birds wings when observed in gliding flight.
..Incidentally the first man to fly, Otto Lilienthal in the 1890's, was aware of washout in birds wings, as evidenced in his drawings - It also appears to me to be present in his hang-gliders and was probably helping him to stay alive in his successful flights. ..I've flown aircraft with and without washout/twist, the first thing it does in an aircraft is make it safer and easier to fly, in particular when close to the stall it helps the pilot to avoid rapid and total loss of control and subsequent spinning.
Regarding the supposed vertical wind gradient up a windsurf sail, I agree with you, I really don't believe that notion is any kind of significant factor - In terms of our actual physical control over the sail I think the vertical wind gradient is negligible - Far more likely is that twist-off simply helps us as windsurfers to manage horizontal shears in the wind.
..
I also watched the Al Bowers video. ..I actually have an image derived from a photo of an Albatross (taken by my son) on the nose of my favourite board. Between us we have around 800 photos of numerous Albatross species in flight. I evaluated all of them, it was a long time ago now, but still I'm fairly sure I didn't seen any evidence of those controversial dynamics that Al Bowers is vaunting in actual Albatross flight.
Select to expand quoteelmo said..
A lot of the problem with race sail rotation on the newer sails is the gap between the boom and clew.
Because huge amount of shape in the sail, if the clew is butted up against the back of the boom.
When you go to flip the sail all this bent batten length has to change over to the other side of the mast, it's fixed at the front so it can't expand there, if it's up against the boom it can't expand there either, so the only other option is for the battens to distort into an "S" shape so the sail can flip over.
If you leave a 2-4cm gap between the back of the boom and clew, and this will allow room for the sail to rotate.
If you want to check this (roughly), when the sail is rigged, grab a tape measure and measure the distance from the mast to the edge of the sail on the leward side.
Although this measurement is slightly longer than reality (the battens are in the center of the luff pocket rather than the edge) it will give you a general idea on how much extra length there is which you have to allow for.
I also believe this is a possible root cause for batten tip breakage.
Bump
If you had looked more carefully MHSA, you would have noticed that all of the back end of my boom is visible in my photo. The clew is actually resting freely on the opposite (lower) side of the boom and was on sufficient rope to float freely from side to side with about 2cms to spare.
Select to expand quotePhromsky said..
If you had looked more carefully MHSA, you would have noticed that all of the back end of my boom is visible in my photo. The clew is actually resting freely on the opposite (lower) side of the boom and was on sufficient rope to float freely from side to side with about 2cms to spare.
Well yea, of course its resting free. You've broken the batten.
MHSA. ..For the record I respect and agree with everything that "Elmo" has written above. And I've actually been rigging the clew of all my sails the way he describes for at least the last 10,000kms that I've sailed.
And so my suspicion is that you haven't actually asked him if you can bump his post to here to serve your latest dubious device.
Back to the important stuff. When do we get to see this gorilla head down the channel with his airplane wing?
