Select to expand quotefangman said..
Maybe because all the best sailors were made 50 years ago too? 
or more.....
Mr Fussy, hey Bugs that's perfect name as your sail making skills are awesome.
The 34.04 knots on a borrowed Bugs sail in 1989 Tangomoana for a then 75kg proves your ability.
The Bugs Sails 4.5 & 4m you made for Glenory were sweet, fast and easy to sail, just didn't get the NW wind for speed sailing.
Then the Hot Sails Maui era was great to be involved at the same factory.
Hope all good cheers Greg
Select to expand quotesailquik said..
Why is it that all these great films demonstrating this stuff, were all made 40-50 years ago
It was the same with all the hyrofoil stuff that Fangy dug up.
Probable took that long to be government declassified.
Unfortunately most developement is now privatised. Boeing, Airbus, SpaceX etc so don't expect any new research turning up on Google anytime soon.
Select to expand quotesailquik said..
I was talking to Mal Wright about his fin design analysis software (Finmaker) yesterday. I wonder of it could handle the shape of a sail?
He says probably not. 
Select to expand quoteyoyo said..sailquik said..
Why is it that all these great films demonstrating this stuff, were all made 40-50 years ago It was the same with all the hyrofoil stuff that Fangy dug up.
Probable took that long to be government declassified.
Unfortunately most developement is now privatised. Boeing, Airbus, SpaceX etc so don't expect any new research turning up on Google anytime soon.
I wonder if it is partly because, recently, research into this stuff is done in computer models and mathematics so there is nothing interesting to show that would make much sense to the general public, especially if it is done for a private investor?
Select to expand quotesailquik said..
I wonder if it is partly because, recently, research into this stuff is done in computer models and mathematics so there is nothing interesting to show that would make much sense to the general public, especially if it is done for a private investor?
That's pretty much the case. When I was involved in the America's Cup in 2007 teams were using CFD, but were also doing extensive towing tank and wind tunnel testing. By the 2013 America's Cup, the top teams were doing everything with CFD, primarily RANS (Reynolds Averaged Navier-Stokes) codes such as Fluent or Fine Marine, as well as potential flow methods such as Splash.
If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.
Select to expand quotePacey said..
If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.
Thanks Andrew. You are right. It is daunting just trying to work out how to install and run it, and I haven't even got to the program itself! I think I'll pass..... 
Select to expand quotesailquik said..Pacey said..
If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.
Thanks Andrew. You are right. It is daunting just trying to work out how to install and run it, and I haven't even got to the program itself! I think I'll pass.....
If you don't know enough to write your own CFD code you probably won't get the right answer from a canned program anyway. For example, canned statistical programs are misapplied and misinterpreted more often than not, particularly in the soft sciences like biology. About the only ones that get statistics right are insurance companies and high stakes gamblers - because their survival depends on it. It has been said that 90% of the statistics quoted by politicians in interviews are made up on the spot.
Select to expand quoteboardsurfr said..
I'm with Daffy on thinking that more experimental data could lead to a better understanding and therefore better sails. I also agree with Barney831 that a successful simulation would be a very good way to "demonstrate a complete understanding". The funny thing is, though, that to call a simulation successful, you need to show that it matches actual measured data (unless you're the marketing guy).
Here is a maximum speed performance polar for the Iron Duck (former sailing land speed record holder) modelled from a 3-view drawing and some coastdown data from Bob Dill. The record speed was 101.3 knots.
The Iron Duck had a symmetrical rigid wing with zero twist and no flap.
Select to expand quotebarney831 said..
It has been said that 90% of the statistics quoted by politicians in interviews are made up on the spot.
Did you just make that up 
?
Select to expand quotebarney831 said..
Here is a maximum speed performance polar for the Iron Duck (former sailing land speed record holder) modelled from a 3-view drawing and some coastdown data from Bob Dill. The record speed was 101.3 knots.
The Iron Duck had a symmetrical rigid wing with zero twist and no flap.
Cool plot. More than 2x wind speed going 45 degrees into the wind is quite impressive. Going at 4x wind speed downwind, any variations in true wind pretty much disappear. Windsurfers are closer to 1x wind speed, especially above 40 knots, so the effects of variations would be much larger. Ice surfers, who also easily reach 2x wind speed, also want tighter leeches.
So, some of the fastest sailing crafts use rigid wings with little or no twist. The fastest windsurfers use tons of twist, PD being a good example. Interesting discrepancy.
One perplexing things about race sails is that we seem to need this huge floppy upper part to get tons of stability lower in the sail. I was pretty amazed to feel the COE of a race sail moving forward rather than back in strong gusts. I have seen a technical editor for a windsurfing magazine and top-level instructor explain how the loose leech allows for more sideway deflection of the mast in gusts before the sail shape is disturbed and the sail becomes unstable. That was for non-cam sails, but I think the same principle applies to cambered sails.
-12 percent less wing area than the comparable elliptical spanload wing
link:
technology-afrc.ndc.nasa.gov/featurestory/prandtl-wing-design
Interesting article.
But there is one HUGE joke in it!
The US government claims a Patent on this wing design!!
And even their own patent design produces unequivocal evidence of 'prior art' quoting it was actually 'invented ' by Prandtl and Horten Bros up to 80 years ago! 
Stupendously ridiculous!!!
Select to expand quotePacey said..sailquik said..
I wonder if it is partly because, recently, research into this stuff is done in computer models and mathematics so there is nothing interesting to show that would make much sense to the general public, especially if it is done for a private investor?
That's pretty much the case. When I was involved in the America's Cup in 2007 teams were using CFD, but were also doing extensive towing tank and wind tunnel testing. By the 2013 America's Cup, the top teams were doing everything with CFD, primarily RANS (Reynolds Averaged Navier-Stokes) codes such as Fluent or Fine Marine, as well as potential flow methods such as Splash.
If you want to try out some serious CFD yourself you can download OpenFOAM (www.openfoam.com/download/), an open source CFD code, but be warned, it's a bear.
RANS!
Reynolds had been dead and gone for so long before acronyms came into usage you would have had to have spelled it out for him as well.
en.wikipedia.org/wiki/Reynolds-averaged_Navier-Stokes_equations
Apparently Feynman spent years mulling over the turbulence issue and gave up.
`Turbulence is the most important unsolved problem of classical physics.'
- Richard Feynman -
But I suppose as computers get bigger and faster they can push the averaging cutoff down and down.
How well do the modern CFD programs predict the specifics of what we see in the old video. Do they nail the transition to turbulence, the exact outline of the turbulent boundary layer? The friction in the boundary layer etc.?
from Sailquik's link
"The new wing has 22 percent more span and 11 percent less area, resulting in an immediate 12 percent drag reduction."
If you reduce the area 11% you get an 11% drag reduction. If you increase span 22% you increase lift in relation to area. So you get back to the original lift with the extra 11% area. The only magic here is the USPTO allows you to patent non-new and non-novel ideas which all other countries would not.
Select to expand quoteyoyo said..
from Sailquik's link
"The new wing has 22 percent more span and 11 percent less area, resulting in an immediate 12 percent drag reduction."
If you reduce the area 11% you get an 11% drag reduction. If you increase span 22% you increase lift in relation to area. So you get back to the original lift with the extra 11% area. The only magic here is the USPTO allows you to patent non-new and non-novel ideas which all other countries would not.
I thought it was implied that lift remained the same without having to go back to the original wing area? The premise is that the Bell curve slantwise flow change reduces induced drag for the tip vortex.
Select to expand quotesailquik said..
Interesting article.
But there is one HUGE joke in it!
The US government claims a Patent on this wing design!!
And even their own patent design produces unequivocal evidence of 'prior art' quoting it was actually 'invented ' by Prandtl and Horten Bros up to 80 years ago!
Stupendously ridiculous!!!
Inconceivable that the US government would do something ridiculous.
If you look at the patent, you'll notice that the primary claim is for "An aircraft that provides adverse yaw control without a rudder", which increases efficiency even further. Prandtl only looked at the wing. The Armstrong guys realized that the wing has some added benefits that can lead to a pretty dramatic design change (no rudder or tail section).
I found the explanation of Prandtl's "prior art" in the patent quite helpful since it's in terms that even a patent examiner can understand. By making wings longer with thinner tips, and twisting the wind upwards towards the outside, he arrived at a design that was more efficient that typical wing designs. I assume that's because the design eliminates the vortex at the wing tip. But since it makes wings longer, it's less practical than winglets.
It is a bit amusing, though, to see that airplane wing designers discovered about 80 years ago that twist improves aerodynamic efficiency.
Select to expand quotesailquik said..
The US government claims a Patent on this wing design!!
And even their own patent design produces unequivocal evidence of 'prior art' quoting it was actually 'invented ' by Prandtl and Horten Bros up to 80 years ago!
When I went to work at the Boeing Scientific Research Lab in the '60s, one of the old timers said to me;
'Barney, it doesn't matter how smart you think you are;
it doesn't matter how smart you really are;
when it comes to aviation there is nothing that hasn't been tried.'
I remember that like it was yesterday.
About Negativ lift
quote
"A slotted wing can be set with deeper cambers than a conventional soft sail, reaching a higher Maximum Lift Force. Secondly, the rigid control arms can force inversion of the upper sections, which creates righting moment by reversing the lift force. But a hard wing is complicated, expensive, and impractical for sailing in general.
Screen grab from Membrain showing an inverted head of a hard wing sail. By inverting the upper wing, the sail/wing is actually pushing backwards. It is also pushing to windward, reducing the sail's tendency to heel the boat. The balance of the inversion and normal camber can in some conditions increase the boat's performance."
You can see from this explanation,as I said before negativ lift cause huge drag on head,becasue lift vector is pointed backwards..
(Bell spanload has lift vector pointed forward,so this thrust will reduce overall drag of sail.)
link
www.northsails.com/sailing/en/2018/04/designer-spotlight-americas-cup-special-edition-developing-softwing-technology-for-2021-ac
Floppy head=no tip vortex
Downwash gives downward velocity component in the free-stream ahead of the wing, at the wing and far downstream.
Here you can see how downwash (caused by tip vortex)behind wing,change local realtive airflow infront wing.This " new" airflow is now effective airflow which wing "feels" it.Wing AoA is reduced and lift vector is tilted back causing more drag.This is induced drag.
This is reason why we must decrease vortex on sail tip,one way to do this is have floppy head,because floppy head is indication that leeward and windward sail pressure is almost equal , so we minimize tip vortex.
It is very counter intuitive how downwash behind wing can change airflow infront wing,but this is way it goes in real 3D wing/sail.
Select to expand quotebarney831 said..sailquik said..
The US government claims a Patent on this wing design!!
And even their own patent design produces unequivocal evidence of 'prior art' quoting it was actually 'invented ' by Prandtl and Horten Bros up to 80 years ago!
When I went to work at the Boeing Scientific Research Lab in the '60s, one of the old timers said to me;
'Barney, it doesn't matter how smart you think you are;
it doesn't matter how smart you really are;
when it comes to aviation there is nothing that hasn't been tried.'
I remember that like it was yesterday.
...in the 60's,....... Jeez Barney, from reading previous posts over the years, I had you down as a 25 year old blond surfer dude! 
I actually had a chance to do some small amount of experimenting last Friday.
I had been playing with a prototype 5.2m speed sail and rigging it on different combinations of masts , comparing it with the production sail that was actually evolved from it and is extremely close in shape.
I had discovered that I could rig it with extreme twist, but still keep the draft depth the same in the bottom half of the sail using different masts. There was quite a lot of difference between the two sails, one rigged normally on the standard mast, and the other rigged to the extreme. So this was an experiment I could do that might tell me something.
My intention was to rig both sails and try them side by side. Unfortunately, eagerness to get on the water (watching the perfect squalls come though while rigging) sabotaged my experiment and by the time I had rigged my 4.7m (normally) and the 5.2m at the extreme, I lost patience and hit the water with the 5.2m. The irony is that I still missed the best early wind.
But, I did get a few good squalls witch I thought should have yeilded more speed. The rig just did not feel 'fast' and my speeds concurred. Not only that, but it did not feel particularly stable either. I was fighting the rig on the square run in and when I hit the course, it didn't feel good, powerful or fast. I perservered for a few runs to make sure it was not just me or the conditions, but eventually got frustrated with it.
Now I had a problem, as I had not rigged the standard sail for comparison, and I knew that I didn't want to waste time doing that now in case I missed the next good squall. So I grabbed the 4.7m, which was looking really nice , hoping the wind would continue to strengthen so I would have enough for the smaller sail.
As luck would have it, that is exactly what happened!
The next good squall was my best run of the day by quite a margin, and this sail felt great. A few more runs in lesser squalls confirmed it beyond doubt. The 'extreme twist' rigged sail just didnt work as well as the standard one, even though the latter was half a meter smaller.
I am sure I will have to repeat the experiment using both the 5.2's, but I am pretty confident that the extremely twisted set sail did not work as well. I noted that the more extreme twist I got, the more 'static' the twist became, and I think that was a important factor as well.
But I think this was a great finding. Sometimes the only way to be sure about an experiment or idea is to take it to the extreme. Yes, that was too far. All the theory in the world is great, but in the end one still has to test the ideas in the real world.
Ticked that off, now to try some other slightly different things.
Oh, and to add another important note. As Kwibai so elegantly points out, The set up as a whole is critical. (I didn't wear any extra weight.)
The other change I tried at the start was a smaller (16.5cm assy) fin. It was too small for the conditions. When i went to a slightly larger (18cm assy) the whole thing came alive and was far better balanced.
Funny, I did the same. Went with a 18 at the start (46 kt fin) and just couldn't get it and crashed a few times. Swapped to a 21.5 board came up and got my fastest times. I don't know that Friday was a good test day. Fun and brutal but couldn't measure much from it. I did think about weight but the lulls killed that idea
Select to expand quotekato said..
Funny, I did the same. Went with a 18 at the start (46 kt fin) and just couldn't get it and crashed a few times. Swapped to a 21.5 board came up and got my fastest times. I don't know that Friday was a good test day. Fun and brutal but couldn't measure much from it. I did think about weight but the lulls killed that idea
Every day on the water is a good test day!
I think I had enough reasonable runs to make it quite clear the way I rigged the sail was not working - I had rigged to the extreme after all, to make it as obvious as possible.
With fins, it is a bit less clear. Some days the smaller combos work perfectly. Both of us have our PB's on the fins that didn't work for us on this session. Some days, they just don't. A lot to do with water conditions and wind angles. Sometimes one does not need/have much fin pressure, and at other times we seem to need it. I think in more steady, more laminar winds, and broad angles on flatter water, we get better results from smaller fins. We had neither of those conditions on friday.
Select to expand quotebarney831 said..
Optimum sail twist is a function of board speed to wind speed ratio (aka Foehn Number; Kenney 2001). When hyperwind sailing at high Foehn Numbers, the optimum twist is zero.
Windsurfers are not very efficient and generally sail at less than Foehn Number 1.5. The optimum sail twist with height for a windsurfer can be calculated if both the board speed and wind gradient (increase in wind speed with height) are measured. Alternatively, a typical spanwise sail twist distribution can be calculated for a typical board speed and typical wind gradient in order to get a feeling for the order of magnitude of optimum twist (i.e. how much twist is too much).
Here is some hyperwind sailing data collected while out for an afternoon sail; not a speed trial.
Conditions:
- light winds typically 8 to 10 knots; 10 knots was used as input to the numerical model computing the maximum speed polars (blue lines on the polar plot)
Results: plotted with GPSResults
- 3.4 sq m sail; ZERO twist; ZERO camber
- GT-31 gps speed data are the red circles on the polar plot
- max speed measured was 37 knots
Ref: Kenney, B.C., 2001. Hyperwind Sailing, Catalyst, J. Am. Yacht Res. Soc., 6, 24-26.
Hi Barney,
Took me a while to ponder over this.
Am assuming that your statement about twist in the first line is in reference to Elliptical span load lift distribution and Gradient.
If this is the case, using a bell shaped lift distribution with perhaps a slightly taller, higher aspect sail, and some twist will change that.
I pointed out in another post some reasons why I don't think wind gradient is a significant factor in speed windsurfing in many of the very flat terrain places we sail. Perhaps this would be true of many ice lake venues also?
That begs the quesion of if, in the high (water) drag environment windsurfing tends to inhabit, (closer to 1:1.25 true wind to speed ratios at top speed) the low centre of effort in the sail, and the drag reduction from something like the Prandl model make more difference?
Select to expand quotesailquik said..barney831 said..
Optimum sail twist is a function of board speed to wind speed ratio (aka Foehn Number; Kenney 2001). When hyperwind sailing at high Foehn Numbers, the optimum twist is zero.
Windsurfers are not very efficient and generally sail at less than Foehn Number 1.5. The optimum sail twist with height for a windsurfer can be calculated if both the board speed and wind gradient (increase in wind speed with height) are measured. Alternatively, a typical spanwise sail twist distribution can be calculated for a typical board speed and typical wind gradient in order to get a feeling for the order of magnitude of optimum twist (i.e. how much twist is too much).
Here is some hyperwind sailing data collected while out for an afternoon sail; not a speed trial.
Conditions:
- light winds typically 8 to 10 knots; 10 knots was used as input to the numerical model computing the maximum speed polars (blue lines on the polar plot)
Results: plotted with GPSResults
- 3.4 sq m sail; ZERO twist; ZERO camber
- GT-31 gps speed data are the red circles on the polar plot
- max speed measured was 37 knots
Ref: Kenney, B.C., 2001. Hyperwind Sailing, Catalyst, J. Am. Yacht Res. Soc., 6, 24-26.
Hi Barney,
Took me a while to ponder over this.
Am assuming that your statement about twist in the first line is in reference to Elliptical span load lift distribution and Gradient.
If this is the case, using a bell shaped lift distribution with perhaps a slightly taller, higher aspect sail, and some twist will change that.
I pointed out in another post some reasons why I don't think wind gradient is a significant factor in speed windsurfing in many of the very flat terrain places we sail. Perhaps this would be true of many ice lake venues also?
That begs the quesion of if, in the high (water) drag environment windsurfing tends to inhabit, (closer to 1:1.25 true wind to speed ratios at top speed) the low centre of effort in the sail, and the drag reduction from something like the Prandl model make more difference?
My first statement refers to the vertical variation in Beta and not the spanwise lift distribution. Assuming both the top and bottom of mast are travelling at the same speed as the board (no pumping, no hobby horsing, etc), the vertical variation in Beta is determined by the wind gradient. At low Re, the laminar gradient differs substantially in shape from the fully turbulent gradient and it is here that a sail benefits most from twist.
The wind gradient is a function of the roughness length but also the friction velocity and atmospheric stability. Because the planetary boundary layer is heated from below whenever the sun is shinning, and cooled from below (by back radiation) whenever the sun goes down, the atmospheric stability is seldom neutral but fluctuates between stable and unstable conditions. It is very important for windsurfers on the Canadian prairies to know this because the wind shuts off completely like a switch was thrown when the sun angle get below a few degrees. In a very short time you can go from a full plane in lots of wind to swimming your sinker back home in the dark.
As I said in an earlier post, top speed of a windsurfer is limited by stability constraints and not by drag. The fact that a windsurfer once held the outright world sailing speed record is a testament to how slow the sail boats were at the time. It will not happen again.
^^ Thats very interesting reading! So solar wind, if i remember correctly Arthur C Clarke wrote about that when i was a kid. Stuck in my mind since then. The piece i read was related to space n zero gravity. But it does exist here on our planet? Wow!!
Barney.
It seems to follow from your statement that in your high Fohn number ice sailing you have zero wind gradient?
Yes, I understand that at high Fohn numbers the apparent wind will be much higher than the real wind speed and significantly reduce gradient effects. But there mast still be some. So why do you say zero twist is optimum?
The fact that a windsurfer once held the world speed record is a testement to how slow almost all other sailing boats still are.
The big foiling cats a trimarans will top out at around 50 knots, hitting the cavitation wall, unless they can figure out how to make supercavitating foils work
Sailrocket is substantially more different from 'sail boats' and 'foiling boats' than even a windsurfer is. They have blown the records out of the water. It has reinvented what we think of as 'sailing'. Their record will be untouched for decades, if not longer.
I just want to get as close to 50kts as I can. Hell, I would be over the moon to even get another PB at my age!
