Select to expand quotesailquik said..
>>>>> Hell, I would be over the moon to even get another PB at my age! 
I haven't quite given up hope.
Sorry for butting in, but what I am missing here is the fun and the fact that windsurfing is a very healthy physical sport.
Why is this important in relation to the topic: twist? Well because we put ourselves on a track where only the mostly older and heavier riders stand a chance to be quick. This is not good for the sport.
There is another route and the answer is with the loadcell itself: the whole rig. We're not into rope pulling. We're into a fantastic sport that can keep you fit and healthy up until a very old age. We now have to ensure the youngsters can enter and can enter competitively, ideally regardless of size. As it is right now, in order to win you need to be 6 foot 2 and over 100 kilo. Only very determinded, skilled and experienced riders knowing how to tune their gear stand a chance. There is work to be done and in person, however interesting this topic really is, I don't see the answers I am looking for.
I don't mean to be negative and write off the very eloquent explanations. The topic itself is hugely entertaining and worthful but still is taken in a direction which to me won't show our biggest challenges in relation to twist and why we need a breathing rig as that's what we actually should be talking about: a responsive entity that consists of sailcloth, battens, cambers, a mast and a boom.
I could not agree with you more mate.
But some of us enjoy what to others is an esoteric search for small truths and more complete knowledge. You know.: Junior amateur Gyro Gearlose's.
Select to expand quotesailquik said..
I could not agree with you more mate.
But some of us enjoy what to others is an esoteric search for small truths and more complete knowledge. You know.: Junior amateur Gyro Gearlose's.
Had to check that one. We call him Willie Wortel.
Hahaha.great comparison and well understood my old friend.
true wind 15kt 90 degress(crosswind)
board speed 20.3kt
apparent wind 25,2 kt 36.1 degrees
sail resultant force 71,5 lbs
sail lift 70,7lbs (lift is allways prependicular to apparent wind, convention)
drive/thrust 32,5 lbs
induced + profile drag 6.2lbs
sailor drag 4,7lbs
total aero drag 10.9lbs
if board is not accelerate,then drive is equal to total drag(aero+water),that mean 32,5 - cos36.1x10.9 = 23.7lbs.. ..board+fin hydrodinamic drag component in direction on travel is 23.7bs
note how small is profile drag comapre to induced drag ( Aero drag (expaneded scale)..
profile drag = pressure/form drag + friction drag .....(or sometimes only pressure drag)
-also sailor drag has big percentage in total aero drag system
Select to expand quoteUSA46 said..
true wind 15kt 90 degress(crosswind)
board speed 20.3kt
apparent wind 25,2 kt 36.1 degrees
sail resultant force 71,5 lbs
sail lift 70,7lbs (lift is allways prependicular to apparent wind, convention)
drive/thrust 32,5 lbs
induced + profile drag 6.2lbs
sailor drag 4,7lbs
total aero drag 10.9lbs
if board is not accelerate,then drive is equal to total drag(aero+water),that mean 32,5 - 10.9 = 21.6.. ..board+fin hydrodinamic drag is 21.6lbs
note how small is profile drag comapre to induced drag ( Aero drag (expaneded scale)..
profile drag = pressure/form drag + friction drag .....(or sometimes only pressure drag)
-also sailor drag has big percentage in total aero drag system
Great!! sketch. This is going indeep into a more complex situation. I can relate to this as this is an overall conceptual thought that forms the root of the tree.
Man is the sidestay and backstay.
Mast is the mainstay.
Think about that. for real.....
See you on the water.
Select to expand quotesailquik said..
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?
When hyperwind sailing, there is always a little gradient above the u-joint but the steepest wind gradient is below the height of the u-joint. The gradient is occasionally visible when it is snowing.
When I said my sail had 'zero twist', I meant the rigged but unloaded sail with no wind pressure. As the wind pressure builds up the sail will twist. The challenge with windsurf sails is to prevent excessive twist because the geometry naturally promotes twist. When the sail twists off to the point that the AOA goes to zero at some spanwise location, the sail at that location becomes a flag. There are lots of photos on the internet of speed sailors with the top third or more of the sail flapping like a flag. BTW, the drag on a flapping flag can be an order of magnitude higher than a rigid sheet the same size (Hoerner, Fluid Dynamic Drag, 1965).
I find zero (static) twist to be optimum because it is one less thing to fuss with when rigging. It allows me to get on the water faster.
Select to expand quoteUSA46 said..
true wind 15kt 90 degress(crosswind)
board speed 20.3kt
apparent wind 25,2 kt 36.1 degrees
sail resultant force 71,5 lbs
sail lift 70,7lbs (lift is allways prependicular to apparent wind, convention)
drive/thrust 32,5 lbs
induced + profile drag 6.2lbs
sailor drag 4,7lbs
total aero drag 10.9lbs
if board is not accelerate,then drive is equal to total drag(aero+water),that mean 32,5 - cos36.1x10.9 = 23.7lbs.. ..board+fin hydrodinamic drag component in direction on travel is 23.7bs
note how small is profile drag comapre to induced drag ( Aero drag (expaneded scale)..
profile drag = pressure/form drag + friction drag .....(or sometimes only pressure drag)
-also sailor drag has big percentage in total aero drag system
Thanks. 
Can you do that exercise for 45 knots speed , 135 degrees off the true wind of 38 knots? 
How were the various proportions of drag calculated?
Select to expand quotesailquik said
Thanks.
Can you do that exercise for 45 knots speed , 135 degrees off the true wind of 38 knots?
How were the various proportions of drag calculated?
Hi Andrew,
I don't know if this is any help but I ran a fairly flat (6% belly-2% head) 5m idealised sail through XFLR5 at 38.8 knots (20m/s) and this is what I got. Best L/D ratio was at AoA of 4 degrees which gave lift of 38.5kg and drag of 2 kg (L/D= 18.7). As said this is idealised. Perfectly smooth foil etc. I image the real drag would be many times that and the lift lower. Sail had 4 degrees twist.
I imagine the only way to get realistic data is to build yourself a rig with pulleys, fishing spring weight measures, anemometer and video camera and take it all out onto the sand bar in a 38kn SWerly
Interesting Dave. Not sure if it is realistic, as you say.
I am most interested in how USA46's model calculates the drag and seperates the components. If it is close to reality, then there is significant benefit to be gained by working to reduce induced drag from the sail.
We know that the sailors is a large component of overall drag, but there is nothing significant we can do about that.
Select to expand quoteKwibai said..sailquik said..
I could not agree with you more mate.
But some of us enjoy what to others is an esoteric search for small truths and more complete knowledge. You know.: Junior amateur Gyro Gearlose's.
Had to check that one. We call him Willie Wortel.
Hahaha.great comparison and well understood my old friend.
Thinking about that, I blame it on on Professor Julius Sumner Miller.
My gereration grew up watching him on B&W TV, and he regularly scrambled my mind. I loved every munute of it. I still love it!
I guess a lot of us are Junior Professor JSM's.
Andrew the drag on the luderitz canal is quite different to normal sailing. Check out this image of Patrik (?)
The sail is sheeted out so far the normal assumptions do not apply.
The induced drag is almost perpendicular to direction of travel as would be the windage on the rider.
Select to expand quotesailquik said..
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.
Andrew, your experiment is not well posed. The only thing you are measuring is doppler board speed. No measurements of beta; no measurements of AOA; no measurements of twist angle; not even one measurement of wind speed at any height. What you 'feel' is meaningless if you know nothing about the wind speed and the forces driving your board.
Anyone who has windsurfed more than once knows that board speed scales with wind speed; the higher the wind speed, the faster the board speed. How do you separate the effects of twist when you don't even know how strong the wind is blowing? It was clearly very turbulent as you emphasize a succession of squalls.
Thanks Barney.
I measured the twist angles of the sails the day before. They were very different.
I think I can modestly say that I am a pretty good judge of the wind speed at this location. I have sailed here forever, taken actual measurements hundreds of times. Felt it intimately. Seen the effects on the water and the sand blowing and a hundred other queues over 25 years.
I think I can modestly say that I am a pretty good judge of the actual angle I am sailing too. Same thing. I go out of my way to observe and see all the queues for wind angle. It's a curved course too, so even if the true wind angle changes slightly, there is still usually somewhere where it is ideal. My ability to judge this has served me well for decades.
Other sailors on the course at the same time are also a good constant to judge against. The first 5 or 6 runs I was slow in comparison. After I changed sails I was equal with the fastest.
But yep. It was probably just stronger wind.......... 
Select to expand quoteyoyo said..
Andrew the drag on the luderitz canal is quite different to normal sailing. Check out this image of Patrik (?)
The sail is sheeted out so far the normal assumptions do not apply.
The induced drag is almost perpendicular to direction of travel as would be the windage on the rider.
Yes, the course if often broader there than we mostly sail. Only possible to sail as the wind can be so strong. But a snapshot like this does not a whole picture make. As said before. the wind is super gusty. Some sailors are sheeting in and out a lot more than you would imagine. This snap may not be very representative of the moment before or after.
The canal became unsailable when the angle exceeded 140 degrees. I spent quite a lot of time trying to carefully measure the wind angles, drawing lines in the sand under the course flags, especailly when it was unsailable.
But as I understand it. Drag is Drag. It balances exactly with propulsive force when accelleration stops. There will still be equal and opposite. Aero' drag will be relative to apparent wind, not true wind.
Select to expand quotesailquik said..
Thanks Barney.
I measured the twist angles of the sails the day before. They were very different.
I think I can modestly say that I am a pretty good judge of the wind speed at this location. I have sailed here forever, taken actual measurements hundreds of times. Felt it intimately. Seen the effects on the water and the sand blowing and a hundred other queues over 25 years.
I think I can modestly say that I am a pretty good judge of the actual angle I am sailing too. Same thing. I go out of my way to observe and see all the queues for wind angle. It's a curved course too, so even if the true wind angle changes slightly, there is still usually somewhere where it is ideal. My ability to judge this has served me well for decades.
Other sailors on the course at the same time are also a good constant to judge against. The first 5 or 6 runs I was slow in comparison. After I changed sails I was equal with the fastest.
But yep. It was probably just stronger wind..........
Sailquik. Methinks you need more practice at your spot.
Select to expand quoteRAL INN said..
Sailquik. Methinks you need more practice at your spot.
Yes. definitely!
And I need to remember how to spell cues! 
Select to expand quotesailquik said..
Interesting Dave. Not sure if it is realistic, as you say.
I am most interested in how USA46's model calculates the drag and seperates the components. If it is close to reality, then there is significant benefit to be gained by working to reduce induced drag from the sail.
We know that the sailors is a large component of overall drag, but there is nothing significant we can do about that.Select to expand quotesailquik said..
Interesting Dave. Not sure if it is realistic, as you say.
I am most interested in how USA46's model calculates the drag and seperates the components. If it is close to reality, then there is significant benefit to be gained by working to reduce induced drag from the sail.
We know that the sailors is a large component of overall drag, but there is nothing significant we can do about that.
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Select to expand quoteBen1973 said
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Yet surprisingly despite all the effort and cost spent on sails, boards and fins no one seems to have made much effort on this front. One guy at Luderitz had a slightly streamlined vest (weight under arms instead of on back).
But in case you are thinking of sticking bits of shaped foam under a baggy wetsuit be warned. It is a good way to drown. I know 
When your legs are buoyant it is almost impossible to keep your head/mouth above water.
Select to expand quoteBen1973 said..
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Well, there have been a few attempts over the years to try to do that. I think it was Fred Heywood back in the early '80's that tried a skin suit. I recall seeing a couple of attempts at fairings as well. No one has gpne on with it, which suggests those attempts were not very positive.
What were you thinking of?
Select to expand quotesailquik said..Ben1973 said..
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Well, there have been a few attempts over the years to try to do that. I think it was Fred Heywood back in the early '80's that tried a skin suit. I recall seeing a couple of attempts at farings as well. No one has gpne on with it, which suggests those attempts were not very positive.
What were you thinking of?
What about both legs in a trailing edge fairing? Battens to help the shape when the speed gets up. How much drag is in that pair of 80-100cm long stumps?
Select to expand quoteTe Hau said..sailquik said..Ben1973 said..
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Well, there have been a few attempts over the years to try to do that. I think it was Fred Heywood back in the early '80's that tried a skin suit. I recall seeing a couple of attempts at farings as well. No one has gpne on with it, which suggests those attempts were not very positive.
What were you thinking of?
What about both legs in a trailing edge fairing? Battens to help the shape when the speed gets up. How much drag is in that pair of 80-100cm long stumps?
How about training those legs...for real!
If you look at us windsurfers, most of us have gotten to be lazy, fat and old bastards. No wonder the sport is in trouble.
Rig, board, fin, rider. All equally important. Looking for silly gadgets is only a diversion from what's the true problem. Just my two cents.
I see a turning point and youngsters are joining. They will beat the **** out of everyone as they are fit and train like mad. No twist can do anything against that :-).
Just sharing ideas and I know it's partially off topic...
Select to expand quoteyoyo said..Ben1973 said
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Yet surprisingly despite all the effort and cost spent on sails, boards and fins no one seems to have made much effort on this front. One guy at Luderitz had a slightly streamlined vest (weight under arms instead of on back).
But in case you are thinking of sticking bits of shaped foam under a baggy wetsuit be warned. It is a good way to drown. I know
When your legs are buoyant it is almost impossible to keep your head/mouth above water.
Most speed locations are only a foot deep so can't drown, I'll see if I can find a pic of things we tried in cycling before the UCI banned them for being to quick
Select to expand quoteyoyo said..sailquik said
Thanks.
Can you do that exercise for 45 knots speed , 135 degrees off the true wind of 38 knots?
How were the various proportions of drag calculated?
Hi Andrew,
I don't know if this is any help but I ran a fairly flat (6% belly-2% head) 5m idealised sail through XFLR5 at 38.8 knots (20m/s) and this is what I got. Best L/D ratio was at AoA of 4 degrees which gave lift of 38.5kg and drag of 2 kg (L/D= 18.7). As said this is idealised. Perfectly smooth foil etc. I image the real drag would be many times that and the lift lower. Sail had 4 degrees twist.
I imagine the only way to get realistic data is to build yourself a rig with pulleys, fishing spring weight measures, anemometer and video camera and take it all out onto the sand bar in a 38kn SWerly
Interesting plot. There appears to be little influence of the sail below the u-joint. About 10 years ago I developed a biaxial apparent wind speed (AWS) sensor that mounts as low and as far forward as possible to avoid the potential flow induced by the sail - as much as practical. The plan was to mount it at least one MAC in front of the sail. It records 2 orthogonal wind speeds and doppler board speed to a SD card at 1 sec intervals.
It records 2 orthogonal wind speeds and doppler board speed to a SD card at 1 sec intervals.
Clever Barney. Good way to solve the Apparent angle/speed for wind to 45 from dead on but what about greater than 45?
Select to expand quoteyoyo said..
It records 2 orthogonal wind speeds and doppler board speed to a SD card at 1 sec intervals.
Clever Barney. Good way to solve the Apparent angle/speed for wind to 45 from dead on but what about greater than 45?
I never go that slow.
The speed sensors were inspired by the Gill triaxial bivane. Much micrometeorology and hydrometeorology research has been done with similar instruments.
Select to expand quoteyoyo said..Ben1973 said
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Yet surprisingly despite all the effort and cost spent on sails, boards and fins no one seems to have made much effort on this front. One guy at Luderitz had a slightly streamlined vest (weight under arms instead of on back).
But in case you are thinking of sticking bits of shaped foam under a baggy wetsuit be warned. It is a good way to drown. I know
When your legs are buoyant it is almost impossible to keep your head/mouth above water.
If Barney is correct that the highest speeds are achieved when the apparent wind angle is 90 degrees to the direction of travel, then drag on the rider is just going to increase side force, rather than adding significantly to the total drag of the system. So skin suits and body fairings are not going to have much effect.
Thats a very good point Pacey!
And I do think that is close to correct.
Just found this again. The wind on this record day is not too broad. This is quite obvious to me as the surface of the canal is still relatively flat. When the wind gets over 130-135 degrees here, is gets rolling chop. That is not evident here. Perfect conditions in that the water is flat enough, water level high enough, angle great and the wind looks less gusty that it often is. This sail is not flapping, it seems to have some nice dynamic reactionary twist. And I am in awe of how AA keeps his body position and sail so steady! 
Select to expand quoteBen1973 said
Most speed locations are only a foot deep so can't drown,
Not so on both counts. Seriously, don't put buoyant stuff under wetsuit below knees. Once prone you can't get your legs back under yourself to get up or tread water.
Maybe open cell foam would be ok like sponge.
Select to expand quotePacey said..yoyo said..Ben1973 said
I think there's a fair bit we could do to reduce rider drag. A wetsuit is the perfect suit to fit some fairings under.
Yet surprisingly despite all the effort and cost spent on sails, boards and fins no one seems to have made much effort on this front. One guy at Luderitz had a slightly streamlined vest (weight under arms instead of on back).
But in case you are thinking of sticking bits of shaped foam under a baggy wetsuit be warned. It is a good way to drown. I know
When your legs are buoyant it is almost impossible to keep your head/mouth above water.
If Barney is correct that the highest speeds are achieved when the apparent wind angle is 90 degrees to the direction of travel, then drag on the rider is just going to increase side force, rather than adding significantly to the total drag of the system. So skin suits and body fairings are not going to have much effect.
The apparent wind angle (beta) is typically 18 degrees off the nose for the standup boards with a windsurfer rig and between 11 and 14 degrees off the nose for my quad miniyacht with a cantilevered mast. The sensitivity of the impellers have a cosine response (relative unit response along the axis of rotation and zero at right angles to the rotating shaft). The rotating shafts are orientated +/- 45 degrees relative to the board or yacht centreline.
The bottom line is 'you can't beat a boat' and the stability speed limit is reached well before the drag speed limit.
