BSN101 said..

BSN101 said..

vortex said..

BSN101 said..
MW, can you advise of price to get a sail to Western Australia, say Perth. Cheaper if 2 come?

BSN101
I will let you know the shipping charge to WA tomorrow.

awesome, and price for 2 wings.

Cheers

OK,, so how many out there want to put some money down to try this damn sail?

Add to list or PM me. Looking for $150ea. WA easiest but east coast can have some fun with it too I guess or one for west one for east.

Dave W $150

I'm in PM Sent

NelsonFoils said..

Chris 249 said..
Tom Speer has been designing America's Cup wing sections much more recently than that.

Would you mind providing links or quotes to confirm that you can have a wingsail with "high lift" (ie comparable to that of a thin sail)????

Yes, I understand that a wingsail can have a wider effective angle of attack.

is there a reason that a wingsail (same size , layout , profil depth) would have less lift than a thin sail ??? less Drag certainly ...

https://www.avweb.com/news/airman/183261-1.html?redirected=1

What in your diagrams shows that a wing will have less drag?

Okay, the angle of attack may change, but that's different. For a start, the illustrations don't show the upwash, which could play a major role. Two of them show the stagnation point in a different area to wind tunnel photos. The others don't show it at all.

Since upwash changes the angle of attack, an illustration that does not allow for upwash is problematic.

The little swirls of turbulent flow on the lower side of one illustration do not conform to what we know occurs with a properly trimmed sail. In a properly trimmed thin sail, the air is flowing cleanly through the windward middle sections. This demonstrated by tufts, streamlines and CFD programmes. If the middle of a sail had flow like that we'd just flatten it with outhaul.

Here's an example of streamlines over sails in a wind tunnel, from an article by Riley Schutt of the Cornell University Fluid Dynamics .(lab.www.sailingworld.com/how-to/boatspeed-jib-and-flow#page-6)



There is none of the turbulent flow in the windward centre of the sail as in your drawing. In fact I cannot find any wind tunnel or CFD study that shows such a breakdown like that in that area.

Secondly, the angle of incidence in the drawing appears to be unrealistically small. In a paper by scientist and windsurfing champ Tim Gourlay (citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.260.991&rep=rep1&type=pdf) it's indicated that the apparent wind angle on an RSX when pointing high is 24 degrees, which sounds about right. Your diagram, if I'm getting it right, indicates maybe 10-20 degrees (ie 5 degrees incidence and allowing the sail to be sheeted as tight as 15% to the CL). If the incidence is not true to life then the drawing is likely to also not be true to life.

Thirdly, as far as I can measure it the sail in that illustration has about 12% draft. Windsurfer sail designer Bill Hansen said that upwind a sail should be about 8% draft- windsportatlanta.com/story/thousand-words-no-17. Gourlay's paper indicates that the middle of an RSX sail has 5.7% camber at the deepest setting, with the head down to 0.2% camber. The bottom of the sail has around 10% draft according to Gourlay.

These illustrations also only deal with sectional shape in uniform flow. Add real world effect including span, planform, wind sheer, the changing draft at different heights in the sail etc and we may get closer to the full story.

As I have already agreed many times, a wingsail may be more forgiving in terms of angle of attack. I'll agree one more time if it helps. But that does not mean that all the other claims for wingsails are true.

2002 called and wants it's double sided wing sail back

www.boatdesign.net/threads/anyone-familiar-with-powerfoil-sails.603/

Chris 249 said..

NelsonFoils said..

Chris 249 said..
Tom Speer has been designing America's Cup wing sections much more recently than that.

Would you mind providing links or quotes to confirm that you can have a wingsail with "high lift" (ie comparable to that of a thin sail)????

Yes, I understand that a wingsail can have a wider effective angle of attack.

is there a reason that a wingsail (same size , layout , profil depth) would have less lift than a thin sail ??? less Drag certainly ...

https://www.avweb.com/news/airman/183261-1.html?redirected=1

What in your diagrams shows that a wing will have less drag?

Okay, the angle of attack may change, but that's different. For a start, the illustrations don't show the upwash, which could play a major role. Two of them show the stagnation point in a different area to wind tunnel photos. The others don't show it at all.

Since upwash changes the angle of attack, an illustration that does not allow for upwash is problematic.

The little swirls of turbulent flow on the lower side of one illustration do not conform to what we know occurs with a properly trimmed sail. In a properly trimmed thin sail, the air is flowing cleanly through the windward middle sections. This demonstrated by tufts, streamlines and CFD programmes. If the middle of a sail had flow like that we'd just flatten it with outhaul.

Here's an example of streamlines over sails in a wind tunnel, from an article by Riley Schutt of the Cornell University Fluid Dynamics .(lab.www.sailingworld.com/how-to/boatspeed-jib-and-flow#page-6)



There is none of the turbulent flow in the windward centre of the sail as in your drawing. In fact I cannot find any wind tunnel or CFD study that shows such a breakdown like that in that area.

Secondly, the angle of incidence in the drawing appears to be unrealistically small. In a paper by scientist and windsurfing champ Tim Gourlay (citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.260.991&rep=rep1&type=pdf) it's indicated that the apparent wind angle on an RSX when pointing high is 24 degrees, which sounds about right. Your diagram, if I'm getting it right, indicates maybe 10-20 degrees (ie 5 degrees incidence and allowing the sail to be sheeted as tight as 15% to the CL). If the incidence is not true to life then the drawing is likely to also not be true to life.

Thirdly, as far as I can measure it the sail in that illustration has about 12% draft. Windsurfer sail designer Bill Hansen said that upwind a sail should be about 8% draft- windsportatlanta.com/story/thousand-words-no-17. Gourlay's paper indicates that the middle of an RSX sail has 5.7% camber at the deepest setting, with the head down to 0.2% camber. The bottom of the sail has around 10% draft according to Gourlay.

These illustrations also only deal with sectional shape in uniform flow. Add real world effect including span, planform, wind sheer, the changing draft at different heights in the sail etc and we may get closer to the full story.

As I have already agreed many times, a wingsail may be more forgiving in terms of angle of attack. I'll agree one more time if it helps. But that does not mean that all the other claims for wingsails are true.

One of the main avantges of a wingsail is EXACTLY that the generate lift as soon as the have some AoA !! great not ?

Are you aware that ALL your theory is from Very flat (4-5% profil) mainsail/Jib boats ?

Did yoy read the " lift doesn't suck !" link ? Then you know how objects with AoA generate lift .

My dear friend Bil Hanson is 100% right , up wind your "thin sail" needs far less profil (5-8%) Wingsails have an "upwind profile that generates lift of 0% !!!

Wingsail have all the avantage of a very flat upwind (low AoA) and deep profil (for higher) looks like a great deal to me ...

The flat intrados (lee site) gives the wing a constant uniform flow , modern cambered sails need to build up an "Airpocked of relatif stagnend air to get a uniform flow .

MWsails said..

Chris 249 said..

NelsonFoils said..

Chris 249 said..
Tom Speer has been designing America's Cup wing sections much more recently than that.

Would you mind providing links or quotes to confirm that you can have a wingsail with "high lift" (ie comparable to that of a thin sail)????

Yes, I understand that a wingsail can have a wider effective angle of attack.

is there a reason that a wingsail (same size , layout , profil depth) would have less lift than a thin sail ??? less Drag certainly ...

https://www.avweb.com/news/airman/183261-1.html?redirected=1

What in your diagrams shows that a wing will have less drag?

Okay, the angle of attack may change, but that's different. For a start, the illustrations don't show the upwash, which could play a major role. Two of them show the stagnation point in a different area to wind tunnel photos. The others don't show it at all.

Since upwash changes the angle of attack, an illustration that does not allow for upwash is problematic.

The little swirls of turbulent flow on the lower side of one illustration do not conform to what we know occurs with a properly trimmed sail. In a properly trimmed thin sail, the air is flowing cleanly through the windward middle sections. This demonstrated by tufts, streamlines and CFD programmes. If the middle of a sail had flow like that we'd just flatten it with outhaul.

Here's an example of streamlines over sails in a wind tunnel, from an article by Riley Schutt of the Cornell University Fluid Dynamics .(lab.www.sailingworld.com/how-to/boatspeed-jib-and-flow#page-6)



There is none of the turbulent flow in the windward centre of the sail as in your drawing. In fact I cannot find any wind tunnel or CFD study that shows such a breakdown like that in that area.

Secondly, the angle of incidence in the drawing appears to be unrealistically small. In a paper by scientist and windsurfing champ Tim Gourlay (citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.260.991&rep=rep1&type=pdf) it's indicated that the apparent wind angle on an RSX when pointing high is 24 degrees, which sounds about right. Your diagram, if I'm getting it right, indicates maybe 10-20 degrees (ie 5 degrees incidence and allowing the sail to be sheeted as tight as 15% to the CL). If the incidence is not true to life then the drawing is likely to also not be true to life.

Thirdly, as far as I can measure it the sail in that illustration has about 12% draft. Windsurfer sail designer Bill Hansen said that upwind a sail should be about 8% draft- windsportatlanta.com/story/thousand-words-no-17. Gourlay's paper indicates that the middle of an RSX sail has 5.7% camber at the deepest setting, with the head down to 0.2% camber. The bottom of the sail has around 10% draft according to Gourlay.

These illustrations also only deal with sectional shape in uniform flow. Add real world effect including span, planform, wind sheer, the changing draft at different heights in the sail etc and we may get closer to the full story.

As I have already agreed many times, a wingsail may be more forgiving in terms of angle of attack. I'll agree one more time if it helps. But that does not mean that all the other claims for wingsails are true.

Chris 249 said..

NelsonFoils said..

Chris 249 said..
Tom Speer has been designing America's Cup wing sections much more recently than that.

Would you mind providing links or quotes to confirm that you can have a wingsail with "high lift" (ie comparable to that of a thin sail)????

Yes, I understand that a wingsail can have a wider effective angle of attack.

is there a reason that a wingsail (same size , layout , profil depth) would have less lift than a thin sail ??? less Drag certainly ...

https://www.avweb.com/news/airman/183261-1.html?redirected=1

What in your diagrams shows that a wing will have less drag?

Okay, the angle of attack may change, but that's different. For a start, the illustrations don't show the upwash, which could play a major role. Two of them show the stagnation point in a different area to wind tunnel photos. The others don't show it at all.

Since upwash changes the angle of attack, an illustration that does not allow for upwash is problematic.

The little swirls of turbulent flow on the lower side of one illustration do not conform to what we know occurs with a properly trimmed sail. In a properly trimmed thin sail, the air is flowing cleanly through the windward middle sections. This demonstrated by tufts, streamlines and CFD programmes. If the middle of a sail had flow like that we'd just flatten it with outhaul.

Here's an example of streamlines over sails in a wind tunnel, from an article by Riley Schutt of the Cornell University Fluid Dynamics .(lab.www.sailingworld.com/how-to/boatspeed-jib-and-flow#page-6)



There is none of the turbulent flow in the windward centre of the sail as in your drawing. In fact I cannot find any wind tunnel or CFD study that shows such a breakdown like that in that area.

Secondly, the angle of incidence in the drawing appears to be unrealistically small. In a paper by scientist and windsurfing champ Tim Gourlay (citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.260.991&rep=rep1&type=pdf) it's indicated that the apparent wind angle on an RSX when pointing high is 24 degrees, which sounds about right. Your diagram, if I'm getting it right, indicates maybe 10-20 degrees (ie 5 degrees incidence and allowing the sail to be sheeted as tight as 15% to the CL). If the incidence is not true to life then the drawing is likely to also not be true to life.

Thirdly, as far as I can measure it the sail in that illustration has about 12% draft. Windsurfer sail designer Bill Hansen said that upwind a sail should be about 8% draft- windsportatlanta.com/story/thousand-words-no-17. Gourlay's paper indicates that the middle of an RSX sail has 5.7% camber at the deepest setting, with the head down to 0.2% camber. The bottom of the sail has around 10% draft according to Gourlay.

These illustrations also only deal with sectional shape in uniform flow. Add real world effect including span, planform, wind sheer, the changing draft at different heights in the sail etc and we may get closer to the full story.

As I have already agreed many times, a wingsail may be more forgiving in terms of angle of attack. I'll agree one more time if it helps. But that does not mean that all the other claims for wingsails are true.

Here Chris, some free education for you. You welcome ! Negative pressure buildup under leading edge , commonly known as leading edge stall.

I am very aware of leading edge stall. Have known about it for years. You're not providing me with any education.

What is this "aerodynamics background" you boast of?

By the way, you agree Mark Drela is right - but since he claims that thin wings have advantages, you claim that your wings are "100 better" in all aspects cannot be true.

MWsails said..

Chris 249 said..

NelsonFoils said..

Chris 249 said..
Tom Speer has been designing America's Cup wing sections much more recently than that.

Would you mind providing links or quotes to confirm that you can have a wingsail with "high lift" (ie comparable to that of a thin sail)????

Yes, I understand that a wingsail can have a wider effective angle of attack.

is there a reason that a wingsail (same size , layout , profil depth) would have less lift than a thin sail ??? less Drag certainly ...

https://www.avweb.com/news/airman/183261-1.html?redirected=1

What in your diagrams shows that a wing will have less drag?

Okay, the angle of attack may change, but that's different. For a start, the illustrations don't show the upwash, which could play a major role. Two of them show the stagnation point in a different area to wind tunnel photos. The others don't show it at all.

Since upwash changes the angle of attack, an illustration that does not allow for upwash is problematic.

The little swirls of turbulent flow on the lower side of one illustration do not conform to what we know occurs with a properly trimmed sail. In a properly trimmed thin sail, the air is flowing cleanly through the windward middle sections. This demonstrated by tufts, streamlines and CFD programmes. If the middle of a sail had flow like that we'd just flatten it with outhaul.

Here's an example of streamlines over sails in a wind tunnel, from an article by Riley Schutt of the Cornell University Fluid Dynamics .(lab.www.sailingworld.com/how-to/boatspeed-jib-and-flow#page-6)



There is none of the turbulent flow in the windward centre of the sail as in your drawing. In fact I cannot find any wind tunnel or CFD study that shows such a breakdown like that in that area.

Secondly, the angle of incidence in the drawing appears to be unrealistically small. In a paper by scientist and windsurfing champ Tim Gourlay (citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.260.991&rep=rep1&type=pdf) it's indicated that the apparent wind angle on an RSX when pointing high is 24 degrees, which sounds about right. Your diagram, if I'm getting it right, indicates maybe 10-20 degrees (ie 5 degrees incidence and allowing the sail to be sheeted as tight as 15% to the CL). If the incidence is not true to life then the drawing is likely to also not be true to life.

Thirdly, as far as I can measure it the sail in that illustration has about 12% draft. Windsurfer sail designer Bill Hansen said that upwind a sail should be about 8% draft- windsportatlanta.com/story/thousand-words-no-17. Gourlay's paper indicates that the middle of an RSX sail has 5.7% camber at the deepest setting, with the head down to 0.2% camber. The bottom of the sail has around 10% draft according to Gourlay.

These illustrations also only deal with sectional shape in uniform flow. Add real world effect including span, planform, wind sheer, the changing draft at different heights in the sail etc and we may get closer to the full story.

As I have already agreed many times, a wingsail may be more forgiving in terms of angle of attack. I'll agree one more time if it helps. But that does not mean that all the other claims for wingsails are true.

Ok Chriss, may be you can explain others why do they need change sail every 6 kt wind increase?

Some people do, because they like the feel of a light back hand. Some people do because they want to go as fast as possible., Others don't - RSXs, Mistrals and many other windsurfers almost never change sails.

You haven't given any independent objective proof from good sailors that your rig has a wider range in which it provides high speeds. If you can, great. Until then, why not stop insulting people and their sails?

Chris 249 said..

Why don't you guys just simply prove your theories by going faster - like so many other soft wingsail guys have failed to do?

That's another nonsense request. MWsails has stated repeatedly that the goal of his current sail design is not higher speed, but rather more stability over a larger wind range. He does, however, seem to fail to understand the need to have his claims verified completely independently (that is, not on his web site, and from someone well known and trusted).

But if you argue that proven top speed illustrates whether "thin" sails or wing sails are better, the Vestas Sailrocket 2 make a very clear statement that wing sails are faster.

Would it be possible for MWsails to beat current records (even just spot records)? That would be absolutely amazing, considering how much effort went into the development of current speed sails. Just for Luderitz alone, the budget from sail brands that are well represented (e.g. Loft Sails and Severne this year) must be huge, compared to the rather limited resources that MWsails has.

Picture fixed / changed amazing that now the air flow is clean and enters the foil smoothly at the front.
Its a more realistic representation of a modern sail but at that angle of attack i would imagine would be getting some separation on the low pressure side.

Your all just posting pictures of stuff that is totally made up no one has defined the conditions under which the sail will operate every picture just has a random profile to prove whatever they want . I can draw a picture of a windsurfer in the moon landing sail blowing the breeze, doesn't mean it's true or relevant .
Does anyone know the answers to these questions i think the must be answered before any technical argument can be made.

What is typical wind gradient between 0 and 5m at 1 m intervals at 15/20/25 knots , (this would be important) ?
What is the typical windspeed / board speed ratio at various angles across wind/ 30 degrees off/ 30 degrees up (obviously needed to determine apparent wind angle and combined with gradient to calculate the twist) ?
What is the angle of attack of a windsurfer sail at various points of sail ? (what foil shape do we even need, when combined with everything else )
How much lateral force can be applied to the sail by the sailor ? ( is a shorter sail faster because the rider can hold more force even though it will obviously have a lower l/d ratio or is the taller one faster because of a lower l/d , no point making a sail that simulates well as a plane wing when the conditions are different here .)

I have no measurements for these i could have a guess but if anyone and offcourse all those numbers could be mashed together in various ways to work out lots of things and would be the basis of any technical argument based on drawings graphs and quotes. If i was to make a sail i would establish these first. Of course there is a lot of people making great sails with experience and knowledge probably not doing this.
Realistically though if we want to see how well an existing product works the results are all that matters even if we don't know why it works its unimportant as long as we get the results we want.

boardsurfr said..

Chris 249 said..

Why don't you guys just simply prove your theories by going faster - like so many other soft wingsail guys have failed to do?

That's another nonsense request. MWsails has stated repeatedly that the goal of his current sail design is not higher speed, but rather more stability over a larger wind range. He does, however, seem to fail to understand the need to have his claims verified completely independently (that is, not on his web site, and from someone well known and trusted).

But if you argue that proven top speed illustrates whether "thin" sails or wing sails are better, the Vestas Sailrocket 2 make a very clear statement that wing sails are faster.

Would it be possible for MWsails to beat current records (even just spot records)? That would be absolutely amazing, considering how much effort went into the development of current speed sails. Just for Luderitz alone, the budget from sail brands that are well represented (e.g. Loft Sails and Severne this year) must be huge, compared to the rather limited resources that MWsails has.

No, it is NOT a nonsense request at all. MW said his sails are "100% better in all respects". If a sail is "100% better in all respects" then it must produce twice the lift at half the drag and twice the controllability and therefore it will win. Simple. If thin sails still go faster, then they are not "primitive" devices favoured by foolish people as Stan claims

Sure, in some contexts (ie C Class cats) wingsails are faster. I have never denied that. The moment that was proven on the racecourse, people accepted it and went 'wow". It was that simple - all they had to do was win.

If the "100% better" claims are true then going much faster than "primitive" sails must be easy.

Simon100 said..


Picture fixed / changed amazing that now the air flow is clean and enters the foil smoothly at the front.
Its a more realistic representation of a modern sail but at that angle of attack i would imagine would be getting some separation on the low pressure side.

Your all just posting pictures of stuff that is totally made up no one has defined the conditions under which the sail will operate every picture just has a random profile to prove whatever they want . I can draw a picture of a windsurfer in the moon landing sail blowing the breeze, doesn't mean it's true or relevant .
Does anyone know the answers to these questions i think the must be answered before any technical argument can be made.

What is typical wind gradient between 0 and 5m at 1 m intervals at 15/20/25 knots , (this would be important) ?
What is the typical windspeed / board speed ratio at various angles across wind/ 30 degrees off/ 30 degrees up (obviously needed to determine apparent wind angle and combined with gradient to calculate the twist) ?
What is the angle of attack of a windsurfer sail at various points of sail ? (what foil shape do we even need, when combined with everything else )
How much lateral force can be applied to the sail by the sailor ? ( is a shorter sail faster because the rider can hold more force even though it will obviously have a lower l/d ratio or is the taller one faster because of a lower l/d , no point making a sail that simulates well as a plane wing when the conditions are different here .)

I have no measurements for these i could have a guess but if anyone and offcourse all those numbers could be mashed together in various ways to work out lots of things and would be the basis of any technical argument based on drawings graphs and quotes. If i was to make a sail i would establish these first. Of course there is a lot of people making great sails with experience and knowledge probably not doing this.
Realistically though if we want to see how well an existing product works the results are all that matters even if we don't know why it works its unimportant as long as we get the results we want.

You are right , nobody has don all the research . It will cost you millions to do so , days in windtunnels , prototype's hours of gigacomputer time...

We , just like airplane designers , concentrated on making a sail that can handle all the different variables in a simple to operate design .

If you feel like it and have de money you can make a high performance sail for every specific condision ...Keep them all ready on the beach and "have the wrong one on the water " all the time Stanislav made a design that is working very good in all conditions !

How good it will perform in all the different conditions time will tell ...

NelsonFoils said..

Simon100 said..


Picture fixed / changed amazing that now the air flow is clean and enters the foil smoothly at the front.
Its a more realistic representation of a modern sail but at that angle of attack i would imagine would be getting some separation on the low pressure side.

Your all just posting pictures of stuff that is totally made up no one has defined the conditions under which the sail will operate every picture just has a random profile to prove whatever they want . I can draw a picture of a windsurfer in the moon landing sail blowing the breeze, doesn't mean it's true or relevant .
Does anyone know the answers to these questions i think the must be answered before any technical argument can be made.

What is typical wind gradient between 0 and 5m at 1 m intervals at 15/20/25 knots , (this would be important) ?
What is the typical windspeed / board speed ratio at various angles across wind/ 30 degrees off/ 30 degrees up (obviously needed to determine apparent wind angle and combined with gradient to calculate the twist) ?
What is the angle of attack of a windsurfer sail at various points of sail ? (what foil shape do we even need, when combined with everything else )
How much lateral force can be applied to the sail by the sailor ? ( is a shorter sail faster because the rider can hold more force even though it will obviously have a lower l/d ratio or is the taller one faster because of a lower l/d , no point making a sail that simulates well as a plane wing when the conditions are different here .)

I have no measurements for these i could have a guess but if anyone and offcourse all those numbers could be mashed together in various ways to work out lots of things and would be the basis of any technical argument based on drawings graphs and quotes. If i was to make a sail i would establish these first. Of course there is a lot of people making great sails with experience and knowledge probably not doing this.
Realistically though if we want to see how well an existing product works the results are all that matters even if we don't know why it works its unimportant as long as we get the results we want.

You are right , nobody has don all the research . It will cost you millions to do so , days in windtunnels , prototype's hours of gigacomputer time...

We , just like airplane designers , concentrated on making a sail that can handle all the different variables in a simple to operate design .

If you feel like it and have de money you can make a high performance sail for every specific condision ...Keep them all ready on the beach and "have the wrong one on the water " all the time Stanislav made a design that is working very good in all conditions !

How good it will perform in all the different conditions time will tell ...

No it's not that hard I can easily make all the equipment to test that It's 2017 not 1960 that's not a gigacomputer it could be done with a tiny budget and a cheap laptop. The point is There are people arguing technical points without knowing the conditions its like saying which is the best wheel without knowing what it will be used for. Even a basic estimation would be far more useful than blindly arguing.

Chris 249 said..

Simon100 said..


Picture fixed / changed amazing that now the air flow is clean and enters the foil smoothly at the front.
Its a more realistic representation of a modern sail but at that angle of attack i would imagine would be getting some separation on the low pressure side.

Your all just posting pictures of stuff that is totally made up no one has defined the conditions under which the sail will operate every picture just has a random profile to prove whatever they want . I can draw a picture of a windsurfer in the moon landing sail blowing the breeze, doesn't mean it's true or relevant .
Does anyone know the answers to these questions i think the must be answered before any technical argument can be made.

What is typical wind gradient between 0 and 5m at 1 m intervals at 15/20/25 knots , (this would be important) ?
What is the typical windspeed / board speed ratio at various angles across wind/ 30 degrees off/ 30 degrees up (obviously needed to determine apparent wind angle and combined with gradient to calculate the twist) ?
What is the angle of attack of a windsurfer sail at various points of sail ? (what foil shape do we even need, when combined with everything else )
How much lateral force can be applied to the sail by the sailor ? ( is a shorter sail faster because the rider can hold more force even though it will obviously have a lower l/d ratio or is the taller one faster because of a lower l/d , no point making a sail that simulates well as a plane wing when the conditions are different here .)

I have no measurements for these i could have a guess but if anyone and offcourse all those numbers could be mashed together in various ways to work out lots of things and would be the basis of any technical argument based on drawings graphs and quotes. If i was to make a sail i would establish these first. Of course there is a lot of people making great sails with experience and knowledge probably not doing this.
Realistically though if we want to see how well an existing product works the results are all that matters even if we don't know why it works its unimportant as long as we get the results we want.

Well said.

Tim Gourlay's paper (linked to earlier) seems to make a good stab at some of the issues you highlighted, but your questions show how complex sail aerodynamics are.

Chris you didn't answer , why do you need sail change every 6 kt? And please put a lot of science behind it .

MWsails said..
Ok Chriss, may be you can explain others why do they need change sail every 6 kt wind increase?

Just FYI ....They really don't. Maybe in the 80's we did but not now. Even with 3 batten wave sails.

gorgesailor said..

MWsails said..
Ok Chriss, may be you can explain others why do they need change sail every 6 kt wind increase?

Just FYI ....They really don't. Maybe in the 80's we did but not now. Even with 3 batten wave sails.

I am in contact with racers who participate this year in PWA and luderitz . They say that they choose sail in 6 kt range. Also in real life on the beach we can see same. I dont know what you trying accomplish here , but your lies too primitive. Please come up with better stuff.

MWsails said..

gorgesailor said..

MWsails said..
Ok Chriss, may be you can explain others why do they need change sail every 6 kt wind increase?

Just FYI ....They really don't. Maybe in the 80's we did but not now. Even with 3 batten wave sails.

I am in contact with racers who participate this year in PWA and luderitz . They say that they choose sail in 6 kt range. Also in real life on the beach we can see same. I dont know what you trying accomplish here , but your lies too primitive. Please come up with better stuff.

Don't know why you are calling him a liar, nothing he said is primitive. I've been sailing since early '84, so you can call me a liar also, if that works for you, but the sail ranges today are so much better than those even from the 90's as well as the early 2000's.
It seems that the range of the sails gets better every year, as they should, and that can't be denied, only somebody ill informed, or a lair would say that isn't the case.
I think your sail needs to be represented by somebody else.