The new sailing twin skin setup

[RobG 816]

4 minutes ago, KiwiJoker said:

Encouraging at first glance ........ except that Standard Operating Procedure for Cup regattas has been special Notices to Mariners and published civil aviation notices prohibiting public activities on and above race courses. It was SOP through the 12-Metre era,  And probably before that but I don't have direct knowledge stretching back that far

Not racing yet. :-)

[barfy 1,302]

7 hours ago, phill_nz said:

and the heliport at northshore hospital would kill most of the rest

 

surprisingly the regs covering the proximity to controlled airspace are not the stupid ones

you can fly shielded operations within that zone 

some countries also have a gradient from a certain range ( ht v distance from port )

 

the sub 400 meter airspace is becoming a shit fight between model flyers and multi national corps who want it for uav deliveries and can afford to buy the regs ( politicians / snivel servants ) that suit them .....  they want to remove the model air enthusiasts .. hence you get so many hate drone stories on the media .. when in reality they are still one of the safest hobbyists around and thats by no means just an nz thing

 

 

No other country as far as I know has shielded operations,a boon to me and my mates who fly low and fast, with only the occasional victory loop. 

[barfy 1,302]

Courses c is out. And problem is to access b from north head is impossible. And you can't fly from doc land ie rangi or browns so d is problematic

[phill_nz 857]

2 hours ago, barfy said:

a boon to me and my mates who fly low and fast, with only the occasional victory loop. 

im a learner

 i have drone ( cfly faith ) and a few fixed wings i have to to learn to fly

[weta27 5,035]

Good view of gap and concave windward shape, courtesy of @airflownz's latest excellent video

[Kiwing 509]

No evidence of "S" there!

[phill_nz 857]

On 9/11/2020 at 3:40 PM, The_Alchemist said:

might be an issue, but only if someone in authority wanted to be a prick.

 there's a planet that has alternatives ?

 

i keep forgetting to send them notice they need to put out a notam

im flying one of my kites today

1,000 mtr string on a large delta form

[The_Alchemist 1,425]

10 hours ago, weta27 said:

Good view of gap and concave windward shape, courtesy of @airflownz's latest excellent video

It almost looks like they are trying to simulate the shape of the two parts in a wing.

[Kiwing 509]

I guess the mechanism inside is the part that will be hard to copy?  A boom which curves in one dimension and is straight in the other?  But the top of the rig is another guessing game.

[Boink 838]

On 9/9/2020 at 4:42 AM, Kiwing said:

Sail shape from Mule.

The only factual picture of early sail shape.  Sorry it is not very good and certainly has no "S" in it!?

@KiwingDo not use or confuse a still photograph from a long time ago as being representative of what we are seeing now. I posted that to quickly illustrate how the twin skins have assymmetry across the two invidual surface to create a wing shape. It clarified for many what was not being explained well in writing. As to how Two shots - neither of which show the windward skin in the area that any "S" Bend might occur, is in anyway helpful, to establish your clearly one-eyed opinion is however, useful.

Your attempt to "Yellow Line" is also very misleading. The actual Draft Stripe is there to show what sort of camber/profile the leeward skin is creating.

I have put a Red Line over this in the photo below to show a more representative profile.

A very different take from your effort......

Worth noting that the shape of the profile is not what is carried through the body of the sail. 

Which raises the age old topic of using just one still photograph to prove or disapprove the evidence of something as well as the much lampooned use of yellow lines........

So @weta27 posts his usual good work, and you respond:

On 9/13/2020 at 2:01 PM, weta27 said:

Good view of gap and concave windward shape, courtesy of @airflownz's latest excellent video

On 9/13/2020 at 2:04 PM, Kiwing said:

No evidence of "S" there!

So you are seeing a frozen moment in time and trying to beat the lack of "S" as being an open and closed case. Because, as I have written before, mainsail shapes are just set and forget, to one predefined shape - regardless of wind conditions, chop, or even direction being sailed in........ Or at least they maybe in your world.

What you conveniently forget is that It was myself who highlighted the picture that clearly showed the S-bending of the windward skin in the first place - but  - it was also myself who cast doubt over over its long term use or usefulness.

But re-read my comments over implications on Drag, AOA and how this will change how the leech tips present as to why I floated the idea in the first place.

[Kiwing 509]

Thank you @Boink Guilty as charged!  I am just putting it out there in the hope someone will correct me so I can understand better myself.
What % of the sailing time will there be an "S" in the windward skin? only during maximum speed to reduce drag?
If someone were to reveal a new shape of wing how long would it take to copy it?

[Sailbydate 3,604]

Is "S" the new wing twist?

[Kiwing 509]

This new engine room - powerhouse is so interesting but no one will discuss it.
Will they be able to reverse the top like they did the AC35 wing?
Will there be teardrop shape in the twin skin?
Will the new twin skin soft wing be only 60% as powerful as the AC35 wing?

There does not seem to be a consensus?

@Sailbydate what do you think?

[Lickindip 541]

Yes - there have been pics of this

no - an aerofoil shape

no - more powerful - higher RM avaiable ... heaveier boat going the same if not more speed

[Sailbydate 3,604]

35 minutes ago, Kiwing said:

This new engine room - powerhouse is so interesting but no one will discuss it.
Will they be able to reverse the top like they did the AC35 wing?
Will there be teardrop shape in the twin skin?
Will the new twin skin soft wing be only 60% as powerful as the AC35 wing?

There does not seem to be a consensus?

@Sailbydate what do you think?

To be honest mate, I'm a skeptic. I think they have their hands full just maintaining a fast shape with this double skin set-up, without all this inside out voodoo. I think if they're trying to de-power the rig, they'd be better off with less sail area. It would certainly help to decrease drag. But, as I said before, what the fuck would I know?

A lot of this stuff is waaaay past my pay grade. ;-)

[arneelof 17]

58 minutes ago, Sailbydate said:

To be honest mate, I'm a skeptic. I think they have their hands full just maintaining a fast shape with this double skin set-up, without all this inside out voodoo. I think if they're trying to de-power the rig, they'd be better off with less sail area. It would certainly help to decrease drag. But, as I said before, what the fuck would I know?

A lot of this stuff is waaaay past my pay grade. ;-)

Isn't the problem with less sail area that you need it to get up on foils, but after that you need to depower and minimise drag?

 

[Sailbydate 3,604]

1 minute ago, arneelof said:

Isn't the problem with less sail area that you need it to get up on foils, but after that you need to depower and minimise drag?

 

As I understand it, Arne, yes.

But I doubt if they can actually invert the top third of the main, that that would actually reduce drag. Surely it would just increase drag?

Better to go for a smaller sail in the first place, no?

[Kiwing 509]

1 hour ago, Lickindip said:

Yes - there have been pics of this

no - an aerofoil shape

no - more powerful - higher RM avaiable ... heaveier boat going the same if not more speed

I'm with you on reversing the top to move the COE down, help steady the ship during maneuvers, just going symmetrical for less drag?
I'm also with you on Aerofoil shape (the "S" is a crude way of contrasting a fully windward concave shape with the aerofoil shape).
Mmmm more powerful is a stretch for me but at least equal over all!

But you give me hope that what I guess at is not so far off, after all.

[Kiwing 509]

1 hour ago, Sailbydate said:

To be honest mate, .......That's what I like about you @Sailbydate you are honest

A lot of this stuff is waaaay past my pay grade. ;-)

It is even further past mine, but it is so much fun observing these little glimpses of odd things that make you wander.  Like the quiver of ETNZ's wing last time.  Still don't know what was for!

[Boink 838]

2 minutes ago, Sailbydate said:

As I understand it, Arne, yes.

But I doubt if they can actually invert the top third of the main, that that would actually reduce drag. Surely it would just increase drag?

Better to go for a smaller sail in the first place, no?

This is the nut they are trying to crack.

As you ask SBD, do you go for additional RM by inverting the wing (but at the expense of significant additional drag) or do you go for less drag and more efficient shapes that allow shallower AOA (thereby improving VMG) and better drag characteristics ?

We have seen that AM are inverting the top of the mainsail. Don't believe we have seen ETNZ do the same. It would be fair to say that if you were to go down this route - then you will only chase such mainsail manipulation when using the Low aspect jib - otherwise you are asking the air to bend one way (by the jib) then entirely another way (by the main) - and these contrary goals will only add drag and complexity. 

If that is the case then do we see a different approach for the lower wind range?

I personally believe that the S-Bend is only seen at that moment of manoeuvre (tack or gybe) where the wind pressure has reduced but the sail has not yet inverted.

But the reson that this may be worth chasing is the uncanny way that the sail resembled those Eppler profiles which are used in sail planes and ultra lights - so are already in a speed range that is much more similar to that which these boats are also operating. If you can manipulate the windward skin to not just permanently fall to leeward then surely that is more flexible and ultimately more desirable solution than a concave only wing?

[Kiwing 509]

16 minutes ago, Sailbydate said:

...
But I doubt if they can actually invert the top third of the main, that that would actually reduce drag. Surely it would just increase drag?
Better to go for a smaller sail in the first place, no

If they can make it symmetrical and point it at the apparent wind it will give stability with little drag and then they can use it to get onto the foils quicker which should be a winning advantage?
Smaller sail area reduces power jumping up on to foils after a battle in the start box or other mistake?

[Sailbydate 3,604]

1 minute ago, Kiwing said:

Smaller sail area reduces power jumping up on to foils after a battle in the start box or other mistake?

I guess that is the trade-off, Kiwing. My own experience with apparent wind sailing is zero. But I keep hearing drag is a big factor at these high speeds. When I look at the cut of Defiant's sails, they look bigger and certainly fuller than Te Aihe's. It seems to me that ETNZ has gone to the smaller, flatter end of the sail design box.

I would guess you only need enough sail area to get flying and not more than you need to maximum speed. Maybe that's why ETNZ's boat has a bustle (to help launch her) in the absence of more power in the sails?

[amc 101]

59 minutes ago, Sailbydate said:

As I understand it, Arne, yes.

But I doubt if they can actually invert the top third of the main, that that would actually reduce drag. Surely it would just increase drag?

Better to go for a smaller sail in the first place, no?

Would it really be that significant though, it is still an airfoil shape producing maybe 15-20 times more force than drag but doing it at mast head height equaling lots of righting moment. Profile drag in either case would be similar. Cool stuff regardless. 
 

edit. Also will do wonders to the tip vortex. Just killing spanwise flow dead. 

[JALhazmat 1,610]

S is the new Ground effect...

[dorox 216]

Has anyone noticed the twist profile of mainsails with upper control "device" is bow-like? Also the AM is constantly sailing with more twist than NZ: that could be punishing in light winds, I guess.

[NeedAClew 1,785]

AM trimmer but maybe some generalizable info

https://www.sailingworld.com/story/racing/sensory-overload-of-an-americas-cup-trimmer/

[Stingray~ 2,259]

46 minutes ago, NeedAClew said:

AM trimmer but maybe some generalizable info

https://www.sailingworld.com/story/racing/sensory-overload-of-an-americas-cup-trimmer/

Already posted but thanks, it’s a really good read! 

[Ex-yachtie 1,622]

On 9/22/2020 at 2:18 PM, dorox said:

Has anyone noticed the twist profile of mainsails with upper control "device" is bow-like? Also the AM is constantly sailing with more twist than NZ: that could be punishing in light winds, I guess.

I get the same impression with AM's headsails too.  They always seem to be more open.

[Boybland 560]

3 hours ago, Ex-yachtie said:

I get the same impression with AM's headsails too.  They always seem to be more open.

The obvious conclusion is it's simply correct trim and they are not going as fast or perhaps pointing as high (or some combination of both).

Of course it might also be largely optical given the much lighter colour of their rig, black makes you slimmer and all that!

[Horn Rock 1,712]

On 9/22/2020 at 12:18 PM, dorox said:

AM is constantly sailing with more twist than NZ: that could be punishing in light winds, I guess.

Yeah I've noticed this. I think their main is cut bigger and they're having to depower it up top.

[the saint 43]

They could have the traveler further up with more twist at the top, this would give the impression of being more open but really just a different set up.

The picks above do seem to show this.

[mako23 632]

On 9/17/2020 at 6:39 PM, Sailbydate said:

I would guess you only need enough sail area to get flying and not more than you need to maximum speed. Maybe that's why ETNZ's boat has a bustle (to help launch her) in the absence of more power in the sails?

At 35 knots all that extra sail is going to generate a lot of drag.

i suspect more drag than the extra power. At high speed any deficiencies in sail shape are going to be glaring in regards to turbulence. 

 

 

 

[Frogman56 122]

The kiwis appear to be sheeted wider and harder, the midleeches in very similar position?

Mako, the inverted or more twisted drag might be less than you think, the skins just hanging in the onset flow.

 

[mako23 632]

50 minutes ago, Frogman56 said:

The kiwis appear to be sheeted wider and harder, the midleeches in very similar position?

Mako, the inverted or more twisted drag might be less than you think, the skins just hanging in the onset flow.

 

You may be correct, I’m being biased and assumed TNZ have the correct solution in a smaller jib.  It’s an assumption based on stupid Patriotism and TNZ  longer history. They have more experience than any one else using a jib on these sort of boats. Also I’ve Seen AM starting to use more this sort of jib. It’s also based on these jibs seem to hold there shape better, they really look wing like. The problem seems to me with a full length jib is there no way to control the leech. The taller the jib the less control you have

to be honest I’m no expert in this area and will happily accept input from people who who no more. 

[enigmatically2 1,463]

1 hour ago, mako23 said:

You may be correct, I’m being biased and assumed TNZ have the correct solution in a smaller jib.  It’s an assumption based on stupid Patriotism and TNZ  longer history. They have more experience than any one else using a jib on these sort of boats.

And of course it is not that long ago that lots of people were lauding the inverted shape at the top of NZ wings as being a reason for their success. Which is really just taking lots of twist further.

Which is correct we cannot of course tell without shit loads more data, It is even possible that both are correct for the different design philosophies of the respective boats (or small differences in conditions at that point and time).

[barfy 1,302]

9 hours ago, enigmatically2 said:

And of course it is not that long ago that lots of people were lauding the inverted shape at the top of NZ wings as being a reason for their success. Which is really just taking lots of twist further.

I don't think the inverted twist was "lauded" as a reason for success, its existence was debated longtime. It's pretty obvious to everyone the etnz main controls were superior to the rest of the pack in bda, and had the best control over twist..and that may have been one of the reasons the cup resides in NZ.

[Kiwing 509]

I liked the flutter existence (or not) ?!?

There are the believers or not here.

[OldWoodenShip 30]

Each of the teams in BDA were capable of inverting the top camber arm, FWIW. What differed were the various compromises made in relation to how this was achieved.

[barfy 1,302]

16 minutes ago, OldWoodenShip said:

Each of the teams in BDA were capable of inverting the top camber arm, FWIW. What differed were the various compromises made in relation to how this was achieved.

Right...

Some with cables, quadrants, and winches.

One with a custom built hand held low latency hydraulic controller. Edit:.big compromise wtf

[weta27 5,035]

Looking at photos from yesterday, it's the first time I've noticed such a gap between the skins from square-on, looking more like Defiant's, and as though the leeward skin (nearest) has slid past the windward skin as it forms a deeper curve. The differential between the skins is also visible in the window.

Maybe just the point of sail, requiring a deeper foil shape than usual?

[Boink 838]

5 hours ago, weta27 said:

Looking at photos from yesterday, it's the first time I've noticed such a gap between the skins from square-on, looking more like Defiant's, and as though the leeward skin (nearest) has slid past the windward skin as it forms a deeper curve. The differential between the skins is also visible in the window.

Maybe just the point of sail, requiring a deeper foil shape than usual?

So Weta, were they going upwind or down at the time of the picture? And what was the approximate windspeed you observed?

If you can shed some light on this we can determine some sail shapes that they employ in different modes and directions. We need your clone (and drone ) to circle the boat whilst taking very clear pictures to confirm twist and any side to side separation, which seems to be entirely only created by the width of the boom holding the skins apart at the tips.

The stagger between the leeches fore and aft seems to be around 80-100mm.

Great work as usual.....

[Sailbydate 3,604]

13 hours ago, weta27 said:

Looking at photos from yesterday, it's the first time I've noticed such a gap between the skins from square-on, looking more like Defiant's, and as though the leeward skin (nearest) has slid past the windward skin as it forms a deeper curve. The differential between the skins is also visible in the window.

Maybe just the point of sail, requiring a deeper foil shape than usual?

Mate, have you zoomed in on that shot?

If so, can you pull back, to get a bit more leech in the frame? Great pic, but I think Wetapix is better at this gig. Just sayin. ;-)

[weta27 5,035]

Here we go ... click and click again to see full-size.

The wind was dead behind them coming down the harbour.

[Ĺudicrous 3]

Red woollie sucking into a gap, or trapped between two touching skins?

[nroose 278]

33 minutes ago, weta27 said:

Here we go ... click and click again to see full-size.

The wind was dead behind them coming down the harbour.

Looks like this is from leeward. So the windward skin reaches farther aft. That seems to me like it would be mostly due to the rotation of the mast, which would be rotated more than the rest of the sail, and the leeward luff would be forward of the windward luff. I would think the skins are not materially different cambers. If anything, I would think the windward skin would be slightly more cambered.

[Sailbydate 3,604]

37 minutes ago, nroose said:

Looks like this is from leeward. So the windward skin reaches farther aft. That seems to me like it would be mostly due to the rotation of the mast, which would be rotated more than the rest of the sail, and the leeward luff would be forward of the windward luff. I would think the skins are not materially different cambers. If anything, I would think the windward skin would be slightly more cambered.

Deepest camber would be on the low pressure side (leeward), otherwise I like your thinking on the mast rotation effect on leeches.

[Frogman56 122]

Nroose,

Think about the possibility that the windward skin needs less camber... ?

[MaxHugen 1,136]

13 hours ago, nroose said:

Looks like this is from leeward.

A bit hard to say, but I think it's taken from the windward side - looks like a crewman adjusting the jib leech line? So we can see part of the leeward skin, which seems right as it would have less camber.

Also, "over-rotating" the mast is sometimes done on single skin sails to increase the overall camber of mast+sail, AFAIK.

[Rushman 264]

1 hour ago, MaxHugen said:

A bit hard to say, but I think it's taken from the windward side - looks like a crewman adjusting the jib leech line? So we can see part of the leeward skin, which seems right as it would have less camber.

Also, "over-rotating" the mast is sometimes done on single skin sails to increase the overall camber of mast+sail, AFAIK.

Crew is on the wrong side of the mast for the photo to be of the windward side...
 

unless they are have the jib “poled out” to windward 

[weta27 5,035]

Definitely taken from the leeward side, the jib is across this side and the sun is coming through the gap and hitting the leeward skin.

Here is the same sail setup a minute or two later, from behind

[Boink 838]

6 hours ago, MaxHugen said:

A bit hard to say, but I think it's taken from the windward side - looks like a crewman adjusting the jib leech line? So we can see part of the leeward skin, which seems right as it would have less camber.

Also, "over-rotating" the mast is sometimes done on single skin sails to increase the overall camber of mast+sail, AFAIK.

Definitely from the Leeward side - otherwise some, if not all, of the Foil Arm would be visible as it would be in the lifted position.

[MaxHugen 1,136]

8 hours ago, Rushman said:

Crew is on the wrong side of the mast for the photo to be of the windward side...
 

unless they are have the jib “poled out” to windward 

   You are right.   I promise not to comment after going to the pub in future! 

[nroose 278]

19 hours ago, Frogman56 said:

Nroose,

Think about the possibility that the windward skin needs less camber... ?

I guess it seems to me that the distance between the skins is widest at the mast, and then they get closer, but they get closer more gradually near the leech than they do near the luff, and that would indicate that the windward skin has more camber. If I am wrong and the widest point is not at the mast, then I can see the windward skin having less camber. That is really just an assumption I have. And not really sure why. And if the windward skin does have less camber over all, that just makes the windward leech further aft of the leeward leech. But in general, I think all of this is mostly just hot stinky air from all of us. Definitely from me, anyway.

[uflux 662]

I don’t think it’s rocket science 

LR and INEOS sail profile in the left and ETNZ (potential also AM) profile on the right. (Not quite that dramatic...but you get the picture)

who seriously thinks the profile on the left is more efficient?? 

[MaxHugen 1,136]

35 minutes ago, nroose said:

I guess it seems to me that the distance between the skins is widest at the mast, and then they get closer, but they get closer more gradually near the leech than they do near the luff, and that would indicate that the windward skin has more camber. If I am wrong and the widest point is not at the mast, then I can see the windward skin having less camber. That is really just an assumption I have. And not really sure why. And if the windward skin does have less camber over all, that just makes the windward leech further aft of the leeward leech. But in general, I think all of this is mostly just hot stinky air from all of us. Definitely from me, anyway.

I found an early diagram of the AC75 double skin proposal... not quite accurate to actual designs but close enough I think. HTH.

[nroose 278]

2 hours ago, MaxHugen said:

I found an early diagram of the AC75 double skin proposal... not quite accurate to actual designs but close enough I think. HTH.

I don't get why that image depicts the D section mast at a lower angle of attack than the sail. Seems like it would be more rotated. It also doesn't look quite symmetrical. Perhaps that is something to do with the fact that it is a photo of a slide projected on a screen. The shots of the actual sails I have seen seem to have the skins near parallel near the leech, too. And that diagram seems to be much thicker relative to chord.

[Groucho Marx 230]

Frog.

[MaxHugen 1,136]

2 hours ago, nroose said:

I don't get why that image depicts the D section mast at a lower angle of attack than the sail. Seems like it would be more rotated. It also doesn't look quite symmetrical. Perhaps that is something to do with the fact that it is a photo of a slide projected on a screen. The shots of the actual sails I have seen seem to have the skins near parallel near the leech, too. And that diagram seems to be much thicker relative to chord.

Pretty sure that was just a quick illustration to show people the "idea" of the double skins, and not to be taken literally. The mast section is this (from the Rules):

[Rushman 264]

6 hours ago, MaxHugen said:

   You are right.   I promise not to comment after going to the pub in future! 

What is thing that you call “the pub”?

I don’t think we have them anymore in Melbourne 

[MaxHugen 1,136]

5 minutes ago, Rushman said:

What is thing that you call “the pub”?

I don’t think we have them anymore in Melbourne 

I've heard they're migratory, but should return for Summer.   Just avoid anyone that says "the new normal". 

[Rushman 264]

Just now, MaxHugen said:

I've heard they're migratory, but should return for Summer.   Just avoid anyone that says "the new normal". 

Covid Normal... avoid the ones that repeat this daily

[Stingray~ 2,259]

https://www.northsails.com/sailing/en/2020/10/foiling-is-the-new-frontier

[Stingray~ 2,259]

by Harken
https://spark.adobe.com/page/VrAT7m1XG60qn/

[bacq2bacq 250]

14 hours ago, uflux said:

who seriously thinks the profile on the left is more efficient?? 

Um, Tom Speer?  I couldn't find his comments that I recalled on thin-sections, but google served up a discussion on boatdesign.net (https://www.boatdesign.net/threads/what-is-a-significance-of-a-wing-thickness.45383/):

Tom wrote: "...at a given operating point, a thin section will out perform a thick section. The reason is simple. When you add thickness to a camber line, you raise the velocity on both sides. Higher velocities mean more skin friction. A higher peak velocity means it is harder to slow the flow down without separation. So, from an aerodynamic point of view, thin is good.

Thick sections have an advantage when you need to operate over a wide range of operating conditions. The thin section will develop a pronounced leading edge pressure peak on either the leeward or windward side when operating outside of its design operating condition. Whether this is a problem or not depends on the operating range you need and your ability to reconfigure the thin section to match the operating condition.

And thick sections provide the structural stiffness needed for the spar. So thick sections can result in less weight.

The wing sails allow the torsion loads to be taken directly into the spar via the control system cables. A soft sail has to react those loads through leech tension, which acts at a much smaller angle, resulting in far higher loads. So there's an order of magnitude reduction in the loads applied to the boat by the sheet, with corresponding reduction in weight. The lighter loads on the sheet also mean it can be trimmed rapidly, which makes the wing suitable for maneuvering on a short course. And, finally, the slotted flap provides a higher maximum lift, which makes the boat faster downwind."

Tom is pretty well respected on this stuff... http://www.tspeer.com/  I think I have some D-section twin-skin drawings I did in the 90's I could dig out of the basement... 

I think Tom's main point on thick/thin that there is more than just "efficiency" in the equation, and that conditions vary so wildly while sailing that an aggressively-trimmed thin-skin will be much more prone to stalling in-use than a wing.

[uflux 662]

48 minutes ago, bacq2bacq said:

Um, Tom Speer?  I couldn't find his comments that I recalled on thin-sections, but google served up a discussion on boatdesign.net (https://www.boatdesign.net/threads/what-is-a-significance-of-a-wing-thickness.45383/):

Tom wrote: "...at a given operating point, a thin section will out perform a thick section. The reason is simple. When you add thickness to a camber line, you raise the velocity on both sides. Higher velocities mean more skin friction. A higher peak velocity means it is harder to slow the flow down without separation. So, from an aerodynamic point of view, thin is good.

Thick sections have an advantage when you need to operate over a wide range of operating conditions. The thin section will develop a pronounced leading edge pressure peak on either the leeward or windward side when operating outside of its design operating condition. Whether this is a problem or not depends on the operating range you need and your ability to reconfigure the thin section to match the operating condition.

And thick sections provide the structural stiffness needed for the spar. So thick sections can result in less weight.

The wing sails allow the torsion loads to be taken directly into the spar via the control system cables. A soft sail has to react those loads through leech tension, which acts at a much smaller angle, resulting in far higher loads. So there's an order of magnitude reduction in the loads applied to the boat by the sheet, with corresponding reduction in weight. The lighter loads on the sheet also mean it can be trimmed rapidly, which makes the wing suitable for maneuvering on a short course. And, finally, the slotted flap provides a higher maximum lift, which makes the boat faster downwind."

Tom is pretty well respected on this stuff... http://www.tspeer.com/  I think I have some D-section twin-skin drawings I did in the 90's I could dig out of the basement... 

I think Tom's main point on thick/thin that there is more than just "efficiency" in the equation, and that conditions vary so wildly while sailing that an aggressively-trimmed thin-skin will be much more prone to stalling in-use than a wing.

Take another look. It is not the thin verse thickness rather the convex  section on the low pressure side of the sail. Which is the difference between LR and INEOS sail shape verse ETNZ. (Relatively speaking)
 

This hasn’t been fast since the Wright brothers

[bacq2bacq 250]

17 hours ago, uflux said:

who seriously thinks the profile on the left is more efficient?? 

@uflux, I took another look.  And I seriously think the profile on the left is more efficient.

But it's not who, it's what:  It's aerodynamics.  And pictures might help.  Tom's key words are: "at a given operating point" and I have seen him try to make his point before.  Here are a couple of sections, sorry I couldn't find that Bleriot one specifically.

An Eppler 376 drawn inside a Clark Y.  Below is L/D versus AOA at Reynolds = 1,000,000:

Skinny (purple) outperforms fat (gold), exceeding L/D of 150, but you just can't sheet and twist fast enough to keep the AOA at 5-7 degrees across the whole "sail".

Fat is more forgiving, though.  Looking at these pics reminds me of my youth: tweaked two-strokes with "peaky" powerbands.

What happens to the airflow on the thin section outside where drawn above is very ugly.  Drag goes nuts:

 

http://www.airfoiltools.com and a few clicks (compare airfoils, select, set reynolds, etc) got that done.  I hope you can see that a skinny foil can have better L/D, ie be more efficient than a fat one.  It's just that the problem of trying to sail quickly (or fly safely!) a very efficient skinny airfoil is really hard because it is so unforgiving.  Now carry on with the AC...

[uflux 662]

Ah no. It’s not that complicated. It’s about laminar flow. As you can see in this image a classic sail shape has about 1% laminar flow. Which is why any modern Performance oriented aero foil shape don’t use this. Unless you can show one that does??
Which is why the performance gain “potentially” for ETNZ is massive.

[mako23 632]

38 minutes ago, uflux said:

Ah no. It’s not that complicated. It’s about laminar flow. As you can see in this image a classic sail shape has about 1% laminar flow. Which is why any modern Performance oriented aero foil shape don’t use this. Unless you can show one that does??
Which is why the performance gain “potentially” for ETNZ is massive.

Laminar flow is also related to speed and I have no idea at what speed the laminar flow was calculated for  the above foils. I imagine laminar flow is going to be a lot different at 50 knots versus 250 knots. 

[uflux 662]

29 minutes ago, mako23 said:

Laminar flow is also related to speed and I have no idea at what speed the laminar flow was calculated for  the above foils. I imagine laminar flow is going to be a lot different at 50 knots versus 250 knots. 

It don’t think it is an over statement to suggest “but you get the picture” 

There is a reason aerofoils with a concave forms are no longer used on any flying platform. So why wouldn’t  high performance sails not head in that direction. I don’t know why that would be a hard thing to accept??

The evidence that ETNZ is implementing outhaul adjustments to flatten the windward side of their main sail makes total sense from an aerodynamic perspective. You get more lift (due to the increase pressure difference between the windward and leeward side of the sail) for less drag.... what is not to like??

[KiwiJoker 370]

8 hours ago, Stingray~ said:

https://www.northsails.com/sailing/en/2020/10/foiling-is-the-new-frontier

Great stuff Stinger.  Kenny Read at his best, plus the piece from Peter Harken.

[mako23 632]

3 hours ago, uflux said:

It don’t think it is an over statement to suggest “but you get the picture” 

There is a reason aerofoils with a concave forms are no longer used on any flying platform. So why wouldn’t  high performance sails not head in that direction. I don’t know why that would be a hard thing to accept??

The evidence that ETNZ is implementing outhaul adjustments to flatten the windward side of their main sail makes total sense from an aerodynamic perspective. You get more lift (due to the increase pressure difference between the windward and leeward side of the sail) for less drag.... what is not to like??

 

I do get the picture, I’m just not just sure  naca foil shapes will be totally relevant. Of course double skin will be better. The fact these yachts are hitting 50 knots is testament to this.  I accept you didn’t state this, but I’m not sure naca 66-415 will be more laminar to the same degree than naca 23015 when at 60 knots. I accept you can use naca foil shapes as a BROAD guide but you cannot guarantee that a shape that’s slightly better for laminar flow at 300 knots will also be slightly better at 50 knots. It might be it might not be

the only way to be sure would be testing in a wind tunnel or CFD simulator

if someone has access to CFD go for it

 

 

[uflux 662]

37 minutes ago, mako23 said:

I do get the picture, I’m just not just sure  naca foil shapes will be totally relevant. Of course double skin will be better. The fact these yachts are hitting 50 knots is testament to this.  I accept you didn’t state this, but I’m not sure naca 66-415 will be more laminar to the same degree than naca 23015 when at 60 knots. I accept you can use naca foil shapes as a BROAD guide but you cannot guarantee that a shape that’s slightly better for laminar flow at 300 knots will also be slightly better at 50 knots. It might be it might not be

the only way to be sure would be testing in a wind tunnel or CFD simulator

if someone has access to CFD go for it

 

 

I’m am not suggesting that they are using a NACA profile that is kind of missing the point...just saying 

it is not just that the sails are double skinned it is the difference between what the teams are doing with those skins to give them a more efficient sail shape. I don’t know how to explain more simply than that...

[mako23 632]

53 minutes ago, uflux said:

it is not just that the sails are double skinned it is the difference between what the teams are doing with those skins to give them a more efficient sail shape. I don’t know how to explain more simply than that...

I totally agree with what you are saying, How you shape the double skin is what that counts. What devices and controls you invent to get the desired shape is the $64000 question. I imagine it could be the critical part of the pie that leads to victory. I’ll be surprised it they invents super cavitation foils, so maybe there’s more to be gained in performance on top than the bottom of the boat. What will be of interest too me is how they deal with turbulence coming of the hull hitting the sails. 

[MaxHugen 1,136]

34 minutes ago, mako23 said:

I totally agree with what you are saying, How you shape the double skin is what that counts. What devices and controls you invent to get the desired shape is the $64000 question. I imagine it could be the critical part of the pie that leads to victory. I’ll be surprised it they invents super cavitation foils, so maybe there’s more to be gained in performance on top than the bottom of the boat. What will be of interest too me is how they deal with turbulence coming of the hull hitting the sails. 

I'm struggling to visualise how they control both twist and the shape of the double skins at the top end?

[mako23 632]

8 minutes ago, MaxHugen said:

I'm struggling to visualise how they control both twist and the shape of the double skins at the top end?

Your not the only one 

[bacq2bacq 250]

10 hours ago, mako23 said:

the only way to be sure would be testing in a wind tunnel or CFD simulator

if someone has access to CFD go for it

We all do!  Above I gave everyone a link to online 2-D CFD: http://www.airfoiltools.com/  Mark Drela's Xfoil is also free: https://web.mit.edu/drela/Public/web/xfoil/  Go try out some fat and some skinny airfoils!  Convex versus concave!  But first draw graphs, THEN draw conclusions.

[bacq2bacq 250]

uflux, you argued with me again on a stupid point, so we must disagree what "efficiency" means in terms of airfoils.  I submit it is L/D.  I ran a couple of your "long laminar flow" sections for you, but they don't beat skinny and cambered Eppler 376.  I ask you: how many birds with convex underwing surfaces have you observed lately?  The reason birds use skinny cambered airfoils that are more efficient is that they can, because they have bone and muscles and feathers that allow them to dynamically adjust the wing to minimize drag, avoid stalling and maximize performance under a huge range of operating conditions, and across its entire surface.  A bird can keep a highly efficient airfoil highly effective over a huge range of operating conditions.  We mere humans must resort to less-efficient airfoils else risk stalling etc. and not effectively performing the task at hand, like flying safely or sailing fast.  The most efficent wing is not necessarily the most effective.  Pics of ancient aircraft do not help.

11 hours ago, uflux said:

...it is the difference between what the teams are doing with those skins to give them a more efficient  effective sail shape...

^^^This.^^^  How do you make a double skinned sail adapt and flex and re-shape to get best L/D across its whole surface and over a wide range of real-world conditions? 
PS: it is entirely possible some team may achieve some windward-side convexity near the LE aft of the mast, and that this turns out to be fast.  But it won't look like a Clark-Y!

[Grog 786]

11 hours ago, MaxHugen said:

I'm struggling to visualise how they control both twist and the shape of the double skins at the top end?

I am expecting articulated booms and corresponing support structure at the head of the sails. These would give more precise control to camber and twist of the mainsail.

At this stage the mainsail alone works like the wing of an airplane. Add the headsail and the main is more like a compression blade of a turbine, at least up to the top of the jib.

Interesting times!

Oh, and I expect to see the leading edge, i.e. the D-section of the mast, to be less blunt.

 

And a big thanks to all the contributors so far, it has been a really interesting read!

 

[uflux 662]

1 hour ago, bacq2bacq said:

uflux, you argued with me again on a stupid point, so we must disagree what "efficiency" means in terms of airfoils.  I submit it is L/D.  I ran a couple of your "long laminar flow" sections for you, but they don't beat skinny and cambered Eppler 376.  I ask you: how many birds with convex underwing surfaces have you observed lately?  The reason birds use skinny cambered airfoils that are more efficient is that they can, because they have bone and muscles and feathers that allow them to dynamically adjust the wing to minimize drag, avoid stalling and maximize performance under a huge range of operating conditions, and across its entire surface.  A bird can keep a highly efficient airfoil highly effective over a huge range of operating conditions.  We mere humans must resort to less-efficient airfoils else risk stalling etc. and not effectively performing the task at hand, like flying safely or sailing fast.  The most efficent wing is not necessarily the most effective.  Pics of ancient aircraft do not help.

^^^This.^^^  How do you make a double skinned sail adapt and flex and re-shape to get best L/D across its whole surface and over a wide range of real-world conditions? 
PS: it is entirely possible some team may achieve some windward-side convexity near the LE aft of the mast, and that this turns out to be fast.  But it won't look like a Clark-Y!

As I said “relatively speaking” the more section the sail profile gains the more efficient it becomes. Yes birds have concave  forms as all the sails in the cup still have to some extent. Like all things nothing is designed in a vacuum. Birds for instance need to be as light as possible. Additional mass in their wings would add unwanted weight. I hope that helps 

[bacq2bacq 250]

2 hours ago, uflux said:

I hope that helps

Nope, the data disagrees with you, and this fat versus thin issue was well covered in this thread long ago.  Curious made the point quite clearly, and put the key points in bold:

@Curious claims (and I believe) Mark Drela wrote: “Thin airfoils are capable of the highest CL and CL/CD values, but only within a narrow CL range (or alpha range).... So a thin airfoil which always has the appropriate camber shape dialed in at any given operating point will in general be superior to a thick airfoil.” 

The trick on these thinner-sectioned twin-skins (as opposed to fat, slotted, dual-element wings) will be to keep the camber and AOA in the sweet-spot.

[Sailbydate 3,604]

5 hours ago, uflux said:

As I said “relatively speaking” the more section the sail profile gains the more efficient it becomes.

Depends on AWA and AWS. Fat is slow at high AWS, no?

Isn't it a question of balancing lift Vs drag?

[Kiwing 509]

3 minutes ago, Sailbydate said:

.....
Isn't it a question of balancing lift Vs drag?

Once up I think it is all about reducing drag because there is too much power?