Kiwing

The new sailing twin skin setup

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On 3/22/2019 at 5:58 AM, NeedAClew said:

So that's why Oracle Team AUS had like one citizen on board...here the local govt is lucky to get us to use 2 or 3, all that dragging out to the curb and back, thinking, etc.

Yes and managed by Grant Simmer. Really GS has under performed in the last 2 cups IMO. You need to think outside the box I think GS may help TeamUK correct some basic's but they can't win the cup with him in charge IMO. 

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Thanks @Horn Rock

1461744515_Muletop19-05-08.jpg.ead1007b0dcd5ab5851c2809c00d746d.jpg Left during gybe, right a couple of seconds later coming out.

Helping with the stability !!

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I would like to Thank the NYYC for letting us see some of this detail.

I hope they don't regret it, these boats are so new, and amazing.

No one will be able to deny the inverted top happened now !

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12 hours ago, Kiwing said:

Thanks @Horn Rock

1461744515_Muletop19-05-08.jpg.ead1007b0dcd5ab5851c2809c00d746d.jpg Left during gybe, right a couple of seconds later coming out.

Helping with the stability !!

Helping with twist to keep the center of effort low in the body of the sail

then powering up the rig

its been done for years by windsurfers with downhaul  tension and adjusted at various points on the course up wind and downwind marks etc

but it’s not done to create righting moment.

 

its done to create an efficient shape as the air flow is exhausted cleanly from the top of the rig. 

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The draft profile towards the foot of that main looks incredible, and powerful.

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Yeah detached from the boom and only held at the clew so a huge range of depth and profile changes are then possible, like they were with the solid wings.

certainly opens up options over a conventional boom set up

 

but sealing the bottom of the sail could be that much harder unless we see the boom sprouting an end plate set up?

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It might not be used for "righting moment on a Kite, but sure as eggs it is used doubly on the mule.

1) pushing the centre of effort of the sail down. so reducing it's "leverage"

2) adding a small opposing force with big leverage.

By doing both together they can have fast and big balancing effects.

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On 5/8/2019 at 5:14 AM, Kiwing said:

Thanks @Horn Rock

1461744515_Muletop19-05-08.jpg.ead1007b0dcd5ab5851c2809c00d746d.jpg Left during gybe, right a couple of seconds later coming out.

Helping with the stability !!

Not during or post a gybe. These are two shots are of the boat on a close reach then heading up to close hauled (3:23-3.26). 

How you've determined it's helping with stability is beyond me... but then if you can;t tell if the boat is going upwind or downwind then...

The very next shot in sequence is a gybe where the sails pops through immediately as the sails fill on the starboard side. 

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Because taking a freeze frame of a video and interpreting it with mystic powers and then forming it Into concrete fact  is what this forum is based on... ;-)

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^ Maybe I do "want to see it".

But I definitely do see it in the video as at the end of the transition (It is all "upwind" regardless of true wind direction IMHO).  While they feel they are vulnerable, before harnessing this over powered rig to the new apparent wind and max VMG.

I'm sorry you "don't see it" and are denying, because I feel a few teams used it in AC35 and all major teams will use it in AC36.

Perception is a wonderous thing, some sailors do amazing thing by instinct not really able to explain why they go faster, they just do.  Fortunately for ETNZ, and us, all Glen does both and with Peter and a few others are able to study those unscientific reactions and enhance them to get an edge.  We all benefit even me on my laser, not foiling but inspired by it all.

Let yourself dream !

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Pretty happy with where I am and who I get info from thanks

 

being able to invert a Rigid wing to get your self out of a head to wind situation is entirely sensible 

 

Nailing it at over 45kts and asking the sail to assume the most efficient shape with the top twisted way off cos another sensible solution

 

suggesting that actually you are going to now stall out the top section of the wing to the point it actually provides physical force back to windward ( given where the apparent wind is actually coming from,  is daft, you are fucking up the entire flow pattern of the rig and how it exhausts the air flow over the leech  causing a huge drag penalty

But hey, believe it if you want. 

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Thank you, for your honesty.

The wind from forward motion is directly on the nose, if you are talking 40 knots boat speed in 10 knots TW , then I feel as you go through the transition using the top on the "other side to the main is feasible during the transition.

I guess we can agree to differ?

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So what are these rigs doing? 

 

Providing righting moment by forcing the top section of the sail against the wind and stalling it all 

 

or twisting cleanly to air airflow over the sail 

 

the rigid wing negative top camber and the mule soft sail head twist are mimicking this that the windsurfers have been doing for years, and never at any point did they go get that twist in the head it really helps me transition better now that the airflow is stalled then reattached on the opposite side 

94122007-380A-404B-A628-7805A5F3C646.jpeg

AF6BC34C-94AB-4452-A992-09F3166DB448.jpeg

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4 hours ago, Kiwing said:

I feel a few teams used it in AC35 and all major teams will use it in AC36.

I agree.

But this looks identical to my top batten not popping after a tack. 

I'm not saying it isn't intended inversion, but, from what we see it's impossible to say. 

But visually it's no different to these 18s at 2:46:21 

 

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@Mozzy Sails I was born in Sydney, sail a 16 foot skiff with my cousin Terry many years ago and a NZ mate won the 12 skiffs international (he is now 80!) in Sydney harbour no doubt putting a few noses out of joint.  Starting some new trend in boat and sail design.

I love those 18s and the videos of them riding the knife edge in that great harbour.

Back to the top of the Mule sail.
In the top picture the boats behind are going upwind so it would appear to me the the sail board is going down wind (no comparison?)

You Skiff video the top of the sail seems to drop power during the transition and not be controlled at all just going with the wind at the top but having a stabilising effect?  Where I believe the good wing trimmers of AC35 could control the top and go through a preset pattern in order to add stability to a rapidly changing, critical balance dance to succeed optimally the transition.

Hey how is the harbour these days?  The Bay of Islands where I live is truly beautiful.  A great place to sail and teach my grandsons how to sail.  Actually they now know better than I, riding foiling wake boards, dabbling with these amazing new small boats.

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32 minutes ago, Kiwing said:

Back to the top of the Mule sail.
 

 

Just watch the video from 3:18 over and over again, 3:23 it is just a simple batten flick (as 2:34). Does it again at 3:26 through the gybe. Top battens like that are so stiff and loaded to keep the sail supported they dont always kick over and you can see it just did not kick through. We had that issues with the bigger cats when we went to square top mains and even before when we had straight runs between the 2nd and 5th battens with super hard battens to support the upper cloth and shape. 

 

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Thanks, @DHFiend but I am still convinced they control the top, I know ETNZ did in AC35 and it was a big contributor to their superior transitions, no look tack etc.

Actually I am surprised at how many don't believe.  I hope one day Glen comes clean and talks about his "screen trimming" in AC35 but I guess he is fuelling the unbelievers so as to keep most of it secret.  But I think Dean has had a mate whisper something to him.

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52 minutes ago, Kiwing said:

Thanks, @DHFiend but I am still convinced they control the top, I know ETNZ did in AC35 and it was a big contributor to their superior transitions, no look tack etc.

Actually I am surprised at how many don't believe.  I hope one day Glen comes clean and talks about his "screen trimming" in AC35 but I guess he is fuelling the unbelievers so as to keep most of it secret.  But I think Dean has had a mate whisper something to him.

Not really an unbeliever thing, or a secret, we all saw the video of it dating back to the 72s and those of us one the water in SF and BER saw it first hand.  What you are seeing in this video is battens.... If they were able to do that now, they certainly would not show it in a marketing/promo video.

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The biggest contributor to the no look tack magic was a ridiculously controllable rink that functioned of a multi function controller.

 

one push or combination of button presses and off we go a pre set range of movement was initiated resulting in a perfect tack 

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"one push or combination of button presses and off we go a pre set range of movement was initiated resulting in a perfect tack"

But of course the F50s are better?

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3 hours ago, Kiwing said:

"one push or combination of button presses and off we go a pre set range of movement was initiated resulting in a perfect tack"

But of course the F50s are better?

Don’t be a bell end, how can they F50s have a better control system when the kiwis didn’t share the toys? 

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13 hours ago, Kiwing said:

You Skiff video the top of the sail seems to drop power during the transition and not be controlled at all just going with the wind at the top but having a stabilising effect?  Where I believe the good wing trimmers of AC35 could control the top and go through a preset pattern in order to add stability to a rapidly changing, critical balance dance to succeed optimally the transition.

Hey how is the harbour these days?  The Bay of Islands where I live is truly beautiful.  A great place to sail and teach my grandsons how to sail.  Actually they now know better than I, riding foiling wake boards, dabbling with these amazing new small boats.

Well, i don't see a whole heap of difference between the skiff video and American Magic. But it's very hard to tell from a 3 second clip how controlled anything is. 

In the INEOS video it looks for moments their top batten is inverted too. But again, having stubborn top battens is a soft sail square head problem more than a relation to the solid AC wings trend for inversion.  

I also don't get where your idea about a stabilising effect during manoeuvres is coming from. I thought all the chat during the two previous cups was about increasing righting moment when over powered. I thought they would increase twist and get to inversion as they needed to de-power, not during manoeuvres and not when accelerating. Of course they have to pop through the camber from tack to tack, but again, that's not a feature of stability, that just a feature of changing tack. 

Unfortunately I don't sail in Sydney, but my harbour on the south coast of the UK, is actually very nice currently. The 18 video was just a good example, but the same applies in the RS800 which i sail. 

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11 hours ago, JALhazmat said:

The biggest contributor to the no look tack magic was a ridiculously controllable rink that functioned of a multi function controller.

 

one push or combination of button presses and off we go a pre set range of movement was initiated resulting in a perfect tack 

How do you come by this new information? What the team has spoken of gives the kudos to the fact that all functions could be controlled from the helm, partly due to the control system burling engineered there. And both sides of the boat had all controls for maneuvers. Pre-sets were allowed, but we haven't heard how elaborate they were.

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The fact you think Burling engineered jack shit  speaks volumes.

 

the controller was principally held by Ashby and having pre sets meant that any crew member could execute a pre set move from any position on the boat within a button press  means they were miles ahead of the competition.

 

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^ and they didn't need it or use it until the last, to show off!!

Their moment of doubt can after the pitch pole!!

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1 hour ago, JALhazmat said:

The fact you think Burling engineered jack shit  speaks volumes.

 

the controller was principally held by Ashby and having pre sets meant that any crew member could execute a pre set move from any position on the boat within a button press  means they were miles ahead of the competition.

 

If you paid any attention you would know burling designed and 3d printed all the controls at his station. He is studying engineering, and was mentioned that he was very involved in design with the engineers. The crew that handled controls, as you said, had most controls at every station. The no look was said to be possible because of this. Ashby had one control, if you think he controlled the boat using this because the x-box control got the press this speaks volumes of how much you paid attention.

Pre-sets were discussed on here as soon as the interpretation was published that they were allowed, I'd be very surprised if etnz was the only team using them.

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10 hours ago, JALhazmat said:

Don’t be a bell end, how can they F50s have a better control system when the kiwis didn’t share the toys? 

Ya,I guess no-one else can engineer a ten dollar arduino board that can link up a bunch of timed out puts.

Shows where your head is at: thick.

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So what you are saying agreed with everything  I have said except you think genius Pete designed it all, if he did any controls at HIS station cool 

but not the system for control of the entire wing and foil integration

 

i am not having a go at what they did, far from it but I am not pinning responsibility on the front line jock when so many others made him look like a rock star. Especially when it was Ashby and others doing the clicking, burling drove and drove well,  don’t big it up more than that 

 

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4 minutes ago, barfy said:

Ya,I guess no-one else can engineer a ten dollar arduino board that can link up a bunch of timed out puts.

Shows where your head is at: thick.

My head might be at thick but having spoken with designers on AM and crew from Both Bar and the GB F50 I know where my money is 

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33 minutes ago, JALhazmat said:

front line jock

 

The hate is strong with this one...

He tongues Ratcliffe's arsehole on a daily basis and bleets at anyone suggesting JR's actions demonstrate ego-centricity, meanwhile he has the audacity to scoff at one of the greatest modern sailors who is does not seek limelight, and exceptionally also happens to be contributing to a winning AC teams engineering effort by calling him a jock...

jog-on mate... aren't there some other anti-fracking threads on reddit you'd be better off astroturfing?

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1 hour ago, JALhazmat said:

My head might be at thick but having spoken with designers on AM and crew from Both Bar and the GB F50 I know where my money is 

Soooo, I actually have no idea where your money is:

no-one except etnz had control pre-sets in ac35 and because they didn't share their tech with OR or ART no f50 will ever do a perfect Tack ? And the designer mates back this up?

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1 hour ago, JALhazmat said:

 I have said except you think genius Pete designed it all, if he did any controls at HIS station cool 

but not the system for control of the entire wing and foil integration

Where did I even imply PB designed the control system? I said he designed his control system. 

Really thick.

 

 

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6 hours ago, rh2600 said:

The hate is strong with this one...

He tongues Ratcliffe's arsehole on a daily basis and bleets at anyone suggesting JR's actions demonstrate ego-centricity, meanwhile he has the audacity to scoff at one of the greatest modern sailors who is does not seek limelight, and exceptionally also happens to be contributing to a winning AC teams engineering effort by calling him a jock...

jog-on mate... aren't there some other anti-fracking threads on reddit you'd be better off astroturfing?

Seriously this again?

 

it was a light hearted expression, not an overly aggressive or critical one. I have been consistently at pains to point out how fucking good the boat and it’s systems were, not once have I suggested impropriety or anything untoward yet you interpret it as hate? 

Jeez, 

 

if you want to take issue do it with Barfy for suggesting it was no more than a ten dollar circuit board and a bunch of outputs linked up, that’s more demeaning of the design teams talent than calling burling a jock in jest. 

 

And yeah if it was that easy don’t you think the F50s would be doing it already?

Celebrate the fact it was an incredible boat sailed really well rather than moaning about what the 50s cant do, if wussel wants to gob off about his new toys cool but be better than trying to draw comparisons because in terms of functionality and control systems there are none 

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^

Fair. Etnz had a brilliant automation guy or guy s well documented working on hydro flow. They didn't share. Seems they only had two accumulators when time came to share that. Seems it wouldn't be a big leap for a factory programming guy to sort a few boat sequences.

10 hours ago, JALhazmat said:

The fact you think Burling engineered jack shit  speaks volumes.

 

Point is, pb was involved, it was widely reported, and your comment speaks to bias or rum :)

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Anything to stop teams filling the “twin skin” with a gas lighter than air?

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2 hours ago, Teaky said:

Anything to stop teams filling the “twin skin” with a gas lighter than air?

Hmmm, helium may be? You'd probably get a lift. Very hard to seal though, as it's such a tiny molecule.

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5 hours ago, Horn Rock said:

Hmmm, helium may be? You'd probably get a lift. Very hard to seal though, as it's such a tiny molecule.

Aren't these just going to be basically wings after a few generations of a ton of money thrown at them? 

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Suggestion of helium is nonsense as:

6.15 Gases shall have a minimum density of 1.1 kg/m3, except for nitrogen used within hydraulic systems.

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I hope That these twin skin soft wings do manage 20% improvement on standard soft sails.

Then I hope a little more development to bring the prices down and then we will have serious trickle down.

I hope !

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6 hours ago, pusslicker said:

 

Aren't these just going to be basically wings after a few generations of a ton of money thrown at them? 

Thats the idea, some of the performance gains of a wing, but still with most of the convenience of a soft sail.

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Hi,

When i asked before about filling the twinskin sail with air, they said it's not allowed to sew the leech together, or whatever.  i had imagined a rotating foil, ram-air filled(or pump filled  like a bouncy castle), but it's nothing like that.

Now, i see that the NY test boat has fixed spreaders with shrouds attached to the hull, so they don't rotate the mast.  Maybe they want a low windage mast for anchoring.  A wide chord mast could maybe tip the boat over at anchor, idk if the ballast is like a normal keel boat or not.

i'm guessing maybe the twin skin just fairs out a special mast, and maybe the apparent wind is always forward, so its better to just have a rock solid rig/foil profile.  The sail has to be raised and lowered, and this 2 skin thing is all there is to try; other than a giant A cat rig as the M32 does, or a giant formula 18 rig like the GC32.

maybe a rotating system will be tested?  20%better seems like a subjective marketing type projection...

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3 hours ago, Kiwing said:

I hope That these twin skin soft wings do manage 20% improvement on standard soft sails.

Then I hope a little more development to bring the prices down and then we will have serious trickle down.

I hope !

Put some of this into perspective. The 20% improvement is possible, maybe even more, but what you need to be considering is what percentage improvement that gives to boat speed and on a conventional boat, 20% improvement in rig efficiency would probably give you only a few percentage points gain in speed because hulls have a bigger impact on speed than rigs.

Then consider the cost. It doesn't matter how much development is done, it is still going to cost something close to double a standard rig. Mast cost is a function of size, in this case sectional size, and for the double skin rig need to be significantly bigger section than you would need for a conventional rig, plus you need 2 tracks. Then you need the equivalent of 2 mainsails instead of 1, including 2 sets of battens, 2 sets of track sliders or bolt ropes while the only saving might be that you can use a slightly lighter cloth for each skin. Then there is the additional hardware needed to make the 2 skins work together.

For arguments sake, let's say you are correct that development reduces costs so instead of double, we look at 50% more than a standard rig which I personally cannot see happening. Would you pay 50% more for a couple of percent improvement in speed? If you race with it, you will get stung on handicap anyway and if you use it in a new one design class, everybody will have it anyway, so what's the point?

There might be some mileage in a very few development classes, but that isn't going to drive the cost down. It's already been tried in the A Class with little success, because our current rigs are so refined and nobody is going to spend tens of thousands developing something for a fairly small market.

The double skin rig has its place and it is easy to understand why they have gone for it for the AC. That doesn't mean there is a logical tricle down for the mass market.

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Frog has a double skin wing with D shaped forward section and I've found mast rotation is close to, maybe a few degrees less, than that of a conventional wing mast. And the leeches of the double sail have to be able to move, otherwise you get weird distortions in the fabric, well, the fabric I've got, maybe some hyper exotic stuff will distort less.

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I believe that there are more boats planing/foiling now than there were and there will be even more in the future.

One design racing is a great place to compete were the sailors skill is the deciding factor.  Most of these events are non planing/foiling.

However Moths, A Class cats, Windsurfers, Kite sailors are examples of people pushing the speed/thrill/skill limits and I think we will see more of it.  A lot of those are individual and when you want to share the thrill with a friend it is difficult.  Crewed boats are waiting in the wings, so to speak.

I believe wing sails have an advantage in apparent wind sailing were the thrill/skill people seem to be going!

So a soft wing is an area that is crying out for development -  Thanks Glen and ETNZ !

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Sorry, Kiwing, but tracking participation in various ways indicates that there isn't actually a real trend towards faster boats. Take something like the boats that turn up to nationals in England - there's been a move AWAY from fairly fast boats like Fireballs and 505s towards much slower singlehanded hiking dinghies.  Looking at NZ one can see fast boats like Rs and Javs sadly collapsing in numbers. In many places, the off the beach cats are much less popular than they used to be, which has dragged down the average speed of the overall sailing fleet. Sportsboat fleets in some major sailing countries seem to be fairly quiet. Windsurfer has collapsed dramatically since it went to high performance gear.

There seems to be no real objective evidence of any swing towards high performance in boats (kites are quick but also irrelevant since they already use double skins) and in fact it's easy to see good reasons why slower boats may become more popular. The middle classes are suffering an economic squeeze in many countries, so they can't afford new high tech boats. Young adults in many countries are facing uncertain times, so they may lack disposable income. Many sources say that there will be a move towards rented sports gear, and you're unlikely to see high-speed craft surviving in that situation. Many people are moving from one sport to another rather than sticking to one sport for years, and that means fewer people who can develop the skills to sail ultra-fast boats, and fewer people who will sail for long enough to get bored on slow ones. So there's lots of reasons why there is arguably a swing to slow boats.

By the way, one of my boats is in one of the very fastest International classes; the second fastest of the popular ones. I've sailed some of the fastest classes and plenty of slow ones so I've got no reason to be biased. Speed is fun, but there is no real trend towards it.

By the way, I thought you were a Laser sailor. Great boats, but not fast. If you are happy with a medium-speed boat, why do you think other people will go out and buy fast ones? One of the strangest things we are seeing these days is tons of people sailing slow boats themselves, while saying "hey everyone else should race fast boats". If fast boats don't work for you, why would they work for many other people?

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@Curious Yes I love sailing my laser on a light wind day when I don't have to stack, just lie on the lee deck and glide.

But there is an expert foiling kite surfer who zips across the Bay and I lie on the sand and watch fantasizing about how great that would be to do that.  At 74 it is unlikely, but..

You are right of course and my laser mast and rig personifies the real direction.

But who knows what will develop in these climate change futures of making the most of the free power.

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Using the Moth as an example, wings without slots aren't seen as competitive so they've been abandoned. Even slotted wings didn't turn out to be speed demons: they were fast upwind, but not down. Maybe more development would fix that, but they're not legal so that's the end of that. Maybe there were some attempts at slotless wings with attached flaps, but I can't recall.

Looking at dual luffs, there have been attempts in Moths but development didn't go very far because they didn't show promise. It seems a pocket luff is close to ideal for fairing the mast into the sail and produces a reasonably stall–resistant leading edge. Moths have also gone for minimum mast thickness as thin sections tend to be faster than thick ones. At least one wing mast with soft sail has been tried, but the section needs to be much thicker. Performance wasn't anything special and it didn't catch on. Maybe for practicality reasons, but I'm sure if it was faster than a pocket luff it'd be adopted.

Anyhow, it seems to me that the AC75 rig has more in common with a pocket luff than wing, particularly as it doesn't have a slot or independently trimmable trailing edge or flap.

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This topic has become circular, driven more by speculation than fact.

If you recall, there are a number of reasons both primary and with additional spin offs that make their selection a no brainer.

The AC has always been a Tech race - as much about design development as it was a boat race. 

The current class choice is very developmental and being a hydrofoil based platform it has a primary need for power BUT also power at low drag.

The rule has taken mast, foil struts and hyrdraulics into a one design prescribed package. This leaves hydrofoils, hull and sails as the primary fields of research to making your package the most competitive. 

There was much industry whinging that the AC50's had little if any relevance to enable product sales and trickledown - small percentage of full foiling boats as representative of the total yachting market, relatively little use of high pressure high speed hydraulics outside of the superyacht world, almost zero hardwing rig use out side of AC or Little AC worlds, and no development by sailmakers for downwind sail inventories.

The current rule is the bastard love child of Bertelli's desires mashed in with ETNZ's desire to maintain their hydrofoiling superiority - both design, executiojn and control systems. 

So we are back to monohulls, soft sails (sort of) and ballast (sort of)

The softwing ticks the boxes of North sails and other sailmakers who had felt previously marginalised and with zero opprtunity to translate it into real world sales.

The softwing is a fruitfull avenue of development - it will generate more power than its singlesided parents, but most importantly - it will be a lower drag package than its parents - allowing foiling to reach the performance standards that comparison to AC50's will ultimately generate. 

There is also the opportunity to extend 3Di into areas that have only been hinted at previously. Control of the two surfaces will be important - whether control gets to hard wing levels is moot - there are no slots allowed - but it will reinvorgorate the sailmaking community - which will keep them happy for this cycle at least. 

The internal control systems and actuators will remain out of sight - frustraing for us - but good for the rumour mongers and tinfoil hatters.

The rotation of mast spars will be considerably less than witnessed on the multis of present - purely as a function of apparent wind direction and drag reduction. Once these boats are flying - flat, low drag shapes are more important than twist and depth. 

The equation of Cost vs Power generated, will be in the extreme levels - but that is nothing new to those in the development game where the last few points refinement and performance gain will cost stratospheric sums of money.......

lets see where this goes. Will you see a Tarten 10 with a double skin mainsail - No, but a spin off in the TP52 class - in say 5 years time - possibly.

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Thanks @Boink you speak with apparent authority? and give me hope that we can still have fun guessing and speculating.

I dare not suggest they will get near the hard wings in performance but a decent improvement one existing soft sails would be great.

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39 minutes ago, Boink said:

This topic has become circular, driven more by speculation than fact.

A nice summary, which could have been written as the first post. ;-)

The problem is that because there is nothing comparable, this AC will not determine whether the dual luff sail is a worth while investment, even for an AC75. The challenge in this AC is make the best dual luff sail within the AC75 rule, not the best non–rigid sail for an AC75.

Even if it does work well for an AC75, it's so far removed from anything a typical yacht (racing or otherwise) might use that it's difficult to see what aspects would trickle down. E.g. it's not reefable and requires additional controls to trim. That everyone seems to expect internal control systems is a hint firstly to the difficulty of making a dual luff sail work well, and secondly to the overall complexity of the system.

The only novel aspect of this incarnation of a dual luff mainsail is that it will have a complex computer assisted and hydraulic powered control system. Are there any others? And is a dual luff a prerequisite, or can similar systems be applied to single luff sails?

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2 hours ago, RobG said:

A nice summary, which could have been written as the first post. ;-)

The problem is that because there is nothing comparable, this AC will not determine whether the dual luff sail is a worth while investment, even for an AC75. The challenge in this AC is make the best dual luff sail within the AC75 rule, not the best non–rigid sail for an AC75.

Even if it does work well for an AC75, it's so far removed from anything a typical yacht (racing or otherwise) might use that it's difficult to see what aspects would trickle down. E.g. it's not reefable and requires additional controls to trim. That everyone seems to expect internal control systems is a hint firstly to the difficulty of making a dual luff sail work well, and secondly to the overall complexity of the system.

The only novel aspect of this incarnation of a dual luff mainsail is that it will have a complex computer assisted and hydraulic powered control system. Are there any others? And is a dual luff a prerequisite, or can similar systems be applied to single luff sails?

I don't really see how this scenario differs from flying a 72 foot cat on single none flapped weird shaped L foil driven by massive hydraulics and we already know there is trickle down from there into a number of different types of yacht. 

If the twin skin generates significant performance and the way that it ends up working is obvious enough to watching designers I think we can assume they will at least try to utilise this information on other vessels.

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19 hours ago, Boink said:

lets see where this goes. Will you see a Tarten 10 with a double skin mainsail - No, but a spin off in the TP52 class - in say 5 years time - possibly.

No way. Besides it being against the rules, why would they? It would make every boat/rig obsolete over night, meaning everybody would need to buy a new mast and 2 mainsails costing 100's of thousands while giving little added benefit.

15 hours ago, Boybland said:

I don't really see how this scenario differs from flying a 72 foot cat on single none flapped weird shaped L foil driven by massive hydraulics and we already know there is trickle down from there into a number of different types of yacht. 

I believe you are mistaken, because of a key factor. There is a huge difference between a foiling boat that does 3 times wind speed and a conventional "leadmine". On foiling boats, a 20% improvement from the rig will probably give a 5% increase in performance. On a leadmine, you will be lucky to get 1% improvement. 

15 hours ago, Boybland said:

If the twin skin generates significant performance and the way that it ends up working is obvious enough to watching designers I think we can assume they will at least try to utilise this information on other vessels.

I am sure some will try it, but in very limited circumstances. All handicap systems would kill off double skin mains because of being so punitive on rating. On one designs, or a box rule class like the TP52, there has to be a significant speed increase to justify the cost and the risk of disenfranchising the existing fleet. For new one designs, why make the class more expensive for marginal gains?

this leaves a very few opportunities. There are a few true development classes with open enough rules to allow this type of rig, but I cannot think of any bigger than the A Class where it has been tried and despite some promise on certain points of sailing and in certain wind condition, it was found to need more development than  people were prepared to pay for because the demand would never be high enough to justify the development costs. The same applies to the Moth, where again it was tried but showed even less potential.

There are very good reasons why the double skin rig is a reasonable choice for the AC, but just like the solid wings of the last to cycles, it is hard to see a real trickle down, although to be fair, we have seen trickle up to the AC so is it really trickle down as Glenn got the concept from development work that has been going on for a number of years.They really did have to find a solution to the problems you get doing foiling tacks and gybes that had made the solid wing so good and which become a lot harder with a conventional rig due to drag as you go through the wind and the challenges of maintaining flow across the rig (having a sail flap in the middle of a foiling tack is not good!).

In the end, I come back to a very simple equation. No amount of development is going to change the need for double the sail material, hardware and labour to make the sails, plus a mast that has to be significantly more expensive than a standard rig.This is why it will not trickle down.

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Will you see a Tarten 10 with a double skin mainsail - No, but a spin off in the TP52 class - in say 5 years time - possibly.

@A Class SailorNo way. Besides it being against the rules, why would they? It would make every boat/rig obsolete over night, meaning everybody would need to buy a new mast and 2 mainsails costing 100's of thousands while giving little added benefit.

So which bit of "a spin off" do you not comprehend?????? 

Spin Off - read that again. 

That is not claiming class wide adoption - unravelling the pinancle of Level rating class racing - No.

Back it up.

But the chance that someone might want to adopt new technology to help a generation old design that can no longer keep with the latest designs in said level rating and chooses instead to go pot hunting at various regattas. Money is no obstacle to these owners - but playing with ideas appeals - upwind sheeting angles for headsails are already under 3.5 degrees on deck. It has merit to apply such technogy to such platforms.......... but not to Tarten 10's

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One point that seems to have been overlooked in this discussion is the significance of the drag off the large mast on a boat like the AC75 doing 50 knots and having a large righting moment.

Compared to a Moth or A class where the speeds and the righting moment are lower, the size of the mast is not a factor, the mast on the AC75 is a huge drag factor and the twin skin will help to reduce the drag in comparison to a single skin in such a large mast.

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1 hour ago, Terry Hollis said:

One point that seems to have been overlooked in this discussion is the significance of the drag off the large mast on a boat like the AC75 doing 50 knots and having a large righting moment.

Compared to a Moth or A class where the speeds and the righting moment are lower, the size of the mast is not a factor, the mast on the AC75 is a huge drag factor and the twin skin will help to reduce the drag in comparison to a single skin in such a large mast.

Not at all. Moths use a pocket luff and the thinnest mast they can get away with (38mm dia I think) which is probably a reasonable approximation of what the AC75 designers are trying to do. A Class use a short chord wing mast as I think it gives them easier control over the sail shape compared to the massive vang loads required on a Moth.

An approach similar to the A Class should work for an AC75 to provide stiffness and lower drag. It seems to work for big foiling trimarans, which have similar speeds to an AC75. They also have no issues dropping the main when at anchor/dockside, or reefing.

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I think Terry is saying you need the the width in the mast perpendicular to the 50 knot apparent wind for strength?

So you are forced to have a thicker soft wing cross section?

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1 minute ago, Kiwing said:

I think Terry is saying you need the the width in the mast perpendicular to the 50 knot apparent wind for strength?

So you are forced to have a thicker soft wing cross section?

I fully understand his argument, I just don't see how it applies to an AC75 but not a 100' ocean going trimaran that can sit on +40kn boat speed for weeks on end and can handle winds far in excess of 50kn (true or apparent).

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i sorta wish they had left the rig open for development, just dictated no solid wings. Imagine a pocket luff main with camber inducers for a 75'er

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40 minutes ago, RobG said:

I fully understand his argument, I just don't see how it applies to an AC75 but not a 100' ocean going trimaran that can sit on +40kn boat speed for weeks on end and can handle winds far in excess of 50kn (true or apparent).

I don't think you do understand the argument .. you are comparing an inshore racer that never reefs the sails with an offshore racer which spends most of it's time reefed.  How could an offshore racer reef a twin skin sail??

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Surely Rob's point is that since a standard wingmast can handle the forces on G Class offshore racer like a 130 ft cat offshore then a standard wingmast (or even a standard mast) must be able to handle the forces of a 75ft boat sailing in 20 knots at 45 knots. The righting moment in the AC75 may be less, the seas will definitely be much smaller, and the apparent wind may not be dramatically higher.

 

 

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1 hour ago, Terry Hollis said:

I don't think you do understand the argument .. you are comparing an inshore racer that never reefs the sails with an offshore racer which spends most of it's time reefed.  How could an offshore racer reef a twin skin sail??

What Curious said. I don't think a dual luff sail can't be reefed in general. The only thing stopping an AC75 reefing is the special 4m zone at the top of the mast. Whatever goodness they have planned for that area won't work (or won't work as well) if the sail is reefed (noting that part of it is an anti–turtling flotation device).

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^This prompts the question, will there be multiple sets of sails, or do we think a twin skin sail can perform through a wider range? Swapping twin skin mainsails on the water sounds...hard. 

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^  I believe they will be able to invert the top of the sail providing stabilizing forces during tacks (it is all up wind sailing?) and depowering when the guts or overall wind is too strong.

Like they did in AC35.

They will be able to reduce power and drag by shaping the two skins for less power but less drag too.

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9 hours ago, Ex-yachtie said:

^This prompts the question, will there be multiple sets of sails, or do we think a twin skin sail can perform through a wider range? Swapping twin skin mainsails on the water sounds...hard. 

To me it's likely they'll have more than one mainsail. Since they're allowed 3 masts, it's likely they'll have light and heavy wind versions so it follows they'll have sails to suit.

Dunno about changing mains on the water. Difficult, but not impossible. But does that infer changing the mast too?

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^  They sailed with the same head sale most of AC35.  I think controlling the power is the name of the game.

Using the two element (jib and twin skinned main) to extract the most power and using amazing control to fly most of the time.

Of course I do but dream !  IMHO

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Actually I think reducing drag will be important for these sails as they would seem to have plenty of power.

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On 6/3/2019 at 6:36 PM, A Class Sailor said:

It's already been tried in the A Class with little success, because our current rigs are so refined and nobody is going to spend tens of thousands developing something for a fairly small market.

Remember the Heru sails?  Looks cool, but seemed to not go anywhere...

https://herusails.com/2019/other-wing-sail/a-class-wing-sail/

This is going to be the challenge with the two skin sails, simply using a d-shaped mast with two luff tracks and full battens won't make it as efficient as a rigid wing.  You have to control the chord depth and shape to a greater degree than you can with just a full batten soft sail.  The magic is going to be figuring out how to manage the relationship of the windward vs. leeward side of the sail to obtain/maintain an efficient shape.

Back to the first windsurfer pic, I think that people missed a major point there; just because the top was twisted off like crazy doesn't mean that he wanted the top in that specific shape.  It just means that the overall trim resulted in the top being like that.  Think about trimming a small jib going down wind, typically, the leads can't be setup to ensure that the trim is even top to bottom in that case.  As such, if you trim to the top of the sail, the middle and bottom will certainly be over trimmed, stalled and probably backwinding the main.  In the first pic, that crazy twist is likely just where the sail ended up as he bent the mast and sheeted to get the appropriate angle (power) that he needed.... it's only faster b/c the average trim was right and the top twisting off was part of that.  (clear as mud?)  Like with the jib example, I wouldn't trim to the top or bottom of the sail, but somewhere in the middle that gives the best overall performance.

For the pics of the inverted leech; as a cat sailor, looks to me like when the top batten isn't tight enough and can't support the leech for the given mainsheet tension... or when I've seen guys with just &^% aftermarket sails with bad shape.  (You can also get some inversion with too much cunningham, but it doesn't look like that to me and probably not likely given the stiffness of that mast.)  The top batten on my Nacra 20 FCS is like a 2x4 and I still have a handful of old top Tornado battens that you could go bear hunting with.  It takes a lot of force to support that part of the sail and if you don't get it right (batten too soft or too little tension) it looks like that picture.

I swear that I saw a video comparison of ETNZ and Oracle from behind the boat where they were evaluating wing trim on the AC50, but can't find it.  It was obvious that ETNZ was working the twist more, while Oracle was adjusting the sheet.  Since the sheet on a rigid wing is almost more like the traveller, twist (more like what we're used to with a main sheet) provides a smoother and more gradual adjustment (better flow).

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Grant says "This thing should be 6 minutes faster" (around the course than an AC50)

This twin skin can't be all that bad after all !!

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Can't wait to see the thing flying and try to guess what cross section it has through it's phases from start to foiling in amazing apparent wind.  I will be in Auckland 11th and 12th of Sept.  I hope I can get a glimpse before I go home.

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Wonder if pumping the main is going to be part of popping on foils in marginal conditions of say 5 knots...  again a parallel with windsurf foiling?

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hijack: every time i see that promo cgi vid i'm reminded of this a-cup doozy...

 

 

WIND.jpg

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1 hour ago, Stingray~ said:

 

Wow.  Life as a yachting hardware guy...  Looks tough innovating in that market.

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On 9/1/2019 at 3:34 AM, Kiwing said:

Grant says "This thing should be 6 minutes faster" (around the course than an AC50)

This twin skin can't be all that bad after all !!

The reason it should be faster is not due to the sail. The AC75 has more RM, more main sail area (about 40%), far better potential for ride height and lift control, more rudder control and effectively unlimited power for foil adjustments. If it isn't faster there's something wrong.

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42 minutes ago, RobG said:

The reason it should be faster is not due to the sail. The AC75 has more RM, more main sail area (about 40%), far better potential for ride height and lift control, more rudder control and effectively unlimited power for foil adjustments. If it isn't faster there's something wrong.

Exactly, but a wing would make it even faster.

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50 minutes ago, Colomba said:

Exactly, but a wing would make it even faster.

 

 

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On 9/3/2019 at 8:25 PM, aA said:

hijack: every time i see that promo cgi vid i'm reminded of this a-cup doozy...

 

 

WIND.jpg

Sorry, the boats remind me more of this:

7mK.gif

- Stumbling

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On 9/4/2019 at 7:49 PM, Colomba said:

Exactly, but a wing would make it even faster.

That is a non sequitur

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On 9/4/2019 at 7:49 PM, Colomba said:

Exactly, but a wing would make it even faster.

So would a Hamilton jet.  What about a second hull and turn it into a catamaran, what about if we add a ....

You need to read up on what the Brief was for this boat.

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Unfortunately due to not letting the cat out of the bag we will not see ETNZ sailing to full potential for some time.

I wonder how they are going to cover that up?  By TC's unstable line ?

Anyway sailing an AC75 like a moth will require some amazing control of the soft wing ?

I wish I understood 5% of this !!

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boom up inside the sail looks promising,  a real wing configuration.

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I wish I could put that interview when those Italian Guys talked in English about the Prada Boom.

I guess now some people might be dragged screaming into this new world.  I expect ETNZ to unvale a similar system but not talk about it.

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This one?

 

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