Confusion Surrounds ETNZ Final Development

ETNZ have just launched their final test foil... twice. At least according to media reports. But don't let that confusion misdirect you from the really interesting features packed in to this newest foil wing.
Recon video and photos credit to Recon Photographer / @America's Cup
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[@michaelrosspearson9756]

Quoting from Blackadder, Team NZ will have a plan so cunning 'you could put a tail on it and call it a weasel '.

[@timransby1774]

The other teams will be looking at what’s NOT come out of ETNZ, and having seen the straight leading edge, be quietly pooping themselves.

[@bradclifton5248]

She's an old team that has seen every trick. Always tight on budget against billionaire bottomless pockets. Failure to keep secrets has cost them at least one cup.

[@brendonnz1964]

Was that the 2013 Campaign@@bradclifton5248

[@Spartan902]

😂 I'm a big Blackadder fan! Good old Baldric ( Tony Robinson)was my favorite character.

[@robbyhuntf2b]

Thanks for all your content. It makes following the AC the most accessible and interesting it's ever been!

[@MozzySails]

Thank you for the kind words and kind donation.

[@ronanlavelle]

I think we all know that ETNZ has a track record of releasing innovative designs so late that the other teams find it almost impossible to replicate them. Grant Dalton alluded in a recent interview that their new race boat will be 10% faster than the previous boat. They definitely have something up their sleeve!

[@Anaruhoneheke]

As a sailing noob and a cup fanatic I have to say I love your work keep it up. Cup year let’s go ETNZ

[@simonolsen1158]

I can’t wait to see all the next big AC boats, and key design features and differences. The suspense of the long AC build up really draws me in, THEN we get to see actual design and sailing performance on the water. I’ll be completely obsessed by that point!

[@MozzySails]

It's a slow burn and the next couple of months before we see launches will feel long, but this whole summer should be awesome

[@mburmester719]

Not sure if someone pointed this out before, but part of the idea for the straight leading edge might be the following: The shape of the foil means that the elastic deformation is helping reduce ventilation. The 25% chord line is pointing forwards from wing root to tip. So as a lifting force acts on the outboard part of the foil it will twist the foil so it gets a bigger angle of attack there. As soon as the tip pierces through the water, the force basically disappears and the induced twist will do so as well - lowering the angle of attack. This would mean that ventilation might be reduced and the foil becomes more self balancing regarding ride hight. Compare that with a conventional swept back foil: The angle of attack would rater increase when the tip loses lift by piercing through the surface. I am not sure if this effect is big enough to make a reasonable difference. But the mechanics of is should work in principle. What do you guys think?

[@valdataipari2091]

Thanks always enjoy your content. Thanks so much

[@MozzySails]

Thank you for your support, that's super generous

[@73engineer]

There will be twist in the outer third of the span of that straight leading edge to reduce the AoA towards the tip, this will reduce the entrainment of air as it breaches and then returns to below the water line, you can actually go very negative on the twist without changing the overall lift of foil, so the twist will help with having less entrainment plus reduce the loading across the span allowing higher aspect ratio to be designed, so this means they can run a straight leading edge without any issues compared to having no twist

[@timransby1774]

@73engineer Prandtl twist 😮 😊 Unswept leading edge is an unexpected “twist” though .. My money is on the features on the port side of the test foil being taken forward into the next iterations

[@MozzySails]

Good point engineer. Generally the best way of reducing ventilation is to allow the ends of the foil to do less work... the trade off being that whatever they do with the outboard end will have to be mirrored on the inboard end which is the deepest part of the wing where possibly they'd live with less washout / twist

[@barryscott6222]

@@MozzySails As regards a symmetrical foil for the Cup. Is that purely a planform and foil shape matter? Because if you build the foil to be the same shape, inboard and outboard - BUT - altered the materials used, or tempering etc... then you could definitely get a different bending modulus, and completely different behaviours/twisting between the two tips due to their loading.

[@MozzySails]

@@barryscott6222 good question. The rules says "A foil wing must be symmetric about WSP in foil measurement condition, with a build tolerance of 3.0 mm." That appears quite open and dependent on your definition of symmetric. However, symmetric is a defined term in the rules which is given as: "Symmetric A component that is required to be symmetric must be designed to be exactly symmetric, and the built shape must lie within the specified tolerance of the designed shape everywhere on its surface. Such a component must also be designed to be almost exactly symmetric in its structure, where any structural asymmetry can only result from details such as: (a) asymmetries at the individual ply level (e.g. lap joints or staggers), provided the overall laminate has symmetric structural behaviour; (b) fastenings across the symmetry plane; and (c) right‐handed screw threads; which are not designed to induce asymmetric structural behaviour. So, I think it has to be as close as possible to being symmetrically, both in shape and structure.

[@barryscott6222]

@@MozzySails Yeah - a.) would appear to rule out asymmetrical physical behaviour.

[@alanshearing7515]

Interesting video, thanks for taking the time to make it . I fly RC gliders and your comparison to the foil is interesting, they look very similar looking. Even the bulbous piece looks like the fuselage at the front now. Obviously the shape reduces drag , I don’t know if the same applies in water ?. Team NZ know something it seams. Look forward to your next video.

[@peterebel7899]

The differences are: a) cavitation at high load b) the surface of the water

[@CarkeekW]

I have been waiting for someone to make a "plank" and give Peter Wick a call

[@like-the-cut-of-your-jib]

Thanks for indulging us foil folks Tom! Hope you’ve have your tickets booked for Barcelona!

[@CarkeekW]

Thank you Mozzy , great video . The analysis of the tnz crews faces after trying the final foil was telling , they seem very happy , holding back grins. I still have respect for the other teams so no one is counted out yet although ineos have suffered some time consuming setbacks

[@real2gone]

Another great analysis, Mozzy. That '5th foil' had me scratching my head! Thanks mate.

[@MozzySails]

Glad you enjoyed it! Usually the simplist explanation is true!

[@charlestoast4051]

In aeronautics, it's common to keep the point of maximum thickness of a wing in a straight line, at least for low speed flight, in order to have an efficient structure, maximising the depth of the main spar. Therefore on a tapered wing, the leading edge would have a moderate sweep back, with more of an angle in the trailing edge, since the point of maximum thickness is generally at 30% or 40% of the chord length. With the AC boats, this probably isn't a significant factor, since the foils are so much smaller and weight is not so critical.

[@SilvanMarty]

Thanks was waiting long for your new video. .. happy u doing about foils now. We see of course different foils at final boat. Its great all having one foil and this its till the end. Not creepy laws from oracle in San Francisco where oracle was building halve new boat in a handful days! There money was bringing winning only! What exiting if we see every boat with they tech and foils.

[@gregdavison3562]

Agreed entirely!- they are the ultimate chess masters - their final move with all the various elements won't be played until its too late for any other team to copy!

[@salvatorecasula8931]

Ogni foil è adatto alla propria barca ,vincerà chi complessivamente avrà il progetto migliore e non il foil migliore

[@rusbur]

The straight leading edge and elliptical trailing edge looks very similar to the form of the new T foil for Season 5 of the F50 SailGP circuit based on their recent content.

[@Spartan902]

The leading edge of aeroplane wings are straight so it makes sense.

[@GordonjSmith1]

Interesting and thought provoking as always. I will need to sit and think about this a little more!

[@peaknut1]

Great banter

[@blinkybagger8342]

So ETNZ have a foil testing strategy that doubles the amount of testing permitted on the water, but not without complicating the perspective provided. Most of the foil testing will be performed via computer modelling, with on-the-water testing used to determine how much gap between the computer models and the reality. Doing the public facing development so late that the others cannot copy in the same cup cycle, seems to be provide some advantage (if actually winning the design race) but adds some risk, should they need to address problems.

[@MicrophoneAssassin13]

Great video/production quality. Cant wait to see your boat launch videos.

[@MozzySails]

I'm really looking forward to the boat launches. Might be as early as March or April for the first!

[@fightinfalcn1]

Thanks heaps Mozzy! Insightful as always!

[@MozzySails]

My pleasure!

[@timjones3094]

Thanks for great analysis

[@MozzySails]

My pleasure!

[@henrycartwright7124]

Great vid! Thanks!

[@robbyhuntf2b]

Thanks!

[@MozzySails]

Cheers Robby, very generous, thanks for the support!

[@Mrlang74]

One thing that always happens etnz will pull something out of the bag , experts at looking like a dog but actually have a greyhound , as a kiwi we want people and teams to think this way

[@wk1607]

Not really, they showed their hand far to early in 2013

[@roslynhita6149]

Yes!..but they "learned from it"..and will NEVER do that again @@wk1607

[@zlm001]

Thanks.

[@peterdelange6940]

Thanks Mozzy, I love your work, but I'm not so sure about your summary of the ETNZ lack of innovations, they were the first and most successful team to lower the mast base and raise the mast step effectively lowering the sail plan closer to the centre of lateral resistance and all the extra force that negates. Cheers' from Aus.

[@MozzySails]

Sorry I didn't mean they hadn't been innovative, but that they don't display any innovations early in the cup cycle and haven't shown any so far this time. Instead they hold them back until its too late for others to copy. I think that's something they've learnt from the lead up to the San Francisco Cup

[@kiwidiesel]

The thing to keep in mind is we are not going to see any massive increase in boat speed with changes to the foil shape and design. Instead the performance increase will be small and possibly only a benefit in a certain speed range of the envelope. All changes have am effect to the performance but as with any modifications there are always negative factors that can be introduced in other areas in the pursuit of increasing performance. The same applies with aircraft wings, its always a trade off between handling characteristics. Reducing parasite drag over as much of the speed range while maintaining efficient flow and performance is a knife edge balence at the best of times.

[@simonpuxley7374]

Love it thanks Mozzy. Also saw that and was super interested. Elsewhere what do you make of the Ultim trimarans heading around the world - leading one putting down 13,000nm at an average of 30kts is pretty sensational don’t you think?!

[@jons6125]

Hopefully the racing will be as interesting as this channel

[@LondiniumEspresso]

The boat seems to accelerate extremely quickly on the new foil

[@ChrisCanMakeStuff]

re: Nothing exciting from TNZ. Maybe we're already in a corner of the rule box? We'll get to see soon enough I guess!

[@djholster676]

Have you thought about the centre of pressure of the foil being well behind the outrigger arm. As the foil loads up the arm will twist ever so slightly and reduce the attack angle for reduced drag.

[@peterwor]

Another very insightful video. However I'm more curious about what Garmin you're wearing, 7X pro or Epix2 pro? I'm a quatix 7 user myself.

[@gerryvandyk5551]

Do you think there might be some merit to keeping the mounting point of the foil back on the bulb, but pulling the center-of-lift forward a few inches with the sweeps of the leading and trailing edges? I'm thinking about perhaps the onset of cavitation around the bulb and changing the loading that the rudder lifting foils might see.

[@73engineer]

The bulb has a few functions in this case, houses the mechanics is one thing but from a foil perspective it is the way to reduce junction drag where the strut Ts into the foil and also to allow the flow at the junction to result in the least loss of lift over the profile, so the better the flow is as close to the root/junction as possible the less lift is lost as a result of pressure and drag at the junction There is an imaginary line along the leading edge where the flow separates to the top and bottom of the foil surface, this is also the highest pressure zone, the result is if you disturb this line then you interrupt the flow to the upper and lower surface and hence lift/drag. If the bulb can ensure the junction flow arrives closest to the root on the leading edge then you make best use of the lift across the span For this reason you will see the bulb is set forward of the leading edge to try control the flow onto the leading edge as best a possible, so within reason the more distance from the bulb to the leading edge the better to allow the flow to be optimised

[@zlm001]

I’m still looking for underwater spy footage of the foils in action.

[@ScottSummerill]

Is ETNZ working with any aerospace company to develop their foils? Or just winging it …

[@jonfinderup2437]

ETNZ is an aerospace company?/

[@warrenyoung173]

There's been a steady stream of engineers with sailing related specialisation coming out of University of Auckland since the 1990s.

[@simonolsen1158]

Does anyone know what happened to Luna Rosa’s big boat from the last AC? I’m surprised they haven’t tested adaptations on that, like others have been

[@greybuckleton]

Whilst your points about the entrainment are interesting. Straight leading edges are more efficient in general, and will still have span wise flow just not as much. It is under the teams control to some extent how high they will let that foil get out of the water. Straight leading edges ultimately give a better aspect ratio within a given area.

[@waynerussell6401]

Not in sailplanes. Highest performance wings have faceted leading edges and extremely high aspect ratios. Typically, less than 10sm in 18m span.

[@greybuckleton]

@@waynerussell6401 sailplanes largely do have a straight leading edge. Compared to say an airliner with substantial sweep. I've never seen a sailplane with a stepped leading edge. Which model has that? Or do you mean a dog tooth? But as I said and you confirmed there is a greater span to chord ratio with a straight wing. Swept wings will always generate greater spanwise flow due to the lower effective aspect ratio. A wing could be faceted or not without changing the amount of wing sweep. The second thing to consider is sailplane performance is very concerned with L/D ratio, whereas a fast aircraft or boat is more concerned with minimizing high speed drag, so "best" depends on what your trying to achieve with the wing. I feel that in this past competition the wing sweep may have been used to give more wing area given span was restricted in the box rule, the more you sweep the foil the more span you get without leaving the box, but this would have made for a higher drag foil at speed.

[@AdrianChapmanlaw]

Do you think we will ever see any of the foilcam (tm) footage? It would be amazing to see that!

[@MozzySails]

I think we saw a very brief clip from INEOS of the last cup, so maybe after this cup has finished

[@fluiditynz]

I think it's moved from foil performance to foil structural integrity for speed. That's been my personal DIY foil design experience anyway.

[@SilvanMarty]

This doubble foils different its not easy to see what they good. ... How u saying on port or starboat side they totaly different. .... How they getting out what on end form its better?

[@nSnowCrow]

Why do they limit the amount of foils they can built? Won’t that force the use of advanced computer models and discourage an iterative design process?

[@thedoctor907]

Because if you open that up then the better resourced teams just crank out foils because money isn't an issue.

[@rydenkaye9735]

because they want more teams competing. same reason they limit number of test boats and use of tow tanks. its too costly to compete with the best funded teams if they aren't limited on what they can do

[@timransby1774]

Doesn’t the use of computer modelling supported by correlation testing with a limited number of foils encourage an iterative process… albeit iterative inside the computer??

[@CarkeekW]

its cheaper and less wasteful , it promotes the use and validation of computer modeling which not only benefits these craft but all of the world creating better container ships , other foiling craft etc etc .

[@jackaroo5]

This is exaclty what they want you to hear! Don't talk them up......Reminds me of the Late Sir Peter Blake playing down the speed of Black Magic quoting that their new boat was like a dog and was getting beaten up by the previous generation boat. I'm absolutely certain the World land speed record they broke not so long ago was not the Objective. Kiwis are quite shrewd and resourceful .

[@James_Hallam]

Seems to me a tapered trailing edge would help maximise lift (perpendicular flow across the full span) while minimising induced drag - that strong trailing edge taper should cause a weaker/bigger vortex as lift profile reduces gradually to the tip (?). Low/negative lift near the tips should help limit ventilation for similar reasons.

[@raicancro]

The ETNZ are the son of wind and kings the ocean, the technology is a little part as then will be ever

[@johnnoyorston4903]

Lets go back to WWii. The Spitefire wing was designed aroung the elipical shap. Once they had perfected the geomatry of the shape, and aerofoil shape, greater lift and tighter turning. So, why try to invent a new concept but take on what has worked in WWII and develop upon that shape. Foils shaped to this wing and then hav the foils slightly more positive leading edge to be 1 or 2 % up on the front edge. Only my thought from a boat builder. Oh the other thought is that most aircraft have thes wing tips that are shaped above and below the end of the wing. Stops the voitex at the end of the wing. This must happen at the end of a water wing? Your thoughts? Johnno

[@rigidrobot]

Wouldn't be surprised if wings converge to remote control glider shapes that are getting to close to supersonic speeds...

[@bphillips06]

Just curious. Do these foils adjust or have any particular adjustments once deployed? Or are they in essence Static once in the water ?

[@MozzySails]

They have a flaps along the trailing edge, but they can also adjust the angle to which they're deployed which also affect the amount of lift

[@rodboese7041]

Soo it is a good guess that that their current 75 can hit 55kts then by daults saying 10% increase 60kts is on the table?

[@MozzySails]

I think the speeds around the course, or rather VMG, so a combination of angles to the wind and speed could be as much as 10% better, especially in lighter conditions. However, I doubt top speed will improve as much as its not really as important. Top speeds also rely on getting a good gust at the right time, so there is a good chance we don't see their potential for top speed in racing.

[@desmondcrosland7884]

@@MozzySails you are annoyingly sensible. 😎. Love your channel. Got into it last cup and been following you since. Great team. Looking forward to your reviews once the big boats emerge.

[@johnsausau6925]

😕 😂 not the Kiwis, GO ETNZ

[@barryscott6222]

One thought... If you have a curved rear foil profile, then potentially, you don't need a full span flap.

[@73engineer]

Normally the curved flap is to keep the cord/profile ratio fairly constant so that the lift gradient across the span is smooth as you move out across the span to reduce 3D flow over the foil

[@MikStorer]

What happened to the Tubercle foil on Allinghi that was used last year for a brief period and doesn't seem to have been used since. That is worth a bit of a story because of the internet hype about tubercles which never seems to pay off. After all humpbacks are the only whale that has them and their typical migration speeds are 0.5 to 2 knots. None of the fast whales use them at all. Would be great to hear from the Allinghi team if there is an opportunity.

[@MozzySails]

Alinghi's next foil didn't have tubercles, but Tey jave only launched two test foils and have now gone back to using one design foils for thier match race practice based in Jeddah

[@zlm001]

Do you think that AC teams need to be allowed to use a greater range of foil shapes and sizes? Open the box up a bit and maybe allow more development on the arms. Too much money I guess.

[@robbyhuntf2b]

They have already said each foil will be looking at something different, so I'm not sure there is much to take from any of them individually. The latest planform is also similar to aerobatic planes with mostly straight leading edges and swept forward trailing edges (though not as severely swept forward of a hinge line in this case...appears curved?). Maybe they are trying to be closer to a zero sweep quarter chord.

[@sam1812seal]

There’s a part of me that’s sad that the days are gone when teams would try everything to get an idea of what the other teams’ boats looked like below the waterline. Now everything’s on show there must be a few diver/photographers out of work

[@rocarroll1533]

Do you really think they are going to tell you the secrets,dream on buddy

[@desmondcrosland7884]

The interview with Grant Dalton a week or so ago has me intrigued. He predicts a 10% improvement in the new 75’s. As a kiwi I’ve learned not to put to much faith in “claims”, hula, but this team seems very focused. And I hate to say it but the move to defend overseas appears to be the strategy most likely to have a positive result. Hate to say it because I overlook the harbour they defended on. Then again, it’s better to watch streamed.

[@billhanna8838]

Clones in the well ?

[@peterebel7899]

It is time for Luna Rossa to win the cop. But will Alinghi steal the cup again?

[@fredsickert6268]

Straight leading edge is my guess

[@lowellthomas446]

We'll Up Yu' Some Mango's ❤ it's the cup we keep our eyesight on 😊 Ash'ent Mariner 🌎 âyâπn

[@VMVarga-yf6eg]

So in summary they cannot model the foil on a computer so they are trying disparate concepts and viewing it on video to try and figure out what the hell is actually happening

[@djholster676]

The do model on computers, but is always essential to validate models in reality.

[@morrisanderson818]

Not confusing at ETNZ,

[@victorlarkins2404]

Snitch blehhhhhhhh 😛👊💪

[@VECTOR_HUNTER]

😂