Answers to your America's Cup Foil questions

[@MicrophoneAssassin13]

Hey Mozzy, just wanted to shout out the notable increase you've made in overall production quality and narration from last run or the cup. You've become an excellent "public" speaker and the technical quality now matches that of the content. Super excited to watch this AC cycle with you

[@MozzySails]

Wow, thanks!

[@colin7242]

Cannot second this enough! Your production value is really impressive man

[@myleswillis6938]

Nice thumbnail too.

[@julian4548]

Here here

[@aaronfranklin324]

@@MozzySails Pictures of the Auckland University windtunnel. And a CAD model of a 2012 Autonomous concept variant designed as a saltwater spray cloud brightening, Cloud condensation nucleating blue water vessel, I designed for the Arctic Methane Emergency Group. Based on the 1993 cruising yacht design that the recent generations of hip mounted lifting ballasted keel monohulls were inspired by. kzbin.infoUgkx_S6L8qGqB5fdbP39k4OobYyURoXpNZ8w?si=tXbwqLPgC8c12irV

[@MBCGRS]

I work for the engineering company that makes the foils for ETNZ. The mono-blocks of billet these are machined out of are huge. It's great just standing and watching the machine cut. (It's very large). Great video.

[@pkpwnerful]

Have watched every one of your videos front to back this past year Mozzy! I get so excited when I see a new one in my feed. And nice job shutting down that know it all at the end there, twice the stress of a F-16 wing spec! Wild. Definitely gonna bring that up at the dinner table sometime soon.

[@MozzySails]

Wow, thank you!

[@nickl2681]

@MossySails - great format. Great idea to draw such interesting content and discussion from your viewers and their comments. As I guess most here viewing your channel are either skilled enthusiasts or, like you and the guys, proper pros in the fields you cover, thanks for keeping your coverage focused on the engineering and racecraft!! You've got the tone spot on!

[@adrianthompson5322]

Brilliant analysis leaving us some lovely nuggets of design to chew over. Your calculated foil loading of 7000 plus kg is based on the full planform area. The teams that have split flaps with no structural continuity through the centreline will be even more challenged. You can probably knock off nearly 40% of the effective structural foil area at the root, leaving an even higher loading on what's left.

[@yellowpitch1080]

Juan K has entered the chat!?! Famous to me as well. Great segment.

[@gheckolock81]

What if the forward sweep has to do with surface piercing? The tip that breaks the surface will have its lift twisting off while the tip in deep water will twist on lift. I think they figured out a way to make the foils act as if they are asymmetrical. Reducing cavitation at the surface and increasing lift in deep water.

[@instantchow]

Interesting, smooth the lift profile for various positions!

[@kanedewilde]

The center of pressure will also shift back as more wing sticks out of the water. It would be very small but could help with stability.

[@instantchow]

@@gheckolock81 have we ever discussed yaw related lift profiles? The boats turn quickly, perhaps extra lift makes sense I'm a quick yaw, again perhaps to even put the total lift applied to the hull...

[@dinky9216]

An interesting comparison of aircraft and sail boats. Both count as extreme in different ways. But I've seen almost every part of boats break when pushed hard enough.

[@kevingerald8286]

Hi Mozzy, great analysis and interaction with your followers. Keep them coming. 👍

[@charlottescott7150]

Thank you Mozzy. I am a sailing enthusiast and know little about engineering but can follow a lot of what you say!

[@TheLDunn1]

DARPA have been experimenting with active flight controls. These have no moving flaps, but instead have outlets on the wings where air is vented to modify the lift characteristics. No moving flaps leading to more efficient, lower drag designs. Just wondering if any team has considered something similar (but maybe with water) to control the lift from their foils. Evidence from aircraft experiments seems positive, and maybe something AC boats could exploit.

[@jakeashell9906]

Please correct me if I'm wrong but i would think that the need for an intake to supply the flow from the control surfaces on what would otherwise be a completely fair Fuselage and the different flow speeds would create a lot of drag and cavitation risk and at lower boat speeds without some sort of active control would be fairly inefficient. could fall short in system latency when compared to a system using flaps?, Does the DARPA system rely on bleed air from the engine?

[@freeaccess5905]

Mozzy, you are the Premier source of information about the AC. Great technical video.

[@MozzySails]

I try, thank you

[@bishopdredd5349]

Respect for answering the comments

[@greenstripeypaint]

Thank you Mozzy - the excitement ramps up another notch

[@jameslittlewood7821]

#1 sailing content!

[@warp1963]

I think one aspect was not mentioned yet. The flap percentage along wingspan. It is beneficial to have max percentage in the center and decreasing percentage further out. Since the hing-line is given, forward sweeps allows to decrease flap percentage more aggressive towards the tip. And maybe even have the tips fixed and twisting the flap while its deflected.

[@AlanMerry]

Very happy to watch your updates on the AC37. Not sure if it is possible but would be great to see any analysis of the current on water activity in Barcelona.

[@Coolcmsc]

Very interesting about the extreme loads, although I had at least worked that out. But what I hadn’t considered is the distribution of those loads onto the flaps. Or, more specifically, into their little hinges and their presumably thin couplings to their actuators. Intuitively, that hinge functionality seems extraordinary to me under these loads. I’d love to hear you explain this aspect of the foil loading please. Also, for those who’d like a real world example of how much load that is: those really big round bales of hay we see in a farmer’s field wrapped in plastic (which are almost impossible to move for a human) weigh - just - 400Kg each… So, it’s something like 18 of them = this amount of load on the little foil. And that is more of those bales than can fit on a really big trailer behind a giant farm tractor!

[@ChimeraActual]

Do they need trim tabs on the flaps?

[@Buggerupsvideos]

Grate video mate. I would be very interested to learn more about cant angles and the relationship of use with the traveller to maintain boat speed.

[@JanHolland3000-w2d]

Love the technical discussions on this channel as I am learning lots! Remember Sailrocket? I guess you do. Back in the day they claimed to have made a breakthrough regarding cavitation. There's an outfit on your side of the Channel by the name of Aerotrope who've claimed to have been involved with SR. Would be interesting to find out if they are YT interview material ...

[@patrickchase5614]

I think that the question about whether the ETNZ foil is truly forward swept is indirectly onto something. While I agree with you that it technically is forward-swept, it's only slightly so, and that matters here. The distance by which the tip is advanced relative to the root is a lever arm, the length of which determines the magnitude of the torsional load causing divergence. Going back to your saw example, as you reduce the amount of "forward sweep" you'll find that it takes more force on the tip to produce any given amount of twist. It may be that ETNZ were able to make their steel foil rigid enough to withstand the (relatively small) torsional loads created by its small amount of forward sweep.

[@Diceloader]

Good point. I believe that combined with the flap reducing twist that it results in the effective sweep being neutral.

[@ChimeraActual]

There appears to be force aplenty.

[@glenmcgillivray4707]

My suspicion is that forward swept wings increase lift when under increased loading, like when the far wingtip slips out of a wave, because air won't generate useful lift. The leading edge will resist aeration, and boost lift at the core while resisting variable loading in a positive manner. Which would mean less energy used on adjusting your flaps, the boat naturally wants to fly kissing the waters surface. Which means more energy for optimizing the sheet or tacking.

[@ChimeraActual]

Another great vid, TY. Thank you for calculating the forces on the wing, I knew they had to be right up there, but that's more than I expected. Steel may be the only material with the mass and rigidity to work. BTW, even if the flaps appear continuous, that doesn't rule out the possibility that the center section has some flex. Not saying it does, just that it's possible.

[@MozzySails]

Yeah absolutely correct on the flaps. We also know many curve in to the tips where there must be some flexure as well

[@warwicktaylor347]

My thanks to @SeanFChannel for the resultant excellent information [twice the wing loading by area than an F22 @ 9 g's! etc.] And I hope his mates at the pub keep reminding him of it for years to come...

[@chriscochrane6319]

Excellent review and rebuttals

[@maarten8868]

In the discussion about forward sweep and twist there is no mention of the pitching moment generated by the foil, which may be very relevant. These foil sections probably do not lift neutrally at the quarter chord line, they probably lift much further aft. This would cause twist on a straight foil. The forward sweep may be there to counterbalance this and still get a positive or zero twist behavior. Also twist seems to negatively impact ventilation.

[@davidcis59]

Mozzy, congrats for the quality and depth of your review. Is there a comparison of foil size for the different teams? Thanks

[@tobydimmock1224]

Could the assumed sacrifice of upper limit speed be offset by superior vmg?

[@Spartan902]

I am still blown away by the fact that such a big beast can get up on such a small foil in 5-6 knots of breeze. Just think where technology will take these boats into the future. Step aside F1, you have competition in the technology development department. It's brilliant to see because F1 is now boring as bat sh-t. Cheers Mozzy. Less than 2 weeks to the start!!!!!!!! You bloody beauty!

[@aaronfranklin324]

It is possible that team New Zealand have eliminated the potential twist issue with the forward foil sweep, by milling a groove in the top and bottom of the foil surface at a larger forward sweep angle than the lift centered chord line, and filled said groove with unidirectional carbon fibre. It is also possible that they have found that an advantage in upwind stability can be obtained by allowing it to twist. As the foil enters the front of a swell where the water movement is vertically upwards, it increases angle of attack experienced by the foil, increasing the loading and lift. More, obtained by twist could be advantageous . As the foil enters the section of the back of the swell the reverse could apply. It would likely improve surface contouring travelling into the swells. But be detrimental downwind. As most of the time in a race is upwind, and staying on foil in light air conditions is Easier downwind it could prove an overall benefit.

[@timransby1774]

Taking your thinking a step further (or sideways) , @aaronfranklin324 , what if they’ve gone down the route of the Japanese sword maker and have steels of differing hardness in the core of the wing, in such a way that the wing has different bend and twist characteristics across its span. Further down that route , what if the inboard wing surface on each leg had different bend and twist properties to the outer, surface piercing wing surface …. !!! ??? Such a wing would be compliant (symmetrical) at rest, but not under load

[@aaronfranklin324]

​@timransby1774 yes the possibilities are endless. 🤭 And, as the designer and builder of the Americas cup windtunnel at Auckland University, that has tested all the winning rigs and boat models since our historic first successful defense in 2000, and also the designer of a cruising yacht variant with the hip mounted curved, ballast bulbed, keel configuration our boys have decided to copy. 🤭(Not the lifting foils, that would be stupid on a cruising monohull).... I hope I'm not giving away any tips to the competition. 😋🤭 I'm sure they won't mind actually. We've been getting dead sick of having to throw every second race and cup, to keep the sport interesting to watch on TV. Kinda why we decided not to hold the defense here. It was friggen embarrassing in the last one, having to stay on the slow side of the course and pretend that these beasts can't just punch Straight through the windshadow of the opponent. Anyway, you could indeed mill parallel diagonal shallow grooves to reduce stiffness, and promote twist in any direction you want. You could fill and fair those grooves with a high hysteresis dampening material to suppress flutter. Or better yet skin the whole thing with such a material. I've been suggesting they look at things like hydroelastic flexible bulbs to turn vertical accelerations and variations in lift into thrust for years. Such as a urethane waist section in the bulbs, with a leaf spring core cast into the bulbs. Kinda "bending the rules " a little, pun intended 🤭😋. It's the sort of smartass stuff that makes them too chicken to give me a job, they always lose my CV if I apply. 🙄 The bosses are always afraid I'll have their jobs within a few months if they let me in the door. 🤭😋 Still, keeping things in the bag for next time is how we keep it interesting I suppose.

[@aaronfranklin324]

Pictures of the Auckland University windtunnel. And a CAD model of a 2012 Autonomous concept variant designed as a saltwater spray cloud brightening, Cloud condensation nucleating blue water vessel, I designed for the Arctic Methane Emergency Group. Based on the 1993 cruising yacht design that the recent generations of hip mounted lifting ballasted keel monohulls were inspired by. 😉 kzbin.infoUgkx_S6L8qGqB5fdbP39k4OobYyURoXpNZ8w?si=tXbwqLPgC8c12irV

[@TheCruisingKiwis]

You lost me at hello😂

[@aaronfranklin324]

@@TheCruisingKiwis How DARE you. 🤭 . All the New Zealand yachts and many others were developed using my technology since 1999. Have some respect! 😋😘

[@jamesaron1967]

Great Q & A!

[@MozzySails]

Glad you enjoyed it!

[@richmondatkinson8111]

In terms of foil loading compared with aircraft, a more telling comparison would be with dynamic soaring RC gliders. These are now reaching top speeds approaching 1000kph and pulling 60G in their turns. Interestingly, they are beginning to experiment with swept wings, but necessarily backwards swept, as the required tortion resistance of forward sweep cannot be accommodated in the thin carbon fibre wings.

[@graemeclarke7186]

would love to see what your comments are of the footage seen with ineos and team nz practice racing and team nzs nose up profile seen while racing thanks mozzy

[@BeePee66]

An interesting comparison of wing loading with aircraft, but you need to consider the effect of the vastly different Reynolds Number for water compared to air.

[@peterfisher541]

Yeh you ok for a pom not sure about yuh boat might be too clever looks like prada and the kiwis very slippery but boy oh boy its all gunna be rather close keep up the good work respect from an old kiwi wind jammer

[@real2gone]

Hope that wing foot turn (at the bulb) is good, Tom. A hell of a lot hanging on that one, eh? Another great vid.

[@benedicttan88]

Thanks for your great insights. I noticed practically all the teams ride with the leeward wing tips sticking a little bit out of the water, with the tip ventilating. Won't that add to the drag? Why don't the fly with the wing totally submerged?

[@MozzySails]

Good point! Surface piercing is a source of drag, but the reduction in area you get can make up for the losses if done well. If you can sail with some piercing it also allows you to run with more foil cant and therefore a bit more righting moment and less leeway (or even positive leeway)

[@richlatvala8143]

Love the analysis! Keep up the amazing work! Loved the comparison to other wings and loads associated. I really wonder about the F1 wings and foils in that sport since it seems to be such an adjacent sport. No idea the foils were made of steel. That is amazing. Always assumed carbon fiber but didn’t know how they were modifying them. I wonder if you can comment on how much they can “adjust” or fair the foils with resin or I dunno what? How do they treat the surfaces? Any ideas? Thanks!!!!

[@danknox9986]

Thank you.

[@TheCruisingKiwis]

How on earth do the scrutineers ensure all teams are operating within the boat build rules? It must be a nightmare to navigate.

[@MozzySails]

I think it is. Would make an interesting video on its own

[@TheCruisingKiwis]

​@@MozzySailsof imagine it is performed over multiple stages from lay up of Hull through to each piece of technology eg main sheet, self tacking jib etc

[@nils1407ify]

Does lifting foil drag give any heat differences here and there? If so than a NiTi (nikkel titanium alloy, fairly used in orthodontics) memory steal could be an option for deforming under load and spring back to designed form with less load.

[@odysseydesignandmarketing8091]

Correct me if I am wrong, but surely going down the rabbit hole adding in opposing flap to unload the the wing, would be creating more drag and become a nil some game in the end. If we think two yachts racing at the same speed across the water, for one with more drag to stay at the speed of the other, in turn means they will have add more horsepower. They all have the same sail area under the rules so the only real way to add horsepower is to have a lower VMG. So I would have thought any benefit you gain from unloading the foil wing for structural integrity, would be outweighed by a significant VMG penalty over a race...Or as the apparent wind on these boats is so far forward, can you just add more camber to the double skin main to add horsepower without the VMG penalty? Cheers Dylan.

[@garyjanssen5388]

How are things Mozzy, Ive have this saying, The bigger the Rooster tail off the back of a Motor Cross bike the more grunt they have, I seem to see the same with these amazing boats. thants

[@alleycatproductions3443]

Consistency wins championships, NZ maybe going down that wave (road)

[@merlinm69]

perhaps by reducing the torsional constraints compared to the inflection, the new New Zealand foil allows a better sensitivity, clearer, frank, of the adjustment of the angle of attack. At the same time, the elongation at the limit of the gauge and beyond when the foil is increasingly under stress allows a better oriented lift of the boat part of the T of the foil, which allows to reduce the submerged part of the external side of the T. Also the end vortex is lower with these ends more flexible in bending. in short, under the constraint of the denser isotropic material (steel) does this shape allow an easier adjustment, a condition of performance in different conditions?

[@peterebel7899]

When comparing to F16 loads: Never forget a good part of the F16's lift in high g conditions is coming out of the fuselage, not the wings. This gave an Israeli pilot the chance to even land safely after the loss of a wing! Another comparable case in Kansas, USA. So, the loads in fighter jets are by far less than in these boats.

[@stuartcudlip223]

Loved the video 👍🏻

[@SuperReasonable]

Talking twist, forward sweep and ellipse, look at a modern glider wing. The wings on my aircraft for example are 28m in span and we have no problem with twist and that’s with a max speed of 142 knots. For that reason I simply don’t believe the foils have a twist problem. It’s more about foil area/induced drag, the right angle of attack controlled by the flaps, chord or thickness and tip vortex control.

[@barrypope4358]

The density of sea water is constant, however air density dissipates with altitude. To compare aerodynamics to hydrodynamics is just not the same. The F16 wing is designed to function at low speed at low altitude and high speed at high altitude with all the inclusive variables and loading. You cant change out the wings. Apples and Oranges really, regardless of scale.

[@MozzySails]

All very true. But, it's not really true to say that because these wings are relatively low, they are low load. That's clearly not true.

[@noahhume9743]

I have a question. Most of the racing venues have both natural and human debris in the water. What happens when one of these foil strikes of floating log? or maybe what do you think the largest object is that they could strike without damage?

[@Cruising_Pamela_B]

I never realised the foils were steel - I guess I just assumed they had to be carbon like the hulls and mast. I was always anticipating the first foil strike on a tree branch or log in the water and the carnage that would follow as the carbon fails on impact. Now I know why that has never happened. But in another way they are carbon - steel being kinda carbon reinforced iron.

[@laurenceturner9346]

What about differentially hardening the steel, sounds crazy but it's been done on gears for years with surface hardening the gear to massively increase life.

[@Kiwi17714]

They are limited to certain modulus steel, so not exotic alloys or hardening techniques are allowed.

[@mcgilling]

7700kg/m2 = 75kPa. This is a similar pressure you would design house foundations for.

[@andreab2125]

Hi Mozzy, thankyou for your straordinary work for this ac campaign. Do you think that the new kiwi’s foils working with very different results in comparation with the othe challenger’s foil or for you is another street for the same target of use? If is to much different , can polarize the match: or win like 7-0 or loose like 0-7 🤪

[@8cervezas648]

I understand the design is based on a solid statistical analysis of previous years conditions but what if the wind is not as predicted? My son sails here in Barcelona and no two sept/ oct regattas have been the same year on year.

[@Robin-o3z]

GREAT QUESTION! I've been wondering about that too. Love to hear about the strategies around that.

[@julian4548]

Each team has to take a punt and tune to that. As always in a regatta is a case of “ it’s not usually like this” for some …

[@tedkeenan6803]

The question I have is how does ventilation impact the amount of twist on the forward sweep? It seems that at higher speeds NZ always sails with the weather tip out of the water. With what we know about how much they are adjusting the cant arms, this is clearly intentional. Does this minimize the impact of the forward sweep?

[@timransby1774]

The amount of lift any given wing is proportional to the square of velocity. They’re lifting the same amount of boat out of the water at speed, and poking a tip out to reduce drag would appear to make sense ( assuming there’s no drag added by doing that )

[@73engineer]

If there is no visible flap line in the etnz foil and it seems like there is a carbon skin that covers the “steel” foil, I would have a guess that they are using a hydraulic bladder, or using the carbon as the bladder between the steel and carbon skin to alter the camber of the foil, effectively working as a flap to change the foil section, not sure what the rules say about morphing foils or how they have termed morphing foils if there have in the rules, is an idea I have had over the years for creating and eliminating flaps and mechanisms under the water

[@skeetamacgyver1821]

Hi Mozza, how much articulation do you think the flaps have at the trailing edge of the foils. Are we talking about ? Is it 1 mm or 10mm or 100mm? It must be quite modest given the nature of the construction.

[@grantjchristie]

You could harden the steel which would make a huge difference in the foil strength. No need to add cf skins… it would make the foil brittle??

[@tkiers2603]

Hey Mozzy, I got a question about the mast rotation of the D-section. Does the D-section also twist higher up the mast like sail twists out, or is it straight all the way up? If so that would seem like it would create a sharp angle between the D-section and the twin sails when the top of the sail twists out, which would be against the whole point of this sail design. Or is the twist on boats with these speeds so little that the apparent wind doesn't change that much and it doesn't create a sharp angle between the mast and sails?

[@MozzySails]

Yes, it goes straight up with little twist. So down at the bottom mast rotation will add depth / camber, but up higher where the leech isn't as well controlled the mast rotation can really change the AoA. This is discussed briefly in my video with North Sails / Southern Spars

[@tkiers2603]

​​@MozzySails Oh so simply put; the mast rotation is used to change the AoA in the upper section of the sail, and the traveller for the AoA of lower section of the sail?

[@MozzySails]

@@tkiers2603 yes, pretty much

[@NZbluesky]

BeSpoke extreme loading!

[@Silvius.2]

In rules written thats separate flap sections are forbidden? And in rules must both sides of foils be same shape.

[@MozzySails]

@Silvius.2 both sides must be identical (mirror). But they are permitted multiple flap segments on each side.

[@Robin-o3z]

I'm completely clueless about much of what is referenced here and in the discussions; but you are clear that Team New Zealand has a significantly different foil - even just from appearance in that it is the only one with forward sweeping - and that it might improve speeds in the mid range while limiting top side. My question is, is it too late or is it possible for other teams to change their foils? Could they now mimic Team New Zealand or - as it were - has that boat sailed already?

[@Kiwi17714]

Too late. Teams can only change less than 20% of the mass of the foil after they are built.

[@nine8three310]

Way too late.

[@real2gone]

@@nine8three310 The tyranny of distance from New Zealand to the rest of the world, is often times beneficial. Slow fruit boats can help.

[@Kiwi17714]

@@real2gone it's almost like they planned it that way.

[@Robin-o3z]

@@Kiwi17714 thanks for the replies guys.

[@robertspelman-marriott2366]

Mozzy, thanks for answering foil material question. I’ve a reasonable source which tells me Ineos used a titanium billet; any reason this could not be true?

[@MozzySails]

Well, I would think steel because it's heavier and they need to get weight in to the wings to meet the rule. Titanium would then mean putting more weight (volume) in elsewhere

[@Dschickler]

Rudder/elevator?

[@robertspelman-marriott2366]

@@MozzySails possibly…. I don’t know the answer. These are all question post cup which would be nice to have an answer to… you always end up with myths and legend post cup which are never known; might be a good follow up! ;)

[@rbcg105]

@@Dschickler Stainless Steel. Seen it on the bed

[@BlueJazzBoyNZ]

I was wondering are the rule measurements taken when unloaded, static load. and have teams used F1 Tech to change the foil profile when under dynamic load.. Arh so no.. But clever mind's...

[@floodo1]

Juan K famous indeed

[@chrisauld7630]

ETNZ foils seem to be working ok…

[@riverebro]

Do the teams have to stay on there foils in the two minuet prior to start or could they play dead please answer

[@riverebro]

Does nobody know

[@MozzySails]

they don't have to. But once off the foils they are sitting ducks for penalties and it also take a lot of time to get up and flying again so they'd risk missing the start

[@greybuckleton]

I still feel like you are incorrectly labelling this forward sweep. In aircraft this would be called trailing edge taper. Trailing edge taper has been on aircraft since 1940, it's not a structural problem. I understand there is some similarity, but I feel it has sent you down a rabbit hole of forward sweep structural problems rather than the more likely answer of taper for favourable pressure distribution. I know you talked to this in the video, but in the previous video you talked about the experimental fighters with forward sweep and all the problems they had, not just any aircraft where the quarter cord moves forward (Which is many), and didn't have structural issues. The P40 is an example from 1938.

[@sukocoimam4519]

Nope what the guys say aircraft (I do recon he refer to jet plane) loading is more structural loading is for.. moment of force (distance x force) not just simply divide gross weight vs wing area. structural load on foil is less because simply the short (from point of structure to the tip) .. and yes density of water is wa 800-1000 x of air, but also the provide support as normal force (the cancel each others) so as stuctural less complicated. Speed, presure, temperature, density variaton.. range operation on aircraft also wider so they more complex (on a jet plane, not glider) .. yes the main differ is cavitation, but sice human knowledge are not improving since Reynold make te table.. this section (we still using reynold number for fuild dynamic- less accurated more specific condition- but easy to calculate) we still trial and error.

[@honahwikeepa2115]

ETNZ using Russian SU 47 Berkut Fighter Jet swept forward wing technology.

[@joshmolloy1280]

So a comment from you in this video saying the foil that Orient Express has before the cut off, are you referring to a foil that isn't race foils that ETNZ has? Many videos of the French team commented that it is a sister ship of the Kiwi teams boat, and they were expecting kiwis race foils to be added. Do the rules now say they can't get these foils?

[@MozzySails]

They seem to have a kiwi design from around November 2023 on the foils whereas etnz foils are more similar to the test foil from January this year. It's the only real difference between boats, bit I am sure both will be developed over the coming months

[@julian4548]

Well maybe it won’t be an advantage but great to see etnz has thrown the ball a little further. Again. Sadly not a common mind set in much of nz.

[@tullochgorum6323]

It seems unfair that TNZ are able to optimise their foil for late season conditions, while the other teams have to focus on qualification. Do the rules prevent the challenger from changing their foils for the final?

[@jaaaaapor]

Some videos ago you did a big teaser about ineos possibly having their rudder pulling down and contributing to the righting moment. What came of this hypothesis?

[@MozzySails]

Basically wrong. Although the mechanics could be possible, because they are limited with centre of gravity postion they can't always be producing downforce. When the rudder was mounted it had the elevator behind the vertical, so further back toward the transom

[@paulhammett1]

As ever this was interesting but doesn’t mention the elephant in the room. The NZ foil bend issue is only relevant if their foils and not the others are bending. It could well be that neither theirs or the others bend as they operate within the design tolerance. TNZ wrote the rules don’t forget so perhaps they had a mind to allow flexibility to do this design path when they wrote the rules. If that’s true then the bending foil issue isn’t an issue at all.

[@MckayGeoff]

Hey Mozzy, does Orient Express have same foils as etnz?

[@real2gone]

Looks like an earlier iteration from ETNZ's LEQ12 (AC40) development programme.

[@Silvius.2]

Maybe or hopefully u watched video from Vittorio d Albertas about kiwi foils🤷. Your friend was very quickly telling this not working.... Most teams go to limits and calculated all hundreds times.... like alinghi broken mast they found out where to mutch load or failure. ..

[@SailFlyTri]

Thanks for discussing my comment. I mean to say the forward sweep of TNZ is not extreme enough to cause extreme twisting load requirements. Steel and carbon should easily be able to handle the loads, but it might help with cavitation in the tips due to flow direction control from the tip towards the root vs rear swept designs. My guess is that what they are shooting for. Extreme fighter designs like the X29 had a forward sweep of 35 degrees and the Russian SU47 was around 45 degrees and at those levels of sweep the twist control material dynamics must have been very extreme. I completely agree the wing loading is high on the AC boats but I also think the forward sweep of TNZ is around 2-4 degrees at most. Just enough to begin slightly reversing the flow towards root. Maybe just enough to stop the cavitation problem or at least create a slower stall condition for better consistency during maneuvers such as tacks. kzbin.info/www/bejne/rHvcnKVngraNZrc

[@rhendersbee685]

Weeds?

[@karlw7764]

Why are you assuming these foils have torsional stiffness issues? All this planform stuff will be dwarfed by the hinge drag. Water is about 700 times more dense than air, so the wing loading will differ by that factor to aircraft wings. But that is why these are milled from solid steel, whereas aircraft wings are not. All pretty basic. The use of pre-stored power for flap actuation makes this whole circus a lot less interesting. Unfortunate cop-out. Funny how Moth guys managed to work out a real, no-stored-energy system, but huge teams with supercomputers cannot.

[@Dschickler]

Again, look at the magnitude of the loads: moth v AC40/75. Moth is not a model except in flight balance for the AC75, also not for hinge drag.

[@Lennyfromwork]

So boring! A good prestart move or hard luff from the right position at the start can ruin any teams day and win races. Every challengers foil designers from the last cup should be embarrassed.