Sail control: key differences emerge between Cup teams 

Great video Mozzy! I think you guys were hinting at this towards the end of the video, but I honestly think that sail trim and foil cant automation will be the key tech that separates the winner and loser of this cup cycle. With correctly designed automation, the potential is enormous. You can do insane things like: - Create a 'one button' tacking program that syncs foil cant, sail trim, and mast rotation perfectly through the maneuver while providing the helm with a steering angle target that they can follow. Essentially guaranteeing a perfect tack/gybe every time. You could also do the same with mark roundings. - Set up a series of perfectly optimized (computer modeled) sail trim modes that can each be accessed by the press of a single button. With the trimmer only being responsible for small adjustments for shifts/puffs/ducks etc. The possibilities are truly limitless, and in an event where being just 1 knot faster all the time gives you a massive advantage, this is really where I think the winning team will stand out.

I am not familiar with sailboat design, but I find these AC boats fascinating from an engineering standpoint. From the standpoint of wing design, being able to adjust the thickness of a wing at such low speeds (compared to aviation wings) makes huge sense. The relative speed between the air and these wings is probably similar to STOL aircraft wings. While airplanes in STOL mode are ok with drag because they have lots of available HP, clearly drag in these boats needs to be minimized. Plus EVERY airfoil has a stall speed. Check out the airfoil of Mike Patey's "Scrappy" build where he built a double leading slat design to change the wing shape to provide a wider range of air speeds with one wing (lower stall speed while maintaining a high maximum speed with low drag.) It is hard to change the thickness of an aluminum wing, so in aviation they change the chord instead. If I recall years ago NASA experimented with a variable thickness/variable shape airfoil. I think there were benefits in flight envelope, but the design was just too complex and expensive to justify the benefit. Since minimizing drag is critical in these boats, and you can't significantly change the chord, changing the camber and the thickness is all that is left. The thickness may be a second order effect, but being able to change airfoil shape for different wind speeds and angles of attack, while minimizing drag, could be a huge benefit (these are airfoils that need to generate lift at just a few knots without stalling nor significant drag, but also enjoy minimum drag while at up to 50 knots or more. Few aircraft have wings that can provide lift across a ratio of minimum stall speed to maximum speed exceeding ten. These boats need to. Clearly a minimum stall speed, and minimum drag across the entire "flight" envelope are key to winning the America's cup. And in such a tightly contested event, optimizing second and even third order effects seems justified, especially when it comes to the mainsail (wing.) So changing the foil's camber and thickness seems completely logical to me. Dave Evans

It is amazing that these foils replace a big heavy lead keel.

Yes, the AC boats are getting ever more complex; what if they used CrowdStrike and couldn't sail for the Cup? (great video. thanks!)

your coverage just keeps getting better and better, last cycle was well researched and very insightful, and this cycle youve gone even further. just watching your interviewing skills improve over the last few years has been impressive. youve been a major force in making the cup more accessible and interesting for people like me who dont have the time or interest or knowledge to pour over recon photos. other sports have full coverage of a season to keep fans interested and invested until the championships/finals, our sport, not just the cup, doesnt besides a few people like you, thank you for all of your hard work and time and knowledge, keeping both sailors and non-sailors interested in our niche and sometimes dying sport.

New zelands main sheet looks so clean.

Thanks Tom and Rob. Another deep dive into AC75 sail control systems. Much appreciated.

More education! Keep it coming. It really makes me enjoy watching the sailing even more

In 1990, I patented this wingsail system and the differential clew outhaul. I produced ultra low drag windsurf wings that could plane the board in 5 mph drafts. Good to see it used here.

On the topic of creating thickness in the sail profile between the skins... I have been rewatching the previous cup races, from the pre event onwards. And one of the main things i have noticed is that Ineos seem to not be able to create as thick of a profile in the mainsail. In particular, this seems to restrict their power production in the speed build before foiling. So, while you share good points here about creating smooth flow off the mast, i do believe that being able to create more power for takeoff is actually a key component of being able to "thicken" the profile.

One idea I had if allowed was to connect the forestay - halyard - tack round into a circular loop. With a tensioner arm to tighten the circuit/ circle. Meaning that the luff could be adjusted up and down the forestay whilst maintaining luff tension. This could be mounted under the foredeck down low. Would allow for a simpler single sheeting point at the clew on a below deck track.

Its great listening to your analergys while having a beer, An knowning that Team NZ have you guys so perplexed in there inovations

The teams and the sailors gets a vote from me. This is amazing stuff. Nobody else is doing this (they think they are 😂), so thanks 🎉

Hey guys, another great analysis. Have you noticed that team nz seem to be sailing with leeward heel quite often? Particularly in a stronger breeze. But I’ve noticed it in most conditions I’ve seen them in. Seems to be a very different mode compared to the last foiling cup cycles.

Thank you again for the best analysis available for the public 👏👏👏

jeez’ you guys are going deeper every time. good job.

Responding to Rob's point at about 2:40 about the jib head being locked in place by the halyard lock, it might be worth thinking about small hydraulic cylinders (perhaps with mechanical advantage to trade stroke for force) one at the lock, and one at the tack, moving in a coordinated way to control sheeting angle, and differentially to control luff tension.

One of theses boats and crews will have max speed in all conditions and be able to sail closer to max angles. It may fall to the simplest boat to control. 😊

I think to that first point about sheeting angles relative to forestay adjustment, I think all this other stuff is because that would first off be far too crude an adjustment in terms of actual sail shape compared to what they're chasing. They probably also want to maintain the end plating at the tack through the range of clew adjustments. HAve we seen jib cunninghams on these boats? They definitely play with those on the F50s

From my experience of sailing a Class 3 land yacht, and sailing at high apparent wind I find the following. Getting going lots of mast rotation, even in a honking blow, the mast gets you going. Then it will be a matter of sheeting the main like never before and stopping the mast over rotating. The fine trimming is often made using the traveller. Easing the main causes it to fill, create huge amounts of drag and losses boat lengths. You only ease the main when you are about to capsize, except at the windward mark and you want it to hike and are look for a huge kick to accelerate as you bear off downwind. A friend as a final year engineering project built a wing mast with double skin sail. One of the outcomes was the need to be able to trim each sail independently It was never done but I don't think other than making the windward side not look awful, and would not have been actively trimmed. On an AC main the amount of friction between the two sails as they would be touching I would have thought it very difficult to have a positive effect. The key to speed is simplifying the controls, to work in harmony (linking them). On a land yacht the main sheet and cunningham are combined, so sheeting in flattens the main.

Excellent once again - the AC organisation need both of you on the core team!

Very informative and engaging - as usual! my thnx

SO lovely and nerdy! Txs so much 4 keeping us updated on details! I learn much each time and have sailed since I was 7-8yrs

Fantastic bit of tech talk. Thanks yet again.

Thanks for posting this info. Very informative.

These AC 75,s are becoming more technical than F1 I reckon. Love it! Cheers Mozzy.

One of the few times I've really enjoyed being taught! Thanks guys.

In retrospect, the D-mast dual-skin system is an overly complex affair for the primary purpose of eliminating the separation bubble to streamline the mainsail. There are commercially available 3D sail systems that do the same thing. They aren't that much more complicated than traditional sails and have low weight. They are highly adjustable for more camber and don't require a special airfoil mast at all. The main reason for the high performance of the AC75 is the tiny hydrodynamic drag and righting moment afforded by the articulating foil arm design, not the rig design. If the AC75 class is going to be retained for at least one more cycle, I think a simplification of the mainsail system is in order.

As a long time sailor and engineer I'm intrigued by the topic of linked controls. The engineer side is fascinated about linking sail and foil controls to enable modes. With automation I can foresee push button settings. My sailor side sees this as taking away from the art of sailing. As a skipper you are constantly receiving feedback to adjust modes. Now that will be taken away and given to a computer. Rob's point that should this system fail you are "stuffed".

Excellent illustration graphics. Also, I had to chuckle at the comment about American Magic using "off the shelf" jib clew hydraulics - show me where you can buy something like that!

Outstanding analysis ! Thanks guys

Well done both of you, very informative. Can you have a dense smoke dispenser coming out of the mast D section to show laminar flow along the skin?….as in an aircraft design wind tunnel

Another great analysis. Imho: the problem is that too many engineers and not enough sailors are providing input to their innovation...true sailors know that the predominant rule in sailing efficacy is KISS.

When did jobs stop overlapping mains? They did on 12m, and still on the IACC boats in Valencia in 2007. In the first foiling cats in 2013 there looks to be no mast avoidance needed at all while taking or gybing, but I think there is a little on the 2010 big cats. Was over lap never any good? Or it's the difference between 20 knot boats and 40 knot ones?

Really interesting video, I don't agree with the comments about the extra hydraulics. It allows you more control over the aerofoil shape... that can only be a good thing. As the boat accelerates it will change everything 1000's of times.

I think the differing foil cross-sections are going to far more important than they are common, despite broad appearances.

Does the ETNZ system allow them to pump the main in light wind to help get onto the foils 🤔

Its worth bagging out the leeward skin slightly more for takeoff in marginal conditions, if you take off 2 seconds before the other boat you carry that gain of being momentarily 3x faster and also a few knots faster for the entire time you both build to maximum speed.

Amazing recon as ever

hey man i love the coverage. i search for new videos every single morning and when a new one comes out its kids out of the lounge time. i have one question ineos seem to be going down a totally different path with the jibs they are running pin head jibs it seems. any clues what they are doing.

Thanks.

Great vid thanks guys. I wonder if you can tell me: the job sails (certainly some codes) are fairly upright triangles, I would have thought guiding the airflow through the slot from foot to the highest possible point would give best lift. Why do the jobs have a bigger and bigger slot size as they go up?

Great job guys

Could you use camber control to reduce the drag of the sail at speed? Some wings have a reflex (negative) camber to delay flow separation or transition to turbulent flow.

Some footage looks like tnz is pumping the main

Could you kindly give us your thoughts about why the INEOS hull seems to have so much more windage?

Although it sure is true the jib halyard must be under high load and basically locked, this does not prevent moving the sail luff up and down the forestry… assuming its a ‘stuff-luff’ style ??

Thanks!

Thank you for the discussion on how mast rotation plays with the double skin. Really helped to understand that. Question - how are they attaching the skins to the masts? Car and track for each skin? Is there a big variation in this? And smoothing the transition to the mast?

What are your plans for covering the cup?

With a straight track you can have a longer foot of a jib.

What happened to those foiling chase boats? I only ever see RIBs in these videos...

mmm things are heating up. GET PUMPED

Where can I follow Rob? Seems like he knows a lot.

Re the sunken Bayesian and link to the AC. Someone should ask Dean Barker (if he's floating around in Barcelona) if he knows, or knew Bayesian's captain James Cutfield. I think they may have gone to high school together, or are familiar with each other via sailing. Bayesian might have been expected in Barcelona at some time during the coming months.

Why don't they place the yacht below the water line, huge stability and speed improvement?

As usual, ETNZ have the drop on the rest.

it is not sailing

needing cyclists to sail ... because rules won't allow electric motors or pumps?

"Self tacking" means not sailing the boat yourself. Pathetic. I hate these boats. They might be a hell of an exciting boat to sail on..... but the racing is terrible. Use foiling cats..... MUCH better, and closer, racing.

So much appreciate the deep dive into the sail controls. Wish you could distill them into a first principles summation.

Hey guys, another great analysis. Have you noticed that team nz seem to be sailing with leeward heel quite often? Particularly in a stronger breeze. But I’ve noticed it in most conditions I’ve seen them in. Seems to be a very different mode compared to the last foiling cup cycles.