Vortex Cup

The University of Auckland offers a Masters course in Aeronautical Engineering and if you want to find the next generation of America’s Cup sailors then that’s probably as good a place to look as the Tauranga Yacht Club where Pete Burling cut his teeth. Understanding how vortices work at high speed to create the wind shadow or ‘shedding’ explained within the ‘Froude number’ and subsequent mathematical equation and theory is the key to winning this Cup.

In layman’s terms it’s far more simple than the university lecturers will say – get a boatlength ahead and the race is yours such is the ‘shedding’ effect on the boat behind that they may be able to keep relatively close but at the level that these crews are sailing at, no matter what the opposition does, they won’t get through. There are no passing lanes and that’s all down to wind shadow and disruption.

©ACE / Studio Borlenghi

Today proved as much. William Froude, the Devon-born, English engineer, naval architect and hydrodynamicist would have had a field day as his theory was so beautifully explained in practice. Team New Zealand and Luna Rossa shared a race apiece and left more questions on the racecourse than answers.

This is rapidly turning into a classic match up in the vein of a Nadal/Federer final on the clay at Roland Garros where everything is currently going to serve. The port entry to the start box is absolutely key and to date, all races have gone the way of the boat entering from that side such is the powerful lead position that it offers in the long haul out to the starboard starting-box boundary. Get the time-on-distance back to the line right and execute the leeward vortex inducing position and you win the race. Get it fractionally wrong as Luna Rossa did in race two and you are in a swirling world of evil gas and your race is effectively done.

Such is the level that the sailors are racing in this final, far and away above anything we’ve seen to date, and it’s the tiniest mis-execution that is deciding the outcome and leaves this regatta absolutely hanging in the balance. Set in conditions that we normal sailors would class as marginal with a desperate wind in the 7-9 knot bracket only occasionally hitting double figures and the smart money would all have been on the Italians today and their beautifully detailed steed with its rapier-fast tacking speeds and high mode that looks so satisfying to sail – oh to sail a boat that points to the moon and has speed to burn in the tacks. What a joy that must be. And after race one, acres of copy could have been filed about what a cakewalk this was looking for Luna Rossa with more of the same conditions for the rest of the weekend. We were looking at a 3-1 scoreline by the end of the day right up until the moment we weren’t.

©ACE / Studio Borlenghi

That first race was majestic for Spithill and Bruni. They hit the line with the Kiwis to leeward and enough gauge to hold out to the port boundary, tacking first in the perfect vortex position allowing them to sail in their delicious high mode and eke out to windward as they tracked along on port tack – so gassy was the trail that Te Rehutai was forced to dial away to leeward and may as well have just raised the white flag there and then and wished them well on their travels. Toodle-pip, it was a procession and so confident were the Italians in their outright boatspeed that they could sail their own race from there on in, keeping a loose cover but simply pulling away. The second upwind leg was about as close to perfection as we’re ever going to see in an America’s Cup Match. Luna Rossa hadn’t just bought a ticket, they were off to the races as they extended into an unassailable delta that silenced the massive spectator fleet, proving that Auckland was firmly shut down this sunny summer Friday.

But having witnessed the home team being effectively slaughtered in the Hauraki Colosseum, the spectator fleet were understandably notably muted. The beer didn’t taste quite as good. The sausage rolls stuck in the throat. The Prosecco was just a fraction warm. This wasn’t in the script for their nautical heroes. At 2-1 down and with Luna Rossa looking mighty, worst fears were starting to be emoted and cheeks were being sucked. To say race two was pressured, was an understatement. Burling remained upbeat in the onboard interview and it sounded like denial of the highest order but in truth, it was anything but. “Yeah we’re pleased with how the boat is going,” was what he said but whether anyone believed it, other than the team onboard, was a different matter. Luckily, they are the only ones that matter.

©ACE / Studio Borlenghi

And wow, did they perform. It was the port entry again but this time the Kiwis nailed the leeward start sucking the Italians in just a boatlength closer than the first race and with the vortices funnelling off the double-skinned mainsail like whirling dervishes it was Luna Rossa that couldn’t live in the dirty and was forced to tack off early. Team New Zealand hit the boundary on the port side and put the hammer down on the resultant speed race out to the far right hand side where the stage was set for the cross as the Italians came back on starboard. If Luna Rossa really was as rapid as we had seen in the first race then this was looking like a beautiful starboard call but in reality, these boats are so close that Team New Zealand crossed with two boatlengths to spare. A quick vortex tack beneath ensured a lead at mark one and with perhaps a click of extra downwind speed, the Kiwis could hold down to the leeward gate. One slow board drop on the final gybe into the mark by the Italians and it was goodnight. Team New Zealand sailed off into the sunset, made no mistakes and levelled the score at 2-2.

The tale of the tape was quite simply that this is too close to call. This is Formula One on the water with two works teams absolutely equal and only the pole position of the line is deciding it. Such is the starboard entry disadvantage and so small are the margins that it’s coming down to pilot judgement in milliseconds. Lewis Hamilton would be in his element.

And whilst the University of Auckland alumni would be salivating at the aerodynamics and hydrodynamics in play, the winner ultimately is going to be the talent in the afterguard that cracks the code of winning from the starboard entry. That’s where this Cup will be won. Right now it’s a straight gunfight between Pistol Pete and Pitbull and just too close to call. Two-all going into the weekend, it’s a fascinating battle of nerves, precision, execution and outstanding sailing ability.

This is going to the wire. Even the dog’s interested.

Advertise here completely free of charge. See ‘Contact’ tab for details.

8 thoughts on “Vortex Cup

  1. GO LRPP GO.
    We must get back to normal sailing. The current setup creates fascinating boats yes, but boring races. Thank your God at least they are short.
    Watch the start , go and have a beer or coffee pending your time zone, and come back for the next 80seconds an hour later.

    Liked by 1 person

  2. Understand comments about the racing, and share some nostalgia for slower yachts to spice up the contest. But these boats are magnificent and the AC has to be all about technical innovation. Winding back the clock to a flatter earth won’t be the answer. Spot on Magnus; a helm unlocking a strategy to win starboard entry will throw this match open. And perhaps a course evolution for the next cycle?

    Liked by 1 person

  3. Magnus some of us like the challenge of racing in 7-9 knots hard work but tense and testing. With regard to the racing it is a bit like watching a penalty shoot out, it looks like a case of who blinks first. That said the Kiwis have port entry if it goes to a deciding race…

    Liked by 1 person

  4. Wonder if Froude would be pleased to now see how his discoveries play out on the Hauraki Gulf!? The Rules of Vortices and the perils of “dirty air” also play out in the air races every year in Reno where 4 similar planes (usually piston engined propellor driven and nimble like Sea Furys or the P51 Mustang “Cadillac of the Sky”) fly around a circuit at dangerous speeds, distances, heights and courses. Health and Safety were not allowed a ticket of entry when Reno was set up. In 2017 or 2018 (or perhaps earlier) the organisers began miking up the protagonist pilots and putting cameras in the racing planes, mainly to expand their Youtube reach. What became apparent was that with similar engines, shapes and performance, those that followed each other closely could not overtake. Thought the sky was great and large, the shortest course around the track was in a very narrow band or airspace and dirty air was a problem although “slipstreaming” of a sort also took place so it was a trade off that led to stalemate at 418 mph. Those that got the lead usually held it. Until of course, the pilot who understood that vortices could be used to ones advantage in a turn to make in sailing terms, a “Split”, found that swinging out past and up from behind to clean air to a greater height around the course would give them an opportunity at a later point in the race to cash in that height to overtake. Although dirty air and vortices trail a wake behind the AC boats, spending as short a time in it is the rule here when coupled with speed. Listening to the pundits after 4 races of this Final, I was struck by Freddie Carrs’ observation that “we are all still learning” when it comes to what to do and when. He was a grinder in Ineos Britannia. A grinder has his head down for most of the race and he confessed to having to go back over old footage of races to see what the data was showing about these two lovely vessels in this Grand Finale. It seems to be his conclusion that the way one handles the vessel will determine who eventually comes out on top. I would concur with that. Boat speed is only possible with a good crew and the crew that will win will be the one that seeks to sail in clean air for as much time as possible.

    Liked by 1 person

  5. Woah boy! Oh man, *I* wasn’t wearing a heart monitor, but I’m sure if I had been during that final race, I would have had a higher heart rate than either Pete or Jimmy’s on-screen! That lead change had me gasping and my right foot was bouncing up and down for the whole race, I was so excited!

    I don’t have conventional red socks but I’ve been wearing a fluffy pair that are red with white polka dots.

    Liked by 1 person

  6. Who am I to get in the way of a good story line………..Sorry I am going to anyway……..When its foils and turbulent flow, including wind shadow Its all about Reynolds Number. When the boats are not foiling, then the hull in the water in displacement mode, its all about Froude number, ie. when you are making waves. So Aerodynamicists have no interest in Froude, but yacht designers use both. When you are on the foils its all Reynolds Number. Both are super simple, just three numbers in the calculation.
    If I was running an AC campaign, I would need aero and hydro people (CFD). But I would not want them to design the boat. The whole package needs a design engineer to make the hard decisions and come up with the ideas that define what the aero/hydro/structural engineers/ systems engineers/sailors are given the optimized platform package to work well within. Its a balance, formed by understanding and communication. It is still not just a numbers game, its about the balanced package of good ideas and optimization. And it will be for along time to come, or until AI truly rivals the human mind!
    Perhaps this is where Ineos, and previous British challengers have struggled. The clever British are perhaps a bit insular and as such not as good communicators, and I would say, a lot more than F1, you need more of that in yacht design. You are dealing much closer to a natural environment, wind and water, which actually makes it more complex and more of a balancing act than F1 design engineering. You need smart, well balanced and integrated engineering design to win the cup.


  7. On the subject of aerospace engineering, what do you think of the narrative in the NZ press that Rocket Lab would not exist without TNZ creating a base of local engineers experienced with aerodynamics and carbon-fiber manufacturing? It would be very apropos given all of the press during the 1995 Cup that the Black Magic campaign was “like landing on the moon” if it was true that the America’s Cup helped New Zealand have a space program.

    Liked by 1 person

Comments are closed.

%d bloggers like this: