Fly Higher. Travel Faster. Last Longer. - Part Three
by John Curnow, Sail-World.com AUS Editor 9 Sep 00:30 PDT
Gitana 18 during offshore testing © Yann Riou
In Part One of Fly Higher. Travel Faster. Last Longer. we got to see just how different Gitana 18 is, and most importantly, why so. Part Two raised the stakes, literally, by seeing how much higher Gitana 18 will fly, and at what speeds.
OK. It's finale time - bring on the next set of sub-headings...
New Owner's Manual
In terms of high speed work, particularly in the Southern Ocean, you just can't help get the feeling that what Gitana 18 is going to experience is going to be something that no one else has seen to date. Caudrelier states, "We are designed to go to have a better experience in the South, because it's designed to go in the sea states and to perform more in the waves. Safety is part of the performance, because the limit sometimes is safety. When you feel uncomfortable to 40 knots, you reduce the speed, but if you can go on, why not?"
"We've done everything to design this boat to go around the planet. This is the goal. We would have probably done a different boat if it was only to cross the Atlantic on the Route du Rhum. Some opponents have done some boats, I think, which are really performing well, but would struggle to go around the planet. You have to make some choices. When you want to go in the big sea states, the big South means always take some weight, so as to have a more reliable system. It's against performance, but this Gitana 18 was really designed to break the Jules Verne Trophy."
Most people maybe can't get their head around or don't care about 1,000nm, point to point, in a 24-hour period, because they're used to monohull type numbers, but this is more like a car-type number. At our speed limit here in Australia, that's Brisbane to Melbourne. Alternatively, if Charles took off from Brittany with Gitana 18 bound for Portugal, and Sebastien went by car, it would be Charles that would get there first and have to wait!
Sainson commented, "I think it's something one day. If we had the time in the programme, we'd go ahead of a front somewhere, and as discussed, this boat is designed to be easier, faster, and not lose control. So, if you chose your weather, it will take you three and a half, four days to go across the Atlantic. (Editor: which is at the speedier end of the Great Liners' efforts). Gitana 17 was between six and seven, just to deliver her back home from Guadeloupe.
Capturing learnings
Everything is crucial for the programme moving forward. So, what's the net?
Sainson said, "The design side is always the complex period for the first year or two, because you're in between a phase where you have to make the boat reliable, and when it arrives it needs tweaks. Obviously we keep our secrets and we don't show everything, but sometimes you think you're going to be working on the evolution of a foil, for example, and you're spending your time working on how to get the one you already have to work."
"We have a big design office, and in 18 months we're going around the world. So, if we want an upgrade on a foil, rudder or something, we have to design it now because it's going to take a year. In short, it's a balance between making the boat we have now go as fast as possible as it is, without forgetting to innovate and continue thinking on what we could change to the boat."
"So, we have to work well with Charles and the team to get the boat as it is to work as quickly as possible, so that they give us the best feedback on the problems and also the positives, which will help to deliver the playbook in the shortest time possible. Don't forget, that after the Route du Rhum, we'll bring the boat back in the shed for four or five months, and we need to have something to do. If we don't design everything now, well, the guys in the shed will have nothing to do this winter. I think this is really something that's very important in our project."
"I further think it's one of the main sources of performance and of the team's success with Gitana 17 is that when we launched that boat in 2017, people were looking at us and for two years were a bit like, 'I'm not sure it's working'. We were always looking ahead and confident that we'd manage to get that boat working. It's the same with Gitana 18. Our biggest gain compared to the others that are going to come with new boats in a few years (Banque Populaire), is to keep the two or three years advance that we have already, and for that we need to continue innovating. They're going to launch it in three years. If we do nothing, they're going to launch the same boat on us, and one year later, maybe they catch up."
"It comes down to getting the boat you have to be reliable, but at the same time thinking ahead and marching forward."
Underpinning this is a file trace system, as well as no less than 800 sensors on board. AI helps them to organise the data, and therefore understand it quicker. For every sailing day in the design office there is at least one or two souls tasked with going through the data, looking at what's changed, trying to find trends between settings for the sailors, and Sainson knows that is really important to do that work, constantly. Why?
Because we'll get the playbook faster. Yes. And if I get the playbook faster, we can get the new design quicker.
No manure (or, This is the real foie gras!)
Rags moulded with North Sails 3Di do not move. The shape is 'locked in', as Julien Pilate, Director of the North Sails FRA Design Office, says. Yet here's a vessel where everything 'folds', articulates, retracts and more, also noting that there are multiple degrees available for and of each, therein. Initially, you would be like, 'Hey! Wait a minute. That's two ends of the spectrum?' Essentially it is, for Pilate's first answer to that very question was both yes, and no.
So, pull the pens out of the pocket protector, get the HP scientific calculator fired up, and make sure there are lots of spare lead cartridges in the propelling pencil. Time to nerd up! It also needs to be stated that the team for North Sails in both the UK and France for this project was comprised of Olivier Douillard in the lead as the Project Manager/Sail Designer, with Design Services (CFD and aeromodelling) from Jeremy Elliott, Tono Martinez, Dominic Mortimer, and Jean Truffier, as we'll as of Pilate.
In regard to the aspect of being 'locked in', and inherently changing the flying shape, Pilate stated, "A useful parallel is an aircraft wing. At high speed, the wing is optimised for lift-to-drag (L/D) efficiency. During takeoff, however, it is morphed to increase the lift coefficient (CL), compensating for the lower airspeed, and keeping the aircraft airborne."
That's very true, and if you look at Interceptors like General Dynamics' F-111 Aardvark, and Grumman's F-14 Tomcat. The swing-wings were forward for low speed lift and manoeuvrability, and back for lower drag when they punched out to Mach 2.5, and 2.34, respectively, which is way faster than a General Purpose Fighter like say the F-35 Lightning II at Mach 1.6
Back to Pilate then, who sates, "The same principle applies to mast bend. Adjusting mast bend changes the sail depth (Ed - namely via those incredible spreaders), effectively adding another degree of freedom to the aero package. With 3Di, and the North Design Suite software, we can engineer the soft composite structure to sustain the required strains, whilst maintaining an efficient flying shape across the entire operating range."
To make that all a little bit more real world, people in the window seats of a commercial airliner will note that the flaps (trailing edge), and slats (leading edge) of the wings are extended (between say zero and 25 degrees) for maximum lift when going slow, such as take off and landing, when the kerosene canary far more resembles a brick, than an aluminium Romeo Y Julieta cigar case.
The physics is the line between the bottom edges is far shorter than the path the air has to travel over the 'hump' that is now the upper surface. There's your lift, and it is also why you find the throttles of the turbines well advanced whenever the aircraft is in this configuration. Stall in this situation, and you cannot just throw the clutch in with the left leg, then roll on in Angel Gear. She's a no good, mate. Like really!
Other nuggets
Deformation not defamation. 3DI is about 'locking it in', but it's also about having the deformed shape that we like. It is what we're trying to do with the America's Cup, and also Gitana Team - being able to increase the range of the sail by deforming the sail shape. So, the word 'performance' is back, and it is about a much bigger groove.
"The mechanism that allows us to increase the mast bend is through the spreaders. Southern Spars has developed a diamond concept where you've got hydraulic rams on the spreaders, and you can change the swept back angle of the spreaders. By increasing the swept back angle, you are playing with the load vector through the spreaders and through the cables, which will force the mast to bend. When the mast is bending it's going to pull the cloth, so the luff of the main sail will be pulled forward, and effectively this will flatten the sail. Why do we want to generate a flatter main sail? So you are able to carry the sail at a higher upwind speed, meaning you can take a reef later, which is one advantage, and the other is decreasing the drag to a flatter profile, which can create some substantial gain at a low AWA."
"I call foiling boats 'rewarding boats', because small improvement can translate in big gains. For example tweaking some hydro or aero setups can change quickly the boat balance which can result in substantial gains. The opposite can be also true: a failure in one system can have significant impact on the boat performance."
In short, the beauty of it all is comes down to 3Di allowing far greater control over the nature and scope of any deformation, thereby coming straight back to best performance, overall, which as you have seen by now is THE complete name of the game here.
In front of the stick, it is a all about matching the headsail to the various stages of the mainsail, via the different furlers, and then the amount of pressure applied through the tack, as well as the application of Helix structured luffs for load sharing. The difference is that the jibs in AC have full battens, which don't go so well with furlers required by mammoth ocean going tris.
Possibly the biggest point to note here is that unlike the AC, it is not about holding a certain AWA, but more SOG, like 40 knots upwind. This of course goes to the route evil, drive versus drag, which we set up with the wing discussion earlier. Boat hits a wave, decelerates smartly by 10 or 15 knots, AWA rapidly and dramatically increases from say 15 to up to say 35 degrees momentarily, and a blade won't get you going again fast enough without a serious change of shape.
For what it is worth, the AC75 will race with an AWA of 12 to 19, whereas the Ultim has to work from 15 to maybe 17 or 18, but out to say 80 degrees when it is required.
This is why you might see the luff of a flying headsail flapping, and you have to find a trim that's not an average, but is optimal, and crucially it takes into account those apparent wind angle variations. "We also take that into account when we design the sail, because we are actually investigating different design that allows us to have the best design across a variation of apparent wind angle and speed," added Pilate.
Remember too, that it is not just AWA to factor in, but up and down range in TWS, as well. You need the power to get going again, but as soon as you've done that, you need to get rid of it. Pilate refers to this as like giving the engine an extra gear. Think about it in terms of being available to avoid having to put a slab in, just because for a couple of hours it might get a bit breezier. It is not one manoeuvre you have avoided, but two, for there is the shake afterwards to consider.
Speed and other forces
In other words, not just outright speed, but also rolling average. If it was car racing, one less pitstop can make a huge difference to the final outcome!!!
Now let's ponder how Gitana 18 is going to fly somewhere between 500 and 750mm higher, and a thing called centre of effort. Now yes, there will be fewer friction stops when the boat slams into waves, but stilts are stilts.
"Typically you try to lower it as much as possible, but you just have to make sure the increase of drag from the foils will not be too high, because it's all about the balance. There is no general rule, but you try obviously to lower the CE in order to increase your driving force, but this lowering of the CE will make the foil to warp harder, and as a consequence they generate more drag, meaning you are going to lose performance. This is the reason why we use the VPP, and also the simulator to quantify this effect."
"You have to marry the aero part and the hydro part, because they have to talk to each other. This is the key," added Pilate. "We're driven by performances. That's in our DNA, and having customers that are always keen to push the limit is quite exciting."
The Gitana 18 trilogy is now complete. Thank you for being a crucial part of Sail-World.com
Want more? Well here is the link to the Gitana Team channel, and below is a list of the great content you can find there -
Flying Offshore Web Series
This series captures the high-stakes journey of the Maxi Edmond de Rothschild as the team prepares to defend their Route du Rhum title.
Episode 1: In the Beginning - The transition from carbon reality to the liquid element as the boat hits the water.
Episode 2: Step by Step - The technical "first steps" involving rigorous stress-testing of the latest foils and rig.
Episode 3: Ehe Sailor and the Machine - A deep dive into the physical and mental preparation required for Charles Caudrelier to master the high-tech 32-meter giant
Episode 4: First foil, first flights | Flying Offshore - A behind the scenes look as the team head out offshore to try foiling for the first time on the first foil
Episode 5: The first lessons learned | Flying Offshore - Season 4 - Since the launch of the Maxi Edmond de Rothschild on 14 February, the team has been getting to know their new flying maxi-trimaran — and with it, a host of new, sometimes entirely unprecedented, challenges.
Episode 6: Turning to Offshore | Flying Offshore, Season 4 - Turning thousands of hours of onshore work into concrete offshore sensations takes time, method and commitment.
DNA Web Series
This series delves into the entire creation process of the Gitana 18, from the initial concept and design to the final manufacturing.
Episode 1: Conception - Focuses on the initial design and the hydro/aerodynamic risks taken during the project.
Episode 2: Construction - Details the physical building phase of the vessel.
Episode 3: Artistic Identity - Explores the visual and aesthetic design and the "kinetic" livery.
Episode 4: Du Virtuel au Réel - Features the transition from digital models to the physical boat.
Episode 5: Expertise Internationale - Highlights the innovation hub in Lorient and specialized testing tools.
Episode 6: Teamwork - Showcases collaboration between the hydraulics, electronics, and design departments.
Episode 7: Reveal - The official unveiling of the finished Maxi Edmond de Rothschild.
John Curnow
Sail-World.com AUS Editor