AC40: Getting Technical with Dan Bernasconi

Hinzugefügt: 2026-05-22

[00:00:00]We've had plenty of chances to take a look at an AC40 before. We've seen them racing on the water. We've even been able to get up close, but never have we been able to get up close with one of the people that is responsible for designing and seeing this boat come to fruition. So, Dan Bulisone, thank you so much for taking the time this morning to talk us through. Um, I mean, this is this is your baby, right?

[00:00:21]>> Yeah. Um, we designed this as part of the design team. Um, so yeah, I mean, I one one off the team. Yeah, I know you don't want to take the full credit and I totally go for that. Is it all right to go down and take a look?

[00:00:32]>> So, I think the first thing that I just want to kind of ask you about >> just how it looks so different from any boat at any dinghy park, any yacht club.

[00:00:42]I mean, there's a marine around there. I can't see. I mean, there's one winch, but that's just to haul up some of the systems that's going to come off the boat. Did you design this with aerodynamics in mind?

[00:00:53]>> Yeah, totally. Um, I mean, the boat spends hopefully most of its time racing above the water. So, it's mainly about aerodynamics. It's about a really clean deck. Um, sealing the main cell down to the deck. And >> And why is that? Why why do you want to seal that main cell down to the deck?

[00:01:10]Cuz we see it on the 75s as well.

[00:01:12]>> Yeah. Um, I mean, just like on a on a any sailing yacht, on a dinghy, you're trying to seal the seal the sail down to the deck as much as possible. um you effectively want the sail to look bigger than it is. You you have high pressure on one side of the sail, low pressure on the other side of the sail, and any path that there is for that high pressure to leak under the sail and get round to the other side is bad for efficiency. So you want to seal the the sail down to the deck. And then what you also see under the boat, you've got along the center line and particularly on the 75s, we we call it a SKG, which is sort of a a knife edge um that runs all the way along and >> down the center line where the left side joins the right side.

[00:01:55]>> That's sort of a continuation of the sail. You're just trying to stop as much air flow as possible coming from the high pressure side to the low pressure side. Um, so you're sealing to the deck and then you're continuing and trying to seal that to the water. If if you could sail perfectly on absolutely flat water, you wouldn't have any gap. You'd be just just touching that SKG down to the water.

[00:02:18]>> Right. So So we look at that hole and we look at that sail, but what you're looking at is one thing, one object flowing through the breeze.

[00:02:26]>> Yeah. So when we look at the boat in in um what CFD we call it computational fluid dynamics, we're looking at the aerodynamics. You you can't look at the sail or the boat in isolation. You have to model it right from the start as a complete package of >> sail plus boat and the water surface.

[00:02:44]And it's how that works as a package and how how the lift and drag and the ratio of the the lift drag ratio how how that works when you put it all together.

[00:02:54]That's important.

[00:02:54]>> Right. Okay. So I it's pretty space age this this boat and obviously there's loads of things that are similar to the 75. There's loads of things that are different. One thing that it's different is that if the boat behaves itself, it's very much working with you as in there's got quite a lot of automation.

[00:03:12]>> Um and if I'm understanding the rules correctly, this boat can measure where it is in space relative to the water, relative to the wind, and it can make decisions. The AC75 you can't.

[00:03:24]>> That's right. Yeah. So, there's what we call an IMU, inertial motion unit in the the middle of the boat, which is a pretty expensive bit of kit, which has accelerometers and solid state gyros in it, and that detects the the angle of the boat, the rotational velocity. Um, and then coupled with that, we've got an ultrasonic ride height sensor on the bow sprit that measures the distance from the bow sprit to the water. You stick it all together and you you do some maths, put it through some what's called a calman filter and out of that you get an estimate um 50 times a second of exactly how high the boat is above the water.

[00:04:02]That then feeds into an algorithm uh that controls the foil flap. So when it's in autopilot mode, um the foil flap is continually adjusting um along with the the rudder rake. Essentially, when you're foiling, you've got two control surfaces. Um, two two inputs to control the the two outputs, which are effectively ride height and and trim or pitch. So, we're controlling the rudder rake, which is the angle of the the rudder elevator.

[00:04:33]>> The rudder when it comes down, you've got that that fall in the bottom that doesn't have a flap on it. It's the whole swing.

[00:04:38]>> So, if you see here, there's a there's a bearing down there.

[00:04:42]>> Hang on. Hang on. I'm going to be good.

[00:04:43]I'm going to take off my shoes and I'm going to jump on.

[00:04:46]>> Cool. It's a bit bit more of a step than I wanted. Okay. Can I touch that?

[00:04:51]>> Yeah, you can touch that.

[00:04:53]>> So, oh, I see. So, here the the whole rudder is pivoting um for aft and I mean it's rotating in a that's the top of the rudder.

[00:05:02]>> Yay. I see.

[00:05:03]>> So, the rudder rotates in your like a normal rudder, but it also pivots for around that lower bearing. Yeah.

[00:05:11]>> Um the upper bearing is in in here. Um what you can see here is the end of a a car.

[00:05:18]>> Yeah.

[00:05:19]>> So this has got um hydraulic it's got twin twin hydraulic cylinders on it.

[00:05:23]>> Oh. So a piston in here and a piston in here.

[00:05:25]>> And that that moves the the top of the rudder um forward after and that changes the whole angle which changes the angle of attack on the the Tpiece the elevator. So, so this here is media station camera, but actually this frame here is the p is where the force is being applied to.

[00:05:44]>> Exactly. So, we we've kind of got a bit of a tripod here.

[00:05:46]>> Um, we got this and the these are the two parts that are taking most of the load and transferring that rudder load back into the hole.

[00:05:52]>> So, that bearing down there, that takes a hell of a lot of force.

[00:05:57]That takes a hell of a lot of wallop when you when you pitch pole and it desperately tries to kind of fight against it.

[00:06:03]>> Yeah, that's right. The autopilot's using what we call an MPC, a model predictive controller, which sort of has a physics model of the boat uh internally. And so in sort of many times a second, it's predicting what is the most optimal trajectory uh for the boat to get from its current position back to a stable position.

[00:06:26]>> Um and it's then saying, okay, this is the best trajectory. These are the control inputs I need to put to get to that. Let's make those controlled adjustments, set off on the new course, and then straight away into the next iteration, take another set of measurements, work out where you are in space, do another trajectory optimization, >> and apply the next.

[00:06:45]>> So, it's not just a case of the sensor says you are high, go lower. Oh, you are low, go high. It's like, well, you're this high and this is happening, and that might be going on. So it's it's trying to replicate, I guess, the decisions that a sailor would do when they look out and they go, "Well, I'm high, but actually there's a bit of this coming or there's a little bit of that happen."

[00:07:03]>> Yeah. So So many times a second, it's actually saying, "What is going to happen over the next 2 seconds?"

[00:07:10]>> Why?

[00:07:11]>> Um what what do I think is going to happen over the next two seconds? What is the optimal rudder and flap that I could put in the trajectory of those rudders and flaps over the next two seconds to get me back to a stable ride height? What it then does is it says, "Okay, over those next two seconds, that's what I should do, but I'm just going to look at what it does in the first tenth of a second, and I'm going to apply that rudder and that flap because everything might have changed next time. Next time it does the same again." So, it's never actually getting to the end of that 2 seconds, but it's always predicting looking ahead and saying, "What should I do so that if everything happens as I expect in two seconds time, I'll be in a really good position." What's fascinating about that is the fact that as we've just said >> the AC75 rules don't allow that to happen. So it's a really interesting insight as to oh we need a computer to do that on the AC40 but on the AC75 you got to find a different way. Is it is it all right to set on the deck >> here? Yeah.

[00:08:08]>> Where does that system not work?

[00:08:12]>> What we don't have on the yacht is is something that's looking ahead at the waves that are coming. So, a really good sailor can actually do better in some cases than a an autopilot because they can say, "Okay, there's a wave coming."

[00:08:26]Before I get to that, I want to change my ride height or change my flap angle so that when I hit that wave, rather than going up and starting to adjust when I see the reaction, I can adjust before that. And, you know, that's that's what sailors do. They they look ahead, look at gusts, they trim the sails before they feel the effect of the gust. Whereas on this system, you've got your sonic sensor at the bow. And so the most sort of ahead you are is from the foils to there, which I guess you're doing 35 40 knots. That's not very far at all. That's a fraction of a second.

[00:08:58]>> Yeah. I mean, that's why we have the the ride height sensor on the bow, not on the transom, but you know, ideally you you'd have it further >> even further out.

[00:09:06]>> Okay. So it's in the waves is when the sailors have to get a little smart with the autopilot system and have to try and kind of coax it through its weaknesses.

[00:09:16]>> Yeah. I mean in the AC40 they don't really have the option to do that. The AC40 it it is a an autopilot boat. um you you can control you can say I want it to sail um 100 mil lower or 100 mil higher um or at a different trim angle but you can't you're not actually controlling the flap live like you are on the AC75s and the reason for that is I mean there's two reasons one primary one is that we wanted to make the boat a bit more accessible and it's it's a difficult skill to learn um particularly for the the youth and women's teams that don't get a lot of time in these boats um for them to be able to get fully up to speed with and being able to control that really well is would be a really tough challenge with with limited onwater time. The other thing is that as boats get smaller that the the speed of which things happen gets quicker.

[00:10:06]>> Um so it it gets harder and harder to control um a boat manually. Like you go down to the size of a moth that that would be impossible to control manually.

[00:10:16]Um but everything slows down as you get bigger so it gets easier. That's the automation and that it's impressive and I think is a really interesting window open into the 75. What I'm also interested in is like the other aspects of this boat that just feel really different and for one of them for me don't fall down that big hole now. One of them for me is like the the Mar system. So you've got twin main sails, twin skins. There isn't a wing that we've seen in the past with the America's Cup of Foiling boats as well.

[00:10:47]Why the twin sails? that obviously give you some benefits in this setup over a wing. What are they?

[00:10:53]>> Yeah, it's it's about um aerodynamic efficiency again, right?

[00:10:58]>> Um so if you've got a mast, I mean your mast has to have some thickness. It has to carry the the loads of the sail and the riding moment. So you need you need a certain thickness. If you've just got a a single skin coming behind that, you've got all this area um on either side of that sail. And whether that's a round tube or a D section like this, you you've got that area which is effectively slowing the boat down.

[00:11:23]You've got you've got low pressure here.

[00:11:25]It's not pushing. So you've got high pressure on the front of the mast and you haven't got anything counteracting that. And that's why um high performance single sail single main sill boats have have more of an air foil section. And that that compensates to some extent, but it doesn't get anything like the efficiency that you get from this twin skin.

[00:11:44]>> So let let me just make sure I've understood you correctly. You you realized that you needed to have a thicker, wider mask with some stiffness >> and then because of that you realized you had to go double skin, not the other way around.

[00:11:57]>> Well, any mask needs thickness, right?

[00:12:00]And so I'd say it might be more the other way around that because because you have got double skin it's all wrapped up in >> I know you go around the design loop and you go around the design loop.

[00:12:11]>> So because because you have got twin skins then you're not nearly as limited on the thickness. That means you can go thicker and you can go lighter because >> um trying to get the same strength out of a mast which is thinner uh you need a lot of laminate. I mean this this mast is is super light. Um it's just it's got, you know, thin thin sandwich structure over the the whole D section.

[00:12:35]>> Um so it it enables you to have a lightweight rig. Um you carrying the weight of two main sails obviously. Um but it's really about aerodynamic efficiency.

[00:12:44]>> We'd seen wing sails before. So when wing sails came back in, it was kind of Yeah. Okay. Can I have them on a plane?

[00:12:50]Can I have them on various things? The twin the twin main sail was one that I'm trying to wrap my brain. I'm trying to sort of see it. Who was it that first kind of suggested it in a meeting and was it a case of well of course we'll go twin main or did someone say it and they went well you you bar me?

[00:13:05]>> No, we debated it quite a long time on the for the 75s. Um and we even looked at more extreme options of having a >> what were some of the ones that got rejected >> like a a double element um hoistable main cell.

[00:13:19]>> So in in takeoff conditions where you want to really maximize the lift coefficient having a a double element helps. It allows you to achieve higher lift coefficient.

[00:13:28]>> What do you mean by double element?

[00:13:29]Sorry.

[00:13:30]>> Um so like um a wing where you've got one element here and then a second nose section and a slot a slot between them.

[00:13:39]>> Why I see.

[00:13:40]>> Yeah. Um cuz I think that that's a very interesting thing for I think for people to understand when they're trimming this is how when you are trying to take off to a certain extent you're you're dealing with very different air flow.

[00:13:52]>> Yeah. And then you take off and then rapidly that wind angle changes, everything changes and suddenly you want something else.

[00:13:58]>> That's right. The sailors have got a lot on at that point of takeoff because the boat's accelerating very quickly. Um the course wind angle, the true wind angle is changing quickly. Um so you need to be able to convert the sail from a very high lift device to a very efficient lower lift device.

[00:14:14]>> Yeah. Right. Um, so yeah, that's that's sort of the where the hydraulics are working the hardest.

[00:14:19]>> And I'm guessing a a sail skin, a material allows you to make some of those changes in a way potentially that a wing wouldn't. You know, you you can't turn off the top of the sail on a wing.

[00:14:29]It's still it's still there.

[00:14:31]>> Yeah. I mean, you can control the twist in some wing setups. And um what I mean a lot of the design process in the sales and the the cell control systems is about being able to manage that the twist and the camber and the angle of attack accurately. Um I think the the twin skin main sail you know is now at a point where you you can control it really well and and you you can depower it. Um you know you you see here is the Cunningham system. So that's so so so I mean I I love the fact that this is really space age and I love the fact I look at it and everything's carbon weave and it's all you know your brain powers all over along with the rest of your team but there's still Yeah. You got to get it in this feeder.

[00:15:10]>> Yeah, you got to some things that don't change.

[00:15:13]>> Yeah. Yeah. Some things that don't change. So it's one heliard that comes down. You connect both up and you just put them up and then you you clip onto this.

[00:15:20]>> Exactly. So this is um this twin tracks here.

[00:15:23]>> Right. She fix the downhole of the cunningham of of both skins and you can adjust that hydraulically. And then at the the back of the boat there, um you can see that's the the clue control in the main sheet assembly.

[00:15:36]>> That's a big ram.

[00:15:38]>> Yeah. Yeah. So it's the main sheet uh ram and then you can adjust the position which is kind of like an out hole. The equivalent of an out hole. Um >> it's still a sailing boat.

[00:15:47]>> It's still a sailing boat, right? You still sort of go I've got to ease the main sheet.

[00:15:51]>> It's got a main sheet. It's got a traveler. It's got a cutting. It's got an out hole.

[00:15:54]>> Yeah. The speed at which the sailors do normal things is pretty impressive.

[00:16:00]>> Yeah. And because they've got the hydraulic control, everything at their fingertips, they they sort of got the capability to make all those adjustments pretty much simultaneously.

[00:16:10]>> You know, you haven't got to get a line onto a winch. Um you haven't got to point your winch handle this.

[00:16:15]>> Yeah. Yeah. Yeah. So, if and I'm not going to do this.

[00:16:20]How much would I need to move one of the sensors on this boat to move the gyroscope or something? How much would I have to nudge it, breathe on it, cough on it in order for the boat to think that it was sailing at this angle rather than that angle? How sensitive is the equipment?

[00:16:37]>> The the IMU, which is is down inside the the body of the boat, um I mean the the calibration of that is incredibly sensitive. And I mean, if if that was a little bit loose, then the boat would literally fall out of the sky. Yeah. I mean, it would just, you know, if if it rotates a fraction of a degree, you you've got a problem.

[00:16:56]>> And then what about just tell me about the um uh the batteries and everything that you've got on board this boat?

[00:17:03]Because it feels like a lot of the technology that we're seeing going up into the 75 has been tried and tested onto the on the 40. And part of me wonders whether when are we going to start seeing some of that technology coming down, you know, when are we going to get to the point where you go, "Oh, you don't need a winch handle. You just have this and the hydraulics are here, you know."

[00:17:20]>> Yeah. I mean, the batteries are a big part of these boats and the 75s now, particularly with no cyclers on board, right?

[00:17:26]>> Um, so yeah, and it's it's uh an area that we work closely with battery suppliers on to find um the best types of batteries. Um it's a really harsh environment. These batteries are being lifted in and out of the boats every day getting salt spray on them.

[00:17:40]>> Do you ever get a fire?

[00:17:41]>> It has happened. Yeah. There's a one of the um GB1 boats is is known as Crispy um because it had a pretty nasty fire incident um in the last campaign. I mean, they they they rescued it and brought it back to life, but it's now the heaviest AC40 in the fleet because of the repairs that gone on. So, we're all ballasting up. the the rule allows sort of up to a limit. I mean, the weight weight is the most important lever you've got on these boats. So, it's crucial that when we're racing, they're all exactly the same weight.

[00:18:13]Otherwise, one team would just sail away with it. So, at the moment, we're all ballasting up to the weight of Crispy.

[00:18:18]>> What's your tolerance?

[00:18:19]>> Um, I mean, the the all up sailing weight of these boats is around 2 tons, 2,000 kg. Um, the difference between the lightest and the heaviest, I think, is around 20 kilos. So, about 1 1% of the boat weight.

[00:18:30]>> So, not not much at all. And then the crew is also equalized as well.

[00:18:34]>> Yeah, that's right. So, um the crew weigh in um they weighed in yesterday um with all their gear. Uh actually two two configurations of gear. Sort of >> a sunny day and a cold day. Um and then you ballast up. So, uh if if you're a light crew member, then you you carry 15 kilos of lead under your seat.

[00:18:56]>> Right. Okay.

[00:18:58]So because otherwise you just get all the heavy people on one side on starboard.

[00:19:02]>> Yeah.

[00:19:02]>> Give you a pretty strong start.

[00:19:03]>> I mean and again just that that that same standard sailing system of hike a little faster, hike a little harder and you know you'll go better. Obviously we don't have the um the possibility to do this.

[00:19:14]>> Well, they they can actually in the in the takeoff crew allowed to get out of the boat.

[00:19:19]>> So this is where we see them going going out here, right?

[00:19:21]>> Yeah. These boats generate their riding moment from the foil. Um, but the foil when you're going 10 knots is doing very little. You need you need boat speed for the foil to do anything. So the the holes themselves have got pretty low form stability. I mean, you can see by the fact that we're sort of healed at a few degrees here.

[00:19:37]>> Yeah.

[00:19:38]>> Um because the holes are developed for takeoff and for aerodynamics. So the the form stability is low.

[00:19:45]>> Uh so at at that sort of 8 10 knot boat speed, it's a pretty difficult time for these boats to accelerate. And that's why you get the crew hanging out on on here. Um, as soon as you sort of get the 1214 knot that you you've got plenty of riding moment from the foil. Interesting thing you mentioned about the rudder. I mean, when we ride at the beginning of the AC75 class development, we we were sort of toying with two rudders or one rudder. Um, but having a single rudder, strong driver for that was so that if someone didn't miss them.

[00:20:17]>> It's pretty unlikely to happen now, but back in >> My god, you'd feel bad though, wouldn't you? we would and um the the 75s were a lot more open you know they they didn't have those deep cockpits right at the beginning and we you know it's hard to predict the direction the class will go in but um yeah I think it was the right decision and actually you know you're faster by only having one rudder uh it's harder to control but um it's one less thing in the water it's one design you seen anyone doing anything that you go well that's in the rules like that's fine like you're allowed to do that but that's making your boat a little different and and And and hats off to them. Like that's good. And I'm asking you this because it's a loaded question because I have I've seen some people doing something and you go, "Oh, really?

[00:21:00]Oh, >> what have you seen?"

[00:21:02]>> I was sworn to sec. But to the point where to me, I'm not talking like, "Oh, we've got a bigger sale or we've bent the foils or we've done what like something that you go really does that make a little difference?" it.

[00:21:13]>> No, there's some there's some uh very live topics right now and there's you know on the one side we've got everyone going out sailing every day on the other we've got a whole lot of rule issues and um debates back and forth.

[00:21:27]>> Oh with with complaints >> with the measurer. Yeah.

[00:21:29]>> Right. Oh >> so that's very live and um >> so who's been naughty?

[00:21:35]>> Well so one example um call them out.

[00:21:38]>> Yeah, call them out. the French. Um, there's a join between the end of the foil arm and the >> That was what I was getting at. That was what I was getting.

[00:21:47]>> The rule says you're allowed to fill the gap between the steel foil wing and the composite foil arm. It's just, you know, a 10 mil gap. You're allowed to fill that um with see or whatever. Um they went a little bit further than that and >> it comes out >> pushed that that filling the gap to actually create a little uh ridge which effectively is acting as a spray rail so that as the spray hits the foil rather than dragging along the foil surface it gets deflected out.

[00:22:15]>> Yeah.

[00:22:15]>> So I think every team saw that it was a little bit too obvious.

[00:22:18]>> Um but smart and the measurers saw it and the measurers have told them well you know you need to sort that out.

[00:22:23]Another sort of more subtle example is uh the rules the rules are incredibly tight. Like you you basically can't do anything to these boats. And I think some teams had been putting uh lubricant on the the lacks of of the main sails, which you'd say, well, that's just something normally you do just to help the sail run.

[00:22:44]>> Just to help the sale go.

[00:22:45]>> Oh, and I missed and it went onto the mast.

[00:22:47]>> Yeah. Um but but the rule doesn't allow you to put that lubricant on the sail.

[00:22:52]um it's pretty difficult position because you can't really get it off you know once it's in these these tracks. So we we're currently um just in discussion all the teams together to say okay well some teams have already done it there's not much we can do so we better change the rule to allow everyone to do it um and there is a performance advant I mean there's two there's two things there one is um it helps you get the sail down >> which oh we've got a problem with the baton I can do this in two minutes rather than three >> but the other is it it makes the cunningham more effective if if the >> if the cunningham can actually change the tension in the sail all the way you don't get any just just at the bottom And you know, it's a performance advantage.

[00:23:29]>> So, there's little things like that and that are happening all the time.

[00:23:32]>> And and is there some things that I know what your answer to this question is going to be, but I'm going to ask it anyway. Is there is there anything that you guys are doing that you're not allowed to tell me what it is, but you are doing a couple of things like that's within the rules. The measures have said it's okay, but I hope nobody else notices that we're doing it.

[00:23:47]>> No, I would say that, wouldn't I?

[00:23:49]>> Yeah, you would say that. Yeah, you would. I mean, I I like to think we're sort of the the squeaky clean team here.

[00:23:54]Um, we feel protective about the rule and hope the rule is stopping anyone exploiting anything. We wrote that rule.

[00:24:01]So, I I guess we're generally on the side of of trying to ensure everyone else is sticking to the rules that that we created.

[00:24:14]It's a soft little pack.