This is a great discussion - thank you. It is mentioned that the depth of the foils below the water surface may reduce cavitation. Another important aspect may pertain to "ground effect". Airplanes obtain an induced drag reduction by flying low over the water. The water increases the mass flow influenced by the wing, reducing the air's downwash angle and induced drag. Conversely, hydrofoil induced drag may be increased by flying close to the underside of the water surface. In this case, the air reduces the mass flow influenced by the wing, increasing the water's downwash angle. This increases induced drag and diminishes lift (for a given angle of attack). Second point: It was mentioned that a wider stance is beneficial to providing heeling moment. Perhaps a laterally asymmetric planform with more area outboard would prove beneficial despite a modest increase in induced drag...
I'm a sailplane (glider) pilot, and in sailplane design things like span, aspect ratio, intersection drag, lift distribution, and tip vortices are massively important for overall efficiency (often visualized with an L/D polar). Its awesome to see the merging of sailing and flying... (I mean, sure its all fluid dynamics in the end; but its still fun to have these worlds colliding).
One topic you guys didn't discuss was the actual effect of dihedral/anhedral on the lift and roll moment. Dihedral on aircraft is used because it increases stability - when the airplane rolls away from vertical, one wing produces a greater lift vector in the vertical direction and thus tends to roll the aircraft back upright. With anhedral, the situation is reversed. On an AC75 that means the outboard foil section will be providing a greater lifting force (as its closer to horizontal); but it almost means the foil section closer to the boat will be providing less lifting force. While this does provide some roll moment (towards the windward side) that you might intuit to be a good thing, I'm not sure that the moment-arm is big enough to actually be advantageous. That roll moment is acting on the foil arm, NOT the hull; and remember how far outboard the arm is from the hull's longitudinal axis (i.e. the center of rotation when the boat heels)**. By contrast, a "T" foil will have its outboard section producing slightly less lift than the anhedral foil under the same conditions; but the inboard section of the "T" foil will be producing more lift. Depending on the mechanical, structural, and rules constraints on the foil arms this may allow the "T" foils to generate greater net lift and thus enable the boat to fly at a lower speed, and/or allow for a thinner foil section (with corresponding lower drag) at high speeds. ...Fascinating to think about! I'm sure the teams have some insane modeling and testing data around these tradeoffs. **Think of the bending loads this roll moment can put on the lower foil arm... woof!
One of the main effects of anhedral is that it changes the angle of attack of each side of the foil due to the leeway. Flat foils have the same angle of attack on both sides.
It's also interesting that only TNZ has made 5 different foils and then I guess will make a matching for the best one. Why would all the other teams cripple themselves in design options with matching pairs. Seems kind of obvious to go the TNZ way.
I love your technical view on it, Mozzy. I am following you on a regular basis. It is great for our development team to see how close the footprint of the AC75 of the defender is to iFLY philosophy. No doubt about the superiority of T-foils over L-, J, or Z-foils. One important point we found in endless test runs is stability in waves. With the T-foil travelling deep under the water surface, first there is higher pressure, and second it will travel calmly, like a submarine in a storm, despite the built sea.
Thanks guys, nice to see your faces now. I'm really enjoying your videos, and your focus on the design minutiae that is so significant in this class, thje racing has been so good and to get the chance to totally nerd out is brilliant. What a shame the BBC has so little coverage so far. Wish my dad (50 years of boat designing and building) could see your videos but unfortunately he doesn't really do the Internet and he lives in the middle of France so i can't really help him right now. Keep up the excellent work.
Facinating as ever, great insight into the technology and the science. I am sure you are all content in your respective day jobs as caped crusaders or pneumatic stage separation system specialists 🤔but if not give Graham Miller a tinkle sure he’d love to hear from you ! 🏎💨💨Go Team INEOS! ⛵️ More videos please....
Not since Aus 2 in the early 80’s have ‘keels” and ‘foils’ been talked about so much on a monohull. Amazing how the boat speeds have changed but the physics and math remain similar. Enjoying your content, and the new more personal format.
Interesting analysis of some of the design aspects of these racing machines. With a background in naval architecture as well as flying practice, I couldn't help thinking that the anhedral shape will have very different stability characteristics. Especially because the flow is not always in line with the symmetry plane of the two foil wings, there will be cross-flow along the span direction. After all the foil is not just a wing, it is also acts as a centreboard to counteract the drift force. The gravity and the drift force are not at a constant ratio as speed and course vary. The straight foil will slip more easily in cross flow condition, while for an anhedral shape the drift increases angle of attack on the inboard foil wing keeping the foil flying more straight. Incidentally, this 'flying straight' with no slip is a major task of a glider pilot optimizing the glide performance. Like you said, a myriad of parameters and requirements can lead to different design optimizations.
I also agree that cross flow should be considered in the equation. Unaligned flow would happen when tacking, for example. The V shape, as in planes, would induce a tilting moment that influences the manouvre. It's not all about top speed in a match race.
Another great video. Thought provoking and certainly adds to the enjoyment of watching how this whole thing unfolds. The ETNZ approach almost resembles the old style surface piercing foils (a la Grogono/Icarus from 40+ years ago). Whilst so much has moved on since then, presumably this also has the advantage of inherent lift stability, assuming the dreaded cavitation can be avoided?.
Good one Mozzie! As mentioned, RM is increased with the T foil, and this must be quite critical as there's not much else that can be done to enhance RM. Together with efforts to lower the CE, such as NZ's "camber adjustment device" to help power up the lower section of the main whilst depowering the top, this could make the difference between a fast boat, and another that is just one knot VMG better.
Just like RC plane technology. V- shaped control surfaces can fly an entire airplane. But most hobbiest know that a flat wing with separate pitch, yaw, and roll control surfaces is much more efficient and fun in the hands of a skilled pilot
Great job guys. One thing that does not seem to get mentioned is the lateral resistance provided by the foil/arm assembly to counter leeway. A "T" foil with a high cant angle (outer tip piercing the surface) must be providing a significant portion of the lift vector horizontally to windward, whereas a "Y" foil with the outer half of the foil roughly horizontal under the surface may be producing more upward lift but less horizontal component providing resistance to leeway. Do you think this could be a significant factor affecting windward performance?
Great stuff. A coupleof times we have seen these boats bury their noses. I'd be fascinated to know how they manage to maintain 'level flight'. Of course, airplanes manage it but they are immersed in the fluid, not at a boundary of huge density differences.
Great content, can't wait for the upcoming videos, many-many thanks for your work guys! By any chance you can tell us, where the foil drawings and diagrams such as drag breakdown, etc. are coming from? :D
Fascinating stuff. Great stuff and great format. Keep it up. Definitely learning loads and the fact that all boats have used their six allocations already does mean that there are probably winners and losers already. Let’s hope Ineos are on the right side of the equation and therefore they have the best possibility for improved development...
Really interesting and, as much as I liked your previous videos, this Q & A (with supporting illustrations) was very helpful to my better understanding of foiling in general this series in particular. Great having Tom and Rob alongside with you. Nice to not to have to stare at your logo;-)
The anhedral foil of Luna Rossa has some advantages and explains her ability to sail higher than Te Rehutai and tack and gybe with less side-slipping. First, the arrangement is not deficient in righting moment. The leverage that creates righting moment increases further out from the side of the hull. So the outer foil wing generates more righting moment than the inner. In addition, the closer that the plane of a foil wing passes through the center of effort of the sails (minus the center of the mass of the boat), the more righting moment it generates. The outer wing of an anhedral foil can be set closer to level than a flat foil and so it can create more righting moment than the inwardly canted outer wing of a flat foil, like that of Te Rehutai. Meanwhile, while the outer wing is level, the inner wing of the anhedral foil is down relatively deep and is acting much as a leeboard. To get the same combined righting moment and leeboard effects, the Te Rehutai crew must cant their entire foil. They therefore get less righting moment from their outer wings than does Luna Rossa. When tacking and gybing, the extra depth of the foils on Luna Rossa prevent the sort of side-slipping that has plagued Te Rehutai and cost her distance at mark roundings as well as upwind distance coming out of tacks. All that said, having the one outer wing do more of of the weight-lifting has required the Italian team to make their wings bigger. The New Zealand design allows for less surface area and so less drag. The New Zealand boat seems to have gone for flat-out speed (pun intended) while Italian design seeks a compromise between speed, pointing ability, and maneuverability. Te Rehutai is more of a drag racer while Luna Rossa is more the Monaco street-fighter. Te Rehutai needs to avoid getting into tacking duels with Luna Rossa. Luna Rossa needs to mix it up as much as possible, especially at the start. The action on Course C will be especially interesting, if we get there.
a Tee foil allows for one drive mechanism. sure you ""can" do this with anhedral but much more complicated mechanism. why to planes have (or don't have) anhedral ? I believe it gives some advantage when banked (or when the boat in this case is canted). with a canted boat, and therefore foil, the anhedral foils will have different angles to the water surface. I'd've thought breaking the water surface was something you really didn't want to do. boat flying height would help this. the guys are spot on ... this is all compromise, and advantage will have some cost. great post !
I think that T foil allows also a bigger and gradual statical stability along the vertical axis: the bigger foil tip surface out is, the lower lift you have which keeps distance of skeg from the water almost constant
The RM is one aspect but a T-foil configuration offers more lifting force at lower canting angles just because of the geometry. The Lift is the force perpendicular to the foil, with a V-shape, the Lift is almost a lateral force till the outer side of the foil is under water. With a T configuration when the inner side of the foil the Lift force has a much higher vertical component. But it is as always in engineering a trade off of many optimisation factors that in many cases go in opposite directions.
Thanks to all your thoughs and discussion my mind began to wonder about and one big question came to me. What about sailing with both foils in the water being the weather foil a suction tool and therefore have more sails to power the boat. Would the drag be so important there would be no extra gain. What about now that the wind will be up to 23 knots. I have no mathematical formula to make the calculations, it was just brainstorming...
Thanks for the great technical discussion. What about if the Y foils placed greater mass at the foil tip, this would bring their centre of righting moment closer to the T principle.
Looking forward to the discussion on the flaps. Seems to be a very difficult mechanical problem with any kink. Needing two flaps, one per side, adds to the complication. Any idea how they are addressing this? Good reports
Anhedral reduces stability, therefore the boat is easier to turn. Reverse gullwing gives more lift at low speed, enabling the boat to foil quicker. It could also be more effective while the boat is healed over. The straight foil is probably more efficient at speed. The "turn ups" at the ends are winglets. They effectively increase the aspect ratio of the foil, therefore efficiency by reducing tip vortices. The "cavitation/ventilation" could be the foil stalling (laminar flow breaking away from the wing). This could be used (like Concord) to lower the pressure above the foil to produce more lift at low speed. The "T" foil looks to have less cord, therefore a higher aspect ratio, = more efficient at high speed. I suspect Ineos have a big development advantage from their partnership with Merc, as they will have mature software for modeling these things.
I agree with most of this except for a few points. If NZ is sailing with surface piercing foils, they then have less righting moment, not more. And on the topic of induced drag, I'm pretty sure what counts is overall span as measured perpendicular to the overall lift vector. Or put another way, a y-foil might have a longer span if you stretch a tape measure along it, but the two halves of the foil are working against each other pulling outwards. All in all, great video, intelligent and well informed discussion
With the wings of a single foil counteracting each other, it seems there must be some contention, so a loss of efficiency. T foil (if we assume sustained flight is only ever with wings parallel to the surface of the water...can this be assumed?) has only 1 primary direction for the forces. Seems a battle between efficiency/speed and controllability. Anhedral likely provides each wing can be controlled independently, but perhaps with greater experience the less the teams need the crutch of control.
@@leuvenisaplace I'm pretty sure they cant the foil and lift force to windward as much as they dare to get lateral resistance, when sailing to windward, because there's very little of the vertical foil arm in the water. Much like the Mothies heel to windward.
@@leuvenisaplace In the previous video, Mozzie said that accrdong to the class rules, the two halves of the foil need to be able to be controlled independently of each other.
@@paulgush nb. Independently of each other doesn't mean that they can't be controlled to behave in the same way at the same time. Do the foils need to operate much of the time as turning surface to control the heel of the boat? If the control surfaces allow the wing to minimise forces whilst the foil arm cants up & down, then having lift forces that counter each other isn't doing much except adding drag. These are essentially low flying aircraft, not rockets that need to articulate so much in 3 dimensions IMHO, though 3D control is likely very nice to have.
Hey Mozzy, I am doing a research paper on the America's Cup and was wondering where you got all of this data, the graphs, blueprints, etc for the hydrofoils and sails. I am hoping you see some of these comments and can point me the right direction. Thanks.
Great video guys. Could you explain in a video why we don't see more leeward heel when the boats are midway through a turn with both foils down? I would have expected a lot more heel as the windward foil which was providing righting moment when airborne is suddenly providing heeling moment when dropped in the water, or are they differentiantly trimming windward and leeward foils so both provide righting Moment? They must be I think...
Good question! The windward foil will still have weight even when submerged. But I guess your quest is whether this is negated by hydrodynamic lift which would heel the boat to leeward? I think when they drop the board like this it has almost zero angle of attack, and without flaps engaged would provide very little vertical lift. Or, with flaps inverted may even provide additional downforce. Dropping an extra board is of course a lot of extra drag, and inverting a flap to create extra downforce would be a lot of drag too. So not something you would want to be doing in a straight line, but the latter grip of an extra board certainly helps them make tighter turns and therefore sail less distance.
Very good and thank you. I am curious though, and in debate with a number of friends, to know what the equivalent HP the sails are generating to propel these beauties to 50kts? Any thoughts, scientific or otherwise, would be appreciated? Thanks.
The point on depth of foil is interesting. There is also I assume a lot of complexity from the waves even when relatively small. Looking at coverage shots from above it looks like the upper surfaces are cavitating on and off a lot. Unfortunately we can't see undersides where presumably cavitation would be disastrous which I guess is where the root discussions were centered and also previous conversation on winglets. Is there not also a major component in this discussion re lateral forces which would impact slippage from high lateral forces on rig and how this affects design.
Amazing to hear a modern reference to Sailrocket. It has been 9 years since his record and it seems like Paul Larsen is still a one man show on super cavitating foils and force aligned craft. Have you heard anything about his development of Sailrocket 3?
I dare say that with the CFD software available they could use Monte Carlo methods to determine the optimal foil configuration, but the difficult question would be against what criteria the results would be measured. How do you think they set the desired criteria to be achieved? They would have to integrate many sea/wind states and weigh them individually. Then there are the delta scenarios such as how to recover from a splash-down. Looks really complicated. What do you think?
With regard to T foils, nobody mentioned that you need to cant the foil to provide side force (to resist leeway) and I bet this is why the NZ foil tips are through the surface.
What’s the effect on the stability of the boat of the different foil geometries? Ultimate performance is great but only if you have the stability to fly the foil (and sails) optimally for as much time as possible.
I find these foils quite fascinating as each team seem to have different shapes and sizes. My question is with all the different styles, do they actually look at a say a plane or even better a bird in flight with the shape in there wings, ie diving down or say lift, which is the game in sailing where a bird hits wind when not flapping the wings/ gliding in a breeze hence more speed. No one seems to have a foil say in the shape of a birds wing gliding with no energy, but seem to absolutely take off in air speed. Just my thoughts, but to me makes sense
I guess it means you have the lift to get up but, as you lift out, the required lift required drops and therefore, that reduced lift are, also reduces drag.
Has anyone seen ETNZ last set of foils as I have not see anything yet and are you going to talk about the power plant the sail as I think this is interesting how teams have done this defiantly and where in the sail they what the power as well as boom or no boom?
Not my area of expertise, so this might be a stupid question... With the Y shape if you can control the flaps independently could you use the outboard (more horizontal) one to control the flying height/righting moment, and the inboard (more vertical) one to control how high you point?
I would like to know more about the effect of the windward foil as in the drag and how it effects on leeward or windward effort, ? Like can it be used to help pull the boat to windward
Mozzy 2 questions. Qu 1 - do any of you think that letting a foil break the surface might just be a clever way of reducing drag - by making them effectively smaller. So meaning that you can design the foils for lighter conditions...in the same way that you might lift your daggerboard/raise a centreboard in breeze in a dinghy? And Qu 2 - do the bend characterisitics of either side of each foil need to be exactly the same? So they may look the symmetrically the same, but when loaded (under the water) might it not be clever to have the outer end flexing more than an stiffer inner section? Just wonder what you all think happens at the time when it really matters (and we cannot actually see them..!!) What do you think?
1) Yes, that is exactly what ETNZ are doing. The trick is stopping ventilation whilst achieving that reduction in area. 2) The foils have to be completely symmetrical in construction. So, the only way they can get more lift one one side of the arm compared to the other is by setting the flaps different. However, ETNZ only have one flap. So even operational flap angle would appear to be symmetric
Cavitation at 50 knots is a red herring. We are rarely seeing these boats hit 50 knots so why design around avoiding cavitation when the issue may not even raise it's head, and the benefits of running cavitation susceptible foils could translate into far more significant gains elsewhere
I ware concrete boots, however, I too am fascinated by the physics involved in this format. Question, is the small foil on the rudder able to rotate akin to the elevators on the rear control surfaces of aircraft, and thus help control the pitch of the boat.
As I understand the rules there are no control surfaces on the rudder T section. Any pitch movement is controlled by adjusting the angle of rake of the complete rudder. Not sure if this is something which is adjustable during a race or is preset before a race.
Questions perhaps you know or can find the answers to: 1) Is the cant angle a design variable or a flight variable? Does the flight controller tweak it along with the foil flaps while flying? What about upwind vs downwind? 2) Do you think different foils are relatively better or worse under different wave and wind conditions? Is there any evidence that the teams are swapping out foils based on the weather forecast? 3) The cant mechanics spec talks about being able to tell it to achieve a specific cant angle, but how this is controlled is opaque. Shots of Patriot during Semi Race 4 showed only "Up" "Down" buttons. What do you know about the Cant control interface? With regard to the foil design, it seems to me that just as important as the vertical lift is the horizontal component of lift to help prevent skidding. This, if true, would point away from T shaped foils and to Y or W.
3) they must preset the 'down' position for the boat or for the conditions of the race, so the up and down buttons allow the foil arm to move to the preset position quickly in a tack.
@@stevenallan4829 I'm sure there would be a number of selectable presets that the 'down' button works to. As you suggest the righting moment required is probably less on the downwind leg. This is conjecture not backed up by evidence from the boats.
@@robingimblett2171 It seems to me that a traditional keel has two functions: righting moment and resistance to slipping. With the latter the boat just slips sideways. The righting moment is derived from the extension difference between the up and the down foils. Only the down foil provides the resistance to slippage and this is an important aspect not yet discussed.
Love the insight and analysis. Would be great to hear the commentators incorporate some of this...instead of explaining what a course boundary is or who gives way
With the anhedral designs, the outer wing is significantly improving righting moment while the inner is contributing to into-wind thrust. Do you think the lower, inboard half of the foil is trimmed out (to reduce drag and this effect) or is this a useful contribution to improving heading higher while pointing lower?
It is certainly not trimmed - the class rule says that the foil has to be symmetrical, so both wings of a foil have to be identical - same angle to the arm, same length, same shape and weight distribution. Unless I misunderstood, and by 'trimmed out' you mean that the flap on the inboard wing is trimmed (as in: adjusted) differently to the outboard one.
Has anyone tested two arms (on each side) with an elongated foil between them? It would likely eliminate the foil from vibrating, undulating (reducing speed).
Like an upside down car wing? I think the issue with this is the extra drag from the added support arms that have to reach all the way out to the end of the lifting surface. The next issue is that now you've moved the vibration from the tips of a 'half' foil to the middle of a longer foil. Pick the right harmonic and you could end up with a nasty little snap.
I am using foil to surf for a while .SINCE 2001 . We are going to use more a high aspect ratio . Now we are coming back to a medium aspect ratio . . But both with more a T Design . The discussion is long and there are man issues . But this view of the foil is only part of the design . On the surf we saw that the T design you can take out the tip of the foil from the water and the foil keep the lift . On more y foil or Anhedral you can not take out the tip of the water . You loose all the lift and you have a ventilation and loose the lift . But this is part of all the problem
Interference drag is not really about cavitation. It is about drag. And you have to look at the change in lift distribution away from optimal with the anhedral foil if the flaps run at different angles.
To what extent do the rules allow the teams to control the position of the cant arms (how far down/up the arm swings)? Also are they allowed to make small adjust the cant arm height while the foil is flying in the water (almost like trimming the sail in the wind)?
when it's up, it has to be in a 'stowed' position. However, when down, it can be at any angle they like. They can make small adjustments to cant angle whilst flying, however, the foil cant system (FCS) is glitchy and not really designed for this. So, the teams tend to minimise changes to cant, running a few degrees more cant upwind compared to downwind.
Is a "V" or "M" (upside down "W") allowable? It would mean shorter foils but allows at high speed the outer leg comes out at a fast rate to allow less drag but also extends the righting moment centre distance further outside?
It's allowed. The downside to the these configurations is basically a more extreme version of T, in that it increases frontal area and further decreases the angle the wings meets with the foil arm intersection.
T foil theoretically has better righting moment through the cant arm. Lift is pushing up at the angle of the cant. V foils have to be run more vertically
Team NZ has more data history than the other teams. Keep in mind the reason we have foiling boats now is because team NZ tested and got the first cats on foils but were caught foiling 2 years before the actual race. Most teams at that time werent sure it was even possible.
I think that with the t foil you have higher induced drag and higher profile drag, cause you have the biggest surface area (at same cord length) considering the longer arm (and that extra piece underwater does not make any lift, only drag), but is interesting the half submerged mechanics, that could actually make the difference. I found it extremely difficult to operate though, cause if all the profile stay underwater u can maybe think that the force is only function of speed, flap angle ad boat yaw angle, but if a part of that foil is gonna be out of the water that force will be first fluctuating (cause waves) and second dependent on how much foil is underwater. And I have a question, does the induced drag half if the tip of the profile get out of the water?
Some of the commentators were saying that the Patriot crashes in their last races might have been caused by cavitation - they were doing over 50 knots at the time.
If as I suspect, they are using cavitation (ie: stalling the foil) to reduce the pressure above the foil and produce more lift at low speed. A sudden increase in lift a 50 mph wouldn't be conducive to keeping the foil in the water.
A picture in your presentation show water spilling out of a hole just behind the starboard foil. Where is it coming from and why would they want water in the foil or is it coming from a different source?
You did some videos on the crew roles for each team but I think because of the AM crash you forgot to do ETNZ. Are you still planning to do that video?
Yes, we have the ETNZ done. I was just waiting to post it until after the challenger series, when the focus will shift to the ETNZ and Cup match itself.
Pretty much the best technical coverage of the America's Cup I've seen.
Just keeps getting better! Thank you so much for doing this
This is a great discussion - thank you. It is mentioned that the depth of the foils below the water surface may reduce cavitation. Another important aspect may pertain to "ground effect". Airplanes obtain an induced drag reduction by flying low over the water. The water increases the mass flow influenced by the wing, reducing the air's downwash angle and induced drag. Conversely, hydrofoil induced drag may be increased by flying close to the underside of the water surface. In this case, the air reduces the mass flow influenced by the wing, increasing the water's downwash angle. This increases induced drag and diminishes lift (for a given angle of attack). Second point: It was mentioned that a wider stance is beneficial to providing heeling moment. Perhaps a laterally asymmetric planform with more area outboard would prove beneficial despite a modest increase in induced drag...
I'm a sailplane (glider) pilot, and in sailplane design things like span, aspect ratio, intersection drag, lift distribution, and tip vortices are massively important for overall efficiency (often visualized with an L/D polar). Its awesome to see the merging of sailing and flying... (I mean, sure its all fluid dynamics in the end; but its still fun to have these worlds colliding).
One topic you guys didn't discuss was the actual effect of dihedral/anhedral on the lift and roll moment. Dihedral on aircraft is used because it increases stability - when the airplane rolls away from vertical, one wing produces a greater lift vector in the vertical direction and thus tends to roll the aircraft back upright. With anhedral, the situation is reversed. On an AC75 that means the outboard foil section will be providing a greater lifting force (as its closer to horizontal); but it almost means the foil section closer to the boat will be providing less lifting force. While this does provide some roll moment (towards the windward side) that you might intuit to be a good thing, I'm not sure that the moment-arm is big enough to actually be advantageous. That roll moment is acting on the foil arm, NOT the hull; and remember how far outboard the arm is from the hull's longitudinal axis (i.e. the center of rotation when the boat heels)**. By contrast, a "T" foil will have its outboard section producing slightly less lift than the anhedral foil under the same conditions; but the inboard section of the "T" foil will be producing more lift. Depending on the mechanical, structural, and rules constraints on the foil arms this may allow the "T" foils to generate greater net lift and thus enable the boat to fly at a lower speed, and/or allow for a thinner foil section (with corresponding lower drag) at high speeds.
...Fascinating to think about! I'm sure the teams have some insane modeling and testing data around these tradeoffs.
**Think of the bending loads this roll moment can put on the lower foil arm... woof!
One of the main effects of anhedral is that it changes the angle of attack of each side of the foil due to the leeway. Flat foils have the same angle of attack on both sides.
It's also interesting that only TNZ has made 5 different foils and then I guess will make a matching for the best one. Why would all the other teams cripple themselves in design options with matching pairs. Seems kind of obvious to go the TNZ way.
I love your technical view on it, Mozzy. I am following you on a regular basis. It is great for our development team to see how close the footprint of the AC75 of the defender is to iFLY philosophy. No doubt about the superiority of T-foils over L-, J, or Z-foils. One important point we found in endless test runs is stability in waves. With the T-foil travelling deep under the water surface, first there is higher pressure, and second it will travel calmly, like a submarine in a storm, despite the built sea.
Great videos and insights to the AC75 and the cup. Production quality is great and these have been keeping me sane through the current GB lockdown.
Thanks guys, nice to see your faces now. I'm really enjoying your videos, and your focus on the design minutiae that is so significant in this class, thje racing has been so good and to get the chance to totally nerd out is brilliant. What a shame the BBC has so little coverage so far. Wish my dad (50 years of boat designing and building) could see your videos but unfortunately he doesn't really do the Internet and he lives in the middle of France so i can't really help him right now. Keep up the excellent work.
Thanks for getting into the weeds of alternatives to foil design. Appreciate the thoughtful effort.
Can’t get enough of these vids! Learning lots. Thanks a ton. Keep ‘em coming!
Thank you for doing a good job of balancing really technical Vs too complicated for non engineers like me. Great job.
Brilliant explanation of this design feature. A real pleasure to watch and listen. 👍🏽
Magic! Great to dig deeper into the tech. Thank you! Superb format too.
Facinating as ever, great insight into the technology and the science. I am sure you are all content in your respective day jobs as caped crusaders or pneumatic stage separation system specialists 🤔but if not give Graham Miller a tinkle sure he’d love to hear from you ! 🏎💨💨Go Team INEOS! ⛵️ More videos please....
Not since Aus 2 in the early 80’s have ‘keels” and ‘foils’ been talked about so much on a monohull. Amazing how the boat speeds have changed but the physics and math remain similar.
Enjoying your content, and the new more personal format.
Interesting analysis of some of the design aspects of these racing machines. With a background in naval architecture as well as flying practice, I couldn't help thinking that the anhedral shape will have very different stability characteristics. Especially because the flow is not always in line with the symmetry plane of the two foil wings, there will be cross-flow along the span direction. After all the foil is not just a wing, it is also acts as a centreboard to counteract the drift force. The gravity and the drift force are not at a constant ratio as speed and course vary. The straight foil will slip more easily in cross flow condition, while for an anhedral shape the drift increases angle of attack on the inboard foil wing keeping the foil flying more straight.
Incidentally, this 'flying straight' with no slip is a major task of a glider pilot optimizing the glide performance.
Like you said, a myriad of parameters and requirements can lead to different design optimizations.
I also agree that cross flow should be considered in the equation. Unaligned flow would happen when tacking, for example. The V shape, as in planes, would induce a tilting moment that influences the manouvre. It's not all about top speed in a match race.
Loving your analysis (speaking as an engineer)! Watched these races in person, they are an amazing sight to behold.
Another great video. Thought provoking and certainly adds to the enjoyment of watching how this whole thing unfolds. The ETNZ approach almost resembles the old style surface piercing foils (a la Grogono/Icarus from 40+ years ago). Whilst so much has moved on since then, presumably this also has the advantage of inherent lift stability, assuming the dreaded cavitation can be avoided?.
Good one Mozzie! As mentioned, RM is increased with the T foil, and this must be quite critical as there's not much else that can be done to enhance RM. Together with efforts to lower the CE, such as NZ's "camber adjustment device" to help power up the lower section of the main whilst depowering the top, this could make the difference between a fast boat, and another that is just one knot VMG better.
You are onto it max. Team NZ has an Imoca 60 designer onboard as part of their design team. The Imocas use huge foils for righting moment.
@@philmole5294 They just need to change the rule that prohibits foils on the rudder. For now, they have to drag their butts along.
Just like RC plane technology. V- shaped control surfaces can fly an entire airplane. But most hobbiest know that a flat wing with separate pitch, yaw, and roll control surfaces is much more efficient and fun in the hands of a skilled pilot
Brilliant explanation - the races are so much more interesting because of you guys - Thanks !
Thank you for this very interesting and civil discourse .
Great job guys.
One thing that does not seem to get mentioned is the lateral resistance provided by the foil/arm assembly to counter leeway. A "T" foil with a high cant angle (outer tip piercing the surface) must be providing a significant portion of the lift vector horizontally to windward, whereas a "Y" foil with the outer half of the foil roughly horizontal under the surface may be producing more upward lift but less horizontal component providing resistance to leeway. Do you think this could be a significant factor affecting windward performance?
Great stuff. A coupleof times we have seen these boats bury their noses. I'd be fascinated to know how they manage to maintain 'level flight'. Of course, airplanes manage it but they are immersed in the fluid, not at a boundary of huge density differences.
Great content, can't wait for the upcoming videos, many-many thanks for your work guys! By any chance you can tell us, where the foil drawings and diagrams such as drag breakdown, etc. are coming from? :D
All the talk about the foils is amazing but I haven't heard anything about the rudder. That thing looks tiny to what it is asked to do
It's probably because they're almost the same as the rudders on the cats in the past two cups?
Loving the videos down here in NZ mate!
Fascinating stuff. Great stuff and great format. Keep it up. Definitely learning loads and the fact that all boats have used their six allocations already does mean that there are probably winners and losers already. Let’s hope Ineos are on the right side of the equation and therefore they have the best possibility for improved development...
The deeper the better! (technical analysis obviously). Great analysis. Thx
Really interesting and, as much as I liked your previous videos, this Q & A (with supporting illustrations) was very helpful to my better understanding of foiling in general this series in particular. Great having Tom and Rob alongside with you. Nice to not to have to stare at your logo;-)
The anhedral foil of Luna Rossa has some advantages and explains her ability to sail higher than Te Rehutai and tack and gybe with less side-slipping. First, the arrangement is not deficient in righting moment. The leverage that creates righting moment increases further out from the side of the hull. So the outer foil wing generates more righting moment than the inner. In addition, the closer that the plane of a foil wing passes through the center of effort of the sails (minus the center of the mass of the boat), the more righting moment it generates. The outer wing of an anhedral foil can be set closer to level than a flat foil and so it can create more righting moment than the inwardly canted outer wing of a flat foil, like that of Te Rehutai. Meanwhile, while the outer wing is level, the inner wing of the anhedral foil is down relatively deep and is acting much as a leeboard. To get the same combined righting moment and leeboard effects, the Te Rehutai crew must cant their entire foil. They therefore get less righting moment from their outer wings than does Luna Rossa. When tacking and gybing, the extra depth of the foils on Luna Rossa prevent the sort of side-slipping that has plagued Te Rehutai and cost her distance at mark roundings as well as upwind distance coming out of tacks.
All that said, having the one outer wing do more of of the weight-lifting has required the Italian team to make their wings bigger. The New Zealand design allows for less surface area and so less drag. The New Zealand boat seems to have gone for flat-out speed (pun intended) while Italian design seeks a compromise between speed, pointing ability, and maneuverability. Te Rehutai is more of a drag racer while Luna Rossa is more the Monaco street-fighter. Te Rehutai needs to avoid getting into tacking duels with Luna Rossa. Luna Rossa needs to mix it up as much as possible, especially at the start. The action on Course C will be especially interesting, if we get there.
Good discussion! I have noticed this and it's pretty frustrating that no one bothered to talk about it previously!
On other great discussion. Looking forward to the platform/ bulb vs.
a Tee foil allows for one drive mechanism. sure you ""can" do this with anhedral but much more complicated mechanism.
why to planes have (or don't have) anhedral ? I believe it gives some advantage when banked (or when the boat in this case is canted).
with a canted boat, and therefore foil, the anhedral foils will have different angles to the water surface.
I'd've thought breaking the water surface was something you really didn't want to do.
boat flying height would help this.
the guys are spot on ... this is all compromise, and advantage will have some cost.
great post !
Excellent Commentary and Production values.
Very interesting discussions on foil shape. I am wondering whether shape has an effect on the drift during windwards sailing.
A change in direction uch as caused by gusts requires a change in rudder will plafe more change in force on the T foil than W.
I think that T foil allows also a bigger and gradual statical stability along the vertical axis: the bigger foil tip surface out is, the lower lift you have which keeps distance of skeg from the water almost constant
The RM is one aspect but a T-foil configuration offers more lifting force at lower canting angles just because of the geometry.
The Lift is the force perpendicular to the foil, with a V-shape, the Lift is almost a lateral force till the outer side of the foil is under water. With a T configuration when the inner side of the foil the Lift force has a much higher vertical component.
But it is as always in engineering a trade off of many optimisation factors that in many cases go in opposite directions.
Such great and learned commentary. Thanks!!!
Great conversation fellas. Thanks.
Thanks to all your thoughs and discussion my mind began to wonder about and one big question came to me. What about sailing with both foils in the water being the weather foil a suction tool and therefore have more sails to power the boat. Would the drag be so important there would be no extra gain. What about now that the wind will be up to 23 knots. I have no mathematical formula to make the calculations, it was just brainstorming...
Thanks for the great technical discussion. What about if the Y foils placed greater mass at the foil tip, this would bring their centre of righting moment closer to the T principle.
Great theorizing, interesting stuff, I looked at the Bermuda cat on the side of the building, with the footprint shaped rudder foil and wondering why
Looking forward to the discussion on the flaps. Seems to be a very difficult mechanical problem with any kink. Needing two flaps, one per side, adds to the complication. Any idea how they are addressing this? Good reports
Love your insight mate🙏wish I’d found you sooner. Great when you have discussions too✌️
The boat that creates less outrigger disturbance seems to go faster for a given speed range. Ineos was almost invisible behind the spray at Christmas.
Anhedral reduces stability, therefore the boat is easier to turn.
Reverse gullwing gives more lift at low speed, enabling the boat to foil quicker. It could also be more effective while the boat is healed over.
The straight foil is probably more efficient at speed.
The "turn ups" at the ends are winglets. They effectively increase the aspect ratio of the foil, therefore efficiency by reducing tip vortices.
The "cavitation/ventilation" could be the foil stalling (laminar flow breaking away from the wing). This could be used (like Concord) to lower the pressure above the foil to produce more lift at low speed.
The "T" foil looks to have less cord, therefore a higher aspect ratio, = more efficient at high speed.
I suspect Ineos have a big development advantage from their partnership with Merc, as they will have mature software for modeling these things.
When ETNZ foil with the tip out what's stopping the air getting sucked all the way down the T foil surface?
I agree with most of this except for a few points. If NZ is sailing with surface piercing foils, they then have less righting moment, not more. And on the topic of induced drag, I'm pretty sure what counts is overall span as measured perpendicular to the overall lift vector. Or put another way, a y-foil might have a longer span if you stretch a tape measure along it, but the two halves of the foil are working against each other pulling outwards. All in all, great video, intelligent and well informed discussion
With the wings of a single foil counteracting each other, it seems there must be some contention, so a loss of efficiency. T foil (if we assume sustained flight is only ever with wings parallel to the surface of the water...can this be assumed?) has only 1 primary direction for the forces. Seems a battle between efficiency/speed and controllability. Anhedral likely provides each wing can be controlled independently, but perhaps with greater experience the less the teams need the crutch of control.
@@leuvenisaplace I'm pretty sure they cant the foil and lift force to windward as much as they dare to get lateral resistance, when sailing to windward, because there's very little of the vertical foil arm in the water. Much like the Mothies heel to windward.
@@leuvenisaplace In the previous video, Mozzie said that accrdong to the class rules, the two halves of the foil need to be able to be controlled independently of each other.
@@paulgush nb. Independently of each other doesn't mean that they can't be controlled to behave in the same way at the same time. Do the foils need to operate much of the time as turning surface to control the heel of the boat? If the control surfaces allow the wing to minimise forces whilst the foil arm cants up & down, then having lift forces that counter each other isn't doing much except adding drag. These are essentially low flying aircraft, not rockets that need to articulate so much in 3 dimensions IMHO, though 3D control is likely very nice to have.
Hey Mozzy, I am doing a research paper on the America's Cup and was wondering where you got all of this data, the graphs, blueprints, etc for the hydrofoils and sails. I am hoping you see some of these comments and can point me the right direction. Thanks.
Great video guys. Could you explain in a video why we don't see more leeward heel when the boats are midway through a turn with both foils down? I would have expected a lot more heel as the windward foil which was providing righting moment when airborne is suddenly providing heeling moment when dropped in the water, or are they differentiantly trimming windward and leeward foils so both provide righting Moment? They must be I think...
Good question! The windward foil will still have weight even when submerged. But I guess your quest is whether this is negated by hydrodynamic lift which would heel the boat to leeward? I think when they drop the board like this it has almost zero angle of attack, and without flaps engaged would provide very little vertical lift. Or, with flaps inverted may even provide additional downforce.
Dropping an extra board is of course a lot of extra drag, and inverting a flap to create extra downforce would be a lot of drag too. So not something you would want to be doing in a straight line, but the latter grip of an extra board certainly helps them make tighter turns and therefore sail less distance.
Really great commentary, thank you. Keep it up!
Very good and thank you. I am curious though, and in debate with a number of friends, to know what the equivalent HP the sails are generating to propel these beauties to 50kts? Any thoughts, scientific or otherwise, would be appreciated? Thanks.
The point on depth of foil is interesting. There is also I assume a lot of complexity from the waves even when relatively small. Looking at coverage shots from above it looks like the upper surfaces are cavitating on and off a lot. Unfortunately we can't see undersides where presumably cavitation would be disastrous which I guess is where the root discussions were centered and also previous conversation on winglets. Is there not also a major component in this discussion re lateral forces which would impact slippage from high lateral forces on rig and how this affects design.
Another great video, thanks once again.
Amazing to hear a modern reference to Sailrocket. It has been 9 years since his record and it seems like Paul Larsen is still a one man show on super cavitating foils and force aligned craft. Have you heard anything about his development of Sailrocket 3?
I dare say that with the CFD software available they could use Monte Carlo methods to determine the optimal foil configuration, but the difficult question would be against what criteria the results would be measured. How do you think they set the desired criteria to be achieved? They would have to integrate many sea/wind states and weigh them individually. Then there are the delta scenarios such as how to recover from a splash-down. Looks really complicated. What do you think?
Excellent discussion for us laymen.
Where do you get your data feed and graphics for your videos?
With regard to T foils, nobody mentioned that you need to cant the foil to provide side force (to resist leeway) and I bet this is why the NZ foil tips are through the surface.
Interesting to know if the reduced drag outweighs the loss of lift?
INIOS, well she's trimming like never before, wonderful fore n aft attitude
What’s the effect on the stability of the boat of the different foil geometries? Ultimate performance is great but only if you have the stability to fly the foil (and sails) optimally for as much time as possible.
I find these foils quite fascinating as each team seem to have different shapes and sizes. My question is with all the different styles, do they actually look at a say a plane or even better a bird in flight with the shape in there wings, ie diving down or say lift, which is the game in sailing where a bird hits wind when not flapping the wings/ gliding in a breeze hence more speed. No one seems to have a foil say in the shape of a birds wing gliding with no energy, but seem to absolutely take off in air speed. Just my thoughts, but to me makes sense
I guess it means you have the lift to get up but, as you lift out, the required lift required drops and therefore, that reduced lift are, also reduces drag.
Has anyone seen ETNZ last set of foils as I have not see anything yet and are you going to talk about the power plant the sail as I think this is interesting how teams have done this defiantly and where in the sail they what the power as well as boom or no boom?
hi, why not a parabolic foil / anchor shaped foil? would that work?
Not my area of expertise, so this might be a stupid question... With the Y shape if you can control the flaps independently could you use the outboard (more horizontal) one to control the flying height/righting moment, and the inboard (more vertical) one to control how high you point?
Really interesting, thanks guys.
Great discussion, thanks.
I would like to know more about the effect of the windward foil as in the drag and how it effects on leeward or windward effort, ? Like can it be used to help pull the boat to windward
Mozzy 2 questions. Qu 1 - do any of you think that letting a foil break the surface might just be a clever way of reducing drag - by making them effectively smaller. So meaning that you can design the foils for lighter conditions...in the same way that you might lift your daggerboard/raise a centreboard in breeze in a dinghy? And Qu 2 - do the bend characterisitics of either side of each foil need to be exactly the same? So they may look the symmetrically the same, but when loaded (under the water) might it not be clever to have the outer end flexing more than an stiffer inner section? Just wonder what you all think happens at the time when it really matters (and we cannot actually see them..!!) What do you think?
1) Yes, that is exactly what ETNZ are doing. The trick is stopping ventilation whilst achieving that reduction in area.
2) The foils have to be completely symmetrical in construction. So, the only way they can get more lift one one side of the arm compared to the other is by setting the flaps different. However, ETNZ only have one flap. So even operational flap angle would appear to be symmetric
Cavitation at 50 knots is a red herring. We are rarely seeing these boats hit 50 knots so why design around avoiding cavitation when the issue may not even raise it's head, and the benefits of running cavitation susceptible foils could translate into far more significant gains elsewhere
fan bloddy tastic, love the granular tech
I ware concrete boots, however, I too am fascinated by the physics involved in this format. Question, is the small foil on the rudder able to rotate akin to the elevators on the rear control surfaces of aircraft, and thus help control the pitch of the boat.
As I understand the rules there are no control surfaces on the rudder T section. Any pitch movement is controlled by adjusting the angle of rake of the complete rudder. Not sure if this is something which is adjustable during a race or is preset before a race.
Questions perhaps you know or can find the answers to:
1) Is the cant angle a design variable or a flight variable? Does the flight controller tweak it along with the foil flaps while flying? What about upwind vs downwind?
2) Do you think different foils are relatively better or worse under different wave and wind conditions? Is there any evidence that the teams are swapping out foils based on the weather forecast?
3) The cant mechanics spec talks about being able to tell it to achieve a specific cant angle, but how this is controlled is opaque. Shots of Patriot during Semi Race 4 showed only "Up" "Down" buttons. What do you know about the Cant control interface?
With regard to the foil design, it seems to me that just as important as the vertical lift is the horizontal component of lift to help prevent skidding. This, if true, would point away from T shaped foils and to Y or W.
3) they must preset the 'down' position for the boat or for the conditions of the race, so the up and down buttons allow the foil arm to move to the preset position quickly in a tack.
@@robingimblett2171 So there is no upwind/downwind cant angle difference?
@@stevenallan4829 I'm sure there would be a number of selectable presets that the 'down' button works to. As you suggest the righting moment required is probably less on the downwind leg. This is conjecture not backed up by evidence from the boats.
@@robingimblett2171 It seems to me that a traditional keel has two functions: righting moment and resistance to slipping. With the latter the boat just slips sideways. The righting moment is derived from the extension difference between the up and the down foils. Only the down foil provides the resistance to slippage and this is an important aspect not yet discussed.
Excellent goldmine right here...!
Love the insight and analysis. Would be great to hear the commentators incorporate some of this...instead of explaining what a course boundary is or who gives way
With the anhedral designs, the outer wing is significantly improving righting moment while the inner is contributing to into-wind thrust. Do you think the lower, inboard half of the foil is trimmed out (to reduce drag and this effect) or is this a useful contribution to improving heading higher while pointing lower?
It is certainly not trimmed - the class rule says that the foil has to be symmetrical, so both wings of a foil have to be identical - same angle to the arm, same length, same shape and weight distribution.
Unless I misunderstood, and by 'trimmed out' you mean that the flap on the inboard wing is trimmed (as in: adjusted) differently to the outboard one.
I'd assume that a T-foil, when angled and with the outer tip just at surface level, the whole foil will not only add to lift but also improve reach?
Thanks for explaining!
Has anyone tested two arms (on each side) with an elongated foil between them? It would likely eliminate the foil from vibrating, undulating (reducing speed).
Like an upside down car wing? I think the issue with this is the extra drag from the added support arms that have to reach all the way out to the end of the lifting surface. The next issue is that now you've moved the vibration from the tips of a 'half' foil to the middle of a longer foil. Pick the right harmonic and you could end up with a nasty little snap.
I am using foil to surf for a while .SINCE 2001 . We are going to use more a high aspect ratio . Now we are coming back to a medium aspect ratio . . But both with more a T Design . The discussion is long and there are man issues . But this view of the foil is only part of the design . On the surf we saw that the T design you can take out the tip of the foil from the water and the foil keep the lift . On more y foil or Anhedral you can not take out the tip of the water . You loose all the lift and you have a ventilation and loose the lift . But this is part of all the problem
Interference drag is not really about cavitation. It is about drag. And you have to look at the change in lift distribution away from optimal with the anhedral foil if the flaps run at different angles.
Can you do a video on the sails. American magic batwing catastrophe at the weekend!
To what extent do the rules allow the teams to control the position of the cant arms (how far down/up the arm swings)? Also are they allowed to make small adjust the cant arm height while the foil is flying in the water (almost like trimming the sail in the wind)?
when it's up, it has to be in a 'stowed' position. However, when down, it can be at any angle they like. They can make small adjustments to cant angle whilst flying, however, the foil cant system (FCS) is glitchy and not really designed for this. So, the teams tend to minimise changes to cant, running a few degrees more cant upwind compared to downwind.
Is a "V" or "M" (upside down "W") allowable? It would mean shorter foils but allows at high speed the outer leg comes out at a fast rate to allow less drag but also extends the righting moment centre distance further outside?
It's allowed. The downside to the these configurations is basically a more extreme version of T, in that it increases frontal area and further decreases the angle the wings meets with the foil arm intersection.
love the TOPPER 6th Prize!
Fascinating analysis. When will you guys be designing your own AC 75? Andy UK
T foil theoretically has better righting moment through the cant arm. Lift is pushing up at the angle of the cant. V foils have to be run more vertically
Team NZ has more data history than the other teams. Keep in mind the reason we have foiling boats now is because team NZ tested and got the first cats on foils but were caught foiling 2 years before the actual race. Most teams at that time werent sure it was even possible.
I remember foiling boats being tested by members of the AYRS about 50 years ago...
I think that with the t foil you have higher induced drag and higher profile drag, cause you have the biggest surface area (at same cord length) considering the longer arm (and that extra piece underwater does not make any lift, only drag), but is interesting the half submerged mechanics, that could actually make the difference. I found it extremely difficult to operate though, cause if all the profile stay underwater u can maybe think that the force is only function of speed, flap angle ad boat yaw angle, but if a part of that foil is gonna be out of the water that force will be first fluctuating (cause waves) and second dependent on how much foil is underwater. And I have a question, does the induced drag half if the tip of the profile get out of the water?
and how did you found the induced drag and the pressure drag separately? Are those cfd results or theoretical calculations?
Great stuff!
Great insight, How can I email you guys a question?
Brilliant stuff!
Some of the commentators were saying that the Patriot crashes in their last races might have been caused by cavitation - they were doing over 50 knots at the time.
If as I suspect, they are using cavitation (ie: stalling the foil) to reduce the pressure above the foil and produce more lift at low speed.
A sudden increase in lift a 50 mph wouldn't be conducive to keeping the foil in the water.
Great content as ever
A picture in your presentation show water spilling out of a hole just behind the starboard foil. Where is it coming from and why would they want water in the foil or is it coming from a different source?
It's a drain hole for the cockpit I believe
@@MozzySails OK. thanks. The Brits had water pouring from their foils prior to the Christmas Cup races but it looks like they are all buttoned up now.
You did some videos on the crew roles for each team but I think because of the AM crash you forgot to do ETNZ. Are you still planning to do that video?
Yes, we have the ETNZ done. I was just waiting to post it until after the challenger series, when the focus will shift to the ETNZ and Cup match itself.