Boats and foils comparison

Tornado-Cat

Super Anarchist
16,290
1,025
TNZ

-          My first meeting with TNZ was in 2009

-          I begain to work in 2010

-          I have aneye on everyting on the boat but works part time because busy on other projects

-          I give ideas but it’s a lot of work, you have to develop it each idea

-          I like a small team because it’s efficient, we are even too many, lots of people coding, too many, we have to keep a global vision

AC75

-          One day day Ray Davis asks me to meet Howard Spencer, willing to get a fun 40 ft.

-          I design a foiling mono

-          Ray says that the keel is too much

-          I tell him it’s possible, however we need stability

-          I remember that a french architect, Martin Defline has made two queels boats who are pretty efficient, so we can do the same thing with ballast at the end of the foil

-          It’s counter intuitive to put weight where we want a lift but calcules show it is 50% more efficient that with the keel for the same mass.

-          The project doesn’t work as too expensive

-          The Italians want a big mono for AC36, we could have a had a smaller boat for economic reasons

-          Ray Davies puts my drawing on the table, everybody laugh. He tells us: I give you one month to test the concept to test If it works in a simulator. I was not there, I did not test, Bobby tested the design and they said it was a fun concept and it works

-          They tried other concepts but came back to the initial one

AC75 rule

-          I was willing two rudder foils for better stability to avoid diagonal heel instability like the hydrotère.

-          I was against it but we went to one rudder for a good reason: to avoid cutting a crew falling in the water. That is also why the rules prevent going on the bow.

-          I did not write the rule, Dan Bernasconi did it, I gave my advices.

-          We chose a close rule to avoid mistakes, it took us a year

-          We were very reassured to see that the british model worked, simulation works but is not always reassuring.

-          We surely took some advance compared to the other teams but I don’t think it was so much

-          Once I chose a concept I like to push it to the end.

-          We got symetric foils at the end only in order to learn as much as possible

-          The bulb at the end of the foil arm is just to put ballast, it has nothing to do with hydro but with the rule

Our AC75

-          We are given a rule that I hate, the inertial stability in the harbour that imposes a wide flotation beam

-          I understand it but it was not required with the ballasted foils in the water, we did not need that. 10’17

-          I understood that it was obvious that we have to make a central tube like a trimaran hull and a wide ass for the rule and stability, I don’t think other teams understood it right away: narrow hull and wide as far on the back as possible.

-          So we have a narrow hull in the front like a trimaran and a wide ass for static stability in the harbour.

-          Not a big evolution between B1 and B2, B2 is even more like a multi

-          We want a boat easy to foil that lift the stern first and get early on the foils for lower drag asap

-          The brits were capsizing when bearing away as they could not get enough lift from the foil vs the pressure. They were afraid of the transition and they were right to have a first boat with more stability.

-          B1 was an hydro dynamic concept, B2 an aero + hydro

The foil

-          The dihedral is more equlibrated and does not require a big “shaft” that maintain the foil and which creates drag

-          On the other hand a flat design is simpler and has lower drag. Both concepts are good.

B  
I did not have time to finish the translation, here it is, really worth reading it.

Link: https://voilesetvoiliers.ouest-france.fr/regate/coupe-de-l-america/america-s-cup-guillaume-verdier-du-vendee-globe-a-la-coupe-de-l-america-sur-tous-les-fronts-16505d9a-7daf-11eb-a530-8257a05e6295?fbclid=IwAR1NxsAj3wAuWdzn6_P7iVTxshZyq76ZeZcZfnogKPj0O9F0JBzZQrROne8

What the secret of TNZ success

-          When I begun in 2010 what really asthonished me was the horizontal organization, people can speak, there is no real boss. It has advantages but it can be the mess sometimes too, nobody is responsible of anything and everybody responsible for everyting. It works with a small structure, it is not a pyramidal but horizontal structure.

-          The is no restriction to possibility to speak, sailors are integrated to the design team. They often take the decision. They are part of the design meetings.

-          When we decide the piece to design we give ourself a time table and we don’t come back on our decision, we finish the construction as decided. In other places people sometimes come back on their decisions and want modification before finish which causes further delays, not here.

-          We don’t subcontract the construction of the boat, it’s integrated in the team to we control it directly

The simulator

-          The simulator took less place that in the previous edition

-          We did less design on the simulator than the last time, we did more fondamental design

-          We modified the simulator

-          Some speak about artificial intelligence, in fact it’s not ture it’s everything but intelligent and very artificial. However we have many persons working on scripts in order to automatize the calcules

-          We use the artificial intelligence for foil profile. We give an objective of lift on a section of the foil, or an objective of ratio of lift vs drag + a few variables. We let the computer work all night, it will draw a part of the section. Then the computer tells what section is best when we give it a criteria. So in fact the machine does  what we ask it but if we think well ourself we can do the same. We have to think and not let the machines do stupidly any objective or it can be very dangerous

How do you find your ideas?

-          We learn the different knoledge in different fields like paragliders who need loft of lift or wing profile of aerobatic plane who need a lot of tolerance to the requirements.

-          We mix all that, we have to look at what is done in other fields of aerodynamics. We are lucky as we can find everything on the net now, NASA studies, European Space Agency.

-          Everything is here and for free. When I remember that when I began to work I had to go and try to buy some book in bookstores. We can even fin Excel sheets with lift/drag, cavitation calcules. All students work on that in all universities

Is there a Verdier method ?

-          No, I work from home, we are a group of architect working from home, the lock down had had no impact. I don’t like working in an office with people around, I prefer working alone.

Do you have a way to approach a project ?

-          Yes, but I can’t tell it is the good one. When I am asked to work on a design I like to work on the full project and I have a feedback loop very quickly, I draw my design very quickly. In some other methods differents persons work on different bricks of the pyramid and it takes months. For me I draw the AC boat in 3 weeks, I judge it, I see the caveouts and do another loop immediately. I want to go quickly otherwise we spend too much time on a detail and another, and another, for me I want to work on the global vision and refine it at each loop.

 
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MaxHugen

Super Anarchist
One of the issues with the current design is their rather poor or have tricky performance in the marginal light conditions.

I think they could have an out board only foil above the current foil that would lift the boat at a lower speed  say at 10knts once the wetted area declines and the speed builds it would rise above the surface sort of a ladder foil from old.

the benefit would be smaller main foils possibly and much less foil fall of angst. The light wind sailing was great but marred by some wind holes that reversed entire races in what was a bit silly at times.

ETNZ had smaller foils it was an advantage at bigger speeds probably optimized to 30knts if they were 10% smaller and the outboard foil was say 50% of the full area but built for 15knts for max lift these boats would engage more in the starter area and would be game to go slow as a tactic. luffing, or daring a hook it would be fun and light winds with patchy air did extract a good sailing race.     
You may have noticed that NZ had no more issue getting onto the foil than other teams, despite their smaller foils. They had a slightly higher AoI, around 2°, compared to ~1.5 for Ineos and LR (IMO). No doubt they had to use more flap angle too.

The problem is that more lift produces more drag. One part of the equation is acceleration, and the inertia from a mass of 7.8t plays a significant part.

That's why a Moth can get on the foils at a much lower take-off speed.

 

coercivity

Member
63
6
Auckland
yes but what about getting on and up quicker so you can slow the team behind into the entry or know that in a light patch you can stay up.

they were very careful they had the the smallest jib possible for the high speed runs so the slow stuff was tricky

 

coercivity

Member
63
6
Auckland
I think there were no teams that would not have welcomed an extra 100% foil lift at takeoff, all the racing would have been different.

A high AoA smaller but upper foil would have allowed a much harsher approach to racing.

We want aggressive competition not this pansy can't do a hook to risky in the lee BS we want passing upwind and being mowed down again downwind wild mode differences.  

We had a glimpse I want more.

Sail changing, brood reaches at 50knts, dummy tacks all that stuff and more. To much paint drying for masses.   

 
Interesting, except there was an excellent side-on video of NZ's take-off, which clearly showed that they maintained a very level pitch throughout  the maneuver. It would seem that the foil AoI of 2° (my estimate) plus flap angle were quite sufficient to get NZ foiling.

Note that at 0° pitch, NZ's canoe shaped bustle presents a minimal wetted area, and with less total drag, would enable NZ to get onto the foils no slower than any other team. IMO.

As to why "T-foils work only if they are small"...  that claim has me stumped. :unsure:
Looking at the videos and race data ETNZ looks flat pitch=0 for take off and then -2 to -4 when sailing. That seems to make sense. +2 to +4 AOA for take off plus tab would be sufficient. If its a cambered foil flying at -1 to -2 AOA  can give a higher performance Cl/Cd than sailing at 0 or +2.

Which video of the take off have you been looking at?  There is a good capture of take off from ETNZ in the Finals Race 1. I want to look at the ride height data to confirm how long it actually takes for take off.

 
Hi @erdb or anyone else on this forum. Can you get me race data from the Finals R1 in a .csv file? I want to look at the take off in more details. Plus the downwind speed in the AC Finals is impressive compared to the Prada RR. in similar breeze (12-14kn) the downwind speed has gone from 37kn to 40-42kn downwind. That's a huge improvement.  So I want to use the finals data to compare with my VPP.

As for the boats working in a wider wind range.  I wonder if allowing the foils AOA to be set at the beginning of the race day instead of being fixed when the measurement certificate is issued would allow tuning of the boat depending on the weather conditions. I.e. AOA=2 for wind speed above 12knots and increase for wind speed below

below is my VPP models comparison of an AC50 to an AC75 in 16kn. big difference in upwind performance.

image.png

 

MaxHugen

Super Anarchist
Looking at the videos and race data ETNZ looks flat pitch=0 for take off and then -2 to -4 when sailing. That seems to make sense. +2 to +4 AOA for take off plus tab would be sufficient. If its a cambered foil flying at -1 to -2 AOA  can give a higher performance Cl/Cd than sailing at 0 or +2.

Which video of the take off have you been looking at?  There is a good capture of take off from ETNZ in the Finals Race 1. I want to look at the ride height data to confirm how long it actually takes for take off.
I did see an excellent side-on video of TR taking off, I think not long after B2 was launched. It looked very level throughout.  Can't find this video, but another forum member found this one: https://youtu.be/ccpq7MeoSFk. It's not entirely side-on though.

TR foils at an average of -2° pitch, so I believe that the foil is at +2° Angle of Incidence. Once the boats are up to 30+ knots I think the foil AoA is very close to or at 0°, and only needs to use a small amount of flap angle to manage flight height.

This is my estimation of an AC75 foil profile, which I use in XFoil. I set the flap hinge at 60% from LE.

image.png

 

Rasputin22

Rasputin22
13,687
3,263
The program that Rhino was developed from (I think) was free and available last time I looked. Buggered if I can remember the name of it though, haven't had it on the last few laptops.
Rhino3D was not developed from Freeship. If you can't afford Rhino at its price then you should take up crochet.

 
I did see an excellent side-on video of TR taking off, I think not long after B2 was launched. It looked very level throughout.  Can't find this video, but another forum member found this one: https://youtu.be/ccpq7MeoSFk. It's not entirely side-on though.

TR foils at an average of -2° pitch, so I believe that the foil is at +2° Angle of Incidence. Once the boats are up to 30+ knots I think the foil AoA is very close to or at 0°, and only needs to use a small amount of flap angle to manage flight height.

This is my estimation of an AC75 foil profile, which I use in XFoil. I set the flap hinge at 60% from LE.

View attachment 438638
Good video.  Agree with an angle of incline set around +2 degrees

 
I added a simulation in Youtube about the bad air zone/wind shadow behind the AC 75: 

Upwind, there is not that much difference to the sub-wind speed case, even if the bad air zone is wider and lasts longer behind the boat. Downwind, however, the bad air zone is totally different: When foiling at several times the wind speed, the wind shadow is left in the wake as a persisting wind shift, extending nearly right behind the boat and for a long time. There is no effect to the side or to downwind of the boat, as would be in the case of a traditional yacht, sailing at sub-wind speeds. You cannot speak at all of a wind shadow in the traditional meaning.

In both cases, the influence of the bad air on the wind speed is small, while the influence of the direction of the wind is significant, nearly 30 degrees.

The performance data courtesy of AC36 telemetry https://ac36.herokuapp.com/map. The simulation was performed by WB-Sails on Dassault Systèmes XFlow XFlow | High Fidelity CFD - Dassault Systèmes® https://www.3ds.com/products-services/simulia/products/xflow/.


Comments/critics/interpretations/explanations are most welcome :)




 

Zaal

Anarchist
515
698
Italy
https://sumtozero.com/about-2/

Really interesting to see that rather than using the same simulation / CFD firm, ETNZ and LRPP actually founded it together, or something like it. 
Sorry to quote myself, maybe I got it wrong, maybe LR hired two of the founders, Mark de Gids and Davy Moyon, while Bernasconi and Jean Claude Monnin are ETNZ's. Anyway, I think this firm is "the" simulator everybody were talking about. If I remember correctly, ETNZ developed it for the 35th AC, along with some LR people (after LR retired). So maybe it's possible that they founded the company together. 

Anybody knows what happened ? 

 

Lakrass

Member
276
155
Interesting comments about early take off and cavitation, we are not done with foils development and we might see the result for the next AC cycle. And they admit taking some ideas from AC into Ultim.
Wish we could have similar visit of an AC75 (which is highly unlikely to happen).




 
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Sailbydate

Super Anarchist
11,344
3,060
Kohimarama
3 hours ago, Lakrass said:

Interesting comments about early take off and cavitation, we are not done with foils development and we might see the result for the next AC cycle. And they admit taking some ideas from AC into Ultim.
Wish we could have similar visit of an AC75 (which is highly unlikely to happen).


A very fran(c)k, Cammas. ;-)

 
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