34th America's Cup: multihulls!

Which is why AoA should be actuated by some form of sensor rather than be fixed.

Is the forward foil on C-Fly sprung in some way, or does it just look that way because of refracition?

 

Agree, but at the same time, controlling AoA (automatically or by hand), trim momentum becomes very strong nullyfying pitch momentum.
C Fly posted by Stephen (amazing!) is roughly what I was thinking about. His builders highlight the pitch controlling behavior:
http://www.youtube.com/watch?v=KXW6D7gmBDU&feature=plcp
Anyway, some other ideas?

 

Ac 34

Lets try to keep this relevant to the AC which pitchpole is now-but pitchpole prevention is a big topic which might deserve its own thread. My take on the Oracle pitchpole is that there was probably a failure somewhere in the foil control system. The foil(s) are extremely powerful and should have been able to prevent a pitchpole.

 

Quite a good article by Richard Gladwell on sail-world.

http://www.sail-world.com/Australia/Gladwells-Line:-Oracles-options-to-get-back-into-the-Game/103265

 

34th AC- Luna Rosa "L" vs TNZ "C/L/S"

Thanks for that Corley. It amazes me that in all the articles and interviews I've read the subject of "altitude control" has never been raised. If somebody reads something along the lines of an analysis of the altitude control system on the two boats please post it here.
For now, I'm convinced that something malfunctioned on Oracles altitude control system which is what allows them to fly. With that broken they could not increase the lift on the lee hull enough to keep the windward hull out.
If the system had not had a malfunction of some sort there is no doubt whatsoever that the boat would not have pitchpoled.
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Great sailing days coming up with Luna Rosa and TNZ: TNZ will get to race against foils similar to the ones on Oracle. Not enough info to know whether or not the Luna Rosa foils are exact copies of Oracle ,bigger or smaller but what is known is that the main foil is "L" shaped. Interesting days ahead....
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More on the Luna Rosa/TNZ agreement from Scuttlebut tonight:

USEFUL OSERVATIONS

It was November 2, 2011 when the team Luna Rossa Challenge 2013 announced their Notice of Challenge for the 34th America's Cup had been accepted.
Having decided to re-enter the Cup arena quite late, Italian team boss
Patrizio Bertelli said the challenge would not have been viable without the
technical design sharing arrangement they had engaged with Emirates Team
New Zealand. The two teams entered an agreement to build identical boats
and conduct trial races against each other in Auckland over the next five
or six months of the southern hemisphere summer.
"The objective is for us both to get to the Louis Vuitton Cup finals and
then we will beat each other up on the water," Bertelli said. "We have two
virtually identical boats that can be mutually beneficial. We can compare
boats and improve boats better that way than in isolation. It is going to
be very interesting."
The plan appears brilliant from the outside. The Protocol for the 34th
America's Cup restricts teams from having more than one boat until
February, so this arrangement allows the New Zealand and Italian teams to
get an earlier gauge on their performance through comparative testing.
When the agreement was announced last year, there was concern among the
other team that it violated Protocol rules. However, the Jury disagreed,
issuing their decision on February 13, 2012. With both the Kiwis and
Italians now having their boats launched, it is expected this relationship
will now be closely scrutinized.
"We still contend the Jury has allowed these teams to circumvent a training
rule that has been in the Protocol since 2000," commented Artemis Racing
(SWE) CEO Paul Cayard. "What Patrizio is saying they will do is exactly
what our team and defender Oracle Team USA had asserted in the jury case in
February. However, the Jury ruled that you can't 'observe' anything useful
for design or performance in sailing, a hard to understand ruling which
allows the protection for their deal."
While the team's are not allowed to share performance data, it is suspected
their two-boat testing program will provide valuable dividends similar to
the type of training commonly conducted in one design classes. "Ask any
Olympian whether they or their coaches can benefit from observing a
competitor," noted Cayard."Of course there's a benefit. Same is true for AC
yachts, especially ones from the same design."
With the Koreans looking unlikely to 'graduate' from the AC45 to the AC72,
Challenger of Record Artemis Racing is the lone challenger on the outside
of this alliance. Or perhaps, will we see another alliance as the Swedish
team crosses tacks with the defender on San Francisco Bay?Source: http://www.sailingscuttlebutt.com/archived_Detail.asp?key=5063

 

You might be right, but I don't think this is obviously true. Are there accounts that support this theory?

 

34th AC

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No, just my theory based on what I've learned. It could be said to be "obviously true" because the pitchpole happened.
There are the comments that have been posted where one of the Oracle head honchos specifically stated that the design relied on the foils to prevent a pitchpole in a bearaway...

 

Hi Doug - I'm not sure how the foils can prevent a pitchpole (PP). The daggerboard is near the centre of gravity in the current arrangment. The boat CG has to be aft of the daggerboard. The daggerboard is providing the majority of the lift. As it does not have a trim tab its response time will be quite slow. This is because the entire foil has to be rotated to trim it. The rudder is the obvious element to trim the platform but that is difficult under the rules. Observing 17 and TNZ they seem to be very different in terms of steadiness. 17 has never been really steady in the videos I've seen. Back to the PP. Once the boat starts pitching, if the CG moves past the daggerboard then the weight of the boat plus the sailing load overturning moment wants to pitchpole the boat. 1) I can't see how the foils can provide a restoring moment, the only chance is using the rudder and I don't see how this can be done, especially since it is now out of the water 2) The bouyancy force (bouyancy is always up) is the only restoring moment in the system. 17 is very slender fwd and as we have seen does not have enough bouyancy in this condition. From watching videos of many multis PP,ing it seems to me about 45degs is the critical angle. So if the designers figured out the sinkage and CG etc at 45degs the only thing left is the sail drive moment. This is up to the operator. If the bear away provides more pitching moment then this design point, its going over. If the bearaway provides less then this moment it will recover. Its operator error, it may not have been intentional error its was new territory and they now should have a better feel for the edges. In an interview of some time ago Spithall was asked to explain about how not to PP the AC45 and he said the main had to be eased. I believe this is wrong the main has to be pulled in to depower (in a bear away) not eased which increases the pitching moment. It would be tough trying to sheet in an AC72 in that situation. This points to the facts that the sytem is not "automatic" and needs operator input & judgment. Peter

 

Hi All - Plus its an interesting hindsight that the AC72 club voted to remove the use of the small rig. In draught 1.0 they had a small rig and a big rig. It would have been sensible to remove the small rig but require the big rig to be able top be split like they have added a panel to the AC45. This would have allowed a training rig and a heavy air rig. Its also interesting that hydroptere is much wider then an AC72 yet its rig is much smaller. The diagonal righting stiffness or moment of the AC72 is not much compared to its rig. The AC72 has an enormous rig and its not very wide (overall beam) Its a very very overpowered boat and must be handled with the outmost of respect. Its like a lorry with a very high load going around a tight corner too fast (foils or no foils) Peter

 

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I'm not convinced of that, Peter. The daggerboard on Oracle is further fwd than it is on TNZ. And if 17 is designed like most multifoilers I am familiar with then the daggerboard supports about 80% of the total weight which means the center of lift of the daggerboard foil is ahead of the boat CG.
It's my contention that the foil control system failed on 17 or the boat wouldn't have pitchpoled. One of their top guys said that they relied on the foils to prevent a pitchpole. So, that would probably mean the control system failed. I think that they have some sort of push-pull rod connected near the top of the foil trunk and that they can very quickly move the top of the foil fore and aft-as they would have to to be able to reliably fly manually. The mainfoils are incredibly powerful and I'm pretty sure that the pitchpole would have been averted had something not malfunctioned.
An example of moving the whole foil in a smaller system is the Hobie Trifoiler that has long "feelers" out front connected directly to the foils.
Sooner or later we'll get the real scoop on what happened and why but thats my tentative conclusion for now.

 

An interview with Iain Murray ostensibly about the new rig on the Channel 7, 18 footer skiff but also discuss San Francisco AC.

 

There's no need of a greate pitch angle to get CG and Lift Force vertically aligned (see my rough sketch, over a F. Chevalier drawing). When in a pitch angle, rudders get nearest surface and loose their righting power.
Lifting daggerboards are powerful at high speed, but any small loose of speed makes them stall (lift varies with velocity squared). Anyway, after certain pitch angle, central lifting-force will not right the boat but, on the contrary, it will contribute to capsize it. At the same time, while in a bearaway, a sudden braking caused by the stall and hull landing, can increase pressure on the windward side of the wing.
From pictures, Oracle17, Lunarossa and NZ all have their front-edge daggerboards at 42-47% of hull LOA from the bow. Not so different. So probably NZ has better skills and/or materials...
25 knots is not an extreme condition, my feeling is that this incident will not be the last one, unless something changes. Untill now, we are just talking about a cup of millons and no personal injuries. So, I hope I'm wrong...

 

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Well done with the illustration! If the foil control system was working properly it is my opinion that the boat would never reach that angle.

 

They could have stalled it pulling it back......which is a crew malfunction. Not having a boat with reserves is a design error....Are they going to accept the crash test and modify the design or try the same thing again? The America's Cup has a long tradition of drastic modifications to fix problems or attempt to speed things up and I think this occasion warrants such development. If it was the Boatdesign race boat and we were on a budget we'd be suggesting modifications .....so lets make suggestions. Adding height to the bows is one approach, a pod forward could help with buoyancy and the excessive twist, then there are the foils.....the Luna/NZ testing should sort that one out, what they need is a better platform to handle the variables. A design that needs foils to bear away is pretty silly considering the new ground. The boats are already oversquare as they pitchpole before capsizing. Could weight be saved on beam to bring them back to a 50/50 nose over or capsize ratio letting them have a shorter mast or are bow mods the better approach?

 

Ac 34

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I don't think I'd change a thing except that part of the altitude control system that malfunctioned. Now, if the altitude control system was working right(I don't believe it) then its a whole new game.....