34th America's Cup: multihulls!

[groper]

No, i dont they are bedding anything... the same twisty behavior was also very noticeable on BMW Oracle`s 90ft tri - which appears to have many similarities to their AC72, more so than their AC45`s... their 90ft tri also appeared to trim very bow down aswell... not sure what their design approach is, but its clearly very different to team NZ...

 

[petereng]

BOR90 (USA17) was used 3 times so definitely hadn't bedded in! I'm sure bow down is not what they want! Has anyone any comment on why the new Oracle AC72 is called USA17 yet the AC33'rd tri was USA17? Is this for good luck? Or did they cut the old one down ?Peter

 

[Doug Lord]

34th AC on Foils!

Hey Doug - How you doin??
On the point of the the boards. Team NZ used different foils for day 1,2 and 3. They had Toyota on them. They were curvier than their flying version. Either day 4 or definitely day 5 they went with quite different boards and rudders (no Toyota). Plus I saw a photo of Oracles AC45 and it had different daggerboards on each side. So they could do a run one way then do it the other way and get immediate feedback on the differences very neat. Don't need two boat testing. I suppose a cat is two boats!! I'm sure we will see many variations of boards and rudders before the testing is complete. Seems your not a prophet anymore. Peter S

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Peter, I'm hanging in here-trying to digest the exhilerating AC developments.
Just a great time to learn!
At this point I tentatively think Oracle is flying manually by pivoting the daggerboard in the lower bearing. I don't know how they do it but I think they do it.
I think TNZ is using what is, basically, a surface piercing foil system that doesn't require direct angle of incidence control like I think Oracles system does. And the one video where they stuff the bow points out a possible problem with ventilation-typical of some surface piercing foils-especially those w/o fences.

 

[petereng]

Hi Doug - There is no point in the inboard end of the foil to be surface piercing. If you mean the "free" end of the board. Obviously the hull end is piercing too. Any lift generated near the surface just wastes foil area. It would ventilate badly. The "dihedral" produces a steadier more stable lift then a perfectly horizontal foil. A dihedral produces a lift "bucket" area vs a small balance point.

The rules allow the daggerboard and the rudder to have two axis of control. I'm interested in whether the control is manual of electronic. There is no express rules against electronic control (I'll have to read through the rules again) so you could just hook them into a gps height control. Does anyone know about this side of the problem?

 

[Doug Lord]

TNZ surface piercing lifting foil

Yeah, the inboard tip may not be above the surface but it could be with enough speed. The curved lifting foils in trimarans like ORMA's and MOD 70's are designed as fully submerged foils. Even disregarding the tip the TNZ foil is acting like a surface piercing foil and would be subject to ventilation. You can see the "crash" that I believe was caused by ventilation in the video,next post.

click-

 

[Doug Lord]

34th AC on Foils!

Good article here: http://www.sail-world.com/USA/Americas-Cup:-Kiwis-on-Day-6-and-counting/101979

TNZ: decisions decisions 2nd boat to be launched early next year:
http://www.youtube.com/watch?feature=player_embedded&v=wcMEz32VhS0

 

[tom28571]

Doug You have taken a lot of flak over the years for your unbridled enthusiasm for lifting foils . I for one am now a believer . It is a revolution.

Ditto. I appreciate your willingness to get out there and take whatever anyone throws at you. Right or wrong, its always interesting and often enlightening:idea:.

 

[Doug Lord]

34th AC on Foils!

Ditto. I appreciate your willingness to get out there and take whatever anyone throws at you. Right or wrong, its always interesting and often enlightening:idea:.

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Thanks, guys. It's a fantastic time to be alive!

 

[Gary Baigent]

Agree'd on hull shape, they will lift the lee hull as much as possible (via foils) yet retain longitudinal stability. Yes Oracle was very twisty but you have to remember the boat is just out of the box and they haven't settled/bedded the structures in yet. Probably not on full pretension yet. The AC45s used to twist horribly when new. They bed in the connections and wet set them in after they settle/stretch a bit. Plus I'm not sure what the huge rear beam is about yet. Everyone is saying its for aero lift. I havn't done any numbers to figure out how much lift it could provide, but its improbable to do this as it needs to be trimmed somehow. Plus its at the back in all that dirty air. I suspect it has some purpose yet to be disclosed. Its simplest use is a walkway. If you watched AC33 they crawled from side to side on narrow beams. This is impractical in the coming short races. Especially for the helm. Jim can run back and forth over that easily, steer anywhere as needed. So as "simple is best" I think its a runway. Peter

People underestimate the loads and important work the rear beam undergoes, concentrating more on the main beam.
The wide and aerodynamic chord on Oracle's rear beam may be there besides less drag, but mainly an attempt to help stop platform twist - which so far doesn't seem to be working that well.

 

[Corley]

An article on some daggerboard interpretations and their legality (apparently hinged foils are ok) may be old news saw some of the diagrams on Sailing Anarchy.

http://www.sail-world.com/Australia/Americas-Cup:-Hinged-foils-approved-by-Measurement-Committee/101999

 

[Doug Lord]

34th AC on Foils!

Corley, I saw those on one of the threads on SA as well. Problem is that, contrary to what the article says, they are in no way like the foils on Hydroptere. Hydropteres foils pivot close up under the crossarm and when retracted are out of the water. These(in the article) rotate about a pivot on the bottom of the hull and a substantial portion of the foil would still be in the water when retracted. So far I see no advantage with this sort of system.
The article also states the the "S" type foil used by TNZ is the only "style" seen so far. Wrong-Oracle's slightly angled "L" foils have been used successfully on AC 45's and are entirely different than the TNZ foils.


Pictures: 1) Hydroptere.ch with main foil retracted, 2) Hydroptere with retracted main foil. Both have the foil pivot above the waterline.

 

[Corley]

I agree Doug it does not look like an optimal way of mounting the foils at all. L foils and a T rudder seem to be a better overall proposition.

 

[Doug Lord]

34th AC on Foils!

Note: if the "F" word used in joyful exuberence offends your sensibilities turn the volume down before playing this video!
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Some guys were out sailing today in NZ when low and behold tnz's foiler shot by them-must have been really cool!

http://www.youtube.com/watch?feature=player_embedded&v=jRHkrCiQYhg

 

[Doug Lord]

34th AC on Foils!

TNZ from Sail-World: what an incredible boat! Look at the picture of the boat going downwind. You know its downwind because of the sheeting angles of the leadbelly in the picture-wow!

click-

 

[groper]

Doug, are there any videos of the #5 oracle ac45 foiling? i cant seem to find anything but still photos???