Boat Design Forums

Boat Design Forums (http://www.boatdesign.net/forums/)
-   Multihulls (http://www.boatdesign.net/forums/multihulls/)
-   -   34th America's Cup: multihulls! (http://www.boatdesign.net/forums/multihulls/34th-americas-cup-multihulls-34612.html)

Doug Lord 07-28-2013 10:34 AM

34th AC
 
JNavas video posted today-not as good as normal for him.TNZ and Oracle practicing-not a whole lot of foiling but when they did within close up camera range it was easy to spot the inboard foil tip(lee hull). You can almost always see the wake from the proximity of the foil tip to the surface.
TNZ foil tip at: 49sec. in and at 4:17 in. Oracle foil tip at 2:34 in. Scary angle of heel for TNZ at 8:20 in.


http://www.youtube.com/watch?v=i0sy34OD2_s#at=70

Doug Lord 07-28-2013 10:39 AM

34th AC
 
Quote:

Originally Posted by Earl Boebert (Post 642249)
Fixed that for you. (Just kidding :-)) A minor addition to the lagging indicator list.

Cheers,

Earl

----------------------
Earl, please don't misquote me like that-somebody just tuning in might actually think I wrote what you posted. I'm not trying to put a damper on your sense of humor-only that portion of it that rewrites a direct quote of mine.

Doug Lord 07-28-2013 11:47 AM

34th AC
 
Quote:

Originally Posted by catsketcher (Post 642219)
Thanks Doug and Peter

I am getting the idea now. Having a look at the Oracle video I can see the top of the board clunk forward once the boat is up. It seems to be in some way like a plane with different wing geometry for climbing and cruise. I can understand the board operations a bit better now - my mind was clouded with the wand driven Moth type foils.

I wonder if they will get so good at using non trim tab foils that they would not want Moth type active foils in the next AC (assuming the AC 72 goes around again)cheers

Phil

===========
Thats a real possibility, Phil: A few years ago a couple of guys decided to modify their Rave foilers with manual control
instead of the wand system used until then. The dual ,independent wands(one for each of two main foils) controlled not only vertical lift but also the RM of the whole boat. So when the guys set up the manual control system they needed two joysticks-one for the port side and one for the stb side:differential movement controlled RM collective movement controlled lift!
Sounds complicated but their manual system was faster than the wand system......

Doug Lord 07-28-2013 11:52 AM

34th AC
 
2 Attachment(s)
This is an improved version of the sketch I posted on the previous page. Keep in mind that this general configuration is used by all the boats and was pioneered and refined by TNZ. All the teams have refined it as well.
In my opinion, this configuration(left below) is a main reason why it doesn't pay to foil upwind: a large portion of the lift from the "L" foil is aimed directly to leeward(see the little red arrows)-this becomes very apparent upwind.
My tentative idea(right below) shows all lift force going for vertical lift or for lateral resistance-no force vector pointing to leeward. Lots of work to find out if this is viable or not.
click-

P Flados 07-28-2013 02:01 PM

Two items:

The videos do clearly show the tip right at or above the surface as Doug has noted. This very much duplicates the V shaped surface piercing foil configurations that are known to be stable. And yes they are inefficient due to both air entrainment at the surface and due to the more horizontal portion (wing) pushing out while the more vertical portion (board) pushing out.

Second item is something that I am not sure that ETNZ really wanted public at this point. Over at the SA forum "Luna Rossa 72..." in post 2842, Strider470 provides a translation of a Max Sirena interview.


Boat generation 2 and 1 differ a lot, not only from an esthetical point of view:

The newest has far less volume, the hull is 150 mm less in height in correspondence of the daggerboards, which are also positioned 200 mm outwards. I give you an example: one of the biggest problems this kind of boat has, is the fact that when you sail downwind the speed is so high that the rudder often stalls, because it is always in the turbulence generated by the daggerboard. Moving the daggerboards outwards has the result that the rudder is no more influenced by this disturbance, and this fact is very clear looking at the footage. When you sail at 35 or 40 knots, losing the control of the rudder is not the best thing that may happen to you, especially while gybing.

Another big difference is the system that controls the daggerboards and the angle of attack much bigger than in Luna Rossa. It is like a trim tab, and when sailing at 20 knots upwind this causes a lift, and more speed means more lift...

... In a perfect world I would like to cut the daggerboard section of the boat and replace it with a new one, and we actually thought about doing it at some point. We even thought about building two new floats but we would not have had enough time.



At first glance, I thought that the first item may not directly help that much with speed as much as it helps with stability. On the other hand, the statement "the rudder often stalls" could mean that LR just can not push as hard as ETNZ and there is a direct link to speed.

The second item is possibly more interesting. I am thinking that B2 for ETNZ (and AR given some comments I seem to recall) may have better ability to fly the boat using active control of main foil rake. The magic "joystick" concept Doug has brought up many times may be more real than many assume.

And by the way, this kind of goes against all of those that keep saying "ETNZ got it right first try".

petereng 07-28-2013 03:40 PM

Hi Doug - Sorry you will have to explain it clearer or we just agree we think different on this. Just because we see the wing tip breaking the surface more means nothing. To clarify, you (and others) are saying that the wing tip breaking the surface is used for heave control? Does someone out there have a very good picture of the board in the down position that I can estimate sizes from and I'll do a calculation. Do we agree that an AC72 takes off at 10 kns? and tops out at 40kn round figures? Regards Peter S

Doug Lord 07-28-2013 04:00 PM

34th AC
 
Quote:

Originally Posted by petereng (Post 642290)
Hi Doug - Sorry you will have to explain it clearer or we just agree we think different on this. Just because we see the wing tip breaking the surface more means nothing. To clarify, you (and others) are saying that the wing tip breaking the surface is used for heave control? Does someone out there have a very good picture of the board in the down position that I can estimate sizes from and I'll do a calculation. Do we agree that an AC72 takes off at 10 kns? and tops out at 40kn round figures? Regards Peter S

=======================
No, I'm saying that the primary heave control is the lift from the curved foil-designed similarly to a surface piercing foil except without the speed range of a traditional surface piercing foil. So when the boat falls below or exceeds the "current" speed range the angle of incidence (rake) is adjusted manually(electro-hydraulically). That allows fairly long periods requiring no use of the hydraulic systems for angle of incidence adjustment.
The inboard tip breaking the surface is just confirmation that the boats are using the "V" formation which creates tremendous leeway upwind since the "L" foil is at such an angle that a large part of its lift is directed to leeward. I guess it would contribute to altitude control a little by removing area from the foil(only about 50% of which is vertical lift). It would also cause a bunch of drag and seems like it would subject the foil to ventilation. Works for downwind foiling but not for upwind foiling.
PS-I'll look but I don't recall seeing a picture of the foil down(in downwind foiling position).

Doug Lord 07-28-2013 04:32 PM

34th AC
 
The Lion Roared Again! TNZ did its foil trick again, approaching the finish line off the foils then just as they were about to cross the finish line kicked the foils into max lift and pitched the boat up in the air to the roaring of the crowd. So very cool!

Leo Lazauskas 07-28-2013 04:40 PM

Quote:

Originally Posted by Doug Lord (Post 642301)
The Lion Roared Again! TNZ did its foil trick again, approaching the finish line off the foils then just as they were about to cross the finish line kicked the foils into max lift and pitched the boat up in the air to the roaring of the crowd. So very cool!

That was about the only exciting moment in an hour or so.
The race was essentially over after about 60 seconds.

But Well done NZ!
Fly Emiratees still sounds like a condition requiring sheep dip or insecticide.

Doug Lord 07-28-2013 10:51 PM

34th AC
 
Video highlights of todays race by JNavas:
http://www.youtube.com/watch?v=--LS8F4eR6U

Doug Lord 07-28-2013 11:42 PM

34th AC
 
NZ annoncement about the semi-finals :
http://www.youtube.com/watch?v=K1bX_IMdnSk

Emirates Team New Zealand today announce they will advance directly to the Louis Vuitton Cup finals and let Luna Rossa and Artemis fight it out in the semi finals.

xarax 07-29-2013 10:06 AM

Quote:

Originally Posted by petereng (Post 642225)
If we could use a canard we could prevent pitchpoles easier as well. Perhaps the ideal arrangment is a lifting canard and a daggerboard for leeway control?

I hope that the number of appendices would not be restricted next time... Canard rudders may be preferable, also because they will not suffer having to work into the dirty water disturbed by the daggerboards, as conventional rudders do.

Doug Lord 07-29-2013 10:28 AM

34th AC
 
1 Attachment(s)
Great picture showing the inboard foil tip breaking the surface:
click to see it--

Doug Lord 07-30-2013 10:30 PM

34th AC
 
JNavas video of Artemis vs Oracle in practice racing:
http://www.youtube.com/watch?v=lGRpU5v5wpg#at=386

catsketcher 07-31-2013 05:46 PM

Foiling upwind?
 
I was watching JNavas above video again and I saw Oracle really put some speed on Artemis. Interestingly the leeward hull gets very light at 3.58 and it looks like it is is certainly foiling, although not fully out of the water, I can see right up to the board of the leeward hull. I have't seen anything like that on TNZ or LR in their races.

cheers

Phil


All times are GMT -4. The time now is 04:01 PM.

Powered by: vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2014 Boat Design Net