Little America's Cup 2010-C CLass-the real one..

Discussion in 'Multihulls' started by Doug Lord, Apr 12, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

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  2. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Curved boards: Fredo:Nah Clark:Yeah

    Fredo,4/30/10 on SA:

    "Yeah. Speaking personally, I don't understand curved boards. That is, I know what they are supposed to do, but I'm not comfortable with the tradeoffs.

    Let me start with curved (or J) boards. Sailing upwind, when I need sideforce above all, the boards are fully down. Now, in the case of curved boards, they develop less side force per unit of length, because they are curved. They also develop some lift. So I need to put more board down to generate equal side force, which comes with added drag. The lift may or may not cancel the excess drag but hey, if you want lift upwind, why not simply incline a straight board?

    Now, sailing downwind, you need less sideforce to travel straight, so the boards are half down and generating less drag. To get the lift from a curved board, you have to deploy it fully, which is extra drag. Not only that, but the extra sideforce is now dragging your boat sideways upwind at an impressive rate.

    Now maybe in an A cat, where the financial cost of a capsize is way smaller, you might want to build a boat so close to the edge that the only way to get downwind safely in a blow is with lifting help from the foils at any penalty to course made good or efficiency - that is to say being able to push the boat harder is more valuable than the inefficiencies of the curved board - but it's an expensive risk in a boat with a wing, so I would prefer my boat be able to get downwind without help.

    Now to S shaped boards. I also saw that Alingi tried them. To me it just compounds the problem. Sure, the second curve pulls the board back more vertical under the hull when sailing upwind but, my goodness, that's some shape. Think of your cat as a leveraged monohull sailing upwind, since that's effectively what it is once established on a tack. I have seen few monohulls with keels that curve back and forth under the boat from port to starboard and back. I don't think it's because the Mono guys got it wrong. There has to be a bit of drag associated with that shape.

    Look, the guys who try these boards out are smart, and they have reasons for doing what they do. Sometimes it's boat specific. But me, I don't get it, which is why I have tried to avoid them, and why the boats that we've built have not had them."
    Fredo






    Steve Clark,5/1/10 on SA:

    "We are going to drive down the curved board route.
    We have the option of going back to straight boards, but we are going to give the curved boards a thorough work out.
    The curved boards are about 5" longer than the straight boards to achieve the same projected side area. So they have more wetted surface, but this is offset by a reduction in induced drag courtesy of a better aspect ratio.

    We will have the ability to alter the angle of the dangle from about 20 degrees to about 40 degrees, so we will be able to tune our side force/ vertical force mix. The block and tackle to do this is pretty impressive. But we expect use excess lift from the boards to reduce wetted surface and to improve sea keeping.
    I don't argue with Fredo's logic, and if all we had to do was go upwind, I would not be looking to do anything except build deeper and skinnier boards.
    But there is a problem we have to overcome down wind. We think that we need to improve the high speed efficiency of the catamaran by several knots in order to get the next major step in down wind speed. As it is we are stuck using high lift/ high drag wing configurations that further limit our ability to take the next step of acceleration, which will pull the apparent wind forward, and allow us to sail deeper and faster using more righting moment.

    That's my theory at least, and I think that if you can reduce wetted surface drag, wave making drag and spray drag by rotating the force vector off the leeward daggerboard upward, then you should try to do it. Particularly if you figure you don't give up much of anything when sailing upwind.

    I'm also pretty convinced that you need T foils on the rudders once you start playing this game, so we have those as well. Time will tell how much we have to adjust these things. But I think there is a lot of development possible in hydrofoil managed sea keeping, all of which should make boats faster and more secure.
    Naturally we have to have races to see if this is correct.
    Some call it a sport."
    SHC
     
  3. Chris Ostlind

    Chris Ostlind Previous Member

    Yawn...

    Wake me when they get their stuff sailing as stipulated. Right now, it's puff between the two major opponents in the next C-Class haggle. One group egging-on the other so that they go off on a wild goose chase and not spend time dialing in their basic machine for all that might happen.

    Basically, Doug, until we see something concrete and it is well integrated within the boat just days before the event... you are reporting nothing but smack talk.
     
  4. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    ===================
    Both these guys have made serious points-saying the comments above are "smack talk" is just not correct-or appropriate. Steve and Fredo have shown no hesitation to discus the trade-offs and technical considerations of many of their design choices openly and publically. This kind of discussion is a real contribution to design and shows great insight into the philosophy driving both teams. I appreciate their comments.
     
  5. yipster
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    yipster designer

    beeing curious; what speeds in what winds do these little america cup boats make?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    As I understand it : up to about 25 knots.....
     
  7. yipster
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    yipster designer

    in what wind, or put different, how much faster than the wind
     
  8. Chris Ostlind

    Chris Ostlind Previous Member


    Of course you do. But then, you found a speculative use of helium to be one of the most important developments in sailing over the last 50 years. As important as carbon fiber, as Dynex shrouds, as GPS, etc....

    What do you say we just wait until its time to roll-out the cats for the first day of racing? Then you can wildly speculate about anything that you see... which is actually installed.

    Everything else is vaporware.
     
  9. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    ----
    1.5-2 times windspeed( I think)

    "the boat can double the windspeed in moderate winds and has a top-end speed of 24 knots."
    http://www.sailmagazine.com/cclasscats/

    ======================================================
     
  10. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Little Americas Cup: Team Invictus and Orion

    Orion doing her wave piercing thing and Team Invictus:

    pix from the Teams/SA:
     

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  11. yipster
    Joined: Oct 2002
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    yipster designer

    Thanks Doug, Cogito, Invictus and Patient Lady are getting classics
    site could be updated with the new big AC results doing 30 in 6 knt wind
    not that i'm gonna race but find it intersting to know, like how is this on the big AC ones
    "measure of the wing's performance is lift coefficient. The C Cat has an LC of 2.1, compared to a soft-sail boat's LC of 1"
     
  12. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    ---------------
    You're right: the 11' Moth will do 2.5 times windspeed in 8-10 knots of wind.
    The in-class GPS(peak) speed record is slightly over 30 knots!
     
  13. captainsideburn
    Joined: Mar 2009
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    Location: Tasmania

    captainsideburn Junior Member

    do they have a website that talks about these boats?
    I want to see more about the wing masts etc
     
  14. Doug Lord
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    Doug Lord Flight Ready

    ------------
    Captain, this is probably the most up to date info anywhere right now:

    Steve Killing with loads of info on the last Canadian boats.....
     

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  15. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Steve Clarks C Class foils( no, not smack talk!)

    Clark is using a trunk molded in such a way that the boards can be canted athwhartship to increase or decrease the area of the board that is lifting vertically. Steves design also uses rudder t-foils-not seen in many curved board applications but surely a good idea for enhanced pitch control.
    Pix from Clark/SA:
     

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