America's Cup 2010: Race Thread

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

  1. Ilan Voyager
    Joined: May 2004
    Posts: 1,244
    Likes: 160, Points: 63, Legacy Rep: 758
    Location: Cancun Mexico

    Ilan Voyager Senior Member

    You're right with pipes...wings are a different task. I'll give you a little pleasure; lets say "general laminar flow is easier at high reynolds". No air slow extrados pockets well known of people working on laminar and hyperlaminar wings, because of a energetic ventilation. Look at the polars of the same wing profile at different reynolds, the efficiency gets better at high reynolds.
     
  2. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    My understanding is that the increase in efficiency comes from the reduction or elimination of separation. At higher Re the boundary layer is turbulent and does not separate from the foil surface as easily as laminar flow.

    I'm not familiar with using the term laminar flow to describe flow outside the boundary layer. I am fairly certain that the airfoil accuracy required to maintain laminar flow over a large percentage of chord has not been achieved on sailing wings.

    R
     
  3. catsketcher
    Joined: Mar 2006
    Posts: 1,298
    Likes: 143, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Back to roll damping

    On my hobby horse here

    The trimaran configuration with its wave piercing amas in certain circumstances will have less pitching than an equivalent cat. This makes the whole platform more stable fore and aft with the wing then able to be tuned to a much more narrow range of wind speeds than a pitching cat rig.

    This means you can power up the rig and not have the anenometer at the top going 20 down to zero. The cat did seem to pitch more so this may be a factor in why they seemed to be either under or over powered and hence hunting around a lot more.
     
  4. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    When is a trimaran not a trimaran? When its flying two hulls. Then its a catamaran. The rules about pitch damping apply equally.

    I think we are missing an important point. Tell tails have been replaced with lots of pressure sensors, interpreted by a computer algorithm that says exactly what corrections should be made. Replace the myriad strings (and string pullers) with an instant and precise, engine driven trim mechanism controlled by a dedicated dial watcher and button pusher, and the flying angle remains incredibly constant. Is that automation? The helmsman virtually need not concern himself with flying a hull, someone else does that. They talk to each other constantly, for sure, but the helm's principle concern is heading where he wants to go, and boat speed is governed by committee!

    Meanwhile on Alinghi, all these duties combine to be a formidable task for a single person. The helmsman must (as in the bad old days) interpret a multitude of ephemeral signals, and make an endless series of instant decisions and communicate them to the rest of his crew, who may not be able to respond to changes as fast as Oracle's button pusher.
     
  5. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    You might want to actually look at the boats before you post. :)

    One of the most striking things about the wing was that it had MORE tell-tales than the soft rig. Are you saying that the pressure sensors read the tell-tales? Or is it likely that humans use them?

    I'm pretty sure that the main was trimmed manually, looking at instrument readouts ... just like any other boat.

    R
     
  6. Chris Ostlind

    Chris Ostlind Previous Member


    I guess that if we carry your point to its logical conclusion, then both boats, when flying their respective hulls, are morphing into monohulls, or nonarans, as it were. No, Sandy, BMWO is still a trimaran and it'll stay that way no matter how much you'd like to describe it differently. I'm OK that you have some energy on the whole thing, but it would be somewhat better if it were being applied correctly.

    Yes, the rules about pitch damping apply equally. It's just that the boats, which are not both catamarans, solve the issue in different ways. A careful look at the shapes of the hulls in question, their distances apart and the manner in which they are sailed, will be a good source of information.
     
  7. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    Oracle has a series of small holes in the wing over pressure sensors. These provide data about angle of attack and possibly span wise pressure differentials for each articulated wing panel. Gross and fine adjstments can be made to each panel independantly.

    Check your attitude at the door.
     
  8. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    Forgive me. Chris for trespassing on sacred ground.
    Is there some science to support differentiating how many hulls are flying? Does the water or wind have an opinion?

    Note: I am not a baptised catamaranophile, I have owned and loved both. I don't care one way or the other. You do. Why?
     
  9. Chris Ostlind

    Chris Ostlind Previous Member

    It's not sacred ground, but it does deserve to be taken with a bit of specific accuracy.

    Because you use the name, Sandy, I'm pretty sure that you've heard all the jokes* about being a girl, etc. Yet, a reasonable check of the plumbing would quickly set the record straight... I assume ;-)

    So, you know the argument already


    *Yes, I have heard all that, as well, when I use Chris and not the formal, Christopher, so I'm not tossing grenades here.
     
  10. RHough
    Joined: Nov 2005
    Posts: 1,792
    Likes: 61, Points: 0, Legacy Rep: 793
    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    The point was that the wing has tell-tales, if the trim was automated with input from the sensors there would be no reason for the tell-tales.

    I think if they ever share more detailed information on the wing, the control system will turn out to be much simpler than people assume. Much more human input than pressing a button marked "Trim".

    USA was very stable sailing with the soft rig, before the change to a powered deck and the addition of the wing. She was better with the wing, but just fine without it.

    R
     
  11. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    Run the interviews Oracle released after the first race. Spithill et al discussed the electronics in the wing, and the buttons controlling the hydraulic actuators that moved the panels via cables up the leading edge sections of the wing. Further details were discussed in a subsequent interview but I can't recall which one I was watching.

    Spithill didn't seem to spend much time looking up at the wing, and his gentle movements of the wheel did not coincide with changes in the hieght of the amas. Contrast this with the 20 degree heading changes repeated by Alinghi in race one. She dipped a hull a dozen times in the same wind that Oracle sedately flew through as if she was riding an invisible stand.
     
  12. CT 249
    Joined: Dec 2004
    Posts: 1,701
    Likes: 78, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    I think that the difference between cat and tri in this respect was highlighted as long ago as Rod James' book of the early '80s, when he had a sketch of various types of tri (Shuttleworth and Hollands, IIRC). The F40 tris really brought the idea home, IIRC.

    A tri can be designed so that the amas (which can be supporting about 0% of total displacement in light winds or in turns, but 100% of the boat's sailing displacement when sailing in strong winds) have very different shapes and characteristics to the main hull (which is supporting about 100% of displacement when the boat is sailing in light winds, but 0% when flying two hulls).

    I think Lock Crowther or his draughtsman JB may have said that it was almost like being able to switch hulls mid-race. In light stuff you sit on the hull optimised for light air speed and pitch dampening and almost fly the other two, in strong stuff you fly that hull and use the ones designed for heavy-air speed and the pitch dampening characteristics you need in strong winds.

    On a cat, you're varying displacement much less (from 50% to 100%) and you have to compromise more, because the same hull that's got to slip through the water well in 5 knots of wind when carrying 50% of displacement also has to blast fight off nosediving when blasting downwind at 30 knots when carrying 100% of sailing displacement.

    So to that extent, the rules don't apply equally.
     
  13. CT 249
    Joined: Dec 2004
    Posts: 1,701
    Likes: 78, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    Another thing is that it looked just like what happens when someone is trying to go wild in an underpowered cat, and another person is trying to go wild in a powered-up cat. The underpowered boat has to either steer a lot more as the apparent changes, or crash back down whenever the pressure drops. The powered-up boat has more of a 'cushion' of apparent wind and sail power that makes it much steadier.

    We used to notice just the same issue when we were trying to race our F16 type cat in one design form (without spinnaker) against clubmates who had put spinnakers on to race in F16 form. Guys who were about the same level of skill (as demonstrated when we all raced in OD form) could keep the hull flying much more steadily due to the sheer power of the kite - just as JS may have benefited hugely from the sheer power of the wing. And it's much easier and steadier to go wild on a Tornado than on a boat with less power and speed; greater beam and moment of inertia also probably help.
     
  14. Doug Lord
    Joined: May 2009
    Posts: 16,654
    Likes: 326, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    As I said in posts 47,49,54 and 58 I think the lifting foils used by USA played an important role in allowing her to be able to fly two hulls so consistently-not the only factor that facilitated it but an important one. The extra power and height of the wing(as well as its controllability) was certainly a major factor as well.
     

  15. sandy daugherty
    Joined: Jun 2008
    Posts: 132
    Likes: 4, Points: 0, Legacy Rep: 52
    Location: Annapolis, MD

    sandy daugherty Senior Member

    I agree with Doug. I wonder if there was some flexibility built in that would allow the curved boards to bend slightly and develop more vertical lift in a puff.

    I'd love to hear the theory behind the question-mark foils, too.

    CT: my point is simply that Oracle was designed to fly two hulls in these conditions, and the center hull stayed DRY most of the time, so this event proves nothing in the great (but silly) tri vs cat debates. In my mind, the only reason for the center hull was to house a lot of mechanical and electronic equipment and to provide a rigid structure to keep the fore sails' luffs taut.

    Neither am I criticizing either boat. They are both orgasmicly beautiful! I SINCERELY hope the next cup is multihull. And I hope it,s held in Newport to finally shut up the monomaniacs' complaints that multis are too fragile for 'real men' and real weather.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.