America's Cup 2010: Race Thread

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

  1. bruceb
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    bruceb Senior Member

    Foil lift

    For the record, I really enjoyed watching the races, I just wish there had been more. Does anybody here have a "guesstimate" of the amount of lift the foils give on these boats at 20kts? I noticed both boats were using them most of the time. I watched the BMW feed and they had more aerial shots than on the water, so it was hard to see the leeward hulls. Also, it appeared that Alinghi was catching up on the last leg as the wind got lighter, although different wind conditions might have been effect. BMW seemed to keep going higher to keep their wing working (and jibed) while Alinghi was able to stay lower.
     
    Last edited: Feb 17, 2010
  2. Doug Lord
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    Doug Lord Flight Ready

    =====================
    On the ORMA tri's, that used a similar type of curved foil to USA, lift was up to 70% of total weight. The 30% remaining was required to ensure pitch stability since most of them didn't use rudder "T" foils. It is probable the same was true on USA-though their system may have allowed variable lift.
    I sure enjoyed the races-watching those magnificent machines was awe inspiring!

    PS- I think the lift from the foils was part of the reason USA appeared so stable in roll-able to fly both hulls 90+% of the time compared to Alinghi.
     
  3. RHough
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    RHough Retro Dude

    You would be wrong. :)

    USA-17 is just as rock solid with her straight foils in.

    The key is steering. USA can trim faster than Alinghi and hold the heel angle they chose with next to no input from the helm. Alinghi was solid in roll/heel when Ernesto was not driving (Race 2 beat) and they had the right sails up. When they were overpowered (Race 1) they could not work sheet and traveler fast enough to keep the heel constant or to even stay on one hull. An amateur helmsman didn't help.

    R
     
  4. Doug Lord
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    Doug Lord Flight Ready

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    I've been wrong before-but in this case I don't think so. I haven't watched her sail for several hours with the straight foils in ,have you? At any rate, if you draw out the foils,and the boat at an angle of heel you'll see that the lift vector is to windward of the hull CB-so I don't think I'm wrong at all. This would tend to reduce the effect of gusts making the boat less likely to have the fluctuations seen in Alinghi. The effect would be a damping of roll-it seems obvious from a drawing..... The damping effect of a hydrofoil in roll is well illustrated in the Moth Class where those that have sailed the boat remark on the much greater roll stability on the foils as opposed to off the foils. Though this instance is not an exact parallel of that it is close enough for jazz-I think.
    Randy, here is a rough illustration assuming 50% buoyancy and 50% vertical lift= 100% total weight:
     

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  5. Chris Ostlind

    Chris Ostlind Previous Member

    I agree with you, Randy.

    I feel that the primary applications for the curved foils on BMWO are for leeway resistance and to an unknown degree, a lift component to stabilize pitching moments. I don't see them contributing much of anything in roll resistance. Rather, I see ama shape, stiffness of platform, a steady, applied power from the vastly tuneable wing and exceptionally good steering input from Spithill, who obviously grasped the feel of the boat with a gifted degree of touch on the helm.

    Driving a big fast trimaran that size (and also Sodeb'O) is a group of sensations all unto themselves. One has to be smooth, relaxed and with full ability to read the sea and wind well before the need to move the wheel comes into the present. It's a place unlike anything I've ever experienced before in any boat.

    After watching this AC event, that guy Jimmy Spithill is a real piece of work.
     
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    The AC was as boring as death.

    The legal battles announced nothing good. Just two big egos of multimillionaires... Only two boats...:rolleyes:
    Technically, a part maybe the gigantism, there was nothing new...For someone following and having participated in the development of multihulls since 30 years, the victory of the US team was as predictable as the the sunrise next morning after the night. The lone chance for the Swiss team of winning was a major structural failure of the American trimaran.

    Since 1987, with the Formula 40 races, trimarans have shown they were the best in triangular regattas and catamarans had no hope. "Biscuits Cantreau" trimarans dominated outrageously the races of 1987 and 88, with "Adrenalin" (a trimaran by the Gougeon Brothers) being the only serious contender, but this design had a major flaw. All the French 60 feet multi racers are trimarans because of a good reason...they are faster.

    It's known in Class C since mid eighties (and even before) that the power and the stability of wings are unmatchable by soft sails. The true inventor of the slotted wing sails is Lindsay Cunningham ("Victoria" and the "Yellow Pages" Class C catamarans) and the other slotted wings made after are just extrapolations.
    In 1987-88 if I remember well the year, "Yellow Pages" was able of 12 knots in a 4 knots wind. No need of a 90 feet tri to get three times the speed of the wind...

    The first curved foil I have seen in 1987, was on a project (never built) of Class C designed by the NA Philippe Harle. After it has used many times on the 60 feet trimarans made in France, well before the 2010 AC. The lines of the 2 contenders are in the actual trend (see the pics of my thread about "Banque Populaire") , and do not show anything new. The reversed bows have been tried on warships at the end of the XIX century for exactly the same reason: to cut the waves.

    Ultralight big boats in carbon fiber have been already made...and these multis are able to circumnavigate at 20 knots with top speeds around 40 knots, in any kind of weather and sea state. IDEC weights only 11 metric tons for 27 meters, and it's a sturdy high sea boat designed to be driven by a lone man.

    So there are not technical novelties for me as I have seen them more than 20 years ago, there was nothing thrilling with these two boats.
    A lot of money spent for the total non-event.
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    Ilan V, Agreed Lindsay Cunningham with his Quests was first with the THREE element wing, but the first wing was also Australian, the Martin/Buzaglo Miss Nylex, (with flaps) first launched in 1972 and winning in 76. Also the early di Mauro Patient Lady 11, (I think) had a double element rig and certainly PL111 had that setup - and they were early boats too.
    And the first curved foil that I know of was a drawing from Derek Kelsall on one of his tris - and that was before Phillippe Harle's effort. I even drew a curved foil on my Flash Harry micro multihull way back then too, also never built ... so they don't count. Kelsall was very early into foils on his ocean racing tris, VSD 1 and 2 (winner Transat en Double in 1979) for example. So all these clever farts were doing these things .... BUT no-one has seen a monster like BMW-O with these inventions before. Big is difficult, to say the least - and you have to admire that.
     
  8. RHough
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    RHough Retro Dude

    Doug ... you point out that the lift from the foil ... reduces RM. :)

    Roll damping must resist rotation around the axis. Moving the foil "sideways" through the water. Roll damping is a function of distance between the roll axis and the CE of the foil. The foil could be lifting down and not change the damping effect.

    If we take your drawing and for the sake of discussion the position of the foil's CE is inboard of the CB of the ama. This reduces RM, the boat rolls(heels) higher. The foil as you show it then has greater area lifting vertically ... reducing RM again ... the boat rolls higher .... RM goes down ...

    This reduction in RM as more wight is transfered to the foil continues until the foil area reaches its maximum projected area.

    The forces you drew have a roll amplifying effect. This requires greater trim response not less.

    R
     
  9. Doug Lord
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    Doug Lord Flight Ready

    I don't think so-if you consider the whole assembly at a relatively consistent speed then the system will damp roll-certainly more than a vertical board. One thing was sure-USA's speed was pretty consistent and her angle of heel rock steady most of the time. It seems to me that the separation between the two areas of lift would act as a damper. I've written BMW-O asking what the design lift on the foils was when flying two hulls-maybe I'll get an answer-stranher things have happened.
    I wonder if the loss of RM with a curved board explains why Alinghi went with straight boards?
     
  10. Chris Ostlind

    Chris Ostlind Previous Member

    Doug,

    All this thought on the immersed foil as a wonder product and not a whiff of a comment as to the roll damping potential of the wing sail. Take another look at the mast height differential between Alinghi and BMWO.
     
  11. RHough
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    RHough Retro Dude

    Doug, your statement requires the buoyancy from the ama and the lift from the foil to be a stable system in roll.

    Take your drawing and change the roll (heel) angle 5 deg either way.

    When the boat heels more, to provide roll damping the foil lift must become smaller, this would act to return the system to its steady state.

    When the boat heels less, the lift from the foil must become larger to act to return the system to its steady state.

    This cannot be the case in your drawing. At greater heel (rolling up) the lift area of the foil INCREASES, amplifying, not damping the roll. At lower heel (rolling down) the opposite happens, the foils needs to provide more left to counter the roll and it has LESS lifting area.

    All you have to do is isolate the ama/foil and look at it as a stable system. Stable systems are self correcting, this one is not.

    R
     
  12. RHough
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    RHough Retro Dude

    Hmmm ... roll damping from tiny foil or roll damping from the inertia of a 3500kg wing with a span of 230 feet ... :)

    I know where I'm putting my money. :p

    R
     
  13. Doug Lord
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    Doug Lord Flight Ready

    ------------------------------
    First, I think Chris makes a good point but I don't think I'm wrong either. Look at where the athwhartships center of lift is-its between the hull CB and the foil center of lift. Therefore ,the axis of roll is between the two. From a steady state at speed more roll would depress the ama increasing buoyancy and the pitching from the gust that inspired the roll would reduce lift on the foil. If, from a steady state the wind eased slightly the initial reaction would be reduced buoyancy from the ama and increased lift from the foil due to the pitch up of the boat. Damping.
     
  14. Ilan Voyager
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    Ilan Voyager Senior Member

    You're right, it's why I wrote "slotted wing", it's the slot which permits to ventilate the extrados et to get better Cz on a large range of angles (the wing won't stall so easily). An analog disposition is used by the STOL planes and the big jets. That's the invention (or better the solution of the engineering problem of symmetry) of Cunningham.
    The former wings had not used the slot effect and controlled it (not a piece of cake of engineering as the wing must work on the two sides).
    I didn't know about Kelsall on curved foils. I mentioned that the first one I saw was on a Harle's design and only on paper, I didn't say that Harle was the first. I think that many people had the same idea...so we won't never know who was the very first.
    I was just illustrating that all these famous innovations are more than 20 years old...and if in AC it appears as brand new it's because the AC is so conservative (they raced on 12 meters during decades....woooh A lot of money for sooooo slooooow boats)

    About BMW oracle I'm not so admirative about design and construction. Let me explain my point of view; we have now the materials and techniques and bigger carbon boats have been made before the US contender. They limited the accepted stresses by not sailing when the wind is above a good breeze or when the water is not more flat...
    It' may appears curious at first sight but if you have the materials a big wing and big foils are easier to design and make than small ones, and the result will be lighter proportionally.
    First the Reynold number becomes very high, so laminar flow is easier to achieve.
    Second the effect of scale: the inertia rises at the cubic while the surfaces are simply proportional. If you design a foil twice the surface, the inertia for a same thickness of for example ten percent of the chord will go by power 3 of the thickness. Or you decide to go to higher aspect foils with better efficiency.
    You're working with thicker materials, more fiber plies, you can use at full advantage the sandwiches (foam or honeycomb). And dimensional tolerances are easier to respect.
    When budget is not a problem to go big on only 90 feet is a rather easy task with the actual materials.

    I can say that a 60 feet multis regatta is far funnier to watch (and probably to sail). Dog fights at the buoys, close performances so a 1% difference of speed costs a lot of places and tactics are primordial. The boats are strong so the regatta take place in a very wide range de wind and sea state and they go full gas. And it's far less expensive, so innovation is possible. As proof look at that video http://www.youtube.com/watch?v=E4BCSKTbB98.

    I must confess I fell asleep while watching the videos of the 2010 AC.
     

  15. RHough
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    RHough Retro Dude

    What?

    Flows with high Reynolds numbers usually become turbulent, while those with low Reynolds numbers usually remain laminar.
     
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