35th Americas Cup: Foiling Multihulls!

Discussion in 'Multihulls' started by Doug Lord, Sep 26, 2013.

  1. champ0815
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    champ0815 Senior Member

    Well, to take this further - since speed is no longer correlated directly with waterline length, why not open the challenge to smaller boats, the qualifying events will separate the wheat from the chaff. I think weight limits would restrict innovations as a proa will always have less weight than a tri or a cat also without unreasonable light weight construction.
     
  2. redreuben
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    redreuben redreuben

    AC in shunting proas !

    I'd like to see that ! Crew work or what !
     
  3. xarax

    xarax Previous Member

    No rotating mast / soft sail combination can achieve the same L/D ratio of a sophisticated clean wing sail, of course... but the soft part of the sail can be ( in-mast or in-boom ) reefable, so there would be no need for the upper wind limit.
    The real question is the weight of such a reefable rig configuration. It would be great if can be significantly lighter than a wing of the same area - but is this possible ?
     
  4. Corley
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    Corley epoxy coated

    I agree keep the tight course boundaries and you have a natural handicap for the crew of a shunting proa somewhat negating the lighter weight of the platform. I'd love to see a super fast foiling shunting proa developed would be quite a sight.
     
  5. waynemarlow
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    waynemarlow Senior Member

    You are all so engrossed in wind limits but in truth it's not wind strength that is the problem, after all the crews got the ac34 boats to and from the race course safely.

    What the next major hurdle will be the 50 knot zone where foils suddenly cavitate and start to do weird and wonderful things which won't be good TV viewing. So how do we limit speeds in all wind strengths ?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    2nd Foiling America's Cup

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    Why not design foils than can go faster as well as slower? Don't like the idea of limiting speeds....
     
  7. xarax

    xarax Previous Member

    :) A ball rule ! :)

    Do you believe that those less restrictive rules should allow really odd crafts - like the Sailrocket, for example, which, besides its proa hull configuration ( probably unsuitable to match racing... ), can also be described as a sailboat / sailplane or a sailboat / kite hybrid ?
     
  8. RHough
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    RHough Retro Dude

    As long as crew safety is addressed at the same time. Sooner or later one of these things is going to crash at 45+ knots. I another crew dies or is seriously injured it will be the end of big foilers.

    Sailing has moved into life threatening speeds with these boats. In other sports that include the possibility of death, it was not until many had died and others refused to race that safety became a priority. Lets not have that happen with sailing and the AC.

    As far as trying to limit the speeds with a design rule, we have seen how well that works ... the AC72 rule was a 35+ knot boat rule (relatively safe to sail in breeze ~30knts) and turned into a 45+ knot boat rule (putting the ability to control the boats into question).

    Limiting the boats to sub 40 knot speeds will reduce the R&D costs and go far to make the AC72 'affordable'. Once the boats are gen 3 or so, then open the rule to allow R&D $$$ to explore transition speed foils.
     
  9. RHough
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    RHough Retro Dude

    The need for the upper wind limit was not sail area, more than half of the wing area was trimmed to provide righting moment. This is something a soft sail cannot do. The wings had near zero heeling force and low CE drive. A reefed soft rig cannot do these things.

    The wind limit was due to *boat* speed and control issues more than anything else.

    As far as building a soft rig as light as a wing ... maybe ... building a boat with a soft rig and the structure to handle the loads as light as a wing rig is not likely. In all the posts from people that have made those choices I get that lower total weight due to reduced loads is one of the reasons to chose a wing.

    #Doug
    Moths use soft rigs for the ability to recover from capsize and ease of transport. If they could make a wing rig that was as crash proof an easy to transport and store as the soft rig, they would.

    Bottom line. Struts, wires and pressure dependent airfoils are not used when high performance is the primary consideration. A case can be made for soft rigs but they are practical not performance related.
     
  10. Doug Lord
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    Doug Lord Flight Ready

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    Randy, the wings that were made in the Moth class were not faster than the "soft" windsurf type sail as I remember it.The Class "interpreted" the rule to mean there could not be a slot between the forward and aft element. And Ben Hall made a wing for the A Class that also was slow and heavy. Just examples that don't really knock wings but show how important the details are.
     

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  11. RHough
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    RHough Retro Dude

    Agree 100% To get full value from a wing rig the entire boat has to be built around the wing and its loads. Putting a wing on a Moth or A Class designed for a soft rig may not give valid data for performance evaluation.

    To get the full advantage of a wing the boat has to be fast enough to use it. Putting wings on "America" would not have made her much faster around the island.

    I had forgotten about the controversy about the lead element being the "mast" and the trailing element the "sail" for the Moths.

    It may well be the Moth is not fast enough to show a great advantage to a wing. Before you get your hackles up, I'm talking about 2.? x wind speed boats. If a Moth can sail 45 in 20 I think you would have posted about it.
     
  12. Doug Lord
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    Doug Lord Flight Ready

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    Moths are approaching 3 times wind speed in light air on foils. Funny about the Moth wing: some guys back then were saying the front element was the jib and the back element was the main! Oh,well....
     
  13. Doug Lord
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    Doug Lord Flight Ready

    Second Foiling America's Cup

    Whatever configuration is used, it will be essential that there is a single mainfoil when foiling-that three foil configuration and the foil that goes with it has revolutionized catamaran speed more than any other single advance in history, in my opinion.
    I'm looking at ways a trimaran could be configured with a single main foil system that was an advance over the TNZ/Oracle configuration. Don't see it yet but I may have more information before long.
     
  14. Skyak
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    Skyak Senior Member

    Wings lack of success in Moths tells us little or nothing about wings vs cambered cloth in anything close to what is sailed in the AC. The Moth has low Reynolds number despite their increasing speed because the sail chord is short (remember, chord is a factor in RE). At low RE values flat camber sails can do just as well as thick wings -2D CFD shows this. Take the RE up past one million and thickness pays. What is the RE on the AC72 wing? 10,000,000+?

    The other oddity of the Moth is it's reverse heal. The fast technique is to foil high and lean back against the wind. My only experience with reverse heal is on a sail board and it went like hell when I could lean back and scoop the wind against the water. It doesn't surprise me at all that moth sails are most like windsurfers. I have been over these forums for a while now and I have not seen anything about reverse heal on the sail or wing. It's certainly cuts displacement. I wonder what it does to induced drag and stall characteristics. We seem to be rehashing lately, maybe we should look into this.

    The last reason should be self evident. One guy developing a wing has little chance against the 'industry' refining the status quo. Due to the RE level the theoretical advantage is not great. His resources cannot match the collective mass of his competitors and their suppliers, and even if he does manage to win one there are the armies against him with flat sails in one hand and a rule book in the other!
     

  15. Doug Lord
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    Doug Lord Flight Ready

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    Lack of success of wings in the Moth Class had absolutely nothing to do with Reynolds Numbers-it had to do with a rule that prevented the wing from working properly.
    Veal Heel on a Moth is not like windward heel on any other boat because it moves the center of gravity of the hull(and almost everything else) to windward and ,among other things, increases the RM up to 40% without the crew having to move. It also reduces the loading on the daggerboard to prevent ventilation and allows the sail to lift some of the weight. I did an experimental thread " 60' Moth..." under the "Sailboats" forum on boatdesign and that kind of boat would be real fast but it requires fast movable ballast. The problem is how to do that.
    I'd like to see the movable ballast problem solved-hopefully without an engine-and then we'd see the true performance potential of a large monofoiler.
    But the single main foil AC system has come a long way toward making the cat faster than almost anything including the 60' monofoiler-certainly easier to sail. For a few years the Moth has been the fastest sailboat under 20 feet beating cats and Aussie 18's-now the fastest sailboat* under 20' is the Flying Phantom(18') at close to 35 knots using the three foil, single main foil AC72 configuration and a foil that allows altitude control like the 72's(except that the Phantom foil does not require manual angle of incidence adjustment as do the 72 foils).
    It's an exciting time-can't wait to see the next magic boat!
    ----
    PS don't want to get into the windsurfer/kiteboard discussion we've had that many times-the fact is the the USCG clasifies both as "boards" and says they are not "sailboats". But they are among the fastest sailing devices on the water with the exception of SailRocket-the fastest sailboat and fastest sailing craft on the water!
     
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