Volvo Inshore Foiler--Technical Design Information

Discussion in 'Hydrodynamics and Aerodynamics' started by Doug Lord, Nov 18, 2017.

  1. Doug Lord
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    Doug Lord Flight Ready

    See the pdf below for more tech info than is usually presented with new designs on any forum:
     

    Attached Files:

  2. markdrela
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    markdrela Senior Member

    Hmm. The PDF shows the boat is in trim upwind and downwind, but nothing about stability. It definitely looks hydrodynamically unstable in both pitch and yaw due to the lightly loaded forward wing and rudder. They mention using PID controllers to stabilize the thing, but that seems rather sporty.
     
  3. sigurd
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    sigurd Pompuous Pangolin

    Since all (?) submerged T foilers are fly by wire anyway (referring to the wand sensors etc), is it still important to maintain pitch balance for them?
    I attached a couple pics where the CG seems to be maybe closer to the rudder than the main foil.
    3262_864993705_Foiling_moth.jpg mothEuropeen2.png
    Also, since cars steer so well with the front wheels, and forklifts steer so poorly at speed with the rear wheels, what is the problem with fore rudders?
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ==================
    Mark, just a guesstimate: it looks to me like 75-80% of the load on the main foils and 20-25% on the forward foil. Is that what you were thinking?
     
  5. markdrela
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    markdrela Senior Member

    Pitch balance (or pitch trim) is always required, with or without active stabilization.

    A fore rudder makes the moving boat behave like a dart thrown backwards. It's unstable, and will tend to do a quick 180 while still moving in the same direction --- not a good property in a fast boat.

    The analogy with wheeled vehicles is fallacious, since non-skidding wheels are constrained to move along a fixed path. Aero and hydro surfaces have no such constraint.
     
  6. sigurd
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    sigurd Pompuous Pangolin

    From the numbers in the presentation, the rear foils carry 72%.
     
  7. sigurd
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    sigurd Pompuous Pangolin

    1. Stability and balance
    Ah, I mixed up the terms. I think I meant to say: Can not the traditional requirement for a lighter loaded tail, to create stability, be relaxed in these actively stabilized craft?

    2. Forward rudder
    This boat went over 200 mph.
    http://histarmar.com.ar/InfGral-7/Crusader.htm
    Another, Miss Britain III:
    s-l300.jpg
    I don't understand your explanation for why the car analogy is fallacious, also when disregarding the fact that tires do slip, sometimes a lot, and the vehicles can still be controlled. I never tried driving a forklift on ice, but my hunch says the car will still be better on ice, as it is on asphalt.
     
    Last edited: Nov 20, 2017
  8. markdrela
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    markdrela Senior Member

    It's hard to make out from the drawings, but I see a "forward rudder" that isn't too far ahead of the CG, and additional rudders fairly far aft. That can be stable if the rear rudders provide more stability than the front rudder provides instability.

    The Volvo boat is the opposite -- the front rudder is far forward and the rear rudders are not very far aft. One thing which might help is the relatively aft sail. This will provide additional yaw stability, but only if the sail yaws rigidly with the boat. If the wing is allowed to pivot free, even momentarily, its yaw stabilization will disappear.

    The Volvo boat is basically the same layout as the Decavitator, which when on the foils was unstable in yaw and required very fast active steering at high speed to avoid spin-out and likely destruction. This was doable for a 20 second sprint effort in calm water, but I can't see it being practical on a sailboat running at high speed for hours in any kind of significant sea state. An active control system could do it in principle, but as a minimum that requires adequate sensing of the unstable mode, and adequately fast rudder actuation to suppress the yaw instability which is strongly being excited by random waves banging on the rudders. If they pull that off I'll be impressed.
     
  9. sigurd
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    sigurd Pompuous Pangolin

    I think those are the driveshaft supports you are referring to as rudders on Miss Britain III - I suppose the better analogy is fins.
    So what would happen if there was no rig and one pushed the Volvo boat along like a dart, letting go of the presumably balanced rudder. Won't the rudder turn with the flow, essentially doing nothing to the boat?
     
  10. OzFred
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    OzFred Senior Member

    In Moths, in general, the main foils carries nearly all the weight nearly all the time because that is more efficient, the rudder is almost solely for pitch. In certain conditions the rudder might be more loaded, but it can also provide negative lift (pull down).

    Aircraft use much the same principle, with nearly all the weight on the main wing. The centre of gravity is usually designed to be just behind the centre of lift.

    The front wheels on a car have castor to provide a strong, positive tendency to correct to a straight line. Otherwise, steering would be very unstable. It's very difficult to get the same dynamic in a boat.

    Moths are a development class that have tried just about everything you can reasonably imagine for a monohull foiler within the class rules, including bow mounted foils, dual wands with independent flaps, diamond shaped main foils, etc. They are the way they are because it has been proven to be the best configuration around a windward/leeward course in typical sheltered water race conditions.

    BTW, one of the biggest issues with putting the foils at the extremes of the main hull is bending moment on the hull. Both Moths I know of that tried a main foil on the bow snapped in half, since the boat is supported at the ends and rig tension is trying to drive the mast through the centre. So the boat must be built stronger and heavier than if the foil is more or less aligned with the centre of mass and effort (so just behind the mast).
     
  11. Doug Lord
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    Doug Lord Flight Ready

  12. sigurd
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    sigurd Pompuous Pangolin

    Why?
     
  13. TANSL
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    TANSL Senior Member

    Technical information, the truth, very little, main dimensions and 4 more truisms. Nothing relevant.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    ===================
    The center lifting foil is new and very relevant......

    Volvo--FoilerCatVMGYachtDesignVOR_1render by Fabrice Germond -VMG Yacht Design.jpg
     

  15. TANSL
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    TANSL Senior Member

    I do not understand why it is so relevant and what advantages it offers over other configurations. In any case, drawing a central foil is not giving any technical information. Another thing would be to talk about the type of profile used, why its longitudinal position, if it is retractable, why it is much shorter than the other foils, talk about why hulls have so much volume or why it does not need spinaker and many other issues.
    I, the truth, every day I feel less admired with the renders. They are very nice but as much as a vase for flowers can be. I would need, not to see certain things, but to know why these things and the explanation of why they are the way they are and are not otherwise. Maybe I have a too engineering mind.
     
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