Monohull Speed: Speed Dream by Vlad Murnikov

Discussion in 'Sailboats' started by Doug Lord, Jan 8, 2010.

  1. CutOnce

    CutOnce Previous Member

    The error is clearly arguing with the forum prince.

    You fail to understand these arguments are NOT Socratic discussions where the truth is found through reasoned, objective debate. Arguments here are a highly enjoyed conflict environment that provides a stage upon which the forum favorite poster gets to feel like an expert. Two years from now, the same arguments will rage on, new gladiators will step up and our hero will still never build, test and deliver anything. Just like Vegas, you can't win here. The game is rigged.

    If you are looking to learn something here you'd be better off to go spend the same time reading from texts and papers where the authors do not reach conclusions before doing the experiments.

    --
    CutOnce
     
  2. Cheesy
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    Cheesy Senior Member

    I see the 'disconnect' between both arguments now, since Veal heel is a coined term its definition may well be variable to a degree... Anyway the board is analogous to the lifting foils on a moth (or similar), so to compare the application of Veal heel to the two cases, it should be considered that a windsurfer or kite boat does not have a hull, the rider is standing directly on the foil. The lever arm is a virtual arm which does increase with heel, the end of the arm is the centre of gravity of the rider/board which is essentially the same as the COG of the rider. I can see not every one is going to agree on the similarities here and change or add to definitions to bolster their arguments.

    One aspect of this thing that hasnt been touched on so much so far is the force vectors generated by the rig/kite, both a windsurfer and a kite have a big advantage over the moth in that the rig can be canted independently of the Veal heel, this somewhat complicates the applicability of the SCP number in the fact that lateral power can be traded for vertical lift, in the case of a kite this is even more significant than Veal heel.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    ==============
    Its not really a variable definition: it refers specifically to a bi-foiler heeled to windward where:
    1) the hull physically moves to windward of the vertical lift vector,
    2) the rig and crew move physically to windward.(not just lean to windward)

    No other sailboat allows this to happen-and it has particularly important implications for bi-foilers larger than the existing ones today.
     
  4. Cheesy
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    Cheesy Senior Member

    So in that case the Veal heel on a moth is exactly the same as on a kiteboard other than the lack of a hull, which as it turns out is functionally the same as the riders body from feet to harness. To preempt the argument that legs cannot be compared to a hull I will say that while foiling a hull is an unnecessary source of drag and weight offering exactly nothing in terms of functionality Mirabaud sailing without a hull is the perfect example of this
     
  5. RHough
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    RHough Retro Dude

    Fine. The CG of the vessel is to windward of the vertical lift vector.

    The forces at work are righting arm, weight, heeling arm, sail force, lift force.

    Geometrically there is no difference between what you chose to label Veel Heel and any other sailing craft.

    The mechanics are identical. It is the distance between CG and whatever keeps the boat from sinking (buoyancy or lift) that is Righting Arm. Righting Arm x weight = RM. It is the distance between the sail force and the lateral force that is Heeling Arm. Heeling Arm x Sail Force = HM. HM must equal RM.

    The only thing that makes "Veel Heel" unique is calling the mechanics of sailing by a different name.

    This is just marketing hype using words that are unfamiliar to give the impression that a Moth (or Bi-Foiler as you now call them) gets it's sail carrying power by some new set of sailing mechanics where in reality it does not. This is intentionally misleading and that is the only reason I wasted any time looking for unique mechanics at work.

    It is just RM and HM just like every other sailing vessel.

    You don't seem happy to look at numbers that put the Moth in a bad light. Sorry about that, numbers are part of design evaluation. There have been many theories and proposals here on boatdesign.net that the supporters cannot or will not back up with data. They all get mad when you try to create numbers that might make sense and those numbers do not agree with the claims.

    There have been a few times when after the best analysis I am capable of I find some claims believable. If my gut reaction was wrong I stand up and say so. I like to be wrong, that is when I learn the most.

    You have to prove that the mechanics of "Veel Heel" are different than other boats. You have not. If you can, I will again stand up and say I was wrong.

    R
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ============
    Seems to me that the demonstrable fact that with veelheel the hull actually moves substantially to windward is quite significant and unique to the bi-foiler configuration.
    It is not "new" physics but it is a new application of the same physics to sailboat design. What happens when the boat heels to windward is unique-there is no other configuration that I am familiar with where the HULL physically moves to windward with weather heel. It offers designers extraordinary new opportunities in high speed sailboat design.
     
  7. cardsinplay
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    cardsinplay da Vinci Group




    Doug, When are you going to come clean with respect to the questions asked in the above post?
     
  8. Cheesy
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    Cheesy Senior Member

    As I said the 'hull' is an irrelevant construct which is being used to try and make 'Veal heel' exclusive to a moth type craft in the face of basic physics. When resolving the forces (with the rider in a fixed position relative to the board/boat as you stipulated earlier) the size (volume) and distribution of the total mass is not important (for these simple calculations anyway), the total mass is equivalent to a force acting in a vertical direction through the centre of mass. This force does no know or even care if it is a heavy hull, a dozen beer stashed away or a high tech carbon structure.
     
  9. RHough
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    RHough Retro Dude

    The result is greater RM. As long as the CG is to windward the mechanics are the same. It really is no different than a multi sailing on the leeward hull. The CG is to windward of the lift/buoyancy.

    There is something different in the mechanics.

    Conventional boats that do not "fly" (lack of a better word) cannot do what a single track foiler can.

    Go back to the upright case. 7.5 ft beam and a 165# helm at extreme beam.
    RM = 619

    If the boat cannot fly that is the limit of RM.

    As soon as you pick the boat out of the water the single track foil system allows freedom of heel that other layouts do not. If you can heel the boat 30 deg to windward the the mechanics give RM of a boat with a beam greater by twice the lateral displacement.

    With the windward heel the Moth has the mechanics of a 9.5 ft beam with a physical beam of only 7.5 feet.

    Instead of 165 x 3.75 = 619 you have 165 x 4.75 = 794

    That is the unique benefit of windward heel on a boat with a high CG. The 60# hull is a minor contributor only 60# ft (just under 8%).

    I think the 1.73 to 1 ratio of the sides of a 30 deg triangle is misleading. I don't have the time or inclination at the moment to think this out completely. I have a feeling that it may be a near even ratio when you factor in the lateral contribution of the heeled foil.

    So there you are. I made the case for you, Veel Heel = Virtual Beam Increase with a 8% freebie from the hull as icing on the cake.

    :D
     
  10. P Flados
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    P Flados Senior Member

    I tried to stay out of this one, I did, I did. It is no use, so here goes.

    Basic physics should be studied and understood in all pertinent aspects. Discarding facts you do like and ignoring what you do not understand does not help. Getting emotional, twisting facts, making personal attacks, going off subject etc. just make things worse.

    The righting moment vs. overturning moment balances for the moth and kite are entirely different, but in both cases, a skilled sailor can get a whole lot of speed with less (if any) need to "depower" than is common on most types of craft. Some amount of "depowering" is not bad when it puts lifting surfaces at better angles of attack, but eventually you get below optimum and the craft just reaches a max speed.

    When a moth is healing to the windward it is benefiting from several items where basic physics are coming together for the good. There are also some offsets. This is not magic but it is pretty cool.

    Under the water the primary lifting surface (main horizontal foil) is at a really good angle. It is close enough to horizontal such that you still get very efficient vertical lift supporting the weight of the boat. At the same time you get some "nearly free" force pushing to the windward. I say nearly free since the this foil is probably the most efficient lifting surface on the craft at this time and at the angle involved the additional drag associated with this force is very low. This lateral force from the main horizontal foil is very beneficial as it reduces the required lateral force to the windward normally provided by the vertical foil. This foil is less efficient (more drag for the desired force) as it is a symmetrical foil and it is surface piercing. The rudder is more lightly loaded, but the effect of the heel works pretty much the same way for what ever portion of the loads that are carried back there.

    The heel angle does have one negative effect below the surface. The angle of the vertical foils is such that they are generating some amount of down force. The good news is that above the surface, the wing is probably producing close to the same amount of up force (i.e. they tend to cancel).

    If the tee foils included less than full length flaps and the outboard tips were turned down enough for the windward tip to be closer to vertical at max heel, the boat could be brought up a little higher during this maneuver and more of the lateral load could be shifted to the windward tip of the horizontal foil. This would reducing loading on the vertical foils even more. This would probably be a good thing for top speeds, but may be less efficient overall at low speeds.

    The other big effect of the heel angle is in generating righting moment. This is the biggest plus since an upright foiling moth is challenged with limited righting moment and more than normal overturning moment since the center of effort is so high. The fact that the boat is so high up hurts when talking overturning moment, but it creates that big CG shift that generates lots of righting moment. I am sure there is a heel angle that is optimum for most reasonable wing speeds, but at some point more angle is going to start causing problems and/or reducing efficiency. This is part of why I do not see a moth type platform going for any outright speed records.

    The above discussion is an attempt to break things down into simple explanations that help us understand why this efficient little boat goes so fast. The boat is efficient since it has a pretty good rig, is very light and has excellent hydraulic performance. The foils seem to be operating in a "sweet spot" with good structural aspects, good profiles, good aspect ratios and good planforms. The ride height and attitude control features seem to work, but this seems to be an area where improvement would be nice. The biggest efficiency hit is probably the all of the air drag associated with everything above the water but below the rig (see the CSYSPaperFeb09 Beaver paper on Moth.pdf that Doug has included in numerous posts)

    The kite achieves great performance largely because it does not need much righting moment from the sailor. The moment arm for the overturning moment is small to start with (waist to water). When the kiter leans to the windward, he is actually generating more righting moment and reducing the moment arm for the overturing moment at the same time. The sailor can make a small adjustments in his body position that handle huge load variations (as long as he has the leg strength). The apparent efficiency of the kite board has been discussed many times, but for now I will just say that is seems to perform better than I would expect and if someone will publish some good studies on why it works so well, we would all be grateful.

    As a side note, the above explains part of why kites can go real fast in heavy air. When you start including foiling into the equation, there is a large percent change in overturning moment for the same amount of sailor lean. More leaning is therefore needed for the same kite force. As such, foiling on kites may be more advantageous in light to mid air conditions and less advantageous in more wind.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    The calculations I did for the Moth show that at 20 degrees angle of windward heel the percentage of total RM of Vealheel is 31.8% and for a 60 footer at the same angle is 42.7%. Thats serious RM for "free"-no additional weight or crew movement required to achieve-just windward heel. And independent of altitude as long as the boat is 100% supported by foils.
     
  12. TINHO DORNELLAS
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    TINHO DORNELLAS Junior Member

    1 person likes this.
  13. RHough
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    RHough Retro Dude

  14. Paul Scott
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    Paul Scott Senior Member

    Tinho, welcome! Always liked AHD. In all it's incarnations. Had one of the big boy light air boards, which was Most Excellent. Did you do it?

    Have lurked on your forums too.



    Paul
     

  15. Paul Scott
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    Paul Scott Senior Member

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