AYRS/Bolger meets Maltese Falcon

Discussion in 'Multihulls' started by Anatol, Jan 25, 2016.

  1. Anatol
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    Anatol Senior Member

    Agreed on both points. The shock of an 'instant shunt' on a full scale boat could be huge.

    has anyone (here?) persevered on this? I can't find any current results.

    thanks for the explication, worth thinking about.

    huge respect for his work
     
  2. upchurchmr
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    upchurchmr Senior Member

    Disastrous drag consequences.
    I don't think so.
    Actually the system of sail and mast have pretty high lift to drag.
    That is why it is the system of choice when going to weather.
    Granted typically with a jib of some size.

    Can you do better - yes, but it is not a disastorous difference. Losts of boats sail quite well, so well it is the rig of choice for most everyone.

    I never heard of a square sale being claimed as best for anything but down wind work. Why would you want a Squaresail which is being used as a leading edge. Except of course, that if it is all you have you will want to be able to use it as well as possible. That doesn't make it good.

    So Anatol, its about time.

    If the solution for a 300' superyacht is not right for a 30' boat (and that is all you have as an example) - what is your proposal?

    Here is mine: Twin freestanding rotating aerofoil shaped masts with square topped mains (reefable) able to fly a jib at the fwd end in light winds. Cheers with a minor development (rotating and aerofoil). A significant option would be to stay the masts to weather for less weight aloft.

    What is yours?
     
  3. hump101
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    hump101 Senior Member

    Your jib analogy is a good example. The jib is very sensitive to angle of attack, which is why it is used as the primary indicator of heading when beating to windward. Any sail supported at its leading edge by a wire has to have a hollow leading edge which varies with sail load, even with very high forestay tension, and thus the angle of attack along the length of the leading edge is hard to control. This is just one of the reasons that jibs are less efficient than mainsails, and why all classes with restricted sail area end up with a single mainsail.

    I would dispute your claim that a mast has "generally disastrous drag consequences". If you consider a 2D non-rotating section in steady flow then the recirculation around the mast can be considered poor, but in the real 3D world with fluctuating flow speed and direction the mast provides a resilient flow regime that maintains lift across a much wider range of conditions, and hence on average produces a more optimal result. If you have a rotating wing mast then the rigid mast surface can be used to force depth into the flow, creating a high lift sail with relatively low drag.

    For a proa I would be more interested in the opposite idea - a single sail with two wing section masts - at leading and trailing edges, which can then be reversed. Not sure of the practicality or weight aspects, but from an aerodynamic point of view a wing section on the trailing edge would be less invasive than a wire rope, and a wing section on the leading edge would definitely be better than a wire rope. You could also then use the trailing mast to hook the trailing edge to increase Cl downwing.
     
  4. Anatol
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    Anatol Senior Member

    Are you saying an 'ideal' sharp (jib like) leading edge is better than any mast, but in the real world, the rigidity of the mast outweighs any drag?

    ok, a bit of hyperbole there. But the rectangular section spruce mast on my boat is pretty bad ;)

    right

    provocative idea, but hard to imagine how you could move it around.

    But, here's the rub - I don't see how any mast luffed sail (or sails) can produce a reversible balanced rig without tom-foolery like a jib at each end. OK, it may be that the 'jib at each end' solution is most pragmatic. Especially on a furler. And it may not be needed for drive, just for correcting weather helm.

    thanks!
     
  5. redreuben
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    redreuben redreuben

    Well isn't that exactly what a wing masted Balestron does ?
     
  6. Anatol
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    Anatol Senior Member

    lots of *tacking* boats.

    granted, me neither. They claim the dayna rig is 'twice as efficient' as squaresail - whatever that means. Anyone know how high MF points?

    The central problem for me is designing a rig that is balanced in both directions
    while being quick and easy to shunt. I was working on balanced lug designs, working on the logic that getting the luff fwd of the mast would lead to better balance on reversing, but the leading edge problem was still a challenge. Then
    I saw that the AYRS/Bolger rig was essentially a 50/50 balances rig, and that switching leech for luff makes shunting an entirely different operation. *This* is a fascinating idea.

    In addition, it occurs to me that locking the AYRS/Bolger rig down to the deck - or mast- with a centrally pivoted boom would reduce some of the wild behavior reported of the rig. I can't imagine I'm the first to think of this - but you can see that this line of thought would lead me to the DynaRig. Do I have a design based on this principle? - no, that's why I started this thread :)

    Makes perfect sense. Development of well tested systems. How do you fly a jib from a freestanding rotating aerofoil mast?
     
  7. Anatol
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    Anatol Senior Member

    granted. I'm just leery of having the force of the whole rig focussed on one point in the hull. My general design instinct is to distribute the stresses.
     
  8. hump101
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    hump101 Senior Member

    No, a sharp leading edge is not necessarily better, and is frequently worse, and not just because the mast provides rigidity, but because it also reduces sensitivity to angle of attack and allows the sail to operate at a reduced angle of attack.

    The problem with any luff-for-leach sail is that during the shunt you have the sail flat against the wind at some point - like duck-gybing a windsurfer sail - and during this moment there is high load and little control, exactly what you don't want when trying to shunt in severe weather. On a windsurfer you duck the rig as you are going downwind, typically at or above windspeed, hence there is little load on the rig, but in a proa shunt you are stationary. The combination of a tacking rig and shunting is a very safe, controlled process, a near ideal combination from a control point of view, and dealing with rig asymmetry is a relatively minor issue in comparison (balanced wing, Balestron, moving jibs, moving CLR, moving mast base, etc.).
     
  9. CT249
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    CT249 Senior Member

    Nice analogy about duck gybing, hump!

    Anatol, Tom Speer, Mikko Brummer and other experts on BDF have demonstrated clearly that the mast is not the problem that old theories (including some which were based on tests using ludicrously oversized masts) said it was.

    The same thing can be proven by looking at the classes that have tried using wingmasts. For various reasons they work well for cats but most mono classes have found that they are not worthwhile. If normal masts were as slow as claimed, then wingmasts would win everything in Moths, skiffs, windsurfers etc.

    About the Kauri video - from the wet weather gear (and the apparent age of the person who I assume is Russell, as well as the Ocean Surfer reference) that looks like it was taken in the 1980s on a very low-budget boat. It would be pretty damn easy to have roller furlers (as boats like Eterna Quartz had already done by that time) so it could be said that it is not a fair representation of the shunting speed of a "conventional" proa (although one assumes a Harry would still be quicker).
     
  10. rob denney
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    rob denney Senior Member

    With 2 rigs, you "have the force of the whole rig focussed on one point in the hull", twice. The boat must be strong enough for one rig to take all the load. ie, dump one sheet in a squall and the other rig takes all the force.

    Distributing the stress over the entire boat (with stays) instead of only the area between the beams on one hull (unstayed mast) is certain to result in a heavier, more expensive boat with more things to break. On a 15m harry with a single unstayed mast, with the same righting moment as a 6m wide, 6 tonne cat, the beefing up is an extra layer of double bias between the beams, a ring frame and a couple of kgs of carbon tow. Less than 50 kgs on a 3,000+ kg boat.

    The issue with shunting a sloop rigged proa is not so much the time taken or the danger (though both are worse than I would be happy with), but the hard work of lowering, raising and sheeting in the headsail each time you tack or shunt. Furlers reduce the work a little, but replace it with extra cost and windage. Why have all that hassle instead of a ballestron?

    The same applies to conventional booms. Most of the sheeting effort goes into pulling the boom down, not in. The bigger the roach, the more force required. A ballestron (if you want a jib) or a wishbone boom and an unstayed mast keeps the sail vanged during the shunt so the only sheet loads are to adjust the angle of incidence of the sail.

    Non headsail proas work, as long as the centre of lateral resistance is adjustable and the windward hull is designed for it's load. The easiest way to adjust the clr is with 2 rudders on or near the beams, which is also much safer than mounting them in cases in the hulls.
     

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  11. Anatol
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    Anatol Senior Member

    thankyou - this was very helpful
     
  12. Anatol
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    Anatol Senior Member

    Aerorig thought experiment

    Thanks all for useful replies. I now understand a little better the issues around mast and forestay leading edges. Let me pose a thought experiment.
    Imagine a standard balestron/aero rig. Now imagine a rig of same area comprising just a big genoa-like sail, on the same balestron structure. ie the area of jib and main on the former equal to the genoa or the latter. Which rig would perform better and why? (Ignoring the fact that the mast is in the way on one tack, ie considering the rig only on the favorable tack.)
     
  13. Anatol
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    Anatol Senior Member

    Basic aerodynamic question

    Ideal wingmasts are symmetrical and conform to naca profiles (right?)
    Conventional sails do not have the cross section volume of a naca foil, ie they are more like just the lee side of the foil. Which is more efficient in terms of drive and lift, particularly when close hauled?
     
  14. Anatol
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    Anatol Senior Member

    the venetian blind rig

    As I understand it, the advantange of a high aspect ration rig, and a Bermudan over a cat is that there is proportionally more leading edge. it If leading edge is most important in sailing close hauled, why do we not see rigs like a venetian blind standing on end? I guess, in effect, a high aspect 3 or 4 mast schooner approaches this?
     

  15. upchurchmr
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    upchurchmr Senior Member

    Ideal?? wing masts are not symmetrical.

    That has been tried - with flaps. Meaning the majority of the sail is the NACA profile (or other) and just a small portion of the sail is a flap.

    The two or three part vertical panel wing sail is better because it has more camber going upwind and lots more camber going "down" wind. IE., it is better because it is not symmetrical.

    In fact, the cat rig has been shown to be better on the race course over the sloop if you have a very high aspect ratio. This applies mostly if you have a limited sail area (due to class rules) and you have enough righting moment (cat or tri)
    As I understand it, the high aspect ratio is best going up wind, and a lower aspect ratio is better going down wind (unless the boat is fast enough to sail "close hauled" even going down wind).

    Wing sails have beaten soft sails on fast boats. If you look at the "little America's cup" around 76 you will see the last time a soft sail won - Aquarius (I think).
    Not true on slow boats - monohulls
     
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