Wingmast - how much kick is needed?

Discussion in 'Sailboats' started by sigurd, May 20, 2016.

  1. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    Thanks a bunch,

    A-class (blue), Groucho (red), Sid (green)
     

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  2. Doug Lord
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    Doug Lord Flight Ready

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    no idea-not related to the noggle....
     
  3. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    CT, you had an argument about how more aspect ratio is not always better.

    What do you guys think about the A-class. Are they at the limit of AR in respect to sail construction, or do they just not want any taller rigs?
    The C has about 3.5 (?) times the RM, and only double the area. If they had kept the planform of the A, they would be much more stable than the A.
    So it makes sense they could benefit from a higher AR, and thus were pushed into the heavy, but slick and powerful rigid rigs - if it's sail construction that is the issue.

    If it is sail construction that is the issue, does it make a difference that A's have a small mast chord so that the sail needs camber?
    With a bigger mast chord the sail works fine even if flat - especially higher up - I believe.
    Doesn't that make a higher AR feasible, as long as the sail and rig can withstand the leech tension? As seen in Sid for example? What say you Gary? Do you have 'more than adequate' (if that is a valid quantity) leech control? Do you use any amount of camber down low, does it make a difference?
     
  4. Gary Baigent
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    Gary Baigent Senior Member

    Some experimental A's went through a period of even taller masts (if I remember correctly, 31-32 maybe more feet) with higher aspect ratio sails but then settled back to what they have now - which is still extreme. imo.
    The C Class wing rigs are also extreme; for example, Sid has 11.5 metre mast but the C's are 2 plus metres taller, so Sid is a wimp compared to them. But they are full wings with far less loads on their sheeting systems. Whereas old time wing mast/high AR soft sail combinations require plenty of muscle to get the leech set correctly ... but I worry about tearing the stern off - have already beefed up the traveller base area - which formerly flexed the deck when the loads went on.
    IMO, high aspect rigs, in comparison to lower, longer footed versons? .... well actually there is no comparison, especially in lighter conditions.
    However, no matter how superior high AR rigs are, you have to stop the over balanced weight and mass aloft causing pitching - hence the ultra-lightweight, sophisticated C Class rig construction and the arrival of foils.
     

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  5. CT249
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    CT249 Senior Member

    Well, all I'll say about aspect ratio and light wind performance is that people like Glen Ashby have told me, on the record and for publication, that the singlehanded version of the Taipan 4.9 (which is basically an old A with two feet cut off) was faster than a newer A Class in very light stuff because the Taipan had more sail, although on a 2' shorter mast.

    When I referred to theory over-estimating the advantages of high aspect rigs earlier, it was a reference to examples such as the fact that (as Gary correctly notes) the As now have a 30'/9m mast and have abandoned attempts to increase AR. In addition, theories seem to assume flat water and steady winds, and in reality there are conditions in which you can't sail high enough downwind to achieve the proper VMG targets; for example in a chop it sometimes seems that if you head up you end up sailing further without gaining sufficient speed to make it worthwhile. There are also places where you have to try to stay in a streak of breeze or run very low for tactical reasons, and in those situations high aspect rigs can be quite painful. As Skyak notes, when you're running low and stalled a low aspect rig has more power.

    Sure, at other times a high AR is fantastic, but the point is that theory tends to assume you've got "steady state" conditions in which the boat is already up to speed and the wind is steady; it doesn't allow for bouncing through chop, or struggling to keep the boat up in a 30 knot gust, or getting around a bottom mark in 4 knots with a pack of boats around you.

    About double surface sails; that link isn't working for me. The double-luff sails I've used don't over-rotate but from the theories I can see, it's not actually required. The theories and tests that claim they would have vast superiority don't appear (from the accompanying diagrams and illustrations) to require them to over-rotate.

    I'm not sure about the one I've raced against.

    People have been working on double surface sails for eons. I don't think I've ever heard on one actually winning a major race, or any race for that matter. They may also be affected by the basic issue that if your sail area is not restricted you are often better off just by adding a bigger, taller rig instead of adding excessive complexity, and sometimes even just a simpler and lighter rig works better. The C Class cats that used the double-surface sails were beaten by wingsails but the single-surface cloth sail on Aquarius beat the wingsails around the same time, IIRC.

    Since people have been promoting and developing double surface sails and soft wings for so many years, surely if they worked someone would have entered races against comparable craft and won.
     

  6. Gary Baigent
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    Gary Baigent Senior Member

    All good stuff, CT - but in the case of Aquarius V; the boat was for its time. extremely light and especially so in comparison to full wing Miss Nylex (and they won 4-3 so it was very close in conditions that mostly suited the lighter boat). Also Aquarius had a rig following the Californian tradition set by Dashew's Beowulf IV (from the 1960s no less) of a deck sweeping main. Which puts the A's revelation of the last year or so (like near half a Century later) into perspective.
    About double luff sails: looking at the Italian design images it appears that their mast spanners are well rotated.
    Interesting too are the 45 degree angled boards.
    Agreed, the double luff designs haven't been mind boggling in performance wins; I remember French double luff headsails and mains on their large race multihulls not living up to theoretical expectations.
    But ... although very sophisticated solid wings have proved to be superior to double luff soft sails (in the C Class Italians' case), for amateur nutcases like myself, the idea of a very efficient wing sail (though admittedly I repeat, not superior to full wing) that can be reefed, and can be lowered on a mooring in strong winds, and yet performs very well, appeals very much. I keep looking at my over rotated masts and windward side draggy area immediately behind mast, and think that is a drag area that can be improved upon.
    And what the hell - if I fail, on Frog's 9 metre rig, it is no great loss. And it is fun to try.
     
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