Questions Wishbone - Birig, Rotating, Unstayed Wing Masts - Catamaran

Discussion in 'Multihulls' started by jorgepease, Feb 23, 2018.

  1. rob denney
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    rob denney Senior Member

    Wishbones adjust the sail shape the same as a boom and track. Ease the snotter (the line attaching the front of the boom to the mast), the top of the sail twists off. The foot also gets fuller unless there is a control moving the wishbone point of attachment up and down the mast. As Hump said, with a properly engineered unstayed rig, this is not a problem as the top of the mast falls off automatically when overpowered.
    Wishbones should ~bisect the angle between the leech and the foot to achieve this effect. Horizontal wishbones need a separate line from the end of the boom to the base of the mast (or to a traveller) to control the leech, plus a snotter or outhaul to adjust the foot.

    The advantages of wishbones are 1) ease of control, 2) low mainsheet loads as the mainsheet only adjusts the angle of attack, not the leech tension. Therefore, the leech tension (which is only adjusted a small amount) can be a many part purchase and the mainsheet (which is adjusted a large amount) can be a not-many part purchase. 3) with a bag under them, they provide automatic sail storage without flaking or lazy jacks to worry about when hoisting/lowering. With a bit of thought, the top of the bag can open/close automatically, so lowering the sail on any point of sail or wind strength is simply a case of releasing the main sheet and at some stage tying off the halyard so it doesn't bang against the mast. This is far less work at the end of the day than flaking and covering a conventional mainsail. Similar bags can be arranged on conventional boomms, but lazy jacks are required.

    The other option is a fixed boom. Has the same low sheeting loads, but needs lazy jacks. Lazy jacks are not as big a hassle on an unstayed rig, which can be eased till it weathercocks, but are added complexity. Fixed booms are heavier and a nuisance when the rig is lifted out. Again, not that big a deal on an unstayed mast where the mast only needs removing every 10 years or so for a repaint.

    A wishbone is harder to build, because curves in the plane of the cloth are a pain to lay up. Tow is a good solution.
    They are much easier to install.
    In my experience, a half wishbone is not as light, for a given load, as a full wishbone. Wishbones banging against masts is not good. The full one is also easier to keep flat and stow the sail in. The half wishbones on the super foilers are glorified battens, not relevant to a cruising boat.
    Full wishbones also make it easier to attach them to the mast so that the mast rotates when the sail is eased.
    A non rotating unstayed mast loses a lot of benefits compared to a rotating one, but needs bearings which for a 75'ter may not be cheap. The cheapest (no bearings, track, or batten cars) solution is to attach the sail to the mast with lashings, which is what I have done on Bucket List. The first iteration didn't work wonderfully well, there are some changes to try next time.

    Deck sweeping mains that limit visibility are not a good idea. Not a problem on Jorge's boat.
     
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  2. catsketcher
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    catsketcher Senior Member

    I love my wishbone. It has been one of the few things I haven't mucked around with in years years of owning and sailing my 38ft Chamberlin.
     

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  3. UpOnStands
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    UpOnStands Senior Member

    Any problems with chafe on the running lines?
     
  4. catsketcher
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    catsketcher Senior Member

    4:1 mainsheet only, no winches, preventers or barber hauls. Same mainsheet and blocks for 17 years. About to replace. Hardly any chafe. Main in great condition for age as the wishbone keeps it pulled nicely and evenly all of the time and protects it from the rigging wires. Sometimes thought about selling my boat but then thought, how could I ever find another one as easy, fast and fun to sail?
     
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  5. UpOnStands
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    UpOnStands Senior Member

    Time to replay your video. Your coach house is the only design that makes me rethink my preference for open bridgedecks. Very practical and does not look heavy at all.
     
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  6. jorgepease
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    jorgepease Senior Member

    Nice boat!!
     
  7. catsketcher
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    catsketcher Senior Member

    Oh no! She has had a heap of work done since then and looks much more loved. I should do a new one but it does show me pumping the main. Notice how the wishbone protects the main against the shrouds.
     
  8. UpOnStands
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    UpOnStands Senior Member

    Time for a new video? Demonstration of tacking would be great, along with all other points of sail ;)
     
  9. CT249
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    CT249 Senior Member

    Having sailed her a fair bit I can say that she tacks very nicely, and the wishbone really does make the mainsheet extraordinarily easy to handle. The rather spartan bridgedeck is great for those of us who spend lots of our cruising time being active; you can leap out of the water, drop your snorkelling gear, and slide into the bridgedeck without dripping salt over velour and teak.

    The issue of being unable to independently adjust twist and depth is an issue with windsurfer rigs, despite the fact that they have had enormous amounts of development. It does limit their effective wind range despite the excellence of design.
     
  10. UpOnStands
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    UpOnStands Senior Member

    On which angle would you see the biggest penalty?
     
  11. rob denney
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    rob denney Senior Member

    Great video. Nice boat.

    If independant depth and twist control is important, rig the snotter on a bridle. Tension it from higher up the mast to tighten the leech, lower down to flatten the foot. Won't work on a windsurfer, but works on a non luff sock rig. Easier is a barber hauler/vang from the sheet end of the boom to the deck, same as one would on a short traveller mainsail. This controls the twist. Easiest, a line from the clew to the base of the mast to control the depth. Sail setting techniques on a large rig are very different to those on a windsurfer.
     
  12. jorgepease
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    jorgepease Senior Member

    Sock Rig? what is that?

    I think in my case the line from the clew to foot of mast is the only option but I was under the impression that if you pulled down on the top end of the wishbone, it would push the clew out and down taking out the twist and flattening sail.... or is that not how it works? I read where one guy put his wishbone on a traveler on the mast, so that is the imagery that comes to mind.
     
  13. UpOnStands
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    UpOnStands Senior Member

    Sock rig = main sail is attached to a sleeve that encloses the mast. To allow reefing, no lines can pass through the sleeve.
    To flatten the sail, the nose of the wishbone is pulled aft to the mast by the snotter.
    Not sure about the clew to base of mast technique.
     
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  14. catsketcher
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    catsketcher Senior Member

    I use a snotter to adjust the depth and leech tension at the same time, so the angle is very important. It seems to be right with this rig, although I do have too much leech tension in light airs upwind till about 6-8 knots. Apart from that it is pretty good and I am happy to adjust the snotter in an out to increase depth and twist downhill and in light winds, or pull it on and reduce twist and depth in heavier breezes. Reefing is done with a clutch on the end plate. It works pretty well but you do need a way of tightening the topping lift of or the boom end drops.

    There is the potential to make an open boom/cover like some other Chamberlin cats do, then have the wishbone end run along a track near the end of the boom. This would enable you to remove the topping lift and better adjust the twist and depth. I probably won't bother, but in a few years time I may do it.
     

  15. Angélique
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    Angélique aka Angel (only by name)

    I'll think Wharram calls it a Wingsail Rig . . .

    [​IMG]

    [​IMG]

    [​IMG]

    "sock" - - Wingsail with 4 reefs. -

    [​IMG]
     
    Last edited: Feb 27, 2018
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