WishBone Sailing Rig

Discussion in 'Boat Design' started by brian eiland, Aug 17, 2003.

  1. gar37bic
    Joined: Feb 2009
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    Location: Bellingham MA

    gar37bic Junior Member

    More about Kolika, and bipod mast engineering

    As it happens, I am proceeding with purchase of Kolika, having gone through her with the surveyor and have done some more research. Globaldude (if you are still around) - your visit to the boat and discovery of some of the problems turned out to set the stage - they lowered the price some more. :) It's not a done deal yet but well along the way.

    According to the builder Mr. Klimmek, the bipod mast weighs only 400 lbs. It is hollow wood with fiberglass skin. As he wrote, it weighs about 2/3 what a single mast would weigh. (You can read more at the web site for the boat, http://www.sail-works.com/KOLIKA/

    This makes sense to me, as the masts do not have to deal with any significant bending moment - all forces are either tension or compression, and the rigid spreaders (with crossed tension wire) allow the two to act together as a single trust. I think that a single mast has to deal with much higher bending forces.

    Also according to the builder, aerodynamically, the masts do not cost as much as might be expected. They are airfoil-shaped, so their windage is lowered. If I recall correctly a round object has the same drag as an airfoil ten times the width.

    Perhaps most importantly, a single mast 'dirties' the air flowing across a sail significantly causing loss of lift, especially at high angles of attack. On the Kolika the sail's leading edge is almost completely clean, with only the roller furling to impede the flow.

    I finally learned about the unusual prop and rudder design. The rudder has two sections behind the prop that are angled about 10 degrees from straight, in opposite directions. It turns out this has the effect of straightening out the propwash, eliminating prop walk. The circular foil around the prop is called a 'Kort nozzle'. This increases the efficiency of a prop - there is an article in Wikipedia. Overall though I think this arrangement has more drag when sailing than a more typical setup.

    The trim tab apparently did not work as expected, and Mr. Klimmek locked it in place at some point.

    [edit: One more interesting tidbit. The surveyor discovered that the original painted waterline was incorrect, and a new one applied. The boat evidently rides about six inches lower in the water than planned, which means the boat is heavier than planned. With 320 gallons of water and 180 gallons of diesel, plus 80 additional gallons hot water storage, that amounts to roughly two additional tons to haul around.]
     
    Last edited: Jun 30, 2009
  2. Norman Brown
    Joined: Jan 2009
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    Location: Hartlepool, England

    Norman Brown Junior Member

    I am glad someone is purchasing this yacht. It opened my mind to bi-pole rigs and started me doing figures for rig loads (a A frame does not need increadible wire loads. Hence it stands 'easy') and chain plates (most disapear). This makes the rig lighter eaven though it looks bigger (hence Pirocon). I will be interested in her sailing characteristics once she is back sailing. I have split my masts again as 4 masts with cross spars in carbon is more ridgid and just as light. Windage is no problem as the sections are smaller and give less windage than the single mast and wires. (search 'Lionhart of Hartlepool').
     
  3. nelsonyachts
    Joined: Aug 2009
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    Location: alameda, ca

    nelsonyachts New Member

    Wishbone Rigged, Kevlar "Relentless" Currently For Sale

    Dear Wishbone Enthusiasts,

    One of these fine Kevlar vessels is currently for sale at Nelson Yachts in Alameda, CA. The Rig has been cut down to just above the wishbone. The price on this boat is excellent given the effort that went into her. Please contact Chad at Nelson Yachts to purchase this boat.

    HERE IS A LINK to a .pdf of photos.
     
  4. multihullsailor
    Joined: Nov 2007
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    Location: Cape Town

    multihullsailor Junior Member

    Why was the rigg cut down? Are pictures available of the current mast situation?
     
  5. yipster
    Joined: Oct 2002
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    Location: netherlands

    yipster designer

  6. nelsonyachts
    Joined: Aug 2009
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    Location: alameda, ca

    nelsonyachts New Member

    47' Northwest kevlar wishbone rig pictures

    Hi all,
    Attached are large pictures of the current rig situation on Relentless. A second jib is to be added below the existing one. The double sail on single furler idea has been scrapped in favor of two low aspect headsails on furlers. Contact Chad at Nelson Yachts in Alameda for more info. [​IMG]<br> [​IMG]
     
  7. ChiefOren
    Joined: Aug 2009
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    Location: Israel

    ChiefOren Junior Member

    I am building a 50' sailboat, here in Israel. I have been interested in an A-frame configuration. But I would like opinions on the Idea brought about by www.runningYachts.com for an Aft-Mast configuration. I was thinking of using an Aft-Mast configuration, but with an A-Frame. I would then use 2 jibs for main sails, as was discussed here. A third jib could be used as a Storm Jib. Thus the boom would be eliminated completely. And with an Aft-mast configuration, there would be no loss of sail area.
    Any ideas?
     
  8. multihullsailor
    Joined: Nov 2007
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    Location: Cape Town

    multihullsailor Junior Member

    ChiefOren,
    check out this website for some more infos and maybe ideas on just such an arrangement:
    www.sail-the-difference.com

    Roger
     
  9. yipster
    Joined: Oct 2002
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    Location: netherlands

    yipster designer

  10. walltar
    Joined: Apr 2007
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    Location: czech republic

    walltar Junior Member

    Now i could say i am in love with that ship and for that price i would buy it in a minute. Pitty i am in europe and i dont have money right now. :(
     
  11. Spiv
    Joined: Jun 2007
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    Location: The Big Wide Blue Brother

    Spiv Ancient Mariner

    Hello ChiefOren,

    I am about to build a 17 x 8.3m composite cat.
    I had the hull designed by Richard Woods and I designed the superstructure and whisbine style CF mast with 3 furling sails two conventionally in front of the mast, one (mizzen) aft.
    Mizzen and Genoa are self tacking.

    I designed the mast in an oval Carbon Fiber sectio, but still have not obtained detailed engineering calculation.
    I'd be happy to share the design with you if you will participate with the engineering costs.
     

    Attached Files:

  12. Kojii
    Joined: Oct 2006
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    Location: Ensenada, BCN

    Kojii All is remodelling

    Quasi-catenary mast

    Another reason for the wishbone rig. Can you find it in the photo taken in very light wind in the harbor. The hook knocked most surface winds down to a breath. Rowed Orca out of the slip using 10 foot carbon fiber sweeps, and got the sail up as we quietly slipped out of the marina.
     

    Attached Files:

  13. gar37bic
    Joined: Feb 2009
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    Location: Bellingham MA

    gar37bic Junior Member

    What's the advantage of the catenary vs. straight mast legs? My understanding of the straight mast legs is that the major forces are all in line with the mast - no bending moment, so they do not have to be as large and heavy. On my boat the pair of mast legs only weighs about 400 lbs. - I can pick up one end of a leg (barely) even with full rigging and hardware.

    It seems to me that the catenary curve would require more strength in the leg. However, in my case the main sail is rigged on a roller furling at the center, not following the mast leg, so the forces applied to the mast legs are all at the top and bottom. Perhaps that is a difference?
     
  14. gar37bic
    Joined: Feb 2009
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    Location: Bellingham MA

    gar37bic Junior Member

    I should say, my boat's mast legs are hollow sitka spruce, not lightweight composites. The boat is not build using high tech lightweight composites. According to the builder, a single mast would have been over 600 lbs.
     

  15. Kojii
    Joined: Oct 2006
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    Location: Ensenada, BCN

    Kojii All is remodelling

    Whatever works

    The observation is not meant to imply that there is only one way to build a wishbone or an a-frame mast or even to compare the two directly. A boat is a synergy of forms and motions. Weights are certainly one concern.
    The important thing is - how it works in a seaway. Obviously, your a-frame has been proven, as has the wishbone we sail. They address the mast "problem" differently.
    The straight line must be held straight or "in column" as the technicians like to say. Forces tend to induce bending. A-frames (essentially a double mast) are strong, but are they synergistically stronger together. By linking them do you gain twice the strength of a single doubly big stick, or something more.l
    A curve, likewise, is not so vulnerable as a single straight stick, being already bent. It needs to be held within the parameters of the modulus and the arcs integrity limits. And two arcs linked together...again speculatively...stronger than a single straight stick of twice the size of a single arc?
    I was looking for some considerate thoughts re the arc of the leach in relation to the arc of the mast leg. I have done some experiments on the foil mast and wonder what the experts on aerodynamics think of the reaction between the mast and the sail spilling wind across it specifically re drag.
    Cheers,
     
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