Main-less rig

Discussion in 'Multihulls' started by Spiv, Feb 10, 2008.

  1. MAINSTAY
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    MAINSTAY Junior Member

    Brian asks:
    The tension on the forestay is maintained by the mainluff stay, which acts like a backstay. See attached files.

    As with a backstay, the relative tensions are directly proportional the the angle of each stay from the mast.

    In a sloop rig the angles, and therefore the tensions, are equal when the mast is at 50% of the distance between forestay and backstay.

    In this rig, the tensions and angles are equal when the mast is around 55% to 65% of the distance from forestay to mainluff stay, depending on the rake of the mast.
     

    Attached Files:

  2. RHough
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    RHough Retro Dude

    What effect does tacking have on the mainluff wire tension?
     
  3. Spiv
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    Spiv Ancient Mariner

    SMG 50plus

    Hi Brian,
    yes the SMG 50plus is very close to the kind of boat I want to go and live on.
    They are being built is S.Africa, apparently they have orders. The basic boat is U$925,000, pricelist attached.
    Perhaps if I had that kind of money I would consider it, but I am sure I can get a similar or better (for me) boat built in Thailand cheaper. As a matter of fact, I could get it built in Western Australia cheaper than that.
    Additionally, I think you and I can develop a better rig than that...
     

    Attached Files:

    Last edited: Mar 21, 2008
  4. Spiv
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    Spiv Ancient Mariner

    Catenary arch mast.

    Pericles said:
    I suppose that is could be a development of the 'Wishbone' mast we have been discussing above.
    Made in Carbon fibre and with Spectra or Dyneema connecting the two spars for rigidity, it would make a very light and slim rig.
    Hinged aft and raked forward it would cause no interference with the sails.
    It could be lowered in seconds, and it will not protrude forward too much.
    Just the mast I am dreaming about...:D:D
     
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  5. Pericles
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    Pericles Senior Member

    Well, as the catenary shaped "A" frame mast, has received some approval, I may as well reveal another secret incorporated into my cruising catamaran design. http://en.wikipedia.org/wiki/Catenary

    The catenary shape is also superb if used as the cross section outline for the catamaran hulls. Assume for a moment the vessel is floating correctly to her lines. As the vessel is loaded more and more and further immersed into the water, the wider shape of the arch resists immersion and improves the buoyancy. This happens whichever profile is chosen for the hulls, fat or thin. This shape will deliver the minimum wetted surface, par excellence.

    Using the characteristic shape throughout from slim, vertical stem bow to wide, weight carrying stern also increases the internal volumes within the hulls without the ugly bulges that I have seen in some catamarans.

    This brings me neatly to the almost ideal method of constructing such hulls, which has nothing to do with me. The credit goes to Kurt Hughes and his Cylinder Mold method.

    http://www.multihulldesigns.com/pdf/cm33.pdf

    http://www.multihulldesigns.com/

    Kurt is very candid about his process. "Every building system has
    limitations. CM is no exception.There are some restrictions on the possible hull shapes. To keep building time down, CM hulls should be simple curve
    sections.
    Flares, steps, and hollows are not easily possible. These hulls must have slenderness ratios 10:1 or thinner at the waterline if they have reasonable amount of rocker in the profile. Within these constraints however, virtually any hull shape is possible."

    Those shapes highlighted in red are NOT used in catenary shaped hulls. The upmteen panels used to create the molds will be catenary shaped and the flat surface profiles are patterned to ensure the port and starboard halves of each hull mate accurately together along the keel line and open up as the correct shape. There having been much discussion elsewhere on this forum about the benefits of rocker, I submit that the least amount be used, to minimise hobby horsing, whilst retaining fast tacking ability.

    Comments welcome please,

    Pericles
     

    Attached Files:

  6. Spiv
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    Spiv Ancient Mariner

    Catenary Hull shape

    Very, very interesting idea Pericles.
    Why don't you start a new thread, I will gladly subscribe to it and we should get a lot of interst and hopefully good ideas will develop.
     
  7. masalai
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    masalai masalai

    Pericles, Certainly Kurt Hughes produces a sweet and fair underwater hull but topsides - Yeuch... & I am not sure I like the aft sections on the powercats for long distance cruising efficiency... But them's my perception - as with most designs it is a "personal thing" else there would be just one efficient design and no need for other views or architects.... Viva la difference!
     
  8. sigurd
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    sigurd Pompuous Pangolin

    mainless cat

    what are the little strakes, or what to call them, in the bows?

    [​IMG]
     
  9. masalai
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    masalai masalai

    Sigurd, I am only guessing, to deflect water? You will see different solutions on many very skinny hulled powercats, such as the maincat, Malcolm Tennants designs, Kanga Bartles, Robin Chamberlin & other power cats use a full length "rail"... My model was supposed to have one but lost most during "fairing" and build process by the model-maker... Have a look at my photo galery for the Chamberlin C-10 metre version which I nearly bought but I wanted significantly more (fuel tank) range... If you look at the model video and from bow on you can see the water flowing up the hull and under the bridgedeck to fall off around midships. I am guessing this is the reason - but I could be VERY wrong... as another thought - to house a mechanism to furl the sails remotely... Or to provide the engineering to facilitate electric or power furling... Looking again at the image I am inclined to figure on the latter as the hulls are VERY slender. . . That is John Hitche's design & build called "X-IT"
     
  10. brian eiland
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    brian eiland Senior Member

    That's it
     
  11. sigurd
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    sigurd Pompuous Pangolin

    Apparently John Hitch is the correct spelling.

    You know whether it works well? I thought it looks like it will throw some spray because of the steep angle.
    Is it ment to give any appreciable lift, or just break up green water coming back towards the bridgedeck.

    I think it is nice with those skinny hulls and also the faired shape of the bridgedeck seems nice.
     
  12. masalai
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    masalai masalai

  13. Triroo
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    Triroo Junior Member

    Here are a couple of photos of X-IT going to windward in light airs.
     

    Attached Files:

  14. sigurd
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    sigurd Pompuous Pangolin

    It looks like the bows should have been pointier, or what do you think.
    I'm thinking about the small, short spray "bow-wave" or whatever you'd call it.
     

  15. masalai
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    masalai masalai

    Triroo, Thank you very much. I admire his work, If you know how to contact him and John Hitch is amenable, please PM me
    Brian
     
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