The all-in-one Mast

Discussion in 'Sailboats' started by katfish, Apr 1, 2006.

  1. katfish
    Joined: Mar 2006
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    Location: Brisbane, Australia

    katfish Wharram builder

    I am not a sailor, have very little sailing experience, so would like to ask you experienced and senior sailors if the following is possible and practical. I am building a 42 ft Wharram Polynesian Catamaran. I do not want wires everywhere. I consider booms to be potentially dangerous, I want quick simple one person mainsail furling, and I want the mast to rotate +/- 45 degrees for stress release, efficiency and sail comfort. I am therefore considering designing a ply/epoxy/carbon fibre unstayed rotating wing mast with in mast furling. Am I asking too much?? Is this too outside the "box", or might it just be possible?
    I might add that as a helicopter pilot, I have a background in low speed aerodynamics and stress systems.
    Any help, advice, criticism (constructive only please) or otherwise would be appreciated. my email address is also available for communication.
  2. SeaSpark
    Joined: Mar 2006
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    Location: Holland

    SeaSpark -

    Cat, unstayed mast.

    If you build a cat with an unstayed mast it would be very impracticle to put it in the middle. The nice thing with a cat is it has a wide base for the stays.

    Putting an unstayed mast in the middle of the beams would require the beams to be very heavy. The one option for an unstayed mast on a cat is like the way they were used on Team Phillips from Peter Goss, see picture, these are unstayed rotating wingmasts. Concidering the way the cat was lost stress calculations on these sort of designs are still hard.

    Eric Sponberg of has lots of knowledge on free standing masts and visits the forum frequently.

    In mast furling has the disadvantages of a high centre of gravity from the furling installation and the sail beeing fully up the mast when furled. When you are at the point of furling a sail you also want the COG to go down.

    When something goes wrong the problem is going to be high up the mast , out of reach. Stress bending the mast is a likely course of the sail jamming at a moment conditions are rough.

    I am a great fan of unstayed masts so good luck with your project!

    Attached Files:

  3. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    Probably best to stick to something more mainstream until you have a reasonable amount of experience. It sould be interesting to see a Cat with a chinese junk style rig on each hull, but while having the reputation of being easy to handle those rigs are also horrendously inefficient. Plenty of folk have donme Ocean crossings on the standard Wharram rigs, probably worth sticking to that for the first tranche and then maybe thinking radical for the next project.
  4. SeaSpark
    Joined: Mar 2006
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    SeaSpark -

    Narrow Pahi 42

    If your Wharram is a Pahi 42,

    this catamaran seems a bit narrow to me if you want to put a mast on each hull.
  5. nero
    Joined: Aug 2003
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    nero Senior Member

    EZ rig. One free standing, fully rotating unstayed mast. One main sail. One foresail. More efficent than traditional rigs. Easier to use.

    This is all the hype. Being about like you, this is my choice. It will be inbetween my cat hulls. The rig will be shorter than a normal bermuda, so I will loose a bit of ultra light wind advantage. Mast will be 10.5 m on a 14.5 m /7,000 catamaran.

    Again, I have no experience with this, only a bunch of surfing the net.

    Look at
  6. SeaSpark
    Joined: Mar 2006
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    SeaSpark -

    Convert cat to proa.

    Putting an unstayed mast in the middle of two catamaran hulls is engineering nightmare. Why not convert wharram 42 to proa?

    Thanks for the link to harryproa , found there, nice example of what may also work with Wharram.
    Joined: Feb 2005
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    MAINSTAY Junior Member

    Mainstay Rig

    The simplest rig with the least wire is probably the Mainstay Rig. There is no backstay and only one shroud.

    Imagine a 3-guy pole that leans toward you, has one guy vertically from the top of the pole, and has a guy run diagonally back on either side so the pole is stable. Now walk right or left until the vertical guy and one of the other guys are aligned in your sight. They are in a vertical plane. Imagine the centerline of your boat also along this line. The diagonal guy is the forestay, the vertical guy is the mainsail stay. Adjust the other guy to be a shroud at the gunwale, and adjust the mast step to the middle of the base triangle.

    Mainsail and foresail can both be roller furled on their stay. Neither needs a boom.

  8. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Cats and booms


    As a cat drawer and builder I can understand some of your reluctance about booms but I would warn about going unstayed. Cats are great boats out on the ocean but they put huge loadings on their rigs. When our 38footer is reaching in a side sea the rig really gets some loading when the windward hull drops down over a wave.

    I am not convinced wires are a problem. In a real time use analysis of how you will use you cat the extra drag from the wires is not a problem. Most cruisers sail downwind so a little extra drag is not bad. When going upwind in tradewind conditions having an inner forestay for a little jib is really nice. I guess I am saying - a cruiser doesn't care about drag so much because you are usually slowing the boat down. Our 38ft cat did three Barrier reef trips and we only let her rip a few times. Usually we eased her back.

    Our boat has a wishbone boom to get around a few of the problems as I see them that are inherent in cats. It reduces sheet loads dramatically, I have a 4:1 mainsheet system and can pull it in anytime. The wishbone reduces compression on the mast as it feeds the leech tension back up the mast and it is much safer on two fronts.

    The first is the obvious one - lack of something hard to hit your head and the second less so. The traveller is not whizzing past you every gybe near feet or hands. I built our boat to be kid friendly and it is. I like the idea of keeping all the load away from hands. Rob denney does this by his rig on the Harrys but you can do much the same by having a wishbone and cutter rig on a standard cat. The Captain Cook can have wishbones.

    Give me an email at if you want some pictures of our 38ft Kankama. I love my wishbone on a large cat. Small cats aren't so scary but a wishbone cutter rig is very low loading and safe


  9. yokebutt
    Joined: Aug 2004
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    yokebutt Boatbuilder


    Have a look at the "Ljungstrom rig".

  10. OldYachtie
    Joined: Jan 2006
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    OldYachtie Junior Member

    Tandem unstayed mast biplane rigged catamaran

    This may be an old thread, but it is still found by Google, so more people will read it in the future. The Hasler designed Junk rig tacked through a 100 degrees, no better, but the new rigs with camber will tack through 90. My version of an unstayed tandem rigged catamaran with a efficient junk-like rig can be viewed at There are many relevant links at the bottom of that page, as well.

  11. BigCat
    Joined: Jan 2008
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    BigCat Junior Member has changed

    My new website URL is - where you will find catamaran designs that feature unstayed masts, lots of watertight bulkheads, and no hull protrusions (aka "shelves",) to slap, bang, and drag in the water.
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