A frame masts

Discussion in 'Boat Design' started by rgbeuk, Jul 22, 2013.

  1. pool
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    pool Junior Member

    Where would you put that performance advantage of a conventional rig vs. A-Frame in numbers?
    Same boat, same sail area, boatspeed close-hauled = + ?? %?
     
  2. yipster
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    yipster designer

    Many configurations for Amasts are imaginable, few years back i dreamed up inflatable double sails into half wingmast A frame motorsailer that lowers the wings onto the hulls. A rough study in my galery as ladybird. Must still have load etc formulas i found on the net ;)
     
  3. PAR
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    PAR Yacht Designer/Builder

    Without specifics a comparison is not possible, but if you want to go slower and not point as high, just pull a single stick off the boat and install an A frame. I understand the curiosity of novices with the rig, but there's not much of a debate in regard to what they do to a performance envelope, when comparing apples to apples.
     
  4. pool
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    pool Junior Member

    It is about making an otherwise difficult boatsize manageable for a small crew.
    Example:
    An Atlantic 57 catamaran is about the max. size conventionally rigged cat a well-aged and experienced couple could safely handle under all conditions. Switching to an A-Frame rig (same foresails, rollerfurling main) would make handling much easier and safer.
    Upwing in 10 or 15kn TWS - what % loss of boatspeed, and tacking angle, would you expect to see with the A-Frame? Or what % loss of daily run miles in tradewind conditions when crossing the pond?
     
  5. peterAustralia
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    peterAustralia Senior Member

    hi PAR

    I can totally see where you are coming from. I accept that in all probability there will be a weight penalty, a windage penalty, a pointing ability penalty, and possibly a small speed penalty. Those are the downsides, how much the exact penalty is, I guess is hard to say. Yes a comparison with identical boats excepting rig would give real numbers, though much much easier said than done

    The upside though may well be is easier sail handling and lower cost.

    Example, low tech rigs, Hans Klaar can steer his very large tacking proa/unequal length catamaran by himself (70ft or so). Maybe such a thing is possible on a high peformance, high cost modern catamaran, to be honest I just dont know.

    I think this is a very important point. Is it possible for a single sailer to raise and lower the mainsail on a large cat? If the sailer has such a vessel, is he or she forced to carry additional crew at all times? What if that person is single, or whose spouse is not interested in such things?

    Dragon wings catamaran, had twin junk sails, one in each hull. Obviously performance was much less than a modern high tech catamaran, but my guess is that price way way less too. The builder, Gary Lepak was apparently very happy with his boat.

    Hans Klaar, who built his boat in 'The Gambia' had a split mast (by split, I mean damaged). On arriving in Portugal all he needs to do is get a timber felled, and trimmed. In no way would such a vessel compete with a modern cat for a starters it seems to have dificulty making progress to windward, but price is likely to be a fifth or thereabouts of a modern style boat at a rough guess. the original Ontong Java was for sale in about 2010 asking $65K, . Is $65K what it cost to build the original boat in 2007, thats only speculation, my guess is that it is in the ballpark.

    I do accept that its hard to compare, a modern cat has electrics, fittings etc etc, all of which can cost more than the hull.

    I guess my rant can be summed up as this. The a-frame mast may not be a higher performing rig,, but it could appeal to some people interested in lower cost rigs and those interested in easier sail handling

    So, there may be a niche there, for those with a little less money, wanting easier sail handling, and to whom going a fraction slower is no big deal. Modern catamarans are great boats, have made great advances in recent decades, they tend to be just a little pricey though.

    aside,
    Othmar Karschulin is currently building a fairly large proa (12m?) with a bipod mast. The boat is almost ready for launching. In this case the a frame is aligned fore and aft. I guess Othmar's idea is to provide heaps of support against being backwinded, and elimate some of the stays. See link below

    http://proafile.com/forums/viewthread/116/P15
     
  6. groper
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    groper Senior Member

    Your not comparing apples again.... if your willing to sacrifice power, then you can use a cheap and easy to handle rig which has a poor efficiency...as you said... but you can also reduce the size of a highly efficient rig and also make it more manageable and also reduces the cost. Can you see where this is going?
    When you look at the whole package, low efficiency never wins except maybe on cost alone...
     
  7. waikikin
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    waikikin Senior Member

    Maybe it's a case of pears & bananas.......... I've been working nearby Team Australia Orma 60 in the last week or so, I see she's on display at the boat show now, terrific boat & massive wing mast & some impressive performances...... really terrific stuff. I also see that for a cruising vessel that magnificent wing may have some shortcomings. Let's imagine that Mrs X wants a cruising boat.... to live on, cruise around, do a bit of fishing/diving/free boarding behind the dinghy.... usual fun stuff that people do. Maybe Mrs X builds a boat in steel/ply/whatever say a motorsailer in steel even.... so a "dog" under sail, gunna wind assist on all points & blow along down wind, sailing efficiency isn't at the top of Mrs x's list but she wants to do the fun at anchor stuff as well as move around in comfort, an A mast might be the best thing.... stable lowering & raising for bridges, can be used as a Sheerlegs crane to load the dinghy into chocks on the wheelhouse/ stores, a great basis for outriggers for paravane stabilisers & Mrs X can sail along also , so the beauty lies in the versatility....... & low cost of alu tubes/simple fabrication etc. Pears are delicious & perfect for some requirements & conditions....& tastes bananas are delicious & ideal for other requirements & circumstances;)
    Jeff.
     
  8. peterAustralia
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    peterAustralia Senior Member

    here is another one, kinda weird though

    http://www.multihullcompany.com/Trimaran_for_Sale/Custom-Brown_Marples/Liberty_II

    is described as a 'river boat'. I assume that means it cant really go to sea. I guess you could use it for a few years, potter around. Then sell it for half or take it apart and use the fittings for a new boat

    this is good though
    http://www.multihullcompany.com/Article/The_Ten_Commandments_of_Buying_a_Catamaran
    i like the one that says buy for what you want now, not what you want to do in 10 years
     
  9. PAR
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    PAR Yacht Designer/Builder

    The side by side comparisons have been made and if you're willing to accept the cons of the rig, than the pro's should keep you happy.
     

  10. brian eiland
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    brian eiland Senior Member

    I see you are new to the forum, so I might make the suggestion that you make use of that 'search function' on the forum. you can even 'search' within a particular subject thread as well.

    I'm surprised no one has made a link to this subject thread with lots of references to A-frame rigs
    http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999.html

    And has been pointed out Catbird Suite's rig is real interesting in its performance variations:
    http://www.damsl.com/site_files/enter.html?section_id=10001661

    The owner/developer of that Catbird Suite joined in a number of ongoing subject threads to describe his rig. Here is one early posting of his, and if you click on his name "High Tacker" you will find a drop down menu that will find ALL of the postings he made:
    http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-18.html#post630804
     
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