"semi-stayed" riggs

Discussion in 'Multihulls' started by champ0815, Aug 14, 2010.

  1. champ0815
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    champ0815 Senior Member

    Well, I have followed with interest the different threads about the pro and cons of stayed and unstayed riggs on multihulls and was asking myself if it is possible to combine the best of both worlds... .
    Starting point of my thoughts was the often used reference of surf riggs for the advantages of unstayed riggs.
    In my opinion, this kind of rigg is no true unstayed rigg, since the surfer is keeping it upright by the means of counter-balancing the wind load with his weight via the connection he has with the boom. Therefore the unstayed part of the rigg is only the part above the mast boom connection, making it a "semi-stayed" rigg.
    Following this general idea, it seems to be useful to mimic this kind of rigg (stays hold the mast on height of the boom) on other sailboats, especially cats since there a real unstayed rigg is difficult to install on the beam.
    Advantages would be:
    • large stay angel reduces compression loads on the mast base
    • shorter cantilever reduces loads in the mast(above the stayed part)
    • control of stays without need to climb in the rigg
    • on large cats the support of the mast could be integrated in the structure of the deck house
    I know the advantages of a stayed rigg, especially in terms of using fore sails in different sizes and light wind sails (in this last aspect I am still waiting for a usable kite solution;) ), but I am interested in the opinion of engineers and experienced sailors about the physics and the usefulness of such a rigg concept.
     
  2. ThomD
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    ThomD Senior Member

    Basically you want a half fractional rig.

    To me that might be a little half pregnant. If one has an unstayed rig, there are certain issues like it needs to be carbon (etc...) . With a stayed rig there are certain issues like it needs to deal well will load take-offs and compression. Both seems to mean evolving a hybrid and facing all the problems in one product. Not sure where the payoff would be.
     
  3. champ0815
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    champ0815 Senior Member

    The starting point of my thoughts was the feasibility of recycling used surf riggs (at least the masts - cheap and lightweight) on a platform like small catamarans (up to 6m) without to much violating the specifications of the masts.
    Therefore, the use of an attachment at the height of the boom seem to be the natural solution, especially with regard to the problem of mounting an unstayed rigg on a catamaran.
    An interesting side effect of this kind of rigg could be the mimicking of the use surfers make of their sails by canting the rigg. To implement this, a surf mast base can be used and some means to manage the length of the stays (without getting demented by the need for handling even more ropes while sailing:p ).
    Leaving aside this technical gimmick, i asked myself (and this forum) if in some modification this kind of rigg could be useful on multihulls generally.
    As Eric Sponberg stated somewhere in his very useful explanations about free standing masts, the righting moment of multihulls requires relatively heavy masts.
    By attaching the mast somewhere in the lower third of its length, could this reduce the bending loads on the mast structure significantly to allow for lighter "free standing" masts on multihulls (and solving the problem of attaching a large cantilever on the beam of a catamaran)?
    To be absolutely clear in this point: this thread is not about the pros and cons of free standing masts on multihulls, just about the feasibility and usefulness of using them by the means of some kind of "hold it upright" attachment in the lower part of the mast.

    Thanks for your attention!
     
  4. Scrumble
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    Scrumble Oram 46'C MS Builder

    This concept would interest me.
     
  5. garydierking
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    garydierking Senior Member

    I use windsurf spars on some of my outrigger canoes and sometimes support them with a shorter stub mast. A halyard connects to the boom height reinforced area of the windsurf mast, allowing you to easily lay the rig down. Windsurf masts will also free stand with as little as 300mm bury, allowing the possibility of a small tripod to support it on a catamaran.
     
  6. ThomD
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    ThomD Senior Member

    Windsurfers are a fairly comon choice on multis, so that will work, for the reasons you mention. I don't particularly see the point in scaling them up though. I suppose the idea behind fractional rigs is like the idea behind joist that cantilever out from a wall. There is an actual benefit up to a point. In this case the sail above and the sail below load the spar and it ballances out a little bit. And then on top of that there is whatever aero cleanliness you also get. Don't know, just a guess. If 1/2 fractional rigs were better than 3/4 fractional rigs, it is hard to see why we wouldn't already have them in wide use. I think it spans a neatherworld where aluminum would be working way out of it's comfort zone, and carbon would be expensive without getting all the benefits one could sumon up from a freestanding spar, or some kind of carbon stayed rig. But then that is just conventional thinking.

    I knew one guy who did a 24 foot tri with 2 windsurfer rigs on it, one on each ama. Apparently it worked well. This was pre-Ketterman, I think.
     
  7. Dryfeet
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    Dryfeet Junior Member

    Hello all! Longtime lurker, now registered.

    So, I've been thinking Sliding Gunter rig. Fixed mast is short but properly stayed for headstay tension. Carbon 'gunter' above the masthead. Yup, a fractional rig. The big question is--- What's the practical upper size limit for such a mainsail on a catamaran?
     
  8. ThomD
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    ThomD Senior Member

    Are you thinking of the K-Designs Gunter? That is probably a 2/3rds fractional, or not fractional at all I suppose. It is a perfect example of some of the problems since it is both aluminum and carbon, so two technologies for the builder to handle. Really like the concept though because it is an easily hand raised mast for boats that would otherwise need some kind of more complicated mast raising routine. I think the perfect size very light cruising boat for 1-2 is in the 18-21' range, and this spar could make single handed cruising/raising a reality with ease, in those sizes.
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    A sliding gunter, like a gaff rig can be made any size as long as the engineering is adequate. I use a composite-molded sprit fitting to save weight on my canoe and really like reducing the rig height as I reef. It works great with full battens but you have to live with a smaller jib. The navy used them in the 1800s but didn't like the expense of the sprit fittings. For a small boat you get tall mast performance on a rig that can store inside the boat.
     
  10. Dryfeet
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    Dryfeet Junior Member

    Thom,

    Yes, much like that or this link-- http://proafile.com/view/weblog/comments/beach_cruiser_reloaded/ as I really like the squaretop 'look' also, despite the probable awkwardness of handling that last batten.

    I am looking for ability to ease the main significantly when off the wind without shroud chafe. I'd prefer unstayed but that would appear to have to be hull mounted and I've yet to see a sufficient discussion of the consequences of having everything in one hull. I'd be very open and have closely followed Ray A's investigation into a single rudder. I'm still of a mind to have two similar hulls as opposed to a tacking proa with different sized hulls.

    The sliding gunter is less of a leap than these other concepts so probably $afer.
     
  11. Alex.A
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    Alex.A Senior Member

    Rob Denney did a cat (?) like this. Proa hulls thread-page5. I too was curious...
     
  12. Dryfeet
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    Dryfeet Junior Member

    Not quite enough info in that thread (thanks for the heads up though). Too many variations. Sounds like the rudder needs to be a bit bigger/deeper if only one is used. When you do the heel/stability calcs, off center makes no difference but from a turning moment perspective, it seems that some sort of compensation is needed for at least one of those tacks. Much like having a port engine pushing turning a boat to stbd kind of thing. However, long and narrow hulls might not really 'feel' that difference. It would be nice to hear from some bi-rig owners how things work when only using one sail.
     
  13. Alex.A
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    Alex.A Senior Member

    Search radical bay 800? Bi rig that had issues.... they dropped one sail to tack easier..... i think rudder size too was an issue?
     
  14. champ0815
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    champ0815 Senior Member

    Ok, I see the topic has moved a little bit in an unexpected direction... .:D
    Nevertheless, the sliding gunter is an interesting concept for a hybrid rigg between stayed and unstayed.
    Am I right with the assumption, that the "sliding" refers to the gaff which is movable in vertical direction without changing its angle to the mast?
    If so, I see the advantages for reefing, instant depowering in gust response and the availability of fore and lightwind sails.

    Has anybody ventured in the direction of telescoping masts (where the "gaff" slides in the mast for reefing)? This seems to me the next step in this direction, solving the problem (if there is any) of gaff tension... .

    And to come back to my initial questions: :cool:
    Since nobody challenged the feasibility of using boom height supported surf poles on small multis, what about the upscaling of this idea to larger boats? No advantages seen, neither in rigg maintenance nor in weight of an adequately designed mast (in contrast to a real free standing pole) or in support and compression loads on the beam of a cat?
     

  15. GTO
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    GTO Senior Member

    Look at these pictures...

    http://www.microcruising.com/more1.htm

    So it has been done, but I fail to see the benefits when just a slightly beefier unstayed mast does away with the deck clutter.

    The mast in the pictures is designed to drop to the side for passing under very low bridges with minimal bother. If you don't need that ability, I can't see the idea being worthwhile.

    Masts for small (and how small are you talking?) boats are relatively easy to glue up. I'm very happy with my 19' spruce mast. Took a weekend to build and that was due to the cure time.
     
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