Catamran with four masts

Discussion in 'Multihulls' started by PrimoPiatti, Oct 8, 2006.

  1. PrimoPiatti
    Joined: Jul 2006
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    PrimoPiatti New Member

    We have a project in the conceptual stage inspired by several successful cats witn biplane rigs, especially the Radical Bay 8000 by Schionning Designs:

    http://www.multihull-maven.com/Boats/Radical_Bay_8000

    In racing the original Radical Bay the crew found that they had to reef later than other boats, probably due to the lower centers of effort. As a consequence the design sailed well against larger competitors.

    We have a pair of 10 meter hulls already built to use for the project. In discussing scaling a rig like Radical Bay's to a larger size we've also discussed carrying the low COE strategy even further by subdividing it into a ketch rig on each hull, four masts total (all carbon, unstayed).

    This would maintain the benefit of the low COE and perhaps add further benefits: higher potential sail leading edge and thus high aspect ratio efficiencies; incremental sail lowering, mast by mast, to distribute driving force to best advantage; double wing and wing downwind; less weight aloft to reduce pitching moment; less actual force required to positon sails; and redundancy in case of part failure.

    On the other side of the equation we might be looking at greater cost in materials and labor; lower effective available wind speed due to lower rig height; more sailhandling controls to deal with; and of course blanketing of one aft sail on most tacks.

    Still, it's a tantalizing direction and well within our capabilities and budget. Any comments or suggestions?
     
  2. Doug Lord

    Doug Lord Guest

    4

    Sounds interesting except that the lee aft rig would almost certainly always be in the windshadow of the forward windward rig upwind. As a suggestion: why not build an rc model and test it thoroughly. Parlier did that with Mediatis Region Aquitaine and I'm certain you'd gain valuable information in the least expensive way possible. I hope you'll keep us informed!
     
  3. nick storm
    Joined: Oct 2006
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    Location: Queensland Australia

    nick storm Junior Member

    Great to see another four master out there, Ive been working on basic
    designs and models of 4 mast cats for a couple of years on and off, so I obviously think you are on the right track with this idea,
    in reference to the possible problem with the wind shadow cast on to the lee aft rig , I have tested basic models and found that by staggering the masts, ie not placing them in the absolute corners of the deck, but, aligning them with the most common sailing directions, of say 40 and 90 degrees, you can feed clean air to them , obviously depending on size of rigs and vessel.
    One of my ideas is to build rigs that are solid wing sails, that are able to be stored on the cabin top and then swivelled up and down as required,on s/s stub masts.
    On a cat of say 45' x 22' beam, the cat would have 4 x 24' x 6' rigs, the super slick wings will give 2-3 times the power from conventional sails and the ability to drop or raise 25% of the power will make reefing, sailing backwards, holding station, and crabbing sideways all possible, and all done from the flat deck below
     
  4. PrimoPiatti
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    PrimoPiatti New Member

    Thanks --

    to both of you! The finished boat would incorporate many details specific to this rig (like bulkheads positioned and engineered to support the masts), so it would be good to generate specifications with as much simulation as possible, actual and computer. We're working now to get enough of a schematic together for meaningful model testing.

    This is where Nick's experience is especially valuable. Our hulls are shorter than your example, but my first round of sail calcs sounds a lot like yours. The shorter masts are a real benefit, since we expect to be cruising and and want to have simple and safe sail handling. As you say, this might be a good vehicle for testing wing masts. Here's a link to an interesting wing sail project done recently in my area:

    http://www.soe.ucsc.edu/~elkaim/Documents/ElkaimDesignCat.pdf#search="wing mast bearing"


    This is an abstract, but there is a link to a longer version. Dr. Elkaim makes the case that his wing profile has very low windage when luffing -- so low that reefing is unnecessary. Sail angle is positioned with the trim tab using the force of the wind itself! It seems like the way of the future but I'm not sure how much to take on.

    Of course the lee aft mast is blanketed -- or is it? With a wide boat on some tacks it might actually draw well if the forward sail in the lee hull were reefed (good thing to test in models!). This would be an ideal arrangement for keeping downward pressure off the lee bow.

    In general the potential for distributing sail force among four masts adds a whole new dimension to reefing. Basically we have the option of 'trimming' or 'tuning' center of effort around the deck plan. For example, as wind rises the foward sails can be taken out of action, moving the CoE well aft to keep the bows from burying.

    As Nick points out, potential for non-traditional maneuvers is there, which could be useful in an anchorage an in docking, at the least. I'm wondering Nick what your mast positions are -- not quite sure from your description.
     
  5. nick storm
    Joined: Oct 2006
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    Location: Queensland Australia

    nick storm Junior Member

    four master catamarans

    Thanks Primo,
    well, I think the rig positions should be staggered according to the vessels and rigs width,( on a 45' x 26' cat , using a wing sail of say 6' chord then they should be staggered around 8' from each other), although this may not always feed very clean air to the rigs, they wont flutter and stall as easily as a sail will, naturally you could also make the rig taller and narrower if needs be, personally I like the rig on Macquarie Innovation, its very much the sort of thing I am advocating, though mine is just a bit taller. Thanks for the article, funnily enough found it 4 days ago and thought it was very well done and answered so many questions, I was particularly interested in his findings on symmetrical wing shapes, with these tacking will be so easy.
    Basically I love the idea of having a simple sailboard type rig, and thats what this is, light, strong, flexible and folds away when you dont want it upright....A 24' mast on a 5' stub should be around 30kg and quite easy for one person to swivel up into position
    If you can stow these tall skinny wings athwartships on a flat cabintop or on the deck alongside the cabintop then , not only do you have an easily hoisted, easily reefable and ultra fast (see Macquarie Innovation.!!!) rig, its something you can make in a weekend in the garage, from a myriad of materials to suit your budget, not forgetting that you would make the rigs balanced, so that they are easily controlled, thus depriving the coffers of messrs Harken, North,etc, and the need for sheets,winches,stays, shrouds, halyards, solid heavy masts, booms, poles, windage, and a ton of weight up where you dont want it, I believe that the walker wingsail was doomed to fail, because although it handled rough weather and big seas well, and the rig always weathervaned into it, sailors just looked at it and shook their heads, because anyone could see that the rig was unstable if for some reason that it didn't swing around into the wind, and we all know that out at sea anything can happen. Well I believe that we have to folow nature, and just like the dragonfly the maybug or the falcon we should have wings we can fold away, or in my case swivel down onto the deck and thus reduce windage to a minimum, going downwind in light airs you could fly a massive spinnaker or kite, from the tops of the forard rigs, and drop the aft masts. Naturally designing such a wide base for the four masts will entail the total redesign of the hulls and deck and thats what I am really interested in........phew , its all good fun
     

  6. Roger Dann
    Joined: Dec 2006
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    Location: Canada

    Roger Dann New Member

    4 sails on a radical bay?

    I was seriously considering getting a Radical Bay 8m built while I am here in China. Unfortunately costs are still high for this 'weekender' cat, even here. Looking at other rig options got me also researching the windsurfer masts & sails. The rough max windsurfer area 4x10sq. M will give the 40sq. M Schionning has in two and the cost is way down. The possibility of lowering onto the cabintop for under bridges is also very nice. I hoped to incorporate solid bridgedeck and solid sunshade over with solar panels for electric drives. Unfortunately putting a lot of time and $$ into this 4 mast design is not possible at the moment. I may end up getting a used Gemini for 1/2 cost of a Schionning Radical Bay. Too bad. I hope someone gets the guts to do it.
    Roger
     
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