two trailer sailers to make a cat

Discussion in 'Multihulls' started by markcampbell, Apr 17, 2006.

  1. markcampbell
    Joined: Apr 2006
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    Location: new zealand

    markcampbell markc

    and why??
     
  2. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Definitely the dedicated catamaran hull. A dedicated cat hull will be far faster, more manoeuverable, easier to sail, safer and a lot more fun than a cat made of similar monohulls.
    Explanation: Monohulls must be fat and wide, relatively speaking, or else they'd tip over. Long narrow hulls are much faster and more efficient than wide fat hulls. Hence the advantage of a cat, and the main reason for their existence- you get long narrow hulls AND stability. For further explanation, see previous posts in this thread.
     
  3. CT249
    Joined: May 2003
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    CT249 Senior Member

    Well, I'm no designer or mathematician, but .......

    I think you'll find that one rule of thumb (pretty well accepted as far as I know) is that form drag rises by the square of the waterline beam. Therefore the form drag of two Noeleda hulls (total waterline beam say 12') would be about nine time the form drag of a 2' waterline beam cat. That will rather restrict your pace.

    I would also have thoought that wetted surface of the broad mono hull will also be considerably higher than that of a cat hull, which can come much closer to the elliptical/round form that reduces surface area for volume.

    So you may find you go a lot slower than a "real" cat which will make tacking hard (less momentum, less flow over the foils, plus having the slew one hull around the other).

    Secondly, there was nothing in your first post that made it "obvious" that you were not relying on the narrow alloy beams.
     
  4. frosh
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    frosh Senior Member

    Mark, believe me we are trying to be a helpful as possible, and even though it might appear that some of us are trying to ridicule you, it is definitely not the case.
    You mentioned that the Noeleda hulls have a waterline beam about 10% wider than that of a dedicated cat hull. If that was so then your concept could have some merit, but please check your math first. I would be extremely surprised if you were right. L/B ratios of 26 ft.trailer sailers are in the order of 3.25 overall and maybe 4 at the waterline.
    A cat hull of the same length (cruiser) would have a waterline L/B ratio of around 8 to 10.
    Your costing also of $200,000 sounds at the very high end. I have seen a demo cat Radical Bay, design also 26ft. approx advertised at $100,000 ONO.
    Just for interest I have given you the link to the web site for the Radical Bay design. http://www.schionningdesigns.com.au/www/page.cfm?pageID=271
     
  5. marshmat
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    marshmat Senior Member

    Mark, none of us care how it will look. Everyone who has replied so far has commented on how it will perform and sail. The consensus so far is that it will be as manoeuverable as a sewage barge and not much faster than the average chunk of driftwood. We have given you exact replies with regards to L/B ratios of real cats, price of real cats, etc. And it has been pointed out several times that the thing would be a hydrodynamic oddity at best and a dangerous failure at worst. Please, take the advice of everyone who is trying to help you out.
     

  6. Figgy
    Joined: Feb 2006
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    Figgy Senior Member

    It sounds like you have it all figured out. What do you need from us?
    We told you and you don't like the answers. I'll say it again, slow. Your pushing two hulls through the water.
    Your talking about two monohulls tho'.
    Frosh is correct, we're not ridiculing you, but you're not listening to us. We answered your questions. Its frustrating. Just go to a design office and talk to a NA there.
     
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