Catamaran vs Trimaran

Discussion in 'Multihulls' started by Maciek188, Jul 17, 2005.

  1. creightonious
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    creightonious New Member

    In all this talking of the advantages of great beam in multihulls, let's not forget the dirty little secret of tris (which configuration I favor): Once the windward ama is clear of the water, we are dealing with the tri's half-beam, not the overall beam.
    This accounts for the increased heel and the increased susceptability to wave-induced capsize.
    It also introduces a fairly powerful set of reasons to take a very serious look at Rob Denny's Harry Proa concept.
     
  2. Doug Lord

    Doug Lord Guest

    tri vs cat

    I'm not sure I agree with that: the square or over square tri puts the CG furthest from the center of buoyancy(when mainhull is just clear) of any multihull and that's good for enormous power. Combine that with the banana boards in the ama's and a rudder t-foil and you have enormous power and the means to use it all with the least wetted surface and greatest pitch resistance. When all that power can't be used in light air you still have more power and less wetted surface than a cat. At least so far....
    Rob Denney's innovations in proa's are extraordinary-I sure do agree with that.
     
  3. rob denney
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    rob denney Senior Member

    G'day,

    Thanks for the compliments.

    Tris are wider for structural reasons, but also because when it is time to tack, they only have half the width in the water. A square cat struggles to tack, particularly in waves. Proas don't tack so can be much wider than cats, possibly even than tris. There limit is diagonal stability, which could be augmented by foils (bit tricky as they have to work in both directions) or, my preference, a longer lee hull. Because there is nothing attached to the ends of the hull, this is neither expensive, nor draggy.

    I am currently building a proa for the 2008 solo Transpac (SF-Hawaii) which has the same sail area and weight as a 7m/26' Firebird cat. However, the proa is 7.3m/27' wide and 15m/50' long. Should be an interesting test of the above theory.

    regards,

    Rob
     
  4. Doug Lord

    Doug Lord Guest

    fast multi's

    Rob, would the windward hull of a racing harryproa still be the"heavy" hull as it is in the crusing version? And would it be designed to fly-just kissing the water-for minimum wetted surface and maximum power?
    I've gone oversquare on rc model foiler tri's with no negative effects on tacking with the lateral resistance disposed equally at the ama's-no main daggerboard. From that -and what you said(good point!)- I don't see any limitation on beam(except structural at some point) on your boats or tris -as long as diagonal stability/pitch stability are controlled.
     
  5. rob denney
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    rob denney Senior Member

    G'day,

     
  6. ActionPotential
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    ActionPotential Junior Member

     
  7. ActionPotential
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    ActionPotential Junior Member

    Doesn't the load from the rig ease the load on the beams?
    Like the windward hull being lifted by the sidestay rather than by the beams.
     
  8. rob denney
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    rob denney Senior Member

    Steering is from the windward hull, but will be done with a wind vane on a long arm (minimal electrical equipment to save money, weight and complexity of generators,). Nothing to stop a keen crew shifting gear (liferaft, anchor etc) and self to leeward in light air to lift the hull. Windward hull is sitting in my garage at the moment, weighs 27 kgs, has bunk and shelf to be fitted, so should be pretty easy to fly if unloaded.

     
  9. Vega
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    Vega Senior Member

    Hey guys, take a look:cool: (photos from "The Route du Rhum" 2006):
     

    Attached Files:

  10. ActionPotential
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    ActionPotential Junior Member

    Great photo's! No cats there. These are built to a rule and they can't build a competitive cat to that rule (they tried and failed). For the same money they can build a longer faster cat. Maybe they should alter the rule to allow 60' tris or 80' cats? When they built 60' cats tothe rule they were not competitive but were significantly cheaper.
     
  11. brian eiland
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    brian eiland Senior Member

    Seahorse Article

    Dear RMG,
    I forgot to thank you for posting this article. I missed seeing it as I do not get this publication anymore (got rather pricey here in the US, & I already get tooooo many publications).

    For reference I reposted under this very applicable subject thread, "Sail Loading on the Rig, Rig Loading on the Vessel". and specifically here:
    http://boatdesign.net/forums/showpost.php?p=114487&postcount=59

    If you have any more such material please contribute it. And you might be interested to contribute to this other subject thread. Thanks
     
  12. brian eiland
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    brian eiland Senior Member

    some more 'Structured' Cats

    ...two recent postings related to this Alinghi cat. Wonder what we will see from Alinghi for the America's Cup??
    Another 'Structured' Cat
    http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-6.html#post277098

    Boat with NO HULL
    http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-7.html#post277099
     
  13. ThomD
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    ThomD Senior Member

    Whille we are waiting, we have the Gougeon racing cat/tri supposed to make it on the water this summer according to the lattest issue of Epoxyworks. Always interesting to hear what blend of features Jan comes up with. I thought it might be G32 ish, with amas for greater stability in blasting mode, but I now don't think so.
     

  14. oscarvan
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    oscarvan Junior Member

    Greetings....new around here and I see there's lots of reading to do, which is good as I have many hours to kill holed up in hotels on various continents. (Airline pilot).

    To me the Cat/Tri is the same discussion as the snow board/ski discussion. It's a different motion. I grew up on two boards, and never was able to change my mindset to a single board.

    I also grew up a mono huller. When I realized that carrying all that lead around (8300 pounds on my last boat) was pure insanity I saw the multihull light. So I went tri, because to me it's a mono hull. Minus the lead, just two floats for stability....LOTS of stability....:D A cat is, again to me, a snow board.
     
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