Trimaran with accomodation in the amas

Discussion in 'Multihulls' started by eiasu, Nov 23, 2012.

  1. El_Guero

    El_Guero Previous Member

    How deep your floats ride will certainly affect stability.

    1 inch deep, little help. 2 feet deep, a lot more stability.

    But, on your amas, the more you can keep them narrow, Richard Woods may need to correct me on this, but if you can keep your amas narrow and long; you will keep better speed performance over making them thicker.

    You will still want around 200% buoyancy. But, that is naval architecture above my skill level.

    What I am understanding in design, is that the greater buoyancy with thinner hull beam leads to better overall comfort.

    To a point.

    I hope I made a little bit of sense.
     
  2. El_Guero

    El_Guero Previous Member

    However, I keep coming back to what Richard implied, wrote, in one of his posts.

    If you keep the amas in the water, you are better off with a catamaran over a trimaran.

    From what I understand, each hull impacts the other hull(s). When you have more than one hull. The hulls affect each other to about about 20% drag. So, the two extra hulls in the water defeat the purpose of speed ....

    You are better off with just a catamaran.

    Speaking of which:

    http://www.multihull.com.au/site/www/pdf/pdfs/hemisphere.pdf from a different thread on boatdesign.
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    Floats somewhat immersed also keep overall draft down. With enough in the water to carry their own weight the main hull can be shallower. A skinny tri mainhull is pretty deep as it carries everything at rest.
     
  4. mcarling
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    mcarling Junior Member

    No, I don't. The greater the beam, given typical 3rd generation trimaran geometry, the greater the vertical distance the amas will move during a roll.

    As others have pointed out, it's possible to use geometry in which both amas are immersed, but then I would argue that it wouldn't be a 3rd generation trimaran. As others have observed just above, it would lose much of the trimaran's natural advantages over a catamaran, without gaining any of the catamaran's natural advantages over a trimaran.

    I'm having difficulty understanding the motivation for putting accommodation in the amas. If I were designing a trimaran large enough to even consider it, I would use electric propulsion, heating, cooking, etc. and look into putting one diesel tank and one diesel DC genset in each ama. Keeping all hydrocarbon fuel out of the vaka would make for a more pleasant (and arguably safer) boat as well as freeing up some space in the vaka, as no engine room would be needed, just a small space under the sole for an electric motor, water tanks, A/C condenser, etc. Of course, when flying an ama, the windward genset could not be used (no cooling water) but that shouldn't be a problem. Intermittent supply of cooling water in very rough seas would be tough on the impellers.

    If you want more space in the vaka than a trimaran can provide, but don't want a catamaran, you might consider the possibility of a quadramaran based on a very narrow, very high-performance, low-stability catamaran stabilized with amas. Please forgive my primitive graphics, but something like this:

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    There is probably a good reason why no one builds these. Cost would be my first guess. The best solution to more space in designing a trimaran is probably added length.
     
  5. Alex.A
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    Alex.A Senior Member

    How about this?
     

    Attached Files:

    1 person likes this.
  6. cavalier mk2
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    cavalier mk2 Senior Member

    The more moderate beam is refreshing. A common design mistake is thinking a trimaran has to conform to the wide stance developed for racing. I don't like the wing bunks as they'd either be head up or down depending on the tack unless they had a leveling system which would add weight and possibly use power.
     
  7. eiasu
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    eiasu Junior Member

    looks like something like the neel
     
  8. mcarling
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    mcarling Junior Member

    That's a Neel 45 in charter configuration. I think the berths in the amas are meant to be used only at anchor.
     
  9. eiasu
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    eiasu Junior Member

    Thank you all for the answers.
    So all back to the original question now it is in this form:
    a trimaran design of 78 feet with accomodations in the amas
    and a with flare central hull and huge living spaces
    does still take advantages of the trimaran design,
    like superior performance and confortable motions,
    or for such lenght is better to go on a catamaran design
    to have good performance, confortable motion
    and still very large interior spaces?

    thank you very much for the patience to deal with a complete
    beginner
    eiasu
     
  10. mcarling
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    mcarling Junior Member

    eiasu, I don't think there is a one-size-fits-all answer to your question. Start with your budget and how much space you need or want. Then prioritize speed, ease of handling, comfort, safety, ease of maintenance, etc., etc. Design is all about compromises. The compromises that I would make would be anathema to some other people and vice versa.

    I can tell you that I would try to keep berths reasonably near the centerline if they will be used while sailing.
     
  11. eiasu
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    eiasu Junior Member

    Here there is my anathema,
    I want to start to figure out the best-compromise vessel for us,
    then calculate the budget needed for such a boat
    and then prioritize the way exactely you describe.
    The 24 meters size is to have the biggest lenght possible for all kind
    of EU rules.
    The prioritize the way you describe i also agree 100% and looks like
    Chris White is oriented in the same way with his designs,
    that's way i like his designs very very much.
    Still I will have to experience directly the different designs,
    like horstmann and hammerhead for example,
    just because all ideas and numbers they do not give the
    feeling of space, pleasure of sailing of the different designs.
    ciao
    thank you
    eiasu
     
  12. mcarling
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    mcarling Junior Member

    A custom 24m trimaran (with so much accommodation that the question of putting accommodation in the amas would even arise) is probably going to cost $3-10 million. Is the Hughes 71 really not large enough for you? Have you sailed anything that large? How much sailing experience do you have?

    If a magic genie told me that I could have a 24m trimaran to my specifications for free, I would start by scaling the vaka and amas of a Dragonfly 32 by 2.4 in length and 1.8 in beam and draft. But what I want and what you want are almost certainly different.
     
  13. Alex.A
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    Alex.A Senior Member

    SOR matched to budget is a good place to start. Why the the insistence on the accommodations in the ama's? In a boat that large, I can't see the need...
    That's why I posted the neel 45', as it covers much of your needs in a far smaller boat.
    Truly, I think a catamaran will suit better in a larger size. Or a condo(tri)maran.
    With berths in the ama's you are not going to get performance anyway. Not with any comfort.
    As budget hasn't been discussed, you could go with a Wharram pahi 63 or a islander 55 or 65 and still get what you want plus. Islander 55 quoted reasonably recently at 165 k at a Wharram approved builder in Thailand.
    Not the epitome of performance but a comfortable, large boat.
    Hans Klaars new "cat" was quoted by helper builder at 75 k. 72'.
    Or at the extreme - Inigo Wijnen's proa at 70'.....?
    Budget and statement of requirements. Length is meaningless - unless designing to a racing rule and then length is everything.
     
  14. Corley
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    Corley epoxy coated

    My personal view is a trimaran with excellent sailing performance and lots of accomodation are two directly opposed requirements, build a cat. If you can be happy with moderate accomodation and float berths to be used at anchor you can strike a reasonable compromise and still see the trimaran benefits. There is a reason why there are so many cats out there it's because they tick the boxes for more people in practical terms. If it has to be a trimaran then some compromises are required. Most of the time will be spent at anchor if you dont mind tighter quarters while on passages I can see how a trimaran could work quite well.
     

  15. mcarling
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    mcarling Junior Member

    Even with a catamaran, lots of accommodation and excellent sailing performance are mutually exclusive, though to a less severe extent than with a trimaran. Mostly it's less noticeable with the catamaran because expected performance is lower.

    I just don't understand why someone would want a sailing trimaran with accommodation approaching that of a small cruise ship.
     
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