Trimaran with swath and regular hull shape?

Discussion in 'Multihulls' started by Joris ypd, Jun 19, 2012.

  1. Joris ypd
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    Joris ypd Junior Member

    Hey

    I'm currently doing research on designing a trimaran using SWATH-technology for my thesis. The basic idea is to have the two sides mounted on SWATHbodies and the middle part to be just a regular hull shape, placed in forward position of the SWATH bodies.
    With a minimum length of 130 ft the total body is supposed to have a goal displacement of more than half of it's monohull brothers. Stability-wise it should have even more stability on seawaters than a regular SWATH duo hull.

    Is there anything similar done like this before? I have looked upon a lot and I might consider combining a slice swath in the hull shape. The problem is this is a new idea and therefore normal SWATH calculations on stability and resistance might be inaccurate.

    Thank you
    Joris Van Aelst
     
  2. Munter
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    Munter Amateur

    Amas on multihulls traditionally use their bouyancy to give stability to the craft. If you make these hulls swath hulls there will be little change in the displacment of the amas for a given angle of heel, therefore they will contribute relatively little to lateral stability. I've not seen anything like this before.
     
  3. dantnz
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    dantnz Junior Member

    Joris, is this a power or sail project? I'm going to assume power.

    I haven't seen a ship of this design, but Austal is the obvious example of a similar concept for the US LCS. http://www.gizmag.com/ship-design-austal-102-trimaran/12433/picture/89233/

    Obviously its a research project so you are doing it to find out the characteristics of such a design. But I can see some problems with it.

    Isn't the conventional main hull going to negate the swath effects of the amas? i.e. the main hull will be surface riding waves while the swath hulls lie beneath.

    Wouldn't this lead to higher than normal stresses in the structure as the two different hullforms will have very different wave motions?

    How do you get to the hypothesis of greater stability than SWATH given the above?

    Please don't take any of this as criticism of the idea, I'm an engineer not a nav arch, so just trying to understand the design.
     
  4. mydauphin
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    mydauphin Senior Member

    To be a true swath the hull must be completely out of the wave action. In other words a shorter boat that is much above the waves, therefore the four legs of the traditional swath. Otherwise it will just fall over to one side Most swaths are nearly as wide as long, like a barge. There is probably a stability formula like length = beam x two, Height = beam / 2.
     
  5. Joris ypd
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    Joris ypd Junior Member

    Sorry for the late reply, I've been away for quite a while.
    Thank you for responding.
    It is power driven indeed.
    I based my idea on a conversation I had once and I was asked wether the 3-point stability theory of an object on dry land is similar to that of one on the water. It seemed interesting enough to do some research upon the subject. It is obvious that swath has an enormous advantage on transverse stability. However the longitudinal aspect could possibly be improved to place a point of support in forward position of the vessel.

    The swath vessel shown on the link is obviously known to me and my design is very similar apart from the middle part which doesn't continue 'til the stern.
    The Chinese Adastra is also very similar to the style I'd like to pursue.
    http://www.gizmag.com/astrada-superyacht-launches/22135/pictures#4

    Thank you
     
  6. basil
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    basil Senior Member

  7. yipster
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    yipster designer


    thx for the link, like the pdf too ;-)
     
  8. Doug Lord
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    Doug Lord Flight Ready

  9. lucdekeyser
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    lucdekeyser Senior Member

    proa Grainger logic

    Using the logic Grainger proposes a proa configuration is even better

    Luc
     

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  10. Joris ypd
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    Joris ypd Junior Member

  11. Joris ypd
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    Joris ypd Junior Member

    Could you please clear out in what way that configuration would be better?
    Thanks for replying.
     
  12. lucdekeyser
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    lucdekeyser Senior Member

    Well, Joris, all else staying equal (if that is possible at all), Grainger makes essentially the case that the larger the area of the triangle and the more equilateral it is, the better. If I combine and "melt together" a delta side hull and the delta central hull to form the proa long hull and keep the other delta side hull as the proa short hull, the triangle is larger and still pretty much equilateral (although not symmetrical lengthwise but breadthwise)

    Furthermore, you have the following advantages:
    - of having only two hulls, one of which has a doubling of the length/beam ratio
    - a boat that goes in both directions equally well (simplifying man overboard)
    - the opportunity to hang the propellers from under the deck to push or pull in less disturbed waterflows
    - you can choose the best hull to face incomming waves, current, wind ...
    - you can add a sail more safely on the long hull to save on precious electricity

    Members of this forum will not defer for long listing the disadvantages ;-)

    Luc
     

  13. Ad Hoc
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    Ad Hoc Naval Architect

    Any two hulls, whatever its shape, separated by an ever increasing distance shall do this. It is simply the waterplane inertia. A SWATH has a low WPA so if your goal is better transverse stability, then ignore the draggy swath hulls and use a simple long slender hull shape like a canoe.
     
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