drag vs global strength - cat vs tri (non ILAN) or even quad

Discussion in 'Multihulls' started by big_dreamin, Oct 20, 2016.

  1. big_dreamin
    Joined: Jan 2014
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    big_dreamin Junior Member

    Hello, something i'm curious about that I thought I posted about in the past but couldn't find my own post, so at least I haven't posted it recently. :^)

    Is there a width/size at which "catamarans" become at a disadvantage vs other multihulled craft? I'm thinking in terms of tradeoffs of wetted surface drag of the extra hull(s) (third or even fourth), wave physics between the hulls (does the wake 'stack up' in the middle the wider the cats are separated in a bad way?), and global strength issues. (just like in buildings, when you have a clearspan of a certain size you start having to get stronger and stronger beams until at some point they become unfeasably heavy and it makes more sense to say have two buildings 150ft wide side by side than trying to make something with a 300ft clearspan)


    A picture from someone I think who used to be here (and whose design/logic I actually was a fan of) actually kind of shows the idea:


    Two hull version:

    [​IMG]

    Three hull version:

    [​IMG]

    AKA same boat, just varying how many hulls are under it.

    Cats being what they are, i'm wondering if there is a point where adding a hull in the middle actually makes more sense than not. (yes this is a deliberately open ended question, please educate me :) ) Put another way if you didnt mind the aesthetics of every cat looking like a square on the water (as wide as it is long, unless there's extra hydrodynamic reasons not to do that?) is there a size class (especially out of certain materials like wood) where having that third hull in the middle is a better design choice than two? (or even having it four across)
     
  2. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    Waayyy to many topics to be covered at once. There are too many space and weight considerations to be considered to address the topics you bring up. FWIW, the design shown is PPE (Power Point Engineering) and has nothing to do with reality. It is not a viable real vessel. Looks like a Second Life construct.
     
  3. big_dreamin
    Joined: Jan 2014
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    Location: Minnesota

    big_dreamin Junior Member

    That being said can you get me started?

    I'm aware it's not the worlds most beautiful rendering that's not the point - just trying to show basically the same vessel with two or three hulls basically equally shaped. Or potentially the same displacement just two wider cat hulls vs three slightly narrower tri hulls.

    An example realization being that wetted surface drag will be worse on the tri - but the drag may or may not be any worse because the narrower hulls create less wave drag in general.

    I already pointed out i'm aware that wake interference off the back of the hulls may be an issue.

    I'm pretty sure global strength will be superior in a tri hull version. You're not asking long wide panels or boxes to take as much forces. You might even reduce the bridgedeck weight a bit though i'd think the third hull would still weigh more than any savings.

    Etc. I'm just looking to expand this list with observations and insights for consideration.
     
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