Optimum Cat Hull Separation?

Discussion in 'Multihulls' started by alidesigner, May 23, 2009.

  1. alidesigner
    Joined: Nov 2006
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    alidesigner Senior Member

    Does anyone know of any good papers that discuss the optimium separation of cat hulls in displacement, semi displacement and planing modes?
     
  2. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Leo Lazauskas, one of our forum members, has co-written several good papers on hull shape and spacing optimization for multihulls in the displacement mode:
    http://www.cyberiad.net/multihulls.htm
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    alidesigner

    yes plenty, but all for varying reasons and varying different types of hull forms and speeds etc, with of course, varying results. So what is the objective?

    Just buzz me, and i'll give you some ideas...now you're back from "your hols" :)
     
  4. Guest625101138

    Guest625101138 Previous Member

    You need to be aware that a lot of the analysis done on wave reduction is related to environmental disturbance. So "optimal" placement in this situation has nothing to do with powering the vessel.

    If you are relating "optimum" separation to minimum drag then this yields a different answer to the minimum wave case.

    Rick W
     
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    "... a lot of the analysis done on wave reduction is related to environmental disturbance.."

    Where does the post mention wave reduction or environmental impact?

    I know alideisgner is more than capable of reading the reports/studies to see where the analysis is focused upon! It isn't rocket science..
     
  6. Alik
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    Alik Senior Member

    As general reference on multihulls resistance, I can recommend a book 'Multihull Ships' by V.Dubrovsky.

    For hull separation - as I understand we are talking about optimization of resistance R as function of c/L, where c is spacing between demihull centerlines, L is waterline length of boat.

    Optimum hull separation for displacement (FnV<1) and semi-displacement mode (FnV=1...3) is related to particular Froude number, but some c/L ratios are always unfavorable. We used to perform analysis by Molland's method (for round bilge hulls) that gives clear idea of R=f(c/L). Another useful method for chine hulls is published by Australian Maritime College - it needs validation but so far proved to work well with our designs.

    For planning hulls is not that critical, excerpt some poor designs. For pure planning FnV>(3...5) I recommend w/L=0.1...0.2, where w is width of tunnel (i.e. clearance between inner sides of hulls). Of course this depends on shape of planning hulls, but some useful data are again in Doubrovsky's book.
     
  7. gonzo
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    gonzo Senior Member

    Adhoc sounds like alidesigner's mom. Also, you critizise results based on varying conditions. As in other posts, you demand the magic solution that solves every problem. All designs are a matter of compromise and application purposes.
     

  8. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    gonzo

    No idea what you're on about: what results, what conditions, can't see that in the posting. However, if you wish to read more into a posting than is actually stated and make assumptions based upon that for providing advice, that is your prerogative. Not sure how that helps the originator of the posting though..
     
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