Roll Damping

Discussion in 'Boat Design' started by muthubd14, May 31, 2014.

  1. muthubd14
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    muthubd14 Junior Member

    Hi, Can some one suggest how do we compare seakeeping of two almost similar hulls.. with little difference in dead rise and aft cut....
    How can we arrive at Roll Damping coefficient of a hull..???
     
  2. BMcF
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    BMcF Senior Member

    Analytically?..or by testing the actual hulls?
     
  3. messabout
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    messabout Senior Member

    Dave Gerr has done an explanation about this in one of his books, The Nature Of Boats, I think it was. His intent was to establish comfort level if I recall correctly. Simple test using only a stop watch for instrumentation.
     
  4. muthubd14
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    muthubd14 Junior Member

    Ya analytically.. in initial stages of design ... To compare two hulls basically...
     
  5. jehardiman
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    jehardiman Senior Member

    Strip theory. Or for emperical estimates from measured ships, see Theory of Seakeeping by Korvin-Kroukovsky and SNAME.
     
  6. NavalSArtichoke
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    NavalSArtichoke Senior Member

    The rolling of a hull is unfortunately a lot more complicated to analyze than the other degrees of freedom. It is a non-linear phenomenon which resists having itself linearized when trying to predict the motions of a vessel in a seaway.

    Most of the roll damping coefficients which you see published have come from some sort of test, and the roll damping calculated in strip-theory programs is based on these empirical results.

    The following paper is from a Japanese researcher in 1981:

    http://deepblue.lib.umich.edu/bitstream/handle/2027.42/91699/Publication_No_239.pdf?sequence=1

    The calculations used in strip theory programs for roll damping are based on the work of some of the authors in the references, particularly Vugts, Tanaka, and Tasai.
     
  7. muthubd14
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    muthubd14 Junior Member

    Thank you...

    How do we design a stabilzer fin for 90 m long vessel .. Beam at WL = 12.5 m and which displaces 2200 T at 3.6 m draft...

    Is there a standard procedure for practical fin design.. Theoretical methods from books like Bhattacharya give fair idea but how do we decide aspect ratio span etc of vessel is not mentioned anywhere..

    Could some one help me out.??:)
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    It's called 'design'.

    You design a fin, then calculate its added mass etc and thus the overall effect on pitch heave and roll. If it is not what you expect, you try again, until you obtain the desired effect. It is an iterative procedure, commonly known as 'design'.
     

  9. BMcF
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    BMcF Senior Member

    Typically, the selection of the fin size and the integration of the fin actuation (top plate) equipment is taken care of by the supplier(s) of the fin stabilization equipment. It is rather pointless to take that task on in house; What are you going to design?...the fin equipment already exists and is available from several well-known suppliers. Certainly you are not proposing to design and build your own?....:confused:

    Fin sizing support and basic space/weight/interface drawings are always available from the fin suppliers.
     
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