Hydrodynamic quality comparison.

Discussion in 'Hydrodynamics and Aerodynamics' started by Alexanov, Jun 25, 2021.

  1. Alexanov
    Joined: Feb 2003
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    Alexanov Senior Member

    Hello everyone. What is a best way to comparison of hydrodynamic quality of two similar hull shapes?
     
  2. baeckmo
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    baeckmo Hydrodynamics

    Mmmm.. first I'd try to define "hydrodynamic quality", say as "the ability to carry a payload and a crew a specific distance at a given speed with the lowest power demand with acceptable accelerations and movements, including course-keeping, in a specific sea/environment condition"??

    Major key qualities would then start with lift/drag ratio, vertical accelerations, roll and pitch in general and in resonance (if that may occur in the specific condition).
     
    Erwan likes this.
  3. Alexanov
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    Alexanov Senior Member

    May be I am wrong. Simply I need to predict resistance for new ship from existing prototype I know resustance.
     
  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    What you are describing is a simple scaling or geosim.
    If the new ship is an exact scale of the original (a geosim), then it is a simple task to calculate.
    If it is not an exact scale of the original, then it becomes a tad more tricky...
     
  5. Alexanov
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    Alexanov Senior Member

    Simple scaling is too simple. Ship is similar, but with different hull shape…
     
  6. baeckmo
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    baeckmo Hydrodynamics

    "Ship is similar, but different......"!!
    If the shape of both fit within the limits of a regression analysis of a known hull type, that might give an indication of the respective qualities. Otherwise a CFD simulation could be useful, starting with validation runs for the model with known performance.
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Indeed.
    I assume you can calculate the WSA, if so that is your frictional taken care of.
    Then you need to find hulls which are the same or very close/similar to yours in the length-displacement ratio, with varying L/B and B/T ratios, to establish the residuary resistance.
    Then you can make a very good approximation.
     
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  8. jehardiman
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    jehardiman Senior Member

    Yes, this is where the Taylor series or Series 60 data comes in handy. Blubs, however, complicate matters.

    Edit: brain fluctuance 64 for 62 and back again to 60...as planing hulls were not mentioned
     

  9. Erwan
    Joined: Oct 2005
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    Erwan Senior Member

    Look for MICHLET on BOATDESIGN for slender hull it seems to work fine
     
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