Metacentric Height - FREE!Ship or Michlet

Discussion in 'Stability' started by Guest625101138, Jan 20, 2007.

  1. Guest625101138

    Guest625101138 Previous Member

    I produced a hull design in FREE!Ship and then exported the hull to Michlet.

    The hull is for a canoe so stability is marginal but very important. The GMT is critical. I want it to be at least 250mm.

    For the particular hull, FREE!Ship gives a value of 280mm while Michlet gives 197mm. Hence I have a dilemma.

    Does anyone have any idea which one is likely to be correct?

    Rick W.
  2. PI Design
    Joined: Oct 2006
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    PI Design Senior Member

    Are you talking KM or GM? Freeship only gives KM (I think), as this is just a function of the geometry and is independent of mass distribution. At any rate I would suspect Freeship to be more accurate, if that is where the original model is produced. Are the two models sat at the same waterline? Your difference is quite big, so is not likely to just to due to inaccuracy in the calculation, there is probably something more fundamental.
    Sorry this is a bit incoherent - I'm typing as I'm thinking (both of which I struggle to do!).
  3. Guest625101138

    Guest625101138 Previous Member

    KMT or GMT

    FREE!ship uses the acronym KMt.

    Michlet uses the acronym GMT.

    Both are described as the Transverse Metacentric Height.

    I would appreciate any light you can shed on the likely difference in derivation although they use the same description.
  4. fcfc
    Joined: Feb 2005
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    fcfc Senior Member

    As far as I know, M is the metacentre. G, the center of gravity, and K the base of the Keel.

    GM = KM - KG.
  5. Guest625101138

    Guest625101138 Previous Member

    YES!! - That makes sense now. The draught in Michlet is given as KG = 88mm.

    So the numbers add up. I should meet my stability requirement.

    Thank you fcfc.

  6. PI Design
    Joined: Oct 2006
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    Location: England

    PI Design Senior Member

    Yup, that's right. But note, KG is not the same as draught (unless the centre of gravity is on the waterline).
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