How to calc the L/W ratio for hulls with LAR keels?

Discussion in 'Multihulls' started by UpOnStands, Feb 1, 2018.

  1. UpOnStands
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    UpOnStands Senior Member

    Title says it all.
    If the LAR keel is an appreciable percentage of the submerged hull area how should the L/W ratio be adjusted?
     
  2. DCockey
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    DCockey Senior Member

    What purpose is the L/W ratio being used for? What do you mean be W - width (beam)? weight?
     
  3. UpOnStands
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    UpOnStands Senior Member

    waterline hull Length divided by hull Width at the waterline.
    The convention is that L/W values under 10 mean a slow boat.
     
  4. gonzo
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    gonzo Senior Member

    1:10 ratio is way too low, unless it is a catamaran hull. Actually, many really fast boats are beamy and plane.
     
  5. redreuben
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    redreuben redreuben

    My rudimentary understanding is that the L/W function is all about the potential for wave making and therefore the lar keels have nothing to do with it.
    Wetted surface is where they are going to have the biggest effect but that is a different dynamic.
     
  6. UpOnStands
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    UpOnStands Senior Member

    This query is for catamarans.
    The hull prismatic must have some impact on the wave making characteristics of the hull.
    But how to assess this?
     
    Last edited: Feb 2, 2018
  7. Doug Lord
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    Doug Lord Flight Ready

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  8. UpOnStands
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    UpOnStands Senior Member

    Thanks for the Spoonberg document. Still working through it but find this on page 11
    "Usually, in sailboat design, the keel and it’s draft is left out of the calculation of volume. This is because, as in the Cb calculation, the keel tends to make Cp less sensitive. So we ignore the keel for calculation of Cp. "
    The Bruce number for multihulls also makes no mention of keel shapes. Bother.
     
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