converting moments of inertia into metric

Discussion in 'Multihulls' started by Corley, Dec 18, 2014.

  1. Corley
    Joined: Oct 2009
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    Corley epoxy coated

    I'm looking for a rotating mast section for my F40 project and have been given a moment of inertia value for the two axis in imperial units just wondering if anyone can give me the heads up on how to convert to a metric measure? These are the values I've been given least axis 27 in^4 and other 63 in^4.
     
  2. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Well, which ones? m^4, cm^4, or mm^4 have all been used at one time or another.
     
  3. TANSL
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    TANSL Senior Member

    1 inch = 2.54 cm
    so
    (1 inch)^4 = (2.54 cm)^4 = (2.54)^4 cm^4 = 41.62314256 cm^4
    can that help?
     
  4. rcnesneg
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    rcnesneg Senior Member

    I would try Unit Analysis, a cool trick where you convert from one unit to another.

    Ie: 1 inch (2.54 cm/1 inch) = 2.54 cm. The inches cancel out, you multiply by everything on top, and divide by everything on the bottom.

    Another example:

    52 mph = 52 miles/hr (5280 ft/1 mile)(1 meter/3.28084 ft)(1 hr/3600 s) = 23.2460792561 meters per second.

    If you have squared units, or to the fourth, or whatever, just use that conversion.

    Ie: (1 inch)^4/(2.54 cm)^4 or (1/41.6231), etc.

    The easy way: Use this thing: http://www.unitconversion.org/unit_converter/moment-of-inertia.html
     
  5. Corley
    Joined: Oct 2009
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    Corley epoxy coated

  6. Ad Hoc
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    Ad Hoc Naval Architect

    I'm curious. Do you regularly quote values down to 9 decimal places in plate thickness for example, or the scantling of a transverse frame when designing a boat?
     
  7. gonzo
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    gonzo Senior Member

  8. TANSL
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    TANSL Senior Member

    No, it would be nonsense, I only use 8 decimal places. See my post.
     

  9. gonzo
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    gonzo Senior Member

    Garbage in- garbage out. Pay attention to the sig figures.
     
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