...tpc / Tpi...

Discussion in 'Stability' started by fradrigo, Oct 22, 2007.

  1. fradrigo
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    fradrigo Junior Member

    Hi all, I need a little help in deriving ratio between metric and imperial unit immersions ( Tonsmetricpercentimeter / Longtonsperinch ) Obviously we need less mass to immerse a boat one centimeter then one inch ( 1 longTon correspond to 1.016 metricTon ), but whatever trick I pull from the bag I keep geting larger than one ratio ( 2.5 to be precise ) What am I doing wrong :confused:
     
  2. Guillermo
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    Guillermo Ingeniero Naval

    1 lt/inch = 1.016/2.54 mt/cm = 0.4 mt/cm

    1 mt/cm = 2.5 lt/inch
     
  3. fradrigo
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    fradrigo Junior Member

    Thanks Guillermo, I'm geting the same result...but the common sense tells me that TPC should be less then TPI ( ratio TPC / TPI less than one ) ?
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    ....TPC should be less then TPI....
    And they are!

    0.4 < 1
     
  5. fradrigo
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    fradrigo Junior Member

    ...1 lt/inch = 1.016/2.54 mt/cm = 0.4 mt/cm

    1 mt/cm = 2.5 lt/inch...



    mt/cm = TPC
    lt/inch = TPI

    according to your second line:

    TPC = 2.5 TPI

    TPC / TPI =2.5 > 1

    ...still confused :)
     
  6. fradrigo
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    fradrigo Junior Member

    ...I've checked in one of Hydromax's sample models ( varying units for same waterplane area ) and got :

    TPC = 1.097 tm/cm

    TPI = 2.743 lt / inch
    -----------------------

    So TPC/TPI = 0.4 ,

    Inverse what we derived for the same ratio ( 2.5 )...I'm not very good in dimension analysis..Anyone out there ??? :)
     
  7. Guillermo
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    Guillermo Ingeniero Naval

    :rolleyes:
    1 mt/cm = 2,5 lt/inch
    (1/2,5) mt/cm = 1 lt/inch
    0,4 mt/cm = 1 lt/inch

    This implies you need less weight to sink a boat 1 cm than to sink it 1 inch (as is evident).

    An example:
    If you take a parallelpipedic hull, of 1 sqm section, floating in fresh water (density = 1), you need 10 kg to sink it 1 cm but you need 25,4 kg kg to sink it 1 inch.

    Check: 10 kg = (25,4*0,4)/1,016

    What's the doubt....:confused:
     
  8. fradrigo
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    fradrigo Junior Member

    :idea: It's clear now, thanks ! :)

    ' ...open mind for a different view... '
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    Veritas lucet omnibus....:)
     

  10. fradrigo
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    fradrigo Junior Member

    Tempus omnia revelat ;)
     
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