J29 pounds per inch immersion?

Discussion in 'Stability' started by wjmuseler, Dec 11, 2016.

  1. wjmuseler
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    wjmuseler Junior Member

    Does anyone know what the pounds per inch immersion? Comparing different boats and trying to understand some of the differences.
     
  2. SamSam
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    SamSam Senior Member

  3. wjmuseler
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    wjmuseler Junior Member

    Sam,

    What I am trying to figure is that different 29s have differing displacements and drafts but they don't seem to correspond to each other. Lbs/in displacement is a number designers have to determine how much weight will move the boat up or down.
     
  4. bregalad
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    bregalad Senior Member

    Pounds per inch immersion is primarily an indicator of the area of the waterline plane.
    Two boats with identical PPI immersion will be nearly identical in the area of the waterline plane.
    Nearly .... because flare will affect the PPI immersion but the boats would have to differ greatly in flare for it to have much effect over just one inch of immersion.
     
  5. wjmuseler
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    wjmuseler Junior Member

    bregalad,

    I am trying understand how some boats can have larger displacements but shallower drafts and vice versa.
     
  6. gonzo
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    gonzo Senior Member

    Draft depends on several things that are related to the shape of the hull's section. For example, the depth of the keel. A beamy boat will draw less than a narrow boat of the same waterline length. A boat with a lot of flare will submerge less than a boat with slab sides. PPI is a function of the displaced volume. The volume is area x height(draft)
     
  7. wjmuseler
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    wjmuseler Junior Member

    I know what PPI is what I am looking for is the number specifically for a J29. All of them will have the same number.
     
  8. TANSL
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    TANSL Senior Member

    All this can lead to erroneous conclusions if one does not qualify a little more of what area and volume are concerned (what about specific weight of water?).
    But it seems that the OP understands the concept of PPI so, I think, he does not need explanations inconsistent or misleading.
    Perhaps the OP could get more help if it specifies to what depth he needs to know the PPI.
     
  9. wjmuseler
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    wjmuseler Junior Member

    The base spec for the J29 from JBoats is 6000 lbs at a 5.6' draft and a 25' LWL.
     
  10. Chuck Losness
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    Chuck Losness Senior Member

    Why don't you just contact JBoats and ask them. You'll get the correct number straight from the builder.
     
  11. Joakim
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    Joakim Senior Member

    You can find that data from an ORC certificate. Here is one for J/29 showing sink 13.12 kg/mm. It will not be exactly the same value for all J/29's due to differences in displacement and trim.
     

  12. wjmuseler
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    wjmuseler Junior Member

    Thanks Joakim! That is exactly what I was looking for.
     
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