Deeper keel span in OD boat

Discussion in 'Sailboats' started by wjmuseler, Jan 17, 2017.

  1. wjmuseler
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    wjmuseler Junior Member

    With all else being equal...what kind of gain would you expect if on a 30 OD keel boat you had a keel that was 1-2" deeper?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    ==========
    I'd guess that there would be a very, very small gain-probably depending somewhat on if you're moving the ballast lower as you increase the span.
    Good Luck!
     
  3. wjmuseler
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    wjmuseler Junior Member

    Doug,
    It would be at most ~30lbs of lead. Would it prove an advantage say off the line or tight boat to boat going upwind?
     
  4. Doug Lord
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    Doug Lord Flight Ready

    keel

    In my opinion -slight advantage. Probably not worth the work involved-but a slight advantage is still an advantage......
    What limits you to 1-2"?
     
  5. PAR
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    PAR Yacht Designer/Builder

    With all things being equal, I doubt you'd notice any discernible difference in the performance envelop. In light air, you might be a 1/10 of a knot slower do to the additional wetted area, eddies, etc. Uphill, technically there should be a very slight advantage, but you'd have to have the boat in the groove consistently to prove this, as any minor trimming or set inconsistencies would negate any advantages, not to mention make it all but impossible to quantify (was it the keel or just staying in the groove, for a higher percentage of the upwind leg).

    What boat is this? Is it the C&C design that was produced in several countries, with a lifting bulb keel or one of the others, that had a different keel? I think it was the MEGA 30?
     
  6. wjmuseler
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    wjmuseler Junior Member

    I posted this to try and figure a reason for the anomaly I found in one keel. Out of five other boats measured this one was 1-2" deeper. Most were ~1" shorter. Based on those measurements it is out of OD spec but the class is no longer active. The keel and one rig dimension are the anomalies.
     
  7. PAR
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    PAR Yacht Designer/Builder

    If this is the C&C design, it had a few different keels installed. That last few dozen of this boat built (assuming I have the right one) replaced the drop keel with a fixed one. Which do you have?
     
  8. wjmuseler
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    wjmuseler Junior Member

    It is not my boat the design is an old MORC design.
     
    Last edited: Jan 17, 2017
  9. Stumble
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    Stumble Senior Member

    So putting some numbers to it...

    Assuming the keel is a flat plate that is 5' long and weighs 3,000lbs. Each inch of keel weighs in at 50lbs.

    So adding one more inch to the bottom of a 5' keel adds about 41.65 foot pounds of righting moment at 90 degrees. Assuming the boat is 10' wide, that's about the same as an additional 8lbs sitting on the rail when the boat is flat.

    I mean it's not nothing, but I can't believe it would ever be the deciding factor in a race.



    As always I am a lawyer not an engineer, so never trust my numbers (I don't).
     
  10. PAR
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    PAR Yacht Designer/Builder

    If this is the lifting keel version, the lifting mechanism might have stretched, dropped, shifted, moved or worn out a bit to cause the additional draft.
     

  11. wjmuseler
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    wjmuseler Junior Member

    Par,

    It is not a lifting keel. Basic early 80's vintage keel. This one stands out when compared to other boats. It's measured rating cert is what started the curiosity, measurements were then taken to confirm.

    Will
     
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