From winged keel to bulb keel

Discussion in 'Sailboats' started by Mad for sail, Nov 15, 2011.

  1. Mad for sail
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    Mad for sail Junior Member

    I have notice that on the keels like J111.
    Instead a linear thickh increase a kind of "bell" shape.
    I will simulate the linear profile and later use the bell shape to trim CG and weight
     

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  2. sorenfdk
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    sorenfdk Yacht Designer

    Thank you!
    Personally, I prefer Youngs Laminar Body, but you can't find it anywhere on the 'net!
     
  3. sorenfdk
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    sorenfdk Yacht Designer

    That's too thin! You should go to 10-12% thickness for the keel fin. Have you thought about the keel bolt arrangement? With a thin keel section you won't be able to "spread out" the keel bolts.

    And you should go to 15% for this kind of bulb.
     
  4. Joakim
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    Joakim Senior Member

    6.5-8% was for the keel fin that's not going to be replaced. It has a very long chord, about double compared to a modern keel for the new ~1.9 m draft, thus it's actually wider. Keel bolts are already there.
     
  5. Mad for sail
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    Mad for sail Junior Member

    The bolts will be fastened along the 1500 x 125 mm fin section.
    It's wide enougth to drill 3/4 to 1" threads.
    I didn't calculate it yet but i guess I can easily place 8 to 10 bolts.
    Should be enough!
     
  6. sorenfdk
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    sorenfdk Yacht Designer

    Sorry - forgot the long chord!

    "Should be enough" is not enough when lives are at stake!
     
  7. Mad for sail
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    Mad for sail Junior Member

    Soren, I appreciate your concern!
    Eventually I will share the fasten strategy and you will have the opportunity to give me some hints!
    Thanks again...
     
  8. Mad for sail
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    Mad for sail Junior Member

    I am back with the wing keel model rebuilt. The file has been reduced to 13Mb so I guess Mikko can now you use into the CFD simulation (if you still have interest and time for that Mikko!).
     

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  9. Mikko Brummer
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    Mikko Brummer Senior Member

    This works! I will try to run it as soon as I have time. Funny stripes it has in the bottom - wonder what the designer has wanted with them
     

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  10. Mad for sail
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    Mad for sail Junior Member

    L keel concept is also alive! I made some simulations and tghe geometry resulted in something like this picture ... how do you like it?
     

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  11. Mikko Brummer
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    Mikko Brummer Senior Member

    Run with the wing keel. As expected, the wing keel produces much more side force than the bulb keel with the same fin, so leeway could be reduced by 2 degrees for approximatively the same side force.

    The pdf shows the different components of lift & drag, bulb keel in red & wing keel in green. Additionally, there's separate numbers for the wings: the leeward wing has a down force (Y) of 70 kgf, while the windward lifts with 26,4 kgf, so both increase the heeling moment. Yet the windward wing contributes much more to side force (Z, 5,3 vs 27,6 kgf).

    The plots show pressures on the surfaces, red & yellow are higher pressures, blue shades are low pressure (suction, green is neutral.

    I think this all may suggest that the bulb keel is too small in area, and you would need to increase draft, as Joakim suggested, if you want to get rid of the wings.
     
  12. Joakim
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    Joakim Senior Member

    What simulations did you make? It looks OK, but you should give some dimensions in order to get more opinions.
     
  13. Joakim
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    Joakim Senior Member

    Your simulations show the same drag and lift for the same speed and TWA (=same VMG). The only clear difference is in the leeway.

    How would 2 degrees more leeway effect the sail forces while AWA (measured against COG, not keel line) and AWS are the same?

    One important thing missing is the effect of leeway on wave drag, which your calculations do not show. Another one would be the ability to point higher. 46 TWA is no good at all, around 40 would be a better one and then the difference between these keels would be bigger due to more lift and less speed.

    Have you tried using free surface to capture wave drag?
     
  14. Mikko Brummer
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    Mikko Brummer Senior Member

    Not much I guess, something you could handle with sailtrim.

    Never thought about the effect of leeway on wave drag... How would you quantify that? The 46 deg twa comes from the vpp with the bulb keel, leeway becoming excessive if you point higher.

    My flowsim does not do free surface... It would be quite a demanding extra task.
     

  15. Joakim
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    Joakim Senior Member

    I don't think wave drag changes due to leeway are taken into account in VPP programs, but at some point there must be an increase and 7 degrees is already quite much. But some (most?) VPP's do have heel dependent wave drag for keel, which your simulation omits.

    What is flowsim? This one? http://www.flowsim.com.au/ I think OpenFoam has free surface and you could run a free surface simulation in 1-2 days with one processor for one point of sailing.
     
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