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

    Mikko, thanks for the offer! I'll send the files tomorrow!
    GggGuest, my intuitive approach agrees with your statement but quantifying it is actually the issue.
    All I know is when We sail above 15 knots true wind the boat really points high like a true racing boat. Below 10 knots I see the whole fleet in from of us.
    Hope Mikko's results will help me!
    Thank you all folks for the support so far ... Very interesting suggestions
     
  2. Mad for sail
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    Mad for sail Junior Member

    Files are too big: 11 and 180Mb?
    How do I transfer it?
     
  3. Mad for sail
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    Mad for sail Junior Member

    files are too big to post: 11 and 180 Mb ...
    How do I send it to you guys?
     
  4. Joakim
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    Joakim Senior Member

    Is your main objective to increase performance and especially in the light air? If so, a bulb is just added drag in the light air and I don't think there will be much of a difference between these two. You have somewhat less area (not that much compared to ~25 m2 total wetted area) and your bulb is rather fat thus it will have quite much form drag. With the same draft a wing keel will be somewhat more efficient upwind compared to bulb keel, which is worse than a normal fin keel. Thus you would probably be little faster downwind, but the same or even slower upwind.

    Is increasing draft out of the question? If not, replacing the wings with an extension + small bulb or just an extension would give much better performance than your bulb. Even better would be replacing the whole keel, which is very inefficient now (very low aspect ratio, lot of surface area, too long chord for a deeper keel). I have a similar sized boat with 2.0 m draft and the keel is about 3.3 m2 (painted area, about 1.5 m x 1.0 m rectangular) and 1800 kg.

    In the Finnish magazine VENE (10/1991) there was a comparison of three different keel options for a 30' C/R boat. All the keels had same weight and center of gravity (1360 kg, 0.45 m below hull). The deepest one had a 1.9 m draft and was a pure fin keel (area 2.37 m2). The bulb keel had 1.4 m draft (2.7 m2) and looked somewhat similar to yours (the bulb is clearly flatter). The wing keel had 1.15 m draft (3.9 m2) and looked somewhat similar to your wing keel. Otherwise the boats were identical and had identical sails.

    Unfortunately the wind was only light (1-5 m/s) and varying. The conclusion was, that the wing keel was about 15% slower than fin keel in the light wind both upwind and downwind. The bulb keel was marginally slower upwind and as fast downwind compared to fin keel. The difference upwind was said to come from the better pointing ability of the fin keel. According to VPP-programs I think there should have been ~5% difference upwind between bulb and fin keel.
     
  5. Mad for sail
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    Mad for sail Junior Member

    Hello Joakim,
    can you manage to send me a link or a scan of this magazine issue?
    Looks very interesting ...
     
  6. Joakim
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    Joakim Senior Member

    It's in Finnish, thus not very helpful to you. And I'm sure there are much more accurate comparisons somewhere.
     
  7. Mad for sail
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    Mad for sail Junior Member

    Thanks Joakim,
    as additional info, the data in the dwgs are not correct:
    - current surface: 6,41 sqm
    - proposed surface: 4,81 sqm
    About 25% less ...
     
  8. peterchech
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    peterchech Senior Member

    I try not to sail at 45 degrees ;)
     
  9. Mikko Brummer
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    Mikko Brummer Senior Member

    I received the files OK, and manage to open them. Unfortunately they don't lend themselves for CFD as is... For CFD you need solid models, with no gaps or hollows in them. Your models are like like mosaic pieces, maybe because it comes from a scanned point cloud-file? I probably could patch them, but that would be quite a lot of work.
     

    Attached Files:

  10. yipster
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    yipster designer

    why not mention this thought of a 180deg rotating halfbulbwingkeel
    not enough lift.. swaying to much.. complexity.. turning lead heavy.. does that sumonise it or what?
     
  11. Mad for sail
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    Mad for sail Junior Member

    Ok Mikko, we wil build it and send it back to you for your appreciation.
    Hope we can finish this week.
     
  12. Mad for sail
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    Mad for sail Junior Member

    Yipster, I must confess this new to me. I have seen something similar on a Beneteau First 40.7 I was a crew member. How would you rate it in the keel comparisons presented by Joakim (Vene magazine)? I think is kind of difficult to adapt my winged keel to this design but I am interested in details ....
     
  13. yipster
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    yipster designer

    with the discussion wing/bulb i thought i might as well mention this halfbulbwing idea witch was a fantasy reading to much on canting keels
    never calculated the idea tho and without seeding to much confusion i would be interestest by Mikko and Joakim's opinions too
    perhaps i can help drawing some solid models and slip a rotating halfbulb in there too?
     
  14. Mikko Brummer
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    Mikko Brummer Senior Member

    Halfbulbwing?
     

  15. yipster
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    yipster designer

    Mikko hi, see post #25 yes a "halfbulbwing" was the thought
    half a bulb is a wingprofile rite, that can rotate 180deg giving lift eigther side, hanging in a keel frame
    just a thought looking at canting keels yet this one should give more lift -how much- at speed but area against drag, lift, complexity i lose it, never even gave it a rough calculation
     
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