The new keel for the old boat

Discussion in 'Sailboats' started by Alexander UA, Feb 6, 2013.

  1. Alexander UA
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    Alexander UA Junior Member

    In aviation, the ends of the wings and tail are rounded?
     
  2. Alexander UA
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    Alexander UA Junior Member

  3. sean9c
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    sean9c Senior Member

  4. Alexander UA
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    Alexander UA Junior Member

  5. Alexander UA
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    Alexander UA Junior Member

  6. Alexander UA
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    Alexander UA Junior Member

    Diamond keel shape

    Two years ago I have read an article about diamond-shaped keels.
    The idea was that it can be not a classical NACA foil shape, but asymmetric diamond shape. Something like this.
    http://www.delftship.net/delftship/media/kunena/attachments/41074/KR_generator_VolCOG_Q.JPG
    Is this a perspective design?
    Has anybody built and tested keels with this foil shape?
    If so, I think there will be good to make 10%-width shape for keel and 20%-width shape for bulb.
     
  7. Petros
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    Petros Senior Member

    shapes like that only work well for high speed foils. at slow sailboat speeds it would have a lot of drag, flow separation, and will stall easy which means you would not be able to point very well.

    Better leave the current keel in place than use that. just pic a symmetrical low speed naca section and you will do good.
     
  8. sean9c
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    sean9c Senior Member

    the 6% thickness would be a challenge
     
  9. Alexander UA
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    Alexander UA Junior Member

    why the 6% thickness would be a challenge
    6% - small frontal resistance
     
  10. CT 249
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    CT 249 Senior Member

    One designer who used "Flying 15" keels in yachts was John Spencer. His greatest boat, Ragtime, was later later modified to take a Peterson type keel and Spencer himself moved to such keels. In the Spencer thread there is an interesting post about modifying an old Spencer to make the keel more Peterson shape. Ragtime now carries a modern high aspect bulb keel.

    The Flying 15 keel is known to be inefficient in hydrodynamic terms even by F15 owners. It does, however, make for a pretty boat with shoal draft and great downwind performance. But that doesn't make it ideal for an old half tonner.

    Some late IOR boats have been fitted with modern keels and they do increase speed according to those I have spoken to. But they were modern designs and not F15 keels.
     
  11. Martin B.
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    Martin B. Junior Member

    More on keel reshaping

    I take slight issue with CT 249's comment regarding John Spencer using “Flying 15” keels on some of his designs and also with Garry Baigent's similar assertion in his marvellous book “The Light Brigade”.

    IMHO the Spencer/Uffa keels were similar only in that both hung under innovative shaped hulls and had the majority of the “lead” hung low.
    But Uffa's ff15 keel was shallow or shoal draft with heavily raked leading edge.
    Whereas JS's fin keels on Scimitar, Infidel and the like were deep draft by the standards of that age (late 1960's thru early '70's) and had moderately raked leading edges up by the hull with a sweeping curve to near vertical at the keel's toe as per pic of my Scimitar's keel about to be “re-sculpted”; see http://www.boatdesign.net/forums/at...07898-john-spencers-designs-m-flinders-7s.jpg

    CT 249, as the “keel hacker” referred to in your above Post, I like your description of my modified Scimitar keel as “Doug Peterson shape” – very apt although I have never heard of that description before. My 'technical' information on keel shape and section, circa 1974, came mainly from the American magazine “Sail”.

    At the risk of starting a s#^t fight with ff15 owners, I looked at buying one back in 1972 and found it to be hard headed (weather helm) and extremely heavy on the tiller (not sure how much they may have changed much since ). This was a well sorted racing boat at RFBYC and my immediate reaction was that the “steering oar” at the back should have a near vertical shaft and near vertical blade with a small amount of balance to reduce the tiller load AND move the keel about 120mm aft to reduce the excessive weather helm. I noticed many ff15 racing on the Swan at that time with flat mains and full headsails which seemed to me to be a result of trying to get rid of the excessive weather helm. On the other hand, the Scimitar, with sailplan corrected to near JS's design, had no keel location or balance problems with weather or lee helm.

    Re the ff15 rudder, a very similar comment could also be applied to the YW Diamond, again, lots of them on the Swan and I crewed on them in the 70's. Make the rudder shaft vertical and rotate the blade shape to vertical (with some balance) and you would have a more controllable "lighter tillered" hi performance flyer.
     
  12. Alexander UA
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    Alexander UA Junior Member

    NACA profile found 6% thinner than not. That the profile of less than 6% does not create lift?
     
  13. Alexander UA
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    Alexander UA Junior Member

    I can't find any NACA profiles with thicknes less than 6%. Is it because such profiles couldn't create lift or some other reasons exist?
     
  14. jehardiman
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    jehardiman Senior Member

    You can make a 2% or 1% NACA 000x profile, it just scales with the thickness. FWIW though, a profile that thin is subject to the unpredictable onset of stall...might as well be a flat plate.
     

  15. Alexander UA
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    Alexander UA Junior Member

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