NACA # for a long keels?

Discussion in 'Hydrodynamics and Aerodynamics' started by Howlandwoodworks, Jul 9, 2019.

  1. Howlandwoodworks
    Joined: Sep 2018
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    Howlandwoodworks John Howland

    I have been read about long keels, most of what has been written about NACA foil # would be about fin keels or air plane wing foils.
    I have over sized my keel on a 1/4 scale model so that I might shape it to a 63-0010, 64-0010, or 65-0010, on the model the OOXX number/percentage is at 10%, it could be enlarged on the full size boat if there would be an advantage to doing so.
    Does anyone know of any paper written for long keel specifically, how it relates to a connecting rudder, and a table of offsets or any words of wisdom?
    I am read the Principles of Yacht Design 2nd edition by Larsson and Eliasson hoping that the older edition would have less computer modeling information. I know there are programs out there that would generate offsets and calculate other information for me, but they would takes the sport out of it at this point for me.


    upload_2019-7-8_12-2-34.png
     
  2. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    In your research, did you adjust for size and speed?
    Any symmetrical NACA foil will suffice.
    However, if you're in need of more lead,
    then a chubbier NACA foil would be better.
    Edit: I think following the lines of the wood keel you're building on would be more important...
     
  3. Howlandwoodworks
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    Howlandwoodworks John Howland

    Blue Bell,
    Sorry I didn't explain my intent of the model.
    I have decided not to use the 1/4 scale model as a working model for any information other than the mode of operation for building a full size boat.
    You are not the only person that has commented on the size or weight of the keel. I am working on the Dellenbaugh Angle calculation number now, that should shed some light on the how far we will have to climb up the high side in thick air.
    Just calculating the full size boat will be enough for my first build.
    John
     
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  4. BlueBell
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    BlueBell Ahhhhh...

    Okay, thanks for that.
    Sorry I couldn't be of more help.
    Good luck, nice work.
    Carry-on.
     
  5. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Your keel doesn't generate lift like a fin keel. It doesn't need a NACA section except something vaguely like that at the root. What it needs is careful attention to the radius joining the hull to the keel. This radius needs to develop to match the draft and drag of the keel. You are trying to accommodate a growing vortex tucked in the hydrodynamic lee of the keel. You don't want to impede this vortex in any way with corners or flat surfaces. Also, a flat bottom with two edges isn't as good as a single edge from a beveled tip, except for taking a grounding or blocking the vessel on land, then flat is better. That proud chin is also not good. Let the leading edge flow back gracefully and not steeper than 45 degrees. There isn't any attached flow on the lee of this type of keel.

    from Doug Halsey's post on this thread - Vortex at the tip of a classic long keel https://www.boatdesign.net/threads/vortex-at-the-tip-of-a-classic-long-keel.55055/#post-765714

    [​IMG]

    See also Long keel leading edges https://www.boatdesign.net/threads/long-keel-leading-edges.10180/

    The rudder should continue the line of the keel. Up to 80% of the turning force from an attached rudder can be from the pressure change on the keel. But most are less than this, about 50/50, due to the design of the keel and rudder not being optimized for steering gain. Rudder aspect ratio is fairly important as far as getting the keel to do the actual turning work is concerned.

    Aida 6 meter

    [​IMG]

    Herreshoff 28
    [​IMG]
     
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  6. Howlandwoodworks
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    Howlandwoodworks John Howland

    Blue Bell
    Thinking about a model boat that works, from the plans of a full size boat has given me some ideas about things that I wouldn't have thought on my own.
    Thanks for your in site,
    John
     
    Last edited: Jul 11, 2019
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  7. Howlandwoodworks
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    Howlandwoodworks John Howland

    Phil,
    Thanks for the related posts they are much help.
    What I think I understand you are saying is to create a uninterrupted viscous sublayer in between the hull/keel surface and the turbulent boundary layer as long as possible. Then just in front of the rudder the desired effect would be the loss of said layers and the creation of presser over rudders wetted surface the same as the surrounding sea, easier said than done.
    The keel, deadwood, and lead have not been married or shaped on the model yet. I have been reading about the NACA # in a effort to create said effects. Maybe the NACA # is not the theory that I am looking for maybe laminar flow and Reynolds number would be more effective.
    I have been looking at PHRF # for clues to the effect of long keels but there are many factors that are in play.
    The International Dragon and the Herreshoff 15' One Design Class have a PHRF of 216 and the Dark Harbor 17.5 is 248. All things said I think the Int. Dragon is a superior craft and the H 15' / BB15' PHRF # would be for the keel/center board #503 plan not the full keeled. As for the Dark Harbor 17.5 maybe I it's just heavy in construction methods.
    The photo from Marchaj's Sailing Theory & Practice must be a model in a tank or wind tunnel. I have learned to not put much faith in models and how a full scale boat will preform, mostly because of my limited knowledge.
    Well back to the drawing board and spreadsheets.


    IMG_4196.jpg IMG_4192.jpg
     
    Last edited: Jul 11, 2019
  8. Dolfiman
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    Dolfiman Senior Member

    For the Dolfino 2019 on progress project, I have adopted for the long keel wing a geometrical definition based on the Modified Naca Four digits series according to the document attached (chapter 4 page 3), with coefficients according the 00xx-44 profile. Attached also as illustration the Dolfino keel definition and, in case of, a spreadsheet for this Naca profile (just input your data in the 4 yellow cells). This profile has its maximum thickness at 0,4 c (4 the second digit following the dash, is a good trade off for a long keel ?) and practically maintain sufficient thickness towards the aft which can comply with the insertion of the rear threaded rod fastening the lead ballast.
     

    Attached Files:

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  9. jehardiman
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    jehardiman Senior Member

    Howlandwoodworks, While NACA 00XX can be the preferred shape for control surfaces, for a full keel l would not recommend them because they are too fine aft (especially in sections with t/c < 10%). A 3:1 elliptical leading edge and a 7:1 hyperbolic trailing edge with any PMB or a true EPH would be better. 6x-00xx have no place in a full keeled boat, the drag bucket will never be used because the AOA will always be too large.
     
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  10. Howlandwoodworks
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    Howlandwoodworks John Howland

    Dolfiman,
    That is most helpfully,
    Seeing the Profiles stations in the horizontal plan / z levels in the: Dolfino 2019_Long keel definition.pdf is a help.
    Looking at the profiles numbers in between the numbers or the differences between the stations helps me internalized a shapes entropy or negentropy.
    John
     
  11. Howlandwoodworks
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    Howlandwoodworks John Howland

    jehardiman,
    Most helpful,
    I had to cut 15 to 20 % of the aft section of the 63-0010 and 63-0010 (t/c of 10%) just to add rudder. The AOA was always a concern and the NACA 00XX foil had 10 deg. AOA for a air foil.
    Going to start on the sails and rigging again, have already done some rough drawings of both Gaff and Marconi rigs with a optional bow sprit for a Cutter to calculate CE
    Larsson's Design Spiral in the Principles of Yacht Design have be much help.
    Thank for sharing your knowledge,
    John
    Design Spiral Larsson.png
     
    Last edited: Jul 13, 2019
  12. Howlandwoodworks
    Joined: Sep 2018
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    Location: Columbia MO

    Howlandwoodworks John Howland

    I appreciate any and all information.
    Sorry, I didn't understand what you were saying and what you were saying wasn't about a model. As for the size and speed in my research, most of what I found so far about NACA# is about fin keels, rudders and air plane foils, this was a concern.
    What my real question was about is how to create a uninterrupted viscous sublayer in between the hull and keel surfaces and the turbulent boundary layer as long as possible. With more research this is most likely a fools errand. My boat is in real condition, waves and current. Maybe the long slow curve in between the hull and keel on say the Int. Dragon keeps the laminar flow intact as the boat rides from waves to trough. To quote America’s Cup designer Dave Pedrick “We’ve used electronic sensors and microphones to test for laminar flow. You can get some, but not much”. So let’s concentrate on turbulent flow.
    A low Emissivity of the surfaces is important as well as the shape and the relation between hull and keel. Easier said than done.
    jehardiman, Suggested a 3:1 elliptical leading edge and a 7:1 hyperbolic trailing edge with any PMB or a true EPH would be better than NACA foil #. Type that into a search and see how few hits you get. Found this in the Boatdesign.net archives.
    Rudder Centre of pressure with PMB Foil ?? https://www.boatdesign.net/threads/rudder-centre-of-pressure-with-pmb-foil.18688/
    Another hit I got is in a book I'am already reading The Principles of yacht design - Larsson, Eliasson. I have read it over, and over, and over, and over again, I think I understand about 20% now. I'am also reading A life in Boats at the same time.
    One must temper the epistemology with the ontology to balance out the day.
    I am on to sail and rigging design while I digest the hull and keel turbulent boundary layer. Round and round the design spiral I go.
     
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  13. jehardiman
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    jehardiman Senior Member

    The paper you are looking for is DTMB report 933, May 1958,"Free Stream Characteristics of a Family of Low Aspect Ratio Control Surfaces". Don't let the title put you off, is directly relatable to low aspect keels and specifically addresses sweep. Additionally have you looked at "Aero-hydrodynamics of Sailing" by Marchaj and the HISWA International Symposium on Yacht Design and Yacht Construction 1973 papers "Sailing Yacht Keels", Yacht Hull Research" and "The Influence of Fin Keel Sweepback on the Performance of Sailing Yachts". Hoerner also addresses low aspect foils in "Fluid Dynamic Lift" and "Fluid Dynamic Drag".
     
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