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Thread: NACA- what?

  1. #36
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    Default Re: NACA- what?

    The profile drag depends almost entirely on thickness - thinner is faster.
    Lets use a NACA 63-ooXX foil for an example. A 63-0012 would be faster than faster than a 63-0016.
    The name of this thread is NACA what?


  2. #37
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    Default Re: NACA- what?

    kbowen,
    If you had a photo we might be more help.

    These are not NACA foil shape but for the most part

    3:1 elliptical leading edge and a 7:1 hyperbolic trailing edge with PMB, lead bulb and connected flap.
    I have been working on this design for a while now and I am stand on the shoulders of giants.

    3 different long keels w/ flap:

    3 Long keel.jpg

    Rough draft
    Long keel.jpg

    1/4 scale model not faired
    Attachment 105271
    Attached Images Attached Images
    Last edited by John Howland; 02-17-2022 at 12:08 PM.

  3. #38
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    Default Re: NACA- what?

    Quote Originally Posted by John Howland View Post
    The profile drag depends almost entirely on thickness - thiner is faster.
    Perfectly true, if you are motoring.

    When sailing, the foil has an angle of attack, so it is not that simple. Your designer would have to get hold of the booklet of lift/drag curves, and work through it looking for the best compromise, whilst watching out for stall angles.
    It really is quite difficult to build an ugly wooden boat.

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  4. #39
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    Default Re: NACA- what?

    Nick,

    I have a great deal of respect for those working in the field of naval architecture.
    Thanks for sharing your knowledge freely.
    John

  5. #40
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    Default Re: NACA- what?

    Here is a free Airfoil tool that you can generate NACA 4, 5, and 6 digit foil Table of Offsets.
    It is for aerodynamics not hydrodynamics but it does generate a set of offsets and has a lot of other apps.

    http://airfoiltools.com/airfoil/naca4digit

  6. #41
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    Default Re: NACA- what?

    Quote Originally Posted by SHClark View Post
    It's probably worth going to some effort to get the board to pivot to a more vertical position. I'm not sure what you are planning for a pivot bolt arrangement, but perhaps it could be a two stage arrangement where it would be shifted after the board has been put half way down. As in all things aerodynamic and hydrodynamic. span is king.
    If this results in some open slot, it is well worth the trouble to put gasket flaps to cover the slot. There are many ways to achieve this, but 5 oz sail cloth with a tabled edge is arranged so it overlaps just a little and is held to the bottom with half oval on each side of the trunk. Pulling it tight as you fasten it down is a key. If you want more, I can paint a picture.
    Putting the centerboard far forward increased the loading on the rudder, often called weather helm. This can be mitigated by increasing the size of the rudder and moving the rudder center of pressure closer to the pivot axis of the pintles. The balance of the boat and how difficult it is to turn the rudder are different things.
    Years ago we built some very light cold molded Delaware Duckers. I have been putting cast off rudders and dagger boards from International Canoes and A Class Catamarans in one of them and it took quite a while to get to a dagger board that was too small...Less than 1/2 the area of the original plan form. it wasn't that the boat didn't sail upwind beautifully, but she was very slow out of a tack because the board would stall as we loaded up on the new tack. It took about 5 second to reestablish flow, which seemed like a long time when beating up a narrow river.
    The fact that the board was also twice as deep as the original also had structural consequences for the center board trunk. I have always wanted to do a similar project with a racing dory, probably with a hull shape that was more like a Gloucester Gull then an Alpha.
    SHC

    Again, I am deeply appreciative... humbled, actually by the feedback this has generated. This will go in my deeper storehouse, and hopefully will also help others. Some logistic constraints made us shy from the total high-tech realization of the theoretical ideal. A boat coming to a beach under command of middle schoolers argued for a pivoting centerboard over a dagger board, this implied a parallel trunk that was rather narrow and not conducive to a fatter board. Previous problems with leaking pivot bolts (and rot) urged us to try a pivot bolt above the waterline, and the fact that the historic board apparently never went lower than 45 degrees seemed to make this possible. I made cardboard mockups of the old board in it's lowered position as well as the new one and crudely balanced the mockups on a straight edge to find the theoretical centers. This implied a board and trunk 3" longer than the original drawings, which we are now building. To suffer abuse on the beach, the new board has a leading edge of 1/4" Garolite / G-10, and similar treatment to allow a thinner / stronger feather on the after edge. The board will get 3 layers of 6 ox glass and epoxy with extra at the leading edge and lower tip. That is where we are at the moment :-)

    Ken
    NWMC

  7. #42
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    Default Re: NACA- what?

    I have posted more than once about my preferred solution for a leak free pivot bolt.Basically you use a bush through a hole in the board to take the compression load from the pivot bolt.The bush should be a firm fit between the sides of the case and the bolt itself should have a washer beneath it's head and a rubber washer next to the case,with the same arrangement mirrored on the other side of the boat behind a nut.There was a period when we had a few postings on this forum from people who were going to engineer the best,most reliable pivot system imaginable,because they didn't really understand that it wasn't necessary for a modest sized boat.The lateral load should be taken by the keel and garboards at the lower part and the thwart or some hefty knees at the top.

    I have been trying to get to grips with Freecad for a while and I have used a centreboard installation as a learning exercise.The (hopefully attached) image shows the arrangement I trust together with a rubber hose friction device that has been common in the UK since the late 40's/early 50's.I believe it was introduced by Jack Holt for the GP14 but it could have been somebody else.I do know that over 45,000 boats have such a system and it works.If there is any interest in it,I could put the file on grabcad for those who are curious.

    partly transparent view.jpg

    cross section.jpg
    Last edited by John Meachen; 02-28-2022 at 03:24 PM. Reason: extra image added for clarity

  8. #43
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    Default Re: NACA- what?

    I posted my CAD model of a generic centreboard and installation on Grabcad for those who might be interested in seeing how I would approach the construction.You can download a step file if you have the means of reading it. https://grabcad.com/library/centrebo...sailing-boat-1 Feel free to adapt any elements that might be applicable to your needs and please be tolerant of the somewhat untidy CAD model as I am still learning the software.

  9. #44
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    Default Re: NACA- what?

    NACA (National Advisory Committee for Aeronautics) it became the NASA (National Aeronautics and Space Administration).
    As for the attached laminar flow of the wetted surface area of a hull, keel, and rudder that are in a real case scenario. Anyone who has any empirical data in qualitative research with peer review on NACA foils in real case Hydrodynamics environment that would be most helpful.


    Quote Originally Posted by stromborg View Post
    Is that entirely accurate? I thought the point of developing the foil shape was to move the water over the surface smoothly so it didn't break free and create drag inducing turbulence.

    Stromborg,
    I posted:
    "The profile drag depends almost entirely on thickness - thiner is faster."
    It was not entirely accurate because I did misspelled the word thinner.
    I do agree with you on why we use foil shapes but it's not entirely accurate and not that simple.
    Since this is a public forum some discussions are sometimes beneficial to everyone else's understanding. I don't mean to question anyones knowledge just looking for knowledge.



    In my opinion a sailboat has no "lift", only "drag into the direction one would want to go." The term Lift is a misnomer and doesn't explain how sails, hull, keel, and rudder work together to get me from point A to B even if it were in a zig zag line. The term Lift can leads one to some inaccurate assumption about how a sailboat works.
    I see a foils so called lift as a potential difference in ∆G between two Gibbs free energy equations. (∆G=∆H-T∆S)



    Disclaimer:
    I am not a naval architecture or marine engineer.

  10. #45
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    Default Re: NACA- what?

    Quote Originally Posted by John Howland View Post
    NACA (National Advisory Committee for Aeronautics) it became the NASA (National Aeronautics and Space Administration).
    As for the attached laminar flow of the wetted surface area of a hull, keel, and rudder that are in a real case scenario. Anyone who has any empirical data in qualitative research with peer review on NACA foils in real case Hydrodynamics environment that would be most helpful.




    Stromborg,
    I posted:
    "The profile drag depends almost entirely on thickness - thiner is faster."
    It was not entirely accurate because I did misspelled the word thinner.
    I do agree with you on why we use foil shapes but it's not entirely accurate and not that simple.
    Since this is a public forum some discussions are sometimes beneficial to everyone else's understanding. I don't mean to question anyones knowledge just looking for knowledge.



    In my opinion a sailboat has no "lift", only "drag into the direction one would want to go." The term Lift is a misnomer and doesn't explain how sails, hull, keel, and rudder work together to get me from point A to B even if it were in a zig zag line. The term Lift can leads one to some inaccurate assumption about how a sailboat works.
    I see a foils so called lift as a potential difference in ∆G between two Gibbs free energy equations. (∆G=∆H-T∆S)



    Disclaimer:
    I am not a naval architecture or marine engineer.
    Abbot and von Doenhoff published a very significant book in 1949 which may be useful.For fast planing monohulls,Frank Bethwaite is the most relevant.Fabio Fossati wrote an excellent book that was marred by a very poor translation into English and an ability to read the original Italian would overcome the damage done.


  11. #46
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    Default Re: NACA- what?

    As for the total drag of a boat wetted surfaces with a swing keel made out of a 1/4" flat steel plate with well rounded leading and trailing edges vs one of wood/FG of a NACA w/ PMB or not of 3/4" to 7/8" thick. The slot in the keel of the 1/4" plate boat is around 3/8" wide vs the 1” to 1 1/8" wide slot for a 3/4” to 7/8” wooden/FG one, times the length of the keel.
    Also the steel plates weight will lower the displacements center of buoyancy. In less one weights the wooden/fiber glass one with lead.
    There is a lot of robbing Peter to pay Paul in a sailboat design.

  12. #47
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    Default Re: NACA- what?

    Quote Originally Posted by John Meachen View Post
    Abbot and von Doenhoff published a very significant book in 1949 which may be useful.For fast planing monohulls,Frank Bethwaite is the most relevant.Fabio Fossati wrote an excellent book that was marred by a very poor translation into English and an ability to read the original Italian would overcome the damage done.

    Thanks,
    I have been using Hoerner "Fluid Dynamic Drag" I think it is similar but both have much to do with airplanes not sailboats and a handful of others books.
    If anyone is
    interested in Naval Architecture they should start here.
    https://www.ericwsponberg.com/
    THE DESIGN RATIOS A Naval Architect’s Dozen (or thereabouts)
    By: Eric W. SponbergNaval ArchitectBSE, PE (CT)CEng (UK)
    Here is a old version of my spreadsheet on the ratios for three versions of my Diotima.
    Untitled 9.jpg

  13. #48
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    Default Re: NACA- what?

    Nothing wrong with Eric Sponberg's advice,but the more common reference for the last twenty five years has been Larsson and Eliasson.It covers every aspect of the design process.

  14. #49
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    Default Re: NACA- what?

    Eric Sponberg's will get you started or you will find out it may be over your head.

    There is a free pdf of a older version of Principles of Yacht Design By Larsson and Eliasson on line that I use as well as Elements of yacht design Skene, and Sailing Theory and Practice C.A. Marchaj, is not free.

    http://protei.org/download/20110417Principles%20of%20yacht%20design%20-%20Larsson,%20Eliasson.pdf

    I like the design spiral in the front of Principles of Yacht Design a basic engineer design spiral but it lets you know how much work is ahead of you.
    design spiral.jpg





  15. #50
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    Default Re: NACA- what?

    I own or she owns me Wishing Star an old wooden 1954 International Star class.
    They flatted out the aft section to give them a little more speed in the late 50's mine has the old section aft.

    https://www.woodenboat.com/register-...wishing-star-0

    Here is a great paper on the Star boat keel. I have pulled a few pages out and pasted them below. It is a 900 lb. not exactly a flat plat with a bulb. They changed the bulb over the 100 years that they raced in the Olympic.
    https://starclass.org/history/the-de...star-boat-keel

    THE DEVELOPMENT OF THE KEEL
    In Star Boats
    By David Bolles
    When the Star was designed in November 1910 in the office of William Gardner, there was no thought given to the idea that the Star boat would outgrow its being used as a local New York / New England one-design racer. While the hull was built at various boatyards, Gardner’s office was the designer and provider of the various fittings needed to complete the boat. Concerning this the original Gardner specifications read as follows:

    The Star keel, as shown on the Gardner plan of November, 1910, from all appearances looks like the keel of today.

    The Star Keel as shown on the Gardner Plan of November, 1910


    In July, 1979, during the period when the Star Class was tightening up on hull tolerances, Drawing No. 4 was redrawn by Carl Schumacher, showing the same shape and dimensions given in the Etchells drawing but now including data in both English units and Metric units. Furthermore, a “Table of Limitations” for the keel was added to the plan. The number of measuring points on the “Table of Limitations” increased from 3 to 14. This is in addition to the various points (53 in number) given in the “Table of Drawing Board Offsets for Bulb Sections”. Also added were various “General Notes”. Some of the more pertinent ones to this article are as follows:

    .
    Keel Cross Sections
    In note 2 to the original Gardner plan above mention was made of the fact that the cross section of the bulb in these later plans is shown to widen out more abruptly at the top. Also the thickest part of the bulb was moved up to the middle of the bulb, in general giving the bulb more of a torpedo-like shape. In fact, the General Notes specify that the “maximum width of the bulb shall be between 77 (3”) and 127 (5”) above the keel base line.”
    To give some idea of the changes in bulb shape here are some keel cross sections:

    Relative to the original Gardner keel plan, some of the bulbs today flair out very quickly near the top of the bulb. On some bulbs, as for example on the 7700 series Follis, this feature is so abrupt that there is almost a flat shelf created on the top side of the bulb. These keels have been dubbed “beer can” keels because supposedly one could place a beer can on the shelf created by this abrupt flair.

    Leading Edge
    One of the subjects not touch on in this article is that of leading edge in keels. While this may seem minor compared to what has been talked about above, in fact there is reason to believe that this factor has more to do with the keel’s performance than other factors such as bulb shape and orientation.
    In the Spring 2001 issue of Starlights there appeared an article by Paul Bogataj which addresses this topic. In it he shows three different leading edge shapes and gives a graph showing the up-wind and down-wind performance for each of these leading edges. Briefly stated: A rounded leading edge has good lift for up-wind performance but high drag for down-wind performance. The opposite is true for a fairly narrow leading edge. He gives a third leading edge which he suggests is the best compromise between the two extremes. Although seldom talked about, for years top skippers have paid attention to this detail, and today practically all of the variations mentioned here can be found on Stars. The preference is related to what type of racing the skipper plans to do most, whether short course racing where high lift is needed, or traditional long Star course racing were speed is more important.


    Last edited by John Howland; 04-12-2022 at 06:12 PM.
    John H.

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    Default Re: NACA- what?

    Does the trailing edge stay the same or vary as well?
    Steve

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    Default Re: NACA- what?

    You can reduce the chord thickness to something more suitable on a percentage basis; in other words, reduce the chord thickness by 10% (or whatever fits) at each data point across the profile. A fellow Shearwater Yawl owner who inspired me to construct lifting foil leeboards for my Shearwater used a NACA12 foil for the lifting side of his leeboards, and a foil reduced by 10% on the opposite side of each board. His leeboards worked wonderfully, however, instead of copying him, I used a laminar flow foil given to me by a hydrodynamic engineer. Mine worked, too.

  18. #53
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    Default Re: NACA- what?

    Quote Originally Posted by The Q View Post
    . If thinner was always faster we'd all be sailing with thin steel plate keels..
    The historic Mackinaw boats of the Great lakes are said to have had centerboards of scrap boiler plate, but we also know that they were over-rigged, expecting to reef early, so it would seem that stability may have ruled over any finesse in the shape of the board. My reading has not yet discovered historically when there might have been spare boiler plate lying around, and whether Mackinaw boats had centerboards before iron plate was readily available. ??
    Ken

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    Default Re: NACA- what?

    stromborg,
    The connecting plate is tapered to less than 1/8" aft and I didn't see any hyperbolic or parabolic curve from the maximum camber aft it did taper a little faster in the last 4" to 6" and didn't seem to have a PMB. I think part of the shape had to do with structural support as well as laminar flow. The maximum camber is about 3/8" thick and very far forward 15% or less and with an elliptic leading edge. The connecting Plate is 48" long on the average. The flap/rudder is semi connected.
    The bulbs look to be NACA foil shapes but i am just guessing. The Table of Offsets are out of focus. Why am I am not surprised.
    star aft view keel.jpgstar foward view keel.jpg

    Nicholas,
    Yea, NACA foils are not the only foil shape out there.
    I had a 1984 Prindle 18' cat that had laminar flow foil shaped hulls though much thinner. 18' long with 8" wide at the maximum camber at the water line or there about.
    Had it for 15 years and sold it off. We were both getting much to old for that kind of nonsense. I sure miss it some days.
    Last edited by John Howland; 04-12-2022 at 11:41 PM.
    John H.

  20. #55
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    Default Re: NACA- what?

    ^^^ NACA foils date back to olden days. The North American P-51 was the first military aircraft to incorporate laminar flow wings. We'll let the record of that speak for itself. My Shearwater with laminar foils did outperform my friends NACA foils on one tack extending over a distance of about ten miles, with me starting abeam 100 yards to leeward and finishing 1/4 mile ahead and 100 yards to windward. And he was a more accomplished sailor using slightly better sails.

  21. #56
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    Default Re: NACA- what?

    The problem with laminar flow surfaces is it takes very little disturbance to break the flow conditions.
    It's unlikely a good laminar flow shape could be made to fit a centreboard case, any scratches caused by drawing the board in or out whether it being a vertical or swinging board would break the flow.
    Similarly a laminar flow fixed keel is unlikely to be as successful as a good NACA shape, unless the boat is dry sailed and the keel kept well polished.
    At higher speeds laminar flow has more of an advantage, if you can keep the board clean and smooth....
    Just an amateur bodging away..

  22. #57
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    Default Re: NACA- what?

    Keels that travel parallel and opposed to the water flow have no lift, they only have drag. That is also what happens, as said above, when motoring without turning.

    Keels that don't travel parallel to the water flow, as the hull yaws slightly for example, will create lift from a wing viewpoint. A flat plate will do that too if the plate angle differs from the flow direction.

    We tend to think of lift as a vertical necessary lifting force for an aircraft wing, but under the water on the hull of a sailboat it becomes a (mostly) lateral force. The term lift, while correct from the fluid dynamic perspective, is awkward from viewpoint of the sailor or hull designer. And then there's the more complicated airflow around the inclined (heeled) sails. Mentally sorting these out is a headache without using the force diagram illustrations shown in Larsson and Eliasson, among others.

  23. #58
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    Default Re: NACA- what?

    Quote Originally Posted by xkdrolt View Post
    Keels that travel parallel and opposed to the water flow have no lift, they only have drag. That is also what happens, as said above, when motoring without turning.

    Keels that don't travel parallel to the water flow, as the hull yaws slightly for example, will create lift from a wing viewpoint. A flat plate will do that too if the plate angle differs from the flow direction.
    I am under the (potentially wrong) impression that a sailboat keel or centerboard is always in a state of "yaw" in relation to it's direction of travel.
    Steve

    If you would have a good boat, be a good guy when you build her - honest, careful, patient, strong.
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    Default Re: NACA- what?

    Well, if you're in irons by being greedy then the yaw could be zero --- but you aren't going anywhere until you do creative things with the boom.

    Otherwise to your point, my yaw comment may have been redundant, but I was intentionally descriptive to further the point in the absence of a good sketch with forces shown.

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    Default Re: NACA- what?

    That is the sole reason symmetrical foils are at all useful on sailboats; on a beat they are always moving along a vector to leeward of their heading. They are effective only in minimizing leeway. OTOH, a boat with a pair of lifting foils instead of a symmetrical keel or centerboard (typically leeboards or bilge boards) incorporating a bit of angle of attack relative to their heading, can effectively move along a vector that ACTUALLY IS the heading.


    Quote Originally Posted by stromborg View Post
    I am under the (potentially wrong) impression that a sailboat keel or centerboard is always in a state of "yaw" in relation to it's direction of travel.

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