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Re: foiled again

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  • wwbaginski
    Well actually I like the translation of my question... Tom, please. wojtek
    Message 1 of 24 , Oct 6, 2007
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      Well actually I like the "translation" of my question... Tom, please.

      wojtek

      --- In Michalak@yahoogroups.com, john h wright <jhargrovewright2@...>
      wrote:
      >
      > Thomas H.,
      > Most people that know what they are talking about answer a question with
      > a question....because the question is never complete. The question was,
      > (paraphrasing here) "tell me what number to use"....or give me the best
      > answer that you can think of that answers the question that I don't know
      > how to ask. Better yet, just give three foils with the basic
      > characteristics of each that would likely work with a small boat.
      > Please.
      >
      > John in Bastrop
      >
      > On Fri, 5 Oct 2007 05:21:50 -0700 (PDT) Thomas Hamernik
      > <awellbalancedgun@...> writes:
      > There are many, many NACA foils from which to choose.
      > For our application, the simple four-digit series
      > seems to suffice, with choices limited further to the
      > symmetrical sections, or those beginning with a "00"
      > (digits other than "0" indicate the magnitude and
      > position of foil camber). From there, it's a matter
      > of compromise - lift versus drag, range of
      > angle-of-attack and stall angle. Then, there are
      > structural considerations - the foil has to be
      > sufficiently thick for its size.
      >
      > I've placed NACA Report No. 460 in the files section
      > if anyone is interested in digging deeper. There are
      > performance curves for all the foils evaluated under
      > that study.
      >
      > TJH
      >
      > --- wwbaginski <wwbaginski@...> wrote:
      >
      > > what a timing: I 've found "Foiled Again" by Gary
      > > Blankenship & Helen
      > > Snell - Tallahassee, Florida - USA at today
      > > Duckworksmagazine just
      > > before the weekend during which I expect to start
      > > making a leeboard
      > > for my polepunt. Thanks Gary, Tom and Chuck. Very
      > > interesting things.
      > >
      > > What are criteria for choosing the suitable NACA
      > > profile?
      > >
      > > wojtek
      > >
      > >
      > >
      > >
      >
      > __________________________________________________________
      > Looking for a deal? Find great prices on flights and hotels with Yahoo!
      > FareChase.
      > http://farechase.yahoo.com/
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >
    • Thomas Hamernik
      John in B. & Wojtek- I m not a designer and have not made a thorough study of foils. But, if we accept that the NACA four-digit foils have application to the
      Message 2 of 24 , Oct 6, 2007
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        John in B. & Wojtek-

        I'm not a designer and have not made a thorough study
        of foils. But, if we accept that the NACA four-digit
        foils have application to the small boats we home
        builders build, I'll offer my thoughts.


        The short answer: NACA 0009 for centerboards and
        leeboards and NACA 0012 for rudders


        The long answer:

        First, let's consider what we require of our boards
        (both in reducing leeway and for maneuvering).
        Ideally, the board should provide lots of lift with
        minimal drag. A thin section weighs less than a thick
        section, should cost less since it requires less
        material, and is probably easier to construct since it
        requires less material be removed if carved from a
        rectangular blank. But, it has to be thick enough to
        be stiff enough and have sufficient strength. The
        boards are expected to operate on each tack, so the
        sections should be symmetrical.

        In reviewing the range of foils tested in the NACA 460
        report, we find that they are all based on a single
        shape, a shape that was essentially common to many of
        the successful craft of the time of the study (first
        published in 1933), but have varying degrees of
        thickness and camber. Since we are interested in
        symmetrical boards, we can focus on the seven 00XX
        sections tested and the corresponding discussion and
        conclusions related to these sections.
        The ratio of the maximum lift coefficient to the
        minimum profile-drag coefficient is useful as a
        measure of section efficiency and is tabulated for the
        various sections in Table IX. For symmetrical
        sections, the ratio of the maximum lift coefficient to
        the minimum profile-drag coefficient is greatest for
        moderately thick sections having thickness
        designations of between 09 and 15.

        Also of interest is the shape of the curve of
        lift-to-drag. For the thinnest section studied,
        section 0006, the curve is very sharp, with the
        lift-to-drag ratio falling off very rapidly above 4
        degrees of angle of attack. While the lift-to-drag
        ratio still falls off above about 4 to 6 degrees of
        angle-of-attack for the thicker sections, the ratio
        diminishes much less rapidly, suggesting that the
        thicker sections will perform better than the thinner
        sections over a wider range of angle of attack. Since
        rudders need to operate over a range of angles,
        thicker sections for rudders makes sense.

        So, optimum sections seem to be those having thickness
        designations between 09 and 15, with the thinner
        sections appropriate for leeboards and centerboards,
        provided the thickness is adequate for strength, and
        the thicker sections better for rudders.

        Try 0009 for leeboards and 0012 for rudders, though
        0012 seems to be a good all-around section and
        anything from 0009 to 0015 should work well for
        either.

        While my recommendation to use 0009 for leeboards
        matches Matt Layden’s recommendation to Gary B (refer
        to Gary’s article), my recommendation for a thicker
        foil for rudders runs counter to Matt’s
        recommendation. I’m not sure why we don’t agree,
        here. Performance of the 0006 section appears to
        diminish rapidly above four degrees of angle of
        attack. In referring to Figure 4, the graph of the
        performance of the NACA 0006 section, the L/D ratio at
        4 degrees is about 23.5, the coefficient of lift is
        about 0.31 and the drag coefficient is about 0.013.
        In referring to Figure 6, the graph of the performance
        of the NACA 0012 section, the L/D ratio at 4 degrees
        is about 22, the coefficient of lift is about 0.30 and
        the drag coefficient is about 0.014. Note that
        reading the numbers from the graphs is difficult and
        may introduce some error.

        But, at 12 degrees, the 0006 section has an L/D of
        just 5.5, a coefficient of lift of about 0.8 and a
        drag coefficient of about 0.15 while the 0012 section
        has an L/D of nearly 16, a lift coefficient of about
        0.9 and a drag coefficient of about 0.06. So,
        although the thinner sections perform a bit better at
        small angles of attack, the thicker section continues
        to perform well at larger angles of attack. I know
        that Matt covers long distances in his boats. So,
        perhaps the slight (if any real) increase in
        performance at lower angles of attacks is of value to
        him and others who tend to hold a course, rather than
        tack sharply (I’m just guessing, here).

        I’m interested in others’ thoughts, as well.

        TJH

        --- wwbaginski <wwbaginski@...> wrote:

        > Well actually I like the "translation" of my
        > question... Tom, please.
        >
        > wojtek
        >
        > --- In Michalak@yahoogroups.com, john h wright
        > <jhargrovewright2@...>
        > wrote:
        > >
        > > Thomas H.,
        > > Most people that know what they are talking about
        > answer a question with
        > > a question....because the question is never
        > complete. The question was,
        > > (paraphrasing here) "tell me what number to
        > use"....or give me the best
        > > answer that you can think of that answers the
        > question that I don't know
        > > how to ask. Better yet, just give three foils
        > with the basic
        > > characteristics of each that would likely work
        > with a small boat.
        > > Please.
        > >
        > > John in Bastrop
        > >
        > > On Fri, 5 Oct 2007 05:21:50 -0700 (PDT) Thomas
        > Hamernik
        > > <awellbalancedgun@...> writes:
        > > There are many, many NACA foils from which to
        > choose.
        > > For our application, the simple four-digit series
        > > seems to suffice, with choices limited further to
        > the
        > > symmetrical sections, or those beginning with a
        > "00"
        > > (digits other than "0" indicate the magnitude and
        > > position of foil camber). From there, it's a
        > matter
        > > of compromise - lift versus drag, range of
        > > angle-of-attack and stall angle. Then, there are
        > > structural considerations - the foil has to be
        > > sufficiently thick for its size.
        > >
        > > I've placed NACA Report No. 460 in the files
        > section
        > > if anyone is interested in digging deeper. There
        > are
        > > performance curves for all the foils evaluated
        > under
        > > that study.
        > >
        > > TJH
        > >
        > > --- wwbaginski <wwbaginski@...> wrote:
        > >
        > > > what a timing: I 've found "Foiled Again" by
        > Gary
        > > > Blankenship & Helen
        > > > Snell - Tallahassee, Florida - USA at today
        > > > Duckworksmagazine just
        > > > before the weekend during which I expect to
        > start
        > > > making a leeboard
        > > > for my polepunt. Thanks Gary, Tom and Chuck.
        > Very
        > > > interesting things.
        > > >
        > > > What are criteria for choosing the suitable NACA
        > > > profile?
        > > >
        > > > wojtek
        > > >
        > > >
        > > >
        > > >
        > >
        > >
        >
        __________________________________________________________
        > > Looking for a deal? Find great prices on flights
        > and hotels with Yahoo!
        > > FareChase.
        > > http://farechase.yahoo.com/
        > >
        > >
        > >
        > > [Non-text portions of this message have been
        > removed]
        > >
        >
        >
        >



        ____________________________________________________________________________________
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      • Kevin O'Neill
        ... From: Thomas Hamernik While my recommendation to use 0009 for leeboards matches Matt Layden¢s recommendation to Gary B (refer
        Message 3 of 24 , Oct 6, 2007
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          ----- Original Message ----
          From: Thomas Hamernik <awellbalancedgun@...>

          While my recommendation to use 0009 for leeboards

          matches Matt Layden�s recommendation to Gary B (refer

          to Gary�s article), my recommendation for a thicker

          foil for rudders runs counter to Matt�s

          recommendation. I�m not sure why we don�t agree,

          here. Performance of the 0006 section appears to

          diminish rapidly above four degrees of angle of

          attack. In referring to Figure 4, the graph of the

          performance of the NACA 0006 section, the L/D ratio at

          4 degrees is about 23.5, the coefficient of lift is

          about 0.31 and the drag coefficient is about 0.013.

          In referring to Figure 6, the graph of the performance

          of the NACA 0012 section, the L/D ratio at 4 degrees

          is about 22, the coefficient of lift is about 0.30 and

          the drag coefficient is about 0.014. Note that

          reading the numbers from the graphs is difficult and

          may introduce some error.



          But, at 12 degrees, the 0006 section has an L/D of

          just 5.5, a coefficient of lift of about 0.8 and a

          drag coefficient of about 0.15 while the 0012 section

          has an L/D of nearly 16, a lift coefficient of about

          0.9 and a drag coefficient of about 0.06. So,

          although the thinner sections perform a bit better at

          small angles of attack, the thicker section continues

          to perform well at larger angles of attack. I know

          that Matt covers long distances in his boats. So,

          perhaps the slight (if any real) increase in

          performance at lower angles of attacks is of value to

          him and others who tend to hold a course, rather than

          tack sharply (I�m just guessing, here).



          I�m interested in others� thoughts, as well.









          It might be that Matt's boat's have minimal weather helm, with the leeboard taking more or less all the side force, so he sails with the rudder more or less straight in the water. If you have a lot of weather helm, like my proa, for example, you need bigger rudders and need them to have good L/D ratios at higher angles of attack.

          Kevin












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          [Non-text portions of this message have been removed]
        • Thomas Hamernik
          That s fine if you want to go straight. But, when you want to tack, a small rudder needs to operate at higher angles of attack than a large rudder to generate
          Message 4 of 24 , Oct 6, 2007
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            That's fine if you want to go straight. But, when you
            want to tack, a small rudder needs to operate at
            higher angles of attack than a large rudder to
            generate the same turning force.

            TJH


            --- Kevin O'Neill <K_S_ONeill@...> wrote:

            >
            >
            > ----- Original Message ----
            > From: Thomas Hamernik <awellbalancedgun@...>
            >
            > While my recommendation to use 0009 for leeboards
            >
            > matches Matt Layden¢s recommendation to Gary B
            > (refer
            >
            > to Gary¢s article), my recommendation for a thicker
            >
            > foil for rudders runs counter to Matt¢s
            >
            > recommendation. I¢m not sure why we don¢t agree,
            >
            > here. Performance of the 0006 section appears to
            >
            > diminish rapidly above four degrees of angle of
            >
            > attack. In referring to Figure 4, the graph of the
            >
            > performance of the NACA 0006 section, the L/D ratio
            > at
            >
            > 4 degrees is about 23.5, the coefficient of lift is
            >
            > about 0.31 and the drag coefficient is about 0.013.
            >
            > In referring to Figure 6, the graph of the
            > performance
            >
            > of the NACA 0012 section, the L/D ratio at 4 degrees
            >
            > is about 22, the coefficient of lift is about 0.30
            > and
            >
            > the drag coefficient is about 0.014. Note that
            >
            > reading the numbers from the graphs is difficult and
            >
            > may introduce some error.
            >
            >
            >
            > But, at 12 degrees, the 0006 section has an L/D of
            >
            > just 5.5, a coefficient of lift of about 0.8 and a
            >
            > drag coefficient of about 0.15 while the 0012
            > section
            >
            > has an L/D of nearly 16, a lift coefficient of about
            >
            > 0.9 and a drag coefficient of about 0.06. So,
            >
            > although the thinner sections perform a bit better
            > at
            >
            > small angles of attack, the thicker section
            > continues
            >
            > to perform well at larger angles of attack. I know
            >
            > that Matt covers long distances in his boats. So,
            >
            > perhaps the slight (if any real) increase in
            >
            > performance at lower angles of attacks is of value
            > to
            >
            > him and others who tend to hold a course, rather
            > than
            >
            > tack sharply (I¢m just guessing, here).
            >
            >
            >
            > I¢m interested in others¢ thoughts, as well.
            >
            >
            >
            >
            >
            >
            >
            >
            >
            > It might be that Matt's boat's have minimal weather
            > helm, with the leeboard taking more or less all the
            > side force, so he sails with the rudder more or less
            > straight in the water. If you have a lot of weather
            > helm, like my proa, for example, you need bigger
            > rudders and need them to have good L/D ratios at
            > higher angles of attack.
            >
            > Kevin
            >
            >
            >
            >
            >
            >
            >
            >
            >
            >
            >
            >
            >
            >
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            > Research Panel today!
            >
            http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.asp?a=7
            >
            >
            >
            >
            > [Non-text portions of this message have been
            > removed]
            >
            >
            >
            >
            > Yahoo! Groups Links
            >
            >
            >
            >
            >



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          • Kevin O'Neill
            Hi Sure. I m assuming the rudder is big enough to turn the boat. My point is, by varying the fore-aft location of the CE and CLR you can either load the
            Message 5 of 24 , Oct 6, 2007
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              Hi

              Sure. I'm assuming the rudder is big enough to turn the boat. My point is, by varying the fore-aft location of the CE and CLR you can either load the rudders up or not. One design might sail straight with 1 degree or so of rudder angle, another might need 5 degrees of rudder angle to sail straight (for both add whatever your leeway is to find the actual angle of attack the foil is seeing). The first would do best with a thinner, more daggerboard like profile, I guess, and the latter with a thicker profile that has a good L/D ratio at higher angles of attack. Though I'm not sure the difference would be noticed except in a one design fleet where you're sailing against identical boats.

              Kevin


              ----- Original Message ----
              From: Thomas Hamernik <awellbalancedgun@...>
              To: Michalak@yahoogroups.com
              Sent: Saturday, October 6, 2007 11:20:48 PM
              Subject: Re: [Michalak] Re: foiled again













              That's fine if you want to go straight. But, when you

              want to tack, a small rudder needs to operate at

              higher angles of attack than a large rudder to

              generate the same turning force.



              TJH



              >

              > It might be that Matt's boat's have minimal weather

              > helm, with the leeboard taking more or less all the

              > side force, so he sails with the rudder more or less

              > straight in the water. If you have a lot of weather

              > helm, like my proa, for example, you need bigger

              > rudders and need them to have good L/D ratios at

              > higher angles of attack.

              >








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            • Thomas Hamernik
              Hi, Kevin- I did catch your point. I am just wondering what I missing with regard to Matt s recommendation for a NACA 0006 for a rudder. Sure, it may hold
              Message 6 of 24 , Oct 6, 2007
              • 0 Attachment
                Hi, Kevin-

                I did catch your point. I am just wondering what I
                missing with regard to Matt's recommendation for a
                NACA 0006 for a rudder. Sure, it may hold his course,
                fine, if the boat is balanced as you suggest. But, why
                not make it a bit thicker and get better performance
                at the higher angles of attack typically experienced
                what tacking?

                TJH

                --- Kevin O'Neill <K_S_ONeill@...> wrote:

                > Hi
                >
                > Sure. I'm assuming the rudder is big enough to turn
                > the boat. My point is, by varying the fore-aft
                > location of the CE and CLR you can either load the
                > rudders up or not. One design might sail straight
                > with 1 degree or so of rudder angle, another might
                > need 5 degrees of rudder angle to sail straight (for
                > both add whatever your leeway is to find the actual
                > angle of attack the foil is seeing). The first
                > would do best with a thinner, more daggerboard like
                > profile, I guess, and the latter with a thicker
                > profile that has a good L/D ratio at higher angles
                > of attack. Though I'm not sure the difference would
                > be noticed except in a one design fleet where you're
                > sailing against identical boats.
                >
                > Kevin
                >
                >
                > ----- Original Message ----
                > From: Thomas Hamernik <awellbalancedgun@...>
                > To: Michalak@yahoogroups.com
                > Sent: Saturday, October 6, 2007 11:20:48 PM
                > Subject: Re: [Michalak] Re: foiled again
                >
                >
                >
                >
                >
                >
                >
                >
                >
                >
                >
                >
                >
                > That's fine if you want to go straight.
                > But, when you
                >
                > want to tack, a small rudder needs to operate at
                >
                > higher angles of attack than a large rudder to
                >
                > generate the same turning force.
                >
                >
                >
                > TJH
                >
                >
                >
                > >
                >
                > > It might be that Matt's boat's have minimal
                > weather
                >
                > > helm, with the leeboard taking more or less all
                > the
                >
                > > side force, so he sails with the rudder more or
                > less
                >
                > > straight in the water. If you have a lot of
                > weather
                >
                > > helm, like my proa, for example, you need bigger
                >
                > > rudders and need them to have good L/D ratios at
                >
                > > higher angles of attack.
                >
                > >
                >
                >
                >
                >
                >
                >
                >
                >
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              • Kenneth Grome
                ... Maybe because tacking consumes a very small percentage of the time the boat is under sail and therefore it makes more sense to optimize for the rest of the
                Message 7 of 24 , Oct 6, 2007
                • 0 Attachment
                  > Why not make it a bit thicker and get better
                  > performance at the higher angles of attack
                  > typically experienced what tacking?

                  Maybe because tacking consumes a very small percentage of the time the
                  boat is under sail and therefore it makes more sense to optimize for
                  the rest of the time ... ?

                  Sincerely,
                  Ken Grome
                  Bagacay Boatworks
                  www.bagacayboatworks.com
                • Thomas Hamernik
                  That s pretty much the same thought I had in my earlier post - I can t think of any other reason. But, this rationale depends on the type of sailing you do, I
                  Message 8 of 24 , Oct 7, 2007
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                    That's pretty much the same thought I had in my
                    earlier post - I can't think of any other reason.
                    But, this rationale depends on the type of sailing you
                    do, I suppose. If you race or sail small boats in
                    small ponds, perhaps tacking speed & efficiency
                    becomes more important. Above five degrees, the NACA
                    0012 outperforms the NACA 0006.

                    TJH

                    --- Kenneth Grome <bagacayboatworks@...> wrote:

                    > > Why not make it a bit thicker and get better
                    > > performance at the higher angles of attack
                    > > typically experienced what tacking?
                    >
                    > Maybe because tacking consumes a very small
                    > percentage of the time the
                    > boat is under sail and therefore it makes more sense
                    > to optimize for
                    > the rest of the time ... ?
                    >
                    > Sincerely,
                    > Ken Grome
                    > Bagacay Boatworks
                    > www.bagacayboatworks.com
                    >
                    >
                    >
                    >
                    >
                    >
                    >




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                  • ptfrohne
                    ... I know enough model aircraft aeronautics to follow this discussion. But what I am curious about is what is the difference in performance of a 12 dinghy
                    Message 9 of 24 , Oct 7, 2007
                    • 0 Attachment
                      > The short answer: NACA 0009 for centerboards and
                      > leeboards and NACA 0012 for rudders
                      >
                      > The long answer:
                      >


                      I know enough model aircraft aeronautics to follow this discussion.
                      But what I am curious about is what is the difference in performance
                      of a 12' dinghy when using an NACA foil vice a simple 1/2" sheet of
                      plywood with rounded edges? Will it point into the wind 1 degree
                      more? 5 degrees more? Will I get 5 knots more speed downwind or 0.05
                      knots more speed?

                      Orville & Wilbur determined that a 2x4 with rounded edges proved to
                      have less drag than one carved to a teardrop at the Reynolds numbers
                      they planned to fly at. Bu that was a 2x4. How does the aspect ratio
                      of the daggerboard or rudder affect which foil to use? Catboats
                      typically have a pretty wide rudders since they operate in the
                      shallows. Racing sailboats will use a higher aspect ratio as they
                      tend to operate in much deeper water (and want less drag).

                      I guess my question is... Is it worth it to the average homebuilder to
                      try to duplicate an NACA foil or just approximate it so that it "looks
                      about right"?

                      Phil
                      St. Louis
                      [Uncle John's Skiff]
                    • wwbaginski
                      Phil, I think the point is not just home or professional construction, but kind of sailing you intend to do. Kind of sailing is usually determined by waterways
                      Message 10 of 24 , Oct 7, 2007
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                        Phil, I think the point is not just home or professional construction,
                        but kind of sailing you intend to do. Kind of sailing is usually
                        determined by waterways you intend to cruise on. In my case a sailing
                        polepunt , being one of simpliest Jim designs, is expected to cruise
                        on the river, thus each additional degree of pointing into the wind is
                        worth making a NACA profiled leeboard.

                        On the other hand there's opinion here that NACA profiles tolerate
                        "approximate shape" much better than other ones.

                        Wojtek



                        --- In Michalak@yahoogroups.com, "ptfrohne" <ptfrohne@...> wrote:
                        >
                        > > The short answer: NACA 0009 for centerboards and
                        > > leeboards and NACA 0012 for rudders
                        > >
                        > > The long answer:
                        > >
                        >
                        >
                        > I know enough model aircraft aeronautics to follow this discussion.
                        > But what I am curious about is what is the difference in performance
                        > of a 12' dinghy when using an NACA foil vice a simple 1/2" sheet of
                        > plywood with rounded edges? Will it point into the wind 1 degree
                        > more? 5 degrees more? Will I get 5 knots more speed downwind or 0.05
                        > knots more speed?
                        >
                        > Orville & Wilbur determined that a 2x4 with rounded edges proved to
                        > have less drag than one carved to a teardrop at the Reynolds numbers
                        > they planned to fly at. Bu that was a 2x4. How does the aspect ratio
                        > of the daggerboard or rudder affect which foil to use? Catboats
                        > typically have a pretty wide rudders since they operate in the
                        > shallows. Racing sailboats will use a higher aspect ratio as they
                        > tend to operate in much deeper water (and want less drag).
                        >
                        > I guess my question is... Is it worth it to the average homebuilder to
                        > try to duplicate an NACA foil or just approximate it so that it "looks
                        > about right"?
                        >
                        > Phil
                        > St. Louis
                        > [Uncle John's Skiff]
                        >
                      • Thomas Hamernik
                        I ve not seen any data for a flat plate - I have only the NACA 460 report. But, experience shows that a flat plate will work. How much poorer or better I
                        Message 11 of 24 , Oct 7, 2007
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                          I've not seen any data for a flat plate - I have only
                          the NACA 460 report. But, experience shows that a
                          flat plate will work. How much poorer or better I
                          just don't know.

                          Jim Michalak (who I'm guessing knows a lot about these
                          things) suggests that rounding the front and tapering
                          the back 1/3 to approximate an proper foil is
                          adequate, and there is little to be gained by going
                          further. I know that often he recommends the simplest
                          solution to keep the building of his designs well
                          within the grasp of the least experienced builder.
                          With this in mind, the very fact that he recommends
                          any rounding and tapering suggests that a foil
                          performs sufficiently better than a flat plate to
                          justify the trouble of approximating it.

                          I think that if you are going to go to the trouble of
                          devloping a true NACA section, you might as well take
                          advantage of what it can offer, which seems to be
                          better performance at a wider range (and larger)
                          angles of attack. The data and conclusions of the
                          NACA 460 report say that the foils having thickness
                          designations of between 09 and 15 are the most
                          efficient (by their definition).

                          Although the models used in the NACA report were of
                          finite aspect ratio, the report presents both the test
                          data and the data corrected for infinite aspect ratio.
                          The testing under that study did not examine the
                          effects of varying the aspect ratio. For a disucssion
                          of this, I refer you to several of Jim Michalak's
                          older essays.

                          I think that aspect ratio is largely a practical
                          matter. High-aspect ratio boards generate more lift
                          and less drag than low-aspect ratio boards. But,
                          they're more difficult to construct, and result in
                          craft that have deeper draft. Another (minor) issue
                          with with high-aspect ratio swinging boards, like Jim
                          Michalak's leeboards, is that the center of lateral
                          resistance changes significantly when the board is
                          raised, such as when approaching a windward beach.
                          The position of lateral resistance of the very
                          low-aspect ratio boards of the traditional sharpies,
                          on the other hand, varies very little as it is raised
                          or lowered. It seems the performance advantages of a
                          high-aspect ratio win out since high-aspect ratio
                          boards seem to be the norm on modern designs - even
                          some modern versions of catboats (as opposed to
                          modern constructions of traditional designs, though I
                          can't name such a design right now).

                          Perhaps I'll dig up some more data so that we can
                          compare thin plates to the four-digit NACA series.

                          TJH


                          --- ptfrohne <ptfrohne@...> wrote:

                          > > The short answer: NACA 0009 for centerboards and
                          > > leeboards and NACA 0012 for rudders
                          > >
                          > > The long answer:
                          > >
                          >
                          >
                          > I know enough model aircraft aeronautics to follow
                          > this discussion.
                          > But what I am curious about is what is the
                          > difference in performance
                          > of a 12' dinghy when using an NACA foil vice a
                          > simple 1/2" sheet of
                          > plywood with rounded edges? Will it point into the
                          > wind 1 degree
                          > more? 5 degrees more? Will I get 5 knots more
                          > speed downwind or 0.05
                          > knots more speed?
                          >
                          > Orville & Wilbur determined that a 2x4 with rounded
                          > edges proved to
                          > have less drag than one carved to a teardrop at the
                          > Reynolds numbers
                          > they planned to fly at. Bu that was a 2x4. How
                          > does the aspect ratio
                          > of the daggerboard or rudder affect which foil to
                          > use? Catboats
                          > typically have a pretty wide rudders since they
                          > operate in the
                          > shallows. Racing sailboats will use a higher aspect
                          > ratio as they
                          > tend to operate in much deeper water (and want less
                          > drag).
                          >
                          > I guess my question is... Is it worth it to the
                          > average homebuilder to
                          > try to duplicate an NACA foil or just approximate it
                          > so that it "looks
                          > about right"?
                          >
                          > Phil
                          > St. Louis
                          > [Uncle John's Skiff]
                          >
                          >
                          >



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                        • gbship
                          Tom: This is great information -- I didn t realize how involved all this NACA stuff was. I wouldn t obsess too much about Matt s recommendations simply because
                          Message 12 of 24 , Oct 7, 2007
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                            Tom:
                            This is great information -- I didn't realize how involved all this
                            NACA stuff was. I wouldn't obsess too much about Matt's
                            recommendations simply because it's always possible I misheard him or
                            forgot the correct number. He and Karen kindly had Helen and me to
                            lunch with his mother-in-law and Sven Yrvind at Cedar Key this year
                            at at some point I asked him for his recommendations. Against that
                            backdrop, it's certainly possible I misunderstood or mis-remembered
                            what he told me. (Helen says that wouldn't be the first time :-)) One
                            thought, though, is if I interpreted your program right, a "lower"
                            NACA number leads to a thicker foil, i.e. 0006 is thicker than 0012.
                            If I heard Matt right, it's possible the recommendation has more to
                            do with strength than maximum efficiency. Oaracle has completed two
                            Everglades Challenges and it would be small consolation to have the
                            maximum efficient shape if it broke at night off Cape Sable in the
                            Everglades in rising winds and seas . . . BTW, if it makes any
                            difference, Oaracle does not carry a strong weather helm and the
                            tiller is usually close to center.

                            That said, I wish I had asked on this list for a recommendation
                            before starting. With Tom's advice, I probably would have done an
                            0009 section for the leeboard and rudder.

                            I'm hoping to get Oaracle back in the water in a week or so. In line
                            with Matt's and Michalak's predictions, I'm hoping for only a slight,
                            but still noticeable, improvement. Something will be posted either
                            here or on Duckworks.

                            A related thought. Around 1980, I was racing an older Sunfish and
                            doing well in a mixed fleet. But some folks got new Sunfish, and
                            suddenly I couldn't keep up with people I had been beating, and
                            noticeably could not point as high as they could on the wind.
                            Eventually we learned that Sunfish had redeisgned the sail and
                            centerboard (and perhaps the rudder), which improved the efficiency.
                            So a small change can make a difference, although you might not
                            notice unless you're sailing next to another boat and the only
                            difference is one has the "upgrade" and one doesn't . . . .

                            Gary Blankenship

                            --- In Michalak@yahoogroups.com, Thomas Hamernik
                            <awellbalancedgun@...> wrote:
                            >
                            > I've not seen any data for a flat plate - I have only
                            > the NACA 460 report. But, experience shows that a
                            > flat plate will work. How much poorer or better I
                            > just don't know.
                            >
                            > Jim Michalak (who I'm guessing knows a lot about these
                            > things) suggests that rounding the front and tapering
                            > the back 1/3 to approximate an proper foil is
                            > adequate, and there is little to be gained by going
                            > further. I know that often he recommends the simplest
                            > solution to keep the building of his designs well
                            > within the grasp of the least experienced builder.
                            > With this in mind, the very fact that he recommends
                            > any rounding and tapering suggests that a foil
                            > performs sufficiently better than a flat plate to
                            > justify the trouble of approximating it.
                            >
                            > I think that if you are going to go to the trouble of
                            > devloping a true NACA section, you might as well take
                            > advantage of what it can offer, which seems to be
                            > better performance at a wider range (and larger)
                            > angles of attack. The data and conclusions of the
                            > NACA 460 report say that the foils having thickness
                            > designations of between 09 and 15 are the most
                            > efficient (by their definition).
                            >
                            > Although the models used in the NACA report were of
                            > finite aspect ratio, the report presents both the test
                            > data and the data corrected for infinite aspect ratio.
                            > The testing under that study did not examine the
                            > effects of varying the aspect ratio. For a disucssion
                            > of this, I refer you to several of Jim Michalak's
                            > older essays.
                            >
                            > I think that aspect ratio is largely a practical
                            > matter. High-aspect ratio boards generate more lift
                            > and less drag than low-aspect ratio boards. But,
                            > they're more difficult to construct, and result in
                            > craft that have deeper draft. Another (minor) issue
                            > with with high-aspect ratio swinging boards, like Jim
                            > Michalak's leeboards, is that the center of lateral
                            > resistance changes significantly when the board is
                            > raised, such as when approaching a windward beach.
                            > The position of lateral resistance of the very
                            > low-aspect ratio boards of the traditional sharpies,
                            > on the other hand, varies very little as it is raised
                            > or lowered. It seems the performance advantages of a
                            > high-aspect ratio win out since high-aspect ratio
                            > boards seem to be the norm on modern designs - even
                            > some modern versions of catboats (as opposed to
                            > modern constructions of traditional designs, though I
                            > can't name such a design right now).
                            >
                            > Perhaps I'll dig up some more data so that we can
                            > compare thin plates to the four-digit NACA series.
                            >
                            > TJH
                            >
                            >
                            > --- ptfrohne <ptfrohne@...> wrote:
                            >
                            > > > The short answer: NACA 0009 for centerboards and
                            > > > leeboards and NACA 0012 for rudders
                            > > >
                            > > > The long answer:
                            > > >
                            > >
                            > >
                            > > I know enough model aircraft aeronautics to follow
                            > > this discussion.
                            > > But what I am curious about is what is the
                            > > difference in performance
                            > > of a 12' dinghy when using an NACA foil vice a
                            > > simple 1/2" sheet of
                            > > plywood with rounded edges? Will it point into the
                            > > wind 1 degree
                            > > more? 5 degrees more? Will I get 5 knots more
                            > > speed downwind or 0.05
                            > > knots more speed?
                            > >
                            > > Orville & Wilbur determined that a 2x4 with rounded
                            > > edges proved to
                            > > have less drag than one carved to a teardrop at the
                            > > Reynolds numbers
                            > > they planned to fly at. Bu that was a 2x4. How
                            > > does the aspect ratio
                            > > of the daggerboard or rudder affect which foil to
                            > > use? Catboats
                            > > typically have a pretty wide rudders since they
                            > > operate in the
                            > > shallows. Racing sailboats will use a higher aspect
                            > > ratio as they
                            > > tend to operate in much deeper water (and want less
                            > > drag).
                            > >
                            > > I guess my question is... Is it worth it to the
                            > > average homebuilder to
                            > > try to duplicate an NACA foil or just approximate it
                            > > so that it "looks
                            > > about right"?
                            > >
                            > > Phil
                            > > St. Louis
                            > > [Uncle John's Skiff]
                            > >
                            > >
                            > >
                            >
                            >
                            >
                            >
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                          • rhaldridge
                            ... One ... The other way around, I believe. 0012 means the thickest part of the foil is 12 percent of the chord. Thomas has posted some terrific spreadsheets
                            Message 13 of 24 , Oct 7, 2007
                            • 0 Attachment
                              --- In Michalak@yahoogroups.com, "gbship" <gbship@...> wrote:
                              >
                              One
                              > thought, though, is if I interpreted your program right, a "lower"
                              > NACA number leads to a thicker foil, i.e. 0006 is thicker than 0012.

                              The other way around, I believe. 0012 means the thickest part of the
                              foil is 12 percent of the chord.

                              Thomas has posted some terrific spreadsheets for calculating foils
                              built up from ply laminations. I used them for calculating the foils
                              for my little cat. I used 0009 for my daggerboard, and 0012 for my
                              rudders.

                              Using the spreadsheet makes it fairly painless to design the foils,
                              and my foils are all rectangular in planform, which makes it a lot
                              simpler, because the sections are the same down to the tip. For
                              fairing the foils, I made up a sanding board for each profile out of
                              2X stock, and used contact cement to hold strips of sanding paper
                              tight to the profile.

                              Ray
                            • rhaldridge
                              ... leeboard taking more or less all the side force, so he sails with the rudder more or less straight in the water. Matt s boats, in general, don t have
                              Message 14 of 24 , Oct 7, 2007
                              • 0 Attachment
                                --- In Michalak@yahoogroups.com, Kevin O'Neill <K_S_ONeill@...> wrote:
                                >
                                >
                                >
                                >
                                >
                                >
                                > It might be that Matt's boat's have minimal weather helm, with the
                                leeboard taking more or less all the side force, so he sails with the
                                rudder more or less straight in the water.

                                Matt's boats, in general, don't have leeboards, though an exception is
                                the 8' dinghy he sailed in this year's EC. His other recent designs,
                                Paradox and Enigma, use chine runners for leeway resistance, but I
                                think the rudders carry a lot of the load, because they're pretty big.


                                If you have a lot of weather helm, like my proa, for example, you
                                need bigger rudders and need them to have good L/D ratios at higher
                                angles of attack.
                                >
                                >

                                I know almost nothing about proas, but wouldn't it make for faster
                                sailing if you reduced the weather helm?

                                Ray
                              • Kevin O'Neill
                                Hi I d forgotten about the chine runners on Paradox, I was thinking of his little dinghy. Where the CE is on a proa is a big problem. The CLR of the hull will
                                Message 15 of 24 , Oct 7, 2007
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                                  Hi

                                  I'd forgotten about the chine runners on Paradox, I was thinking of his little dinghy.

                                  Where the CE is on a proa is a big problem. The CLR of the hull will be way forward, about at 25% of the way back from the bow. So you can move the sail way forward, like in a traditional crab claw, that balances the boat but you have to move the whole rig to the other end of the boat when you shunt. Or you can pick a rig that's easy to shunt like a schooner or cat rig, but both of those have well aft CEs. So now you need big rudders to overcome the big imbalance between the aft CE and the well forward CLR. That's not all bad, deep foils make you go to windward better, but you have to build them and make them work, make the forward one kick up when you don't want it down or lock straight or something.

                                  My proa has had a series of rigs over the last few years; recently I had a big Gibbons rig on it, which had a CE well forward but was difficult to shunt in windy conditions. So I've built a schooner rig, which is easy and safe to shunt but which has a CE well aft. That is, it's aft if you look at the combined CE of both sails, but has the advantage of letting you sheet in the fore sail first. That lets you get going and get the rudders moving and biting in the water, then sheet in the aft sail.

                                  Faster? I don't know. Consider that in racing Hobie 16s, which just use asymmetry and the rudders to resist leeway, it's much faster to rake the mast aft and move the crew forward on the boat when going to windward. Raking the mast aft moves the CE aft, moving the crew forward moves the CLR forward. They put the boats out of balance on purpose! But it's faster that way, the rudders are higher aspect ratio than the hulls, so you load them up as much as possible. So it's not always faster to reduce weather helm.

                                  Kevin

                                  ----- Original Message ----
                                  From: rhaldridge <knobmaker@...>
                                  To: Michalak@yahoogroups.com
                                  Sent: Sunday, October 7, 2007 11:20:19 PM
                                  Subject: [Michalak] Re: foiled again













                                  --- In Michalak@yahoogroup s.com, Kevin O'Neill <K_S_ONeill@ ...> wrote:

                                  >

                                  >

                                  >

                                  >

                                  >

                                  >

                                  > It might be that Matt's boat's have minimal weather helm, with the

                                  leeboard taking more or less all the side force, so he sails with the

                                  rudder more or less straight in the water.



                                  Matt's boats, in general, don't have leeboards, though an exception is

                                  the 8' dinghy he sailed in this year's EC. His other recent designs,

                                  Paradox and Enigma, use chine runners for leeway resistance, but I

                                  think the rudders carry a lot of the load, because they're pretty big.



                                  If you have a lot of weather helm, like my proa, for example, you

                                  need bigger rudders and need them to have good L/D ratios at higher

                                  angles of attack.

                                  >

                                  >



                                  I know almost nothing about proas, but wouldn't it make for faster

                                  sailing if you reduced the weather helm?



                                  Ray














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                                  [Non-text portions of this message have been removed]
                                • rhaldridge
                                  ... just use asymmetry and the rudders to resist leeway, it s much faster to rake the mast aft and move the crew forward on the boat when going to windward.
                                  Message 16 of 24 , Oct 8, 2007
                                  • 0 Attachment
                                    --- In Michalak@yahoogroups.com, Kevin O'Neill <K_S_ONeill@...> wrote:
                                    >

                                    > Faster? I don't know. Consider that in racing Hobie 16s, which
                                    just use asymmetry and the rudders to resist leeway, it's much faster
                                    to rake the mast aft and move the crew forward on the boat when going
                                    to windward. Raking the mast aft moves the CE aft, moving the crew
                                    forward moves the CLR forward. They put the boats out of balance on
                                    purpose! But it's faster that way, the rudders are higher aspect
                                    ratio than the hulls, so you load them up as much as possible. So
                                    it's not always faster to reduce weather helm.
                                    >

                                    I think it's true that most boats go to windward better with a little
                                    weather helm, but where do you draw the line? At some point it has to
                                    be too much, I would think.


                                    Ray
                                  • Sword King
                                    Just a couple thoughts on steering style. If the helm is moved quickly while tacking, a flatter rudder (of the same area) will act more like a brake than one
                                    Message 17 of 24 , Oct 8, 2007
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                                      Just a couple thoughts on steering style. If the helm is moved
                                      quickly while tacking, a flatter rudder (of the same area) will act
                                      more like a brake than one of thicker section. Moved more slowly,
                                      the load will be shared more between the rudder and board. If one is
                                      prone to rapid movement, a thicker rudder section may help by
                                      decreasing drag while tacking, whereas if one tends to be slow and
                                      gentle with tiller movement, decreased drag while going straight may
                                      make up the difference.

                                      But, the added time and expense of making a nice smooth foil-shaped
                                      rudder and board might prevent one from getting out on the water, and
                                      the benefits are comparetively minimal, so for me, the whole
                                      discussion is theoretical (ie. not one bit practical).

                                      SK

                                      --- In Michalak@yahoogroups.com, Kenneth Grome <bagacayboatworks@...>
                                      wrote:
                                      >
                                      > > Why not make it a bit thicker and get better
                                      > > performance at the higher angles of attack
                                      > > typically experienced what tacking?
                                      >
                                      > Maybe because tacking consumes a very small percentage of the time
                                      the
                                      > boat is under sail and therefore it makes more sense to optimize
                                      for
                                      > the rest of the time ... ?
                                      >
                                      > Sincerely,
                                      > Ken Grome
                                      > Bagacay Boatworks
                                      > www.bagacayboatworks.com
                                      >
                                    • rhaldridge
                                      ... There s something to what you say, but I think it partly depends on the performance you expect from the boat. For a simple monohull without a lot of sail
                                      Message 18 of 24 , Oct 8, 2007
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                                        --- In Michalak@yahoogroups.com, "Sword King" <sword_king@...> wrote:
                                        >

                                        >
                                        > But, the added time and expense of making a nice smooth foil-shaped
                                        > rudder and board might prevent one from getting out on the water, and
                                        > the benefits are comparetively minimal, so for me, the whole
                                        > discussion is theoretical (ie. not one bit practical).
                                        >

                                        There's something to what you say, but I think it partly depends on
                                        the performance you expect from the boat. For a simple monohull
                                        without a lot of sail area, flat or minimally shaped foils may be fine.

                                        In the case of my little cat, while it's not going to be as fast as a
                                        beach cat, I expect it to be a good bit faster than most beachcruising
                                        monohulls, so I'm going with shaped foils. Additionally, cats are
                                        notoriously difficult to tack, so shaped foils that resist stalling at
                                        higher angles of attack will, I hope, be helpful.

                                        Also, I'm very concerned with windward performance, since I like to be
                                        able to sail where I want to go, rather than just reaching back and
                                        forth across the bay. According to my research, high aspect NACA
                                        daggerboard and rudders can improve tacking angles substantially. I
                                        have to admit I went through a lot of soul-searching-- my original
                                        plan was to try chine runners. I chickened out, and thought about
                                        minikeels, then a centerboard, but finally chose a daggerboard as the
                                        simplest and most efficient solution.

                                        I can't say I think shaped foils are much more expensive, but you're
                                        right that they're more time-consuming. Still, the hours spent
                                        shaping foils are a tiny fraction of the total time spent building the
                                        boat, and that time seems justified in my case.

                                        Ray
                                      • john h wright
                                        Ray, Why not chine runners for most cruising and a lee board for the occasional beat. Gentlemen don t! It (they) could be attached or just tied to
                                        Message 19 of 24 , Oct 9, 2007
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                                          Ray,
                                          Why not chine runners for most cruising "and" a lee board for the
                                          occasional beat. Gentlemen don't! It (they) could be attached or just
                                          tied to something at the top and tossed over on the lee side when needed.
                                          It could be stored in the cockpit but handy.

                                          I have thought about this but never done it.

                                          John in Bastrop
                                        • rhaldridge
                                          ... needed. ... It might work very well, John. I m a little disappointed in myself that I didn t have the nerve to try the chine runners on the little cat,
                                          Message 20 of 24 , Oct 9, 2007
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                                            --- In Michalak@yahoogroups.com, john h wright <jhargrovewright2@...>
                                            wrote:
                                            >
                                            > Ray,
                                            > Why not chine runners for most cruising "and" a lee board for the
                                            > occasional beat. Gentlemen don't! It (they) could be attached or just
                                            > tied to something at the top and tossed over on the lee side when
                                            needed.
                                            > It could be stored in the cockpit but handy.

                                            It might work very well, John. I'm a little disappointed in myself
                                            that I didn't have the nerve to try the chine runners on the little
                                            cat, but I spent last spring and summer sailing a boat that didn't go
                                            to windward very well, and it caused me to move windward performance
                                            up several notches on the priority chart.

                                            I live on a large bay with the pass to the ocean about 7 miles to
                                            windward in prevailing winds. I like to fish as much as I like to
                                            sail, and the most interesting fishing is out that pass. So, in the
                                            end, I'll have to be doing a lot of ungentlemanly sailing, I'm afraid.

                                            In my case, a leeboard would have been better from the interior room
                                            viewpoint, but I hope to see 8 - 10 knots in the cat, in the right
                                            conditions, and leeboards don't do as well at those speeds.

                                            Ray
                                          • john h wright
                                            Ray, Well thought out reasons. Everything is a compromise but one of the givens is how and where you intend to sail the boat. I live on a large bay with the
                                            Message 21 of 24 , Oct 9, 2007
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                                              Ray,

                                              Well thought out reasons.
                                              Everything is a compromise but one of the givens is how and where you
                                              intend to sail the boat.

                                              "I live on a large bay with the pass to the ocean about 7 miles to
                                              windward in prevailing winds. I like to fish as much as I like to
                                              sail, and the most interesting fishing is out that pass. So, in the
                                              end, I'll have to be doing a lot of ungentlemanly sailing, I'm afraid."

                                              John in Bastrop

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