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Re: Digest Number 4048 (Spar Stiffness.)

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  • tsgosnell
    I agree with Nels, my latest sail was made in a bit of a hurry and the layout was done by myself. I was worried the the rounds were a bit off and I think I had
    Message 1 of 16 , Apr 29, 2013
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      I agree with Nels, my latest sail was made in a bit of a hurry and the layout was done by myself. I was worried the the rounds were a bit off and I think I had too much and or too little, just dint look as fair as it should. But time being an issue I pressed on, thinking I would only be out a small amount if I had to redo the poly sail. I also thought my new spars were too flexible, but to my surprise it sails just as well if not better than the set I took 2 weeks to complete. Go figure? Better yet, just go sail!
      Scott

      --- In Michalak@yahoogroups.com, "prairiedog2332" <nelsarv@...> wrote:
      >
      > Simon,
      > I don't think there is any need to go into it too deeply. Same with how
      > much "round" and "hollow" in the sail, and how much luff tension is
      > required in a lug sail. Same with yard height and mast canting. A
      > little bit goes a long way and can be beneficial. But not a substitution
      > to just getting out and sailing!
      > Some flex is useful in the yard to spill wind in gusts but the yard
      > should never be allowed to flex ahead of the mast when broad reaching
      > for example. Some flex in the boom makes up for a sail without enough
      > rounding on the foot. Some cant in the mast can help keep the boom up
      > above the water when sailing off the wind. The luff should be dead
      > straight as should be the trailing edge on the leeboard. These are
      > things that stuck in my mind.
      >
      > Nels
      >
      >
      > --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
      > >
      > > ah Nels, I love posts the get lots of people involved, especially when
      > there are so many experts, all with a different opinion :o)
      > >
      > > Todd didn't mention the tape method that I recall.
      > >
      > > He did say that a lot of the measurements were based on experience and
      > judgement rather than pure maths (to me that makes it an art form rather
      > than a science - bet that gets some responses), not only the amount of
      > bend in the spar needs to be taken into account, but where in the spar
      > the 'centre' of the bend is, it might not be in the centre of the spar,
      > and does it bend more at one end than the other, etc.
      > >
      > > I will try and find the thread on WB again and extract the advice on
      > allowing for spar bend. Funnily enough, I got a great deal of help and
      > learned a lot, but the original question I posted was never answered.
      > >
      > > Simon.
      >
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >
    • PolySail_Dave
      Scott, Your experience with polytarp sails is not all that unusual. I mentioned in an earlier post that polytarp sails are probably more forgiving than sails
      Message 2 of 16 , Apr 30, 2013
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        Scott,

        Your experience with polytarp sails is not all that unusual. I mentioned
        in an earlier post that polytarp sails are probably more "forgiving"
        than sails made with other polymer laminates or woven materials. The
        reason, as I see it, is their stretch and resiliency--the ability to
        fully recover from any stretching caused by pressures up to an amazing
        amount of lb. per sq. ft. (In one very simple demo, I hauled my 190 lbs.
        up into a small Bermuda sail suspended off the ground by ropes at each
        corner. Afterwards, the sail was not visibly stretched in any way and
        their were no failures even around the brass grommets.) It is also the
        way that polytarp stretches that makes it best used as a single panel
        rather than being divided into panels as with other "stiff" sail
        materials which are normally paneled by sailmakers perhaps because most
        woven sail materials normally can't be purchased in large widths like
        tarps and other laminates. With polytarp, if you want to control stretch
        more, you go up in weight from 3.1 oz. to 4.5 oz. to 5.2 oz. to 6.0 oz.
        to 8.0 oz. etc. I posted a file from one of the largest Chinese
        manufacturing companies of polytarp that is interestingly, owned by a
        woman and "green." It explains the nature of the material in both
        simple and chemical terms and I've added a few notes from my own
        research over the years about the strength and stretch of this unique
        material. I listed the file under "Polytarp Manufacturing" in the Files
        section if anyone is interested in the details of its manufacturing
        process. I found it interesting that the scrim was described as nylon in
        this piece which might account for the stretch or it might have been an
        interpreter's error. I think the scrim is actually polyethylene strips
        woven together.

        Dave Gray


        --- In Michalak@yahoogroups.com, "tsgosnell" wrote:
        >
        > I agree with Nels, my latest sail was made in a bit of a hurry and the
        layout was done by myself. I was worried the the rounds were a bit off
        and I think I had too much and or too little, just dint look as fair as
        it should. But time being an issue I pressed on, thinking I would only
        be out a small amount if I had to redo the poly sail. I also thought my
        new spars were too flexible, but to my surprise it sails just as well if
        not better than the set I took 2 weeks to complete. Go figure? Better
        yet, just go sail!
        > Scott
        >
        > --- In Michalak@yahoogroups.com, "prairiedog2332" nelsarv@ wrote:
        > >
        > > Simon,
        > > I don't think there is any need to go into it too deeply. Same with
        how
        > > much "round" and "hollow" in the sail, and how much luff tension is
        > > required in a lug sail. Same with yard height and mast canting. A
        > > little bit goes a long way and can be beneficial. But not a
        substitution
        > > to just getting out and sailing!
        > > Some flex is useful in the yard to spill wind in gusts but the yard
        > > should never be allowed to flex ahead of the mast when broad
        reaching
        > > for example. Some flex in the boom makes up for a sail without
        enough
        > > rounding on the foot. Some cant in the mast can help keep the boom
        up
        > > above the water when sailing off the wind. The luff should be dead
        > > straight as should be the trailing edge on the leeboard. These are
        > > things that stuck in my mind.
        > >
        > > Nels
        > >
        > >
        > > --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
        > > >
        > > > ah Nels, I love posts the get lots of people involved, especially
        when
        > > there are so many experts, all with a different opinion :o)
        > > >
        > > > Todd didn't mention the tape method that I recall.
        > > >
        > > > He did say that a lot of the measurements were based on experience
        and
        > > judgement rather than pure maths (to me that makes it an art form
        rather
        > > than a science - bet that gets some responses), not only the amount
        of
        > > bend in the spar needs to be taken into account, but where in the
        spar
        > > the 'centre' of the bend is, it might not be in the centre of the
        spar,
        > > and does it bend more at one end than the other, etc.
        > > >
        > > > I will try and find the thread on WB again and extract the advice
        on
        > > allowing for spar bend. Funnily enough, I got a great deal of help
        and
        > > learned a lot, but the original question I posted was never
        answered.
        > > >
        > > > Simon.
        > >
        > >
        > >
        > >
        > > [Non-text portions of this message have been removed]
        > >
        >
      • simonfbroad
        Nels Found a couple of photos of the finished product. http://woodenboatblog.com/blog/2463 Doesn t have quite the polished professional look of one of Poly
        Message 3 of 16 , Apr 30, 2013
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          Nels

          Found a couple of photos of the finished product. http://woodenboatblog.com/blog/2463


          Doesn't have quite the polished professional look of one of Poly Dave's fine productions, but it was a hell of a lot of fun to make it from scratch, and I learned a lot about sails doing it.

          Although only 69 square feet, I'm thinking to put it on my Mayfly 16 (when I get to build it) so that it is underpowered and I can learn to use her gently, and without messing about reefing. Does that sound feasible?

          Simon.
        • prairiedog2332
          Sounds like a great plan to me for reasons you give. It might even do better than the designed sail when reefed. Traditional sharpies apparently often carried
          Message 4 of 16 , Apr 30, 2013
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            Sounds like a great plan to me for reasons you give. It might even do
            better than the designed sail when reefed. Traditional sharpies
            apparently often carried a 2nd smaller sail and you can use it while
            making a larger one to original specs.

            Nels


            --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
            >
            > Nels
            >
            > Found a couple of photos of the finished product.
            http://woodenboatblog.com/blog/2463
            >
            >
            > Doesn't have quite the polished professional look of one of Poly
            Dave's fine productions, but it was a hell of a lot of fun to make it
            from scratch, and I learned a lot about sails doing it.
            >
            > Although only 69 square feet, I'm thinking to put it on my Mayfly 16
            (when I get to build it) so that it is underpowered and I can learn to
            use her gently, and without messing about reefing. Does that sound
            feasible?
            >
            > Simon.
            >



            [Non-text portions of this message have been removed]
          • PolySail_Dave
            Simon, I just sent out a sail to Gene Berry who is also converting his Mayfly to a 60 sq. ft. leg o mutton (Bolger s name for this sharpie sail.) Just for
            Message 5 of 16 , May 1, 2013
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              Simon,

              I just sent out a sail to Gene Berry who is also converting his Mayfly
              to a 60 sq. ft. leg o' mutton (Bolger's name for this sharpie sail.)
              Just for your information, the CE of that sail normally falls at about
              35"-36" back of the luff and about 47"-48" up perpendicular from the
              foot. However, it's always best to check the CE directly on the sail
              using Jim's method. I do it with three 1" wide straight tape measures
              from the corners to the midpoints of the opposite sides. You might have
              to adjust the mast or leeboard position for best handling if you go
              forward with this conversion. Gene assured me that he could simply
              adjust the rake of his mast to bring the CE into the right position.
              Maybe you can do the same. You want the CE about 2"-3" aft of the
              centerline of the board for slight weather helm and best handling.

              Dave


              --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
              >
              > Nels
              >
              > Found a couple of photos of the finished product.
              http://woodenboatblog.com/blog/2463
              >
              >
              > Doesn't have quite the polished professional look of one of Poly
              Dave's fine productions, but it was a hell of a lot of fun to make it
              from scratch, and I learned a lot about sails doing it.
              >
              > Although only 69 square feet, I'm thinking to put it on my Mayfly 16
              (when I get to build it) so that it is underpowered and I can learn to
              use her gently, and without messing about reefing. Does that sound
              feasible?
              >
              > Simon.
              >
            • PolySail_Dave
              Oops! Correction needed, Simon. I misread the area of your sail as 60 sq. ft. rather than 69 sq. ft. I know the Bolger sail well, but I don t know the
              Message 6 of 16 , May 1, 2013
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                Oops! Correction needed, Simon. I misread the area of your sail as 60
                sq. ft. rather than 69 sq. ft. I know the Bolger sail well, but I don't
                know the dimensions of your sail. The position of the CE on your sail
                will need to be calculated. The CE is probably a little further back and
                a little higher than the figures I gave you for the smaller sail.
                However, the CE calculation is easily done using the method I mentioned,
                and it's always a good idea before doing a conversion.

                Dave


                --- In Michalak@yahoogroups.com, "PolySail_Dave" wrote:
                >
                >
                > Simon,
                >
                > I just sent out a sail to Gene Berry who is also converting his Mayfly
                > to a 60 sq. ft. leg o' mutton (Bolger's name for this sharpie sail.)
                > Just for your information, the CE of that sail normally falls at about
                > 35"-36" back of the luff and about 47"-48" up perpendicular from the
                > foot. However, it's always best to check the CE directly on the sail
                > using Jim's method. I do it with three 1" wide straight tape measures
                > from the corners to the midpoints of the opposite sides. You might
                have
                > to adjust the mast or leeboard position for best handling if you go
                > forward with this conversion. Gene assured me that he could simply
                > adjust the rake of his mast to bring the CE into the right position.
                > Maybe you can do the same. You want the CE about 2"-3" aft of the
                > centerline of the board for slight weather helm and best handling.
                >
                > Dave
                >
                >
                > --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
                > >
                > > Nels
                > >
                > > Found a couple of photos of the finished product.
                > http://woodenboatblog.com/blog/2463
                > >
                > >
                > > Doesn't have quite the polished professional look of one of Poly
                > Dave's fine productions, but it was a hell of a lot of fun to make it
                > from scratch, and I learned a lot about sails doing it.
                > >
                > > Although only 69 square feet, I'm thinking to put it on my Mayfly 16
                > (when I get to build it) so that it is underpowered and I can learn to
                > use her gently, and without messing about reefing. Does that sound
                > feasible?
                > >
                > > Simon.
                > >
                >
              • prairiedog2332
                I think the sail referred to is also a lug sail? The one in this photo. http://woodenboatblog.com/node/594 To me it looks
                Message 7 of 16 , May 1, 2013
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                  I think the sail referred to is also a lug sail? The one in this photo.

                  http://woodenboatblog.com/node/594 <http://woodenboatblog.com/node/594>

                  To me it looks like the mast is too far forward but then the centerboard
                  is further forward than on the original plans as well? I think you could
                  get a good idea of the CE just drawing the lines on a copy of the photo?

                  Nels

                  --- In Michalak@yahoogroups.com, "PolySail_Dave" wrote:
                  >
                  >
                  > Oops! Correction needed, Simon. I misread the area of your sail as
                  60
                  > sq. ft. rather than 69 sq. ft. I know the Bolger sail well, but I
                  don't
                  > know the dimensions of your sail. The position of the CE on your sail
                  > will need to be calculated. The CE is probably a little further back
                  and
                  > a little higher than the figures I gave you for the smaller sail.
                  > However, the CE calculation is easily done using the method I
                  mentioned,
                  > and it's always a good idea before doing a conversion.
                  >
                  > Dave
                  >




                  [Non-text portions of this message have been removed]
                • simonfbroad
                  Nels Yes, the mast is a long way forward, and that is because of the centreboard. The original plans had a leeboard and the mast behind the forward bulkhead.
                  Message 8 of 16 , May 1, 2013
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                    Nels

                    Yes, the mast is a long way forward, and that is because of the centreboard. The original plans had a leeboard and the mast behind the forward bulkhead.
                    There is a diagram on the WB thread that gives the actual size of the sail and shows the CE lining up with the trailing edge of the centreboard.

                    Mathematically that all worked out.

                    When I sailed it first time the centreboard jammed, I jibed it too sharply without moving my bulk to the other side of the boat, and the mast step (the only part I didn't use thickened epoxy to glue) gave way.
                    The boat is now at home being re-modeled (back to David Beede's original design).

                    Simon.

                    --- In Michalak@yahoogroups.com, "prairiedog2332" <nelsarv@...> wrote:
                    >
                    > I think the sail referred to is also a lug sail? The one in this photo.
                    >
                    > http://woodenboatblog.com/node/594 <http://woodenboatblog.com/node/594>
                    >
                    > To me it looks like the mast is too far forward but then the centerboard
                    > is further forward than on the original plans as well? I think you could
                    > get a good idea of the CE just drawing the lines on a copy of the photo?
                    >
                    > Nels
                    >
                  • simonfbroad
                    Dave Thanks for the input. I used Jim s method to determine where the CE should be before starting the sail. I had changed David Beede s original layout so
                    Message 9 of 16 , May 1, 2013
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                      Dave

                      Thanks for the input.
                      I used Jim's method to determine where the CE should be before starting the sail. I had changed David Beede's original layout so determining the geometry or mast, sail, foil had to be done from scratch. There is a diagram I made on the WB thread mentioned earlier.

                      I hadn't thought about taking a tape measure to the actual sail itself and verifying it's CE. I'll do that before I start the Mayfly. First of all I need to remodel the SB back to David's original layout - my changes were unwise (and contrary to David's advice) but it's been a highly educational project and I feel much better equipped to take on the next one.

                      Simon.

                      --- In Michalak@yahoogroups.com, "PolySail_Dave" <polysail@...> wrote:
                      >
                      >
                      > Oops! Correction needed, Simon. I misread the area of your sail as 60
                      > sq. ft. rather than 69 sq. ft. I know the Bolger sail well, but I don't
                      > know the dimensions of your sail. The position of the CE on your sail
                      > will need to be calculated. The CE is probably a little further back and
                      > a little higher than the figures I gave you for the smaller sail.
                      > However, the CE calculation is easily done using the method I mentioned,
                      > and it's always a good idea before doing a conversion.
                      >
                      > Dave
                      >
                      >
                      > --- In Michalak@yahoogroups.com, "PolySail_Dave" wrote:
                      > >
                      > >
                      > > Simon,
                      > >
                      > > I just sent out a sail to Gene Berry who is also converting his Mayfly
                      > > to a 60 sq. ft. leg o' mutton (Bolger's name for this sharpie sail.)
                      > > Just for your information, the CE of that sail normally falls at about
                      > > 35"-36" back of the luff and about 47"-48" up perpendicular from the
                      > > foot. However, it's always best to check the CE directly on the sail
                      > > using Jim's method. I do it with three 1" wide straight tape measures
                      > > from the corners to the midpoints of the opposite sides. You might
                      > have
                      > > to adjust the mast or leeboard position for best handling if you go
                      > > forward with this conversion. Gene assured me that he could simply
                      > > adjust the rake of his mast to bring the CE into the right position.
                      > > Maybe you can do the same. You want the CE about 2"-3" aft of the
                      > > centerline of the board for slight weather helm and best handling.
                      > >
                      > > Dave
                      > >
                      > >
                      > > --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
                      > > >
                      > > > Nels
                      > > >
                      > > > Found a couple of photos of the finished product.
                      > > http://woodenboatblog.com/blog/2463
                      > > >
                      > > >
                      > > > Doesn't have quite the polished professional look of one of Poly
                      > > Dave's fine productions, but it was a hell of a lot of fun to make it
                      > > from scratch, and I learned a lot about sails doing it.
                      > > >
                      > > > Although only 69 square feet, I'm thinking to put it on my Mayfly 16
                      > > (when I get to build it) so that it is underpowered and I can learn to
                      > > use her gently, and without messing about reefing. Does that sound
                      > > feasible?
                      > > >
                      > > > Simon.
                      > > >
                      > >
                      >
                    • PolySail_Dave
                      Wow, I got all fouled up on my photos, boats and sails on this thread. Seeing the correct boat and sail clarified the situation for me. Simon did a good job in
                      Message 10 of 16 , May 3, 2013
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                        Wow, I got all fouled up on my photos, boats and sails on this thread.
                        Seeing the correct boat and sail clarified the situation for me. Simon
                        did a good job in paneling and sewing his sail, and I'm sure that this
                        lug sail will fill well, but I would caution him about the use of the
                        lightweight blue tarp material. Often that material has only a 6 x 8
                        scrim and weighs less than 2.7 oz./sq. yd. Of all the polytarp material,
                        this is the tarp that will stretch out of shape and disintegrate the
                        fastest because it often carries no UV protection whatsoever.

                        For future builds, especially if you choose to use a single panel
                        method, I would recommend that you find a polytarp that weighs at least
                        5.2 oz./sq. yd., has a 12 x 12 scrim, and offers UV protection. I
                        sometimes use a UV-protected 3.1 oz. with a closely woven 10 x 10 scrim
                        for racing sails, but I generally warn the customer about their tendency
                        to stretch. I made a good-sized lug for Brad Hickman for the 2011
                        PDRacer Worlds (which he won) but he managed to stretch the sail by
                        applying a 6:1 purchase on the downhaul while trying to keep high
                        tension on the luff. Now I recommend no more than a 2:1 purchase for
                        these lightweight lugs and no more than 4:1 for the 5.2 or 6.0 oz.
                        polytarp lugs.

                        One additional note about polytarp weights. Polytarp weights are for a
                        full 36" x 36" square yard of material and cannot be directly compared
                        to the weights of most materials used by traditional sailmakers.
                        Traditional sailmaking materials are usually measured and weighed by the
                        "sailmaker's yard" which measures 28.5" x 36." So we are talking about
                        the weight of a piece of material that is only 79% as large as a sq. yd.
                        of polytarp. Thus a 5. 2 oz./sq. yd. piece of polytarp equates to about
                        a 4.1 oz. piece of Dacron or other sail material for comparison
                        purposes. I think some sailmakers think polytarp sails must be
                        excessively heavy to come close to matching the strength of Dacron and
                        other sail materials, but that is really not the case. Even the 2.7 oz
                        material that Simon apparently used should be as strong or stronger than
                        1.5 oz. spinnaker ripstop nylon.

                        Dave Gray

                        I hope this information helps for anyone planning to build as sail from
                        polytarp in the future.

                        --- In Michalak@yahoogroups.com, "prairiedog2332" wrote:
                        >
                        > I think the sail referred to is also a lug sail? The one in this
                        photo.
                        >
                        > http://woodenboatblog.com/node/594
                        >
                        > To me it looks like the mast is too far forward but then the
                        centerboard
                        > is further forward than on the original plans as well? I think you
                        could
                        > get a good idea of the CE just drawing the lines on a copy of the
                        photo?
                        >
                        > Nels
                        >
                        > --- In Michalak@yahoogroups.com, "PolySail_Dave" wrote:
                        > >
                        > >
                        > > Oops! Correction needed, Simon. I misread the area of your sail as
                        > 60
                        > > sq. ft. rather than 69 sq. ft. I know the Bolger sail well, but I
                        > don't
                        > > know the dimensions of your sail. The position of the CE on your
                        sail
                        > > will need to be calculated. The CE is probably a little further back
                        > and
                        > > a little higher than the figures I gave you for the smaller sail.
                        > > However, the CE calculation is easily done using the method I
                        > mentioned,
                        > > and it's always a good idea before doing a conversion.
                        > >
                        > > Dave
                        > >
                        >
                        >
                        >
                        >
                        > [Non-text portions of this message have been removed]
                        >
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