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Re: [Michalak] Digest Number 4048

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  • Simon Broad
    Nells Hi, I had one of those long conversations with with Todd Bradshaw on WB forum, he gave me some great help when designing the balance lug sail for my
    Message 1 of 16 , Apr 28, 2013
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      Nells
      Hi, I had one of those long conversations with with Todd Bradshaw on WB forum, he gave me some great help when designing the balance lug sail for my Summer Breeze.
      I don't know about stiffening the spars to match the sail, I suppose it would work, but the amount of bend in the spar I had went into the calculations for the draft of the sail and the amount of broadseeming required. Even a polytarp sail its worth doing right.

      Todd is outspoken, and quite passionate about, good sail design (not a fan of JMs 'darted' method of making sails) and he generally explains why he does things the way he does. His posts a usually worth reading.

      Simon



      [Non-text portions of this message have been removed]
    • prairiedog2332
      Simon, Exactly the impression I had when reading the thread I mentioned. Todd never attacked Polysail Dave in any way nor even mentioned him, but he did
      Message 2 of 16 , Apr 28, 2013
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        Simon,

        Exactly the impression I had when reading the thread I mentioned. Todd
        never attacked Polysail Dave in any way nor even mentioned him, but he
        did mention in passing a few improvements that could be made (by anyone)
        when making a sail from polytarp. One was in fact the darts Jim suggests
        and another was taking into consideration spar bend when calculating the
        shape of the sail. There were a couple others I won't even mention, as
        apparently it is a touchy subject:-)

        To summarize, the original query was from a fellow in the UK (I think)
        who had a small boat designed by Dudley Dix and a problem he had with
        how the sail was setting which was actually more a standing lug than
        balanced. It was Dacron and made by a professional sail maker. So Todd
        asked about the amount of bend in the spars which the fellow hadn't even
        considered. Another person posted saying there should be no bend at all
        in lug spars and off they both went as you can well imagine with Todd:-)
        Wasn't long before all heck broke loose, the original poster was
        apologizing for making the query in the 1st place and bystanders trying
        to cool things down and clearup the debris. Turned out the sail maker
        came out and looked at the sail and discovered he had made the luff too
        long!

        Now I make a query here about spar bend - mention Todd in passing - and
        once again all heck breaks loose!

        So Simon - any suggestions you could share in shaping polytarp sails and
        taking into consideration spar bending. Is there a prescribed method to
        calculate how the two should match? Did Todd mention to you the tape
        idea?

        Ducking and running for cover:-)

        Nels


        --- In Michalak@yahoogroups.com, Simon Broad wrote:
        >
        > Nells
        > Hi, I had one of those long conversations with with Todd Bradshaw on
        WB forum, he gave me some great help when designing the balance lug sail
        for my Summer Breeze.
        > I don't know about stiffening the spars to match the sail, I suppose
        it would work, but the amount of bend in the spar I had went into the
        calculations for the draft of the sail and the amount of broadseeming
        required. Even a polytarp sail its worth doing right.
        >
        > Todd is outspoken, and quite passionate about, good sail design (not a
        fan of JMs 'darted' method of making sails) and he generally explains
        why he does things the way he does. His posts a usually worth reading.
        >
        > Simon
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >



        [Non-text portions of this message have been removed]
      • simonfbroad
        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
        Message 3 of 16 , Apr 28, 2013
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          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.

          --- In Michalak@yahoogroups.com, "prairiedog2332" <nelsarv@...> wrote:
          >
          > Simon,
          >
          > Exactly the impression I had when reading the thread I mentioned. Todd
          > never attacked Polysail Dave in any way nor even mentioned him, but he
          > did mention in passing a few improvements that could be made (by anyone)
          > when making a sail from polytarp. One was in fact the darts Jim suggests
          > and another was taking into consideration spar bend when calculating the
          > shape of the sail. There were a couple others I won't even mention, as
          > apparently it is a touchy subject:-)
          >
          > To summarize, the original query was from a fellow in the UK (I think)
          > who had a small boat designed by Dudley Dix and a problem he had with
          > how the sail was setting which was actually more a standing lug than
          > balanced. It was Dacron and made by a professional sail maker. So Todd
          > asked about the amount of bend in the spars which the fellow hadn't even
          > considered. Another person posted saying there should be no bend at all
          > in lug spars and off they both went as you can well imagine with Todd:-)
          > Wasn't long before all heck broke loose, the original poster was
          > apologizing for making the query in the 1st place and bystanders trying
          > to cool things down and clearup the debris. Turned out the sail maker
          > came out and looked at the sail and discovered he had made the luff too
          > long!
          >
          > Now I make a query here about spar bend - mention Todd in passing - and
          > once again all heck breaks loose!
          >
          > So Simon - any suggestions you could share in shaping polytarp sails and
          > taking into consideration spar bending. Is there a prescribed method to
          > calculate how the two should match? Did Todd mention to you the tape
          > idea?
          >
          > Ducking and running for cover:-)
          >
          > Nels
          >
          >
          > --- In Michalak@yahoogroups.com, Simon Broad wrote:
          > >
          > > Nells
          > > Hi, I had one of those long conversations with with Todd Bradshaw on
          > WB forum, he gave me some great help when designing the balance lug sail
          > for my Summer Breeze.
          > > I don't know about stiffening the spars to match the sail, I suppose
          > it would work, but the amount of bend in the spar I had went into the
          > calculations for the draft of the sail and the amount of broadseeming
          > required. Even a polytarp sail its worth doing right.
          > >
          > > Todd is outspoken, and quite passionate about, good sail design (not a
          > fan of JMs 'darted' method of making sails) and he generally explains
          > why he does things the way he does. His posts a usually worth reading.
          > >
          > > Simon
          > >
          > >
          > >
          > > [Non-text portions of this message have been removed]
          > >
          >
          >
          >
          > [Non-text portions of this message have been removed]
          >
        • simonfbroad
          http://forum.woodenboat.com/showthread.php?129268-Does-It-Matter-What-Shape-a-Sail-Is&highlight=does+it+matter+what+shape+a+sail+is Nels One more thing sail
          Message 4 of 16 , Apr 29, 2013
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            http://forum.woodenboat.com/showthread.php?129268-Does-It-Matter-What-Shape-a-Sail-Is&highlight=does+it+matter+what+shape+a+sail+is

            Nels

            One more thing sail makers have to take into consideration, just came across it re-reading that thread. The direction of the weave and the varying strength it has in different directions.

            Simon.
          • prairiedog2332
            Whoa! That link got my head spinning! ... http://forum.woodenboat.com/showthread.php?129268-Does-It-Matter-What-Sh
            Message 5 of 16 , Apr 29, 2013
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              Whoa! That link got my head spinning!

              --- In Michalak@yahoogroups.com, "simonfbroad" wrote:
              >
              >
              http://forum.woodenboat.com/showthread.php?129268-Does-It-Matter-What-Sh\
              ape-a-Sail-Is&highlight=does+it+matter+what+shape+a+sail+is
              >
              > Nels
              >
              > One more thing sail makers have to take into consideration, just came
              across it re-reading that thread. The direction of the weave and the
              varying strength it has in different directions.
              >
              > Simon.

              That last was one thing I left out deliberately earlier as not sure it
              applied to poly tarp? The other was his comments regarding duct tape:-)

              BTW, Bolger - who originally designed what became known as "Summer
              Breeze" had some 2nd thoughts about it - and had this to say:
              ..." better still, Build "Surf" instead, everybody likes those."

              http://www.instantboats.com/surf.htm
              <http://www.instantboats.com/surf.htm>

              Just supposition on my part but it seems to me Todd has softened his
              stance on polytarp as a material. First in regards to the high retail
              cost of Dacron sail cloth and secondly the improvements in poly tarp
              quality and better tapes that may not need any sewing at all. He felt
              poly might not be strong enough to take stitching very well, and lug
              sails require a lot of cloth compared to triangular sails. If
              reinforcing the corners and sewing them then use Dacron patches that
              hold stitching better. Hybrid sails?

              And if wanting to make your own sail from Dacron he very highly
              recommends Sailrite kits.This is the popular sail as also used on Surf
              and several "Instant boats" for example:

              http://www.sailrite.com/Bolger-nymph-main-Kit-white_3
              <http://www.sailrite.com/Bolger-nymph-main-Kit-white_3>

              And he felt darts were a step backwards from broadseaming which Jim
              originally used. The only book I ever owned on sail making was this one
              -which Sailrite still carries - even though supposedly long out of
              print. And now also have Nichol's on setting up traditional sails.

              http://www.sailrite.com/The-Mainsail-Manual-Book
              <http://www.sailrite.com/The-Mainsail-Manual-Book>


              http://www.duckworksbbs.com/media/books/tradsails/index.htm
              <http://www.duckworksbbs.com/media/books/tradsails/index.htm>


              Anybody have their preferences? As well as best tapes to use?

              Nels


              >



              [Non-text portions of this message have been removed]
            • prairiedog2332
              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
              Message 6 of 16 , Apr 29, 2013
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                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]
              • 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 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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