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Re: Traditional Polytarp Sail

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  • 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 1 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 2 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 3 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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