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Re: Decreasing Sail Camber

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  • jleaworthy
    As I m about to give my sail hinged battens I am very interested in these discussions. I have a couple of questions which I d be grateful to have answered: 1.
    Message 1 of 9 , Nov 1, 2002
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      As I'm about to give my sail hinged battens I am very interested in
      these discussions. I have a couple of questions which I'd be grateful
      to have answered:

      1. When correspondents write about a camber being 6% do they mean
      that the depth of the belly of the curve is 6% of the length of the
      curve or do they mean that the hinge has a 6 degree angle?

      2. I am planning at the moment to put two hinges in each batten to
      give 30% 20% 50% divisions. Does this give problems?

      As a newly joined member of this group and living in the Isle of Skye
      in Scotland there are few sailors resident here and no junkies (well
      not the sort I mean). Forgive me if my questions go over old ground
      but I should be grateful for advice.

      John Leaworthy

      Newbridge Pioneer - Red Admiral


      --- In junkrig@y..., "Mike" <n6pfk@p...> wrote:
      > --- In junkrig@y..., "Victor Winterthun" <victor.winterthun@c...>
      wrote:
      > > Yes, but a litle less camber in the upper panels.
      > >
      > > Victor
      > >
      > > >
      > > > Do you have a hinge on every batten?
      > > >
      > > > Paul
      > >
      > > >
      >
      > I use seperate cambered panels on my West Weight Potter P-15. It
      has
      > 5 panels and the lower 3 are identical with the same camber in the
      > upper and lower edges. The upper panel is flat and the 2nd panel
      down
      > only has camber in the lower edge. I did this to reduce drive as
      the
      > sail was reefed.
      >
      > Mike Westfield
      > P-15 #2248
      > Water Toy
      > Union City, CA
    • Paul Stewart-Day
      ... grateful ... Skye ... (well ... Hi John, Your questions are very pertinent to me in particular, as I am planning to convert my boat from a flat junk sail
      Message 2 of 9 , Nov 1, 2002
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        --- In junkrig@y..., "jleaworthy" <jleaworthy@y...> wrote:
        > As I'm about to give my sail hinged battens I am very interested in
        > these discussions. I have a couple of questions which I'd be
        grateful
        > to have answered:
        >
        > 1. When correspondents write about a camber being 6% do they mean
        > that the depth of the belly of the curve is 6% of the length of the
        > curve or do they mean that the hinge has a 6 degree angle?
        >
        > 2. I am planning at the moment to put two hinges in each batten to
        > give 30% 20% 50% divisions. Does this give problems?
        >
        > As a newly joined member of this group and living in the Isle of
        Skye
        > in Scotland there are few sailors resident here and no junkies
        (well
        > not the sort I mean). Forgive me if my questions go over old ground
        > but I should be grateful for advice.
        >
        > John Leaworthy
        >
        > Newbridge Pioneer - Red Admiral
        >
        Hi John,

        Your questions are very pertinent to me in particular, as I am
        planning to convert my boat from a flat junk sail rig to one with
        some camber. I imagine that other members of this group may also be
        interested also.

        Firstly, when we talk about X% camber, we are referring to the
        distance of the outer limit of the "belly" in the sail expressed as a
        percentage of the length of the foot of the sail. Take for example
        one solution that I have been considering:

        The 2 hinges would be placed in the lower battens, at least, at 30%
        and 50% along their length working back from the luff. The first
        double ended cone would have tapers of 4% at each end, the second
        would have 3% tapers at each end. (These figures were suggested to me
        by Robin Blain of The Junk Rig Assn to achieve the recommended 6%
        camber.) I did some scale drawings and irrespecitive of the length of
        the batten the camber comes out at about 6%, when I used the
        following method to measure the depth of the "belly": extend the line
        of forward segement of the batten aft, and extend the line of aft
        segment of the batten forward, and use the point at which those 2
        lines intersect as the outer limit of the belly. I don't know if
        anyone else has used this method, but it seems to work.

        A day or two ago Victor posted on this topic and said that he has
        settled for using one hinge per batten, in order to avoid the problem
        of getting an "S" shape in battens with 2 joints when the sail is
        pressed up against the mast. This comment of his has really had me
        thinking as to why he encountered this "S" bend problem while others
        apparently havn't had the problem with 2 joints. I think I have the
        answer:

        If a junk sail overlaps the mast forward at less than 15% of its
        length, and there is a joint at 30% along the battens, the sail
        should not take up an "S". I suspect however, that if the overlap is
        at more than 15%, the forward part of the sail would hinge around the
        mast/fulcrum, when the sail is pressed up against it. I am quite sure
        that if the overlap is greater that 30%, that the "S" would occur.

        So my conclusion is that the amount of overlap of the sail forward of
        the mast will determine whether or not one or two hinges should be
        used to get camber.

        Any comments about or corrections to the above would be most
        appreciated.

        Paul Stewart-Day
      • Victor Winterthun
        Hi Paul. The problem with the S-bend was in the upper batten, which is tight connected to the yard in the front end. Maybe it would not happened if the
        Message 3 of 9 , Nov 1, 2002
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          Hi Paul.

          The problem with the S-bend was in the upper batten, which is tight connected to the yard in the front end. Maybe it would not happened if the vertical distance between yard and the upper batten had been big enough, so the upper battten could move more freely?.
          However. I will recommend only one hinge at 50% of the length of the battens.

          Victor

          ----- Original Message -----



          > A day or two ago Victor posted on this topic and said that he has
          > settled for using one hinge per batten, in order to avoid the problem
          > of getting an "S" shape in battens with 2 joints when the sail is
          > pressed up against the mast. This comment of his has really had me
          > thinking as to why he encountered this "S" bend problem while others
          > apparently havn't had the problem with 2 joints. I think I have the
          > answer:
          >
          > If a junk sail overlaps the mast forward at less than 15% of its
          > length, and there is a joint at 30% along the battens, the sail
          > should not take up an "S". I suspect however, that if the overlap is
          > at more than 15%, the forward part of the sail would hinge around the
          > mast/fulcrum, when the sail is pressed up against it. I am quite sure
          > that if the overlap is greater that 30%, that the "S" would occur.
          >
          > So my conclusion is that the amount of overlap of the sail forward of
          > the mast will determine whether or not one or two hinges should be
          > used to get camber.
          >
          > Any comments about or corrections to the above would be most
          > appreciated.
          >
          > Paul Stewart-Day
          >
          >
          > To unsubscribe from this group, send an email to:
          > junkrig-unsubscribe@egroups.com
          >
          >
          >
          > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
          >
          >
        • Paul Stewart-Day
          ... connected to the yard in the front end. Maybe it would not happened if the vertical distance between yard and the upper batten had been big enough, so the
          Message 4 of 9 , Nov 1, 2002
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            --- In junkrig@y..., "Victor Winterthun" <victor.winterthun@c...>
            wrote:
            > Hi Paul.
            >
            > The problem with the S-bend was in the upper batten, which is tight
            connected to the yard in the front end. Maybe it would not happened
            if the vertical distance between yard and the upper batten had been
            big enough, so the upper battten could move more freely?.
            > However. I will recommend only one hinge at 50% of the length of
            the battens.
            >
            > Victor

            Hi Victor,

            I intend to follow your advice and go with the one hinge at 50%
            solution. As I have explained in the concurrent "Overlap" thread, my
            sail is adjustable for between 25% and 40% overlap. So one hinge at
            50% of the batten length should hopefully enable me to run before the
            wind with a relatively large amount of overlap to help balance the
            helm, while still avoiding "S" bend. When I have made the changes to
            the rig and fully tested it, I will post my results. (That process
            will take me several weeks ......)

            Best regards, Paul
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