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Near Disaster! "Autopsy" Results

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  • geoflyfisher
    ... you ... I did some work with the ripped hammock over the weekend. There is a new theory on what caused the tear. It looks like the tear actually started
    Message 1 of 8 , Mar 31, 2003
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      --- In hammockcamping@yahoogroups.com, "Ed Speer" <info@s...> wrote:
      > Wow! Flyfisher--glad you were able to salvage your hike. Your quick
      > thinking saved the day (or the night).
      >
      > I'm most interested in what caused the ripped hammock, as I'm sure
      you
      > are.

      I did some work with the ripped hammock over the weekend. There is a
      new theory on what caused the tear.

      It looks like the tear actually started in a bartack at the end of
      the velcro. The bartack was perpendicular to the edge of the
      hammock. The tear, once started, pulled through the hem of the
      hammock material and then about 6 inches into the body of the hammock.

      The material was white ripstop. It was listed as 1.9 oz but
      examination now leads me to think it could well be 1.1 oz instead. I
      have not weighed it, but will do so.

      As you know, Ed, the edge of the hammock takes some extra tension
      entering and exiting. Along the edge of my hammock, I had sewn the
      velcro and it ended about 6 inches short of the knot. Because the
      velcro is relatively non elastic compared to the nylon body of the
      hammock, at the end of the velcro, there is a stress point. That was
      the reason I had put the bartack in to begin with... but it ended up
      being the weak point instead.

      Plans for next experiment are to continue the velcro all the way into
      the knot both for strength and better bug protection, and to attach
      the insulator/poncho with snaps instead of velcro.

      <><
    • Ed Speer
      Thanks for the update Flyfisher. I, too have had simialr trouble elsewhere w/ heavy bar tacks--It s easy to reach a point where the additional thread in the
      Message 2 of 8 , Apr 1, 2003
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        Message
        Thanks for the update Flyfisher.  I, too have had simialr trouble elsewhere w/ heavy bar tacks--It's easy to reach a point where the additional thread in the bar tack is not needed for strength, but the extra needle holes weaken the fabric by perforating it too much.  Kind of a catch22.  Best of luck with the remake...Ed
         
         
        -----Original Message-----
        From: geoflyfisher [mailto:geoflyfisher@...]
        Sent: Monday, March 31, 2003 8:28 AM
        To: hammockcamping@yahoogroups.com
        Subject: Hammock Camping Near Disaster! "Autopsy" Results

        --- In hammockcamping@yahoogroups.com, "Ed Speer" <info@s...> wrote:
        > Wow! Flyfisher--glad you were able to salvage your hike.  Your quick
        > thinking saved the day (or the night). 

        > I'm most interested in what caused the ripped hammock, as I'm sure
        you
        > are. 

        I did some work with the ripped hammock over the weekend.  There is a
        new theory on what caused the tear.

        It looks like the tear actually started in a bartack at the end of
        the velcro.  The bartack was perpendicular to the edge of the
        hammock.  The tear, once started, pulled through the hem of the
        hammock material and then about 6 inches into the body of the hammock.

        The material was white ripstop.  It was listed as 1.9 oz but
        examination now leads me to think it could well be 1.1 oz instead.  I
        have not weighed it, but will do so.

        As you know, Ed, the edge of the hammock takes some extra tension
        entering and exiting.  Along the edge of my hammock, I had sewn the
        velcro and it ended about 6 inches short of the knot.  Because the
        velcro is relatively non elastic compared to the nylon body of the
        hammock, at the end of the velcro, there is a stress point.  That was
        the reason I had put the bartack in to begin with...  but it ended up
        being the weak point instead. 

        Plans for next experiment are to continue the velcro all the way into
        the knot both for strength and better bug protection, and to attach
        the insulator/poncho with snaps instead of velcro. 

        <>< 



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      • rosaleen43@aol.com
        Hi, Everyone! There have been several posts trying to study a failure in a hammock, starting at the point of a bar tack. Just to add points to consider in
        Message 3 of 8 , Apr 2, 2003
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          Hi, Everyone!

          There have been several posts trying to study a failure in a hammock, starting at the point of a bar tack.

          Just to add points to consider in sewing.  In my experience, there seem to be materials that perform as if I'd just made perforations indicating where I want to be able to tear something off.  Notably, stitching on pieces of foam/mylar for a reflector.

          There are likely a lot of reasons for this.  Let me throw in one thought for some of you who have less sewing experience.  Manufacturers have come out with different needle points, targeting them to knits or wovens.  There are also some sold as "universal point."

          So, along with length and diameter, dullness and burrs, we may also need to concern ourselves with the actual type of needle point.  Before starting a large project, or one that needs to bear weight, sew a test strip and subject it to the forces you anticipate for you finished project.  I haven't sewn enough silnylon to know, yet, it does best with the sharper needles meant for wovens or the ball points meant for knits.  It may just behave differently from what we expect. 

          Cheers, and happy tinkering!

          Rosaleen

        • geoflyfisher
          Hi Rosaleen, Great points in your post (pun intended ;) ) The hammock material which failed was uncoated ripstop nylon. I was using a standard sewing machine
          Message 4 of 8 , Apr 2, 2003
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            Hi Rosaleen,

            Great points in your post (pun intended ;) )

            The hammock material which failed was uncoated ripstop nylon. I was
            using a standard sewing machine needle... not ball point, not
            cutting needle, just sharp... When I made the bar tack, I had just
            sewn dozens of feet of hook and also loop velcro, which tends to
            cause burrs on the needle occasionally.

            I believe that ripstop nylon would be less likely to be weakened by
            sewing than silnylon is. The silicone stablizes the fabric thread
            and may allow it to be cut by a needle when regular woven cloth
            threads would be allowed to be separated by the needle.

            For this reason, silnylon and tyvek may have some inherent weakness
            for the weight supporting part of hammock making which the woven
            ripstop does not.

            I pointed out what I did to allow others to avoid over sewing the
            velcro at such a vulnerable location. As Ed Speer noted, it is
            likely the many needle punctures of the material which caused
            weakness instead of strength.

            <><

            --- In hammockcamping@yahoogroups.com, rosaleen43@a... wrote:
            > Hi, Everyone!
            >
            > There have been several posts trying to study a failure in a
            hammock,
            > starting at the point of a bar tack.
            >
            > Just to add points to consider in sewing. In my experience, there
            seem to be
            > materials that perform as if I'd just made perforations indicating
            where I
            > want to be able to tear something off. Notably, stitching on
            pieces of
            > foam/mylar for a reflector.
            >
            > There are likely a lot of reasons for this. Let me throw in one
            thought for
            > some of you who have less sewing experience. Manufacturers have
            come out
            > with different needle points, targeting them to knits or wovens.
            There are
            > also some sold as "universal point."
            >
            > So, along with length and diameter, dullness and burrs, we may also
            need to
            > concern ourselves with the actual type of needle point. Before
            starting a
            > large project, or one that needs to bear weight, sew a test strip
            and subject
            > it to the forces you anticipate for you finished project. I
            haven't sewn
            > enough silnylon to know, yet, it does best with the sharper needles
            meant for
            > wovens or the ball points meant for knits. It may just behave
            differently
            > from what we expect.
            >
            > Cheers, and happy tinkering!
            >
            > Rosaleen
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