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Thread: tarp pull outs

  1. #21
    Senior Member Redtail's Avatar
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    Quote Originally Posted by warbonnetguy View Post
    either way you do it, the sil inside the patch is circumvented. any force gets transmitted from the pull tab itself directly to the stitch holes around the patch, if you add another layer, 100% of the force still gets transmitted directly to the same patch stitches.
    This doesn't make sense to me unless you are presupposing that the thread will be the only possible failure point and not the fabric.

    If not and you are including fabric failure (thread does not break) then that is like saying it is just as easy to rip a stitch through one layer of fabric as it is two. It is not.

  2. #22
    slowhike's Avatar
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    warbonnet & teedee, i'd have to disagree w/ you if i'm understanding you correctly.
    having the second patch on the back side is bound to distribute the force in a significant way.
    sort of like running a thread through the fabric, forming a loop around a stick, then going back through the fabric.
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  3. #23
    2 layers will not distribute the force any differently than 1 layer. in both scenarios, 100% of the force is distributed to the stitches around the perimeter of the patch, the patch will not tear here, the thread will not break, but the perforated sil is what will fail, all the second layer would do, would be to cover the needle holes so that you couldn't see them getting reamed out by the stitches when under load.

    pull back the edge of the patch while its under load, you will see the thread stretching the needle holes in the sil, this is where failure will occur, everything on the other side of this line of stitches (which is the patch and the sil underneath)is irrelavent as long as the patch is plenty strong. only by distributing (X) amount of force to a larger area/more stitches will you lessen the amount of force on each needle hole, and increase the strength of the pull out.

    even with just the single layer patch, the sil inside the circle will not be loaded, and adding another layer, you are only reinforcing the first one, which is plenty strong by itself, the patch can only reinforce the fabric inside the circle, and if one layer takes all the load off of the sil inside the circle, there is no load left to be taken off by the second layer.

    look at it like this: follow the load from the stake. the load goes up the line to the pull tab, from the pull tab to the patch, from the patch to the thread, then to the needle holes in the tarp, this is the weak link, going backwards and beefing up stuff behind the weak link will not strengthen the stitch holes in the sil. everything up to the stitch holes is plenty strong, making them stronger will not increase the strength of the weak link in the chain.

    all a patch can do is transfer the load, usually from a small amount of stitches to a larger amount of stitches, a single layer distributes 100% of the load, adding another layer does not distribute any more load, in either case, the same amount of load is divided among the needle holes in the sil, and enough force can tear the perforated sil, nothing can make the sil stronger, all you can do is distribute the force over more sil by using a bigger patch.

    hope this clears it up a bit, maybe teedee can explain it better.


    Quote Originally Posted by slowhike View Post
    warbonnet & teedee, i'd have to disagree w/ you if i'm understanding you correctly.
    having the second patch on the back side is bound to distribute the force in a significant way.
    sort of like running a thread through the fabric, forming a loop around a stick, then going back through the fabric.

  4. #24
    slowhike's Avatar
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    sorry warbonnet my man, i'm still not convinced. with the 2nd inside patch, the thread stitching the patches together, with the silnylon sandwiched in between, are going to be pulled toward the outside, there fore pulling against the inside patch which is last in the line of pull.
    http://www.hammockforums.net/gallery...5/P7140098.JPG

    besides, in my use w/ these pull outs for over two years now, i have rarely seen them take nearly as much force as the corner tie-outs.
    i often tie them to near by branches. that allows a lot of flexibility too. ...tim
    don`t leave the CREATOR out of the creation!

  5. #25
    yeah, the fact that their round helps alot, distributes the force much more evenly than square/rectangular ones would


    Quote Originally Posted by slowhike View Post
    sorry warbonnet my man, i'm still not convinced. with the 2nd inside patch, the thread stitching the patches together, with the silnylon sandwiched in between, are going to be pulled toward the outside, there fore pulling against the inside patch which is last in the line of pull.
    http://www.hammockforums.net/gallery...5/P7140098.JPG

    besides, in my use w/ these pull outs for over two years now, i have rarely seen them take nearly as much force as the corner tie-outs.
    i often tie them to near by branches. that allows a lot of flexibility too. ...tim

  6. #26
    slowhike's Avatar
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    Quote Originally Posted by warbonnetguy View Post
    yeah, the fact that their round helps alot, distributes the force much more evenly than square/rectangular ones would
    yeah, i'm pretty sure the round patch distributes the force better, but my main point in the drawing is that each thread that penetrates the layers of material, then loops back through, is resting on (& pulling on) a heavier, stiffer, layer of material w/ the inside re-enforcement patch, rather than pulling directly on the silnylon tarp.
    don`t leave the CREATOR out of the creation!

  7. #27
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    Late to the conversation, and only thinking about it and not trying it, but... It would seem that the heavier reinforcement placed on the bottom would be better than on the top. If the thread looping under the fabric is what takes the stress, and the stress is transferred to the fabric it rests on, then the best place for reinforcing would be underneath? At that point the silnylon is just kinda floating on top of the reinforcement and not stressed (again, assuming that the tie strap is also sewn through to the underside reinforcement...)

    The comment about grip clips sliding on silnylon has me thinking about putting a piece of non-slick material on the underside when I attach it to the tarp. Now, just gotta get me a silnylon tarp.
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  8. #28
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    Quote Originally Posted by Shadowmoss View Post
    Late to the conversation, and only thinking about it and not trying it, but... It would seem that the heavier reinforcement placed on the bottom would be better than on the top. If the thread looping under the fabric is what takes the stress, and the stress is transferred to the fabric it rests on, then the best place for reinforcing would be underneath? At that point the silnylon is just kinda floating on top of the reinforcement and not stressed (again, assuming that the tie strap is also sewn through to the underside reinforcement...)

    The comment about grip clips sliding on silnylon has me thinking about putting a piece of non-slick material on the underside when I attach it to the tarp. Now, just gotta get me a silnylon tarp.
    that's a good point. the main problem i see w/ that is that you would have to attach the grosgrain loop that the guy line ties to in a different way.
    you may come up w/ a different way to do it that would be just as good or better, but the way i had been doing it was to sew the grosgrain to the outer re-enforcement patch 1st, then sew the patch w/ loop to the tarp.

    i'm still sold on the extra seam on each side to attach the pullouts to. seams are extremely strong & the loss of coverage in the fold & weight gain in thread & seam sealer would be worth while i'm thinking.

    shaddowmoss, i would get a couple of the grip clips & play around w/ them on the side wall of a tarp to see how you like them before going to far w/ that project.
    don`t leave the CREATOR out of the creation!

  9. #29
    i see what you are saying, but that is not the way the tarp would fail, the stitches don't rip through the material really. failure occurs on the other side of the stitches, where there is no patch, the perforated sil tears right at the edge of the stitches, right where they and the patch begin. There is no way to reinforce this.

    the patch only has an effect on the sil that is on the other side of the stitches, it can only reinforce this inner circle of sil, nothing outside the circle, and a single layer protects it fully, it will not tear, to the point that the next weak link in the chain becomes the weakest link, which is the area of sil immediatly outside the stitches, which is what will fail. the patch is on the other side of the stitches and has no effect on this "failure spot" weather its one layer or two, and only strengthens the inner sil, which one layer does fine. Yes, adding a second layer will strengthen the layer inside the circle, but doing this will not strengthen the area just outside the circle, which is where failure occurs. if the inner circle is already beefed up to the point that it is no longer the weakest link, making it stronger does nothing for the "new" weakest link, and nothing for the overall strength of the system.

    the point is, the patch has a real effect on what's inside the circle of stitches, but it has zero effect on all sil outside the circle of stitches, which is where the failure occurs, when you installed the first layer, the weakest link in the chain moved. the only way to reduce the amount force per needle hole, is to use a bigger patch and more stitches, adding a second layer of patch to serve as "padding?" does nothing, the amount of force on the needle holes in the sil is not reduced, and no strength is gained.

    in order for the system to get stronger some amount of force has to be taken off the weakest link(the holes in the sil), but like the single layer patch does, it takes load off the pull tab stitches, and redistributes them somewhere else(the larger circular area of stitches). redistributing the force somewhere else, is the ONLY thing that effects how strong a patch is, if there is another factor involved besides redistribution of force, i have overlooked it.

    please explain how a second layer takes any load off the weak link and where it redistributes it to. it's stitches are the weakest link, and it doesn't redistribute any portion of its load to anywhere. in other words the amount of force per needle hole stays the same. you cannot effect the strength of the sil, only the amount of force per needle hole, and if the force stays the same, you can only do this by redistributing this force over a larger area of sil. a second layer patch that is the same size as the first one doesn't decrease the force per hole. if the second patch was larger than the first, it would redistribute the set force to more stitches (if it was stitched around its larger circumference), but then there would be no need for the smaller patch, thus just making the single one bigger does the same thing.

    where's teedee when you need him


    Quote Originally Posted by slowhike View Post
    yeah, i'm pretty sure the round patch distributes the force better, but my main point in the drawing is that each thread that penetrates the layers of material, then loops back through, is resting on (& pulling on) a heavier, stiffer, layer of material w/ the inside re-enforcement patch, rather than pulling directly on the silnylon tarp.

  10. #30
    Senior Member blackbishop351's Avatar
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    Patches simply distribute force along a longer stitch length as opposed to a small amount of stitch as would be used to directly attach a tie-out.

    Round patches definitely work better. The forces have nowhere to "collect," as they would at the corners of a rectangular patch.

    As far as force distributions, Brandon is right - double patches make no difference. However, Tim is also right that an inner patch layer will help keep the stitching from ripping directly through the material. So there are two questions that need answering for a particular application - what body material is being used, and how will the forces be applied. If the body material is strong, the perforation problem that Brandon mentions is less of an issue. If it isn't, double patches will likely make no significant difference. If the forces are going to be applied always (approximately) normal to the plane of the body material, then an inner patch will help because direct ripping will be more of a concern than perforation.

    In the end, there's always a tradeoff - more stitch length/area means stronger, but only to a point. With TOO much stitching, the material is weakened. So it really just depends on the material, and that's where patches help. By strengthening the material, you allow for more stitching, and therefore more strength.

    IMO, putting tie-outs of any sort in the body of a tarp (or similar structure) is just a bad idea all around. Begging for failure. But that's just me.
    "Physics is the only true science. All else is stamp collecting." - J. J. Thompson

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