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  1. #1
    Senior Member SC_Dave's Avatar
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    Rip-Stop Nylon Strength

    Anyone know how many PSI rip-stop nylon will support? I googled but could not come up with anything definative. Thanks.
    David

  2. #2
    Senior Member DemostiX's Avatar
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    You'll find a Youtube of one of the boutique / cottage tarp or shelter makers comparing behaviors of cuben he tears at with an awl. The cuben comes in different weights. One punctures and rips. The other does not.

    No numbers. But, what this guy is showing is what matters. Not whether the fabric is strong enough to handle the full load of a 300 lb guy applied with his knee, but what happens when his 115lb girlfriend sits down just above the pointed end of a car key hanging from the carabiner on her belt loop.

    One number, not the right number, doesn't do it.
    Last edited by DemostiX; 06-30-2011 at 14:00.

  3. #3
    Ramblinrev's Avatar
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    Quote Originally Posted by SC_Dave View Post
    Anyone know how many PSI rip-stop nylon will support? I googled but could not come up with anything definative. Thanks.
    David
    You asking an incomplete question. What ripstop? There are a myriad of weights available. If you want to know the PSI what are you planning on doing with it. Warbonnet has a chart that gives recommended weights for safety with the various fabrics he offers. Most of us refer to that chart. PSI is not really a meaningful number for hammocks. The gathering in the hammock and the stretched areas are going to be different in that regard.

    Assuming you manage to keep from punching a hole in it the total weight is what you are going to want to know. If you punch a hole... all bets are off anyway.
    I may be slow... But I sure am gimpy.

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  4. #4
    Senior Member DemostiX's Avatar
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    Well, lets say you've got nothing to swing on to cross a crevass in an emergency but your rolled up hammock. A test of tensile strength.

    We go to
    http://www.engineeringtoolbox.com/ny...th-d_1513.html

    , and find that 1 yard of 1 1/8" nylon rope has a breaking strength of 28,260 lb and weighs 3 x .322lb = .966lb = 1 lb. (close enough) That's the tensile strength of 1lb of nylon strands.

    That's a full pound of it. We'll pretend our hammock is 1.9 ripstop and round up to 2.0 oz. How much does a yard of hammock weigh? If it were 1 yard wide, it would weigh that nominal 2 oz. How does that compare to the nylon rope, then, for breaking strength? Divide 1lb =16 oz by 2 oz = 8 and also divide 28,260 lb by 8 and get 3,500 lb.

    Of course, half the threads are running perpendicular to the load; who knows what they contribute to the hammock not breaking when you're swinging from it? Maybe nothing but adhesion. So, we'll discount them completely and divide 3500 by 2 = 1,750.

    Or was that hammock a GT Nano 7, which might be of 1.1 sil nylon. Better divide 1750 by 2, then = 875. Worse, the Nano 7 is short bugger, and you may drop in the crevass, but maybe not, because under load, the nylon hammock will stretch before breaking.

    Still, you wish you were swinging from one of Warbonnet guy's imports, which gives you greater length, even though, as 1.0 nylon, it may not be as strong. But, we've alread rounded 1.1 down. so 875 lb it is. Enough for (almost) 3 of the big guys who hang here all at once.

    Oh, the engineers derate the minimum breaking strength by a safety factor of 12 !!. That shrinks 875 lb down to 73 lb.

    Well, you can swing your 9 year old daughter across to safety without later facing charges of reckless endangerment. But for yourself: You've got a choice of facing the tiger alone, or knowing the load factor of 12 is conservative, and the hammock likely won't break.

    Error in original. I forgot that the hammock is not 1 yard wide. Typically it is, say 1.5 yards wide, so you'll be swinging from 50% more fabric and tensile strength than in the calcualations above. Now you can send your 110 lb bride safely across.
    Last edited by DemostiX; 06-30-2011 at 22:29. Reason: error in calculation

  5. #5
    Senior Member SC_Dave's Avatar
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    Quote Originally Posted by Ramblinrev View Post
    You asking an incomplete question. What ripstop? There are a myriad of weights available. If you want to know the PSI what are you planning on doing with it. Warbonnet has a chart that gives recommended weights for safety with the various fabrics he offers. Most of us refer to that chart. PSI is not really a meaningful number for hammocks. The gathering in the hammock and the stretched areas are going to be different in that regard.

    Assuming you manage to keep from punching a hole in it the total weight is what you are going to want to know. If you punch a hole... all bets are off anyway.
    I apologize for not forming my question properly and not being familiar with the proper terminology. Please excuse my layman's attempt to gather knowledge. I just bought some rip-stop nylon at the fabric store to make a hammock chair and was trying to determine if it would hold me, that's all. I don't know the weight of the fabric, no big deal.
    David

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    Senior Member traftonm's Avatar
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    DC Dave, Rip stop is very strong in any wt. If you do a gathered end chair hammock I can't think of any reason that it would not hold you., evn if it were 1.1 wt.

  7. #7
    Senior Member SC_Dave's Avatar
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    Quote Originally Posted by traftonm View Post
    DC Dave, Rip stop is very strong in any wt. If you do a gathered end chair hammock I can't think of any reason that it would not hold you., evn if it were 1.1 wt.
    Thanks very much. The lady at Hancocks had no clue if it was 1.1 or 1.9 so I don't know....... I'll give it a try.
    David

  8. #8
    Senior Member DemostiX's Avatar
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    Please accept my apologies for teasing. But, read the end of Ramblinrev's first commentt again: all bets are off if you puncture it. The distributed load on many fabrics is not so great as to burst it, a test of the tensile strength of the fibers. We take it for granted. But only as long as there are no rips, tears, punctures, or weak points.

    Weak points? There's the rub. The thinner the fabric, all things equal, the more likely it is to be dangerously weakened by rubbing: abrasion. So, stay away from abrasion, and thin nylon will be as good as thicker. But, thicker will be tolerate your load longer, if abraded.

    You could determine the weight of what is on offer if your scale will resolve to +-3 grams, about 1/10 oz. . 2/3 yard off the bolt will come to close to a square yard. Measure and do the exact arithmetic, and allow for .1 -.4 oz per yard for coating, if you suspect it has been treated. You can make snake skins or bags from the sample.

  9. #9
    Senior Member SC_Dave's Avatar
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    Quote Originally Posted by DemostiX View Post
    Please accept my apologies for teasing. But, read the end of Ramblinrev's first commentt again: all bets are off if you puncture it. The distributed load on many fabrics is not so great as to burst it, a test of the tensile strength of the fibers. We take it for granted. But only as long as there are no rips, tears, punctures, or weak points.

    Weak points? There's the rub. The thinner the fabric, all things equal, the more likely it is to be dangerously weakened by rubbing: abrasion. So, stay away from abrasion, and thin nylon will be as good as thicker. But, thicker will be tolerate your load longer, if abraded.

    You could determine the weight of what is on offer if your scale will resolve to +-3 grams, about 1/10 oz. . 2/3 yard off the bolt will come to close to a square yard. Measure and do the exact arithmetic, and allow for .1 -.4 oz per yard for coating, if you suspect it has been treated. You can make snake skins or bags from the sample.
    No need for appologizes. Thanks for the info. Just want to be sure I am using the correct materials.
    David

  10. #10
    Ramblinrev's Avatar
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    I was interested in what the PSI number would give you for your purposes. That is obviously going to change by the weight of fabric. For example with a water carrier it could be very helpful to know the PSI so you could have some idea of the workable capacity. I am sure there are other projects where that would be a useful number. As far as hammock bodies I don't think it would tell me much. Trying to convert the PSI number to a usable measure for the hammock would totally max my brain cells.

    If I sounded flip or off putting I apologize. I really wanted to know what the usefullness of that figure was going to be.
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
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