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  1. #31
    Senior Member DemostiX's Avatar
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    A little diversion, but on topic from the OP. I'll respond to Opie's comments later. More sooner than later.

    ===========

    three months ago I bought 200+ feet of white hollow single braided UHMWPE Spectra (tm) cord on ebay, maybe from an amateur rocketeer, because he was also selling Kevlar (highly temperature resistant) line, too, calling it "shock cord." This molecule and fiber is from the same family as Amsteel.

    The Spectra was listed as 1/8" with a breaking strength of 1500 lb.

    When the cord arrived, and very promptly, I thought it too thin and too light to be 1/8". I had 1/8" Amsteel on hand for comparison, another UHMWPE-based cord, rated at 2500 lb or so.

    Well the Spectra is a dream to splice, opening its braids to easily pass a 6mm needle (No. 10), maybe 8mm as easily. Very soft, too. But, with a weight of no more than 7oz for 200+ feet, there was no way this could be 1500 lb breaking strength cord. I told the vendor. He repaid the money in full, accepted without comment my paypal re-payment to him pro-rata for what he did not want returned, and continued to list this and other cord, but with slightly reduced claimed strength.

    I just bought more 1/8" cord from the same seller, again likely NOS, for interest. It is all Vectran, a strong synthetic fiber still made into high performance rope by New England Rope, Samson, and others, into composites, and into bowstrings too, among other uses.

    Vectran tolerates elevated temperatures better than most Dyneema-likes, and has lower creep. NE Ropes offers two lines of Vectran hollow braid, V100 (tm) and V12. The specification sheets show breaking strength to be a strict and tight linear function of weight of the line, with weight and tensile strength listed for each of several nominal diameters, the smallest of which is for 1/8" V12. (Go ahead and divide numbers in column 5 and 6 by those in columns 3 and 4 for several sizes.The ratios will vary +- 5%, some of which is rounding error.)

    KEY: lb/100= lb weight per 100ft of rope
    g/m = gram weight per meter of rope
    lbs = tensile strength in pound
    kg = " " in kilograms

    Weight ............................. ............. Tensile
    ...........................lbs/100' g/m...............lbs.......kg
    1/8" ( 3mm)............ 0.5 7.4.......... 2,100.... 955
    5/32 ( 4mm)........... 1.0 14.9........ 3,300.... 1,495
    3/16" ( 5mm).......... 1.2 17.9........ 4,950.... 2,245
    1/4" ( 6mm)............ 1.8 26.8........ 7,200.... 3,265
    5/16" ( 8mm).......... 3.2 47.6........ 10,900... 4,945
    3/8" (10mm)........... 4.8 71.4........ 17,000... 7,715
    7/16" (11mm).......... 5.5 81.8........ 26,000... 11,795
    1/2" (12mm)........... 6.6 98.2........ 29,200 13,250


    http://neropes.com/product.aspx?mid=...6C&lid=1&pid=5

    V12 tensile strength in lb = (approx) 275 to 298 times cordage weight (in grams per meter. (Call it 300 and de-rate by 10% afterward)

    Now: The line I received weighs an estimated:
    3.6 oz for 115 feet
    = 3.1 oz per 100 feet
    = 88 grams per 100 feet
    =88 g per 30.48 meters
    =2.9 g per meter

    Consulting the New England Ropes chart, their 1/8" hollow-braid all Vectran V12 cord weighs
    7.4 g / meter
    Its listed tensile strength is

    2100 lb, plenty to safely hang from

    But, I weighed and estimate the Vectran I received at just 2.9 g per meter. That is about 40% the weight of the 1/8" NE Ropes V12. There is either some extraordinary exception to the functional relationship in the NE Ropes tables for Vectran V12 or what I have has an estimated tensile strength of:

    2.9 / 7.4 X 2100

    or 285 x 2.9

    which comes to about:

    825 lb. not 2100 lbs.

    Now, that's OK by me, but it is not enough to suspend someone else in a hammock from. The price, delivered, was just $10 for 100+ feet. I get to play with Vectran, I might use it as a sheath. I also got to see how one vendor responded to the challenge that he mis-described the cord he was selling: He just keeps selling it.

    BTW: Grizz at one point expressed dissatisfaction with Vectran for reasons that don't matter here. So far, I like that it is not fuzzy and soft at all, like the Allied Chemical Spectra. It is somewhat "springy." Maybe I'll use it to encase the Spectra in a hybrid soft shackle with greater strength. Or into low-creep whoopies.

    I will tell the vendor, who ships very fast, how the weight of his 1/8" compares to the weight of a major mfg product.
    Last edited by DemostiX; 07-29-2011 at 22:00. Reason: correctoin

  2. #32
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by motorapido View Post
    For both backpacking and kayak camping, the volume of my gear is nearly as important as its ultra-light-weightness. I use long whoopie slings to give me options in areas where trees are far apart. Perhaps as a contribution to this scientific inquiry, I will make a set of whoopies from Amsteel Blue in the length of my dynaglide whoopies and then attempt to create an objective measurement comparison of their packability/compressability/stowability. I spent a fortune to shave barely more than an ounce off my tarp weight (spinn to cuben), and was happy to do so since the cuben tarp compresses and packs well. If the cuben tarp consumed twice the volume in my backpack or kayak hatch, I would have accepted the heavier weight of the spinn tarp in exchange for its compact compressability. Now, again, I'm assuming that the storage/compressability/packability comparison between dynaglide and Amsteel Blue becomes a factor only when you're carrying hundreds of feet of it. But it is important to measure all this stuff, objectively, and share it with our brothers and sisters so that we are fully informed consumers. Plus, for many of us, myself included, all this obsessive measurement and calculating while we're off the trail is a big part of the fun of the hobby.
    Motorapido: Your point is very important for some of us. As a bicyclist who can't stand that drag of excess volume would slow down my descent on hills I sweated to climb, I also want the gear to pack down small. I want light, high performance compression sacks......for cheaper than possible. A Clark hammock is nobody's idea of small, but it can be compressed, with effort, to a little over half the size it compresses to easily. And, if I haven't already cracked this joke, I want bug netting from which all the air disappears, so it can compress to zilch and then have all the openings restored on unpacking . First thing I want to know about bug net is volume; the weight is secondary.

    Ask the HF community members to start reporting about their kits how many quart jars they fill when packed. Pics alongside a Nalgene bottle don't count: Volume is to the third power of line length.

  3. #33
    Senior Member hippofeet's Avatar
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    You are derating line by weight, correct? Is it a simple ratio? Like, manufacturers listed strength at such and such listed weight, to actual weight so strength is x? Be tough to check diameter of a small line. Or is it actual weight is so and so percent lower than listed, so lower strength by that percent? I need to take some time to look at where this all went.
    An emergency of my own making...is still an emergency.

  4. #34
    Senior Member hippofeet's Avatar
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    I ain't givin' up.
    An emergency of my own making...is still an emergency.

  5. #35
    dant8ro's Avatar
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    Dynaglide weight verified for green 200' dead on in the great white north.



    148g = 74g / 100 ft

    None the less this will remain my favorite cord, low bulk, high viz, great versatility, good strength.

    And I do have some cord...





    And yes those are 1/4" Amsteel Whoopie Slings with SMC descender rings and chain links... WE spanned about 35 feet with an ENO once...

  6. #36
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by hippofeet View Post
    You are derating line by weight, correct? Is it a simple ratio? Like, manufacturers listed strength at such and such listed weight, to actual weight so strength is x? Be tough to check diameter of a small line. Or is it actual weight is so and so percent lower than listed, so lower strength by that percent? I need to take some time to look at where this all went.
    I'm not "derating" it, but I understand what you are getting at. I'm just showing how the manufacturer (and likely the distributor) rate the strength of the rope. It is right there in the tables, and the basis seems to be the entirely intuitive physics of mass. If there is fabric engineer here who will tell us why we can't assume that one undamaged strand removed from an 8 strand rope won't have 1/8 th the strength of the rope it was drawn from, I'm entirely interested and believing. Similarly, I'd be amused to learn that some ultra-lights rid themselves of excess weight by extracting surplus strands. Pretty easy to do with line composed of strand as slippery as in such as Amsteel.

    I suppose it possible to make rope less well, such that the strands damaged each other in some disproportionate way as the rope was made smaller or larger. But, that is not what manufacturers tables show for multiple homogeneous ropes. I haven't looked at mfg tables for double braid ropes. The proportions of jacket (mantle) and interior (kern) can vary across rope sizes, so the strength / weight relationship could also vary.

  7. #37
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by hippofeet View Post
    You are derating line by weight, correct? <snip> Be tough to check diameter of a small line. Or is it actual weight is so and so percent lower than listed, so lower strength by that percent? <snip>
    Hippofeet:

    Yes it is hard to measure the diameter of small line, and because it is hard to measure the fractional error in measuring (or labeling) can be enormous.

    The ebay vendor in my long story continues to sell what he lists as 1/8" Spectra, for which he also lists a 1500lb breaking strength. I trust him to be selling Spectra. I believe his posted breaking strength for Spectra which is 1/8" as I think of 1/8" from contemporary tables for line of similar UHDMPE. (For comparison, contemporary Amsteel of that size is rated at over 2000lb.) But, I don't trust my eyes to discern from his photo that he is showing 1/8" line, or that he and I agree about what 1/8" line is.

    So, I'm not going to call him out for selling now something that isn't what it seems. What he sold me as 1/8" line twice, Spectra and then Vectran, can be flattened easily to be 1/8" wide. But, if the weight isn't there, packed into the length of line, then the strength cannot be there either.

    That is where this all started, and your questions are exactly at the crux of the matter.

  8. #38
    WV's Avatar
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    I have similar observations of flat braided 1/8" spectra purchased on ebay. For some reason, I've got it marked as 750 lb. test (possibly what the seller said.)

  9. #39
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by dant8ro View Post
    Dynaglide weight verified for green 200' dead on in the great white north.



    148g = 74g / 100 ft

    None the less this will remain my favorite cord, low bulk, high viz, great versatility, good strength.

    And I do have some cord...





    And yes those are 1/4" Amsteel Whoopie Slings with SMC descender rings and chain links... WE spanned about 35 feet with an ENO once...
    Great pix. Consistent reading, so gravity isn't so different up there. Or maybe it is, but you re-calibrated your scale on site.

    And excellent use of a clothes hanger, keeping it unburdened of........clothes, the better for light to come through to help pick the right color line.

    Now, the next step is to calculate the minimum break strength of the Dynaglide, assuming it is made of fibers no better than in expensive Amsteel Blue. Tables of strength are at http://www.samsonrope.com/index.cfm?...ope=192&inst=1

    For minimum breaking strength, I calculate and estimate from the tables about 300 lb breaking strength. liberally, per ounce of rope.

    What do you calculate, and what are your estimates of average and minimum breaking strengths on that assumption, for 74 grams / 100 ft of Dynaglide?

  10. #40
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by WV View Post
    I have similar observations of flat braided 1/8" spectra purchased on ebay. For some reason, I've got it marked as 750 lb. test (possibly what the seller said.)
    Maybe it is the same seller, "Shawn.....".
    For my first purchases from him, I won two auctions to take advantage of combined shipping. To reduce seller's costs, I told him it was fine with me to not include the cardboard he mounted the hanks on. That way he might be able to mail both hanks by First Class Mail, which has a 13 oz weight limit, and pocket a few extra $.

    He shipped promptly by First Class, and my tip off was that the lightweight mailing envelope contained the cardboard mounts. "Too light for 200+ feet of 1/8" 1500 lb line!!"

    Then I opened the package and was surprised at the visual comparison with 'spensive 1/8" Amsteel Blue I splurged on 10 feet of. Puny, sickly, and so limp!

    Seller disagreed with me, not persuade by the weight / length relationship, but immediately refunded everything, including shipping. He said he would conduct breaking strength tests of his own to confirm his listing.

    Maybe you bought line from the same spool after he had done so -- how hard can it be for amateurs to conduct such tests? A set of barbell weights, an anvil with jaws, and lever? --and he de-rated it.

    But, that Spectra (tm) sure is silky smooth and easy to run large fids through, isn't it?
    Last edited by DemostiX; 07-30-2011 at 10:14. Reason: spelling

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