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  1. #11
    Senior Member hippofeet's Avatar
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    If it is only about weight, I am not worried unless I am packing 10,000 ft. of line. Then I would want to filter water along the way. I do find it interesting that a manufacturer's (or wholesaler's?) advertised weight would be that far off. UNLESS that difference in weight means fewer or more fibers, or diameter (strength) of fibers that make up the line. Then, it would matter, because maybe you could derate line by weight.
    Last edited by hippofeet; 07-28-2011 at 12:51. Reason: thought
    An emergency of my own making...is still an emergency.

  2. #12
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    Thanks SmokeBait for the 2nd assessment.

    The key thing to come out of this is to be careful in extrapolating out from the advertised 0.1 lb / 100 ft. I've done that myself, without thinking through how many significant digits I really had.

    Dynaglide is 50% heavier than I had previously figured. But what's half an oz per 100 ft of cord really matter…? One less bite out of a Snickers bar.
    Briefly, 1/2 oz doesn't matter. Bait and switch rarely does. You did surrender a margin of safety over 7/64th " Amsteel Blue to get there. And probably would not have had it been rated at "950 lb."

    We don't even know what the "1000 lb" rating is. Average breaking strength or minimum? For its market, as a throw line for arborists, it is a very heavy duty line against Fling It, Zing It, Throw-It etc. Nobody in that industry keeps a job or a life hanging from it. Or loses one from a safety factor on it.

    How about some other weight measurements? I'm guessing that nominal 7/64" Amsteel Blue weighs no more than 60% more for its 1600lb average break strenth--what's another 1/2 oz for a safety factor engineers recognize, right? If so it will turn out that there's nothing mysterious or wonderful about Dynaglide's breaking strength at all.

    Disclaimer: I don't work for or have any interest in Samson, NE Rope, or any rope maker, supplier, etc.

  3. #13
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    excellent scientific analysis

    I love this stuff. I've spent countless hours and countless (well, actually countable and heartbreaking) amounts of money cutting grams off my backpacking and kayak-camping pack weight. Gram weenie, yes I am. This type of data is very interesting to me. Wondering if the variance in advertised versus measured could be because the rope is made in a purposely-dry atmosphere? Do rope manufacturers dehumidify their factory air for some reason? To prevent the rope from absorbing water and getting moldy? Hmm. Dunno. It's summertime, and unless those who are measuring rope weight are doing so in super dehumidified air, the rope might have picked up water weight from humid air. Heck, here in Harrisburg, Pennsylvania, I probably pick up a good bit of weight from humid air condensing on me and wicking into my clothes and gear.

  4. #14
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    well now, this was interesting.

    First thing, test the accuracy of the scale. It is reported to be accurate to 0.5 grams. I put 3 US quarters on it, it reports 17g. Standard weight of a quarter is 5.67 which is surely an approximation for 5 2/3, times 3 equals 17, check.

    <snip>
    I wonder where 3 for 17 (grams) came from?!!

    A lot of us get lost in digits. Me too.

    For calibration and mnemonic reasons combined, maybe the best calibration unit for central North Americans is a stack of US 5 cent coins, the nickel: For a long time the standard weight has been 5.00 grams.

    Nickel = 5.00 grams.
    Last edited by DemostiX; 07-28-2011 at 16:43. Reason: grammar

  5. #15
    Senior Member more's Avatar
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    Quote Originally Posted by DemostiX View Post
    I wonder where 3 for 17 (grams) came from?!!
    You might be right and we all need to start using nickels, but I think that what he was saying is that the three quarters he measured have a total mass of 17 grams.

  6. #16
    GrizzlyAdams's Avatar
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    Quote Originally Posted by more View Post
    You might be right and we all need to start using nickels, but I think that what he was saying is that the three quarters he measured have a total mass of 17 grams.
    I think that was understood.

    What happened was that I weighed the cord and saw that the reading was a lot heavier than I expected. Now I use this scale a lot for shipping, and my measurements are always confirmed to the resolution of an ounce by the post office, but I wanted to check the scale somehow.

    Looked around the workshop, didn't see anything with a known weight, but then thought of coins. I didn't know what their weight ought to be, but I figured I could find out easily enough. I had three quarters in my pocket ....
    Grizz
    (alias ProfessorHammock on youtube)

  7. #17
    Senior Member angrysparrow's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    I had three quarters in my pocket ....
    So, serendipity hath declared that henceforth 17grams is to be known as one 'GrizzUnit' ?

    ...just don't use GU's to extrapolate...either mass or currency.
    “I think that when the lies are all told and forgot the truth will be there yet. It dont move about from place to place and it dont change from time to time. You cant corrupt it any more than you can salt salt.” - Cormac McCarthy

  8. #18
    Senior Member DemostiX's Avatar
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    You may find Shug in one of his videos juggling one Grizz-Unit = 3 U$ Quarters.

    In order to impress CJH (aka Clark) owners, it is necessary for him to borrow three S.A. Kruggerands from the crowd and juggle them.

    That would be three (3) Troy ounces.

  9. #19
    Senior Member DemostiX's Avatar
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    If this is the Question

    Quote Originally Posted by GrizzlyAdams View Post
    Thanks SmokeBait for the 2nd assessment.
    Dynaglide is 50% heavier than I had previously figured. But what's half an oz per 100 ft of cord really matter…?
    then

    Quote Originally Posted by GrizzlyAdams View Post
    <snip>One less bite out of a Snickers bar.
    is not the answer.

    Two whoopie slings use not 100 feet, but closer to 1/4 that. The comparison is not to the magnitude of disappointment in what we thought Dynaglide weighed, but to the real difference from an established alternative, 7/64" Amsteel Blue (AB), with an average break strength of 1600lb. It is already very lightweight, something of a revolution for hanging in this hobby. It weighs 4.8 oz per 100 feet by my estimate*. So, the savings of Dynaglide over Amsteel Blue 7/64" is one 1/4th the difference in weight per 100 feet., call it 0.6 oz.

    Of course, this 0.6 oz, "one less bite out of a Snickers bar", gets the user a safety margin that is substantively significant, pushing the breaking strength from a supposed 1000 lb to 1600lb (or 1400 lb ISO certified). You, Grizz, know and will acknowledge that the 600lb strength margin in this region, for common weights of hammockers, has real value to safety.

    So, this isn't a joke about .6 oz, three quarters in a pocket.

    The question, I think, should be:
    Why was Dynaglide ever used for suspensions?

    The answers are that
    • It appeared to be far lighter than it actually is; we were fooled,
    • It was about the same price as Amsteel Blue 7/64",
    (Whether more or less expensive depends on how you treat the hank-purchase minimum.), and
    Dynaglide promised to be at or above 4 digits in breaking strength.

    (When I can, I'll report on whether Dynaglide with its putative break strength of 1000 lb, is with certainty different in its breaking strength from Zing-It (2.2) or Lash-It (2.2mm), made of exactly the same fiber, has exactly the same weight / length. Those cords have an average break-strength of 650lb, (and minimum BS of 570lb) and nobody, responsibly, is recommending them for hammock suspension.)

    Given New England Ropes (NER) marketing of Dynaglide as a throw line, I find no reason to take any more seriously their specification of breaking strength at 1000 pounds even.Their weight specification has already been shown to wrong by 60%, well beyond a margin of copy-edit rounding error. The product description states it is made of the same Dyneema SK-75 as some other products, not a further refinement on Dyneema. There is no reason, for its market, for NER to have paid more for fiber treated for purposes other than its intended use, which would value slickness and freedom from snagging among tree branches.

    *easy as it would be for folks with scales to verify weight-consciousness and trimming achievements, only Smoke Bait has joined catenary-curve-calculating Professor Hammock in coming forth with measurements.

  10. #20
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by Stormstaff View Post
    As a noob I have a question. Is all this scientific stuff just to know how much weight someone is carrying while backpacking or such? Or is the a strength issue due to incorrect weight measurements?
    As a rider of lightweight road bicycles and former motorcyclist I know weight-weeniness as much as many. Check my posts: I know drillium.

    Unless you're training for strength, gear should be as light as it should be, BUT NO LIGHTER.

    In short, I think there's been an inadvertent bait and switch: Get this cool line that is so so light, and still be safe. It turns out it is not so light. Had it been only trivially lighter than the alternative, and more expensive, too, then it would never have been pushed so hard. But, much lighter (which turns out not to be true), well then.... lets jump on board. Search archives, and you'll find one acolyte who claimed a MEASURED weight savings from Dynaglide that was impossible unless he'd previously been using 7000lb rated rope, so much did he / she believe in the lightness of Dynaglide.

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