{"id":20592,"date":"2019-09-25T17:23:12","date_gmt":"2019-09-25T17:23:12","guid":{"rendered":"https:\/\/www.skydivemag.com\/new\/?p=20592"},"modified":"2019-09-29T10:38:21","modified_gmt":"2019-09-29T10:38:21","slug":"choosing-lines-for-base","status":"publish","type":"post","link":"https:\/\/www.skydivemag.com\/new\/choosing-lines-for-base\/","title":{"rendered":"Choosing LINES for BASE"},"content":{"rendered":"\n

Dacron, Spectra, or Vectran: Breaking it Down
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Choosing which lines you need on your BASE canopy is actually a very simple process, so if you don\u2019t want to read a long article, here you go: <\/p>\n\n\n\n

If your BASE canopy will be used almost exclusively for jumping slider up, and you want to minimize weight and bulk, then choose Spectra. For almost any other scenario, Dacron is the answer.
<\/p><\/blockquote>\n\n\n\n

So what else is there to say? And what about Vectran? For those of you who want to know the background on this simple advice, or are curious about what these words mean, here are a few more details on each line\u2019s properties…<\/p>\n\n\n\n

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Spectra Lines<\/figcaption><\/figure>\n\n\n\n

SPECTRA (\u2122 of Honeywell) & DYNEEMA (\u2122 of DSM) <\/h2>\n\n\n\n

Both are: Ultra-High Molecular Weight Polyethylene, or UHMwPE.
 
Spectra is a trademark name of a yarn product manufactured by Honeywell in the USA. It is molecularly identical to Dyneema, which is manufactured by DSM. This material is pretty cool stuff, and it\u2019s worth learning about it. The Epicene is made with Spectra, and this line is an option for Hayduke as well.<\/p>\n\n\n\n

Spectra has some unique characteristics that make it especially well suited for use in certain parachute designs. It is strong, light, doesn\u2019t absorb much water, and has good UV resistance. It ages well, with minimal \u201cfurring\u201d and is dimensionally stable enough for low performance parachutes (which describes every BASE canopy ever made).<\/p>\n\n\n\n

Why we love Spectra for BASE canopies:<\/h4>\n\n\n\n
  1. It\u2019s light, and low pack volume<\/strong>, making a significant difference in total weight and pack volume compared to Dacron lines. The upside here is obvious \u2013 every gram counts on a four hour hike, and every cubic inch of volume matters when you\u2019re dragging your container through the air at 150 mph.<\/li>
  2. It starts smooth, and stays smooth<\/strong> over time as it ages. Compared to Vectran, which becomes a hairy mess as it ages, Spectra stays smoother for longer. This is a positive for tension knots, which become more likely as friction increases between line loops during deployment. Smoother lines make for smoother line deployments.<\/li>
  3. It doesn\u2019t absorb much water.<\/strong> When you land your parachute in wet grass on that first jump of the day, and go to re-pack it, you don\u2019t want to be s-folding soggy lines into your tail pocket \u2013 especially if they\u2019re nice and hairy after a season of use. Vectran, by comparison, absorbs enough water to where damp hairy lines can be an issue after landing in wet grass.<\/li>
  4. Performance<\/strong>. There is a noticeable difference in the glide performance of a Spectra lined canopy vs Dacron. In ram-air canopy flight, line drag is significant enough to affect even low-performance BASE canopies.
    <\/li><\/ol>\n\n\n\n

    Downsides to be aware of:<\/h4>\n\n\n\n
    1. Inelasticity<\/strong>. While \u201cless elongation than steel\u201d is a common and inaccurate refrain, Spectra is inelastic compared to Dacron. It is also comparatively low-friction. This can be a bad combination if your equipment is not configured properly, or if you aren\u2019t aware of the conditions you need to provide your parachute in order to have a safe opening. Is this bad? Not if you use Spectra line for its intended purpose, which is for slider-up deployments at a controlled airspeed. The downsides of inelastic line material have been the source of many old-school opinions about parachute openings, which no longer apply to modern gear. Modern BASE parachute designs are begun from step one with the knowledge that Spectra line will be used. Intentional design features mitigate the drawbacks and now, after more than a decade of use in BASE, the consensus is that Spectra-lined canopies perform well for slider up applications and many wingsuit BASE jumpers swear by Spectra thanks to the benefits. That being said, if we are speaking strictly within the category of openings, Dacron wins.<\/li>
    2. Trim. <\/strong>Spectra\u2019s tendency to shrink out of trim is a common complaint, but this argument has limited application to BASE canopies, which are not highly sensitive to the amount of trim loss Spectra tends to experience. The minor downside in trim stability is far outweighed by the benefits of strength and durability Spectra offers. <\/li>
    3. Cost. <\/strong>It\u2019s more expensive than Dacron. At SQRL, we do not pass this increase on to our customers.<\/li><\/ol>\n\n\n\n

      SPECTRA LINE MANUFACTURING<\/strong><\/h2>\n\n\n\n

      There is a more than 90% chance that if you\u2019ve ever seen Spectra (sometimes called \u201cmicroline\u201d) on a parachute, it was made with Honeywell yarn, by CSR. Here\u2019s how Frank, the owner of CSR, describes the manufacturing process:<\/p>\n\n\n\n

      \u201cSpectra arrives at our factory from Honeywell in a tube of yarn. We\nload the yarn into the braiding machine, and begin to braid a line to a\nspecification. First, we braid about six feet of line through the machine, then\nstop it, and cut the line. That line \u2013 the first few braids of every single\nbraider setup every day, is tensile tested before continuing. If, for example,\nthey braid a 1000lb spec line, the tensile test must show a strength of at\nleast 1100lbs in order for production to continue. \u201cWe\u2019re not making\nclothesline\u201d, Frank says, and the QC procedures at CSR are intense. Once\napproved, the braider will continue to produce around 5,000\u2019 of line over a\n20hr period, which accumulates on a supply reel.<\/em><\/p>\n\n\n\n

      “From there, the line is taken to another zone in the plant, where Frank\u2019s brother, Tim, oversees the rest of the process. The next step is to pre-tension the line at about 80lbs, in an untreated state. This dimensionally stabilizes the line so that its length remains as consistent as possible through the inevitable load cycles in its future. After stretching, a water-based urethane coating is applied, the excess is squeegeed off, and the line is cured for three days. It\u2019s then put onto another reel, stretched a second time at 80lbs, and rolled onto shipping spools. Before shipping, sections of line are randomly selected for tensile testing a second time.\u201d<\/em>
       
      Honeywell\u2019s yarn, and CSR\u2019s manufacturing process, are consistent. CSR fails very little yarn, and braided line tests rarely result in failed batches. At Squirrel, we frequently test components built with CSR line, such as soft links and parachute line, and CSR\u2019s rated strength has been exceeded in every scenario. <\/p>\n\n\n\n

      Interestingly, the lower the line\u2019s elongation, the more the variance is between tests. The higher the elongation, the more consistent it is with a narrower range. For instance, testing five pieces of 1000lb Spectra line may result in failures between 1150 and 1300lbs, but the comparatively elastic Dacron line will usually present a smaller window \u2013 more along the lines of 5-8%.

      <\/p>\n\n\n\n

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      Dacron Lines<\/figcaption><\/figure>\n\n\n\n

      DACRON  <\/h2>\n\n\n\n

      (Originally \u2122 of DuPont, now INVISTA N.A.) <\/p>\n\n\n\n

      It\u2019s Polyester! And BASE jumpers love<\/em> Polyester. <\/h4>\n\n\n\n

      Polyester at its base, Dacron\u2122 has enjoyed a very long history of use in skydiving. Like flubber, you can beat it up with a parachute opening and it will return to its original shape quite predictably. It is resistant to heat, has a nice amount of elasticity, and is generally easy to use. Dacron molecules are not organized into such long chains as Spectra, meaning that more yarn is needed in each braid to achieve the same strength, therefore pound-for-pound it\u2019s thicker.
       
      Dacron\u2019s elasticity suggests that it is more \u201cforgiving\u201d during the opening process, which can benefit us in several ways. It provides a bit of shock absorption for hard openings. If you\u2019ve ever jumped a Spectra lined-canopy slider off for more than a one-second delay (not recommended), you will understand this difference first-hand, and it\u2019s hardly debatable. So for slider-down applications, Dacron is a no-brainer and is currently the best thing going. For slider-up openings, its shock-absorbing properties apply equally well. While the staging of the parachute opening by way of slider reefing is the most important factor, a bit of cushion is undoubtedly a benefit.
      <\/p>\n\n\n\n

      Upsides: <\/h4>\n\n\n\n
      1. It\u2019s Elastic.<\/strong> Softer openings are good when they occur in the same amount of altitude. <\/li>
      2. Water resistance. <\/strong>Soggy lines are not a benefit to BASE jumpers, and wet grass landing areas are a daily occurrence for most of us in the Alpine summer. Dacron resists water absorption better than Vectran.<\/li>
      3. Good dimensional stability. <\/strong>Not great, but good, and better than Spectra. Overall, this is a minor benefit to BASE canopies which are not severely affected by minor trim changes.
        <\/li><\/ol>\n\n\n\n

        Downsides:<\/h4>\n\n\n\n
        1. Heavy, bulky<\/strong>. Pound for pound, Dacron resists less, meaning that we need more material to achieve the same goals. This has consequences for weight and pack volume.<\/li>
        2. Not as strong as Spectra<\/strong>, at the same diameter. <\/li>
        3. Performance:<\/strong> Spectra is up to 40% smaller in diameter at the same strength, which \u2013 even in our low-performance canopies and especially in medium performance canopies \u2013 makes for a real difference in glide performance. Line drag is a major factor in parachute efficiency.<\/li><\/ol>\n\n\n


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