http://www.youtube.com/watch?v=cVAoiLl2B6M
and
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=4366466#4366466
and
Here is what BILL BOOTH has said on dropzone.com about DACRON LINES. Great source of info!:
"My tests show up to a 300% increase in opening shock felt by the jumper using Spectra vs. Dacron suspension lines. It is not always that much different. It depends on how quickly the force is applied...and canopy makers have done a good job of designing canopies that open slowly enough to allow the routine use of Spectra. However, when a rare hard (quick) opening happens, Spectra lines will definitely make it hurt more."
"Anyone who doubts that suspension line stretch is a factor in reducing the opening shock felt by a jumper, should make a bungee jump...only replace the normal stretchy bungee cord with a stainless steel cable. What's going to happen when you hit the end of that steel cable? Your leg is going to be torn off, that's what. Now remember, Spectra line stretches about as much a steel cable."
"If you are not using Dacron lines, they would help. They stretch a little, and also slow the slider down due to surface friction. Spectra (micro) line does not. If you are already using Dacron lines, and still having hard openings, get a canopy that opens slower."
"The best way to avoid injuries from that occasional super hard opening (as well as the hard openings themselves), is not to jump no-stretch lines. Ask yourself, "Do I really need the (slight) advantages no-stretch lines offer?" If not, get Dacron. Your body will thank you, because even if you are not ever seriously injured on any single jump, each even slightly hard opening on no-stretch lines is damaging your body...and it all adds up."
"Spectra (micro line), Vectran, Kevlar, and HMA are "no-stretch" lines. They do not "absorb" opening shock the way Dacron does. This means that the same "hard" opening can hurt you a lot more. It's like doing a bungee jump with steel cable. The same force is applied...but a hell of a lot more shock is felt by the jumper. All the opening shock caused broken harnesses (two PDF tandem harnesses recently broke), injuries (a guy just broke both femurs), and fatalities (4 in the last two years that I know of) have all been on "no-stretch" line canopies, and could probably been prevented if Dacron line had been used. No stretch line is used because it is thinner, lighter, and has less drag than the same strength Dacron. While this is an "advantage" in a high speed swoop, it has no place in tandem. 85 year old grandmothers jump tandem. They, and many other tandem students, need the softest opening shock possible. This is why we only use Dacron line on our tandem products. Not to mention that our tandem equipment was NOT drop tested with no-stretch lined canopies.
I don't care if you have 1,000 jumps on a particular canopy with no-stretch lines with no problems. Ever canopy opens hard eventually. When that happens, I want some "bungee cord" between that canopy and the tandem passenger."
"One thing is for sure, if you jump "no-stretch" lines, especially Spectra (because it's so slippery, and reduces slider drag) your chance of being injured or killed by a hard opening shock is much greater than if you jump Dacron line, which stretches just enough to absorb some of that shock before it hits you."
"Spectra (or micro-line) is strong and tiny, so it reduces both pack volume and drag , which means you get a smaller rig and a faster canopy. Unfortunately, It has a couple of "design characteristics" (this is manufacturer talk for "problems") It is very slippery (less friction to slow the slider), and stretches less than stainless steel. This is why it hurt people and broke so many mini risers when it was first introduced. Now, I must say that the canopy manufacturers did a wonderful job handling these "characteristics" by designing new canopies that opened much slower than their predecessors. However, the fact still remains, that if you do have a rare fast opening on a microlined canopy, Spectra (or Vectran) will transmit that force to you (and your rig) much, much faster, resulting in an opening shock up to 300% higher than if you have Dacron lines. (It's sort of like doing a bungee jump with a stainless steel cable. At the bottom of your fall, your body applies the same force to the steel cable as it would to a rubber bungee cord, but because steel doesn't stretch, your legs tears off.)."
"Reinforced type-17 webbing risers rarely break. They have a new breaking strength of around 3,500 lbs. This is not that much less than type-8 risers breaking strength of 4,000 lbs. The real difference is whether you have mini rings or large rings...and the difference here is in cutaway forces, not breaking strength. While properly designed mini-ring risers can easily release even a 250 lb. jumper in a 3 or 4 "G" spin, the problem is that it is harder to manufacture mini-ring risers correctly. What causes any riser to break is usually a combination of a heavy jumper, a hard opening canopy, and no stretch (Spectra, Vectran, or HTML) line. Broken risers on Dacron lined canopies are very rare indeed."
"Single rear riser break is very rare. Risers usually break where they go around the large harness ring. It is obvious that since the "reinforcement" in type 17 risers is below the confluence, it does nothing to prevent this kind of damage. When this riser broke, it "released" a lot of energy, thus preventing much more serious injury of the jumper. Which is a good thing. The only way I know of to prevent "killer" opening shocks, is not to jump Spectra (Microline) or Vectran. They don't stretch at all, and therefore do nothing to help absorb the energy of a really hard opening. As long as we insist on jumping non-stretch lines, incidents like this are bound to happen. (Canopies with Dacron lines can still open hard, but much less shock is actually felt by the jumper.)."
