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slacklinejoe
Jul 21, 2008, 9:35 PM
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I'm interested in hearing some opinions regarding threaded mainlines.
I'll admit, I have rarely used a threaded mainline, when I have, it was usually someone else's line. I just haven't really felt the need. Whenever the situation dictates for redundancy I tend to just run two 1" lines through the bartacker making them a bonded mainline.
I understand, most people don't have the equipment to bond lines, but is it just that threading is available without equipment to anyone willing to spend a long tedius bit of work or is there some other advantage that I haven't seen yet. Threading is still a PITA, but at least I finally invested in something to do the job quickly so i can at least handle requests for them. Bonded on the other hand seems on the surface to have less limitations / downsides, but like I said, I don't spend time on threaded so I could be missing something.
I personally like bonded lines better since you don't have the whole strength / elasticity difference between the core and sheath line. That said, it seems there are still plenty of folks who use threaded lines so I'm looking to see the pros and cons from other people's perspective. Thoughts anyone? Is there something I'm missing?
(This post was edited by slacklinejoe on Jul 22, 2008, 4:36 AM)
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NJSlacker
Jul 22, 2008, 1:22 AM
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I've never used a bonded line, but my latest and current line is 130' of 1 inch threaded with 9/16ths inch webbing, and now that I've gone threaded, I don't think I'll go without it again. I've only done low-lining, but even so, a threaded line feels more secure (no fear of jumping and snapping a line), and it holds tension much easier, making longer lines much easier to set up.
I have never walked a bonded line, but I imagine they'd probably feel very similar to walk on and hold tension similarly. A bonded line may be a little stronger (I think the 9/16 is rated to 3000 instead of 4000 for my 1 inch), but 8000 lbs to 7000 isn't that big of a difference. I can imagine bonding lines is easier (if you have the equipment). Threading is definitely a PITA.
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taydude
Jul 22, 2008, 2:17 AM
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Are you talking about redundancy as in a high line where you would attach yourself to the line to stop you from falling? I believe you need to have a second, non-tensioned line under the main line if you're doing that. Or perhaps I'm behind the times and these two methods are sufficient back up for that situation. 
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slacklinejoe
Jul 22, 2008, 4:17 AM
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NJSlacker wrote: A bonded line may be a little stronger (I think the 9/16 is rated to 3000 instead of 4000 for my 1 inch), but 8000 lbs to 7000 isn't that big of a difference.
I don't think tensile ratings necessarily add that way since they aren't actually bonded together. You can break each one independantly as they move and elgongate seperately - my limited understanding of elasticity suggests that you could actually have one taking most of the load before it's stretched the other one tight enough to carry much of a share.
An extreme example would be a chain backed up with a climbing rope. The chain doesn't stretch enough to let the rope share the load, thus they both blow at their rated strengths, just one, then the other.
Overall, I'm not sure what to expect realistically but I don't think they simply add together; I'd suggest that break testing should be done to know the resulting strength and mode of failure. In the case of a threaded line I'd expect one to blow at slightly higher than normal then the other immediately taking the load and blowing if the same tension is kept on it, however once the first one blows the tension is lost in a load tester thus having a lower force on the 2nd unless you keep tensioning. It's all just theory though... I think I should make some calls.
My biggest usage complaints so far with threaded lines are the rounding and shifting of the outer webbing of the line. A bonded one stays 100% flat with no shifting.
It also just seems that any redundant line artificially slows the line down, but I'm convinced that that reaction is good or bad - just different.
(This post was edited by slacklinejoe on Jul 22, 2008, 4:37 AM)
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shaun_the_conqueror
Jul 23, 2008, 9:16 PM
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Joe is absolutely right. 9/16" will stretch far more then 1". So when you have a threaded line the 1" is bearing the majority of the load. It will snap under the same conditions as if it wasn't threaded. If you break the 1" on a threaded line, the 9/16" will stretch to compensate for the load being forced upon it. The line will become much more slack. I would talk to SlacklineBuddha on the slackline.com forums. I'm pretty sure he has the actual numbers for when the 1" will break, how much tension will be loaded on the 9/16" then when the 9/16" will break.
Don't let threaded lines act as a false sense of security for you. The reason for using them is to prevent injury not to increase strength. What I mean by that is that it acts as primarily as a back up when highlining. If you're 1" fails (I haven't heard of this happening) it increases your odds of actually dying by provided another line for your leash to catch.
They are also great for long lowlines because they are easier to tension, and they help prevent flying gear if rigged properly, in the event of 1" failure.
I have not used a bonded line as Joe describes, but it makes sense to me that both lines would share the load "equally" if bartacked together. However as he also stated most people don't have the equipment, and I'm generally not a fan of bartacked lines due to the wear and tear the loop at a given end.
As far as Joe's arguments for why not to use a threaded line... I do not agree. Threaded lines are pretty damn easy to make and I can thread a 100' solo in less then 15 mins. It's all about technique, which granted does take a couple of tries to fine tune. Also if you properly bundle, butterfly, wrap, or whatever you do to store your line, you wont end up with twisted 9/16" inside the 1".
But aside from all of that, just remember threading DOES NOT increase strength.
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Buurin
Jul 31, 2008, 7:22 AM
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Whats this talk of threaded holding tension better & being easier to tension?
I dont get it.
I am using a primitive 3 biner system w/ line lockers. Perhaps you guys are talking about in a different type of system.
Thanks.
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slacklinejoe
Jul 31, 2008, 5:04 PM
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Buurin wrote: Whats this talk of threaded holding tension better & being easier to tension?
I'm in a miniority when I say that I don't feel it makes a big difference for me tensioning wise.
Let me explain first though:
First, with a typical line to reach 400 pounds of preload (tension) you need to stretch the line x many feet to reach that load.
If the system stretches more than standard webbing, you pull more feet out of the line, but you ended up having to pull the same pounds of tension on your end to get it tight.
If it has less stretch you pull less feet out of the line to get the same preload, but you still had to pull just as hard to get it there.
The extreme example would be pulling a chain tight enough to move a 300 lb block vs pulling on a stretchy dynamic rope. You still had to pull just as hard (300 lbs), but since the system stretched more you pulled more feet of rope to get the job done. Let me know if that doesn't make sense.
So, if you only care about how hard you pulled, it doesn't make a difference. But, if you care about how many feet your stretching the line, it does make a difference.
Due to the somewhat shared load on a threaded line, it stretches somewhat less. Your necessary pre-load on the line will be the same, but since it stretches a bit less some feel it's easier to get it tight.
Holding tension better, that's simply an elasticity issue. Since the 9/16" and 1" partly share the load it stretches a bit less in use.
Bonded lines on the other hand share the load well, so they stretch far less in use (my opinion, no research to back it up just yet). You still have to pull just has hard to reach the same pre-load though, but you pull less webbing through the system to do it.
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jynckx
Jul 31, 2008, 8:24 PM
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These "Bonded" lines, as you call them, are most likely weaker, and more prone to breaking than a threaded, or even a single line! Even though you are tightening both lines to the same tension, they will not be EXACTLY the same tension, due to slight differences in rigging, and the fact that the elasticity factor will not be exactly the same in each piece of webbing. What this means is that since the lines are bartacked together instead of using tape, and the lines have different tensions, there will be a force exerted on each bartack. So, at every bartack, you have created a weak point! Imagine a slackline with a knot tied in it every 6 feet. Definately weaker than a line with no knots in it. Also, to be a strong bartack, it would take perhaps 5-6 bartacks at each interval to be full strength. Most of the "bonded" lines i have seen only have 1 bar tack at each interval! DANGEROUS! you are creating a very weak point in your slackline every 6 feet! A "bonded" line that uses tape instead of bartacks would undoubtedly test to a higher breaking strength, because numerous weak points are NOT introduced with tape.
The most dangerous highline i have ever seen was a bonded one at the lost arrow spire. It was only 2 pieces of single 1" webbing, bartacked every 5 feet with only 1 bartack/interval! Then, they only tensioned one of the 2 lines. This means that the second line was pulled tight only by the bartacks from the tensioned line, which were only 1 bartack thick! Avoiding bartacks as much as possible is definately the way to go. Much simpler, easier, stronger, and cheaper!
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shaun_the_conqueror
Aug 1, 2008, 7:36 AM
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Did you ever break a bonded line during testing? If so what did it break at?
Edit: I totally misunderstood what you were talking about when you referred to bartacking two lines together. I thought you meant you bartacked to lines together to form a loop on one end then taped the lines together.
(This post was edited by shaun_the_conqueror on Aug 1, 2008, 7:43 AM)
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shaun_the_conqueror
Aug 1, 2008, 5:15 PM
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Well what are your non official results?
You're selling bonded lines that people will purchase to use for highlining? That's pretty ballsy 
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slacklinejoe
Aug 1, 2008, 6:45 PM
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shaun_the_conqueror wrote: Well what are your non official results? You're selling bonded lines that people will purchase to use for highlining?
Unofficial: Stronger than a knotted line of course ;)
Be patient, real results are worth the wait.
Two stitches that reduces line strength by 2% in different parts of the line don't equal a line that is reduced 4%.
Also, we only recommend them as a backup line, ideally minimally tensioned to go under your mainline - or as part of a lowline setup.
Selling webbing for highlining at all carrys the same risk (usually of human error), regardless of it being single stranded, threaded or bonded. Threaded often inspires more confidence in it than it should, single layers risk improper rigging or lack of backup entirely and bonded is no different, it has to be used properly as only part of a SRENE system.
Personally I can't say as I'm comfortable with the concept of a lot of things people do when they start using gear for things they don't fully understand. In my head, gri-gri's or an expansion bolts are the worst as human failure is usually the issue but it looks like the gear failed when the operator was at fault. One just has to hope that they read warnings, follow instructions or at least don't screw up enough to get someone hurt.
(This post was edited by slacklinejoe on Aug 1, 2008, 10:55 PM)
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jynckx
Aug 3, 2008, 5:13 PM
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So, your bonded line tests STRONGER than two single 1" lines taped together? Did you ever test that? If so, any ideas on why? It seems counterintuitive.
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slacklinejoe
Aug 3, 2008, 8:03 PM
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jynckx wrote: So, your bonded line tests STRONGER than two single 1" lines taped together?
Individual tensioning of two lines and then taping them together means different pre-loads, different points on their elasticity curve due to the different loads and all sorts of stuff you can't account for. If done perfectly right they will share the load probably within 10% of each other (a guess) but I don't think anyone could A) get them perfectly the same pre-load tension without measuring it very carefully and B) Account for all of the variables at work as then you have friction between the two lines, tape that allows some slippage, chances of different elasticity characteristics if they are off two different spools (especially if they are different colors) and all sorts of technical crap I couldn't hope to account for.
I'll tell you what I will do though, I'll tape up some lines side by side and send them in to our lab. I'll post how it stacks up in comparison to a single line, a threaded line and a bonded line. Keep in mind though, in a lab you'll be able to tension both the same much easier than when your rigging off the side of a clif. Also, due to turn around time, this could take a month or more to get the results back.
(This post was edited by slacklinejoe on Aug 3, 2008, 8:10 PM)
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jynckx
Aug 3, 2008, 9:38 PM
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slacklinejoe wrote: jynckx wrote: These "Bonded" lines, as you call them, are most likely weaker My industrial load tester has shown different results. It's obvious you haven't actually tested it so I'll let the rest of your post slide.
You said your results show differently, but what do your results show? your bonded line is stronger than a single line? or is your bonded line stronger than a threaded? what exactly is your bonded line stronger than? you quoted me on a fairly vague comment and said your test results show different, but you never said what your test results DO show.
im really not trying to instigate anything, im actually curious, since you are the only person i have heard of testing this.
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slacklinejoe
Aug 3, 2008, 9:45 PM
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My test so far imply that the breaking point of a bonded line is higher than that of a single unknotted line.
I haven't done comprehensive testing to compare it against anything else, yet.
I will however follow up on it and get some nice hard numbers for you to compare the different types of setups, it sounds like something I should be doing to give slackliners real data to make decisions off of rather than them just trusting what they've been taught to use.
(This post was edited by slacklinejoe on Aug 3, 2008, 9:46 PM)
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shaun_the_conqueror
Aug 4, 2008, 5:46 AM
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I'm very interested in the result of these as well! Make sure to let me know when you have them.
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