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freshblade
Feb 19, 2003, 10:08 PM
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i have a 5.5mm dyneema cordalette. I read in a forum that it loses a lot of strength when tied in a figure of eight. Now is that when you tie the ends independently like ears? or does it refer to the Hero Loop/Central point? Also it said that it was prone to weakening due to repeated flexing. does this mean it is weakening even when stored (like a wound willy size stick) or just when loaded around biner radius's? If its durability is in question- how long can i expect to be safely using it for? I climb occasional weekends. Sadly not every weekend. Cheers for the help oh Cordy Wise Men/Women Out
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alpnclmbr1
Feb 19, 2003, 10:29 PM
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The test I saw as far as a figure eight losing strength were refering to the independent end loop not the central power point knot. as far as the rest, unknown. d
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addiroids
Feb 19, 2003, 10:32 PM
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If you use a retraced figure 8 to join the ends rather than a triple fisherman's that might weaken it. You should know the answer to the one of the figure 8 tails -vs- the figure 8 central point. The radius of the turn is what weakens a knot, and the central point is a really big knot with big radii so it is not really weak there. Basically that thing is a strong bastard, and if you just do a triple fishermans to join the ends (keep an eye on those 3" tails) and pull it down into a figure 8 central point, there is nothing to worry about. TRADitionally yours, Cali Dirtbag
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therealbovine
Feb 19, 2003, 10:36 PM
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I think the "knot makes it week" point is valid for all webbing, rope, and cordage. Any time you tie a knot in these materials, you loose strength. For example; If your climbing rope holds 100 lbs, when you tie a figure eight knot in it (like tying into climb) you reduce the overall strength of the rope by 80%, thus reducing the strength to 80 lbs. I don't think the "knot" issue was related to tying the cordalette any other way then normal. Any bend in the material is a weak point, just like a knot (actually, thats why knots are a weak point). As far as other issues with age, watch the sheath. If it looks pretty worn (fuzzy), then retire it. Its cheap to replace! When you have gear for extended periods of time, dirt and chalk will work its way into the core of the cord/rope/web. This then acts as a "sandpaper" effect on the core, making it weak over time. If you try to bend the cord, it should stay curved (not actually bend into a 45 degree angle) if it does actaully bend and is no longer rounded at any point in its length, the core is damaged. Toss it. Just use your best judgment. Good luck!
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flamer
Feb 19, 2003, 11:00 PM
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The problem with your cord has to due with the materials used to construct it. Any cord with kevlar type material will weaken over time- with alot of bending. The reason for this is that the fibers themselves are very coarse and when you bend them they rub on each other. Over time this will weaken the overall strength of the cord. They are making cord now in 5.5mm diameters that use a different material, and it's less abrasive. I think they call it hebron? Supposedly it's just as strong. What has already been said about knots is correct, so there's no point in saying it again. josh
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philbox
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Feb 20, 2003, 12:46 AM
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Okay, dunno where I read this but from memory, If you tie a knot in any rope/cord and leave the knot in it then that knot will not continue to weaken the rope/cord except for the initial strength reduction inherent in all knots. If you were to undo the knot and straighten the rope/cord out then there is a weakness in the rope/cord at that point. I`m talking about knots that are long term weighted knots and not knots that are undone after each loading. For instance a tied cows tail if you were to untie the girth hitch clip in loop then that would then be a weak point. A knot once untied can never be tied back up in exactly the same manner thus the bends that the rope/cord have become used to are in different locations or worse are flipped over and lie 180 degrees from where they want to lie. Rule of thumb is untie all knots after use or leave them tied up permanently. A permanent knot untied develops a weakness in the line that is hard to inspect. ...Phil...
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rrrADAM
Feb 20, 2003, 7:09 PM
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Loss of strength for each type of knot: Figure 8 = 15% loss Double Bowline = 35% loss Square Knot = 45% loss When was the last time you took a "whipper" on your ANCHOR ??? So why would you even worry ??? The vast majority of climbers tie in with the 8 as it creates the least amount of degradation to the strength of the line. A Figure 8 is more than strong enough for use in a cordellete, hell I use a simple overhand since it takes less rope, and I use 7mm.
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fitz
Feb 25, 2003, 11:56 PM
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Ah, but when you DO take a whipper on the anchor (as in *almost* made it to that bolt up yonder...) the fall factor is big... ;) Still, I'm with RRR. The knot is not (pun intended) the big issue. The main concern raised about some of the super-strong 5.5mm cordage is that it is not really meant for the repeated flexing, and this shows in practical strength tests. Like RRR I use 7mm perlonl. It is theoretically less strong than spectra, etc., but strong enough, very durable, and cheap. -jjf
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onamission116
Feb 26, 2003, 2:30 PM
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As far as the strength goes, tie a double or triple f-man's knot like everyone says with an 8 at the power point and you should be all right. As far as how long it will last, I read that nylon slings are generally good for about 100 field days, since sunlight deteriorates it over time, so I suspect that cords will generally last about that long. Keep and eye on it and retire it if you have any doubts Cheers, Matt
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talons05
Feb 26, 2003, 2:42 PM
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The loss in strength is referring to an 8 tied at each end, although who would use this setup anyway? As far as strength loss due to flex, I'm not quite sure what that's referring to. Length of life of a cordellete depends (obviously) on what kind of use it gets. However, the 100 day rule is a good one to apply to most cordellete. BUT - check out the tech cord that has a Kevlar core. These last much longer, and are not sensitive to UV. A.W.
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fishypete
Feb 26, 2003, 3:10 PM
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OK, there are some VASTLY OVERSIMPLIFIED suggestions that have been made above (e.g. Phil and Adam) and even some downright fallacies (e.g. Talon, kevlar is one of the most UV sensitive fibres around!! Technora, a similar fibre, was developed specifically to combat this weakness). There is absolutly no way blanket statements can be made about the reduction in strength certain knots induce - there are MASSIVE variations between the different materials. There are a large number of factors to consider when investigating coredelletes - including weight, flexibility, UV resistance, knot-holding ability, etc etc. The list goes on and on. I am not going into details here, because it would take an hour. Instead, I will offer you a link to a study that was completed a few years ago, which gives REAL DATA about the characteristics of a group of the more commonly available rope materials. In summary, the report clearly shows that although most of the "new-age" fibres (e.g. kevlar, specra etc) are much stronger than traditional nylon, they are SIGNIFICANTLY weaker following knotting, or repeated flexing. Traditional nylon was comparatively unchanged in the tests when compared with the new materials. BOTTOM LINE: Nylon is probably still the best bet - despite the amazing strength of the new comers. To find the article, go to www.fishproducts.com click on "tech weenie", then "Rope Stuff" then scroll to the very bottom to find the article "Comparative Testing of High Strength Cord" Cut through the wives-tales, go straight to the data. Cheers Fishy.
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fitz
Feb 26, 2003, 4:30 PM
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Fishypete, My recollection was that Technora's main objective was to address Kevlar's self-abrasion problems. In body armour and sailing some manufacturers have tried combining aramids and polyethylene materials (ex. combining Kevlar and Spectra) to address the same problem. The Tom Moyer study, which you link to on your site (and which can be directly accessed, along with the actual test data at: http://www.xmission.com/~tmoyer/testing/ ) is well worth reading. But it is still a single study with limited samplings, and involved a manufacturer of one of the tested materials. Even though the results reinforce my own recommendations earlier in this thread, it is always dangerous to stretch a single study or experiment. Remember that in Moyer's practical cordelette test, all but one of the materials exceeded a UIAA 'max' fall (and I think that the odd ball was close). This seems pretty well substantiated by accident reports as well. We see some melting and knot slippage with materials like spectra, and we see some cutting on sharp edges but impact failure with cord is extremely rare. Like flying a small airplane, in climbing it is still the brain farts, not equipment, that is most likely to kill you. -jjf
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fishypete
Feb 27, 2003, 12:09 PM
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Hi Fitz, Thanks for the direct link! It was definitely a pain to fiddle around in Fish's website for the article. You make good points. I would just like to add a couple of clarifications: 1) Personally I dont have any concrete info about what the primary goal of Technora's manufactuers was - I only know that both the self-abrasion and UV resistance were key weaknesses to be improved apon, and that even a black version of Technora was developed specifically to offer better UV resistance. I am happy to defer to your information. My personal exposure to this field was primarily from a sailing manufacturers viewpoint, and the primary weaknesss I had experienced in Kevlar was substantial UV degradation, as long as sheaves of an appropriate radius (and profile!) were used in all pulleys. 2) I agree that this is just one study, however it does use reasonable replication for most tests, and I believe it is sufficient to illustrate the differences between the materials (especially given some of the large decreases in strength that were recorded). It is certainly a better source of info in my opinion than the many "feelings" that are often expressed on this topic. I dont believe that having Chris Harmston as one of the authors would have distorted the facts - in many independent situations he has shown himself to be a knowledgable, unbiased reporter. 3) Excellent point about "brain farts" killing you, not equipment. I couldn't agree more. My aim was only to illustrate that newer cords are not necessarily a better bet (despite their much publicized high tensile strength), and to provide some more solid info to illustrate the point. Personally I believe that people dropping down to 5 mm under the pretense of "new high strength cords" is approaching the danger limit, especially when considering the abrasion problems, and strength reductions when knotting some of these fibres. I dont think there is enough understanding of the weaknesses of these fibres in the climbing community, and think that even a single, replicated study is of infinitely better use to address this problem than large quantities of unsubstantiated or oversimplified offerings. Cheers Pete.
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theooze
Feb 27, 2003, 4:45 PM
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Good job, gentlemen. Bottom line, why risk it? Perlon has a better feel anyway. IMO, 6mm is fine for general cragging, so it's not even much bulkier.
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crackwhore
Feb 27, 2003, 5:24 PM
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unless you are using shoestring, the cordage used in a properly equalized anchor will rarely be the "weakest link" in the belay chain.
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bandycoot
Feb 27, 2003, 5:51 PM
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I've also heard that cordelette (kevlar) loses significant strength over time. Look at it this way. It holds roughly 25kN new (5000lbs+) When you have a 3 point anchor, there are three loops to distribute the force. That means 6 thicknesses of the cord... So if the thing weakens to 10% of its original strength then it will still hold 500 * 6 = 3000 lbs and the rope will break first... That always makes me feel safe. Even if I'm off somewhere by a factor or 2, or even 5 for gods sake, you're cord is NOT going to fail you! The 8 thingy... Some people tie an 8 in each end of a 12' piece of cord. They clip the two ends into a piece each, and the middle into the third point of an anchor and equalize the two loops coming down. It has been tested (results on some website link on another thread about cordelette) and shown that in this case the 8 REALLY reduces the strength of the cord. Something like 45%. This may be due to the small diameter of the cord, and thus small radius for that knot, as mentioned above. Don't remember the exact figure, but it was enough to keep me from trying it. Do a search for "cordelette" in the forums. There is a REALLY good (but long) thread. Pretty much, if you take about 18-20' and tie it with a triple fisherman's knot to close the loop, equalize and tie an 8 above the power point your SET. No worries. If you get fancy and start deviating, you can lose strength quickly. If that bothers you don't do it. If it doesn't you can save weight in some ways.... Josh
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