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Joining ropes of differing diameters for rapping
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When rapping on two ropes, is there a point where the difference in diameter of the ropes is great enough that the EDK is no longer the preferred knot? |
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Ive never done tests on say 4mm joined with a 10.2, 11mm, etc BUT I have experienced more than a few times joining a 6mm tag line to a 10.2 and have had zero issues. My experience says for simple, straight forward situations (which was my experience, cant speak for abnormal conditions) a 6mm and a 10+ is accecptable. |
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I've done this using a 7mm tag line to a 10mm rope. I usually tie a keeper knot with the smaller line around the larger to guard against the knot inverting. |
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Never had any issues, providing (obvious it would seem) they are the same length. We done it with 10.2, and either 9, or an 11. We've always used the double-grapevine, just use the smaller diameter as your "pull" side. |
The Cowardly Noob wrote:When rapping on two ropes, is there a point where the difference in diameter of the ropes is great enough that the EDK is no longer the preferred knot? For example, are you comfortable with joining a 10mm and an 8mm with an EDK for rapping?A couple old threads on the topic. mountainproject.com/v/skinn… mountainproject.com/v/joini… |
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I normally use dynamic ropes ranging from 9.4 - 10.5mm with 6mm cordelette and an EDK. I pull-tested 6mm with 11mm before, a few years back, but I cant find the exact testing data so I will do it again today since this seems to be a reoccurring question. |
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We made at least 15 rappels at red rock a couple weekends ago using a 60mm 10.2 and one of a pair of 8mm BD doubles. Used the EDK every time without any noticeable movement (rolling) in the knot. After having the thin rope snag a few times on the first day, we pulled the double every time when rapping Crimson Chrysalis. This required untying and re-tying the knot at each rap, but that's part of the beauty of the EDK...it's easy to tie and untie. And it doesn't snag. Go for it. Just tie it tight and dress it pretty and put a stopper in each tail. |
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Chris D said: put a stopper in each tail. |
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Make sure to back it up with a overhand on a bight with a Biner through it if you're rapping on the fat strand only. There was a tragic accident where the two edk's pulled through the rap rings that were much smaller than the knots. Oh found it |
bearbreeder wrote:http://blackdiamondequipment.com/en/qc-lab-what-is-the-best-rappel-knot.html thats all there is to it folks ;)It appears that chart is in reference to ropes of the same diameter. The OP was asking about ropes of different diameters. |
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bear has data for everything. I'm sure he'll pull through. |
20 kN wrote: It appears that chart is in reference to ropes of the same diameter. The OP was asking about ropes of different diameters.MPers needs glasses ... as an AZN it fortunate that my coke bottle spectacles are top notch to compensate for you folks ;) |
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Thanks for the responses. |
The Cowardly Noob wrote:Thanks for the responses. Regarding bearbreader's chart, there might be a difference between strength of the knot and "creepability" of the knot. And there might not.the last point on the chart i posted lists the slip values for the 10.2/8mm ... roughly 8-9 KN here what the DAV says ... basically its not the knot strength on 8mm->10mm you need to worry about Der Knoten wird an allen vier Strängen festgezogen. Die Seilenden sollten mindestens 20-25 cm betragen (ca. Handlänge). Deutlich längere Seilenden bergen die Gefahr, dass man sich mit dem Abseilgerät versehentlich in die Enden einhängt. Beim Verbinden ungleich dicker Seilstücke (z.B. 5 mm und 10 mm i) zum Abseilen bestehen keine Bedenken bezüglich der Knotenfestigkeit. Erstaunlicherweise rutschten die dünnen Reepschnüre (5 und 6 mm) bei den durchgeführten Reißversuchen nicht aus dem Knoten. Die Bruchwerte lagen über denen der dünnen Reepschnur mit demselben Knoten (vgl. 2.4), da der Kantenradius beim Verbinden mit einem Einfachseil wesentlich günstiger ist. Die ermittelten Festigkeiten liegen weit über den beim Abseilen auftretenden Kräften. Viel bedenklicher ist das Pendeln über scharfe Kanten für den dünnen Reepschnurstrang. Solche Pendelbelastungen sollten vermieden werden. ------ The knot is connected to all four strands tightened. The cable ends should be at least 20-25 cm (approx. hand length). Significantly longer rope ends run the risk of that you are with the descender accidentally hangs in the ends. When connecting different pieces of thick rope (e.g., 5 mm and 10 mm i) for rappelling There are no concerns regarding the Knot strength. Astonishingly, slipped the thin cords (5 and 6 mm) in the conducted tensile tests not from the knot. the Break values were higher than those of the thin Cord with the same knot (see 2.4), as the radius of the joining edge significantly with a single rope is less. The strengths identified occurring far above the abseiling Forces. Is much concern commuting over sharp edges for thin Reepschnurstrang. Such oscillating loads should be avoided.  ;) |
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As promised, the testing. 11mm and 6mm joined via an EDK: mountainproject.com/v/edk-d… |
20 kN wrote:As promised, the testing. 11mm and 6mm joined via an EDKThanks |
