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Re: [el_layclimber] tying into a belay anchor on a multipitch route:
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rgold
Dec 16, 2007, 2:58 AM
Views: 18964
Registered: Dec 3, 2002
Posts: 1804
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The Lyons tests were slow-pull tests and suggested that, under these conditions, clove hitches do not slip in dynamic rope but may slip in low-stretch ropes. Because of this, they shouldn't be used in static ropes without solid backups.
Some years ago Adam Fox conducted or had conducted for him tests that concluded the clove hitch slipped around 1000 lbf. When asked repeatedly on this site for data backing up his claim that not only these tests, but many others confirmed this result, he was unable to provide either data or references, so it is hard to know how reliable that information is.
Sterlingjim conducted drop tests with dynamic rope and got different results from the Lyons slow-pull tests. The post is over at NE Climbs. I think it was Knudenoggin who pointed it out to me.
When the clove hitch was the knot used to attach the rope to the dropped weight, it slipped completely and untied. When the clove hitch was used at the other end in the position it would be in an anchor, it held 5 UIAA+ falls before the test was stopped.
Here is a relevant excerpt from that post:
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"First three tests performed on same sample of 10.2mm dynamic rope. All knots and or hitches were untied and retied for each test. Rope and knots pretensioned as per UIAA 101 (loaded with 80kg for 1 min). For the sake of simplicity the clove hitch was tied to the mass in place of the usual figure of 8 or overhand follow through.
First test: Clove hitch with 12cm tail and no backup. 80kg mass, fall factor 1.71, peak impact force 4,8kN. Hitch slipped completely, bye bye.
Second test: Clove hitch with 20cm tail and no backup. 80kg mass, fall factor 1.71, peak impact force 5.05kN. Hitch slipped completely, mass was released and fell to ground, adios.
Third test: Clove hitch with 3cm to double overhand backup to limit slippage 80kg mass, fall factor 1.71, peak impact force 9.59kN. Hitch held, backup knot jammed to clove hitch, hitch welded (literally) and not able to untie.
Fourth test: I tried to simulate a more realistic climbing scenario where the leader would take a high fall factor of 1.81kN (not all that realistic but perhaps worst case scenario). Rope was attached to the mass with figure of 8 then to a clove hitch to the frame and then a figure of 8 to another part of the frame . Sounds weird I know but trust me it simulates what is being discussed in this thread pretty well. The force was not falling directly onto the clove hitch but was pretty damn close. I also used a fresh rope sample for this one. The results: 80Kg mass, fall factor 1.81, peak impact force 8.77kN. Hitch held 5 falls before I stopped the test. Judging from the impact forces on the 4th and 5th drops I would predict the rope to fail within the next one to three drops."
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It isn't entirely clear to me what to make of these results, other than the fact that you definitely don't want to tie in with the rope clove-hitched without backup to a locker on your harness, a practice that has not yet shown signs of popularity. (You don't want to use this way with a backup either, if you want to untie it after a major fall.) In the anchor configuration test, the clove hitch did not slip. Nonetheless, these tests do show that clove hitches can slip under extreme dynamic loading.
Personally, I almost never use anchors with master points, so I always have two to four clove hitches between me and oblivion, and frankly, I ain't worried the knots going. If you use cordelettes or other master-point creating systems, it is certainly easy enough to clip a figure-eight backup into the master point (I don't see how this negates the utility of the clove hitch), or perhaps even more simply just tie a second clove hitch in series with the first to one of the anchor pieces. Yet another option, if you don't mind doubling the length of rope used for tying in, is to clip the anchor rope to the master point but then clove hitch it back to the belay loop and climbing tie-in loop at the harness. This way the clove hitch only gets about half the total impact.
Personally, I've never had any trouble untying a clove hitch in forty years of use in climbing situations, including once when it had to bear the brunt of a factor-2 fall directly onto the belay (no slippage there either, by the way, at least none that was noticeable afterwards). Remember that the figure-8 is already notorious for being hard to untie after being loaded.
The clove hitch is not a "no-brainer" knot. (But perhaps there are no "no-brainer knots...) There are two ways to orient it on the biner relative to the load strand, one of which puts the load strand a distance out from the spine of the carabiner and so will contribute to a carabiner breaking strength below the official rating. Users of the clove hitch should learn to automatically tie it the right way every time.
(This post was edited by rgold on Dec 16, 2007, 6:10 PM)
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Post edited by rgold
() on Dec 16, 2007, 6:10 PM: Spelling correction
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