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How effective is clove hitching the rope to reduce shock load?


Original Post
nikhilm Mm · · San Francisco, CA · Joined Apr 2014 · Points: 15

On a recent single pitch climb, the belay was on a ledge. I girth hitched a sling to a tree as an anchor. The sling was _not_ going to be held taut, since the ledge was comfortable, and I didn't want to do a hanging belay. To avoid shock loading the dyneema [1], I tied in to the other end of the rope, and clove hitched the rope to the sling. The length of rope between my tie-in and the anchor was perhaps 3 feet. How effective is this small length of dynamic rope in lowering the shock load? That is, was using the rope actually effective in making the anchor safer?

[1]: dmmclimbing.com/knowledge/s…

FrankPS · · Atascadero, CA · Joined Nov 2009 · Points: 275

Where would the shock-loading come from? Your second falling, then you as belayer coming tight on the anchor? If so, I wouldn't worry about it. The Dyneema will be adequately strong, regardless of the rope in the system.

Edit: With this scenario, you must be belaying directly off your harness?

Brian L. · · Unknown Hometown · Joined Feb 2016 · Points: 90

Short answer: 3ft of rope should be fine. IIRC thats the legth that qas used to test anchors in John Longs book.

Longer answer: ideally you tie in to avoid any fall potential. I'm guessing your concerned abput being pulled off, or slipping off the edge? So what you should have done IMO would be to reduce the length of your anchor so ypu can't fall off the edge. Semi-taut per-say. You don't need to be hanging, but you don't need a bunch of slack either.

FrankPS · · Atascadero, CA · Joined Nov 2009 · Points: 275

One more thing - it's suboptimal to have slack in your anchor. You don't have to be hanging on it, but you should be able to lean away from it, or otherwise take the slack out. Is there a horn on the ledge you can sling, or cracks you can fit cams or nuts in?

If it's low-angle terrain, maybe you can just use your stance to prevent getting yanked against the anchor, but try to get the slack out.

patto · · Unknown Hometown · Joined Jul 2012 · Points: 25

Who cares about the clove hitch. You are on dynamic rope. If you got jerked or fell then the shock would be equivalent to the fall factor. Which could be up to 2, but likely well below 1.

So yeah dynamic rope is great at absorbing impact cause that is what it is designed for.

nikhilm Mm · · San Francisco, CA · Joined Apr 2014 · Points: 15

Thanks! I was belaying off my harness, so my body already introduced some dynamic-ness in the overall system. What I was concerned about is my body/hips suffering due to the shock of suddenly being brought to a stop by dyneema. Since the elongation and energy absorption (not sure if these are the right technical terms) depends on the length of rope out vs the length of rope I fall, in this case it would be a factor 1 fall on about 3 feet or rope. My main concern is if this is enough to reduce the impact on my body.

Firestone · · California · Joined Nov 2015 · Points: 449

I remember reading that rope stretch doesn't do much until something more like 3-5m so more like fifteen feet.

In your case the catch might be harder than normal if the leader fell but I would have just used a locker to lock the sling directly to my belay loop. Easier to escape the system that way. All the messing around with ropes defeats the KISS mantra.

patto · · Unknown Hometown · Joined Jul 2012 · Points: 25
Firestone wrote:I remember reading that rope stretch doesn't do much until something more like 3-5m so more like fifteen feet.
Which is BS.

Let's stick with the facts and realities of pretty simply physics.

Firestone wrote:All the messing around with ropes defeats the KISS mantra.
You serious!? Using the climbing rope is almost as simple as it gets. It is also very fast. Sling around tree. Clover hitch on a locker and you are safe and ready to give a harness belay. KISS.
David Coley · · UK · Joined Oct 2013 · Points: 70
nikhilm wrote:On a recent single pitch climb, the belay was on a ledge. I girth hitched a sling to a tree as an anchor. The sling was _not_ going to be held taut, since the ledge was comfortable, and I didn't want to do a hanging belay. To avoid shock loading the dyneema [1], I tied in to the other end of the rope, and clove hitched the rope to the sling. The length of rope between my tie-in and the anchor was perhaps 3 feet. How effective is this small length of dynamic rope in lowering the shock load? That is, was using the rope actually effective in making the anchor safer? [1]: dmmclimbing.com/knowledge/s…
Reading what you wrote, the 3 foot of rope would have made little difference to the force on the tree, which is what I assume you mean by, "making the anchor safe".

I assume you are belaying off the harness. If you had removed the 3ft of rope and clipped direct to the sling, the rope to the climber would have been 3ft longer at any point he/she might have fallen, and this would have done much the same as the 3ft of rope between you and the tree.

Not sure why it wasn't taut though, hopefully there was no slack.

If the ledge was good and not sloping, and you didn't let slack to the climber build up, it is all unlikely to make any difference, as no force would have gone to the tree as the friction provided by the edge of the cliff and your bottom on the ledge would be far greater than the force from your second.
David Coley · · UK · Joined Oct 2013 · Points: 70
nikhilm wrote:....... in this case it would be a factor 1 fall on about 3 feet or rope. My main concern is if this is enough to reduce the impact on my body.
Can you explain how you get these numbers? Are you falling, or the second?
patto · · Unknown Hometown · Joined Jul 2012 · Points: 25
nikhilm wrote:Thanks! I was belaying off my harness, so my body already introduced some dynamic-ness in the overall system. What I was concerned about is my body/hips suffering due to the shock of suddenly being brought to a stop by dyneema. Since the elongation and energy absorption (not sure if these are the right technical terms) depends on the length of rope out vs the length of rope I fall, in this case it would be a factor 1 fall on about 3 feet or rope. My main concern is if this is enough to reduce the impact on my body.
If you set it up correctly you shouldn't be having ANY slack. I regularly belay off my harness in similar circumstances included belay hang dogging noobs... Shorten the tether and ensure most of the load goes onto the anchor.

But if for some reason you don't do this then you could end up with a fall factor of <1 onto the anchor. Which will jerk you but will still be less than a lead fall of equivalent FF.

David Coley wrote: Reading what you wrote, the 3 foot of rope would have made little difference to the force on the tree
If we are talking about a belayer shock loading the anchor then 3 feet of dynamic rope will certainly make a BIG difference to the force on the tree.
(Though like I pointed out, you really should position yourself so a seconder fall won't jerk you from a stance.)
Optimistic · · New Paltz · Joined Aug 2007 · Points: 300
Firestone wrote:I remember reading that rope stretch doesn't do much until something more like 3-5m so more like fifteen feet.
As patto alluded to, this is incorrect. Just using a nylon sling instead of Dyneema to connect the belayer to the anchor has been shown (by Long et al) to significantly reduce impact forces. 3 feet of climbing rope would do even more. But as people are saying there are are a lot of other factors to consider, especially adding unnecessary extension to the system. Long lays out his data pretty clearly in "Climbing Anchors" although I think that book has now been incorporated into other books (Learn to Rock Climb might be the title?).
Guideline #1: Don't be a jerk.

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