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enkoopa
Jun 30, 2011, 5:01 AM
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First post, yee haw.
Alrighty, I have a question of the diameter of static rope for setting a top rope anchor.
I've got Climbing Anchors by Craig Luebben. In their simple 2 tree TR anchor, they are using 10mm static.
I know some locals who use 7mm static.
I've been reading through a lot of the forums (and will continue to) and dug this one up of someone using 6mm static and nobody seemed to have any concerns.
http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2416111
My thoughts - Mammut 7mm is rated at 2200lbs. I do recall reading lead falls can get up to 7-10kN, which would put this rope to it's max and beyond. Top rope would be a lower impact, unless you had a careless belay. Assuming a V angle of up to 90 degrees (yes, you want it much lower), you'd multiply by 1.5, so your limit would be around a 6kN fall.
Actually, after just typing this out, I realize.. you would have each strand of your V going to your trees taking half the load, making your max load around 12kN. That might be the answer right there?
Anyways, feedback appreciated!
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herites
Jun 30, 2011, 7:21 AM
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Whizzkid
Jun 30, 2011, 8:06 AM
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herites wrote: Don't buy a static rope, you can only TR it with. Buy a 10mm+ (and the one which has the most mass coming from the sheath instead of the core) dynamic rope, you can use it to lead when you're bored with TR. Also, the rope has to get up there somehow, and unless every route you climb is accesible from the top, someone has to lead it to set up a TR.
reading comprehension: fail!
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herites
Jun 30, 2011, 9:51 AM
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True, I was just waking up ;) Didn't notice the anchor part, thought he wants to climb with a static rope.
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gimmeslack
Jun 30, 2011, 11:57 AM
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I won't try to answer "can you" but instead, ask "why bother?".
If I'm TR'ing, I want something burly enough that I don't have to worry about possibility of anchor getting cut, damaged, or margins of safety. At the places where I TR, I'm more worried about integrity of anchor/cord than I am about load ratings.
I do often use 7mm cordelette to build 3x anchor, and I if necessary with 2x anchors - though that's more typically a pair of bolts, and then two slings suffice. But if going off trees set back from edge, I use a length of 8 or 9mm static.
One suggestion: make sure you watch the path of the anchor cordage as it goes over the edge. It's not uncommon for folks to wander laterally on climbs when TR'ing and it can drag your power point across/into unforseen configurations.
(This post was edited by gimmeslack on Jun 30, 2011, 12:03 PM)
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enkoopa
Jun 30, 2011, 12:05 PM
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Also a good point, might as well just buy 8mm instead of 7mm.
I'm heading somewhere new where I'm not sure how far the trees are. To save weight, I might use some 1" tubular webbing instead. A 7mm cordelette and a triple anchor... some serious length of rope needed!
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Whizzkid
Jun 30, 2011, 12:29 PM
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Regardless of the gear you decide to buy and use (30m 9mm static rope in my case) make sure to properly pad edges!
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enkoopa
Jun 30, 2011, 1:07 PM
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Whizzkid wrote: Regardless of the gear you decide to buy and use (30m 9mm static rope in my case) make sure to properly pad edges!
Thanks! Actually, my girlfriend was throwing out some old bathmats last night while I was going through all my gear.. they're bright pink and orange.. she asks before throwing them out, "You sure you don't want these?".. "Yeah I'm sure.. throw them.. wwwait. Yes.. yes I do want one!" :)
I took the pink one. She was confused. 
Anyways, this is what I've picked up in hopes that I can tackle whatever is present. From the reading and people I've talked to, for the most part there should be bolted anchors to setup the TR. I'm not going to drive 2 hours to find out they look sketchy and drive home. So this is in the toolbox which hopefully let's me work out something
- 30ft 1" tubular nylon webbing
- 30ft 7mm static
- 3 shoulder length nylon slings
- 2 double length dyneema slings
- quickdraws
Here's my planning from best to worst.
1) Bolts are well placed: replace the bent gates on a pair of quickdraws with locking biners and I'm done.
2) Bolts are not well placed : use two shoulder length slings to keep the V-angle nice.
3) Bolts are on top (unlikely) : shoulder length slings, throw down the rug over the edge, use some 7mm cord to keep the rug from moving if it seems questionable.
4) No bolts / questionable bolts : Setup TR anchor using trees, 2 if possible. Girth hitch the trees with slings, locking biner. Clove hitch the cord to those biners. Cord gets two figure 8's on a bite, locker through each for the master point.
4b) If the trees are a lot further back, I can use some of the 1" nylon webbing with a water knot.
5) No bolts, no trees, no rocks. Go home. 
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Lbrombach
Jun 30, 2011, 1:19 PM
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6mm minimum. I have a 6mm cordalette loop and a 7 mm one. Depending on where I'm at, I either just use the cordalette and bolted anchors, or I use 1inch webbing to get close then the cordalette to quickly equalize.
I like the 6mm as it's easier to rack and work with, but do feel slightly better with the 7. (and the 6 is a prettier color). That said, I don't hesitate to climb on the 6mm...there are three strands after all the odds of all of them failing has to be fairly microscopic if I'm visually inspecting it. (has anyone EVER even heard of it happening?) I pad the edges and anything that might rub with carpet scrap regardless.
It wouldn't be wrong to drag 50ft of 9 or 10 mm cord around, but I don't want to haul it.
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enkoopa
Jun 30, 2011, 2:21 PM
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Lbrombach wrote: I don't hesitate to climb on the 6mm...there are three strands after all ...
What do you mean by three strands? Do you mean inside the actual cord? Or do you mean your anchor setup has three anchor points?
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j_ung
Jun 30, 2011, 2:37 PM
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The primary weakness of your 7mm isn't it's strength. It's the relatively low resistance to abrasion. Add the fact that you won't be right next to your TR anchors to watch them throughout the day and you have a recipe for disaster.
I think you're on the right track, namely that that you should add a dash of padding and a cup of redundancy to the recipe. Personally, I start with a hearty 10mm, then cook 'em redundant and then pour on the padding. Yummy. I do, however, use 7mm when building my TR anchors on bolts for light and fast fare.
Holy metaphor, Batman.
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enkoopa
Jun 30, 2011, 2:45 PM
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j_ung wrote: I do, however, use 7mm when building my TR anchors on bolts for light and fast fare.
Nice metaphor indeed!
What's your preferred rigging for two bolts?
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j_ung
Jun 30, 2011, 3:15 PM
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Glad you like it!
I prefer two quickdraws reversed and opposed if I'm out for a personal day. I use a cord if I'm guiding.
Edit: specifically, I use a pre-distributed tie-off like the one in the thread to which you linked.
Re-edit: the 10mm comes out when I'm anchoring to trees or boulders.
(This post was edited by j_ung on Jun 30, 2011, 3:18 PM)
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trenchdigger
Jun 30, 2011, 4:01 PM
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Here's a simple answer:
7mm min diameter when tied in a loop as a "cordelette"
9mm or 3/8" minimum diameter when used single-strandedly (is that a word?)
Beyond these limits you'll generally start sacrificing overall anchor strength because legs of the anchor system may be weaker than the piece they're connected to.
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Lbrombach
Jun 30, 2011, 4:08 PM
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enkoopa wrote: Lbrombach wrote: I don't hesitate to climb on the 6mm...there are three strands after all ... What do you mean by three strands? Do you mean inside the actual cord? Or do you mean your anchor setup has three anchor points?
I mean the setup has three anchor points, and if any one loop were to fail, there are two more to catch the climber. In reality, sometimes there are only two anchors if they are bomber, and I just have two of the loops/strands of cordelette going to one biner, and the third strand on it's own.
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enkoopa
Jun 30, 2011, 4:41 PM
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Thanks for all the replies everyone.
So if the trees are further back, I can use 1" webbing to get closer, and then make sure to use the 7m so that any loads are shared on two strands?
Keep chiming in if there's more. In the meantime, you can expect a new post soon with a "critique my anchors".
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Lbrombach
Jun 30, 2011, 5:01 PM
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yup. you can do it all with webbing too, but equalizing is more of a bitch.
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enkoopa
Jun 30, 2011, 8:49 PM
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Thanks again everyone. I said screw it, went and bought 10m (30ft) of 11m static. They didn't have 9 or 10 unfortunately. So.. welcome to bomber-ville.
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puravida9539
Jul 2, 2011, 4:36 PM
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I just use webbing. It is more difficult to equalize than cordelette but I am anchoring off trees a lot and I like the webbing for that.
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