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doxob
Nov 11, 2005, 10:30 PM
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So I've bought some webbing and I'm learning about setting anchors for toproping. I've cut the webbing into appropriate lengths and I'm confident in my water knots. I'd like to know if it's better to tie my loop of webbing around a tree with a new knot every time OR leave permanent knots in the webbing, stick one end of the webbing around the tree, and pull the longer end through the loop that is created. Obviously, the latter method can be pretty convienent, but is it just as safe? Is there any reason why a knot shouldn't be left in webbing for an extended period of time? Is a permanent knot in webbing the equivalent of a sewn sling? And if so, are slings used in the manner I described?
Thanks for any advice I can get. I'll try not to get upset about the flaming that a beginner's question is likely to instigate.
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scottquig
Nov 11, 2005, 10:38 PM
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I suppose you do it either way, but leaving the sling tied is definitely going to save time when setting up the anchor. Yes, sewn slings are used this way. A loop of webbing (knotted) works exactly the same as a sewn sling, except most sewn slings are full strength (22 kN), while the knot can decrease the rope's strength by up to 1/2, by some estimates. Not a concern at all for building toprope anchors, probably not an issue for multipitch. Once you climb more, you may want to switch to sewn spectra or nylon slings to decrease the bulk and weight on your harness. Any of these options should work fine.
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chernabog
Nov 11, 2005, 10:44 PM
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I would not call a water knot "permanent" since they can work loose.
Either way, leave a good tail length and check the knot(s) regularly.
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cracklover
Nov 11, 2005, 10:58 PM
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Leave "permanent" knots in the webbing. However, you should have several inches of tail on each side of the water knot, and you should check the knots each time you climb, as water knots have been shown to "creep" over time with repeated loading.
Cheers,
GO
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srwings
Nov 12, 2005, 1:00 AM
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I've always wondered about leaving permanent knots in my top rope anchors (static rope & webbing) too. I figured it would probably be safer just to untie the knots after every outing in order to make it easier to inspect my anchor ropes & webbing.
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qtm
Nov 14, 2005, 6:46 PM
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What you are doing is called "girth hitching", and girth hitching a sling can reduce the strength of the webbing by 30%, separate from the weakness created by the knot itself. So by girth hitching the tree instead of untying the webbing and tying it around the tree, you're introducing a huge weakness into your system. Of course, 1" tubular webbing is pretty strong stuff. Even if it's weakened by 30%, it's still very strong, 2800lbs or 12KN for new webbing.
But if it's your anchor, why intentionally weaken the system by 30% if it only takes you an extra 30 seconds to tie a knot?
Now, if you've been climbing all day and need to rap down, you're dehydrated, half-frozen, it's dark, and you can't think straight, retying the water knot might not be "safer" than girth-hitching. But for the most part, tying the webbing around the tree is stronger, and thus probably the safer option.
Now, if you had a spare locking biner, you could use that on the end of the looped webbing and avoid the girth hitch... but that's a different discussion.
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scrapedape
Nov 14, 2005, 7:02 PM
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In reply to: What you are doing is called "girth hitching", and girth hitching a sling can reduce the strength of the webbing by 30%, separate from the weakness created by the knot itself. So by girth hitching the tree instead of untying the webbing and tying it around the tree, you're introducing a huge weakness into your system. Of course, 1" tubular webbing is pretty strong stuff. Even if it's weakened by 30%, it's still very strong, 2800lbs or 12KN for new webbing. But if it's your anchor, why intentionally weaken the system by 30% if it only takes you an extra 30 seconds to tie a knot? |
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trenchdigger
Nov 14, 2005, 7:17 PM
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I'm all about the beer knot. It's the best way to go IMHO for "permanent" knots in tubular webbing.
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codhands
Nov 14, 2005, 7:24 PM
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mmmm.......beeer..........
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qtm
Nov 14, 2005, 7:40 PM
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In reply to: In reply to: What you are doing is called "girth hitching", and girth hitching a sling can reduce the strength of the webbing by 30%, separate from the weakness created by the knot itself. So by girth hitching the tree instead of untying the webbing and tying it around the tree, you're introducing a huge weakness into your system. Of course, 1" tubular webbing is pretty strong stuff. Even if it's weakened by 30%, it's still very strong, 2800lbs or 12KN for new webbing. But if it's your anchor, why intentionally weaken the system by 30% if it only takes you an extra 30 seconds to tie a knot? I don't believe that girth hitching will weaken the overall system at all based on what you are saying. If a girth hitch and a water knot each weaken the strength of the webbing by 30%, then a tied and girth-hitched sling should be 30% weaker than the untied webbing. The reason is that the water knot and the girth hitch are independent of one another - neither one is weaker due to the presence of the other. The strength of the system is limited by the weakest link(s), not the combined effects of both.
I didn't say the water knot significantly weakened the system, only that it creates a separate weakness from the girth hitch. The water knot does weaken the webbing, but pull tests have shown that 1" webbing tied with a water knot still break above the 4000lbs rating.
http://www.xmission.com/~tmoyer/testing/pull_tests_11_98.html
Test #5 is for the water knot.
Other tests have shown that girth hitching reduces the strength by 30% or more.
http://www.climerware.com/knot.shtml
So girth hitching introduces a separate weakness into the system, independent of any weakness created by the knot itself. While the weakness of the knot doesn't seem significant, 30% or more from the girth hitch could compromise your entire setup.
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misanthropic_nihilist
Nov 14, 2005, 7:40 PM
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The girth hitch can either be really strong or really weak, depending on the direction of pull. The straighter the load bearing part is, the stronger the girth is (the girth becomes more like a high strength tie off/ tensionless hitch). If the girth creates a 180 degree bend in the load bearing strand, you have just creating a 2:1 pulley system with the girth hitch.
Play around with a girth hitch on your leg, repositioning the joint/elbows/whatever, to see how different directions of pull can drastically change the load on certain sections of the sling.
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gandolf
Nov 14, 2005, 9:26 PM
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Regarding the Beerknot - It would seem that by slipping one end of the webbing into the other end you would loose the ability to inspect the length of the tails on the water knot. I have never used the Beerknot, so am just wondering.
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landgolier
Nov 14, 2005, 9:39 PM
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beer knots do creep, seems like they're worse than water knots in that regard since you can't cinch them quite as tight in the first place. But you can test them by pinching them and feeling how long the tail is. I only use them in some tied over the shoulder runners that are my bail tat if needed, as I find they're a little easier to untie, and I check them bevore every pitch.
Oh, and the OP was a troll
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mingleefu
Nov 14, 2005, 9:53 PM
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I would girth-hitch the tree. You know how hard it is to get a water knot untied after it has been weighted? pretty hard. I'd rather do that on my own time by the campfire or on the drive home than sitting next to some tree.
I think the reduction in strength is less severe if you wrap the sling around the tree and extra time before pulling the tail through the loop.
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waynew
Nov 15, 2005, 4:51 PM
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Mingleefu is on the right track
If you can spare the webbing, a Wrap 3 Pull 2 configuration will relieve the strain on your water knot by isolating it from strain using the friction of webbing against tree bark. Takes a bit more time to rig, but way better than girth hitching in my book. Sorry no reference handy, but it's not rocket science and easy enough to research
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cintune
Nov 15, 2005, 5:03 PM
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In reply to: Regarding the Beerknot - It would seem that by slipping one end of the webbing into the other end you would loose the ability to inspect the length of the tails on the water knot. I have never used the Beerknot, so am just wondering.
It's easy to feel and even see the end of the tucked-in tail. Use a hooked (but not jagged) wire to push at least 16" of one end into the other to make them nice and long, since they don't get in the way like waterknot tails can.
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lonequail
Nov 15, 2005, 6:04 PM
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The issue is overall safety - and to focus on strength is misleading. Climbing accidents overwhelmingly result from poor judgment, not equipment failure. The strength of the sling is more than adequate with both of the methods suggested.
In my opinion safety is promoted by using simple systems that are obvious, and by doing things the same way every time. That way if there is an irregularity it will be more obvious. A tragic example of this principal was a recent accident in which slings were apparently false-looped around a tree, sending the rappeller to her death. We should all learn from this accident!
I prefer a girth hitch around the tree when there is enough sling material. This avoids untying and retying knots which is time consuming, and can add some risk especially if you are tired or in a hurry. Also, I prefer to have the knot in the "free loop" where it is visible, not part of the wrap around the tree.
If the sling is short then a single loop is necessary. In any case, it is not good to use complex loops or attachments with biners because of the confusion factor.
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crotch
Nov 15, 2005, 7:10 PM
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A double-fisherman's in tubular webbing is damn-near permanent once it has been weighted.
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dschultz
Nov 15, 2005, 7:50 PM
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Haven't heard either way about leaving the water-knots in and there isn't mention of it in any of my arsenal of books lying around. The previous posts mentioned many important or just interesting points:
1. Inspect the water knot and webbing every time.
2. Nice to have the knot visible in the free loop.
3. A water knot does have a relative strength of 60 - 70% of the 1" tubular webbing strength of 4000-4500 lbs. ("Knots for Climbers", by Luebben)
4. Sewn slings are stronger.
5. Girth hitching trees is easier than untying previously weigthed water knots.
Bottom line for me is that a girth hitch is a perfectly sound method of an anchor when the conditions are right for it. For long extensions learn how to use a static rope in your anchoring system. Here in AZ we had a very sad accident with one of our climbers and we all miss her dearly. Learn all you can about correctly setting equilized, redundent anchors and keep asking those more experienced.
DSchultz
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