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alpnclmbr1
Sep 7, 2003, 12:18 AM
Post #26 of 34
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Registered: Dec 10, 2002
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In reply to: .... A loop is not any stronger unless each strand is isolated..
the rest of nobody's post is great advice
In reply to: Real World Loop Strength On Fri, 8 Jan 1999, Russ Walling wrote to Chris Harmston : >Hi Chris, >Had a few questions I was hoping you could help me with. >Q: Say a cable or webbing is rated to X. Is there a quick and easy >convert to find loop strength, assuming the bond is full strength? How >about real world loop strength, as loaded between biners, not just >math? Most people would assume that the strength of a loop is twice the strength
of the single strand breaking strength. What I have found is that this is
not correct for two reasons. First is that the tack does factor in. It
is not always easy to ensure that the tack is stronger than the webbing.
So take off 5%. Second is that the single strand strength is obtained by
testing over large radii. Loops are tested over 10 mm pins. The pins
weaken the loop as you should expect. So remove another 5%. What I find
is that the loop strength is about 10% weaker than 2 times the single
strand rating. This is plus or minus 5% or there abouts. >Q: same Q as above, but instead of a loop, a rabbit runner config, ie: >loop at each end, single strand in the center. Load applied in each >loop. Here the tack does not factor in as much. Only the effect of the pins. So take of 5%. This is pure assumption because I have not looked at this data myself (even though we had rabbit ears in the bivy and Big Wall I tent-we use loops now). I forgot to answer the carabiner runner question. Basically the biners are like a 10 mm pin. Sometimes the radius of the biner is too curved and then the runner breaks even lower. Also, wide runners put greater load on the carabiner gate side and biners are found to break significantly below ratings when tested with wide runners. Chris Harmston (chrish@bdel.com). Quality Assurance Manager. Materials Engineer BS, ME. Black Diamond Equipment Ltd. 2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552 DISCLAIMER: Unless otherwise indicated, this correspondence is personal opinion and NOT an official statement of Black Diamond Equipment Ltd. |
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nobody
Sep 7, 2003, 12:52 AM
Post #27 of 34
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Registered: Nov 23, 2002
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alpnclmbr1 - please explain the testing method referred to.
Since we're talking TR anchors here, abrasion is clearly the concern. Did this test conclude that loops are more abrasion resistant?
And, does it even matter? The breaking strength of a single strand of 1" tubular is more than enough for a well-built TR anchor.
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fear
Sep 7, 2003, 1:41 AM
Post #28 of 34
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Registered: Jun 16, 2003
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A single strand of climb-spec tubular nylon sling is ABSOLUTELY FINE for topropes. Especially if you need to sling something 50' away. To make a 50' loop out of 100' of webbing is ABSURD for a toprope anchor. Nothing wrong with it though if your climber weighs 5000 pounds and likes 6' of slack out.
Just have at least two or more bomber anchors, pad the edges, dangle two lockers and you're good to go.
Jeez
-Fear
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tahquitztwo
Sep 7, 2003, 2:16 AM
Post #29 of 34
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Interesting discussion....I'll add my two cents....
Webbing is more abrasion resistant than regular cording materials...I've made TR anchors with webbing for many years and have had it get pretty abraded before having to replace it. On the other hand, one time at JT a spectra cordalette got worn through in three places from a days worth of TRing on several climbs....might have been age, the rock and the swings we were taking :lol:
I was always told that you don't use webbing (whatever length) as a girth hitch for a toprope because (1) it weakens the webbing strength as Alpnclmbr1 stated and (2) in a TR situation, it is possible to actually wear the webbing through at the point of the hitch from friction while TRing....
I've used the loop method....and to protect anything going over sharp edges, I slide the anchor lines through a piece of two inch wide webbing about three feet long...this adds extra abrasion resistence and the weight of the climber/rope etc. keeps it in place. I also finally went to using two sections of static line, each 40 feet long running through the protective webbing. At the rope end, I tie two figure8 knots put on two locking biners with gates opposed and then run the free ends back to the large rocks or trees being used for anchoring and snug them into place and at the same time equalize the two sides so that the rope is suspended from both equally. Sounds complicated but where I normally do a lot of toproping it makes for a reasonably easy setup, easy to double check and no worries about anything going anywhere. :D
I think everyone has their favorite method....just be sure you're always backed up and the knots are safe and secure.
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traddad
Sep 7, 2003, 2:37 AM
Post #30 of 34
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Registered: Dec 14, 2001
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From the "way too much time on my hands department": I ran a pice of 9/16 super tape THROUGH a 30 foot piece of 1 inch webbing. It took me about 1/2 hour to do it, but it makes a bombproof top rope anchor. Just girth hitch it to two beefy trees, tie a loop in the center, snap in two locking 'biners and viola...everything is redundant. AND...the outer piece of 1" protects the inner 9/16 from the sun and abrasion.
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alpnclmbr1
Sep 7, 2003, 2:58 AM
Post #31 of 34
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Registered: Dec 10, 2002
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In reply to: Basically, I wrap an end of the single webbing around a healthy, living tree 3 times and hitch or overhand knot the tail around the weighted end of the webbing so it won't unravel.
In reply to: alpnclmbr1 - please explain the testing method referred to.
In reply to: Since we're talking TR anchors here, abrasion is clearly the concern. Did this test conclude that loops are more abrasion resistant?
In reply to: I've used the loop method....and to protect anything going over sharp edges, I slide the anchor lines through a piece of two inch wide webbing about three feet long...this adds extra abrasion resistence and the weight of the climber/rope etc. keeps it in place. I also finally went to using two sections of static line, each 40 feet long running through the protective webbing. At the rope end, I tie two figure8 knots put on two locking biners with gates opposed and then run the free ends back to the large rocks or trees being used for anchoring and snug them into place and at the same time equalize the two sides so that the rope is suspended from both equally.
In reply to: And, does it even matter? The breaking strength of a single strand of 1" tubular is more than enough for a well-built TR anchor.
In reply to: A single strand of climb-spec tubular nylon sling is ABSOLUTELY FINE for topropes. Especially if you need to sling something 50' away. To make a 50' loop out of 100' of webbing is ABSURD for a toprope anchor.
I would have to disagree as far as the fifty-foot loop, it would be more functional for a variety of different types of anchors. Also for the most part running a single strand piece of webbing a hundred feet to an anchor would be very close to being absurd.
In reply to: I was always told that you don't use webbing (whatever length) as a girth hitch for a toprope because (1) it weakens the webbing strength as Alpnclmbr1 stated and (2) in a TR situation, it is possible to actually wear the webbing through at the point of the hitch from friction while TRing....
You can use a tensionless hitch with a loop also.
Incorporating three bomber trees into an anchor is often silly. If a tree did actually fail it would have a good possibility of destroying your remaining anchor system.
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meataxe
Sep 7, 2003, 8:30 PM
Post #32 of 34
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Registered: Oct 23, 2002
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In reply to: some good points here BUT 1) a loop is twice as strong as a strand, two strands is twice as strong as a strand. 2) How do you girth hitch a strand? You don’t.
1. I believe, that while a loop may be somewhat stronger, because of the two strands, it will not be double. (For the reasons already stated by others.)
2. There is an overhand loop tied in the end of the strand. The girth hitch is achieved by threading the free end of the webbing strand through the overhand loop.
Also, I do a variation on a girth hitch by wrapping twice around the protection sort of like a tensionless hitch without the carabiner. On the escarpment, there are too many tourists to risk leaving something shiny. People have been known to dismantle anchors to steal 'biners around here. :(
Tree padding is mandatory here, so the double wrap helps secure it as well as somewhat reducing the tension on the overhand loop.
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alpnclmbr1
Sep 7, 2003, 9:35 PM
Post #33 of 34
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In reply to: 1. I believe, that while a loop may be somewhat stronger, because of the two strands, it will not be double. (For the reasons already stated by others.)
In reply to: Most people would assume that the strength of a loop is twice the strength of the single strand breaking strength. What I have found is that this is not correct for two reasons. First is that the tack does factor in. It is not always easy to ensure that the tack is stronger than the webbing. So take off 5%. Second is that the single strand strength is obtained by testing over large radii. Loops are tested over 10 mm pins. The pins weaken the loop as you should expect. So remove another 5%. What I find is that the loop strength is about 10% weaker than 2 times the single strand rating. This is plus or minus 5% or there abouts.
So that is apx. 5% less then double the strength of a single strand. Knots will change the numbers but not the relationship between a loop and a strand.
In reply to: On the escarpment, there are too many tourists to risk leaving something shiny. People have been known to dismantle anchors to steal 'biners around here.
That would be a bummer to say the least.
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jackflash
Sep 7, 2003, 11:42 PM
Post #34 of 34
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Registered: Mar 5, 2002
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In reply to: Since we're talking TR anchors here, abrasion is clearly the concern. Did this test conclude that loops are more abrasion resistant?
As I understand it, since each strand of a loop of webbing would have about half the tension of just a single strand, the loop would indeed be more abrasion resistant than one strand alone. Tension, afterall, helps those edges saw through your webbing.
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