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ginger_ninja
Aug 24, 2005, 9:49 PM
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I've seen lots of people on here recommending using a sling or static end of the webbing girth hitched around a tree to form an anchor for a slackline. i have always tried to avoid girth hitches when climbing as i read somewhere that they reduce webbing/rope strength dramatically, and this effect is increased the tighter they get.
Given that slacklines exert huge forces on the anchors surely a girth hitch would reduce webbing strength enough for it to cause the line to fail faster than usual?
- i would appreciate any feedback
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monkeyarm
Aug 24, 2005, 11:10 PM
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I used to work at a day cap and we would set up a slack line and leave it outside set up for about 10 weeks and never had a problem with a girth hitch around a tree, except after its left up that long the webbing kind melts together a bit at the hitch from all the friction, but it never failed
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coldclimb
Aug 25, 2005, 12:24 AM
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I've got a line that's been girth hitched hundreds of times, left up for months at a time both winter and summer, walked on, jumped on, surfed on, used repeatedly as a tow strap, and used as a tensioning system attached to a car for a 125-foot line, and I have yet to break it. I wouldn't worry about girth hitching at all. :) It CAN melt together, like monkeyarm said, though. I believe I've only had this happen on loose lines that I was surfing hard, and it came apart with just a little work, with no lasting important damage.
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northerndrawl
Aug 25, 2005, 6:29 PM
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In reply to: I...never had a problem with a girth hitch...except after its left up that long the webbing kind melts together a bit at the hitch
That IS the problem. That is what a girth hitch will do to nylon if its worked hard enough. Say on a big slackline surfed hard and long.
The girth hitch creates a mechanical advantage situation. The loop of the hitch experiences the force of the load (the slackliner bouncing) plus whatever equalizing force is generated by the change of direction after the loop.
When a girth hitch is teardrop shaped, with its apex towards the load, this works out to about 1.4:1. When the hitch is arranged so that the webbing makes a 180 degree change of direction (say with the hitch on the side of the tree) it approaches 2:1. So the webbing at the loop is experiencing twice the load of the bouncing slackliner.
Coldclimb refers to melting on loose lines surfed hard, that's just good ol fashioned friction. Nylon's melt point isn't huge, and the friction it creates when rubbing on itself is enough to reach it. Because a girth hitch allows for movement (the loop sliding back and forth a bit) it has more potential for building up heat and creating melted spots. This is a different problem than the increased force on the loop due to mechanical advantage.
Will it fail faster? Not a question of speed really. It will probably fail at a lower amount of force than a line rigged with other methods. Especially if the webbing already has melt points as they certainly decrease webbing strength.
Could a slackliner generate the force required? Anything's possible, although ColdClimb and thousands of others have slacked using this method without incident. If you don't like the idea of it use bowlines or better still Wrap3pull2 anchors on the trees. More work and more equipment to set up, but it has more margin of safety than a girth hitch. Or get a couple of big industrial slings.
Short answer--yes it affects it. Too much? Up to you. In my mind any melting is too much.
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niles
Aug 25, 2005, 6:37 PM
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A girth hitch can increase the force exerted on the runner if the end that runs through the bite makes any sort of sharp bend back in the opposite direction (thus applying a MA to the runner itself), but if you tie it so the runner comes relatively straight through the bite you should be fine. Lot's of people use them, lot's of people trust them, but I tend to opt for stronger anchors (when I'm not in a hurry), like a tensionless hitch, slacker's hitch, W3P2, etc, these just take a little more time and webbing.
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veganboyjosh
Aug 25, 2005, 6:44 PM
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isn't the girth hitch bad for the tree as well, since it cinches down on it, cutting off it's circulation more than other non tightening knots/methods?
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areyoumydude
Aug 26, 2005, 3:59 PM
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Slackers use the girth hitch all the time, but it is the weakest anchor you can use. I have busted girth hitched anchors and had a slackjack bust me in the knee. Use something bomber.
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ginger_ninja
Aug 26, 2005, 8:45 PM
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thanks for the input. Definitely food for thought when i next set up a line.
areyoumydude- you said about being hit with stuff when things break. this was a concern when i set up my line for the first time, so i bought some 4mm accessory cord and tie a loop though the biners in my system and i also loop it round the tree that my anchor is on. i leave it loose so that hopefully if anything does break the flying metalwork will be caught and arrested by this before it does any damage. my theory is that although they are under a lot of tension, when something does break the biner will be light enough to be caught, since it will no longer be under tension, because it will have already traveled say half a meter before it hits the cord, and will simply be traveling at speed. and an object weighing 80grams traveling at say 100mph shouldn't cause enough force to break 4mm cord. At least thats the theory...
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smithrockfreek
Aug 26, 2005, 8:50 PM
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i snaped my slack line with a girth hitch, dont try it, flying webbing hurts
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scottquig
Aug 26, 2005, 10:13 PM
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In reply to: i snaped my slack line with a girth hitch, dont try it, flying webbing hurts |
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coldclimb
Aug 27, 2005, 12:08 AM
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In reply to: thanks for the input. Definitely food for thought when i next set up a line. areyoumydude- you said about being hit with stuff when things break. this was a concern when i set up my line for the first time, so i bought some 4mm accessory cord and tie a loop though the biners in my system and i also loop it round the tree that my anchor is on. i leave it loose so that hopefully if anything does break the flying metalwork will be caught and arrested by this before it does any damage. my theory is that although they are under a lot of tension, when something does break the biner will be light enough to be caught, since it will no longer be under tension, because it will have already traveled say half a meter before it hits the cord, and will simply be traveling at speed. and an object weighing 80grams traveling at say 100mph shouldn't cause enough force to break 4mm cord. At least thats the theory...
Ginger ninja, don't get me wrong, but I'm skeptical that this will work. ;) If something heads your direction when things break, it's going to be because it is being pulled, and therefore is still attached to the line, which will snap a 4mm cord like nothing. If the breaking point is on the line and not the anchor, then the metal will still be attached solidly to said anchor, and will be flying the opposite direction anyway. Also, in a girth hitch situation, there would be no metal on that end of the line, or if there is metal there, it eliminates the whole friction problem completely. :) I wouldn't worry about tying things off. If you go to that much effort anyway, just rigging an equalized backup would be better. That way things just won't break. :)
The one slackline I've ever broken sent nothing flying. But then that one was rigged loose, not anything like areyoumydude's. :lol: I'm still waiting for my original slackline webbing to break. I believe it's going on four years old now, and thoroughly mistreated every step of the way. :lol:
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liquidshadow111
Aug 27, 2005, 12:58 AM
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In reply to: In reply to: i snaped my slack line with a girth hitch, dont try it, flying webbing hurts flying gear hurts more
HAHAHAHAHA!! :D :D you just made my day. :D
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goclimbarock514
Aug 28, 2005, 1:15 AM
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In reply to: i snaped my slack line with a girth hitch, dont try it, flying webbing hurts |
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ginger_ninja
Aug 30, 2005, 6:07 PM
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im still using the backup method i described. It takes literally 20 seconds to set up. Im also confident that if somthing did break in the line that caused a biner to fly towards me then this would stop it. my psysics knowledge is rubbish but here goes...
when the line is tight the biners have lots of potential energy in the form of tenison. when an anchor breaks on the biner side due to huge ammounts of force and/or corrosion the biners will transfer all of this potential energy into kenetic energy (i.e flying towards me). A good 6 inches later and the biner will be caught by my 4mil accessory cord. The biner will no longer be subject to the extreme tension that was enough to snap the webbing. The only force that it will exert on the cord is one caused by the speed it is travelling at. To find this we have to work out momentum, which is weight x speed.
So if we say that this this weighs 0.2kilos (for arguments sake, since the av. persons setup could involve all sorts of wierd biner combinations) travelling at a speed of 200 meters per second (to be fair i think this is fair bit faster than a biner would actually travel when somthing breaks).
So when we multiply the two together we get a total of 40 kilogram meter per second, which is far lower than a typical 4mil cord can take.
im pretty sure that my own webbing has several years of life left in it yet. But the risk of my line ever breaking for any reason, especially if someone else was on it at the time is enough for me to spend an extra moment tying this cord around the tree.
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coldclimb
Aug 30, 2005, 6:27 PM
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Yeah, don't get me wrong, I'm sure a 4mil cord could stop a flying caribiner, just not when it's still attached to the slackline, which it would be if the anchor gave. Or am I misunderstanding your system? :?
When I went down to do the Monkey Face with areyoumydude et al., we managed to break a 9mil ROPE while tensioning the line. That was pretty crazy.
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ginger_ninja
Aug 30, 2005, 7:09 PM
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whoa! that does sound pretty crazy :shock: i think that stuff is rated at 14kn or so :twisted:
yeah, the whole point is that the cord is tied really really loosely around the crabs and the tree, so there is lots of slack. This means that no forces act on it at all unless something at the anchor breaks. In which case the biners will fly for a bit through the air before they even meet the 4mm cord. This distance should be far enough so that there is little or no tension in the line by the time the cord takes the strain.
i used this initially when i used a ratchet on the line, but now ive gone back to using biners, and i thought i might as well carry this over.
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niles
Aug 30, 2005, 7:27 PM
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I say we put theory into practice :idea:
Rig up a line with some webbing you're not to keen on keeping for the anchor. Make the line good and tight (probably tighter than usual since no one will be on it), tie up your 4mil and slice the anchor.
If you do, you should video it for us, though.
Niles
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coldclimb
Aug 30, 2005, 10:07 PM
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Yeah, it's a good thought for sure, and keeping flying biners at bay is a good thing. Testing is always fun, especially slicing webbing under tension. :twisted: I was forced to cut an anchor on a 125-foot line last week, when I jammed it up while releasing and didn't want to retension to get the pressure off the jam. That's just plain fun! :D And luckily the anchor was slings I had bootied on a climb two days before, so no big loss.
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ginger_ninja
Sep 1, 2005, 7:50 PM
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i might just do that and let you know the results. sadly, here in the UK webbing isnt so cheap so i may have to make an anchor out of static 11mil nylon rope and cut that instead
(if anyone here knows a cheap u.k supplier of webbing let me know)
:oops: i ended up giving up the search and paying £1.50 (($3.00)) per meter for mine :oops:
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slacklinejoe
Sep 1, 2005, 8:41 PM
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In reply to: i might just do that and let you know the results. sadly, here in the UK webbing isnt so cheap so i may have to make an anchor out of static 11mil nylon rope and cut that instead (if anyone here knows a cheap u.k supplier of webbing let me know) :oops: i ended up giving up the search and paying £1.50 (($3.00)) per meter for mine :oops:
If nothing else, a lot of places will ship to the UK, I know I ship a heck of a lot of slacklines over there so it'd be no different for webbing. If you can, find a place that is willing to ship via the postal system. It might be a day or two slower but it'll be 1/3 to 1/2 the price of UPS or FedEx.
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iltripp
Sep 2, 2005, 7:49 PM
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I noticed this thread a couple days ago, but I've always had confidence in my girth hitch.... until now...
I've used a girth hitch on this line for a long time, but I watch for obvious signs of wear and it seems ok. Today, I re-tightened my line and got it really tight. I got on near the girth hitch and tried to catch some air.... as I was bouncing the line, I started to thinking, "wow... this is tight! I hope it doesn't break. I was just reading about that on rc.com". The second the thought had passed through my head I heard a loud "SNAP" and found myself flat on my back. The line had snapped right at the girth hitch and left me a nasty, purple welt on my foot (seriously, it looked like I had a broken foot).
Anyway... I think I'll go tie a new girth hitch and set my line back up. :roll:
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gymslackerclimber
Sep 2, 2005, 8:14 PM
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although this probabaly has been stated, ( i guess i should have read the whold thread)
but im not a big fan of the girth hitch, it twist the line way too much,, ,, only use it if i cant make both sides of webbing all the way around the ancor.
and geeze iltripp, thats a big bummer about your foot,, i guess i have to consider myself greatful for never having a line break on me..
just rember to be super duper careful.. :tinfoilhat: ...
:righton:
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iltripp
Sep 2, 2005, 10:26 PM
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Actually, my foot's fine... Strange really...
I had a nasty purple welt for about 30 minutes, and then with a little ice, it's faded to a very faint tender spot... no big deal at all.
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veganboyjosh
Sep 2, 2005, 10:42 PM
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In reply to: I noticed this thread a couple days ago, but I've always had confidence in my girth hitch.... until now...The second the thought had passed through my head I heard a loud "SNAP" and found myself flat on my back. The line had snapped right at the girth hitch and left me a nasty, purple welt on my foot (seriously, it looked like I had a broken foot). Anyway... I think I'll go tie a new girth hitch and set my line back up. :roll:
is this the best solution? i think i'd be a little weary of using the same knot that just failed and popped me in the ankle.
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iltripp
Sep 3, 2005, 2:05 AM
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In reply to: In reply to: I noticed this thread a couple days ago, but I've always had confidence in my girth hitch.... until now...The second the thought had passed through my head I heard a loud "SNAP" and found myself flat on my back. The line had snapped right at the girth hitch and left me a nasty, purple welt on my foot (seriously, it looked like I had a broken foot). Anyway... I think I'll go tie a new girth hitch and set my line back up. :roll: is this the best solution? i think i'd be a little weary of using the same knot that just failed and popped me in the ankle.
Yeah... that was kind of a joke. I think I'm going to see if a bowline can be tied without twisting the line too much.
I should say that the girth hitch only failed on an old line that had been taking a lot of abuse (i've been teaching myself to bounce in the air right next to it)
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