Girth hitch discussion

[treesmith]

There was a bit of discussion in another thread about the girth hitch. I mentioned girth hitching my friction saver around a stem, and Burnham mentioned it being weaker due to the girth. I am in no way arguing, but rather trying to wrap my mind around this principle. I'm wondering if somehow I'm missing something obvious. In the charts on loopies and whoopies, the loopie is rated a bit higher, sometimes double that of a whoopie. The way I configure my friction saver when girthing it is rather identical to a loopie, aside from the fact that there are two spliced ends with rings. Same principle as a loopie though. Also consider....if a girth hitch weakens its parent cordage by 50% to 60%, as Adrian said he's heard, how can it be approved to girth a climb line to a biner?

Furthermore, how can my girth hitching my friction saver possibly be weaker than working off SRT with a running bowline at the top? In no way could a girth hitch like I'm talking about be as weak as a running bowline, as the bowline itself weakens the line by some measurable amount, though the principle is the same....an eye with rope running through it.

I would appreciate some discussion pertaining to this, if for no other reason than to satisfy my curiosity.

This is the method I use when girthing to small stems....

 

[MasterBlaster]

Lordy, that looks just fine to me.

 

[RopeArmour]

Definitely looks like your girth has less bend than a Bowline.
You win.

 

[sotc]

 

[lumberjack]

Double the strength then subtract 50%.

Edited to correct the percentage.

 

[bonner1040]

I have been girthing slings since before I knew better. I have connected HMPE, or dyneema to 1" webbing, webbing to rope, and so on. Set up countless anchors doing everything from rock climbing, zip lining, swings, ascent lines, rappelling, industrial rope acess; the girth hitch is an invaluable tool. Usually in a situation where you need every bit of strength out of a textile your experience tells you ahead of time, judge accordingly.

 

[treesmith]

The problem is that none of the configurations depicted show the configuration I'm using. The vertical basket, which would depict normal FS configuration, gives 200% strength. The choker gives 80%. My configuration is rather a morph of the two, so if you averaged their strengths, you'd come up with 160%, or a 1.6 safety factor. This is what throws me on this subject. They say a splice retains close to 100%, but not a full 100%. In the vertical basket, there are two spliced eyes, so how can it possibly retain the full 100% of each leg? That's not allowing any strength loss at all from the splices, nor for the leg-to-load angle at the point of attachment. It seems to me that the size of hook/pin/shackle/whatever the eye was hooked to would make quite a difference here, as simply looping the eye around a 1/2" pin would put far more bend on the line than hooking around a 2" pin, for example.

Another way of looking at it.....in the straight lift, 1 leg = 100%. In vertical basket, 2 legs = 200% (despite the fact that only 1 leg of the sling is bearing underneath the load). How can you arrive at any less than 100% of the material's break strength just by running the two legs back through the "eye" formed by the loop of sling? You only lose 20% by rigging it single-leg choker.

I'll try to post some more pics tomorrow to illustrate what I'm asking in the original post.

 

[sotc]

I believe loopie slings are the same ratings which is where your configuration would come in. These are also rated for stitched slings, not spliced ropes. Not that I have any trouble or issues with your climbing set up. I will snag a photo off a sling today

 

[Marc-Antoine]

In the vertical basket, there are two spliced eyes, so how can it possibly retain the full 100% of each leg? That's not allowing any strength loss at all from the splices, nor for the leg-to-load angle at the point of attachment.

In the straight configuration, the loss by the splices are already taken in count, and that's the reference point. So when you make a basket or a girth hitch, the numbers show only the eventual loss from the sling's disposition. It says nothing about the strength of the rope itself (or what else material), only about the finished product.

(despite the fact that only 1 leg of the sling is bearing underneath the load)

This point has always bothered me !

 

[lumberjack]

I'd always heard 20% for the strength loss from a girth hitch.

In actuality, the diameter of what's being girthed does matter, as well as the angle the sling is being pulled with regards to how much it bends on the girth.

 

[Burnham]

I'd always heard 20% for the strength loss from a girth hitch.

In actuality, the diameter of what's being girthed does matter, as well as the angle the sling is being pulled with regards to how much it bends on the girth.

With all due respect, show me please. I'll happily agree with the second half of the statement.

 

[sotc]

 

[Burnham]

Pretty, but not relevant I think.

 

[lumberjack]

More contact area means more friction, more friction means less percentage of load on the loop of the girth. Less percentage equals higher strength as a system.

Compare girthing around a 2" steel pipe or a 20" bur oak. The rough bur oak has over 30x the contact area.

 

[Burnham]

Not convincing, Carl. I do not see that rope movement around the girthed item is a factor in this scenario. Of course, I could be wrong. Can you cite a reference, or is this solely a LJ theory?

 

[treesmith]

Jerry mentions in the Working Climber that the harder the bend at a girth/cow, the more prone to failure a rope is.

 

[Burnham]

I believe that refers directly to the second part of Carl's statement, which I mentioned agreeing with above, Scott.

 

[treesmith]

Sorry. Long, hot, hard day. My attention span is short. I was in a hurry to get to the supper table when I posted.

 

[Burnham]

No worries, brother. Have a good meal and a cooldown .

 

[treesmith]

Okay. Supper is behind me and my core temp is approaching normality again, it seems. I stepped out back for a minute to snap a pic to illustrate my question a little better I hope. In the pic below, I have my FS set up in a girth hitch configuration on the left, normal configuration in the middle, and a bowline run up to a limb as one would for working SRT (or using a floating crotch on single line).

Based on Willie's sling chart, the normal FS would yield 14000# break strength (strength of rope x 2)...(this also is not allowing for any loss in strength due to the spliced eyes.) In the SRT (running bowline) mode, the Yale XTC Plus is good for 6200# minus the amount that the bowline weakens the line. In the girthed configuration, I don't know of any charts that show its actual strength. It's not a single-leg choker like the sling chart shows. In my opinion, it should be the strongest of the three in the pic.

 

[Burnham]

It's not, Scott. The center config is strongest.

 

[treesmith]

I have no reason to dispute you, B. It just doesn't make sense to me. Would you still think that this girth set up is unsafe? I have never felt in the least bit endangered while climbing on it.

 

[sotc]

I can see Scott's thinking but I am going with Burnham. In both configurations you are putting half your weight on each leg (ring), the difference is your adding a bend in the standing parts with the girth. Slightly weaker but I think, still weaker.

 

[tophopper]

Why on earth would you girth hitch a FS? So you can climb back up and get it?

Seems pointless and counter-intuitive.

 

[treesmith]

Would you not agree though, that it is still stronger than the bowline for SRT? Some folks even fix a floating crotch on the single line to work Drt from. Same principle, but all the weight is supported by a single leg, which is already weakened (a tad) by a bowline.