Girth Hitching with 'Biners

[X-man]

Guys,

I was wondering if girth hitching slings and rope with a 'biner is accepable or does it pull away from the 'biners major axis. I know girth hitching will reduce line strength, but when a lowering line is Girthed or choked off to the limb using a rated 'biner is the 'biners strength reduced due to the pull, and what about the bend ratio where the 'biner meets the line. I'm thinking a shackle might be a better connection for this, or maybe a block on the 'biner to reduce the bend ratio?
In heavy rigging I opt for endless loop slings and connect them into a rigging plate that connects to the lowerng line 'biner on eye splice. I am constantly looking for ways to retain rigging strength to minimize overloading any parts of the system.
What are your thoughts?
Rigging it Down,
X-man

 

[treeman82]

I am just wondering, you speak here of using biners' but you don't mention a thing about blocks? What I like to do is just use a sling and a block and that works fine for pretty much all of my rigging purposes. You can get blocks in all different price ranges. Slings you can make up yourself.

 

[Tom Dunlap]

Take a look at this page:

http://bosphorus.dimebank.com/~klew/knot.shtml


There is information on girth hitching webbing together. Maybe something about GH on a biner.

I wish I could put my finger on an article about webbing strength loss...oh, I can! Look in Arborist News, June 1998. Jeff Jepson wrote an article on webbing slings. Here is what Jeff wrote:

One inch wide tubular webbing has a breaking strength of 4,000 lbs. When doubled, to fashion a sling, the breaking strenth increases to 8,000 lbs. Deduct the strength loss from joining the ends, using the beer knot for instance [20 percent strength loss], and you still end up with a sling with a breaking strength exceeding 6,400lbs.
...and further on...
The girth [choker] hitch...will down grade the rated strength by 25 percent.

As cheap as sewn slings are, it makes sense to pick up a little strength. There are other places in our lives to go cheap. Besides, the knots always get in the way when I use tied slings. To make loops easier to use I sew them into eye on eye slings, leaving eyes about five inches long. My sewing isn't expected to add any strength, just makes them less floppy.

Have you guys looked at the Spectra/nylon slings? They are only 5/8" wide and stronger than 1" webbing. They cost a little more though.

On the other forum there was a discussion about the stitching tearing out of a sling. These slings were made with a box pattern at the overlap. That is about the weakest stitch pattern. Those slings were made by a vendor not a mountaineering equipment manufacturer. Slings should have either bar tacks or long overlaps with many rows of stitching parallel to the length of the sling.

When biners are rated, they are placed on a machine with pins along their major axis. If I had an option of using a straight back biner or an HMS with the same breaking strength, I'm not reaaly sure which I would choose to girth hitch webbing. If I was rigging with such a small margin of safety, I would probably go to a stronger biner, shackle or cut smaller pieces.

What are you thinking X-man?

 

[TheTreeSpyder]

What's up doc?

Interesting info Tom! i think that you should never grind/link line to line, always, always put metal link loaded along its major axis in every joint!

Years ago i called Samson (a few times!) and they told me that as far as slings they made were concerned a loop with a 100% strength joint of its ends, was 165% of the strength of just one leg of the loop. They said that it wasn't 2 seperate lines so didn't have the strength of 2; that there were other things going on with the strength as the forces torqued through the device.

So, in rigging strength for slings and pulley systems, i have always kept that in mind. To me it makes sense the way they explained it, perhaps it is stronger than 165% (ie. conservatively rated); but it is not 2 seperate lines! i then asked if that was true why was a basket hitch with sling rated at 2x that of loop in straight loop configuration; they said that was just convention, and there wer 4 legs there etc.! I'd like to know which is write; perhaps neither is right on, but a combination of both running principles! After calculating strength of straight loop, i think that choke position (with no sharp bends); yields a strength of 80%. That gives grip, basket is stronger, but has no grip, so for both i use round turn/ basket; for a combination of grip and strength at a cost of extra length.

Strength loss in girth hitching flat rope (webbing) will be as any other, dress it as well as possible, and look for deformation of fibers first. This is figured on diameter, as in a tight bight, the stretched fibers on the out side of the curving rope will be carrying the load; while the relaxed inner part of the bight will knot. In flat rope there is very lil' deformation in very tight bights, thus having high strength in very tight bights.

i'm not sure i under stand the primary question. If you choke off a sling, install link to line along major axis, that should be correct use i think. If you girth hitch loop runner to 'biner and carry all day, whip around limb, choke, link to line i think you are okay, been doing it for years! If the girth hitch you are concerned about is to 'biner, i believe that strength loss would be minimum because of deformation of fiber, for 'biner is about 8x that of flat side of loop. But it would be a choke position, but then so on load also.

i think that the wrong position would be to place 'biner in any configuration where it would be a flat instrument flexxed against curve of log with direct pull on it. this would not give maximum strength. Kinda like having a 'biner in the eye of the rigging line and whipping it around load and setting 'biner around line (running bowline, only with 'biner as locked choking ring) is what i'm meaning here. Here i stay off small diameter logs, give preceding half hitch, and place 'biner in flattest part of log. Sometimes i even slab out a small piece of log for flat spot. This gives a positive mechanical catch, protects the 'biner from slapping something directly, and doesn't try to flex 'biner around curve.

Always schedule a preceding half hitch to immediately choke close at incurrance of load; ie. final choking loop of 1/2 hithch, running bowline would be on heavier side of half hitch. Also, the line would come up from under the side of the log towards the overhead anchor, so that as the line tightenned the half hitch would pull close and not open for best security.

Are wee on same page?

 

[X-man]

OK,


My real question is this scenario: Of course I'm using a proper block at my lowering line anchor. Instead of using a runnng bowline on the working end of the line to terminate the limb, I use an eye splice which is tossed around the limb, I choke it off itself with a 'biner. This way I can eliminate any knots, it's an eye splice with a 'biner, way simple and fast to terminate. My worry is that the biner maybe being pulled outside it's major axis since it's choked off around a round surface. I watched a steel 'biner bend like a taco in this same situation because the climber forgot to lock it. I also worry about the bend where the 'biner chokes the lowering line. Is a running bowline stronger than a choked off eye splice via 'biner.
I have used webbing loops before for small rigging, but my loops for big rigging are Double braid and super strong,due to the 4 parts of line like the tree spider mentioned. When rigging big wood off itself, I have shyed away from the loops and use a half hitch and then choke the biner off. This way we keep the fall to it's minimum. I'm thinking a steel shackle may be better/stronger than the 'biner? Tom, how would a small block work on the choking end to help increase bend ratio, or am I getting way to involved in my systems?

Thanks in advance,
X-man

P.S. Thanks for the info Tom and Ken ,good to chat with y'all again. BTW did I mention how much I hate knots!

 

[Tom Dunlap]

X-man,

Your logo would be the universal "No" over a knot

In extreme loads a biner wouldn't be the best solution. Shaving a flat like spyder mentioned is too much messing around. That is a duct tape repair. A shackle seems to be a better solution.

Glenn Riggs has a bunch of steel bow shackles for heavy rigging. I think they are at least 5/8". Time for a word picture: Take the shackle and put the pin at the bottom in the six o'clock position. Cut the shackle at about 8:00 or 8:30 and 3:30 or 4:00. Toss out the pin and loop part. Weld on the loop to another shackle. Consult with a Certified Weldor about the proper welding technique. This will require a better weld than you can get out of your Buzz Box. Keeping the welds out at the ends and small will decrease the change in the metallurgy. When I visited Glenn in September he showed me some old shackles that had been used for lowering [false crotches]. they had grooves polished in them but Glenn has never had one fail and he works BIG WOOD.

If you want to retain [close to] 100% of the rope strength do a High Strength Tie Off. This is what Rick Lipke writes in "Technical Rescue Riggers Guide":

Anchor object for high strength tie off should be at least 10 times the diameter of the rope.
Rope should wrap around the trees two to three times.
Ropes should wrap around smooth objects up to four times.

After wrapping, the rope is secured with a running bowline or a biner. The arbo way of doing a high strength tie off is to use a marl or two. It seems to me that using a rescue HST seems to be more effecient and easier on the rope too. When the rope rubs across itself at the marl their is friction and strnegth loss.

Using a pulley to increase the bend seems too complicated. Too many pieces in the system. Shackles have been pretty standard connectors for rigging for a long time.

Tom

 

[X-man]

Tom,


That's exactly what I ws searching for, I have felt that the 'biner is not the right connection in this scenario for a while now. I like the HST and will give it a whorl. Is there any pics on the web for it? If not, there will be soon!
What do you think of the HST for false crotching wood off of itself, will it still choke or should a marl followed by the choked shackle/'biner be used. I like to set the marl as close to the block as possibly safe to eliminate fall. Would the HST be kosher here?
I will trust Glenn on the shackles! I know he does the BIG WOOD. Besides we always use them on crane removals for the wire choker, the are plenty stronger than a 'Biner and weight is close to a steel 'biner anyway. I don't think I would lower through them though,( maybe in a pinch! ) You can't beat a good block or two for keeping the line safe!
Rigging it down,
X-man

 

[Kneejerk Bombas]

When a large piece of trunk wood is tied off, typically one uses a running bowline tied slightly above center, then a Marl is added below the center.

After the log is cut and tipped over the Marl is on top, just above the center of gravity, and the running bowline is below that.

Two points here, first, replacing the bowline with a carabiner is wrong because a flat carabiner against a round log is subject to forces that could damage the biner, an more importantly, the bowline is at the end of the forces, the strongest part of the system. If rope friction and bend radius concerns you, the hardware should be added at the Marl. Because bend radius is not a big issue with the 90 degree bend of a Marl, adding a shackle, or whatever, would mostly be used to reduce friction. The friction is at the Marl, not the bowline.

The second point here is about some thing X-man said:
"I like to set the marl as close to the block as possibly safe to eliminate fall.
This is just plain false. As long as you have the Marl below the piece's center of gravity, you have minimized fall. There is no need to get the Marl close to the block, because it does not change the way the log falls. All you end up doing is increase the chace that you will hit the rope with your saw, or have the Marl fall off the end of the cut log.

What is HST that you speak of?
I think it was here I saw LS and LF, what's that?
Do you guys use initials to make me feel stupid? 'Cus it works.

 

[TheTreeSpyder]

i believe in 'biners! But, no question shackles are stronger, but not as quick a link, also take a chance on dropping 'bolt'.

In times of question i use stronger ones and/or 2 parallel in joint, and lead into it with 1/2 hitches that pinch off the force before it gets to 'biner. But in crane work i use large shackles too.

i only use marl when at the end of a log, as in catching a top; or when load is wider than long (can't positively pull close). Otherwise, i look for branchings and imperfections as psoitive dogs for hitchings. Is more than that necessary? i imagine that 'The Usual Suspects ' (would that be T'US Tom?) know to make lock side of line pull flat or hooked so it doesn't slide out; but thought it might be worth mentioning to all!

i only shave out a quick slab for 'biner to lay flat and dog in very low diameter log; this is when it is easiest and most necessary; but is rare.

Hitching with slings and 'biners or 1/2 hitches/running 'biners is called knotless rigging by some.

 

[Tom Dunlap]

What is HST that you speak of?
I think it was here I saw LS and LF, what's that?
Do you guys use initials to make me feel stupid? 'Cus it works.

Mike,

High Strength Tie off is in my 1/20 post.

The convention that I follow is to use the name of whatever I'm going to "inititialize" once, follwed by the initials. If this comes up in another thread I do it in my first post. Sometimes with the lenght of theses htreads its hard to keep up with initials. Sorry.

An old friend of mine taught me something about feeling stupid. She taught me that unless someone is holding a gun to my head, no one can "make" me feel anything. Its my choice. at the time, she was the LOML, Love of My Life.

Tom

 

[Tom Dunlap]

What is HST that you speak of?
I think it was here I saw LS and LF, what's that?
Do you guys use initials to make me feel stupid? 'Cus it works.

Mike,

High Strength Tie off is in my 1/20 post.

The convention that I follow is to use the name of whatever I'm going to "inititialize" once, follwed by the initials. If this comes up in another thread I do it in my first post. Sometimes with the lenght of theses threads its hard to keep up with initials. Sorry.

One of the advantages of adding a marl or half hitch to the butt is that some of the load is taken up by the rope being wrapped around the tree. Think of it as one wrap of an HST. With enough wraps you would not even have to tie off the end of the rope. There would be enough bark friction. Think about the antique rigging technique called TTW, Take Three Wraps.

An old friend of mine taught me something about feeling stupid. She taught me that unless someone is holding a gun to my head, no one can "make" me feel anything. Its my choice. at the time, she was the LOML, Love of My Life.

Tom

 

[X-man]

Mike,


Now if you set the marl, let's say 1 foot above the block instead of 3 feet above the block, the fall distance is the same? I agree to disagree on this one, at least for now. I feel the least amount of line from block to marl is a shorter fall? I was instructed to keep fall distances as short as possible to eliminate load/shockloads, I could be wrong though?Tom?

Rigging it down,
X-man

 

[Tom Dunlap]

Look in December '99 issue of Arborist News.

Dr. Pete wrote the article, "All in All, Its Just the Same Distance of Fall." He liked punny titles for his article. [What is the emoticon for a smile with a tear in an eye?]

"Some people ask if the distance of fall can be affected by the way the wood is tied off above the cut. For the scenario illustrated here, the answer is no, as long as the piece is tied so it can't flip over [that would mean the cut is hanging closest to the ground when everything comes to res]. Referring to figure one, the piece can't flip if the marl is below the cneter of the piece."

In the illustration the running bowline is above the center cut and the marl is below the center.

Tom

 

[John Paul Sanborn]

I feel this is only true when the break is properly applied.

Everyone has been in a situation where there is additional friction on the rope running up and maybe you feel a need for an extra wrap. So then there is more "catch" of the load as it comes down.

Slowing the loads fall adds force to the loaded line.

The of the twice distance between the block and the marl is pretty much free fall.

I cannot see how increasing the distance could have a negilgable effect the loading of the system.

 

[Kneejerk Bombas]

I drew a picture, as you will see, I'm not an artist, but it give a visual idea of what we are talking about.

The pictures are supposed to be before and after the cut, little pink dot is center of gravity.


The best location for the shackle being at the Marl, is going unchallenged???

 

[Tom Dunlap]

Mike,

Nice jop with the illustrations. That is just about what is in Pete's article.

Another way to illustrate this is to use a small branch and some shoelace. Cut a face with a handsaw and adjust where the marl and bowline are snubbed.

Replacing the marl with a shackle seems like a nice little addition. It seems like away to pick up a few percentage points of efficiency. To me, if I'm rigging where I need to pick up that small a bit of effeciency, its time to rethink what I'm doing. Maybe cut a smaller piece.

A couple of winters ago I was tele skiing with Pete and he talked about building a system for testing our slam dunk rigging. He talked about adding load cells to the ropes to collect all of the necessary information. The load cells would be connected to the rope at intervals of a few inches. We talked, well, really Pete talked and I asked questions, about building a rope that had load cells built into the fibers. I learned a little more about load cells from an engineer/arbo instructor from Australia. He was at the Tree Dynamics conference in October. His research showed how limbs reacted to winds. He installed the load cells in the tree and then let the computer run. It took a long time to get the information and then they had to go back and analyze the information. That is where the money is made! The same would be for rigging information. In the end, Pete figured that we would have a more fluid understanding of the forces on rigging. Now, all we have is static loads. Most times, we load dynamically but we can;t measure those loads yet. I hope Pete is cranking some turns.

Tele skiing: Half the binding, twice the fun!

Tom
Tom

 

[TheTreeSpyder]

i believe Joe sent this to me before; so of course i had to disagree!

In the Arbomaster films they show to put the marl as low as possible. i think Tom says, that Pete says (sa(i)d); holds true more with a pulley and running line than having high brakeforce and / or pre-tightenned line. i assume that is understood; but Joe said in any instance it is true! i'm not too sure about that.

i try to push over the load or have the guys flex it over with highest leverage through the arc of the hinge to hand it off to the rig as slow as feasible. When they pull it over, i might cut a V in the top of the log on the backside, so the pull comes up and over for non-slipping maximum leverage. This also plays on my theory that the bend in the line will want to torque out placing even more pressure on the log to come forward. Then the hinge delivers it into the line, going for the hand-off, more than the slam. This is aided by all that pressure at a max. pulling it over into a meatier hinge.

 

[Tom Dunlap]

Ken,

You wrote:
holds true more with a pulley and running line than
having high brakeforce and / or pre-tightenned line. i assume that is understood;
but Joe said in any instance it is true! i'm not too sure about that.

You lost me here. Speak my language.
Pulley and running line?
Where does high brake force come in?
Pre-tightened line...

Make a little model and you'll see that Joe and Mike are right. I think that you're looking at a different scenario.

When you put a pull over line on the top of a chunk, is the line just a pull line or is it part of the rigging?

Tom

 

[TheTreeSpyder]

i think that if instead of a pulley/block you have friction at that pivot/redirect point (for lighter loads, or low anchor loads) that the effect that you are talking about is minimized. Wherby if 80% friction/brake force was where the pulley is, then there would be 2 seperate line considerations. If making the marl higher, there would be 2,3x more line to stretch in this occasion? For the line stretch would be mostly from the anchor to marl, so if this was 6", would be better than 18" to marl, of line to stretch? Then more impact, unless fluid run?

Then, taking that theory, if you put pulley back in and pretighten to 300-400# that pressure on pulley as load turned down would bite into pulley (that isn''t 100% efficient anyway) and have this effect minimally. i just somehow imagine the more friction/drag at this pivot point, the more segregated the line from 1st marl to anchor would be, so therefore have diffrent charachteristics. i have done the lil experiments with pencil and line, thought long; this point troubles me.

The line over the top is seperate line for leveraging the top into the face with as much hinge as possible. Sometimes i lock of a muenter on this line for sitting in and cutting perfect face in log too. Going over the top with this pull line maximizes leverage, the bend adds this torque effect i believe. So as to get the load to lean over into rig as far as possible, before tear off occurs. i see this as minimizing the input force, by minimizing the input speed; and think this is of higher consideration than if the marl is placed 1' higher etc.

i think that with block you are more write, but that the effect i try to outline is there too; but also that all these effects multiply out; so at sum point it is important to realize all these factors and minimize that witch you can.

 

[Tom Dunlap]

KC,

You spun off to loads when I was just talking about the distance of the fall. You lost me for a little while.

Whenever the dynamic load can be reduced, the better off we are. I like the idea of setting up the butt over with a tensioning lowering device at the bottom. If a really wide, ninety degree plus, face is cut and a pull over line is installed, you could actually pull over the top and use the holding fibers in the hinge to control the drop. The cut would change from a dynamic to a hinge cut. Less shock loads. Better.

Tom