Anchor Webbing

During rescue work, everything rides on the anchor. This often glossed over component, yet most important as it must support anything attached to it. Recently, while on a job, my sup tells me rig up a wrap 3 pull 2 at that anchor point. So sure I oblige, but I wonder.
Are we one trick ponies, is there a proper anchor for each scenario. Now I am talking web anchors mind you. If the W3P2 is so good, why are other web anchors taught such as, basket sling, girth hitch, double larks foot?
Now I wonder, is there a time when a x2 larks foot would be better than a W3P2 or visa-versa.
If the W3P2 covers all bases, why do training schools bother to teach other anchors?

During the job scenario I was at, our anchor point was a U-shaped beam so, on the back end of the anchor was little support, this led me to think about web anchors and are there times when one configuration is better than another.
What say you?

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Originally Posted by MichaelXYZ

During rescue work, everything rides on the anchor. This often glossed over component, yet most important as it must support anything attached to it. Recently, while on a job, my sup tells me rig up a wrap 3 pull 2 at that anchor point. So sure I oblige, but I wonder.
Are we one trick ponies, is there a proper anchor for each scenario. Now I am talking web anchors mind you. If the W3P2 is so good, why are other web anchors taught such as, basket sling, girth hitch, double larks foot?
Now I wonder, is there a time when a x2 larks foot would be better than a W3P2 or visa-versa.
If the W3P2 covers all bases, why do training schools bother to teach other anchors?

During the job scenario I was at, our anchor point was a U-shaped beam so, on the back end of the anchor was little support, this led me to think about web anchors and are there times when one configuration is better than another.
What say you?

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Michael, all of the methods of anchoring that you mentioned have merit in that they are all tools that should be in your tool box. A one-trick pony? I would hope not. The best idea, as always in rigging, is to select the most appropriate tool for the job at hand. And hopefully, have several tools to choose from.

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Originally Posted by EricUlner

Michael, all of the methods of anchoring that you mentioned have merit in that they are all tools that should be in your tool box. A one-trick pony? I would hope not. The best idea, as always in rigging, is to select the most appropriate tool for the job at hand. And hopefully, have several tools to choose from.

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Agreed, but how does one know when one anchor is the better choice?
Thanks

If I want to use friction to keep my webbing anchor in a certain place I will use a W3P2, Otherwise I will just use a wrap 2, it's a faster setup and you don't need as much webbing, which comes in handy when wrapping around a large anchor.

I'm not a big fan of the girth hitch for webbing anchors, the girth hitch will reduce your load capacity around 25%. Plus, unless the webbing is doubled up, a girth hitch made from 1' tubular webbing wont meet my dept's SSF, 15:1, 600 LBS for a 2 person load. Webbing is rated for 4000 LBS, tied into a loop it's 8000 LBS. When that loop is girth hitched around an anchor that 8000 LBS is reduced by 25% the webbing anchor is technically only rated for 6000 LBS.

When I say girth hitch I am talking about the double girth which is general use. The only benefit I see in the W3P2 is that it stays in place unloaded.

Attachment 22526

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Originally Posted by MichaelXYZ

When I say girth hitch I am talking about the double girth which is general use. The only benefit I see in the W3P2 is that it stays in place unloaded.

Attachment 22526

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Got ya, in your original post you listed the girth hitch and the double larks foot, I figured you were referring to them as 2 separate webbing anchor options.

Yay anchors! W3P2 is a great tool, for it takes the knot out of the loaded sections of webbing (if tied right and has the water knot on the section sucked up on the anchor). Say you are using standard 1" tubular webbing, you are looking at a MBS of 4000#, times that by 4 for the four sections holding the load (16,000#). You probably will dislodge your anchor point before breaking that webbing.

The simple wrap 2 works fine, for figuring out the SSF I would only count the three sections without the waterknot as supportingthe weight, as a water knot looses 25-30% efficency. Still having 12,000# of anchor is plenty for most work until you start talking structural collapse anyways.

I think the anchors that get the least ammount of attention are the load shareing (good) and load equalizing (better) anchors. Here in Texas, you might only find some scrawny mequites to anchor off of. Load sharing or equalizing between 2 or 3 of them helps.

Tiebacks are important too. A simple trucker's hitch between two anchors can add a great deal of back up to a lesser anchor. Picket systems are a great tool, often overlooked or misunderstood.

Better yet, a 20' section of body cord (standard 1/2" rope) works well to form an anchor, about twice as strong as webbing.

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Originally Posted by MichaelXYZ

Agreed, but how does one know when one anchor is the better choice?
Thanks

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Depends on many variables...

Gear resources
What is the anchor you're tying to? Structural steel, tree, boulder, rock pro, etc, etc,?
What is the intended load?
Single or multiple directions of load applied?
Belay, Main, directional, component of a multi-point anchor?

Your question is too broad. I appreciate your thirst for more knowledge in this subject, but I'm going to say you'd do best to seek more courses.

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Originally Posted by Golzy12

If I want to use friction to keep my webbing anchor in a certain place I will use a W3P2, Otherwise I will just use a wrap 2, it's a faster setup and you don't need as much webbing, which comes in handy when wrapping around a large anchor.

I'm not a big fan of the girth hitch for webbing anchors, the girth hitch will reduce your load capacity around 25%. Plus, unless the webbing is doubled up, a girth hitch made from 1' tubular webbing wont meet my dept's SSF, 15:1, 600 LBS for a 2 person load. Webbing is rated for 4000 LBS, tied into a loop it's 8000 LBS. When that loop is girth hitched around an anchor that 8000 LBS is reduced by 25% the webbing anchor is technically only rated for 6000 LBS.

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15:1 is mostly a pipe dream. 10:1 is more realistic.

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Originally Posted by FiremanLyman

Yay anchors! W3P2 is a great tool, for it takes the knot out of the loaded sections of webbing (if tied right and has the water knot on the section sucked up on the anchor). Say you are using standard 1" tubular webbing, you are looking at a MBS of 4000#, times that by 4 for the four sections holding the load (16,000#). You probably will dislodge your anchor point before breaking that webbing.

The simple wrap 2 works fine, for figuring out the SSF I would only count the three sections without the waterknot as supportingthe weight, as a water knot looses 25-30% efficency. Still having 12,000# of anchor is plenty for most work until you start talking structural collapse anyways.

I think the anchors that get the least ammount of attention are the load shareing (good) and load equalizing (better) anchors. Here in Texas, you might only find some scrawny mequites to anchor off of. Load sharing or equalizing between 2 or 3 of them helps.

Tiebacks are important too. A simple trucker's hitch between two anchors can add a great deal of back up to a lesser anchor. Picket systems are a great tool, often overlooked or misunderstood.

Better yet, a 20' section of body cord (standard 1/2" rope) works well to form an anchor, about twice as strong as webbing.

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Drawn on paper, the w3p2 appears that it should be 16,000# in strength. But slow pull tests often average in the 35-40KN range, as the inner section of webbing is pinched between the outer section and the carabiner, creating fusion and then failure.

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Originally Posted by EricUlner

15:1 is mostly a pipe dream. 10:1 is more realistic.

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Agreed. [As an aside, consider the 8 mm ratchet prusik in a haul system, and you're down to less than 10:1, but the dynamic system safety factor still exceeds 1.5; but, that's a topic for another thread...]

W3P2 failure strengths depend on type of webbing (tubular: 18 kN; flat sewn: 25 kN) and interior webbing angle. I think the testing values quoted are for a 90 degree interior webbing angle. I would also guess that a W3P2 tied with flat sewn webbing fails at a higher force than one tied with tubular webbing.

I've seen rescuers, when faced with an anchor that's too big for a proper W3P2 with the longest length of webbing available, tie two pieces of webbing together, rig what they call a "W3P2" with a loaded knot (where the two pieces of webbing are tied together), and call it a W3P2 even though what's actually been rigged defeats the true purpose of a W3P2 (no loaded knot). Makes me want to slap them silly.

Yes, the W3P2 is great, but it doesn't cover all rigging situations.

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Originally Posted by EricUlner

15:1 is mostly a pipe dream. 10:1 is more realistic.

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How does anyone get a 15:1 SSF? This comes from a misunderstanding of NFPA 1983 and instructors passing that misunderstanding to students. For those following that are lost in that statement, 1983 is the standard for rope and equipment makers, in it 1983 defines general load as 600# and states that rope made for general use will have a 40kN (~9000#), that simple math makes 15:1. No where does anything state the systems used will have a 15:1 SSF.

A 9000# MBS rope (standard 1/2") with one knot tied anywhere in the loaded section of rope (the anchor, attachment to the load, etc...) reduces effeciency between 25-30% depending on knot. Looking at a 6000# MBS now, a General Load is defined as 600#, gives you a 10:1.

We strive to keep the SSF above 7:1. Anything less than that requires you to either reevaluate what you are doing (risk vs benifit) or build a better system.

Quote:

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Originally Posted by EricUlner

Drawn on paper, the w3p2 appears that it should be 16,000# in strength. But slow pull tests often average in the 35-40KN range, as the inner section of webbing is pinched between the outer section and the carabiner, creating fusion and then failure.

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Yes Eric, thanks for grounding me in the real world. Also has a lot to do with bends in rope and cordage less than 1/2 the diameter of the rope. Still stand by the statement that I like removing the water knot from the loaded sections of webbing though.

Here is a link to a great study that compares W3P2 and basket hitches using 1" webbing.
http://www.caves.org/section/vertica...tches&W3P2.pdf
Dave

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Originally Posted by FiremanLyman

How does anyone get a 15:1 SSF? This comes from a misunderstanding of NFPA 1983 and instructors passing that misunderstanding to students. For those following that are lost in that statement, 1983 is the standard for rope and equipment makers, in it 1983 defines general load as 600# and states that rope made for general use will have a 40kN (~9000#), that simple math makes 15:1. No where does anything state the systems used will have a 15:1 SSF.

A 9000# MBS rope (standard 1/2") with one knot tied anywhere in the loaded section of rope (the anchor, attachment to the load, etc...) reduces effeciency between 25-30% depending on knot. Looking at a 6000# MBS now, a General Load is defined as 600#, gives you a 10:1.

We strive to keep the SSF above 7:1. Anything less than that requires you to either reevaluate what you are doing (risk vs benifit) or build a better system.



Yes Eric, thanks for grounding me in the real world. Also has a lot to do with bends in rope and cordage less than 1/2 the diameter of the rope. Still stand by the statement that I like removing the water knot from the loaded sections of webbing though.

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Agreed, my friend.

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Originally Posted by EricUlner

Depends on many variables...

Gear resources
What is the anchor you're tying to? Structural steel, tree, boulder, rock pro, etc, etc,?
What is the intended load?
Single or multiple directions of load applied?
Belay, Main, directional, component of a multi-point anchor?

Your question is too broad. I appreciate your thirst for more knowledge in this subject, but I'm going to say you'd do best to seek more courses.

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I don't think my question is too broad, let me explain. 1st. Since I am talking about a single piece of webbing, by default, we are uni-directional. Second, intended load? I always assume general which is two person at 600 lbs. Use whatever SSF you like.

So this leaves your last point, what are we anchoring too? This brings up my original question. Based on the anchor point, how do we decide the best anchor.

Considering Mikes input, the W3P2 seems real good since the knot is removed from the math. So at this point, the W3P2 would seem to be the end all be all web anchor.

But... As I think about it, say I am using the wheel on my rescue rig to anchor to, well, the W3P2 would be tough to do on a wheel. A double girth would be faster, easier and still have a good SSF.

At my job, we rig about 4 times a day for our industrial workers. Sure the W3P2 works well and seems to get the job done, I just wrap my W3P2 all the while wondering if there is a better anchor.

So far, I have had a few rope rescue courses and we have covered a handful of web anchors, but we never discussed when one anchor would be better than the other.

I was seeking collective wisdom here. I can go on doing the W3P2 and will never have a problem from my supervisor, I just wondered if I could explore better ways.

Personally, I like the double larks foot, it is fast, easy and handles a general load.

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Originally Posted by Rescue Dave

Here is a link to a great study that compares W3P2 and basket hitches using 1" webbing.
http://www.caves.org/section/vertica...tches&W3P2.pdf
Dave

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Interesting link. Thanks

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Originally Posted by servantleader

I've seen rescuers, when faced with an anchor that's too big for a proper W3P2 with the longest length of webbing available, tie two pieces of webbing together, rig what they call a "W3P2" with a loaded knot (where the two pieces of webbing are tied together), and call it a W3P2 even though what's actually been rigged defeats the true purpose of a W3P2 (no loaded knot). Makes me want to slap them silly.

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Research from the same guy that RescueDave provided the link for shows that a knot in one of the loaded strands is not the weak point. The failure still occurs where the webbing meets the carabiner.

I don't have the link, but it was presented at this year's ITRS.

Mike - I'll take a quick stab and then it's back to work! I'm working on a disaster exercise project.....

I stay away from w3p2 when my anchor is square and/or has a small diameter. I see a lot of guys force a w3p2 around rigging eyes in drill towers, small trees, or even the hooks on a fire truck. The diameter of the anchor must be large enough to provide the friction to make the w3p2 beneficial. Otherwise it looks jacked-up and is not very clean rigging. I compare my rigging to a prom date. If it looks sexy go with it. If it looks messy and cluttered, try again.

A square beam has very little surface area, so again why use a friction type anchor wrap? Larks foot...I do not use this in life safety situations except in hasty need. An untrained (or undertrained) rescuer can create a pretty good pinch point on the hitch bight if it is not loaded correctly. Climbers use this regularly to place protection, but they are dealing with very short runners, which minimizes a mistake.

Another anchor housekeeping issue is this. You rarely need more than 4 legs of webbing on a life safety anchor. I hate it when I see guys wrap something with 5 or 6 bights and then try to stuff all of that into a carabiner. Ether use a shorter piece of webbing or make your tails longer to shorten it!

Last thing. A while back I made a post about the MPD. Collin with Elevated Safety in Chicago sent me on of theirs to play with...Needless to say I mortgaged the house and bought one; great device. We used it in our last class and the students were very pleased. Let me also give a thanks to CMC, as they called to send me one as well.

Jeff

Sexy like a prom date...I like it, I'll be using that in the class I'm teaching Monday night!

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Originally Posted by jdcalamia

Sexy like a prom date...I like it, I'll be using that in the class I'm teaching Monday night!

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You and I must have had very diffrent prom experiences friend. :cool: