Rigging with slings

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Postby Ralph E. Powers » Jun 26, 2006 5:42 pm

Yes that being said, a back-up knot is a good idea... depending upon what type of working load you're doing. I took a newbie out to a popular pit a few days ago and we discussed the rigging.
While I didn't back up the figure 8 knots that I used directly to the (main anchor) I did use additonal back-ups to the bolts that were there. In this case the main anchor was the tree and a prussik knot was tied around the main line and secured to bolts a few feet away from the tree (towards the pit). With another rope there were two bolt/hangers in line from one another. Again a figure 8 knot directly to the farthest one and then a butterfly to the closest to the lip. Neither 8's were back-ed up.
However; if there were to be a rescue load then certianly to prevent possible slippage a back up of a half-sheetbend/fisherman's knot would be a good idea at the base of the 8 knot.
It all depends I think upon what type of vertical work you're planning to do that day. If it's straight no-non-sense type vertical SRT then less is more. If you're doing tandem type work or pick-off/self-rescue type practices then yeah a back-up wouldn't be such a bad idea.
Actual rescue rigging of course is resplendid with redundancy, and thus backups and rebelays and so forth are the norm.
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Postby NZcaver » Jun 27, 2006 2:35 am

Ralph E. Powers wrote:However; if there were to be a rescue load then certianly to prevent possible slippage a back up of a half-sheetbend/fisherman's knot would be a good idea at the base of the 8 knot...

Just a little FYI - current teaching within the NCRC is no back up knot with a figure 8. :knot:

Not that the NCRC is the last word on this - nor is adding a back up necessarily "wrong" - but the students tend to be more focused on tying the right knot properly in the first place... :wink: Even with a rescue load, a properly tied and dressed 8 in the ropes we (cavers) use simply does not slip under linear loading. (I've never seen or read anything that contradicts that, so please correct me if I'm wrong.)

As for Water Knots in tubular webbing - I've never seen them slip either, even when destruction tested. But perhaps there are inferior types of webbing that are more prone to that? Again, I always dress the knot and leave a generous tail in webbing - like at least 6 inches.
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Re: webbing

Postby Tubo Longo » Jun 27, 2006 1:09 pm

GoHighGoDeep wrote: Oh... someone mentioned backing up a fig-8... and i'd have to agree that backing up an 8 is not always necessary... if you can't tie the 8 right, what makes you think you'll tie the backup knot right? :shock:

Sorry, may be my English is at fault, but I don't understand: back up a knot...?? :huh:

I have learned to back up a rigging, i.e. not to hang a rope from a single point of anchor, whatever it might be. Is this we are talking about? Because, otherwise, I don't figure out "to back up a knot", any knot.. If someone doesn't know how to properly tie a knot, better him/her off any vertical cave, in my own opinion. At least until he/she has learned.
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Re: webbing

Postby Adam Byrd » Jun 27, 2006 3:37 pm

Tubo Longo wrote:Sorry, may be my English is at fault, but I don't understand: back up a knot...?? :huh:


Think about the bowline, which is usually tied with a backup. In fact, let's look at a diagram.

Image

In b we have a bowline knot, plain and simple. In c, the bowline has been "backed up" with an overhand knot.
It's done to prevent knot from coming undone, should the tail slip.
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Re: webbing

Postby Tubo Longo » Jun 27, 2006 4:31 pm

Adam Byrd wrote:
Tubo Longo wrote:Sorry, may be my English is at fault, but I don't understand: back up a knot...?? :huh:

Think about the bowline, which is usually tied with a backup. In fact, let's look at a diagram.
Image
In b we have a bowline knot, plain and simple. In c, the bowline has been "backed up" with an overhand knot.
It's done to prevent knot from coming undone, should the tail slip.


Thanks Adam.

OK, is what we call a "safety lock" in Italy. Exp. on a bowline we are taught to always back it up because it can slip.

Back to the DB, I have never heard of slippage of a figure 8 (properly done and tied, of course). Even if, again, we are always taught (in Italy, guess here too) to leave at least a couple of inches of tail.
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Postby speloman » Jun 27, 2006 5:35 pm

I have never heard of a fig 8 slip. I have never had it happen to me but I was always taught to use a back up and always do. Just habbit for me. Every one is different. I like to double and safety everything. It is not that I am uncomfrotable with my knots it is because I want to be sure I and everyone is safe who gets on that line. Just my opinion and the way I do things.
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Postby Ralph E. Powers » Jun 27, 2006 8:08 pm

Well with so many different RIGHT ways to do it it's a wonder that there isn't a standardized method for everyone. Euro-cavers do things differently from Americans and I assume Aussies and Kiwi's do it their own way as well.

Perhaps this question belongs on a different thread.. but why isn't there a universal standard... it may even help pave the way for a type of Vertical Caving Certification....
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Postby fuzzy-hair-man » Jun 27, 2006 9:17 pm

I don't know if this is what you mean but I have been told that a figure 8 used to join a rope but with the two tails upstream of the knot (no I don't know why you'd do it either) can let the figure 8 roll off the end of the rope.

That said I have never seen it do it and probably never will because I won't rig that way and if someone else rigs that way I a) won't get on the rope and b) will suggest they use a double fisherman's or a back-fed 8 as a rope join.

Where it does become an issue is at rebelays for instance if you use an 8 for your rebelay and the rebelay fails not at the anchor but at the loop in the rope (due to rub or the rope getting cut somehow) then you are abnormally loading the 8 (a 9 is stronger that way) and there is the possibility that the 8 could roll off the the now cut rope because there is no carabiner there to stop it.

In the end a 9 (so I am told) is stronger than an 8 in all loadings so I use a 9 the extra rope it uses and the extra size of the knot are marginal. The only problem is it is difficult to back-feed a 9 but it can be done.
So the 8 is only really left as useful for back-feeding in preference to a bowline.

Same applies to tying out a rub point I suppose do a 9 or a alpine butterfly, a 9 looks less likely to come undone to me but that's just my opinion.

My 2 cents (and remember it's an Australian 2c about US$ 0.015) :laughing:
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Re: webbing

Postby knudeNoggin » Jun 28, 2006 1:32 am

Think about the bowline, which is usually tied with a backup. In fact, let's look at a diagram.

Image

In b we have a bowline knot, plain and simple. In c, the bowline has been "backed up" with an overhand knot.
It's done to prevent knot from coming undone, should the tail slip.


I should think that esp. those users of ropes stiff & slick enough to resist being
turned around even two diameters would be chary of trusting this simple
Overhand back-up knot to do a better job of staying tied than the knot it's
to protect!

Let's look at those revised Bowlines & another designed to protect themselves:

ImageImage

Each of these knots guards against loosening, slipping (unlikely to be realized in usual materials),
and ring-loading failure. All of these knots can be tied--like the common Bowline--after sizing
the eye (i.e., there is no first component to be knotted into the line, such as a Fig.8.
(And there are yet other varations to the Bowline, and other knots.)

... I have been told that a figure 8 used to join a rope but with the two tails upstream of the knot
(no I don't know why you'd do it either) can let the figure 8 roll off the end of the rope.

That said I have never seen it do it and probably never will because I won't rig that way
and if someone else rigs that way I a) won't get on the rope and
b) will suggest they use a double fisherman's or a back-fed 8 as a rope join.

Where it does become an issue is at rebelays for instance if you ...

I remarked about this, perhaps too obliquely, in my post above. It is possible
for the eye of a loopknot to become snagged or otherwise loaded in the way
called "ring-loading", where the loop is pulled apart, and a Fig.8 would
thus be in the orientation just described; it might be possible for the knot
to "flype"/"roll" off of the end.

As for why one might join two ropes using this Offset Figure 8 orientation
--preferably an Offset Overhand or Nine-Oh--, it is done to ease the movement
of the knotted rope over a rough surface: an offset knot (bend) will bounce
up and present the nearly aligned tensioned parts to the surface, readily
moving over bumps, edges; climbers hauling down rappel ropes don't want
the knot to hang up on an obstacle (or jam in a crack).

In the end a 9 (so I am told) is stronger than an 8 in all loadings so I use a 9
the extra rope it uses and the extra size of the knot are marginal.

The strength difference is pretty marginal, too. How close to breaking a knot
do you think you'll come? --or has anyone come? Were you thinking of using
5/16" rope, for instance? (But strength does have an appeal.)

with so many different RIGHT ways to do it... why isn't there a universal standard?

That premise answers the question, doesn't it? (;

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Re: webbing

Postby Tubo Longo » Jun 28, 2006 4:51 pm

knudeNoggin wrote:
In the end a 9 (so I am told) is stronger than an 8 in all loadings so I use a 9

The strength difference is pretty marginal, too. How close to breaking a knot do you think you'll come? --or has anyone come? Were you thinking of using 5/16" rope, for instance? (But strength does have an appeal.)

:exactly: I have also been taught that the strength difference between a 8 and a 9 knot is pretty marginal.

Where a big difference chick in is in untying the knot: on a rebelay which sees a whole load of cavers going thru, a 9 get untied way more easily than a 8.
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Re: webbing

Postby NZcaver » Jun 28, 2006 11:03 pm

Tubo Longo wrote: :exactly: I have also been taught that the strength difference between a 8 and a 9 knot is pretty marginal.

Where a big difference chick in is in untying the knot: on a rebelay which sees a whole load of cavers going thru, a 9 get untied way more easily than a 8.

According to testing done by Marbach and Rocourt in 1980 -

A Figure-8 breaks at about 55% of the static MBS of the rope under normal loading, and 40% under abnormal loading (mid-rope knot).

A Figure-9 breaks at about 70% of static MBS under normal loading, and 55% under abnormal loading. Plus it's definitely easier to untie, especially in smaller diameter rope/cord.

Of course, caving rope might have been constructed a little differently back in 1980 - although we are still talking kernmantel type.

For what it's worth, I went through a long phase where I always used a 9 instead of an 8. I'm not even sure why I drifted back to the 8. I guess because everyone else was using them. :wink:
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Re: webbing

Postby Tubo Longo » Jun 29, 2006 12:30 pm

NZcaver wrote: According to testing done by Marbach and Rocourt in 1980 .... Of course, caving rope might have been constructed a little differently back in 1980 - although we are still talking kernmantel type.

To tell the truth I had in mind the tests done by the National Technique and Material Commission of the Italian Cave Rescue in the 1980's and published in the late 1980's or early 1990's. It's a book of about 300 pages, with a yellow cover, thus known in Italy as the Yellow Big Book. Of course they also took into account what Marbach and others have done before.
Unluckily the book has been published only in Italian and it might out of order now, as far as I know.

About how rope are constructed, I agree that both material and tech. have changed. I'm not sure how much these changes might have affected the strength of a knot. In the sense that the knot might break at an higher value, but it would break anyway under certain stress. My guess is all knots would do the same... or not?
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Knot Break Strength vs Rope Break Strength

Postby Tim White » Jun 29, 2006 1:09 pm

Take a look at the recent study titled Knot Break Strength vs Rope Break Strength, by Dave Richards, Technical Director of the Cordage Institute. Some good data.

The article is published in the NSS Vertical Section’s Nylon Highway.

http://www.caves.org/section/vertical/nh/50/knotrope.html
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Re: Knot Break Strength vs Rope Break Strength

Postby knudeNoggin » Jun 29, 2006 3:33 pm

Tim White wrote:Take a look at the recent study titled Knot Break Strength vs Rope Break Strength, by Dave Richards, Technical Director of the Cordage Institute. Some good data.


Great to see this interesting study.
That old Marbach one seems incredible--never have heard of such LOW
figures for a Fig.8 loopknot, and I have to wonder at the wit of those
doing the testing & reporting (I don't believe it).

Please note that "Figure 8" is NOT a specific physical entity!!!
So even though one might find several sources, there's no telling for sure
that the same geometry of rope was put to test. On this point, I'm again
quite amazed that anyone would think to test both a "Fig.8 on a Bight" AND
a "re-threaded Fig.8"--which I take to be what the cited report calls "Fig.8
end" (though at first I thought they were testing the stopper knot, but the
values didn't seem right for that).
As though the knot should care how it was tied? (dressing & setting should
remove any initial differences)
CMC did a similar thing in their Rope Rescue Manual (and got similarly equal
results--no surprise at that).
Too bad this recent test didn't waste time with something so stupid and tested
a truly distinct knot such as the Fig.8 BEND, or Overhand or Fig.9 loopknot!
Conceivably, their different tyings in fact led to different strands being loaded
--as it's natural for the re-threaded tying to go one way, with the intial feed
and turn being made the easy way.

--and tell us HOW the Fig.8 was loaded (on which of the parallel strands)!

The same question arises for the Butterfly qua loopknot: it's an asymmetric
knot, so on which end was the load placed? (Beyond this, there are also
different dressings of it.)

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Re: Knot Break Strength vs Rope Break Strength

Postby Ralph E. Powers » Jun 29, 2006 4:24 pm

NZcaver wrote:
Ralph E. Powers wrote:However; if there were to be a rescue load then certianly to prevent possible slippage a back up of a half-sheetbend/fisherman's knot would be a good idea at the base of the 8 knot...

Just a little FYI - current teaching within the NCRC is no back up knot with a figure 8. :knot:

Thank you for that. I stand corrected :-)

Tim White wrote:Take a look at the recent study titled Knot Break Strength vs Rope Break Strength, by Dave Richards, Technical Director of the Cordage Institute. Some good data.

The article is published in the NSS Vertical Section’s Nylon Highway.

http://www.caves.org/section/vertical/nh/50/knotrope.html



Mebbe I should've finished High-School instead of getting a G.E.D. Mebbe I should've paid more attention to my math teachers monotonic vocalizations of the understanding of mathematical principals.

Either way looking at the charts I tried to decypher the info.

My mind kept thinking. One long continuous pull does not replicate a (SRT) climber or rappeller on rope. There are assuredly weight variations and tension variations that either enhance or negate the strength/effectiveness of any given knot.

The weight would be relatively constant... wouldn't it? It wouldn't, with an average 215 lb. caver, keep increasing until it broke. If it did we vertical cavers wouldn't be here.
Now I understand that the purpose is to see just exactly how much a particular knot/rope will hold under how much stress til it breaks/slips/whatever. But the constant increasing strain isn't what one would say a realistic application of the stresses to said knots/ropes.
I've known a professional (industrial) rope rescue team that wanted to test the holding power of various "catch-devices" i.e. Gibbs, prussik, Petzl ascenders etc. for rescue loads They (to me anyway) applied real-life application of the stresses a knot/rope would experience.
They took a large laundry bag and loaded it with stuff til it weighed 220lbs on a large scale. Then took the same bag and brought it up to a height of six feet with several feet for clearance and tied a "haul-system" to it. Dropped the bag and then observed the results and based their conclusions on it, they did the same with the rough weight of two adult males @ 440 to 450 lbs. as a victim and a borrowman. (by the way the prussik knot held every single time, the other devices literally BIT through the rope they were supposed to be holding).
Thus, they were able to at least IMO give a more accurate representation of the forces at work on our life-lines/nylon highways.

I dunno.. mebbe I'm missing the big picture with these type of tests.
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