Bend radius for ropes

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...As for cavers & nylon vs. polyester, there's significant difference between the sort of loading from towing through an ocean and caving use! The abrasion referred to in some of the towing is internal, resulting from cyclic loading, and cavers aren't likely to be generating this sort of load.

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Well reading only didn't last long did it. I wasn't comparing the cave environment to ocean; I was comparing cave environments to tree climbing. Polyester is touted as being more abrasive resistant than nylon in tree climbing applications. My example of cavers using nylon in very abrasive environments was with respect to trees.
 
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Lazarus2:[ QUOTE ]
Ron, I don't think anyone disputed this statement at all???


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Do you not remember saying this, and I quote,
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Lazarus2: "I think you are barking up the wrong tree - I see what you are saying about the two legs of rope, but thats not how it works in my experience. A 6000# rope with a knot tied to a 'biner (did I just say 'biner'?) errr... a krab, should only be expected to hold around a 3000# load."
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I'd call that directly, clearly disputing.

To quote Mahk, "Have you tested the latter statement? Photos? Info??"

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Hey Ron, I'm sorry you feel that way, but questioning and criticising aren't always the same thing, and this is a discussion forum - without questions there isn't much room for discussion, no? I'm afraid you mis-interpreted my post (which is OK, it happens all the time - there is obviously something wrong with me
grin.gif
).

I can't speak for Mahk, but it seemed he was just questioning???

I found it difficult to decipher what you were on about - my post was relating to a knotted line - i.e. it doesn't matter if the loop is double strength because the bend in the knot can cause the line to fail prematurely - figuring 50% covers all the variables; if there is one thing I've learned from 20 yrs of abusing ropes, its no identical rope failures and break loads even though the ropes and knots were the same. Even if the loop is double strength, it seems that the doubled strength is still reduced by 30-50% over a tight bend.

From KN's example about bend strength loss in the eye on the bend, it does seem that the bend will reduce (doubled)strength by at least 30% (though that was less than 1:1).

I think the difference is, I'm looking at this in a practicable way rather than an absolute way - in the real world not accounting for the variables with a wide berth can lead to absolute disaster. I'm sure everyone appreciates that.

At the end of the day, my focus is I need to cover the variables, make a life threatening decision and get on with the job - I don't see the point in dicussing to death something that hasn't been established - lets get out there and test it!

If an endless sling is 70% stronger than an eye sling over the same bend ratios, then maybe a 1:1 bend reduces the strength by 30%?

KN - the splice pulled out save for a couple of tucks. I have always found the hairy PP ropes slippery in the splice, and very difficult to set. It was a very large dynamic load - the climber came down before we pulled it over - that kind of extreme!

To me, on site, having to make a key decision, I don't rely on breaking strengths of splices (with low safety factors)without a tight thimble and a well set and whipped splice.
 
Over the (f)years as i've read the wet nylon tests; i've had to wonder (because it has never been specifically stated that i saw); if the tensile strength loss statically and pro-posed elastic increase, meant that the nylon ropes were worse on static force but better on dynamic forces(?). Whereby, when we said we had a strength loss wet, it might be a loss depending on the input forces. So, it wouldn't be really a loss/loss; but a trade off as many other things; if the water maid it better suited to dynamic forces(?). this might also be dependent partially on construction of the same fibers; like 3strand, braid or double braid, wet or dry; as the 3strand can take more stretch before snap in 3strand in ratings typically.

MA seems to often mean only gain in our macho/power greedy mindset; but unless the leveraging is Zer0; (meaning 1:1); that is dependent on perspective i think. From one end of the equal opposites; what is a 2:1; is a 1:2 from it's matching forces. So, even if we half an MA of 2x, that is .5x in decimal/non-ratio. The change in machine from 1 leg of pull to 2 could be considered such a change i think; in that 1 leg was causing 2 pulls of .5 pull MA.
 
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Hey Ron, I'm sorry you feel that way, but questioning and criticising aren't always the same thing, and this is a discussion forum - without questions there isn't much room for discussion, no? I'm afraid you mis-interpreted my post (which is OK, it happens all the time - there is obviously something wrong with me
grin.gif
).

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Lazaruz,

Let me digress very briefly. In response to the original post, I stated that the 1:1 bend ratio did not reduce the strength of a rope to 50% of the single strand strength of the rope because there were two strands supporting the load. That is exactly what the guy at New England Rope said also.

In your direct response to my post, you stated, "I think you are barking up the wrong tree - I see what you are saying about the two legs of rope, but thats not how it works in my experience. A 6000# rope with a knot tied to a 'biner (did I just say 'biner'?) errr... a krab, should only be expected to hold around a 3000# load."

And that’s just the starting point, after much discussion, with much evidence supporting my view, now you say, ”…nobody disputed this statement AT ALL” ? ? ? ?

I don’t have a problem with people expressing opposing views, friendly debates, etc. and it should be obvious that I don’t by this thread. But for you to clearly tell me I was barking up the wrong tree and then later claim nobody has ever disputed that, that is a contradiction.

Next, and I’m sure it was not by intent, you took the following statement I made completely out of context:

Ron:[ QUOTE ]
To quote Mahk, "Have you tested the latter statement? Photos? Info??"

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You responded:
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I can't speak for Mahk, but it seemed he was just questioning???

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But my remark had nothing to do with Mahk questioning me. In fact, go back and read my response and explanation to Mahk. The reason I quoted Mahk, is you had just said this statement:

Lazarus2:[ QUOTE ]
I don't think the cumulative strength loss in ropes works quite in the way you have suggested.

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It was to that statement, that I replied with this:
Ron:[ QUOTE ]
Mahk, "Have you tested the latter statement? Photos? Info??"

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I was quoting Mahk, to emphsize you just offered an opinion without any support whatsoever to back it up. And, as Mahk had rightly pointed out earlier, I wanted to re-emphasize that I’m not the only one that would like to see support of claims.

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I found it difficult to decipher what you were on about - my post was relating to a knotted line - i.e. it doesn't matter if the loop is double strength because the bend in the knot can cause the line to fail prematurely - figuring 50% covers all the variables; if there is one thing I've learned from 20 yrs of abusing ropes, its no identical rope failures and break loads even though the ropes and knots were the same. Even if the loop is double strength, it seems that the doubled strength is still reduced by 30-50% over a tight bend.

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I find that extremely difficult to accept. I believe I have been quite clear and unwavering in my statements. But here it is simply stated: for a spliced eye, a loop knot, or two strands of rope over a 1:1 bend ratio with both ends connected to the load – none of these three configurations reduce the strength of the rope by 30% - 50% of the single strand strength of the rope. I was also very clear about the principle involved – the 50% estimate would apply to two strands of rope equally supporting the load which would be nowhere near 50% of the single strand strength. I even gave examples assuming a 50% reduction in strength due to a 1:1 bend ratio and it was amply clear that even if the 50% reduction did occur, it would still only reduce the effective strength of the rope to 100% of the single strand strength. I still stand firmly on that.

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From KN's example about bend strength loss in the eye on the bend, it does seem that the bend will reduce (doubled)strength by at least 30% (though that was less than 1:1).

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Maybe. That is one example, and it had absolutely nothing to do with climbing. And the example did not address the issues of nylon water soaked with salt water, increased abrasion effects, shock loading, loads well beyond what we would see in life support, etc. It was only one example, not well documented, and one incident is hardly enough to be indicative of what is actually happening in a non-climbing related incident.

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I think the difference is, I'm looking at this in a practicable way rather than an absolute way - in the real world not accounting for the variables with a wide berth can lead to absolute disaster. I'm sure everyone appreciates that.

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Doesn’t the 10:1 safety margin account for practicality and variables? Isn’t that exactly what the 10:1 safety margin is for? To take into account bends, wear and tear, knots, etc.?

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At the end of the day, my focus is I need to cover the variables, make a life threatening decision and get on with the job - I don't see the point in dicussing to death something that hasn't been established - lets get out there and test it!

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How about this: we get out there and test it, before we start making unsupported, arbitrary, ‘practical’ claims?

I did get out there and test it. I pulled 15 knots in two different materials and two different constructions, as I have before, and have never seen a single failure in the loop. Then just to be sure I wasn’t doing something impractical, I called New England and they had been out there ‘testing it’ and they got the exact same results I did.

I would also submit that a 'practical' issue that has not even been brought up is repeated stress on the exact same point in the rope over long periods of time. E.g., I have a Velocity rope with an eye spliced in each end. That means that I will repeatedly expose the same part of the rope - the eye at the bend, to loading. Over time this could have an accumlative effect and weaken the eye at the contact point. But this is the first time this has even been mentioned. I'm a concerned about this situation creating a weak spot over time.

And, certainly, if we put a rope over a 1:1 bend and pull both ends of the rope to failure, I would fully expect the rope to fail at the bend, if the two ends are not weakened by their attachment method. But I would be totally surprised if the rope failed lower than it’s single strand breaking strength.

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If an endless sling is 70% stronger than an eye sling over the same bend ratios, then maybe a 1:1 bend reduces the strength by 30%?

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The point is we just don’t know. And if we don’t test it we’ll be here forever debating something we don’t know.
 
Ron

I'm afraid you have my reasoning mis-understood, which you find extremely hard to believe, and state that KN's example supporting my reasoning is not worthy???

Thats too bad. This is not the medium for me to take it further - I just don't have the time to mess around with multi quote posts to iron it out only to have it messed up again.

It'll have to wait till we meet. If you're going to TCI Expo, I'll gladly show you where I'm coming from, Or explain it to Tom.

I can easily say that the point you make about wear on a fixed eye has been discussed by me going on about CTF - its the whole point, also one reason why I insist on a thimble.

Take care.
 
i have many knot resources and test sites listed on my knot page at http://www.mytreelessons.com/Pages/Knots_Links.htm .

Even the original Life on a Line that is getting harder to find with Dr. Merchant's putting out the paid virgin update to his fine book. i've even combined the 3 .pdf's into 1 file; for he gave it away when internet speeds were much slower; and so subdivided it.

Anhother jewel listed is Nylon Highway Issues going back to '74; that of course Mr. Bruce had much to do with.

i'll also offer that there are many fine thoughts here; and they could be extended to the Knot Tyer's Wiki Project; make your own page, whatever. You get something real good going; let me know and you might suddenly find it on the rotary menu project; especially if ya send me a pic to identify it.
 
Lazarus2,
I didn't say KN's example was unworthy nor did I imply that. Nor does "unworthy" represent what I said. If you re-read what I said, it's clear that I said it was not well documented; that doesn't mean it's unworthy in anyway or that it wasn't documented somewhere. It simply means the details of the example and determining factors weren't included.

Guys, it was never my intent or desire to become engaged in a one-on-one struggle about anything. I'm sure this has been most distracting and I want to offer my sincere apologies to <u>ALL</u> for my part in this.
 
I think there's some misunderstanding re the example I relayed:

that was of a "grommet"--endless loop/sling--, and the reduction
that was asserted for that type of structure was about 33%.
As I put in figures, that suggests for the cited 6_000# rope that such
a formed eye of a grommet ("eye" simply meaning that the bight ends
are bound/seized to produce small-opening eyes rather than having
one big circle of rope) breaks around 8_000#--i.e. with about
4_000# on each leg. The theoretical max. of such a rope sling is 12_000#.

And clearly then for the eye of a single strand, you will not reach this.

*kN*
 
kN,

There certainly has been confusion. One erroneous idea was that I was claiming that a 1:1 bend ratio reduced the rope strength by 50%. I never stated that. The confusion arose because someone else stated that and I tried to show that even if the strength of a rope doubled over a 1:1 ratio were reduced by 50%, with would not reduce the strength to 50% of the single strand rating.

Apparently because I used the 50% claim, it must have been assumed that I was claiming that. I was not, never did, and still don't. I simply don't know how much a 1:1 bend reduces the strength of the rope by.

But I do know, based on New England Rope's expertise that loop knots and eyes rarely, if ever, break in the loop.

Then to clarify my remarks about "...not well documented..." They were in reference to this:

kN:[ QUOTE ]
And, hmmm, at the end of the 12.9.2 "A loss under tow", also re nylon ropes, I see the concluding remark that "Placing soft eyes round a small shackle pin with a D/d ration of about 0.8:1 (i.e. pin diameter less than rope diameter) would reduce the strength by a further 33%." That might be a comment to be understood as for cyclic loading, not one-time pull. And I believe that "the ropes were made up into grommets with soft eyes" means that essentially one had doubled material (with "eyes" maybe seized into shape fore each end), and the reduction thus is of roughly double the rope strength.

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My remarks were not in any way intended to be critical or slight you in any way or to imply that this was your opinion or conclusion. As I understood it, you were simply providing info from an article.

There's an old saying that says, "The devil is in the details.", of course meaning one doesn't discover the problems until one gets into the details, and that is what I was aluding to.

For example, we don't have a clue how this was measured, condition of the rope, if it had been exposed to salt water, if it was in the form of a grommet or not, how many times the rope had been exposed to this kind of pull, etc.

In any event, even if it were a new rope, it is interesting that the 0.8:1 ratio only reduced the strength by 33%. As I have posted previously, it is amazing to me that after all this time and experience with rope, we don't have numerous definitive tests exploring this.

I will say this with regard to the claim in the example you referenced. I completely agree with your assessment of the the strength - 33% refers to the reduction of the double strand strength, i.e. assuming the 33% to be true, and I'm not saying it is, I simply don't know, the final strength would be 67% of 12000 lbs = 8000 lbs just as you stated.
 
Laz, you say you use a thimble...Is that with a spliced eye or knot?? And with a biner or with rope snap?? If with a biner, how do you keep the rope/thimble from doing alot of sliding around on biner??

Hope this isn't hijacking the thread; it seems relevant to bend radius matters....
 
Hi Cory

Its with a spliced eye (for rigging, I see no real advantage in splices for climbing). I also use it with a knot on a couple of slings. The buntline keeps it set nicley.
 
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