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Ain't no flatlander
climber
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Dec 14, 2010 - 04:02pm PT
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Kurthicks is right, failure anywhere other than the marked section is irrelevant. The only way the DAV could get their test to show any "problem" was to place the marked section of the rope directly on the orifice of the drop rig. Even then, the difference was pretty minimal. Have yet to hear of a real-world case of rope failure at a middle mark. There seems to be no reason not to use a Sharpie for marking ropes.
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nutjob
Trad climber
Berkeley, CA
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Dec 14, 2010 - 04:28pm PT
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I usually end up cutting my ropes for self rescue or accidentally leaving the tails hanging out of my trunk on the way home, so age-related rope statistics just don't catch up with me.
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Trad
Trad climber
northern CA
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Dec 14, 2010 - 09:16pm PT
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Intrigued by this thread and being the science nerd that I am, earlier today I checked the pH of the acrylic paint and it came out neutral. Whew. ;) I don't know why I never thought of that before.
(I'm not joking, out of curiosity I really did check it this morning - I hadn't seen RURPS's posting at the time, but I'm sure he/she will be relieved!)
Banquo if you decide to test acrylics and want some litmus paper let me know...
Tom
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Clint Cummins
Trad climber
SF Bay area, CA
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Dec 15, 2010 - 01:59am PT
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Dan,
I concluded the same thing you did - it looks like there is a negative effect, but there were not quite enough observations to detect a statistically significant result.
The p-value on the t-statistic for MARVEY needs to drop below .05 to do that, and it's at .061 .
I think if you had 3 observations in each combination instead of 2, that would be enough to do it.
When I ran the linear regression, I used levels (pounds).
Your analysis was in terms of ratios (% of unmarked), which is also good.
I could reproduce your results by using log(pounds) as the dependent variable in the regression.
All the methods reduce to differences in means (or ratios of means, which is differences in log means) of the groups.
The linear regression is just convenient because it quantifies the variation or dispersion and gives you a single test statistic to check.
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bhilden
Trad climber
Mountain View, CA
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Dec 15, 2010 - 02:21am PT
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Banquo,
if you run more tests, I think it would be interesting, as another poster said, to put the treated piece of rope between the two pins and see if there is a difference in breaking strength. That seems to be a much more probable situation that will occur in climbing. It is very improbable that the marked section of the rope will be drawn across the radius of a carabiner given a 200 foot rope and a 9" marked section.
Bruce
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Clint Cummins
Trad climber
SF Bay area, CA
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Dec 15, 2010 - 02:47am PT
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Bruce,
I think the ideal test would be (as others have mentioned) with the rope ends wrapped around two large diameter objects, but this requires a more complicated testing rig with lots of room for such objects between the pullers.
The current setup at least tests how much the marker weakens the rope at the conventional failure point (knot or bend over small diameter object).
The marked section could be put in the middle, but unless the marker weakens the rope more than the knot or small diameter bend, you don't get a measure of what the marker did.
This could be an argument that the marker doesn't weaken the rope "enough", but it would be nice to know how close the comparison is.
For example, if the loop over the steel ring weakens the rope by 1000,
and MARVEY weakens the rope by roughly 510, it will usually break at the ring, and we would not be able to detect if MARVEY weakened the rope by 800 or by 100.
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bhilden
Trad climber
Mountain View, CA
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Dec 15, 2010 - 03:04am PT
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Clint,
Obviously some of the testing is going to be theoretical, but I think the test should mimic the most common climbing situations which for me means seeing what happens if the marked section is not running over an edge. If, in this situation, the knot breaks first then we can rule out about 99% of all climbing situations. No need creating any panic if it isn't necessary.
Bruce
ps - I tend to rule out the "over the edge" testing because the shape of the edge(blunt, sharp, jagged, etc) is such a huge factor in the results.
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Jay Wood
Trad climber
Fairfax, CA
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Dec 15, 2010 - 03:20am PT
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Here's a test for ink bleeding through to core.
Inked liberally, cut several hours afterward.
No noticeable ink on core. Sheath is stiffer where inked.
Maybe the test needs to be double-blind.
Results influenced by expectations of tester?
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jstan
climber
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Dec 15, 2010 - 03:39am PT
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When wrapped around a small diameter object like a biner with a bend of 180 degrees about 1/3 of the force on the other side is lost to sliding friction. When I went to a larger diameter pulling fixture I could not keep everything from getting equally stressed. But how about this?
I don't show it but the rope could be wrapped around each pin several times giving an exponential increase in sliding friction. The rope that is not so heavily stressed could be run off a distance so that its elasticity permits sliding. Note the pins would need some sort of texture to increase friction. With polished pins everything just got strained when I did it.
Tensile machines don't have a lot of travel so you can't go very far off to the side.
I may be failing Mechanics 101 here but I don't see it off hand.
Want the break at the mark. Going to have to have a very good sized control group.
I think Murcy's idea of using dayglow orange dental floss is the way to go.
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Banquo
Trad climber
Morgan Hill, CA (Mo' Hill)
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Topic Author's Reply - Dec 15, 2010 - 11:54am PT
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Large diameter testing is certainly the way to find the strength of a rope - which is not really what I am trying to do. My understanding is that in any real scenario, the rope will break at a knot or where it passes over an anchor and it is the reduction of that strength that I am interested in quantifying.
Black Diamond marked rope tests suggest that a mark will not reduce the strength enough to be an issue if the mark is not at a knot.
http://www.blackdiamondequipment.com/en-us/journal/climb/qclab/qc-lab-can-i-use-a-sharpie-to-mark-the-middle-of-my-rope
Like Clint says, the reduction in strength of the rope due to marking is probably too small to cause a break in the rope someplace other than at a knot or anchor. If my initial data turns out to be reliable, I might expect about a 15% reduction in static strength. So, if that is the case and I test a rope with a mark in either of my test configurations, I would expect it to break at the knot or anchor regardless of where the mark is. This is what the BD tests indicate.
Yes, it is unlikely in the event of a hard climbing fall that a center mark will be at a loaded knot or anchor. Unless the mark is at a knot or anchor, it may not matter if the rope is marked. One thing to consider is that in a fall, quite a bit of rope might pass over an anchor due to slack and stretch.
In a normal lead scenario, it is pretty hard to load the center of the rope at an anchor, to do so the leader has to fall a half rope length above his anchor. A full rope length out and a half rope past the last good anchor is not a fall I plan to take but I suppose it happens and you will want all the rope strength you can get if it does.
This, like all risk analysis, becomes a probability analysis. Will a lead fall occur? Will a lead fall generate high enough force so that a 15% reduction is significant? Will the center mark be at a knot or anchor when the fall occurs?
A better loop test might be to make samples like the BD ones with a figure eight at each end and then fold it in half so it is a symmetric loop and the rope doesn't have to drag over the pin so much. I think it would still break at the pin but maybe not. In my loop tests the upper pin is a bolt which did rotate but had some friction resistance.
All my tests of marked ropes broke at the mark. All clove hitch tests, marked or not, broke at a clove hitch. All loop tests, marked or not, broke at one of the pins.
Even though I was really generous in applying the marker, I didn't see any color on the core. It might bleed through over time though.
All tests broke the sheathing first and then the core. The highest load achieved was always when the sheathing broke. The core had quite a bit of strength but less than the whole rope which I suppose makes sense.
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kurthicks
climber
Washington
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Dec 15, 2010 - 01:56pm PT
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Yes, it is unlikely in the event of a hard climbing fall that a center mark will be at a loaded knot or anchor. Unless the mark is at a knot or anchor, it may not matter if the rope is marked.
True, but the mark can be at the belay device...
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Seamstress
Trad climber
Yacolt, WA
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Dec 15, 2010 - 02:16pm PT
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May I conclude that I should avoid "dropping" onto a rappel when the middle is marked - otherwise I need not concern myself with the very low probability of falling and stressing that rope segment.....
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bhilden
Trad climber
Mountain View, CA
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Dec 15, 2010 - 02:32pm PT
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I think there are some interesting things coming from the tests and the resulting discussion. As I said before, I was always under the impression that the sheath was not designed to add strength to the rope that it was the core which was the load bearing entity.
If, was we have seen, that the marker ink does not penetrate to the core, but the strength of the rope is potentially compromised, then it appears that the sheath does help bear some load. That could be a big wake up call for anyone who has some significant sheath wear on their rope.
I think it would be every interesting to ask someone at a rope company how they view the role of the sheath in a climbing rope.
Bruce
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Hummerchine
Trad climber
East Wenatchee, WA
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I have posted this elsewhere before...
So what if marking weakens the CENTER of the rope? The center of a rope is the part that strength matters the least. There is simply no way to cause a large stress to the rope here! It's near the ends that matters. Even if marking the rope reduces the sheath strength to zero, it's still plenty strong enough at the core. I'm not aware of a single rope failure due to this. BUT, there are quite a few instances of death by climbers rappelling on ropes that were not centered on the rap anchor. I recommend marking the center of your rope by whatever means possible...of course bicolor ropes are the best option!
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Magic Ed
Trad climber
Nuevo Leon, Mexico
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A few years ago Craig Luebben did a bunch of research and concluded that Sharpie and Magic Marker brands were safe for marking ropes. His results were published in one of the climbing magazines, I forget which.
Desnivel, the Spanish climbing magazine also did some research and concluded that the safest way to mark a rope was with a water-based latex paint. I tried that and found that the paint flaked off pretty rapidly so I went back to using a Sharpie.
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chusmacha
Trad climber
Bozeman, MT
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"The recommendation: do not mark your rope with any kind of felt pen. Water-soluble acrylic paints are apparently safe. No information is available how long they stay on."
The paint doesn't stay on very long. It is gone after a few climbs, especially if you're doing lots of rappelling where ropes are pulled through a ring, webbing a tree or whatever. The paint should be re applied just before the last of the old mark is gone saving the hassle of re identifying the center.
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Dingus McGee
Social climber
Laramie
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Circa 1973? Larry Peneberthy, Seattle, of his then recently formed company Mountain Safety Research (MSR now owned by REI?) tested makings on ropes. His conclusion was that paint and magic marker marks have negligible effects of rope strength. In fact a rope he had manufactured for sale had a paint line along its entire length. These ropes were somewhat cheaper than the European kermatle and I purchased one.
He published his findings in a newsletter. Another one of his studies established that wooden ice axe handles are not adequate for belaying falls. Does anyone have some of his newsletters on rope makings? Those that forget the past are condemned to repeat it.
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scuffy b
climber
Three feet higher
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I don't have any of his bulletins though I used to read them.
He contracted with Sampson Cordage, I believe, to try and make the choice
of a kernmantle rope more obvious.
At that time there were still plenty of people using Goldline or other
laid ropes because of cost, and it drove him crazy. He was bothered by the enormous
difference in rope stretch under body weight (which translates to how far
you have to Jumar before you actually get off your ledge, and how far you
go if you fall toproping) and by the vague criteria for retiring ropes.
He sold the ropes uncolored, and recommended using Rit dye to color your
own. A friend had one that was blue on one half, and red and white bands
on the other.
Penberthy also sold ropes unshrunk, with instructions for boiling them to
shrink them and make them dynamic.
Regarding the use of floss as a mark, if you pick out some of the bright
yarn from a scrap of rope or accessory cord, once your mark fuzzes up a
bit, it can be seen at a distance of at least half the rope.
That is, the leader can look down and actually see the middle mark at the
belayer.
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