And, I hope I'm not being a jerk because I really appreciate the effort you have made to do testing on the systems we use, but the article states that Sterling scion was used in the testing of the alpine loop of r and r friction saver, but not what size. It is available in 11.5 and 12.5 mm on tree stuff. The article states that due to time restraints, tests were not able to be repeated and the tests were not scientific. It's too bad you didn't have more time. It would be nice to know if the results were repeatable and how different ropes respond to the same setups. Certainly in the example of a jam knot, a thicker rope would be harder to pull thru a ring and a softer rope of equal size would be easier.
Now, if a climbers rope is to have a minimum tensile strength of 5000 lbs, and even the strongest knots, such as a scafold knot, cause at least a 25% loss in strength and sometimes as much as 50%, what would be a reasonable safe breaking strength of a complete system?
RBJtree, I have quite your post, but my comment are not direct AT you. If my sense of humor got missed in the writing of this please do not take offense. I appreciate the questions because, as you will see, if you read the whole slightly diatribatic (just made that word up. Poetic license!) essay below, they allow me to drill down into the true reason I write and publish.
I’ll do my best to answer the questions. However, it has been a while since we did the testing and I presented the material and wrote the article.
As for the numbers, do not spend too much time looking at the charts and graphs. I hate using them in articles, because so often the message gets lost in the minutiae. ( I only publish them because it is generally expected. Yes, I am a shamless victim to expectation as we all are to some degree.)
Yes, the stats are important and show trends, but without repeat testing and controls, they are but one piece of the puzzle. This is why I am very specific about not labeling these studies/ testing we do as scientific. If there are erros in the graphs, it is most likely to be my fat fingers. Any recorded anomaly would have been noted and explored.
Having said all that! What we learned was that adding hardware reduces ultimate system strenght by about 30% in general. We learned that jam knots pull through rings at low loads and the carabiner in the loop formed by the jamb knot is the holding factor.
As for ring size, we used either DMM rings or Rock Exotica. While I do not recall the actual size of the rings, we kept it pretty standard to what is being used on manafactured products. Would ring size make a difference, yes, but a jamb knot against a ring is still an inherently weak configuration.
At the time of the tests, Scion was only available in the smaller diameter. Would a fatter or skinnier rope make a difference? Yes, but it is still an inherently weak configuration.
I do not think using a delta link would add/deminish strength. The rope parted at the carabiner where the line bent over the carabiner. I cannot envision how a delta link would change this. Perhaps a fatter link, but again. It is an inherently weak configuration.
As for ultimate strenght of an anchoring system. We could look to industry standards that differentiates between non certified (estimated strength by a competent person[competent person as defined by OSHA 1910.140(b) go ahead look it up. I'll wait!]) Work Positioning anchors (think lanyard) as being estimated to hold 3000lb static and the same being true for suspension (think climbing system) anchors. Keep in mind these are minimum, static holds. These numbers seem reasonable to me. Stronger is always better when it comes to your anchors so err on the side of caution. That too is only reasonable.
So what is the take away? I am sure most reading this will be clever enough to extrapolate the numbers and judge a system as "good or bad" based on strength alone. Mathematically I cannot argue with this. Numbers are numbers. However, when it comes to our anchors in production tree climbing we have to factor in strength and stability.
For example, let's look to knots. The bowline, the king of knots! Tied, dressed and set an excellent knot reducing line breaking strength by about 40%. However, it makes a poor termination loop knot because with repeated motion and tension variation the knot will work its way loose or alter. It has strength, but lacks stability. Clifford Ashley addresses this very subject in the Knotting Bible
The Ashley Book of Knots.
Apply this context of strength and stability to your anchoring systems and configurations. The factors of strength and stability
and the tendency to perform reliability under varying circumstances all combine to give anchors resiliency. Resilient anchors are the difference between good and great. The ability of a climbers to select, establish and use resilient anchors, systems, tools and technique is the difference between good and great.
Good enough may get you killed or injured. Good enough requires the minimum of skill, knowledge and time. Good enough may suffice, but for how long? In high level, professional production tree work, good enough is not good enough.
To paraphrase Vince Lombardi. "We cannot achieve perfection, but in striving for it we can achieve excellence." Choosing an anchor based on strength alone is not enough. That is just good enough. It must be stable and work reliably in a changing environment. To put it another way it must be resilient. That is excellence.
I have been working from the end of ropes hung in trees most of my adult life. When it comes to climbing I am closer to the end of my career than the beginning. The last 10 years or so I have dedicated my professional life to teaching, training and giving back the knowledge that was selflessly give to me. As such I am asked so many times "why" when it comes to tools or technique. I have come to learn that sometimes it is far better to ask "why not."
Not, why would I use a ring in an anchor configuration, but why would I not? Not, why tie in twice when cutting, but why not? The list goes on and on... If you have an honest, rational, intelligent "why not", then your decisions are crossing the line from goods to great as well.
Now for all of you reading this you have a preview of some of the articles I am working on for various trade mags here in the next year or so.
Tony
