The problem is that people rely on published specs to make decisions about what to buy. E.g. I bought HTP thinking it weighs 5.3 lbs/100 ft but when I weighed it, I got 5.55 lbs/100 ft. Not that that's a big difference, but it is misleading. But the main reason I bought the HTP is the stretch spec. The major attribute emphasized in Sherrill Tree's catalog is the 'non-stretch' property of this rope supported by the claim that the stretch at 540 lbs is only 0.63%. At my weight, the rope should stretch about 0.25%. If Sterling is correct, Sherrill Tree is publishing a stretch spec with a 300% error - the main attribute of the rope.

I know of know other rope that there is such a wide variance of a parameter claimed, and since the stretch is one of, if not the top, attraction to this rope, it seems reasonable to know what that characteristic is within at least 50%, and that's being generous.

Sounds like a letter is in order to both parties to discover why the spec disparity. I'd go with the manufacturer's spec as the baseline.
-moss

Hmmm, that's an interesting idea - I'll probably try an email first.

So the argument about weight difference is about approximately 113 grams difference between Ron's Calculations and the company posted weights on a 100 ft long piece of rope? (5.5 lbs vs 5.3 lbs)

That is a difference of less than one gram per foot of rope!

I am not disputing the accuracy of Ron weighting techniques but even if his rope was exactly 100 ft long (new) rope without ever being used but just dropping the rope on the ground one time it will pick up that much extra weight in dirt.

The company results were probably done with several duplicate samples in lab etc, etc, etc.
So i suggest going back to the lab and reweight the rope before the letter is fired up to the company.

I personally would not worry about the extra amount of weight on the rope since I probably carry 6 extra binners that all together weight more than the rope. Just my water bottle weights an extra kilo.

OldTimer,

I agree; but my concern isn't the weight per 100 ft, it's the contradiction in stretch percents listed by Sherrill Tree and Sterling rope. There's a 300% discprency between the two and both claim to have measured the stretch. I wouldn't expect the same numbers from two independent tests, but they should be within 20% anyway.

I've often wondered about Sherrill's claim of 0.63% at 540 lbs. That seems like steel cable specs. OTOH, in my limited experience with HTP, it seems like HTP is better, i.e., less stretch, than Sterling's spec of 1% at 300 lbs.

I was on 157 feet of HTP last night with a ground trunk tie and I have to admit that it's very difficult to distingish what is slack, take up, and stretch. But, I know this, once I had the rope fully loaded with my weight, there was no noticeable stretch. I'm sure there is some, but it's so little and once the rope is loaded, the only additional stretch you should get is dynamic due to climbing strokes and that's pretty light compared to the climber's weight.

Anyway, I guess the bottom line is, when you're climbing on it, it essentially doesn't stretch.

One other pertinent characteristic of HTP that I discovered last night. We hit a shot about 78 feet up the tree and did a ground tie. Neither end of the 157 feet of rope touched the ground. We did a trunk tie on an adjacent tree with webbing and to conserve rope as much as I could I tied a bowline with a mountaineer finsh and clipped it to the W3-P2 webbing. When I pulled out the slack and loaded the rope, the end of the rope did touch the ground. I was climbing on a Texas set up and would be advancing the foot ascender (lower ascender) by hand. I fully anticipated having to pull the short down rope through the ascender until I got high enough for the weight of the rope to feed by itself. Well, I got up a ways and realized I hadn't had to pull the rope through a single time - it fed through the ascender from the very first stroke even though there was only about 3-4 feet of rope below the ascender.

I really love this stuff!

Take a look at the diagram at the bottom of this page:
http://www.samsonrope.com/site_files/Co ... gation.pdf

The interesting thing is "permanent elongation". You should be able to see that the first time it is loaded it will stretch a greater percent than on subsequent loadings. If you keep loading it and unloading it over a short period of time where the "hysteresis" component isn't recovered then the only stretch you get is the "EE" or "immediately recoverable extension". I think EE stands for "elastic elongation". I had never thought about this stuff until I saw the diagram.

Otherwise there isn't much difference between 0.63% and 1%. Measuring rope stretch to the hundredth of a percentage point isn't very useful anyway.

Edited:
Someone could round off 0.63% and get 1%. Same goes for 1.3%. But it does seem a little strange they got less stretch with more weight.
But we're still talking very small numbers. Even if you double or triple a small number like 0.63 you still wind up with a small number. If instead you were talking 5%, withing the definition of a static rope, but instead got 15% then that would be pretty significant.

I remember an argument in medicine some years ago where a certain treatment for a particular disease quadrupled the rate of a particular cancer. But since it was a rare cancer then only a few more people (out of 100,000) died. At the same time the treatment saved a lot more lives from a much more common disease. The cancer, even though 4 times more likely, was still rare so it was considered an acceptable consequence... unless of course you were one who got the cancer.

I guess the figures for stretch are all messed up. It makes me wonder if the figures they quote for strength are equally bogus.

By the way, you mentioned PMI Easy Bend 10mm (Sport Static?) with 1.8% elongation. I climb on it all the time and it stretches a lot more than that, at least 2 or 3 times as much.

I climbed on Rons HTP again this weekend. We found a lovely Tulip poplar on the side of lookout mountain and landed a 78' setting. We used a ground tied anchor. We didn't have any webbing, but Ron had a 20' piece of 8mm B-line so we used that. I worked great and it is twice the strength of 1" tubular webbing.

Anyhoo, I was again very impressed with the performance of the rope. I climbed on a YO-YO setup. the lack of stretch was very noticable. When I stood to advance upwards it felt like every scrap of effort went directly towards my progress.

I am convinced that taking up the stretch in a rope contributes to fatigue.

While there doesn't appear to be much difference, the percent difference using 0.63% as the reference comes to:

%diff = 100% * (1.00 - 0.63) / 0.63 = 58%

or, using the 1% as a reference:

%diff = 100% * (1.00 - 0.63) / 1.00 = 37%

To maybe help appreciate what those percentage differences mean, consider that if you currently weighed 200 lbs and your weight increased by 37%, the lower of the two figures, you'd weigh 274 lbs.

And, the difference would be much more if the same load had been in each measurement. If we interpolate Sherrill's stretch down from their 540 lbs to a 300 lb load, their stretch should be more like 0.35% at 300 lbs. Now we're comparing percent stretch at the same load. Dividing 0.35% into 1.00% gives 2.86. That's where I got the almost 300% difference. The difference in 0.35% and 1% stretch at the same load is almost 300% (actually 286%).

I can say this: the difference in feel, observation, and estimation of stretch between HTP and any rope that stretches even 2.5% is night and day.

I do believe though, that initial and dynamic stretch are clouding the issue. Initial stretch will always be greater because the rope is experiencing a no load to full load difference. In addition to that, the anchor (ground anchor in this case) will contribute to stretch, as will slack in the rope up and down the tree. Any small limbs that may be in the path of the rope can also contribute to the initial stretch. But once fully loaded, all that one will feel (presuming limbs in the rope path are no longer contributing) is dynamic stretch.

Dynamic loading is the difference between the static load and momentary force generated by lifting the load. If you lift your weight faster, you generate a greater force. But, the dynamic force component will be much less than the static load and hence the stretch experienced while climbing will be much less than when you first 'sit' on the rope. But, having said all that, the difference in HTP and any rope with a 2.5% or so stretch is simply like night and day. When all the take up comes out of the HTP, it's like someone said - a steel cable. There just simply is no discernable bounce. Well there has to be some, but it's so small I can't even feel it.


Yeah, I wonder if either are all that accurate and if the actual stretch is somewhere in between. I'm under the impression that strength figures are much more accurate. I think most manufactures use a statistical analysis spec of 3 sigmas. I may be remembering this inaccurately, but seems like if a rope is spec'd at 6000 lbs to 3 sigmas, it means that 99.5% of the ropes produced will have a minimum breaking strength of 6000 lbs or something like that.

Stretch doesn't seem to be so accurate.


That's what the PMI catalog says. I have seen some discrepencies in PMIs catalog before though and called them and they gave me correct numbers. So it could be that PMI 10mm has more than 1.8% elongation. It feels like it to me too.

BTW, I don't know if you picked up on this in Hunabku's post, but that 78' TIP means the rope has to be 156' long. My HTP is 157 feet long and the ends barely reached the ground. So when Hunabku loaded the rope, he was essentially on 150' of rope and it felt and looked solid.

I'm not trying to sell anyone on HTP rope - just trying to bring some perspective to the significance of those small percentages. E.g. you could double 150 feet of Chameleon, etc. say in 75' DRT setting, and it would still have significant, more 'feel-able' bounce than a single HTP rope limb cinched at 75'.

And this is just and opinion and not tested by any means, I believe the 75' DRT setting would have more bounce than a 150' of single HTP rope ground tied.

I finally got my hands on 200 ft. of the Sterling HTP 10mm. This rope is superb, it is the best static I've ever climbed on. Everything Ron and Hunabku said is true (I didn't doubt it). I was amazed just doing a load test how little stretch there is. I don't care what the rating is, there was no perceptible stretch. I did five 75 ft. ascents on a trunk anchored TIP. Tested Yo-Yo, Texas System and Tree Frog, it was all good. Descended on a Grigri each time. Some have reported the Grigri being a little "jumpy" on the this rope. I didn't have any trouble, very smooth. I did get some hockling in the last 15 feet or so of the rope after a couple Grigri rappels, was easy enough to take out by running through my hands.

That's it, 5 star rating. My Bluewater II 10.5 mm is now a semi-retired backup rope.
-moss

Anyone ever tried PMI IsoStatic?

Just checked the specs, looks like good stuff, all polyester. The two available diameters are 11.5 and 13mm, this would put it in the "too heavy" class for my typical use (hiking into the woods with a 200 ft. static rope on my back).
-moss