Bee-Line Break Tests

Some months ago Ron reported some interesting break tests on Yale 8mm Bee-Line, and I recently had a chance to supplement his work with some experiments of my own. I wrote all this up at length on ArboristSite, but I thought it worth summarizing here.

All ropes were eye-and-eye slings (e2e), and all pulls were performed on my hydraulic rig using 3/4-inch steel clevis pins to hold the eyes. At the first loud bang, indicating one or more strands had broken, each test was terminated (with one exception).

The first photo shows some ready-to-test ropes donated by Canopyboy from AS:



Three tests were performed on naked locked Brummels (4-in taped exposed tail).

They broke at the Brummel at 3572 lbs., 2862 lbs., and 2424 lbs.

This last and weakest one is the whipped brummel shown at the left of the photo. That one actually had an initial minor break at 2052 lbs., but I continued pulling until the much larger failure at 2424 lbs.

The photo shows one of the broken Brummels. Note failure has occurred on both sides of the Brummel, and that the braid in the tail has become highly condensed as it resisted being torn apart and sucked through the Brummel. The Brummel itself has become, as they alway do, a very hard tight-wound knot.


Two tests were performed on straight bury splices in which the splice slipped:

4-in bury--slipped at 1216 lbs.
5-in bury--slipped at 5030 lbs.

The e2e in the first photo made with double fisherman's knots failed at 3590 lbs. One of the tails crawled all the way through the knot without breaking anything.

The other standard e2e, second from right, failed at 5318 lbs. when one of the splices slipped about 3 inches. There was still enough energy and tension in the system to cause the locked Brummel to cinch up tight and partially fail with breakage of one or two strands.

Since this is a very common configuration (I believe Nick makes a ton of these), I did a careful forensic dissection of the rope. The remaining eye showed no signs of slippage and its bury measured 4.75 inches. The bury of the failed splice was presumably the same length. It appeared to have a long thin taper so its effective length may have been somewhat less than 4.75 inches. The whipping securing the cover at each end included several through stitches which would have significantly enhanced the holding strength of the bury even as it probably weakened the Brummel. The photo shows the rope after the test:


Finally I tested both the core and the cover separately for ultimate strength by creating e2e's with 9-to-10-inch tapered buries. The idea for testing the cover in this way I attribute to Ron--I probably would not have thought to test it at all.

The cover broke at the end of one of the buries at 6020 lbs.

The core broke at the end of one of the buries at 9594 lbs. That is not a typo!

I know this is a very popular hitch cord, and in my one brief 30-foot descent on the stuff I thought it performed very well. But this stuff makes me nervous. A Brummel evidently reduces the strength of the core to 30 % of the 9600 lbs. I measured. There is a strong suggestion that modest stitching significantly impairs the already weak locked Brummel. There is the need for whipping to keep the cover in place. Overall, the vectran core seems to be happy only in a straight pull. When, as we must, we whip it and stitch it and Brummel it (or knot it) it gives up most of its strength. Plus it is just plain complicated. Plus you can't see the part your life depends on.

I have a little bit of empty cover left. I plan to make a hitch cord out of it and give it a try. I'll report back on what I find.

WOW! I like data like this.

I eases my mind as it wanders when I dangle at sure death altitudes.

Is is safe to say that if you configure these in a manor that they are normally used in then the strength would double?

If you tie your VT around your climbing rope and use your fair lead device both ends of the BeeLine are loaded.

I for one would like to see a break test done on a rigging as equal to real usage as possible.

Comments?

See you at the top,
Dan

Moray,

Thanks for the testing info. One thing to consider is at what load does this hitch cord slip on the rope you are using. I suspect that it would slip well below the breaking strength of the cord. For a ballpark figure, prusiks have been seen to slip between 7 and 10.5 kN (from the British Columbia Council for Technical Rescue).

I've made a hitch cord from the sheath only. It performs well in climbing situations. This was a project Hunabku,Nick (from WI) and myself worked on during the Florida meet-up. We'll be break testing it and a few other samples soon and doing a more complete write-up for the articles section.

Moray,

Looks like we’ve come to the same conclusions:
* Locked brumels in 8mm BeeLine weaken the cordage immensely.
* Stitching further weakens an already weak splice
* The tucked eye in the cover is STRONG
* Brumels in 8mm BeeLine make me very uneasy.
* you can’t see damage developing
* locked brumels should be whipped not stitched
* In use, I’ve had several covers pull away from the eye, exposing the core – not good.

What we need to do is test a double braid E2E in BeeLine and test that. I believe it will be far superior to brumels and offer more protection for the core as well. I have a doulbe braid E2E but haven't tested it yet.

I like that number just fine. Considering that if it's used in a well balanced hitch 7180 is a pretty nice number. Luddite that I am I really like tied eyes, in particular for the way they cinch the carabiner and barely slide around compared to spliced eyes.

These tests are really great, helps everyone make informed decisions on cord configuration and use. I agree with Dan and Oak's points on "real world" use, the next step might be to see how various eye-to-eye terminations do in "hitch on rope" loading scenarios.
-moss

Yeah but, let us not forget what moray said, and I fully agree with,



What goes along with the bends, brumelling, etc. is what happens over time? If just splicing it reduces its strength to 30%, what is continued use and flexing doing to it?

Then what if we shock load it once or twice?

What if someone decides to use it straight-line for some purpose where the loading on the eyes aren't halved?

I'm waitin' to see how the double braid E2E fairs before I get too comfortable with BeeLine.

Any life support gear that I theoretically shock load whether it be a biner, climbing rope, ascender, hitch cord or anything else becomes suspect at that point. I've never shock loaded any of my gear in 5 years of climbing. I hear scenarios and stories where shock loading could or did happen. In rec tree climbing for instance have you or anyone you know shock loaded their gear? I want my gear to respond well if it occurs but as we've discussed in the past it's more likely that body parts will fail well before any work positioning gear breaks under shock loading. If people climb above their TIPS they shouldn't be expecting their gear to protect them.

As far as wear over time goes, I retire my split tails after a year or so, when they start look tired so-to-speak. I've never had anything approaching failure in any of my Beeline split tails. Once I tie an eye it doesn't get untied and retied so I minimize flexing at the knot or eye. We may be overselling Beeline's failure potential in real tree climbing situations.
-moss

I see that as a poor use of Beeline, there many cheaper and sufficiently strong alternatives that likely function better for that kind of use. My understanding is that it's designed and intended for doubled use.
-moss

I would just like to put a perspective on this. Many of us SRT folks put our life on a handled ascender, whether it be a jumar, CMI, Petzl, PMI or something similar. According to Petzl Technical Documentation, the fail rate of the cam on a handled ascender is about 4-6.5KN. If 1 KN=224.8, that is only 1461 pounds of force at the most. I would be curious for someone with the equipment to test this theory. If this is the case, I would not worry so much about Beeline breaking at 2500-3500lbs. I would be more concerned about that ascender failing or shredding the rope. Don't get me wrong, I find it interesting that this common splicing technique is being tested and is found that it does in fact reduce the strength of the rope. To go and say that BeeLine that breaks at 3500 lbs is not safe and using an Ascender that fails at half that is safe does not make any sense.

It is always good to know exactly where equipment will actually fail. Thanks Moray for doing the testing on this. I would like the idea of doing these tests when rigged to provide a more realistic result. I would also like to see some of the mechanical progress capture devices tested if possible. I am still in love with my new PMI Pulsar, so you ain't getting that. So who wants to donate the gear you don't like to testing?

Thank you for doing these break tests, Moray, Ron, and everyone who's engaged in them right now. It's very nice to see where the cord breaks and under what circumstances. Like someone said, these are things that help reassure me at altitude!



That's what I'm most interested in. I'm not up to making my own splices yet. As Moss points out, that's a lot of strength when doubled. Even when in a single configuration, 3590 at 1:10 is still a decent margin. As for the splicing - well - I'm glad you gentlemen are working out what's strong and what's not.

I'd be curious how it compares to the Ice Aramid cord that Sherrill sells. Since it's single braid, I wonder how different the results would be.

Testing in 'real world' would be nice, ie the hitch on the rope, but I think this data is necessary as almost a baseline; how much the cords can take, with various knots + splices, in a straight line, no other ropes involved.

Thank you again, breakage-testers, for doing all this work in this thread and others.

Exactly why i won't tie them that way. I'm curious if there is even an insurance carrier (work or rec) that allows for that knot to be used alone as a termination knot. I read on arborsite about the possibility of using whipping/stitching to prevent slippage kinda like using a grizzly type splice for a backup knot... that might make for an interesting break test.

I have been using a figure 8 on a bite with a stopper knot for making i2i split tails but my climbing instructor from way back saw me climb the other day said that a pre-loaded figure 8 on bite is fine by itself... however he said if climbing with a class it would most likely technically need a backup to be covered... i'm guessing the basis for the insurance requirements would be break tests like these where the knot slips and accident reports where people died on just one knot?

The working loads of all this kinda confused me... bee line is like 8000lbs tensile but if it breaks out of a knot at under half that would having the load split on both eyes return it to 8000lbs? Does anyone know if all i2i hitches split the load 50/50? and on DRT is a shock load actualy like a 50/25/25 split because of the standing end?

I think Glenn's got the most relevant point. Most of the mechanical gear we use is rated a lot less than the cords or ropes, even with knots involved.

Adam, what's your insurance say about mechanical gear?

For SRT i was told that you must have two points of contact on the rope at all times... so let's say for example in an SRT climb you go around a branch climbing the tree and not the rope, you then must disconnect your ascenders and take them around the branch with you and put them back on the line... during this change you must lanyard in because you would only have 1 point of contact on the rope. However if the top hole of the ascender is filled then you can have only 1 point of contact on the rope as in a yo yo setup.

The guy telling me all this wasn't really sure he was correct but it all made sense to me... during the change over the ascender is at a higher risk of being loaded incorrectly and popping off the rope or something to that effect.

I would like to find printed documentation on it though... oh and yes i also think glen has it dead on with the ascenders cam being the weakest link of everything we do... the only other exception would maybe be incorrectly tied knots that could slip at lesss than 1kn.

There is no insurance company that mandates that specific knots be used for rec or work climbing. For work climbing there is ANSI and OSHA. ANSI regulations are voluntary consensus standards but OSHA may refer to particular ANSI standards and require that a working tree climber follow them. An insurance company could refer to the OSHA regulations and require that their insured follow them. There are no regulations for rec tree climbing, I don't know of any insurance companies that have the expertise or motivation to create regulations for rec climbing instructors (they are the only rec climbers I know of who have specific tree climbing liability insurance). That's not what insurance companies do, they rely on existing standards and guidelines to write their policies.

The double overhand noose knot is reputed to be the most secure cinching termination knot known for tree climbing. There is a potential issue when the construction of the cord or rope consists of a braided cover and one of the high strength polyester core materials, the resulting core is very slippery. New England Ropes Tech Cord is a good example, in shock loading tests on a tech cord sling joined with a fisherman's knot the core will slip through the cover. It is recommended that tech cord slings be tied with a triple overhand on each side of the fisherman's knot.

Beeline appears to have a fairly slippery cover. Looking at Moray's photo of the double overhand eyes I can tell you which one slipped through. My current Beeline e2e's have long tails on the knots. The other thing I've noticed after climbing on Beeline for at least a year is that the core slips a little after the first couple of climbs and then sets and never move again. Although the last couple sets of split tails I've made and climbed on have not shown any signs of the core slipping. I may be getting better at setting the knots before the first climb. I would like to see a pull test on a double overhand eye that has been climbed on twice, I'll go out on a limb and predict that if the tail is at least 2" and the knot has been preset by two climbs, the core will not slip through. A triple overhand will reduce the probability even further. I don't like the bulk of the triple so I'm staying with the double.

I've heard of only one incident where the core slipped on a climber. The climber admitted they rarely inspected the split tail. They didn't fall. Which reminds me, some hitches will not drop you if one of the eyes fails. I've tested the Knut, it will still hold you. Probably many others will. Doubt the VT would hold if an eye failed. It's very easy to inspect Beeline for core slippage, pinch the cord with your fingers, it's obvious when there is no core under the cover.
-moss

Mechanical ascenders are not used for the same operations that BeeLine is. E.g. BeeLine is used for ascending and descending. BeeLine split tails are used for 'leaps'.

But that doesn't make the characteristics of BeeLine any less significant. The numbers moray and I see in tests are for new, unstressed BeeLine that has not been subjected to in the dynamics of climbing. The relevant issue here is that we take an 8000 lb line and just by splicing a brumel in it, we reduce it's strength by about 70% - remember that's new and unused BeeLine.

Now we take the same BeeLine flex it and work it under load for a year, and we really don't know what we have. But, I suspect that it grows weaker with each use.

As for the legs of a split tail loading equally, I measured that once and to my surprise they do essentially share the load equally.

So just keep in mind as you climb on BeeLine that those reassuring numbers moray and I have posted are for new, unused, unflexed, BeeLine.