Bee-Line Break Tests

[moray]

For some time now I have been interested in testing 8mm Bee-Line, the very popular hitch cord made by Yale Cordage. This rope has a loose 12-strand hollow-braid core of vectran and a tightly braided 24-strand cover of a polyester/technora blend. Several knotted and spliced configurations were tested, including two eye-and-eye (e2e) split tails commonly used by climbers. I was assisted in this effort by a generous donation of gorgeous spliced and knotted ropes by our own Canopyboy.

The picture shows the four rope samples supplied by Canopyboy.

From left, an e2e with two locked Brummels each secured with a whipping. Next an e2e with two locked Brummels and no whipping. The two on the right are, except for their short length, production models ready for use: first a standard spliced e2e with locked Brummels at each end, about 5 inches of bury, and a whipping securing the cover ends; lastly an e2e with eyes formed with double fisherman's knots.

Some people may wonder why the tails of the locked Brummels are left exposed in the two ropes at left. This is to isolate the performance of the Brummels. If the tails were buried, then we would have a combination of Brummel and a splice. Several experiments on isolated splices (no Brummels) are also reported.

 

[moray]

These two photos show some of the details of Canopyboy's artistry.

 

[moray]

This photo shows a locked Brummel under test. Even though the tension is 618 lbs., the Brummel doesn't look much different than it did at 25 lbs. Locked Brummels always constrict this way under load unless there is an upstream splice protecting them. The Brummel will supply a lot of holding force, but only after it has collapsed into the exceedingly tight little knot shown here.

There seems to be a lot of misunderstanding of this point in postings I have read, probably because very few people ever test these things to failure. So I'll say it again: the locked Brummel does almost nothing unless the buried splice slips apart and the Brummel collapses into a tight little knot. Note how the weave in the tail becomes highly condensed.

 

[moray]

Straight Splices

In all of the tests the eyes are held by 3/4-inch steel shackle pins. Significant friction is developed in the 180+ degrees of wrap around the pin, and this assists the holding force of the knot or splice under test. In real-world usage the eye would be held by a metal carabiner which would supply a similar amount of friction; thus the test results should be roughly comparable to real-world performance.

In all of the Bee-Line break tests, when I report a particular rope broke at xxx lbs. this almost always means one or more strands broke at that tension, not that the rope snapped in two. It is pointless to keep pulling after a few strands have broken because the tension will never again reach xxx, and continuing to rip the rope apart simply destroys all evidence of how the initial failure occurred.

There were 3 tests of simple splices with no Brummels:

A 4-inch bury slipped out at 1216 lbs.

A 5-inch bury slipped apart at 5030 lbs.

When a 6-inch bury at one end was matched against a woven non-locking Brummel with 15 tucks at the other, the woven structure broke at 4072 lbs. Since there is nothing special about 15 tucks, and the break occurs at the end of the tucks, any number of tucks that doesn't slip should give the same result of about 4000 lbs. Woven splices, unlike bury splices, don't get stronger as they get longer.

 

[moray]

Locked Brummels

There were 3 experiments; in each case the tail of the Brummel was about 4 inches long and unburied.

With a 9-inch bury at one end and a locked Brummel at the other, the Brummel broke at 3572 lbs.

With a locked Brummel at each end, one of them broke at 2862 lbs.

With whipped locked Brummels at each end, a strand broke at 2052 lbs., and major breakage occurred at 2424 lbs.

The average value for Brummel strength seems to be about 2800 lbs., and the presence of a whipping seems to significantly weaken it.

The photo shows one that has failed; the eye is towards the top. Note that breakage has occurred on both sides of the Brummel.

 

[moray]

Usable Hitch Cords

The e2e with two double fisherman's knots failed at 3590 lbs. when the tail of one of the knots crawled all the way through the knot.

The spliced & whipped e2e with cover in place failed at 5318 lbs. One of the splices slipped causing the Brummel to cinch up and begin to fail. The photo shows the result.

Since this is a very popular configuration among climbers, I did a careful forensic dissection of the cord in the photo to better understand the failure. The next photo shows the cord with cover removed (the eye is out of view to the right). Most of the buried core had pulled out (bottom) during the test.

I marked the core and cover at the exit point of the core and then pulled the remainder out. In the photo both of these points are located at the 4 3/4" mark. Clearly almost none of the tapered bury was still in place after the break. Once the splice started pulling apart there was nothing to stop it until the Brummel had cinched up. Even though the slipping of the splice relieved stress on the rope, there was still enough left to overwhelm the Brummel and break several strands. At this point all the slipping and cinching and breaking stopped and the remainder held.

When I dissected the surviving and apparently undamaged splice at the other end of the rope, I found no evidence of splice slippage. The length of the bury measured 4.75 inches.

This is a very revealing experiment, but it requires some explanation. The fact that the splice slipped but the Brummel held might lead some to think the splice was the weak link in the chain. This is completely false, as the Brummel tests showed the Brummel can hold only about 2800 lbs. Here the splice held 5300! Because we are using a hydraulic cylinder for these tests and not an actual weight, the load goes away as failure progresses. The further the failure progressed, the less load remained for the surviving fibers to withstand. In a real-life situation, the load does not go away and failure will go to completion for a static load. For a dynamic load the situation is more complicated, but that merits another discussion.

Does the Brummel assist the splice in some way? No. However the whipping at the throat, which included some through stitches, definitely does. Without the through stitching the short bury of 4.75 inches almost certainly could not have held 5300 lbs.

So what does the locked Brummel do for us? It provides a guaranteed holding strength that is more than we need. If the splice bury is very short and weak, or of uncertain quality, we can still rest easy because the whole e2e can't be any weaker than the Brummel.

With the locked Brummel in place to protect us, why not make the bury extremely short? This would maximize the amount of supple ordinary rope and minimize the amount of stiff thickened rope associated with the buries. Remember those pictures of the failed Brummels with the highly compressed braiding in the tails? Those tails were about 4 inches long and were tightly taped on the ends. As the Brummel took up the load in those experiments, the intact, taped, well-braided tail simply could not be ripped apart and sucked through the Brummel, which would have caused it to fail completely. In an actual spliced e2e, the bury aka Brummel tail is not taped and the last inch or two is tapered and may be entirely unbraided. Could such a flimsy tail be sucked right though the Brummel causing catastrophic failure? The Brummel is only "locked" if the tail can't be ripped apart!

Anyone who makes Bee-Line e2e's with locked Brummels, unless they have some experimental evidence for minimum safe tail length, is simply guessing that their buried tails are long enough. Until someone does a series of break tests to determine a minimum safe length for a Brummel tail, the prudent thing is to use long buries (5 or 6 inches) that essentially guarantee the splice will never come apart and therefore the Brummel will never deploy.

 

[moray]

In all of the tests above in which actual breakage occurred, the core had been weakened by a locked Brummel. We don't actually know how strong the core is. Or the cover. There was just enough material remaining for me to find out.

The photo shows two slings ready for testing. The top one is the vectran core with simple bury splices about 9 inches long and the lower is the similarly prepared cover. I have to credit Ron, who posts regularly on another forum, for the cover-testing idea. This would not have been my method of choice for testing the cover--better to wrap it around a couple of bollards--but I didn't have enough material left.

In the cover test the rope snapped in two, right at the end of one of the buries, at 6020 lbs.
The core also broke at the end of a bury, at 9594 lbs.

Hmmmm...You remove the 6000-lb. cover from an 8000-lb. rope and get a 9600-lb. rope! Less is more.

One is left to wonder why Yale describes the rope as having a nominal strength of 8000 lbs unless it is very hard in any practical application to achieve any more than that with the intact rope. One has to marvel not only at the pheomenal strength of this cord, but at the marked degree to which the locked Brummel (and probably any knot) weakens it.

 

[outofmytree]

Moray I am beginning to sound like a broken record but here I go again....

Awesome work mate. Thank you for putting so much time and effort into testing ropes, splices and knots. Climbers all round the world read your information and are safer for it.





Grrrrr. Can't rep you yet. Help please. Someone...

 

[Garden Of Eden]

Moray I am beginning to sound like a broken record but here I go again....

Awesome work mate. Thank you for putting so much time and effort into testing ropes, splices and knots. Climbers all round the world read your information and are safer for it.





Grrrrr. Can't rep you yet. Help please. Someone...

Got it covered...

Awesome Moray, simply awesome. Answered TONS of questions. I'm gonna rep Canopy boy too. Nice work, both of you...

God Bless

Jeff

 

[canopyboy]

Great, I've been waiting to read about the results!

Moray - You seem to be referencing some pictures in some of your posts (particularly 3 & 7) that aren't showing on my screen.

Hmmm, a lot to think about. I may be modifying my splices a bit now. But good to know that even the double fishermans or a straight locked brummel holds well more than a climber needs.

 

[Garden Of Eden]

Great, I've been waiting to read about the results!

Moray - You seem to be referencing some pictures in some of your posts (particularly 3 & 7) that aren't showing on my screen.

Hmmm, a lot to think about. I may be modifying my splices a bit now. But good to know that even the double fishermans or a straight locked brummel holds well more than a climber needs.

I too have a picture problem. I assumed he just forgot to load. Wouldn't be too hard with all that information. lol

Since you said it, I'll ask it. I know climbing lines have to be rated over 5200lbs, I believe, whats a typical 4-6foot fall loading a rope/splice/eye like. How much force do you suppose? My rough Math tells me a 180ish lb man falling would have a gravitational force of around 1900lbs. Which is a lot to me. I'm just curious, what kinda stress I'm putting on my ropes when I chunk pieces down, and when I'm climbing, if God forbid, I do take a slight fall on the rope.

God bless,

Jeff

 

[moray]

...You seem to be referencing some pictures in some of your posts (particularly 3 & 7) that aren't showing on my screen

All the pictures were showing on my screen, but I reattached the one on post #3. Can you see it now? If I actually fixed something, I'll go ahead and reattach #7.

 

[outofmytree]

Hmmm, #5 and #7 not visible to me.

 

[arboralliance]

Moray I am beginning to sound like a broken record but here I go again....

Awesome work mate. Thank you for putting so much time and effort into testing ropes, splices and knots. Climbers all round the world read your information and are safer for it.

Agreed...

 

[moray]

OK, I reattached #5 and #7. The message-board software seems a bit buggy.

 

[SINGLE-JACK]

The e2e with two double fisherman's knots failed at 3590 lbs. when the tail of one of the knots crawled all the way through the knot.

...

This is a particularly interesting finding. Because so many people put so much faith in "double fisherman's knots". Not that it failed but it's HOW it failed. Reading that a double fisherman's knot 'untied' itself long before the cord failed is quite disturbing.

I've often wondered if the following was worth the trouble ... maybe it is?

Brion Toss once wrote of seizings; "... they're so strong and secure that they rival Eye Splices." (Chapman's Nautical Guides - Knots, Brion Toss, 1990, pg161)

 

[canopyboy]

I too have a picture problem. I assumed he just forgot to load. Wouldn't be too hard with all that information. lol

Since you said it, I'll ask it. I know climbing lines have to be rated over 5200lbs, I believe, whats a typical 4-6foot fall loading a rope/splice/eye like. How much force do you suppose? My rough Math tells me a 180ish lb man falling would have a gravitational force of around 1900lbs. Which is a lot to me. I'm just curious, what kinda stress I'm putting on my ropes when I chunk pieces down, and when I'm climbing, if God forbid, I do take a slight fall on the rope.

God bless,

Jeff

Jeff, go to Yale's website and download their catalog. They talk a lot about your question. I don't agree with everything they say from a pure engineering sense, but the gist of it is right. Basically low stretch ropes of short length see a huge impact load compared to long and/or stretchy ropes.

http://www.yalecordage.com/pdf/ArborDivCatalog.pdf

As for your climbing rope, that's one of the reasons the working load is considered to be 10% of the breaking strength. If you take a fall hard enough to break your climbing line, I would guess you're pretty much toast from the impact anyhow.

Dave

 

[canopyboy]

Brion Toss once wrote of seizings; "... they're so strong and secure that they rival Eye Splices." (Chapman's Nautical Guides - Knots, Brion Toss, 1990, pg161)

That's interesting, now I'll have to go read that book....

 

[SINGLE-JACK]

Jeff, go to Yale's website and download their catalog. They talk a lot about your question. I don't agree with everything they say from a pure engineering sense, but the gist of it is right. Basically low stretch ropes of short length see a huge impact load compared to long and/or stretchy ropes.

http://www.yalecordage.com/pdf/ArborDivCatalog.pdf

As for your climbing rope, that's one of the reasons the working load is considered to be 10% of the breaking strength. If you take a fall hard enough to break your climbing line, I would guess you're pretty much toast from the impact anyhow.

Dave

:agree2:

Dynamic Energy in Arborist Ropes
"One of the most misunderstood aspects of rope selection is the disconnect between breaking strength and a ropes ability to absorb dynamic loads."



(yalecordage.com)

Dynamic versus Static
"If you are purchasing a rope for general climbing use (top rope, lead climbing etc.) you must have a dynamic climbing rope. Dynamic ropes are designed to absorb the energy of a falling climber, and are usually used as belaying ropes. When a climber falls, the rope stretches, reducing the maximum force experienced by the climber, the belayer, and the equipment.

"Static ropes are more durable and resistant to abrasion and cutting than dynamic ropes, but they lack the necessary protection against shock loads produced in a leader fall. Static ropes are designed for rappelling, rescue purposes and technical climbing situations (i.e. Big Walls). If you take a fall on a static rope you risk injury or death (due to high forces). Logic: Force = mass * acceleration => Force = mass * (distance / time ^ 2) => a dynamic rope increases 'time' and therefore decreases force."

(spadout.com)

-Jack

 

[moray]

Back on the subject of Bee-Line, I made an e2e yesterday from some of the leftover cover using normal straight bury splices and then I put it to the test as an actual hitch cord on some new Blaze. The e2e was long enough that the thickened spliced areas were not involved in the friction wraps.

Using a 5-wrap Schwabisch hitch, descents were very smooth and controllable, but the knot didn't release as readily as I like. When I switched to a VT, ascents and descents both went like a dream.

I plan to resplice the cord so the buries extend from one eye to the other and then retest its performance in the tree.