Testing H.T. Loop Line

[moray]

When the recent thread appeared describing Allgear H.T. Loop Line, I was instantly intrigued. It is something of a hybrid between webbing and hollow-braid rope, but really quite distinct from either. For one thing, there is far more hollow space inside than in any hollow braid. This makes it really easy to splice. The 32 individual strands are much bigger than the threads in webbing, so if feels more like rope than webbing. Interesting stuff.

The easiest way for me to test a hollow-braid rope is to splice one very good eye with a long bury and plenty of stitching at one end, and place the experimental eye at the other end. That was the procedure I used with the H.T.

Here are the first two experiments:

#1 Straight bury splice, no stitching, 3.8in bury length, slipped apart at 336 pounds.
#2 Straight bury splice, no stitching, 8.4in bury length, slipped apart at 3532 pounds.

The photo was taken after the second test and shows the good eye and a few inches of the buried tip that pulled out. One can see from the tight weave and reduced diameter that the bury had experienced a lot of pressure. When I examined the rope with a hand lens, the bury seemed completely undamaged, but there was a small amount of fraying at the entrance wound in the cover.

 

[Blinky]

That's kinda heart warming that a straight bury with something that slippery held that well. I've only used it with locked brummels. Have you tested in the configuration?

Thanks for the info.

 

[moray]

Blinky, I do have some more results, just need to write 'em up.

 

[moray]

In the second experiment I tested two splices that did not slip. Ideally one would like to find the minimum length simple-bury splice that will hold, but there is no simple answer to this because of the effect of certain external variables. Two of the big ones are the presence of stitching at the splice throat and friction between the eye and the pin it is pulling on.

The eyes to be tested are shown in the first photo. One is a straight bury of 12.1 inches, well-stitched with 50-lb. test polyester. I was sure this one would hold. The second eye is made with 6 simple weaves (no locking Brummel) and a final tuck. The actual bury is just over 5 inches long, and the tucks take up about 4.5 inches. Why all the tucks? In earlier experiments I had found that the simple bury doesn't hold, inch for inch, nearly as well as a series of tucks. That was an unpleasant surprise for me because I liked the simple beauty of the straight bury, but facts are facts. Besides making the woven splice significantly shorter than the straight bury, I also used about half the stitches to further disadvantage it.

Another view:

Unfortunately, both splices held. The actual break, at 5616 pounds, fell at the very end of the long bury. Fortunately I still have enough rope left to test some still shorter splices.

 

[PUClimber]

If you don't mind try testing a locked brummel. I have been working on a couple of things using this and haven't climbed or break tested the product yet.

 

[Blinky]

I'm using it for my main tether on the CMI Twin. It was freaky using without a backup so I backed it up with NE 5mm Tech Cord that doubles as a length adjuster.

 

[moray]

[ QUOTE ]
If you don't mind try testing a locked brummel...

[/ QUOTE ]

I tested the one shown in the Allgear video, and I'll try to report on that in the next day or so.

But you are probably referring to the standard locked Brummel one uses for an eye-and-eye sling. I probably will test a naked locked Brummel (one with the the tail unburied) one of these days, just for the sake of completeness, but I have a good idea what will happen. It will get extremely tight under low load and it will break at something like 30% to 40% of nominal rope strength. When the tail is buried as it is in an eye-and-eye, then you have a combination of a normal splice and a locked Brummel. As long as the bury is long enough and the splice holds, the Brummel does nothing. It never gets tight. It doesn't make the rope weaker nor does it make the splice stronger. It doesn't make the splice more secure, either, or only marginally so (but stitching does!). I think of it as a weak knot that will hold the eye together if the bury slips out. If 30% of rope strength is strong enough for your purpose, then the locked Brummel allows you to build an eye with a very substandard bury length and still sleep at night. If you need the rope to be stronger, make the bury longer.

 

[moray]

H.T. Loop Line Brummel♠

Anyone who watched the AllGear video on splicing their Dyneema loop cord may have been puzzled, as I was, at their use of the locked Brummel. I decided to test their configuration of the locked Brummel before I rushed into print saying bad things about it.

The first photo shows my setup. The two upper loops will be mounted at opposite ends of my pulling rig. The Brummel at the bottom is what is being tested. I left a small loop to the right of the Brummel to save material; in the AllGear splice there would be two long tails there instead of a loop. For the purposes of the test, there is no difference at all.

In the second photo we see the rope under 180 pounds of tension. The Brummel and the small loop are on the far side of the rope. The right-hand leg is about to pull part of the Brummel through the rope towards the viewer. The black ink mark shows where part of the Brummel belonging to the left leg is starting to roll and invert toward the left.

At 378 pounds both of the penetrations of the Brummel had rolled and inverted--the small eye was gone! The Brummel, in other words, is not locked. The last photo shows the location of one of the roll/inversions.

Another bad feature of the AllGear Brummel is that it sticks out perpendicular to the rope. In any sort of real-world work situation this is just asking to get snagged. Is there any possible advantage to this ugly exposed Brummel that isn't even locked? I'll look into this question in the next post.

 

[moray]

Re: H.T. Loop Line Brummel♠

There are a number of ways to join the two ends of a stretch of rope to make and endless loop. Here are two views of the Allgear method:

Compare this to the much simpler and neater standard method:

Note that in the standard method each end buries into the opposite rope. Since there is only a minimal deflection where each rope buries into the other, everything stays very straight and tidy.

In the Allgear "locking" Brummel, each end makes some elaborate contortions in passing through the Brummel and then buries back into itself. I'll look at two simpler versions of this in the next post.

 

[moray]

Re: H.T. Loop Line Brummel♠

Two other ways to join the ends to make a loop are with a ring or with two interlaced eyes.

Take the case of the two eyes. If we apply 1000 lbs. tension to the system, we expect each leg of each eye to take half the tension, or 500 lbs. But what if the right-hand bury is way too short and just starts to slip out at 1000 lbs. tension? In order for it to be sliding out, it must also be sliding across the surface of the other eye. Since the two surfaces are pressed together with 1000 lbs. force, the sliding produces friction that resists the sliding. The two legs together still must sum to 1000 lbs., but they no longer share the load equally. In the diagram I show the bury leg with only 333 lbs. tension as it starts to pull out. The 2:1 ratio in the diagram is about right for polyester on polyester or polyester on metal rings. For Dyneema it isn't much different, maybe more like 1.85:1.

The point here is that friction in the eye, whether the eye is hooked to rope or metal, significantly reduces the force trying to extract the bury. In other words it protects the splice.

 

[moray]

Re: H.T. Loop Line Brummel♠

Now look again at the standard simple end-to-end splice.

If, let us say, the right-hand bury is way too short and just begins to slide out at 1000 lbs., we have no 180-degree bend around a ring or a rope eye to help us out. At the midpoint of the splice, the core leg and the cover leg always have equal tension. This sort of splice needs a longer bury than one involving a ring or an eye.

Now look again at the Allgear splice:

Even though the Brummel is not actually locked, it does a terrific job of protecting the splice. The amount of friction and simple mechanical interference in the Brummel, should the splice start to slip apart, would reduce the tension on the core to a very small proportion of the total. With much less force trying to extract the core, the Allgear splice would be secure with a much shorter bury than the standard splice.

While the Allgear splice is an interesting idea, I can't quite bring myself to like it. The simplicity and cleanliness of the standard splice are real virtues, especially for a rigging sling. If it takes 2 or 3 more feet of rope for the buries in the standard sling, that seems like a cheap price to pay.