Bizarre but Informative Splice Break Test

moray

Any time the subject of splicing comes up, someone always announces they don't trust splices generally and certainly wouldn't trust one they might make themselves. This report is for all those people. The idea for this test came to me about a year ago, but I wasn't able to break anything at that time so the idea went nowhere.

Yesterday I was chopping off chunks of some 3/8 in. Tenex Tec for some experiments I was doing when I came to a defective section of rope. Rather than waste it, I realized this was my chance to do my little experiment. The rope was new, by the way, and the defect consisted of a broken yarn and another yarn that had been partially pulled out of the rope. Because the reddish dye was consistent throughout, it seems likely this happened at the factory!

I constructed a test piece from this section about 4.5 feet long. At each end I made a normal spliced eye with a tapered bury. When the eyes were done, the defect was located at the midway point between the eyes. Then I cut another piece of the 3/8 in. rope about 20 inches long and tapered both ends. This short piece I then inserted into the damaged rope so it was completely buried and centered. The center of the buried slug, in other words, was located right at the defect.

Next I very lightly wrapped some vinyl tape an inch or so on either side of the defect to keep any cover strands from unravelling as I worked. Finally I carefully worsened the defect by completely severing cover strands until half the clockwise strands and half the counter-clockwise strands had been cut.

Note that no stitching was applied, and the vinyl tape was about as loose as I could make it.

I installed the rope in my break-test rig and started pulling. The first picture shows the center section at 1000 lbs. tension. (The other, smaller rope seen in the photo is part of my recoil snubbing system.)



I continued applying tension until a loud BANG! announced the rope had snapped. The next photo shows the result. The weird repair in the center was still intact, and the rope broke, as always, at the end of one of the buries. The break occurred at 4754 lbs, whereas another section of the same rope with two regulation eye splices broke at 5554 lbs. The discrepancy shows, I think, that the buried slug was not quite long enough to completely and equally transfer load across the damaged center. Had it been 3 or 4 inches longer, or had I installed some stitching where the tapes were located, I am quite sure the break strength would have been right up there at 5500 lbs.

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Therrin

Ahhhh....

Wait, so why didn't you just do the splice breaking pull test with two normal strands of that rope, one with your home-made splices and one with factory splices... without the goofy crap in the middle?

I may have missed something there.

moray

Ahhhh...

Therrin, I thought I remembered that you were one those splice skeptics...

All that "goofy crap in the middle," as you put it, is at the heart of the example.

Since I play around with this stuff all the time, this test seemed fairly striking to me, but perhaps it needs a little explanation.

First off, the test you suggest--comparing my splices to factory splices--is a waste of good rope. There is no difference whatsoever in break strength.

Perhaps you are imagining a strength rating scale: factory splices rate 100, a good amateur might rate 90, a rank beginner might be down in the low 60's. In truth, the very first splice of a rank beginner would rank 100. Anyone can create a seriously sub-normal splice that is still stronger than the rope. When you test straight-bury splices, the rope always breaks right at the end of the bury, never in the splice. Practically speaking, pulling apart is the only failure mode for a splice, and it is actually quite hard to get even a very bad one to do that.

Hence my example with all the "goofy crap in the middle."

This is a very seriously defective and sub-normal splice, yet it held. Keep in mind we are talking about two back-to-back splices, one on each side of the cut strands. Compared to a normal regulation eye splice in 3/8 in. rope:

1. The buries are way too short. They should be 19 inches, but are only half that.
2. An eye splice throat is stitched with 12 stitches of very strong yarn. There is no stitching.
3. There are no broken strands at the throat of an eye splice. Here, half have been severed.
4. At the throat of the eye, where the bury enters the cover, The distorted cover squeezes hard on the core and tends to hold it in place. In the goofy splice, there is no distorted cover.
5. In an eye splice, all the cover strands squeeze the core and help to hold it in place. In the goofy splice, half the strands have been cut, and near the center, at least, can't squeeze anything.

None of this proves anything. It does demonstrate the amazing force with which the cover grips the core. A properly constructed splice, as the manufacturers will tell you and experiment will show, is far stronger and safer than any knot. As my own experiments have shown over and over again, even quite a bad splice can often meet that standard.

Eric Frei

Old saying goes ....

Even the worst splice is stronger than the best knot.

Tests done on spliced loops like I use show the strongest part is the splice, like you said the rope breaks elsewhere, usually the end of the bury.

How or what equipment do you have for these tests? Maybe some pictures???

I'd like to see some more done if possible, what force can you go up to?

__________________

Therrin

Ahh, actually I was only openly skeptic about my OWN ability to splice with any degree of efficiency. C'mon, thats fair enough for me to be skeptical about isnt it?

Ahah..... um... ok. So that's why its labeled as being "bizarre" right?

As far as I know, noone is arguing that point, we all agree on that.