How Important is it to Taper your Splices?
Dyneema is DSM's brand name for Ultra-High-Molecular-Weight-Polyethelyne (UHMwPE) or plastic for short. If you tie a figure 8 knot, for example, you will reduce the strength of the extremely static material by as much as 70%. However, if you splice it, you can retain 100% of the quoted strength. The finger trap magic only works in a splice if you bury it 3.5 fids long. A fid is a tool used for splicing that is 21 diameters long. So 6mm x 21 = 126mm and 3.5 of those is 441mm or 17 inches. So 6mm x 21 = 126mm and 3.5 of those is 441mm or 17 inches. 6mm Marlow D12 SK MAX 99 has an average breaking strength of 5440kg or 11,993lbf or 53kN. Cutting the end blunt before tapering makes it go from fat (since the other strand is inside the 12-braid hollow rope) to thin too quickly. Cutting it at an angle is also not a proper taper. The idea of a good taper is that it slowly reduces the change in diameter, but what happens if you don't. We aimed to test just that in this video, but we got more than we bargained for.
No taper broke it about 13-20% lower than the ABS. The 3rd test, however, broke in the eye showing how and what you connect it to is just as important as the taper. A diagonal cut was better, but not above ABS. The first two broke at the eye, even though we had it on a proper size pin, but when it did break at the taper it was higher at 50kN.
Marlow's taper specs made every test break above ABS but why did the eye stop breaking??? We are, literally, getting over 15kN more force out of the same test on the same pin on the same eyes.
Samson's Tapers included a brummel splice locking it into place, even if it is NOT under tension. That extra bend did NOT reduce the strength even though I suspected it would. The 3rd test broke at the eye, though. All our tests were above ABS.
Grab your popcorn. Teufelberger's brummel splice did not break, but PULLED OUT. All 3 tests failed about 50% of ABS because the bury wasn't deep enough. This just proves brummels don't add locking value when it is under load, but only when it is NOT under load. I don't know why or what we were misunderstanding.
Behind the Scenes
John Fioroni, who nerds out on dyneema like I do, decided to pursue testing taper differences with me. He spliced all the samples together, which takes a lot of work. Then, I pulled on them. It's pretty frustrating trying to isolate a piece of gear or rope to break where and how I want, so I can explore just that niche part. Having the eye continuing to break was disappointing, but it actually revealed that how and what we connect to can be more important than the taper, if you are trying to achieve the maximum strength.
It's pretty awkward to discover something like Teufelberger's brummel coming undone and presenting it in a way that doesn't throw them under the bus but just to show our data. There has to be an explanation. Maybe I pulled it too fast or too slow compared to "standards". However, what is exciting is NOT knowing or caring about "standards" and just pulling on stuff, because then I don't fit the stuff into a box but explore what's outside of that box. Their brummel is super good enough if you make it longer, and that is good to know if you really need it to hold.
After Posting Thoughts
The main theory behind why Teufelberger's brummel slipped is that it was intended for a 12 braid made of a different material like polyester which is not as slippery and therefore does NOT need to be buried more. However, this PDF does not clarify that and was in the dyneema section of website.
It's very surprising to me how many people think lock stitching, or threading the splice, is to hold it from slipping. It is only intended to keep it from coming undone when it is NOT under load and even brummels benefit from this because they can come undone a little bit. We will test that in dyneema next so demo how little lock stitching plays a role in holding under force.
This was a helpful comment from the technical manager at Marlow copied from youtube comments. "Hi, I'm actually the technical manager at Marlow Ropes, i don't normally comment but I think there are some things to address on this film. BTW it's good to see our ropes performing at, or better than, the figures we quote!I may be able to answer some of the questions raised in the video and the comments so, in no particular order:-Big one first: as was pointed out in the film the splice works by friction, if the buried tail isn't long enough then the splice will slip. Putting a lock (brummel) in doesn't alter that. If the tail is too short then all the force is held by the lock stitch which will eventually fail. Exactly as shown. I've seen this many times before so one simple message to all fans of the Brummel lock: A LOCK IS NOT A SUBSITUTE FOR THE CORRECT TAIL LENGTH. - The lock (done properly) doesn't reduce the strength where the stitches are made because there's double the material content of the rope at ths point (think of the cross section area), i.e. a small loss here does not reduce the strength below 100%. However there is a risk, not observed in this film, if the tail of a locked rope is disturbed then you can get a small loop form below the neck of the splice, this will reduce the strenght of the locked splice. For this reasion I still prefer to whip the entry point and for testing I don't use a lock.- There's a comment about tail lengths and fids etc. I'm not sure where that all came from however we simply recommend the tail length minimum to be 50x the rope diameter, longer is better.- There's always a weak point, that's why no matter how good the taper often that's where the rope breaks.-The ropes that broke in the back of the eye are due to the D:d ratio (ratio of the rope diameter to the pin diameter). When this is large (5:1 or greater) the rope will almost always break in the splice, however when small (less than 2:1) the rope will mostly break in the back of the eye. At the in between D:d ratios the location of the break could be either but it has little effect on the strength. In practice at the very small D:d the rope is often stronger than the shackle as was pointed out early in the video. This assumes the eye size is sufficent, the angle the rope makes at the throat shouldn't be more then 30 deg.I'm sure there's more comments i've not addressed, sorry guys I need to get back to my day job!"
Go see this next video.