A concern about the Arborist Splice

[Brion Toss]

Hi Dan,
My apprentices are currently preparing some splices to be destruction-tested. We do that sort of thing fairly frequently. We have also run cyclic loading tests on occasion. I would be happy to send along the results. This next batch will be broken by New England Ropes, but you can likely find several test facilities in any major city. Typically the samples should have at least 5ft. between the ends of the splice tails, to minimize the distorting effects that the two splices might have on the rope. And typically the eye circumference is a bit over 2ft., so they can fit onto the machine's pins. I'll look to see if we have saved any results from past tests. The most recent one was on some 5/8" Vectran, as I recall, and it broke in the high 90's, but I'll have to dig the file out for specifics.
As for the whipping vs, stitching question, experience in the field and on the testing machine confirms that stitching works just fine. You ask how invisible stitching could hold well. Reasonable question. Because the rope has opposing diagonal weaves, there's always a layer under the surface. So if I stitch such that the thread disappears between two sets of surface yarns, it will always pick up the layer beneath, as long as the stitch has any length to it. And I believe you are mistaken in saying that stitching puts less material into the rope; a whipping has 6 or 8 frapping tucks through the rope, and sometimes only 2, whereas one can stitch as many times as one wants -- though I usually say 6 to 8 is fine. Not only that, but those stitches can be made at a wide variety of angles, and can travel linearly and radially, intersecting the core in more places. As for inspectability, again, why would you need to inspect it, any more than you would need to inspect the "invisible" buried rope tails?
And yes, you could say that the splice is stronger than the rope, but then you could say the same thing about a Bowline or any other knot; there's more mass in the knot, plus you have the two parts of the eye, so that's twice as strong as the rope. Unfortunately, the bowline, and to some extent even splices, distort the rope, weakening it. The goal is not to have a strong splice --- that's easy --- but to avoid having a weak rope. Hence tapers, core/cover balance, and a general effort to minimize distortions.
I recently spoke with the developer of the Grizzly stitch splice. It's a wonderful thing, but as even the developer pointed out to me, it does have some significant limitations, including the size and type of rope you can use it on. No magic bullet here.
I do my best to have viable reasons for doing things the way I do, though of course it is always so easy to fall into dogma. For instance, for years I was emphatic about the need to taper any splice. And it almost always does make a significant difference in rope strength, as well as being less likely to chafe than a square-shouldered finish. But destruction tests on 3-strand ropes consistently showed that untapered splices were stronger.
Fair leads,
Brion Toss