A message landed in my e-mail inbox that came from this buzzboard thread, and I had a few (random-ish) thoughts of my own, and reply. I have wasted a bit of my life bouncing up and down on the ocean in sailboats, so I have some experience with salt, sun, corrosion, ropes, uv degradation.
I continue to agree that testing rope splices is a great idea, but I have at the moment only a 1200 lb load cell (and most of what I would test would go higher than that) so, yes, I have hydraulic cylinders etc. but... time,time,time
That said, I think part of the idea in making things that are good has to do with thinking hard about and solving the problems and issues entailed in the design. (Or, using the stuff in question.) There are some clever ways of doing things for rigging sailboats (and a small few that remain kinda dumb -- but so what). Many of them can be cloned / imitated / adapted valuably. On the other hand, salt and UV are much smaller issues when trees are concerned, and the regular proximity of saw teeth, for one example, certain shock loads when weight is dropped onto rigging, for another, etc. are more significant in tree work.
Which gives a place to thinking and calculating. One of the first parts of thinking comes from a general understanding how some mechanism, even a simple mechanism, ends up working. For example, in sailing, there is a bit of "seizing" -- wrapping cord/wire around two pieces of line/cable laid parallel to each other. Seizing has to be f..in' tight, because each of those two lines laid parallel will narrow, lose dimension, as it is pulled on (at an eye end, for example) even to the extent that the seizing won't hold, and the thing pull apart.
I believe something related can be said about tight eyes and sewing. I happen to use 300 lb dyneema. (in fact, I tested that stuff, just for jollies, and it holds more than that when fresh off the roll.) If I cross the parallel lay 20 times up and back each, that's 40, that's 12,000 lb of "gross" fiber strength in the attachment. Yuh, it is bending where it turns into the rope lays, at the stitch knot, etc. etc. But, it is a woven material... etc. etc. In any case, the chances are pretty good that I have gotten beyond the point where the sewn splice is going to fail at the sewing.
That doesn't mean it is never going to fail Just that the two "issue" places, really (once you've done a good enough job attaching the parallel lay) are a) the turn in the eye, and b) where the splice becomes the single rope again. The turn in the eye 1) is inevitable --- that is why you made the eye, to have a turned end, and 2) will be subject to the radius profile of the 'biner / whatever you are using. So, try to use good carabiners that have a little round to them, etc. And then just keep on smiling...
The "top" end of the splice is an issue somewhat similar. One of the reasons that I think tight is good, but that there is such a thing as "too tight" in sewing up things like an eye, is that fiber strength (many fibers) is a 'collective' phenomenon, and that discontinuities in a loading path can often be sites of rupture. (In other words, if the splice area is rock hard, and the rope is soft...there you have an opportunity for load continuity to be ...'interrupted'.) And some regard in using the rope end, e.g. not having some kind of a hitch/knot event 'break'/sharply angulate the rope right at the top of the splice, is better practice. Etc. And then, again, you just gotta get through life, and every end will become a single line at a point and don't be too foolish trying to break things when using them.
My view .. all of course are free to disagree.. would be that manufacture and use are two interrelated parts of having some thing work well.... Sailing stuff is great. I love it. I have a genny winch that I use as a lowering device for tree work -- much cheaper, much better, than much of the load lowering stuff that is sold for arborism (I make my own port-a-wraps and yes, use them, but sometimes, it is just so nice to have a winch...) But sailing stuff also typically first considers sailing issues....