Regarding rope test terminations, I've spoken with techs at both NER and Samson. NER's standard procedure is to put the splice to be tested at one end, and to belay the other end to a bollard and cleat. Their idea is that this ensures that the weak end is at the splice, and that the rope hasn't been unbalanced by a second splice. Sampson, on the other hand, puts a splice at both ends, as per the standards that Estar mentioned a while back. It would seem that the only way to determine the actual relative strength of both ropes is to test them both by the same method. Where does this leave us?
Estar,<br />You might have addressed this already, but do you have any idea why a knot would test much weaker in New England's rope than in Samson's? If we are talking about Sta-Set vs XLS, the former has a higher published strength...
Regarding the strength discrepancy in double-braid Dacron, bear in mind that rope is always weaker than its components; whole rope is weaker than the sum of individual strands, and strands are weaker than the sum of individual fibers. Only with parallel fiber construction can one approach utter efficiency (a selvagee strop is a classic example of this). What we get for the weakening is a tool that can be used, can be run over sheaves, knotted, spliced, etc. In the case of the cover, note that the braid structure is less parallel than that of the core, and usually with considerably more twist. This makes the cover more snag- and abrasion-resistant. It also makes it weaker and more elastic, but again, that is the price you pay for function. When you take the core out, it would seem that the structure would deform a great deal in a break test, making the cover even weaker. As far as imbalance of loading between core and cover goes, much of course depends on how well the rope is balanced at the end of the splicing process, as well as how balanced the whole rope was when it was fabricated. In any event, I think that well-made double braid makes something like the best use of the materials, given the unavoidable weakening consequences. Regarding those chest-high jacklines, I did misread your data. Apologies. But I will note that, with an appropriately short tether, it is impossible to fall far -- if at all -- past the lower lifelines, and difficult to slide far, compared to on-deck lifelines. I have rigged them on raceboats, though sometimes, as you note, sheets and poles, as well as preventers, can complicate or preclude them. As for being "clipped essentially on the edge of the boat," that is where you walk. I just want a better way to keep you there than tripping-level lifelines and on-deck jacklines provide.
One other way to reduce impact loads: chest-high jacklines. We seize D-rings chest-high, usually to the upper shrouds, and run our jjacklines through them. This gives you the chance to use an extremely short tether, thus limiting acceleration. It also gives you a structure that is very hard to be thrown over, and will keep you out of the ocean should you be thrown over. It is highest where the vulnerability is greatest (the middle of the boat), and there is nothing underfoot, and no tether dragging along behind you. We used to use Sta-Set-X for the line, but now usually use an HM blend double-braid, made off tight. A dynamic tether would still be advisable, of course. As for the data showing that most overboard incidents occur in the cockpit, consider the proportion of time spent there, as opposed to moving around on deck. It reminds me of the accident statistics showing that most accidents occur within 25 miles of home; the meaning is not that roads near home are more dangerous, but that the great majority of driving, for most people, is close to home. Additionally, there's the psychological tendency to be less careful and take more risks when we think we are protected. On deck (or far from home) one tends to feel vulnerable, even when clipped in, and we behave accordingly. In the cockpit, or on familiar streets, hey, what could go wrong?