It is nice to have sources for this data and to be reminded of the limitations our ropes have when knots are tied in them.
Your admonition of splices needing to be well done is, I believe, very well taken when it comes to braid. I taught myself how to splice braid years ago and then decided that if I did not do them regularly, they would not be done well enough to distribute strain equally. And there is so little call for splices that there would be no regular practice. I then hired riggers to do the splices who I knew did them regularly.
I have figured a 50% hit on rope strength generally for most knots used on a boat: this allows for a certain safety margin. On cruising boats, we generally have a fair amount of wiggle room when it comes to rope strength as we like lines big enough to be comfortable in the hand.
For me, bowlines, rolling hitches and buntline hitches are the knots I use that see the most strain. I tend not to use knots unless I use them with some regularity, so I do not use the fisherman’s knot nor sheet bends of any sort, although I see them as good knots. Do you use them regularly? If so, for what application?
As to the strength loss reported for wet nylon, my experience with nylon makes me somewhat skeptical of this. Shock loading always stresses rope: was the break by any chance at the knot or where the line was going over a bend? Luckily, sailing does not subject lines too often to shock loading, tethers being one exception where this needs to be taken into consideration. My nylon line that is often wet for much of its length and gets loaded hard is my snubber, which is fairly light as these things go (7/16 inch) and has weathered squalls and storms and aggressive backing up to set the anchor.
Interesting discussion: thanks for initiating.
My best, Dick Stevenson, s/v Alchemy