Data shown in the charts leads me to several conclusions:
If you don't need to tie your line directly to a mono leader, tie a simple twice-through palomar from a double line to tackle or (for a leader) to a swivel. When I tested this knot with 20-pound braid, the result was an average break of virtually 100 percent, the single strongest knot in this group.
Other than that, the strongest knot was the venerable Bimini twist, either a 12- or 20-turn. (See "The Counterintuitive Bimini" for further information on this.) This creates a double line, which, versus a single main line, is by far the strongest way to connect directly to a mono or fluorocarbon leader. Other knots tested to tie directly to terminal gear just didn't cut it.
The "90% Spectra Knot" (so named on various websites touting it) isn't - not even close. (But here's some pretty cool irony: One of these sites boasts of this knot, "When you are finished you should have ... a 70%-strength braided-line knot.")
To tie a double line to a mono leader, the Yucatan (a.k.a. no-name or bristol) knot is the clear choice with 10 to 12 wraps offering a decided edge over fewer wraps (with somewhat stronger results in 50- versus 20-pound). A surgeon's knot tied with a double line can provide nearly as much strength, though the result is not as neat nor does it have a footprint as tiny as the Yucatan's. (Note: this knot can be tied by looping the the leader around the double line either going up away from the bottom of the double-line loop or starting up above the loop and wrapping down toward it. Per the illustration, I tie - and tested it - the latter.)
To splice braid to braid: Just say no. I won't do it again except in the direst circumstances. When too little line remains on the spool for my taste, I'll simply spool up again. Even with a double-to-double-line splice, I couldn't get better than 59 percent with 20-pound and 63 percent with 50-pound. Unis and even more so blood knots tended to slip out before breaking.
Discovered! The Counterintuitive 12-Turn Bimini
You just can't do enough turns with superbraid: It's slippery stuff that likes to cut into itself. I'd long heard that a standard 20- or 25-turn Bimini won't do with braid and that another 20 turns at the very minimum would help hold the knot. Heck, I often tied 60 turns. Hey, the more wraps the merrier, right?
Much to my astonishment, I found that taking more turns actually weakens the knot. And not just a little bit: The 40- and 60-turn knots broke repeatedly at roughly a third of the line's actual strength, rating these among the poorest I tied. The knots proved marginally stronger if I doubled the line, then tied these many-wrap Biminis, ending up with eight tag ends and a great-looking but not very strong knot. Compare the 27- to 38-percent strength of 40- to 60-turn Biminis with the 80-percent strength, or thereabouts, of 20-turn knots.
That very comparison led me to wonder about going the other direction. That is, if a 20-turn knot outperforms a 60-turn knot, what about say just 12 turns?
The result astounded me - so much that I went back to IGFA to do some quick retesting in the limited time I had. Same outcome: The 12-turn Bimini twist time and again either held its own against the 20-turn or more often actually outperformed it! In 20-pound Fireline the results were nearly identical at 80 and 81 percent (pretty good for a superbraid). In 50-pound PowerPro, the 77-percent 20-turn Bimini paled next to an 88-percent 12-turn Bimini.
At that point, still fascinated but late in the game with time growing short, I decided I had to try mono. I had a spool of 30-pound Stren Hi-Impact mono (45.1-pound break, dry) with me and quickly knocked out five tests. (I can tie a basic 20-turn Bimini in short order; another benefit of the 12-turn - it's even quicker.) Not even close: the 20-turn came out just about 70 percent, but the 12-turn broke at 101 percent! The other line on hand was 14-pound Sufix Siege (21.5-pound break, dry), which tested at 90 percent with a 20-turn knot while tied with only 12 turns it tested at 96 percent. I also tested a few more 20-pound braids; the results showed the same basic pattern.
Can you guess how many turns I'll be tying in my Bimini twists, at least in light- to medium-line-class braids and monos, in the future?
The author wants to offer special thanks to IGFA (www.igfa.org) for graciously handing over to him the use of the Instron line tester for three very long days and a bit more.