I have this knot I’ve invented, a take-off on the trace-8, and am wondering if it would weaken the rope? I tie a figure-8, and then thread the working end through my harness as usual. I trace the tail through per normal, but at the point where the working end follows the standing portion of the rope, rather than trace through just the end of the rope, I poke a bight through. I snug the knot and leave the bight long enough to overhand tie it onto the standing part of the rope.
I have used the knot, but am unwilling to fall on it until I get some feedback.
If you are still alive by the time you read this, abandon this doomed quest for a “better” tie-in knot. Screw with your tie-in knot and you’ll hit the ground faster than shit from heaven. What is with people who just aren’t satisfied with the trace-8 or double bowline? Are these knots scary? Do they not work? Trying to jimmy up your own knot is just crazy, and you know I’m a fan of do-it-yourself, especially for things like surgery, parenting and making beef jerky. But, I think you know this or you wouldn’t have written.
Your knot, while it might be good, is untested, complicated (you’ll be more likely to screw it up) and bulky. Sure, the trace-eight is difficult to untie after you’ve yammed onto it, but we aren’t talking about knitting scarves or doilies. In our world a knot that is difficult to untie is actually a good thing. You think about that.
To answer your question, which was about weakening the rope: Yes, your knot will weaken the rope. All knots, because their tight bends cause force concentrations, compromise rope strength. Recent tests conducted by Black Diamond show that the standard trace-8 weakens a lead rope by 25 to 30 percent, compared to 30 to 35 percent for a double bowline, the other popular tie-in knot.
Rope strength reduction shouldn’t cause alarm, however, because the breaking strength of a typical lead cord exceeds two tons. Even at 70-percent strength, any rope is massive overkill considering a severe fall, one you’ll probably never take, registers around a 2,000 pound force, and most “sport” falls are about half that.
You should, however, concern yourself with knots in small cord. For instance, 5mm perlon, such as the type you might use for a prusik, could have a breaking strength of just 1,200 pounds. Reduce that by 30 percent and the new strength of 840 pounds will barely hold a hop of a fall. (Look for more on cord and knots in an upcoming Gear Guy.) Pay attention when you are rigging anchors or incorporating small cord into your protection chain.