Climber Asks If Knot He Invented Is Safe
Dear Gear Guru: I have this knot I’ve invented, a take-off on the trace-8, or figure eight follow-through, 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.
Gear Guru Replies: If you are still alive by the time you read this, abandon this doomed quest for a “better” tie-in knot. You know I’m a fan of do-it-yourself, but I can’t recommend altering climbing knots even if the new knot might prove save over time.
Your knot is untested, more complicated (you’ll be more likely to screw it up) and bulky. Sure, the trace-eight is difficult to untie after you’ve taken a hard fall on it, but in our world a knot that is difficult to untie is actually a good thing. Your knot looks like it would be easier to untie after it’s held a fall, but I have a saying that goes something like this, “Knots that are easy to untie, untie themselves easily.” Your knot also requires about a foot of additional rope, which by itself isn’t a deal breaker, but isn’t an advantage, either. I can see a freakish scenario—aren’t accidents “accidents” because they are unexpected?—where the back-up portion of your knot gets hooked or bumped, comes undone, and then all that’s required to unravel the remaining knot is a tug on the knot’s tail.
I will add that the climbing knots and hitches we use most often, the trace-eight/figure eight follow-through, double bowline, munter hitch, clove hitch, double fishermans, prusik, etc., were tested by time long before they were tested in labs. Typically, these were knots used on ships, where, as in climbing, a knot failure could spell disaster. The old salts invented and refined and tested their knots over eons. Knots that failed weren’t passed along to the next generation, or survivors if you will. Your knot very likely isn’t new, rather it was probably tied by sailors and discarded because it wasn’t better than existing knots. For more on knots read The Ashley Book of Knots by Clifford W. Ashley. Ashley spent 11 years documenting 3,854 knots and hitches and drew some 7,000 illustrations himself. The book, published in 1944, is pretty much the final word on knots—it has only ever had one knot added to it.
Now, 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. 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 climbing rope exceeds two tons. Even at 70-percent strength a climbing rope won’t break at the knot in a climbing fall.
You should concern yourself with knots tied 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. Pay attention to this point when you are rigging anchors or incorporating small cord into your protection chain. I’d avoid cord this small altogether and not have to worry about it.
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