Does leaving a knot in a static cord damage the cord as it does with dynamic rope?

Question

I've heard to never leave a knot in a climbing rope for an extended period of time as it can deform and weaken the core of the rope. I'm unclear if the same is true for static cord and rope as well.

I have two prusik loops which have been tied continuously for years and used as auto blocks. One of them is also part of my rescue kit, which means that on occasion it's used to anchor the rope and escape the belay. In this setup it's holding 100% of the climber's weight, rather than just engaging my belay device as it does when it's used as an auto block.

So I'm curious, should I be untying the fisherman's knot between uses?

Answer 1

should I be untying the fisherman's knot between uses?

Typically it's simply not possible to untie a fisherman's knot, especially after it's been loaded, so that wouldn't even be an option. This is actually a good reason to tie your Prusik cords with an offset overhand (EDK), because then if you ever need to untie the loop and use it for something else, you can.

In this setup it's holding 100% of the climber's weight, rather than just engaging my belay device as it does when it's used as an auto block.

If we're talking about 6 mm nylon cord, not your spare shoelace, then this is a total non-issue. You can't break 6 mm cord with body weight. E.g., the 6 mm PMI cord I use is rated at 7.5 kN, which is equivalent to 760 kg or 1700 pounds. You have so much extra strength there that it's simply not an issue.

And in the self-rescue situation you describe, if you escape the belay correctly, the Prusik is never the only thing preventing the climber from falling.