All climbers need to know these four basic friction knots used in climbing:
Every climber needs to know at least one of these friction knots so that he can ascend a fixed rope, particularly in an emergency situation; escape a belay for self-rescue; ascend a rope after falling into a crevasse on a glacier; and as a safety back-up or autoblock when rappelling. The four knots are easy to learn, fast to tie, and do not damage the rope like a mechanical ascender, which uses teeth to grab the rope. When climbers use the knots to ascend the rope, the technique is called “Prusiking.”
Friction Knots Grab the Rope When Loaded
All four friction knots are basically just a loop of thin cord, usually called “Prusik slings,” attached to a climbing rope. After the knot is attached, the climber ascends the fixed rope by sliding the knot up it. The knot, using friction created when the knot is loaded with the climber’s weight, constricts and grips the rope, allowing the climber to ascend. Friction knots should not be used on icy ropes since the knot won’t grab the rope. If you’re using friction knots to ascend, it is important to use two slings tied into two knots and to make sure you’re tied into the rope—never trust your life to a single friction knot.
Tie Friction Knots with Thin Cord
Friction knots are best tied with a length of either 5mm or 6mm cord, with the ends tied together with a double fisherman’s knot or double figure-eight fisherman’s knot (both knots used for tying rappel ropes together) to form a loop of cord. The thicker the knot cord in relation to the climbing rope’s diameter, the less friction or holding power the knot will have on the rope. This results in the knot slipping on the rope rather than firmly gripping it. It’s always preferable to use cord rather than webbing for a friction knot, although webbing such as a sling will work if necessary.
How Long Should Your Cords Be?
The length of the loop of cord for a friction knot is a personal decision. I prefer using 24-inch loops, the same length as a sewn sling, rather than a longer loop. The shorter loops are easier to carry on your harness and can easily be made longer by clipping another sling onto it. A 5-foot length of cord is required to make a 24-inch loop. Some climbers prefer to carry a 24-inch loop and a 48-inch loop, clipping the short one to their harness belay loop and the longer one for use as a foot sling.
The 4 Friction Knots
Here are the four friction knots, their uses, and their advantages and disadvantages.
The Prusik knot is the most commonly used friction knot for ascending a rope. It’s easy to tie and very secure when it’s loaded. The disadvantages of the Prusik knot are that it is difficult to dress well and that it tightens up, making it difficult to release and slide up the rope.
The Klemheist knot is a friction knot that is used for ascending a rope and for self-rescue when a climber needs to escape a belay. Like a Prusik knot, it slides easily on a rope. The advantages of a Klemheist knot over a Prusik knot is that it is easier to release its grip on the rope after being loaded, works in one direction, is faster to tie than a Prusik knot, is easily untied after being loaded, and can be tied with webbing.
The Bachmann knot is a friction knot that utilizes a carabiner as a handle and is used to ascend a fixed rope. While the carabiner makes it easy to slide the knot up the rope, it’s smooth surface doesn’t grip the rope so accidents can happen. The Bachmann knot is ideal for rescue situations and as a safety back-up since it releases when it’s not loaded, but automatically grips the rope when it is loaded.
The autoblock knot, also called a French Prusik knot, is an easy-to-tie and versatile friction knot that is used as a safety back-up knot on a rappel rope. The knot is tied on the rope below the rappel device and then attached to the climber’s harness through a carabiner on a leg loop or the belay loop. The knot adds friction to the rappel and allows the climber to safely stop mid-rappel to rearrange the rope or do another task. The knot should never be used to ascend a rope since it slips rather than grips. Nor should it be used as a lowering device since the climber could lose control and burn through the nylon cord.