To rappel, climbers descend a mountain or cliff by using a controlled sliding technique to slide down a fixed rope. After the climber descends to the bottom of the rope, they must retrieve the rope by pulling it through the anchor.
Climbers use a rappel device that utilizes the friction of the climbing rope as it goes through the device. Use of the rappel device controls their decent as they slide down the rope to reach a ledge or the bottom of the cliff or mountain. Rappelling requires basic climbing skills to ensure the climbers safety, including being knowledgeable about rappel anchors, ropes, knots and how to use the rappel device. Climbers must also know about the autoblock knot, and how to pull rappel ropes correctly.
It is preferable for climbers to have three bomb anchors when rappelling off of a cliff. Either one or two ropes are used when rappelling. Climbers should preferably use a doubled single rope instead of a knotted rope to prevent knot failure. Using a doubled single rope also prevents the rope's knot from becoming jammed in the anchor when it's pulled.
Ropes that are knotted typically use a double figure-eight fisherman's knot, square fisherman's knot, double overhand knot or a double fisherman's knot. Stopper knots are also tied at the end of each rappel rope strand to prevent climbers from rappelling off of the rope's end. An autoblock knot is tied onto the rope to prevent climbers from rappelling off the end of the rope as well. This type of knot is also used to help climbers stay in control on long, steep rappels.