A Prusik (or Prussik) is a knot used by Climbers, Canyoneers, Cavers and Arborists to grab a rope (as a rope-grab). Two may be used to climb a rope. The knot is tied using a loop of (for example) 6mm cord around a 9mm rope. The term Prusik is used both for the knot, for the loops of cord, and for the action (to prusik).
Advantages of a Prusik Knot
Prusiks are mainly carried for emergency use, and are lighter than many other options. Prusiks are fast to place on the rope, and with practice, can be placed with one hand. The loops of cord can be used as slings, and are thus multi-functional in a climbing environment.
Prusiks will work around two ropes, even two ropes of different diameters. Prusiks provide a high-strength and fail-safe (ie, they will slip before damaging the rope or breaking) attachment, and are used in some rope-rescue techniques. Prussicks are good to use in hauling systems where multiple rope-grabs may be needed, and enough mechanical rope-grabs may not be available.
Prusiks have the advantage of working equally in both directions. Most mechanical rope-grabs work like a ratchet, moving freely UP the rope, but grabbing when a load in placed down on them. Prusiks will grab when pulled by the tail, either up or down, and will slide when pushed by the barrel.
Disadvantages of a Prusik Knot
For climbing a rope, Prusiks are slow and inefficient. Mechanical devices to grab the rope are available that are easier and faster to use, but of course, more expensive and generally bulkier.
Related Knots and Equipment
The Prusik knot refers to a specific knot. There are other knots that can be used to create a rope-grab from smaller cord (ie, cord that is smaller than the rope being grabbed) or webbing slings. The two main alternatives are the Bachman knot and the Kleimheist. Each knot has its advantages and disadvantages, mainly in how easy they are to use for climbing a rope. Another variation is the AutoBloc knot, used by some people as a backup knot while rappelling.
A Purcell Prusik is a related cord popular among cavers and rope-rescue people. A somewhat longer loop than the normal prusik is used around the rope, then a second prusik is used around the cord loop itself to form a foot loop. The foot loop is then easily adjusted in length and position.
A Prusik Minding Pulley is common in rope rescue. The rope to be pulled is passed through a pulley, and a prusik is tied on the loaded side. When the rope is pulled, the prusik rides against the pulley and the rope slides through it, but when the rope is relaxed, the prusik slides away from the pulley and grabs the rope. Thus, the combination acts as a ratchet.
Equipment
A prusik knot is tied using a loop of nylon accessory cord tied into a loop about 30cm in length. Most people use 6mm cord for climbing ropes of 8mm to 11mm diameter. The cord must be smaller than the rope climbed, or it does not grab well. Cord smaller than 6mm is usually too weak, and can be easily damaged.
Tying the Prusik
The prusik is a simple knot tied by wrapping the loop around the rope 3-5 times (depending on the materials) and then (usually) back through itself, forming a barrel around the rope, with a tail hanging out the middle. When the tail is weighted the turns tighten against the main rope and grab. When weight is removed the loop can be slid along the rope by placing a hand directly on the barrel and pushing. The trick is, if it grabs well, then it is hard to slide along the rope. Breaking the prusik free from the rope after it has been weighted can be difficult and strenuous.
Applications
"Rappel Backup": A prusik loop can be used as a self-belay during a rappel descent. Placed below a descender and controlled with the brake hand, it can act as an automatic 'dead man's handle' should the climber be incapacitated or require the use of their hands. Careful setup of the rappel backup is critical, or it will not work. An AutoBloc knot is most widely used in this application. (Controversy:) Use of a rappel backup knot is not widely accepted, but fervently promoted by those who believe it adds to one's safety.
"Prusiking" or ascending the line: Two prusiks used in tandem can be used to climb a fixed rope. One prussik is attached to the "belay loop" sewn onto the front of a harness and the other is attached to a longer length of cord reaching to one foot. With one loop attached to the rope above the other the climber can then stand up in the foot loop, slide the waist loop up and "sit" down on it. Once sitting, they can slide the foot loop up the rope and repeat the process.
"Escaping the Belay": In a lead-climbing situation, should the belayed climber become incapacitated in a position where they cannot be safely lowered to the ground, then the belayer must escape the belay in order to effect rescue. With the belay rope locked off with one hand, the belayer can tie a prusik to the rope with the other, transfer the load to a fixed anchor, allowing themselves to effect rescue or go get help.
History
The Prusik knot was invented by Austrian mountaineer Dr. Karl Prusik. It was shown in a 1931 Austrian mountaineering manual as a rope ascending knot. It was used on several mountaineering routes of the era to ascend the final summit block of a peak; where a rope could be thrown over the top, one side anchored, and climbers could attain the summit by prusiking up the other side of the rope.
Fashion (Controversial)
Prusiks are carried by some climbers and not carried by others. They are fashionable in an anti-fashion sense - being popular among (less-fashionable) Trad Climbers and disdained by more fashionable Sport Climbers. They are a popular technique to teach at college outing club and large mountain club groups. Choosing to carry prusik loops is a personal choice, and does not differentiate more-skilled or more-prepared climbers from less-skilled or less-prepared, though proponents may argue otherwise.
WARNING: Climbing is a sport with inherent dangers. The techniques described require expertise, practice and judgement to apply safely. Specific instruction by trained professionals is recommended.
External Links
- Prusik Knot at Oz Ultimate with good pictures showing how it is tied.
- Prusik Knot used in Sailing for climbing a mast, with other notes.
