Self-locking device

Self-locking devices are devices intended to arrest the fall of solo climbers who climb without partners. This device is used for back rope solo climbing for 'ground-up climbing' or 'top rope self belaying'. To date, several types of such self-locking devices have evolved.

The earliest type of self belay device used was the ubiquitous prusik knotted sling used by climbers. The method requires the soloer to feed out an estimated length of belay rope so that he can reach his next stance and repeat the process as the rope is difficult to feed through the prusik knot while climbing.

The next level of device development improved on the locking limitations of the prusik sling by utilizing a cam that is activated by the climber's body moving down to rotate the simple grab cam inside a rigid frame. The climber's harness is directly attached to the cam and the frame encapsulates the rope.

Early versions of the cam systems used a Gibbs-style type 1 ascender placed in an inverted position attached to a soloer's sit harness opposite to the manufacturer's intended use. The combination of a climber's body position in a fall and friction between the ascender frame and the rope provides the activating leverage for the cam to grab the rope. Fall forces generated using this device and the cam profile can be enough to damage a rope due to the high clamp loads induced by the cam lever arm. The main drawback to this system is that it is like the prussik knot system where the soloer also has to feed out an estimate amount of rope in order to reach a stance point.

A big improvement over the Gibbs-style type 1 ascender was the design of the Wren Industries 'Soloist' – the device incorporates a floating cam that is activated by the relative position of the rope to the device frame, with the frame secured between a user's sit harness and a chest harness. The Soloist allows the rope to feed without the need for the soloer to manually feed out between stances – so it allows a 'true' hands-free climb.

Knowledge of the correct device position relative to the rope anchor is critical for the correct operation of the cam devices in a fall as they are mono directional in operation, and the soloer must be aware that he needs to put in a runner as soon as he sets off above the belay point on a multi-pitch climb, otherwise he can slide to the bottom of the rope in the event of a fall. The Soloist cam profile design allows the belay rope to be "grasped" rather than crushed as in the early cam devices.

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Wikipedia