The Edelrid Ohm is a clever assisted-braking device that helps alleviate the problems associated with belaying a significantly heavier climber. Ideal for climbing walls, this device acts as a runner on the first bolt of a climb, and in the even of a leade fall, it assists the braking forces that the belayer can generate, allowing them to better control the fall and not be dragged skywards by the heavier climber.
The OHM still enables smooth paying out and taking in rope when climbing and belaying and has no negative affect on handling. The OHM was developed for use at both climbing walls and outdoor sport climbing venues.
The development of the Ohm was supported by the Institute of Mechanical Handling and Logistics at the University of Stuttgart. It is an assisted-braking resistor that is attached at the first bolt with a quickdraw and the rope runs through it. In the event of a fall, the rope is pulled into the device’s braking mechanism. This then brakes the fall. The device does not stop the rope abruptly; instead it progressively brakes the speed it runs through, so that the belayer can still dynamically arrest the fall. The Ohm increases the amount of friction in the safety chain, independent of the belay device used. As a result, the belayer needs to apply significantly less hand braking force to the braking rope to arrest the fall and they wont be hurled against the wall in an uncontrolled manner.
The Ohm is designed not to affect rope handling when belaying a lead climber. It nei-ther increases rope drag for the lead climber, nor has a negative affect when paying out rope. The device’s assisted braking mechanism is only activated in the event of a fall.
The OHM benefits both climber and belayer: The belayer wont be pulled against the wall in an uncontrolled manner. The climber can climb right to their limits, without having to worry that their belayer might not be able to hold them should they fall and with no fear of a hard landing.
The German and Swiss Alpine Clubs (DAV¹, SAC²) recommend that a climber should not weigh more than 1.33 times their belayer, i.e. maximum one third more (for exam-ple: belayer 60 kg/climber maximum weight 80 kg). In the event of a big fall, in particular at the climbing wall, such large differences in weight require extreme care and attention on the part of the belayer.
Including the Ohm into the safety chain increases this factor significantly. With this device, it is now possible for climbers in the lower weight ranges to belay a lead climber, who is up to 100% heavier than the belayer. The Ohm is suitable for ropes with a diameter between 8.6 and 11 mm and is particularly beneficial for belayers with a body weighing upwards of 40 kg.