Rope Soloing Devices part 3
In the third part of my preview of On the Line, a book on top rope soloing (TRS), I move on from eccentric and rocker rope clamps, to lever arm devices.
Lever Arm
A lever arm rope clamp has a slightly simpler mechanism than a frame loaded, sprung and toothy eccentric rope clamp, working around just a jaw that’s mounted into a U shaped frame via a removable axle pin.
Unlike an eccentric device, where the jaw is loaded via the frame, the jaw is loaded directly, and does not require either a spring or teeth in order to function. This gives a lever action rope grab a number of advantages in certain areas, but also some disadvantages in function and efficiency, making this style of grab uncommon in all fields apart from rope rescue.
Examples
Gibbs Rescue, SMC Grip, Petzl Rescucender, CMI Ropewalker, Petzl Shunt, S-TEC - Duck R.
Failure modes and effects
As with all bi-directional devices, there always a risk that the device may be put on upside-down, and so carefull study needs to be made of the instructions and labeling.
A level device, if panic grabbed before it has chance to lock on the rope, may fail to grab, as the device and the climber will be falling at the same speed. In order for the jaw to grab the rope, it must be free to rotate. The same is also true if the climber grabs the rope above the device before it can lock, as this will retard the devices ability to lock, leading to the climber and grab plummeting down the rope.
The pin has to be correctly located and secured, otherwise the jaw can fail, or release under load.
Suitability for TRS
Pros
Self Feeding.
Although there are sprung models of level arm devices on the market, the lack of a spring, or teeth, results in a rope grab that is bi-directional, but clamps the rope when fully weighted. This makes the device ideal for moving around a safety line.
The lack of teeth also results in the device slipping on the rope before damaging it, with a typical slip occurring around 4 kN. This means that if the device had to withstand a dynamic fall, it would slip rather than damage the sheath.
The rope is fixed in place by the jaw and axle pin, meaning it cannot escape unless the pin is removed, resulting in a semi-fixed rope grab (some models are fully fixed, requiring a spanner to remove the pin).
The manner in which the jaw is loaded, and the general construction of lever cam rope grabs, means the overall strength of these devices is extremely high, with the jaw itself breaking at approximately 13 kN, although such a force would be impossible achieve on an unknotted climbing line. This overall strength comes from level cam devices being designed specifically for high industrial and rescue loads.
Back-up knots are more likely to be blocked by the frame of the device compared to eccentric devices.
This style of rope jaw is also less affected by dirty or icy ropes, making it a good choice for winter TRS.
Intuitive
Heavy duty.
Cons
The device does not instantly grab the rope like an eccentric device, which can be unnerving, increasing the risk of panic grabbing.
Device can be disabled if panic grabbed.
Panic grabbing the live climbing line can block the device from functioning.
Can fail if blocked/depressed from above.
Does not fit into a rope climbing system as easily (Texas style or Frog), as an eccentric cam.
Expensive and of limit use.
Heavy for their size.
Conclusion & Personal reflections
This is another puffer fish device, only one that’s a little less risky to try compared to a rocker, yet with many of the features that make a rocker a device to consider. Unlike a rocker, a lever device is far more intuitive, as well as well established, and tend to be more robust and reliable, able to cope with conditions that would disable an eccentric device.
Unfortunately, lever action cams are easily disabled due to panic grabbing, or top strike, which makes then dangerous to use alone. They are best employed as one of the devices on a two rope system, or stacked above an eccentric device.