How many times have we rappelled from a perch, only to end up with the end of a new rope transformed into what resembles a bird's nest? We can't blame the manufacturer for shipping a twisted rope. New ropes are shipped free of any twists and curls. The problem arises when we use the rope for the first time. To prevent your new rope from twisting, try this simple technique the next time out.
New ropes curl because the surface of the sheathing has a well-defined pattern engineered by the braiding design fabricated at the factory. When the rope travels under great pressure through a carabiner or over the surface of a figure eight (as it does when we rappel or lower a climber) the sheathing pattern causes the rope to twist much like the rifling in a gun barrel causes a bullet to rotate. Depending on the rope, this twisting can be as much as one full turn every three feet or so. This means that on a 100' rappel, we can end up with as many as 33 twists in the remainder of the rope. Not at all desirable for efficient rope management.
To prevent new rope curl, or rifling, while descending, do not allow the rope to slide through your brake hand. Instead, grasp the rope tightly while it is at your hip and maintain the grip while simultaneously feeding your hand and the rope to the rappel device. As you descend, you will start to realize that the rope has a mind of its own as it begins twisting, however, do not allow the rope to twist in your hand. When your brake hand reaches the rappel device, your descent will stop. While stopped, slide your brake hand back to your hip while preventing any further descent. Repeat this operation by gripping the rope and feeding both it and your hand to the rappel device again.
With a little practice, it won't be long before you figure out that by using both hands in leap-frog style, you'll be able to descend smoothly without stopping--and without any rope curl, as well. Eventually, as your rope gets fuzzy and breaks in, you'll find that less and less of this technique is required.
By employing this simple technique, we force all induced rope twist back into the rappel device. The net result is a longer lasting rope with negligible twist, making it much more manageable and easier to coil.
Rope curl causes a much greater problem when we lower a climber than it does when we rappel. This is because the bird's nest is generated between the belay device and the rope, which is flaked on the ground. Sometimes this mess can be unmanageable, creating a safety concern for the climber who is being lowered. I have seen a belayer strand his partner in midair for a long period of time when he attempted to undo with one hand the mess created from rope curl. Once, I assisted a frustrated belayer who was so preoccupied in an effort to untangle the rope mess at her feet, that she actually let go of the brake rope. Fortunately for her partner, he did not fall all the way to the deck because, when the botched mess reached her belay device, it was every bit as reliable as a good brake hand.
Anchors cause ropes to twist also, especially while lowering a climber when using the sling-shot configuration. As the climber descends, the rope passes over the carabiner anchor under great pressure, where it twists the same as it does with a belay or rappel device. This problem can be prevented by using two carabiners on the anchor, especially when we use "Ds" with the gates opposed. As the sheathing passes under great pressure through the crotch of the first carabiner, the rope twists in one direction. As the rope continues through the second carabiner, the reversed crotch causes twist in the opposite direction - effectively cancelling out all torque induced by the first carabiner.
No where is rope twist a greater problem than it is when using the Munter Hitch. If you've ever rappelled a full rope length using this popular knot, then you've no doubt had to deal with the unmanageable mess at the end of the rope. When I see climbers rappelling using this method, it is amusing while they struggle with the rope, frantically whipping it around as they descend to remove the curls. Once on the ground, they struggle again while they attempt to coil the rope with troublesome curls induced on descent. Why do double-duty when you don't even have to do single-duty?
Rope curling, when using the efficient Munter Hitch, is not as much a function of rope condition, as illustrated earlier, but rather an inherent problem as a result of rope moving over rope under great pressure. The next time you use this knot, carefully observe how the rope on the tension side of the knot induces a force to rotate the rope on the brake side. This action is not unlike a worm gear which transfers energy from one moving surface to another. While using the Munter Hitch, especially on great distances, it is important to use any technique to prevent rope twist, if you want to achieve efficient rope management.
The culprit is not always the rope when it comes to this problem of curling. I discourage anyone from using odd-shaped carabiners, such as the BD Super Lock, when rappeling or lowering (especially while using the Munter Hitch) because these designs seem to help twist any rope, regardless if it is new or worn. Apparently to me, as the rope passes over the carabiner's angular surface, it rebels by twisting because the mantle, which has its own pattern, is sensed through the sheathing while it makes an unusually tight turn over the sharp surface of the carabiner. These carabiner designs seem to curl all ropes, regardless of the fuzziness of the sheathing.
When using the Munter Hitch, I have found that a true pearabiner, manufactured from round stock, works best. The hitch floats exactly in the middle of the pear-shaped carabiner, away from the spine, which substantially influences the moving rope. The BD Superlock, on the other hand, is a carabiner with a "D" design, which forces the hitch into the tight corner of the crotch. This effectively produces more efficient worm-gear action, which in turn induces even more twists into the rope.