Most rappel ropes are constructed using nylon fibers. The fibers are twisted into yarn. To keep the fibers from untwisting, two or more yarns are twisted together, generally in a clockwise direction. If a stronger rope is needed, several strands are twisted together in a counterclockwise direction to make the rope. This is a standard rope manufacturing process, which is illustrated in Figure F-1 and is called "right-laid." For making left-laid rope, the process is reversed.
The angle of the spiraling in the yarn and strands determines many characteristics of laid rope, such as strength, elongation, spliceability, and stiffness. The greater number of spirals per inch, the weaker the rope and the greater its stretch. In other words, straight fibers offer maximum strength and minimum stretch. However, in order for most ropes to be elastic enough to be safe, fibers must be spiraled.
Very tight spiraling is called "hard lay" and causes the rope to be very stiff, yet very elastic. "Soft lay" ropes have the opposite characteristics. Most rappel ropes are of the "hard lay" type so that they can absorb sudden loads generated during the rappel. The tightly twisted ropes also resist the effects of dirt and abrasion better than "soft lay."
Although laid rope can be used for rappelling, there are three negative factors in its use. One is the fact that it is of twisted construction; therefore, it tends to untwist as you rappel. Second and most dangerous is their great amount of stretch. Most will stretch 8 to 12 percent from the weight of the average rappeller. Third is the loud clicking noise they make when used with most descenders, which could be a problem during certain tactical missions. On the positive side, laid ropes are strong and reliable, and their dynamic, rubberband effects make them less apt to pull out anchors, or break under sudden heavy loads.
Instead of being twisted, yarns can also be braided or plaited. Both types exhibit less stretch than laid ropes. They also have a greater strength for a given diameter and are less likely to twist or kink. However, because these ropes are softer than "hard lay" ropes, they tend to lose strength faster during use.
The finest construction available for rappel rope is called "kernmantel." It consists of a core of fibers covered by a braided fiber sheath. The prime purpose of the sheath (mantel) is to protect the fibers of the core (kern) from dirt and abrasion, thus increasing the life of the rope.
Kermantel ropes are used for rappelling at the Department of Energy Central Training Academy in Albuquerque, New Mexico, and are recommended because of their superior higher safety factor for a given rope diameter and their greater resistance to wear.
Last Modified: Friday, 28-Feb-97 10:09:00