Part One: Climbing Ropes
Kernmantle ropes have two components that work together to create the desired performance. Some kernmantle ropes are static, meaning there is limited stretch. These ropes work best for jugging, hauling, rappelling and anchor construction. Climbers need a different type of kernmantle rope, dynamic. A dynamic kernmantle rope is designed to absorb energy from a fall thus keeping the impact forces low. This is accomplished through elongation or stretch of the rope when loaded in a fall. The material used in ropes (nylon) is not inherently dynamic; therefore materials need to undergo various processes to provide this. The older goldline was a twisted rope without a sheath. They were rough on the hand and when loaded you would spin like top. All modern ropes are kernmantle construction.
Nylon is the raw material that is used to make dynamic ropes. Raw nylon comes in large spools in bundles of a specific diameter. This material is treated with a lubricant from the manufacture to make it easier to work with. This is essential for the construction of ropes and their performance in the field.
Nylon will then heat-treat the core and sheath fibers to relax them and make them more dynamic. Also, some rope companies will dry treat the individual fibers before production. This allows the dry treatment to completely saturate the fibers and reduce water absorption.
All kernmantle ropes have a core (center) and sheath (exterior). Typically, core strands are constructed by twisting fibers together into cables. Sheaths are constructed by braiding twisted fibers over the core. Both the core and sheath are functional components of the rope. The sheath must be in good condition for the maximum performance and security.
The core is constructed of twisted fibers bundles. Core fiber bundles are twisted into a clockwise strand and a counter clockwise strand. These are call S strands (clockwise) and Z strands (counter clockwise). The core of a rope will have an equal mix of S strand and Z strands to make a neutral rope. This prevents you from spinning when one hangs on the rope. The primarily of the core is to provide stretch (elongation) that will absorb the energy of the fall. Some of that energy is converted into heat. .
Around these core bundles a sheath that is braided by a rope-braiding machine. There are different patterns that can be braided. A 2-over-2 bundles braid puts two bundles over two bundles. This braiding pattern reduces fiber exposure and will pick less than other patterns. A 1-over-2 sheath has one bundle going over two bundles. This produces a slicker sheath that is more supple, but more prone to picking out. The sheath determines the handling characteristics of a rope, but also is essential in controlling a fall. During a fall the sheath squeezes the core controlling stretch rate and helping to convert energy into heat. The sheath also protects the core from abrasion. However, if the sheath is badly worn just assume that you need to replace the rope. A worn sheath will break and ropes with a bad sheath do break in testing. Play it safe, get a new rope.
Every rope made needs to begin with quality materials to ensure top performance. However, there are many variables that manufactures can manipulate to determine the handling and performance of a rope. Each rope will have an ideal situation such as alpine, sport climbing, or ice routes. Check out next months tech article at Appalachian Mountain Institute on selecting the appropriate type for your climbing needs.