In the climbing world there are two different types of rope commonly used. Static ropes are usually used for abseiling, rappelling, rescue or for ascending, lowering or hauling gear. They should NEVER be used for lead climbing or for fall arrest applications.
Dynamic ropes are used for both leisure and industrial climbing applications where there is the possibility of a fall and they protect the climber by absorbing the impact. Dynamic ropes come in several different guises- single, half/double and twin.
A dynamic rope is designed to stretch under an impact load. This stretch factor or “elongation” is usually given as a percentage of the ropes length. Dynamic ropes use this elongation to absorb much of the impact in a fall.
The stretchier a rope is the less impact force you will feel. Dynamic elongation is the amount the rope will stretch when someone falls.
For example the Edelrid Shikra has a dynamic elongation of 33 % which means a 60m rope will stretch up to 20m when someone falls on it.
Static elongation (also known as working elongation) is how much the rope will stretch if it is used with a static load of 80 kg hanging on it.
The figure for the 8.5mm Shikra is 9%. An easy way to visualize this is if you tried to lift an 80 kilogram weight off the ground from 60m above with the Shikra will stretch 5.4m before the object leaves the ground!
Every time a dynamic rope is stretched by a fall it weakens it slightly so it's important to keep a log of your falls so you can track the wear on your rope and know when to retire it.
If you fall and the rope you are attached to has no stretch serious injury will occur so it’s really important to match the rope to the job you want it to do.
Dynamic ropes can be used for abseiling and hauling gear but a static rope will perform better and last longer in these applications.
There are different types of Dynamic rope for different uses as follows.
Single ropes are made to be used singly and are usually between 8.9mm and 11mm in diameter. Lengths used vary from 30m to 70m. A 50m or 60m is a good all round length to buy.
A 10mm single is a real workhorse rope that can hold up to lots of use and abuse. The large diameter is easy to hold and belay and the thicker sheath provides sharp-edge protection. The thicker the rope, the heavier it is for a given length and this can be an important consideration for climbers. 50 metres of wet rope hanging out of you can start to feel pretty heavy!
Skinnier singles are also used but they are harder to belay due to the reduced friction and they are more prone to damage.
Half or Double ropes are two separate ropes of the same size that are designed to be clipped independently into pieces of gear. Thinner than singles they are usually 8-9mm diameter and are great for multi-pitch rock or Alpine style routes.
They allow the leader to clip into different protection to the climbers below which places less load on gear in turn providing more safety for the second in the event of a fall on traverses.
As clips are alternated rope drag is also reduced when climbing and when its time to rappel down you can go twice as far by tying the two together. They also provide extra security if one rope is damaged by rock fall, sharp edges, or ice tools. Climbing this way takes a little more time and energy due to the extra bulk and weight of the ropes plus time spent managing belay transitions.
You need to avoid clipping both of the lead climber’s ropes in to the same piece of gear as it will double the impact force if both ropes arrest a fall.
Twin ropes are another useful two-rope setup using separate ropes of the same size that are designed to be clipped together through each piece of gear. These ropes are a reduced diameter, usually about 7-8 mm each. They are usually used for long rock, ice, mixed routes and expeditions that require light-weight gear and like half ropes allow you to rappel further. Since you have to clip both ropes through each piece of protection there will be more rope drag than with half ropes.
As their name suggest static ropes are NOT designed to take dynamic shock loads. They only have a small amount of stretch and are used for ascending, abseiling, lifting and lowering gear. We’ll say it again just so it’s clear, they should NEVER be used in place of a dynamic rope as serious injury can result if you fall.
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