rappel line, rappel cord

3 Keys to Rappel Cords-( Dynamics, Dimension and Lifespan) Rappelling Rope & UIAA Standards

Word to the wise: You really want to rappel with rope/cord that can be used in longevity and not specialized rope that serves a specific purpose and are used for emergency, military training and other specialties. That is of course, you are a recreational rappeler and are looking for rope that will work under ordinary circumstances. This article will discuss dimensions, dynamics and  life span of  the types of lines that are on the market today.

What diameter rope/cord should I rappel with?

When rappelling long distances, the recommendation is to grab somewhere between an 8mm-13mm cord. That way the rope will not be a bear to lug around with you on your journey. Keep in mind though, there are 9mm ropes that will not serve you well for the type of rappelling you plan on doing. The material might not be the correct one to use.

diameter, uiaa, uiaa drops,

Pictured: Chart UIAA drop simulation by amount of rope

In normal conditions, and if you are just starting out, we recommend a diameter no smaller than 7/16ths or 11mm. The majority of rappel rope are made nowadays at 12.5 to 13mm for added safety as far as abrasive properties are concerned. You can even go bigger but keep in mind, the bigger you go, the more weight you will have to carry with you. However, the bulkier the rope the less intimidating it will be to a neophyte.

What Dynamics should I look for in a rappel rope?

Most rappel rope products hold up well when they are brand new. They will be able to take on a very large amount of load when they are first used. However, It only takes one kink, jam or gash to destroy that rope. That is why it is imperative you triple-check your gear every chance you get (station to station) . Most of your rappel ropes will not function as static ropes. That is, most of the time you will need a rope that can handle the swaying, stopping, weight shifting challenges brought on by a typical rappel pitch.

Enter Dynamic rope…These cords will support between 2000-23000 lbs of weight shifting, quick stopping, rope swaying rappel loads. Static ropes The stretch  or elongate to only 3% at breaking. This is a problem for sudden impact stop capacities. Statics break by sudden force characterized by only 1/2 % of its breaking capacity. The sheer force of a person falling only a few feet can max out this capacity!

Besides breaking of human bones or snapping necks from the forceful impact coming from a static setup, if there is no stretch/elasticity in the line, an anchor can easily be pulled out of its station and the line itself can easily snap, plummeting the rappeler down to their fate.

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Keep in mind that wire rope doesn’t have the capability of absorbing a huge amount of weight shifting loads. Add to that , natural fibers don’t do a good job at absorbing weight-shifting load either. Hence, your best bet is a nylon fiber line. When correctly used, nylon truly absorbs practically better than most other materials on the market today.

How does nylon absorb loads?

This is a loaded question but we will give it a go.

Pictured: Normal, Linear extension and failure of nylon molecular fibers

Nylon molecules actually run at sub-90° angles from the fiber axis line. As the fiber begins to  expand when it is being stretched, the molecules begin to coil/bend closer to parrell (90°) with the fiber axis line. This creates more energy being absorbed through the fibers with aid of the fiber molecules.
Once the stretching stops and load is released, the fibers go back their original positions and the molecules go back to their sub 90° angle positions along the fibers (That is if the load was light enough). If the load was extremely heavy, permanent deformation occurs and the molecules are permanently linear, which will lessen the absorption potential on future loads. 
The more the rope is utilized with heavy loads, the worse the elasticity/durability of the line will become. You are essentially converting absorption into heat energy over time. This is the result of the molecules/fibers frictional relationship. This is why it is important to replace the rope after a series of uses. Otherwise, You can be endangering yourself and others when you use rope that has lost its mojo!

How does Dynamic rope hold up as far as strength?

You will be amazed at how well dynamic rope holds up.

Most Dynamics will not exceed their breaking point after stretching to as far as 35-45% of their natural length. The durability of these lines are really something to marvel at. They are made to take on shock loads that most other ropes wouldn’t be able to handle. For instance, Statics can stretch to only about max, half what dynamics can stretch out to, before their fibers break and molecules become permanently damaged. Many Statics are made with way less elasticity then even that (2%-20%). 

Always check the manufacturer ratings but take the reading with a grain of salt, knowing that they can be inaccurate at times. Always go with the conservative minimum reading as your indicato, and not the max readings or even average measured strengths. You are trying to determine what the percentage of break strength your rope has. That is the most crucial of the readings and is termed the work load. 

For your main static rappel lines, you want to shoot for ropes that have a work load of between 10%-13% if you are going for static strength. Keep in mind these are only in situations where you are hard rappelling and not going long distances. For long distances, soft rappelling is recommended and you should always go with dynamic ropes. However static and dynamic strength measurements are important to know.

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If you are using Dynamic rope, dynamic strength (the capability of your rope to absorb abrupt weight changes) is key in qualifying your rope for use. You want your dynamics to stretch like a rubber band would. Like rubber bands, some dynamics are made with extreme elasticity but only made to handle certain load amounts. You want your dynamic to stretch and not break. You want it to act as a buffer against the load, on the rappeler and on the anchor rig.

At the end of the day there are no standards for Statics as far as there dynamic capacities. However, there are standards for Dynamics. Learn about these U.I.A.A. tests here. In order for a rope to pass these thorough tests, they must endure weights of the average rappeler, anchor weight and rig weight. Fall factor data is gathered from how far the weight falls in relation to the ropes end point. Then, the testing happens over and over again. For a rope to pass, it must handle five or more weight drop tests and also carry an impact force reading (restraint force) with the standard guidelines(usually between 2k-3000lbs).

U.I.A.A. TestingUIAA

When reviewing UIAA, make sure to remember that their data serves as a benchmark for the lowest case readings in strength and ratings of your rope. When you rappel, your drops are typically not longer (hopefully you pay attention to the length of the drop!) than the rope(s) you are utilizing. This will give you 1 or less than 1 fall factor. So your impact force are systematically less than when your dealing with greater fall factors.

With your static ropes, they will be able to withstand a few UIAA drops, however Statics are not made to absorb energy that is generated in longer pitches or belays. That is why we discourage you from using them in those scenarios. The impact forces on Static ropes while pitching a long belay can really hurt the person rappelling.

Pictured: UIAA drop test

The construction, moisture capacity, temperature capacity and the radius of the ropes edge are the key factors in determining how much energy absorption your rope is capable of. When testing is conducted, the ropes are elongated with the help of industrial, high powered machinery. Other machines are then utilized to tug the rope through different diameter edges until the fibers tear. The weight force that it takes to tear the fibers x the percentage the rope elongates before tearing will give you the Working capacity at over an edge or WCOE.  This measurement gives the manufacturer an understanding of how durable and safe the rope will be.

WCOE in terms of UIAA

Taking the average 11mm diameter on a Dynamic rope, its WCOE reading would be about 250 mkg/m. A typical rope rappelled at a typical drop with normal conditions loses about 1.5-1.7 mkg/m for every 60 minutes of use. You will notice that the strength of the rope will lose most of its strength within 80-120 hrs. Then the loss will lessen for the rest of the time the rope is used. Once the rope’s capacity falls under 165kg/m , it will no longer be able to leverage even just one UIAA standard drop. This is important to note!

Should I pad my rope edges? A resounding YES!!

The U.I.A.A will test cord that will be run over different diameter edges (typically 10mm or 11mm) like we suggested earlier. A rope that can withstand  six, seven or eight UIAA drops may only be able to handle three or four falls over a three or four millimeter edge or maybe  even less if the edge is thinner (one-three millimeter). As a rappeller, this is important to take note of because this means that you want to avoid sharp edges that can cut the rope or not leverage it properly.

Make sure to pad your edges or even better, use a rope protector! It can mean  your life. Also, keep in mind that nylon and most other synthetic lines will take a 7%-30% loss of durability once they are completely soaked (saturated) with water. Even if you are using a natural rope, or ropes that don’t absorb water, chances are water will in some way effect the durability of the rope.

When rope takes on sudden weight when it is saturated, the fibers will work to squeeze out the moisture. This process will harden the rope and will disallow it to elongate to it’s max elasticity.

Pictured: Water will adversely effect the longevity of your rope

What happens then is you are losing absorption energy within the rope which in turn means you are losing strength. Also keep in mind that manufacturers use appropriate chemicals that work to wick off moisture. This will lessen the blow when water gets onto your rope. You will see the product tagged as dry or waterproof.

How does my rope lose strength during normal use?

Other than losing strength via saturation, cords will lose strength by sheer wear and tear, age and essentially using them in normal ways when rappelling. Take for example a kernmantle cord when tugged on while over a sharp edge. The fibers in the kernmantle rope will be dragged side to side which will shorten  the rope. Flexion will occur which in turn makes it harder to knot your ropes. It will also reduce the amount of friction that you will need for rigging.

Generally, the more rigid the rope is, the smaller the amount of friction is necessary in the descension rig to leverage the load. Look for ropes that are harder and more rigid when rappelling but make sure they have enough elasticity as you will need them to have.

Can I renew my fatigued rope to its original strength by boiling?

boiling rope

pictured:boiling rope

If you are set on keeping your rope for longer periods than recommended, then there is a process for restoring them may or may not be valuable to you in the long run. This process is called boiling! Word of caution on this: Some believe that you will actually lose durability when using this process. Reason being is that when you boil, say nylon, you are essentially stiffening the rope by way of boiling the fibers, shrinking them. The molecules will realign but will not renew their strength because the fibers will shrink! It will feel like a new rope but the rope will essentially be smaller and fibers weaker.

We suggest you do not try and boil your ropes! All you are doing is fixing the aesthetic but causing your rope to become weaker. Thousands upon Thousands of tests have shown that there is no way to reverse rope fatigue. So, until there is solid proof that rope fiber molecules can be restored, avoid trying to restore your ropes! Throw them away and get your hands on new ones.

Key misconception: Some believe that with kernmantle ropes, that until the kern itself is damaged, you can use and reuse the rope forever! This is absolutely false. The more times you use this rope the more the kern loses capacity! Even though the mantel looks unharmed after proper usage, WCOE standards say do not overlook kern wear and tear as kern failure is one of the biggest causes for fatalities when it comes to rappelling.

What is the lifespan of my rope?

Pictured: Abrasive degredations

Your ropes lifespan will be reduced because of the following: cutting by rough abrasive surfaces, temperatures (hot and cold), UV rays, weight, and pollutants.

Loss of life by cutting- abrasive damage is very hard to avoid, especially when you are starting out as a newbie in this wonderful sport. Many times, you will not even notice that your line is gradually being filed by rough terrain. That is why it is imperative to notice if there is an obvious issue when your rope comes in contact with an obvious sharp edge. Sharp rock edges or even sharp tree bark have been known to cut open a line with extreme haste. You will notice a fuzz line beginning to develop.

The fuzz is actually constructed to prohibit the inner fibers from further damage. As a result, it retards the overall aging cycle of your rope. However, the more and more fuzz that sticks out, the weaker the mantle of your rope will become. Don’t wait too long to replace once the fuzz gets out of hand.

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Pictured: UV degradation

Loss of life by temperature- Let’s say you are pitching, and pitching very fast! The heat that is generated through your descender and through the rope coming in contact with edges will lessen the strength of your rope by means of frictional damage. This will not create fuzz but you will notice that the rope has become more rigid. When this happens you run the risk of losing a great amount of strength.

Loss of life by UV rays– Sunlight can cause excessive damage to most ropes on the market today. Your Type66’s will, overtime, lose up to 92% of its overall durability even after only one year of excessive exposure to UV rays. If you plan on rappelling in the northern region of the world then it may lose up to about 25-35% of its strength after a year.

Pictured: Chemical abrasion

 

Your type 6’s lose strength even faster! If you are rappelling in areas with tons of sun, such as Arizona, we recommend you use a polyester like Dacron so that you avoid  as much UV issues in your lines. Keep in mind however, all ropes will be effected in some capacity to UV, albeit sometimes a very small amount.

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Loss of life by weight– How much force and load put onto the rope can determine how much lifespan the rope actually has. Every time the rope is stressed by a large load, the line will get less and less durable. To put this in perspective, one tow of the average car equates to one U.I.A.A. drop, which means the rope must then be thrown away.

Loss of life by pollutants– Most of any hardcore acids, bleach, lard alkalis (battery acid), and even oils can really put a damper on the age of your line! Keep this pollutants away from your cords at all times!

 

 

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