From ropewiki.com

Introduction

This page serves as a comparison for the various canyoneering ropes that are available. There are a number of characteristics to consider when choosing a rope.

Comparison Table

Rope characteristics

Cost

With very good performance characteristics often come high prices. While a good rope may provide a much better use experience, it may be used less if it is perceived to be very expensive. Also, ropes do not last forever so switching to an expensive rope can cost more in the long term than just the one-time purchase. Finally, user skill plays a large part in how long ropes last. Having an expensive rope may make you less willing to take less experienced canyoneers on your trips.

Diameter

Larger diameter ropes are generally stronger, less stretchy, abrade less easily, and are safer for beginners. Small diameter ropes are lighter and pack into smaller spaces, but typically require more care to rig the appropriate amount of friction.

Stretch

Although all canyoneering ropes are "static" in that they are not designed to absorb large shock loads like dynamic climbing ropes, some are more static than others. The less stretch a canyoneering rope has, the better; there are few to no good reasons to have a stretchy canyoneering rope. Stretchiness leads to bouncing during rappel which increases anchor loading, abrades the rope over flat surfaces, is more likely to cut the rope over sharp edges, and feels much worse to the rappeller.

Very static ropes do increase shock loads due to falls, but the presumption in canyoneering is that care will be taken to avoid shock loading scenarios.

Weight

The rope is commonly the single heaviest piece of gear a canyoneer carries. On long, demanding trips with a lot of additional gear, a pound or two difference in rope weight may make a difference. But, also remember that just one liter of water is 2.2 pounds.

Tensile strength

It is extremely unlikely a rope will break due to overloading, but if you are setting up an unusual situation or are performing a rescue, this rating may become crucial.

Sheath Percentage

Assigning a higher percentage of the rope's material to the sheath (rather than the core) may make the rope more resistant to abrasion at a slight cost to the ropes tensile strength. Because the core material and the sheath material can have radically different densities, stating this difference in terms of material volume is probably more useful than in terms of material weight.

Length

The de facto standard canyoneering rope lengths are 120', 200', 300', and a spool (usually a little over 600'). Most canyons can be completed with two 200' ropes and those that cannot are usually noted as having big drops. A single 120' rope is insufficient for most canyons, but a single 200' rope or two 120' ropes are sufficient for a large number of canyons. It is usually prudent to bring at least three times the length of the longest drop in rope.

Materials

A sport rope such as a canyoneering rope usually consists of a core that provides most of the strength of the rope, and a sheath which protects the core from damage but provides little of the rope's strength. Different materials have different characteristics for cost, elasticity, stiffness, water absorption, strength, and melting point. Marlow has an excellent comparison page.

Nylon

Nylon, precisely "Nylon 6", is a DuPont brand name of a polyamide material. Polyamid, Polyamide, or PA, is a generic name for Nylon. Nylon is a low cost material from which most dynamic climbing ropes, and some canyoneering ropes, are made. It is very stretchy compared to materials used in other canyoneering ropes. Nylon also absorbs water, which makes it substantially heavier when wet. Nylon may lose strength when wet, but the magnitude, and even direction, of this effect are unclear. Some experiments show an increase in strength[3] while other report loss of up to 70% of original strength in dynamic loading (30% in static loading)[4]. One advantage of nylon rope is that some find it to have a "good hand"; that is, it is feels nice to handle and is easy to work with.

Polyester

Polyester (sometimes called PES) is another relatively low-cost material from which many static ropes are constructed. It is a very static material relative to other canyoneering ropes. Polyester absorbs very little water weight and shows no significant strength reduction when wet. It becomes stiff more quickly than many other materials used for canyoneering ropes, but generally has good abrasion characteristics.

Dyneema/Spectra

Dyneema and Spectra are two different brand names for the same fiber. It has an extremely high strength-to-weight ratio, but a very low melting point (266-277F) compared to other common rope materials. It is also very slippery, and therefore does not hold knots very well or hold a dye (so this fiber is always white). It does not absorb much water and has not shown a reduction in strength when wet.

Technora

Technora is an aramid fiber with a very high melting point, and therefore commonly used in fire rescue. In canyoneering, it is capable of withstanding the high amounts of heat generated by rope-on-rope sliding friction, which makes tools like the VT Prusik possible. Technora seems to absorb somewhat more water than polyester and Dyneema/Spectra, but not nearly as much as Nylon.

Polypropylene

Polypropylene's chief advantage is that it is lightweight and water-resistant, and marine ropes that need to float in water often use it. Like Dyneema/Spectra, it has a low melting point and is protected by heat-resistant Technora in the Sterling C-IV.

Caveats

The comparison table on this page attempts to provide as much of an apples-to-apples comparison between ropes as is practical from the available data. There are some cases where this effort may lead to unexpected or undesirable consequences which we attempt to document here.

Stretch

To a good approximation, when a given weight is applied to a rope, it gets longer in direct proportion to the starting length of the rope. So, if a 100 ft rope gets 5ft longer when tensioned with a particular weight, a 200ft length of the same rope should get 10ft longer when tensioned with the same weight. This is not exactly true because of end effects: the very ends of the rope stretch a little differently than the middle of the rope, and different rope lengths have different proportions of "middle" and "ends" of the rope. However, it is very close to true which is why static elongation is usually quoted in percent. When a given weight is applied to the rope, the rope is usually said to elongate by X%. This means we assume that a rope twice as long will gain twice as much length when tensioned with a given weight.

To another good approximation, when the weight hanging from a rope is increased, the rope's elongation becomes larger in direct proportion to the weight. So, doubling the weight roughly doubles the additional length of the rope. If a 100ft rope elongates by 10ft (to 110ft) when loaded with 200 pounds, loading that rope with 400 pounds should elongate it roughly 20ft (to 120ft). This means that static elongation (reported in percent) will vary greatly with the amount of weight used to test the elongation. To adjust for this effect, this page "normalizes" static elongations to the percent elongation we would expect if the rope was loaded with 300 pounds. So, if static elongation was measured to be 3% at 200 pounds, we would expect that elongation to double (6%) at double the weight (400 pounds), and increase by half (to 4.5%) at 50% more weight (300 pounds). So, even though the rope was tested to elongate to 3%, this page will report 4.5%, which is the approximate elongation we expect if the rope were to be loaded with 300 pounds. To make it easier to compare ropes, we have normalized the stretch percentage to a weight of 300 pounds using this level of approximation.

However, linear elongation (the previous paragraph) is never exactly true. In practice, most (all?) ropes elongate less as they are weighted more. So, we may expect 400 pounds to elongate our 100ft rope to 120ft since 200 pounds elongated it to 110ft, but instead we are more likely to observe the rope elongating to something like 118ft. This is because ropes get stiffer as they are stretched out more. The consequence of this behavior is that static elongation measured at different weights will result in different "normalized" 300-pound-stretch values on this page. For instance, if we tested our 100ft rope at 200 pounds and observed a final length of 110ft, we would report (110ft-100ft)/(100ft)/(200 lbs)*(300 pounds) = 15% stretch at 300 pounds. If we tested that exact same rope at 400 pounds and observed a final length of 118ft, we would report (118ft-100ft)/(100ft)/(400 lbs)*(300 pounds) = 13.5% stretch at 300 pounds. Even though this is the exact same rope, measuring the elongation at different weights suggests different numbers for normalized stretch.

What's more is that different ropes have different non-linearities. One rope might elongate 10% at 200 pounds and 19% at 400 pounds while another rope might elongate 10% at 200 pounds but 16% at 400 pounds. This emphasizes that elongations measured at different weights will produce different "normalized" stretch values as reported on this page. A good thing to do would be to have a single standard test weight that all ropes are tested against. EN 1891 specifies this weight as 150kg (330 pounds) and many ropes are tested with this weight. But, many (especially US-produced) ropes are not tested at this weight, and this may not be the weight that will actually be applied to the rope during your use of it. A small, skilled canyoneer traveling light may only apply 140 pounds while rappelling while a heavy, inexperienced canyoneer carrying a lot of gear may apply 400 pounds or more while rappelling. A single number cannot capture the full range of rope behavior which varies in many dimensions across ropes. However, the "Stretch" column in this comparison attempts to approximate the characteristic that most normal canyoneers care most about so that they can effectively (if imprecisely) compare various ropes to each other.

Note additionally that the values stated are only an approximation for new ropes. As ropes are used, they will most likely get stiffer.

Static vs Dynamic elongation

Static ropes are subjected to a static elongation test. That is, suspend weight for some period of time, carefully, on the rope and measure its length again. This test almost certainly does not describe how the material will react in an accidental dynamic fall, or bouncing on ascent/rappel. As an example, there are accounts of the Sterling C-IV (polypropylene core) feeling particularly subject to dynamic behavior not reflected by its static elongation testing figure. Be cautious when relying on the static elongation figure alone, however polyester and high modulus fibers seem reliably static for canyoneering use. See Canyoneering physics for a related topic.

References