Climbing tips: Dynamic and Semi-static ropes properties and standards
Climbing ropes are very complex items with very specific specifications. Modern ropes are now days known in the industry as kernmantle ropes. Kernmantle here refers to them having two distinct components. One, an inner “kern” or core and then an outer mantle. The first kernmantle ropes were introduced by the Edelrid Company in 1953. Prior to this, climbing ropes were of the Lawser-laid type of construction, consisting of 3-4 strands twisted together.
The core is made up of literally thousands of very fine nylon and perlon fibres, that run continuously from end to end, and this is where the strength of the rope lies. These fibres lie in small twisted bundles and then the bundles lie parallel to each other all the way along the length of the rope.
The mantle is a sheath which is woven around the core and does not have a very high tensile strength, as its main function is to protect the inner core and to hold the core in place. This aspect is worth noting, in that even if the mantle has a few nicks and cuts visible from the outside, it does not necessarily mean that the strength of the rope has been compromised. During manufacture the mantle is woven from bobbins of thread. The number of bobbins used, affects the handling, elasticity and resistance to abrasion of a rope. Ropes that have 48 bobbins have good dynamic properties. Those with 32 bobbins, do not stretch as easily, but are more resistant to wear and tear. So a rope which is used for high end sport climbing where the rope will catch long falls would preferably have 48 bobbins. Whereas a rope used in a climbing gym would be usually have 32 bobbins.
All proper climbing equipment, including ropes and other nylon and metal equipment have their specifications laid down by the international mountaineering body the Union of International Alpine Associations (U.I.A.A). Use only equipment that carries the U.I.A.A. mark on them. Products made or sold in Europe also carry a quality certification mark shown as the technical reference Standard EN (European Norm) and a CE mark which stands for Conformity to the European Directive. In many instances, the European standards exceed the UIAA standard.
Types of Ropes
Climbing ropes are made in two distinct forms: (1) Dynamic ropes and (2) Semi-Static ropes.
1) DYNAMIC rope is of a type that stretches and is made like this in order to absorb the shock of a falling climber. They are usually sold in 45m, 50m and 60 or even 70 m lengths. Unlike semi-static rope they are usually made with bright, multi-coloured mantles and may have the halfway point marked in some way.
Dynamic ropes are divided into 3 different types: Single-ropes, Half-ropes and Twin-ropes.
Single-rope (also called full-rope) is the term used to indicate that it has the full required strength of a mountaineering rope. This is shown at the end of the rope by a figure 1. Single ropes can sustain 5 test falls of 80kgs (U.I.A.A. test). This is in compliance EN892/U.I.A.A. CE 0120. They typically are made in 10mm, 10.5mm and 11mm diameters. Since 2005, ropes which are even thinner than this, but that are still rated as Single-ropes have come onto the market. Single-ropes are typically used mainly in sport-climbing. Sometimes Single-ropes are used in trad climbing, on routes which follow fairly straight lines.
Half-ropes (also called double ropes) carry a figure ½ at each end of the rope. They must sustain 5 falls of 55kgs in the U.I.A.A. test. They comply with EN 892 /U.I.A.A. CE 0120 and usually are made with a diameter of 8.2mm up to 9mm. They are used in Trad climbing, mountaineering and ice-climbing. They are sometimes called double-ropes, because two ropes must be used when lead climbing, but they are clipped separately through different running belays.
Twin-Ropes are indicated by two inter-locked circles on the ends of the rope. Twin ropes are two thin ropes which, when leading on, are used as if they were a Single rope. When used like this they have similar properties as a Single rope. They must sustain 5 falls of 80kgs (2 strands together) in the U.I.A.A. test. They comply with EN 892/U.I.A.A. CE 0120 and are made in about 7mm diameters. They are usually used on long alpine routes and ice climbing and are very seldom used here in South Africa.
There is actually a fourth type of rope, namely a Walking-rope. This is in fact not a separate rope but simply a single strand of Twin-rope used only in low impact situations, such for scrambling and short-roping. These ropes carry the Twin-rope insignia but are used in non serious situations. They are usually sold in short lengths of 25 or 30 m’s.
One of the many U.I.A.A. specifications with Dynamic ropes is that they must be able to stretch to one and a half times their own length before they start to break. They are also made to be very supple and to resist cutting over sharp edges. Breaking strength varies from about 1500kg for Half-ropes to 2500kg for Full-ropes. However breaking strengths are not usually specified on a dynamic rope, as in theory they should never break if used in the correct manner, while catching a leader fall, of a reasonably sized climber.
Dynamic ropes will usually have 2 ways of identifying their vital information:
One is in the label at the end of the rope which states the manufacture’s name, serial number and type. Then in both dynamic and semi-static there is a tape thread which runs inside the core. On this is printed the name, type, diameter, EN standard and year of manufacture. In addition there is another coloured thread which indicates the year of manufacture. See diagram below.
All Dynamic-ropes are sold in set lengths, cut to size with labels on either end.
2) SEMI-STATIC rope is not actually a climbing rope, but rather a rope used for high angle rescue, industrial rope access work, police rope intervention and commercial abseiling. It is often and incorrectly called static rope. They are made to Technical Reference, Standard EN 1891 and can be safely used to sustain a Fall Factor of 0.3.
Semi-static ropes, as the name indicates, do stretch a small amount and to comply with the standard they must not stretch more than 5% with between 50kgs and 150kgs load.
Semi-static rope is divided into 2 types:
Type A for high angle rescue, caving, intervention and industrial access. These must hold a load of 1500kgs when the load is secured by a Figure 8 knot in a static pull. They must also sustain a 5x falls of a Fall Factor 1 with a 100kg load.
Type B are ropes used in less abrasive situations than type A. These could include tope-roping in a climbing gym. These must hold a load of 1200kgs when the load is secured by a Figure 8 knot in a static pull. They must also sustain a 5x Fall Factor of 1 fall with an 80kg load.
To calculate the approximate strength of a semi-static rope take the diameter squared x 22, e.g. 10mm rope x 10 x 22 = 2200 kg.
Most semi-static ropes need to be shrunk in cold water before use. Simply put the rope in a bucket of cold water for 24 hours and then allow it to dry.
Unlike Dynamic ropes, Semi-static ropes are sold on the running meter, usually from a large real of rope. The purchaser has a length cut off for their individual needs. They therefore will usually not have labels on the ends.
When to use a dynamic rope apposed to a semi-static rope.
A dynamic rope must be used in any situation where a person (i.e. a lead climber) could fall from a position above the highest protection point. This would mean the climber falling a distance through the air before the rope began to arrest the fall. A semi static rope is used in situations where the load is more or less constant on the rope. For example, an 85kg person abseiling down a rope would subject the rope to an almost constant force of 80kN.
Dynamic ropes and their properties
This is the force which occurs on the running belay when a climber takes a leader fall. The U.I.A.A. has a standard test for this and stipulates the maximum impact force a rope can impart on the runner must not be greater than 12kN. This means the more stretch the lower the impact force. The test is carried out with a fall factor of 1,774 with the following weights applied. Single-ropes: 80kgs, Half-ropes: 55kgs and Twin-ropes: 80kgs (2 strands together). The U.I.A.A stipulates that on the first test fall a Single-rope may not exceed 12kN, a Half rope 8kN and 2 strands of a Twin rope 12kN.
With each leader fall, a rope slowly looses its stretch and so the impact force increases over time.
Fall Factors and the safety chain.
The fall factor is an indication of how much strain a rope sustained in a leader fall. This Factor is calculated as a number between 0 and 2. The higher the factor the more strain the rope sustained. It is easy to calculate a Fall Factor to have some idea of what work your rope did during a fall.
Take the distance the climber fell divided by the amount of rope already played out to the leader (i.e. rope length between the belayer and the leader).
For example: The leader fell 6 metres in total and had already climbed up 12 metres.
Example 2: The leader fell 10 metres and was 5 metres above the stance.
(In this case the leader must have fallen below the belayer. The climbers were probably sitting on a ledge. The leader climbed above the ledge and had not put any running-belays in for 5 metres.)
If a Dynamic-rope has sustained a Factor 2 fall or any force near that, it should be discarded.