Thomas Senf
 

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Standards for dynamic ropes

Diameter

Rope diameter is measured under a 10 kg load. Under test, some ropes on the market clearly deviate from the manufacturer’s data.
In practice the diameter has little meaning. Only the clamping effect of particular braking devices or belay devices with thin ropes should be controlled (with back up safety). The advantage of thinner ropes is normally reduced weight and friction.

Weight per Meter

Normal single ropes weigh 60 to 85 grams per meter, half ropes about 50 grams and twin ropes about 45 grams. Mammut ropes in the Challenge Line, treated with COATINGfinish™, are particularly  light. The single rope Serenity weighs 52 grams, the half rope Phoenix 41 grams and the twin rope Twilight 38 grams, with 15 to 17 standard falls. Just two grams less weight per meter already reduces the pack weight of a 50-meter-rope by 100 grams – the equivalent of a chocolate bar, or a few beads of sweat!

Falls Held

The drop test is the point of most interest. It measures how many standard falls a rope will withstand. The standard fall with a fall factor of 1.75 is an extremely hard one, which  very rarely occurs in practical use. A weight of 80 kg (with single and twin ropes) or 55 kg (with half ropes) falls on a single cord (single and half ropes) or doubled cord (twin ropes). Single and half ropes must withstand at least 5 standard falls, a doubled twin rope at least 12. Single ropes, which hold 5-9 standard falls, are designated as standard fall ropes, those with more than 9 falls are designated multifall ropes.
The number of falls is a direct measurement of a rope’s safety reserve. No new rope can break from an impact load, assuming good conditions and good rope management. But the efficiency of a rope decreases: aging and wear reduce its strength. Moisture and particularly frost can reduce it by about one or two standard falls.

Impact Force

The impact force is the maximum force which affects the load in a standard fall, when the rope absorbs the fall energy by its elongation. It is the measurement for the «hardness» of the fall. Ropes with higher impact force, when holding the fall, produce a stronger «jolt» in the falling body and on the safety system. In standard tests the impact force for single and twin ropes may not exceed 1200 daN and for half ropes ‹ 800 daN (approx. 800 kp).
The practical relevance of the impact force is relatively small because it is measured with the standard static fall test, i.e.: the fall rope is completely fixed. In practice, however, a fall is almost always caught dynamically. Belay devices (Munter, figure eight, ATC, etc.) have a certain rope path, and their attachment to a central point, or on the harness, brings a dynamic effect. Through dynamic belaying a large part of the fall’s energy is dissipated and so the impact force is reduced. Measurements by Mammut of typical sport climbing falls show, that with dynamic belaying the difference in impact force between two different ropes is barely discernable. It’s therefore important to provide a truly dynamic belay.

Working Elongation

Working elongation indicates the elasticity of a rope with a static load. A piece of rope preloaded with 5 kg is loaded with 80 kg: elongation may not exceed 10% for single and twin ropes, and 12% for half ropes.
Static working elongation mainly assesses comfort when top roping or hauling on big walls. In these cases, it’s annoying when energy is wasted through rope stretch, or if a difficult sequence has been climbed with a top rope and while resting this distance is lost. Elongation is more relevant to safety when falling (see below), because it determines whether the falling body will, for example, shock load a runner. Roughly speaking, a relationship exists between the two values for static and dynamic elongation.

First Fall Elongation

This parameter measures the elongation of the rope during the first standard fall. The maximum permissible elongation with this test is 40%. This dynamic fall elongation indicates the inertial properties of a rope better than the static value of working elongation. With greater elongation danger is increased, due to the fall impact on protection. All Mammut ropes already fulfill the requirements of the (not yet obligatory) EN standard. With values from 28-32% they fall well under the 40% permitted maximum.

Sheath Slippage

For this test a two meter long piece of rope is drawn five times through a test device – a metal drum, with a zigzag shaped, offset rope guide. The sheath and core are then rigorously tested by the milling action of the drum. The sheath may be displaced by a maximum of 20mm
If the sheath and core slip during use, the rope can bulge and get lumps. If the ends are carelessly welded the sheath or core can slip out of alignment. With modern climbing ropes sheath slippage hardly ever occurs.

Knotability

An over hand knot is tightened with a force of 10 daN and then loosened at 1 daN. Afterwards the inside diameter of the knot is allowed to be a maximum of 1.1 times as large as the rope diameter.
Knotability is a reference point for the stiffness of a rope: with stiff ropes the knot cannot be as tightly tied, compared with a more supple rope, and the path through the belay device is possibly made more difficult. However, too much value shouldn’t be placed on this measurement, as the suppleness of a rope is also determined by care and the weather.

 
 
 
 
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