Dynamic ropes
Semistatic ropes
Technical characteristics of ropes
Impact force:
For a single rope, the Standard EN 892 requires a maximum value of 12kN during the first factor 1.77 fall arrest, with a mass of 80kg, the same value as for twin rope (12kN for 80kg) but on two strands.
For a double rope, the impact force has to be less than 8kN for factor 1.77 with a mass of 55kg.
The impact force given in the technical notice must be no less than the least good (highest) result found by the laboratory in tests on 3 samples of the rope.
Note that the impact force rises as the number of falls sustained increases.
Number of falls:
To meet the standards, dynamic rope must withstand at least 5 successive falls of factor 1.77. The number of falls before break decreases with wear, and the number indicated on the technical notice must be no greater than the least number found after 3 laboratory tests.
A rope with a greater number of falls rating will thus give security for longer.
Diameter and weight:
Ropes of bigger diameter generally have a longer lifetime. At the same time they are heavier and not so nice to use. On routes, where weight and ease of movement are important, it is preferable to choose a thinner rope. The overall performance of a rope may be considered as a balance between its weight and its dynamic performance.
Sheath slippage:
The core and the sheath are two independent components that have the tendency, if the construction is not carefully matched, to act separately and slide one on the other. The sheath may deform little by little under the effect of belaying and create a slack zone around the core and sag outwards “the nora batty stocking effect”. This phenomenon results in more rapid wear, particularly in intensive or top-roping use, and brings the risk of jamming in descenders or belay devices. Note that the risk of sheath slippage is increased in wet conditions.
Number of bobbins
The sheath encircles and protects the rope’s core, it is the visible part. It is formed from groups of filaments: each group woven from a bobbin.
For equal diameter, a larger number of bobbins give better dynamic characteristics, and a smaller number of bobbins give better abrasion resistance. Thus one chooses a single rope of 48 bobbins construction for dynamic performance (TOP GUN II) or of 32 bobbins to maximise abrasion resistance (Wall Master V) by using thicker filament.
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Dynamic elongation
This is the stretch of the rope during the first UIAA test fall. It must be less than 40%.
Static elongation
Measured under a load of 80kg it must not exceed 10% for single rope, 12% for double rope, and 10% for two strands of twin rope together..
The fall factor
The fall factor determines the hardness of a fall: the higher it is, the harder the fall. Its value, lying between 0 and 2 in climbing conditions, is calculated by dividing the height of the fall by the length of rope deployed.
The hardness of a fall is not a function of its length but of this ratio, because the longer the rope, the more it can stretch to cushion the fall.
Source: Beal