In reply to:
From; Helmut Microys, National Delegate to the UIAA Safety Commission
for the USA and Canada.
The UIAA standard deals with three different rope types: single, half
and twin. In the UIAA drop test the single rope is tested with an 80
kg mass, a single strand of half rope with a 55 kg mass and both
strands of a twin rope with 80 kg. The single and half ropes must
sustain at least five falls and twin ropes at least twelve to pass the
standard. There are also differences among these ropes for elongation
and impact force (single and twin < 12 kN; half ropes < 8 kN).
Single ropes are obviously designed to be used in a single strand.
Half ropes, or double ropes, are designed for (aid) routes with many
runners at close spacing and are then clipped in alternately. The idea
was to reduce friction, particularly in the days, when climbers used
only carabiners and no sling extensions (the rope went zig-zag). These
ropes should not be used in this way (i.e. clip in alternately), as
often happens these days, for regular routes with runners further
apart. Keep in mind that the rope is not tested with an 80 kg mass. A
single strand of half rope, when new, may just hold one fall with such
a mass.
The twin rope was designed to be used in the double strand and both
strands must be clipped in every runner. Generally these ropes have a
diameter of only 8 mm. The benefit of a twin rope is its essential
safety and the advantage in the mountains for a full length rappel.
Present day ropes will not break at a runner or at the tie-in knot of
the leader in a fall. This does not even happen with very old ropes. A
rope fails when a sharp edge cuts it. As a rope is used, the capacity
to hold a fall over a sharp edge decreases. Generally speaking, a rope
which holds many falls in the UIAA drop test will resist cutting
better than a rope which hold fewer falls.
A half rope used singly is, therefore, much more likely to be cut than
a single rope. It could potentially be used for all climbing, but you
better not plan on falling off. A twin rope is much safer, because of
the higher capacity and the redundancy (only one strand may be cut).
Using half ropes like a twin, clipping both strands in every carabiner
is, of course, the safest solution (a pair of decent half ropes,
tested like a twin rope will most likely hold over 30 falls).
The maximum allowable elongation for half ropes (10 %) is indeed
larger than for single or twin ropes (8 %), but this would hardly be
noticeable in most fall situations. Elongation is more often than not
only a problem for a second with the rope out 100 feet. An 80 kg
climber could drop eight feet under body weight even though the rope
contains no slack.
Final advice: do not use your half rope as a single strand and when
the runners are further apart, clip both strands. You only live once.
Ice climbers in USA routinely use the double rope technique placing
gear (ice screws) very sparsely using half ropes. So:
1. In this situation is the second half rope for backup purposes?
On pure ice faces and water falls, there are generally no sharp edges
and the danger of cutting a rope are greatly reduced. A new half rope
may be reasonably safe, although I would advice against it when there
is a lot of dry tooling and runners are still far apart (I personally
would not climb on it regardless of the situation). In the latter case
it may be called a back up rope, because of cutting on an edge.
When the climber is on a water fall or smooth ice face, where there is
no friction to speak of, the question can be asked, why not climb with
a single half rope and clip all the protection. The result would be
pretty well the same in a fall situation as having two ropes. If the
rope breaks, it is because the fall energy was beyond the capacity of
the rope. With two ropes clippped alternately and the runners the same
distance apart, if the first rope breaks at the first runner and the
second will fail on the one below.
One of the reason for two ropes on waterfall ice is that one must
generally rappel and two ropes get you down faster and cheaper.
2. If I were to clip both half ropes together into one carabiner,
wouldn't that increase the load on the protection beyond safety levels
for the carabiners and protection as opposed to a single or twin
setup?
Using two half ropes clipped in together will produce forces on the
protection higher than when using a single rope. Twin ropes act like a
single rope.
The forces in the system are, however, determined by the belay method.
Any modern dynamic belay method will limit the forces inherent in the
device. The impact force (the maximum obtained during the UIAA drop
test) and provided on the rope tag, is of no consequence. Thus the
forces generated, particularly in a near frictionless system, which
may occur on a waterfall, are not very high.
These forces are, as a rule, vastly below the capacity of any
equipment (carabiners, ice screws, pitons, slings, etc.). The problem
lies in the holding capacity of the ice screw, piton, nut, etc. If the
ice is of poor quality, a screw capable of holding 20 kN in good ice
is no more helpful than a coat hanger, if that is the holding power of
the ice.
So in a scary, poor ice, situation the only thing, which may be of
value, is to put protection at very close spacing. That unfortunately
is often not possible. But it would help to clip both ropes in the
last bomber protection.
3. How soon/often do I have to retire the half ropes provided I take
falls on them (very few climbers are 55kg and under, I am 90kg)?
If there are no sharp edges, a rope could most likely be used until
the mantle starts shredding and can no longer be used in a belay
device. This applies mainly to a single rope. The half rope is simply
not designed to take major leader falls. But as mentioned before, the
forces in the system are determined by the belay device. With a
properly working dynamic belay, not much will happen to the rope. Do
not belay with a static belay device such as a Grigri, which should be
used for top roping only.
4. Is the conclusion that one just should not buy or use half ropes?
Or they are still manufactured for cases where falls are not dead
vertical, in alpine terrain wit lots of rope drag? Or perhaps they are
manufactured out of inertia and for marketing purposes?
They are most useful in alpine terrain where lots of friction may
result, if the ropes are clipped in all the runners. An additional
advantage is that there is a backup rope of sufficient capacity,
should a rope be cut by rock fall. Finally the rope offers redundancy
in the case of sharp edges. Double ropes have more holding capacity
over an edge to start with. Even if both ropes run over the same sharp
edge, it is less likely both get cut because one will get loaded more
than the other. In a retreat, being able to rappel the full length of
the rope is invaluable.
The other option is to climb with twin ropes. Extra edge strength
(remember twelve UIAA falls minimum), redundancy, lighter ropes, in a
severe case the option of clipping in alternately, rappel convenience.
I personally have not owned a single rope for at least 25 years. I
used to climb with two half ropes and clipped them together when it
was suitable.
Now I climb with twin ropes. I use these ropes in any terrain.
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