One of the requirements for the Explorer Scout badge is to rig and use a ladder pitch, under supervision. Learning a bit about ropes and a few caving knots before the course will set you in good stead.
Types of rope
Modern rope is of the Kernmantle type, from the German kern, meaning ‘core’, and mantel, meaning ‘sheath’.
This has a number of strands enclosed in a woven sheath. The only ropes that should routinely be used in caving are made of nylon (Polyamide). Ropes are available in different diameters, strengths and stretchiness. Rock climbers use a dynamic rope, which stretches a lot under load. This is good for absorbing shock loads from a falling climber. In caving we use almost exclusively static rope, which stretches very little under load. This is good for SRT (single rope technique) as it avoids excessive bouncing up and down under the rhythmic loading of prusicking or abseiling. It also reduces the wear, which could take place if the rope were touching the rock at any point. To avoid confusion we use static rope for virtually everything underground, including lifelining.
Fall factors
Because our ropes are static we have to take care in use to keep potential fall factors to a minimum.
Think about a lead climber who is on the second pitch being belayed by his second. If he falls before he gets a runner in, there will be a length of rope between him and the second. He will fall as far as the second and continue until he is the same distance below the second. He will have fallen twice the distance of the length of rope that stops him. A fall factor of 2. This length of dynamic rope, acting through a climbers harness, will be able to absorb the shock of the fall and the climber will survive (assuming he didn’t hit any thing else on the way down). If this fall were to happen on static rope with a cavers harness the climber could receive severe injuries. (A caver’s harness is designed to be comfortable to sit in rather than absorb shock loads). Because of this we have to take great care to keep our fall factors low, certainly never more that a fall factor of 1, where the distance fallen is equal to the length of the rope protecting oneself. This means we should never go above the point from which we are belayed.
In the picture, if the climber had reached the top, 2m to the side of the belay point and then fallen, the fall factor would be 2 / (8+2) = 0.2
If the climber was 2m directly above the belay point, the fall factor would be 4 / (8+2) = 0.4 because the fall would be twice as far.
If the climber was only 3m high instead of 8m then the fall factor as pictured would be 2 / (3+2) = 0.4
and if the climber was 2m above the belay point, 4 / (3+2) = 0.8
Strength of ropes
Ropes come in different diameters and are tested to two different strength grades.
All of our techniques will work with rope from 9mm to 11mm in diameter. Thinner ropes are lighter and easier to pack into bags but generally have lower safety factors so preventing damage is vitally important. These tend to be reserved for long expeditions by experienced cavers.
Our current ropes are 9mm diameter and are tested to BS EN 1891:1998 Type A which is the highest strength grade.
You can usually spot static ropes from a distance by their boring colours, dynamic climbing ropes (used for Cows-Tails by cavers) are often brightly multi- coloured but that’s probably not a rule so check carefully.
How to tie caving knots
Figure of 8
This weakens the rope a lot more than an overhand knot but has the great advantage of being easier to undo after heavy loading. Can be used as a stopper knot.
It can also be tied in a bight (loop), either at the end of the rope or in the middle. If tied at the end, allow at least 100mm spare rope to prevent the knot from working undone.
Bowline
This is the basic non-slip loop knot, until belay belts and harnesses became commonplace this was the knot used for tying on for lifelining or belaying.
At one time all Scouts were trained to tie this around the waist one-handed in the dark. It is a useful knot for anchoring and is easier to tie and adjust, around a boulder or through a thread than a figure of eight rethreaded. It must always be finished with half a double fisherman’s knot as in the fourth picture or the tail can be taken to another anchor in a multiple bowline anchor.
Alpine Butterfly
Double Fisherman’s
This knot is used by fishermen to tie slippery line together. It is generally considered bad practice to join rope in caving, as the joined rope can’t be used for life lining and is, of course, weakened by any knot. In SRT passing a knot in mid-pitch is a hazardous manoeuvre and should always be avoided if possible. Half a double fisherman’s is very useful for locking off other knots or trapping the snap links on “cowstails”.
Cavers’ Butterfly
Superficially this is very similar to the Alpine Butterfly but comparing them when tied shows that in the Alpine Butterfly there is an interlocking of loops in the centre of the knot which does not happen in the Cavers Butterfly. Nevertheless it is a very useful knot for SRT Rigging and also if mixed ladder/lifeline and SRT is adopted.
