The third exception is when it is necessary for the last man to save time in a race with darkness. Then, after letting the rest down, he follows on the ‘double’ as fast as he can.
And the last is the rare case when it is expressly intended to force the descent of a passage which has defeated all attempts to ascend. In such case we use all the help that we need for safety.
The double rope can be used in these cases of difficulty or haste to assist the descent of every member of a party. Usually it is only to protect the last man.
The method of using the ‘double’ is to lay the rope round any point or knob which prevents it slipping off under an outward and downward strain, and from which it can be conveniently released by pull or flick from below. If such a generally comfortable point is not discoverable, a length of the rope should be cut off and knotted into a secure sling, which is wound in a triple coil round any excrescence good enough to hold it permanently secure. The triple coil cannot break under the friction, and allows the rope to play through more easily. The rope to be used is then passed through the sling.
Some climbers carry ready-made slings; others favour iron rings, which they slip on to the slings, and then pass the rope through the ring. The rope runs more easily, but I have never liked the practice. A ring can never be carried of sufficient size to use on more than a single thickness of rope, to say nothing of a safe triple sling. And not only is the single sling more likely to snap under the rub of the hard ring as we descend than under the more springy pull of another rope passed through it, but if left it is more likely to be a danger to the next party descending. Guides are always ready to use a finished-looking piece of mechanism, like a ring on a loop, without testing it fully, where they would be suspicious of a mere weathered sling of rope. The metal reassures just where it should warn them; for the ring, where it touches, will have rusted into and eaten the rope strands. The same point comes up under the heading of Pegs and Aids.
It must always be remembered that the use of the sling or ring involves unroping, which the ‘double’ on a good belay does not; and in so far it uses more time.
For short descents the last man can use the slack of the rope between himself and the next man as a double, provided he sees that, when doubled, it will allow him to descend as far as his next stance, and there leave him slack enough to flick it off the belay.
He should always use the double as a fixed rope, that is, it should never be paid out to him round the belay, as he descends, by the man below; nor should he ever attempt to pay it out to himself as he descends on the double. Either attempt will certainly fray the rope round the belay, possibly jam it, and probably jerk it off the belay.
For any considerable height it is better to use a spare doubled rope. In this case the last man can at once see if the two ends of the double reach to the next stance below. If no spare rope is available, the next man below may have to unrope, in order to leave the last man enough to double and descend upon.
If the descent is of exceptional difficulty, e.g. an overhang, a spare rope should always be used. The second, or climbing, rope round the last man’s waist is then held by the man below, as a protection in case the effort of clinging to the double exhausts the last man’s hands; or, still better, it also can be laid over the belay and paid out to him, lightly, as he descends. As it will then be sliding upon the fixed rope, and there will be no strain upon it, it will be the less likely to jam on the belay, fray or jump off.