Rigging Philosophy and Strategy
This summary arose from rigging courses held by the NZSS and was presented to those attending the course.
There are two basic rigging philosophies, American and European (referred to as "Alpine" in Alan Warild's book "Vertical"), which are radically different in approach. There are also two variations that I've called "Commuter rigging" (Fixed rigging) and "Exploration rigging" which use different combinations of features from these two styles.
heavy duty (American) ropes required, 11-12mm;
no particular attention to free hang;
no re-anchors or re-directions used;
obviously secure anchors in poor positions are preferred;
few bolts used as anchor position is unimportant;
mats may be used for rope protection.
This is used only by Americans, who find the alpine style totally incomprehensible. Others consider American rigging criminally irresponsible.
lightweight ropes, 8-10mm used;
major emphasis on free hang of rope;
re-anchors and re-directions may be required;
anchor position is paramount, bolts often used;
rope protectors used as last resort.
This style is the basis of rigging around the world, apart from the USA.
Heavy duty ropes (Donaghys abseil braid is acceptable);
other characteristics as for alpine style:
free hang essential;
bolts, protectors, if necessary.
This style is based on the premise that many people (some of them possibly quite careless) will traverse the ropes, and therefore uses the safest elements of each approach.
minor rub points may be OK if the team is small and vigilant;
extensive use of re-directions/re-anchors if time permits;
more use of protectors and less of bolts than above.
Similar to alpine rigging, but with less care taken. Used for a rapid descent of a deep cave when it is expected that only a few people will use the ropes. If the rigging needs to be left longer because cave is still going, it can be improved progressively.
Commuter rigging is being used increasingly, because major vertical caves like Tomo Thyme and Bulmer Cavern require dozens of excursions to complete their exploration, and the ropes may be left in place for months or even years. This requires the best ropes available, and maximum care in the rigging. All rub points must be eliminated, as ropes have been damaged by seemingly minor abrasion.
The key to descending known vertical eaves is to know the rope lengths and rigging gear required. Generally the rope length is the pitch length (which can be found on the cave survey), plus five to ten metres extra. The amount of extra rope needed depends on the complexity of the rigging and the number of anchors and re-anchors, as well as whether any rope is needed for tying back from the secondary (back-up) anchor to the primary anchors at the pitch head, which could be 5-10 metres away. For example,in Bulmer Cavern, the Lion Heart pitch is 44 metres, and the Lion Tamer pitch is 34 metres, with a back-up about five metres from the pitch-head. If 50 metre ropes are used, they just touch the bottom of both pitches. Some excess rope can be wise, as it is embarrassing to reach the end of the rope a metre short of the ground, especially if the rope is a little stretchy!
The rigging gear can be difficult to know in advance. Some pitches require that particular items are used, eg. the right size of hexentric, while others are more forgiving and offer choices. The more that is known about the cave, the less gear needs to be taken. Extra slings can be very useful.
It's always a gamble how much gear to take. Take hundreds of metres of rope, and the cave will die at the bottom of pitch 2. Take a couple of ropes and you'll stop at the top of a gaping chasm, or swinging around in space just three metres off the floor, not quite able to see if there's a lead on the far side of the passage.
Personally, I would rather be optimistic and carry plenty of rope. There are numerous cases of caves being explored at a pitifully slow pace because it didn't really look like going, and each day the team came back with a further 50 metres of rope and extended the depth 40 metres. By contrast, Farrier's Cave in Horseshoe Basin, Mt Arthur, was bottomed at 243 metres in two days by a team of three.
However it's done, the main thing is identify the next obstacle. If there's no rope for the next pitch, make sure you know what rigging gear is needed and the likely pitch length.
On arrival at a pitch-head, there are two separate tasks to perform: placing the anchors, and rigging the rope. These can be done by different people. Normally the first down carries the rigging gear (because there is the possibility of needing some for rigging a re-anchor), and so can start immediately. The next caver assesses the pitch length, generally with a number of large rocks. Using the formula l=5t2, a 1 second drop = 5 metres depth, 2 sec = 20m, 3 sec = 45m, 4 sec = 80m, 5 sec = 125m, and you'll probably never get a six second drop. Some people find it difficult to use this accurately, especially over three seconds. There is a progressive effect of air resistance, which lengthens the time, especially on long drops. Bounces totally invalidate the estimate.
The more accurately the pitch lengths can be estimated, the more economically the available ropes can be matched to the pitch lengths. If you use your only 50 metre rope on a 25 metre pitch, at the 45 metre pitch you'll have a whole lot of bits tied together, or be short of the floor.
The lengths of rope taken are always a gamble - the only really effective method is to take long lengths and cut them off at the bottom of every pitch, but you can't do that for every cave. For some caves long ropes (50 metres) are really useful, while for others a lot of short ones, 10-20 metres are needed. After the first couple of pitches you can sometimes judge the character of the cave.
The rigging gear should be as well organised as possible. It helps if one person carries it all, preferably in a separate little bag. The ropes must all be marked with their lengths. When the pitch lengths are known, the person with the rope for the following pitch can go down second.
If two ropes are to be joined, this is best not done at the top, as there may be a good re-anchor position at which they can be tied. For example, on the Re-entry Pitch in Castle Keep (105 metres), if two 50 metre ropes are used and then a 30 metre, the knots fall at convenient re-anchor points.
The rope must always have a knot tied in the end before being sent down the pitch. On short pitches the rope can be dropped to the floor. On long pitches, the rope can be fed down from the end, and then dropped, with some risk of snagging. If the rope is being carried loose in a bag (which is easier for ropes over 60 metres long), it is best fed down the pitch by attaching the bag below the first person descending the pitch and letting it run out.
With the rope rigged, the first person can descend. Unless the rope can be seen to drop straight to the floor, it's wise to carry some extra rope and rigging gear, as well as wearing ascenders.
Derigging a major vertical cave is an exercise in logistics, and can lead to chaos if not organised carefully. Preferably, derigging should be the only objective of the day's caving. There must be enough people to carry all the gear readily, and the work must be shared around. The derigging of HH (623 metres) was a shambles, resulting in gear being abandoned in the cave. Too many people went deeper than necessary, and the teams weren't coordinated.
Conversely, the derigging of Gormenghast (579 metres) was accomplished in six hours by a team of seven cavers. One caver of enormous experience and competence descended the entire cave and exited by another entrance, travelling solo from -420 metres, and leaving most pitches rigged to enable this point to be reached from the bottom. A team of two cavers derigged all the pitches from that point up, carrying the accumulated gear as they went, until it could be off-loaded onto pairs of porters, who had entered later and were staged at -300 metres and -200 metres. The porters headed out as soon as they had a load.