Abseiling is one of those activities that appears to be enjoyed by those who do not know of its dangers. Consequently, most non-climbers like it whereas most climbers do not. The reason for this is probably because most non-climbers have never done an abseil under anything but tightly controlled conditions. One abseil under normal conditions would convince them otherwise!
Note that abseil rhymes with style not sail.
Why do most climbers have a dislike for abseiling? Basically it is down to two things:
- single system with no backup.
- Easy to get wrong.
However with a little thought many of the risks may be reduced, though not entirely removed. The following tips should help with that thought process.
There is much discussion as to which knot is best to use to join the two ropes together and over the years thoughts have changed
The table below summarises the various knots that are in common use for tying two ropes together for abseiling. One point to note is that for all the knots, the “tails” should be at least 30cm in length to allow for slippage and tightening of the knot.
|Double Fishermans||Easy to get wrong.||This is the knot by which to judge all others. If tied correctly, it is the strongest knot available for this purpose. If your ropes are of different diameters then it is the only knot to consider. It does have some major drawbacks though: it is very difficult to undo after being loaded; it is also symmetrical meaning that it is likely to snag easily.|
|Figure of Eight||Not as easy as is imagined.||To tie the figure of eight correctly requires that both ropes travel a particular
path through the knot. This is very difficult to ensure in a stressful situation.
In addition to this, the knot has an alarming tendency to roll along the rope
when stressed at right angles to its main axis.
|Overhand||Fairly easy.||At first the overhand knot looks as if it would be weaker than the figure of eight but in fact it is both stronger and more resilient to pulls across its axis.|
|Reef||Simple and easy||The reef knot (square knot) is very simple to tie but, like the double fishermans, is a symmetrical knot so suffers from the same problems of being prone to catch. It is a very poor knot to use for ropes of different diameters. Perhaps its best use is in the centre of a double fishermans knot, using the latter as a safety backup.|
So when to use which knot?
- The double fishermans. Or, a reef knot backed up by double fishermans.
- When: Your ropes are of different diameters; You absolutely have to be sure.
- Overhand knot
- When: the face down which you are abseiling is featured and you do not want to chance getting the rope stuck. Most abseils.
See this article at Needlesports for more info on knots for abseiling.
Increasing or Decreasing Friction
When abseiling using a belay plate rather than a Figure of Eight it is more difficult to control the amount of friction and thus ease or retard the speed of the rope through the device. Fortunately there are a couple of simple things that you can do to either increase or decrease the friction. (note that both these techniques can be used in belaying as well).
In order to increase the friction all that is required is a second karabiner, preferably a screw-gate. With the rope(s) threaded through the device and the main karabiner take this second krab and clip it into both the bight of rope and the harness attachment point, thereby doubling up the main krab. This has the effect of forcing the rope through tighter curves as it passes through the system which increases the friction. Note that the gate of the second karabiner is facing the opposite way to the main krab even though they are both screwgates.
To decrease friction, again take a second karabiner but this time clip it into only the bight of rope passing through the device. It must be positioned so that it lies between the back of the device and the main krab. This has the effect of allowing the rope to pass through less severe curves as it passes through the system.
Keeping the gear
You would have thought that a group of four rock climbers with over one hundred years experience between them would not find anything about abseiling new or surprising. How wrong we were! On a recent holiday to Sardinia we decided to go canyoning with a guided party that included some of our wives. At the top of the gorge (which we would have been hard pushed to find at all on our own) we were shown the following method of clipping into a figure of eight descendeur without chancing dropping it.
In the end of each rope you may want to tie individual knots to prevent you from sliding off the end. You need one on each rope as just doing it on one rope could cause the system to pull through the belay. This also helps find the end of the rope in those instances when they get caught after being thrown down, either because of wind or because the rock is heavily featured. In order to help remember which rope needs to be pulled at the next stance (or ground) - clip a krab into the end knot of that rope.
Another tip for remembering which rope to pull is to clip a quickdraw between your harness and onto the rope in question. This also has the benefit of keeping the ropes separated when you come to pull them.
If there is a chance of debris falling on you then it is beneficial to use a French Prusik or Klemheist knot around both ropes. Whether this knot is above or below the abseil device is down to personal preference - I have seen valid arguments for both - my personal preference is to have the knot above the device.
There are rare occasions when you need to abseil a full rope length but only have one good rope available. For example: The other rope has been damaged in some way and you do not want to trust it. Another scenario is if you are climbing lightweight on a single 9mm rope and have brought along something like a length of 6mm cord for emergencies. So how do you make a full 50m abseil?
- Start by passing the good rope through the belay then joining the ropes with either a double fisherman's knot or a reef knot backed up by a double fisherman's.
- Tie a figure of eight on the bight or an alpine butterfly knot into the good rope next to the double fishermans, and clip a screwgate krab into it.
- Clip the krab back onto the good rope.
- Now abseil on the good rope, the krab effectively ties the rope to the belay when tensioned from this side.
- At the end of the abseil, pull on the unused rope. The ropes will pull as normal.
See also Combined knot techniques