Knots and Ropes

 

Knots & Ropes

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.

Caving
knots

All knots weaken the rope in which they are tied to greater or lesser extent. This effect can be reduced by making your knots neat and tidy.

The knots you should use are:

Figure of 8, tied in different ways.

Bowline.

Bowline on a bight.

Alpine butterfly.

Double Fisherman’s.

Cavers Butterfly.

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.

Figure of 8
on a bight

Figure of 8 rethreaded

Some times it is necessary to tie this around a belay. Start by tying a figure of eight in about the right place. Then take the end around the belay and then use it to follow the rope back on itself.

The
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.

"The rabbit hole".

The rabbit comes out of the hole, and around the tree.

The rabbit goes back down the hole.

Finish off with half a double fisherman’s knot. Or the tail could be longer and be attached to another anchor.

Bowline
on a bight

This is similar to the bowline but gives two non-slip loops in the middle of a rope. The relative sizes of the loops can easily be adjusted.

A similar rabbit hole in a loop of the rope. The distance between the end of the loop and the rabbit hole gives the size of the double loops.

The rabbit again comes out of the hole.

 

 

This time he doesn’t go around the tree but turns back and swallows the hole!

Rearranging the rabbit gives the familiar bowline shape. Before tightening the twin loops on the right of the picture can be adjusted to different sizes. No need to lock off this time.

If the rabbit had continued around the tree and gone back down the hole you could have got a triple bowline with three loops, which could be used as an improvised harness.

 

Why use an
alpine butterfly

A Figure of Eight knot should NEVER be loaded in this manner. A load on either line to the loop is O.K., but not this way. The knot to use in this situation is the Alpine Butterfly. This is conveniently tied around the hand.

Alpine
butterfly

Three twists around the palm. The size of the middle loop dictates the size of the loop you end up with.

Lift the loop nearest the wrist and place it on top of the other two.

 

 

Then pick up the loop, which used to be the middle one and lift it over the other two.

Then pull this loop through the other two. If you started with a very big middle loop you will pull lots of rope through.

 

 

Keep pulling through and take your hand out.

 

Pull tight and it should look like this. During the tying process it can be helpful to use the left thumb to trap the loops in place. In these pictures the thumb has been kept straight to show the loops clearly.

 

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”.

Take two complete turns of one rope end about the other.

Double back.

And feed it through the turns.

And pull tight.

Take two complete turns from the other rope end about the other rope.

And double back.

 

And feed the end through the double turns.

Pull this second half-knot tight.

Pull the two ropes to slide the half knots together.

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.

In this picture the rope coming from top left is attached to an anchor. Make a loop

Take another loop.

 

Push this second loop through the first. At this stage it is very easy to adjust the position of the knot and the size of the loop to get the hang just where you want it.

Make another loop and drop this over the previous.

 

 

And pull tight

 

 

When using this knot as the “Y” hang at a pitch head it can be also used for a life-line attachment by putting a karabiner through the two parallel parts of the knot like this.

This enables the belay point to be as high as possible.

 

 

This Knot should NOT be used if the loop is not attached to an anchor as it is unstable if loaded from end to end.

Interested?

Contact the team, or book a place directly from the calendar to join the next adventure underground.

contact us

© Shropshire Scouts Caving Team