Fig. 1

Construction of the Mark III Rig

The above rig was made from 60cm of 1 inch tubular tape and a 1m long 5mm prussik loop.

1. Fold the prussik loop in half
2. Take the centre of the prussik loop ( 4 strands) and thread it through the tubular tape ( Beeston Broddler again).
3. Clip a stopper karabiner into the loop formed by the 4 strands ( bottom left)
4. At the other end, you will have 2 loops formed by the prussik
5. Clip one loop to the suspect protection, the other to the rope

Initial thinking suggests that as you load the rig, the 2 points, protection and rope, connected by the prussik, will start to move apart, compressing and scrunching up the tubular tape against the stopper karabiner. It is this compressing and scrunching action that will absorb the fall's energy.

In practice ( Fig. 1 shows the state of the rig after only one rucsac drop test), the tape does compress and scrunch up and it also rips! This does a very good job of absorbing the energy from a fall but the rig is clearly not reusable. I stopped testing as I didn't have any more tubular tape. I suspect a drop test using a heavier human subject will rip the length of 60cm tubular tape completely. I have no means of determining if this is adequate energy absorption.

Note: Click on the pictures for an enlargement ( 1-2mb)

Additional notes

1. Compression and ripping of the tubular tape is an efficient energy absorber
2. Clearly not reusable
3. Not tested on real human weights
4. Easy to construct on the lead
5. Still made from off-the-rack components
6. Cannot determine if the energy absorption is sufficient

2. You should test this rig in a safe environment using components on your rack, before using it in the field.

1. Your dodgy protection must hold at least your body weight. That will be the minimum load applied to the protection when the rig comes to rest.
2. A good bounce test in a safe environment can generate up to twice your body weight.
3. Bounce test with a variety of configurations ( different lengths of tubular tape and diameters of cord), to find a rigging that either:
   • compresses easily, i.e. less shock on your protection.
   • or one that requires more force.
4. Select a rigging according to the state of your protection.
5. If you are frequently using this rig, you should inspect it carefully for signs of wear and tear. They will be obvious!

3. Some thoughts on loading:

1. The rig should not start to compress/rip with a load of bodyweight or less. It would be pointless as the rig will not be absorbing sufficient energy to safeguard the suspect protection. Furthermore, it would increase the length of the fall.
2. The rig must hold bodyweight ( See 2).
3. I think the optimum set up would be a loading of 1.5 to 2 times bodyweight before compressing/ripping. This will start to dissipate the energy from the fall without overloading the suspect protection.
4. Anything higher than 2.5 times bodyweight will probably overload the protection.

Testing

Note: In a desperate situation, I will use this rig. You will have to make your own mind up!