What’s in this post?
The question we are going to answer in this post is:
When you drill a hole through a rock and thread a cord what is the best setup for bends, cord and rock strength.
We have used an 8mm Nylon cord for cave rescue and a 6mm Dyneema cord for canyoning and caving recreational anchor building.
It was time to find out the performance of these two cords and several others.
Keep reading to find out the results, AND you get to download a detailed testing report at the end.
Introduction
A drilled thread in rock is a low-impact way to anchor for recreational and rescue purposes without leaving behind bolts.
The usual places for applying these anchors are caves and canyons; however, other rock-based disciplines could find this information equally applicable.
In a canyon, threads are a way to leave anchor rigging behind in a section affected by high flows and floods. The cord in a thread, if damaged, can be replaced. A bolt may be destroyed or completely broken off in a flood event. Additionally, threads are lighter weight for carrying up a hill to the start of the canyon, and you don’t need to carry a drill each time you descend in the future.
For rescues, threads allow us to put in additional anchors without leaving behind lots of bolts, just holes. Compared to removable bolts, threads are a cost-effective alternative, especially where you need lots of rigging, such as cave rescue.
In addition to rock threads, we undertook testing of rock V-threads. Where you have a blank face, drill a V in the rock, as you would in ice with ice screws (Ice V-thread equivalent = Abolokov). It is somewhat more difficult and time-consuming to drill and thread, but it is possible.
Threads and V-threads are part of the rigging toolbox for both recreational and rescue situations.
Standards and testing
The standard we are using for recreational use is the New Zealand Canyoning Association Bolting Code of Practice. This standard states that 15kN should be a minimum construction standard for temporary anchors.
Rescue work system strength should be 20kN or more to give additional margin for higher potential forces.
Therefore, this testing aims to ascertain if the following meets or exceed the standards:
- Bends used to tie the loops,
- Cords or ropes used in the rock threads/V-threads,
- Rock strength of the threads/V-threads.
Methods and materials
General setup methods
- As each test destroyed the cord, they were new for every test.
- Carabiners and rapides, where they were undamaged, were reused for multiple tests.
- All knots and bends had hand tension with all strands pulled tight.
- All tails were 4cm.
Slow pull tests
Each testing series recorded the slow pull test set up (in the report download at the end).
The slow pull testing was in one location.
- Aspiring Safety, 1/6 Burdale Street, Riccarton, Christchurch, New Zealand. https://www.aspiring.co.nz/
- Vertical testbed 1.6m Electronic Universal Testing Machine, Model WDW-100
- Maximum Test Force 100kN, sample rate 60 per second
- Jinan Chuanbai Instrument Equipment Co Ltd
Materials
- Beal 5mm Dyneema cord, 23g/m, 15kN
- Aspiring 5mm Dyneema cord, 15kN
- Nautilus 5mm Dyneema/Polyester cord, 19g/m, 9.8kN
- Beal 5.5mm Dyneema/Nylon cord, 23g/m, 18kN
- Nautilus 6mm Dyneema/Polyester, 26 g/m, 13.7kN
- PMI 7mm Nylon, 33.2 g/m, 11.9kN
- PMI 8mm Nylon, 42 g/m, 14.3kN
- Nautilus 8mm Dyneema/Polyester+ Kevlar, Aborist Prusik Cord, 30kN
- PMI 10mm Nylon, 66 g/m, 27kN
- Kordas 10mm Nylon, 68 g/m, 27kN
Results
Loop testing
| Cord / Rope tested | Avg. kN 3.tests | Comment |
|---|---|---|
| Beal 5mm Dyneema 15kN – double fisherman’s bend | 12.74 | Broke at the bend |
| Beal 5mm Dyneema 15kN – triple fisherman’s bend | 18.55 | Broke at the pin and the bend |
| Aspiring 5mm Dyneema 15kN – double fisherman’s bend | 18.54 | Broke at the bend |
| Aspiring 5mm Dyneema 15kN – triple fisherman’s bend | 21.31 | Broke at the bend |
| Nautilus 5mm Dyneema / Polyester 10kN – double fisherman’s bend | 13.59 | Broke at the bend |
| Nautilus 5mm Dyneema / Polyester 10kN – triple fisherman’s bend | 15.51 | Broke at the bend |
| Beal 5.5mm Dyneema / Nylon 18kN – double fisherman’s bend | 13.38 | Broke at the bend |
| Beal 5.5mm Dyneema / Nylon 18kN – triple fisherman’s bend | 17.26 | Broke at the bend |
| Nautilus 6mm Dyneema / Polyester 14kN – double fisherman’s bend | 17.71 | Broke at the bend |
| PMI 7mm Nylon 11.9kN – double fisherman’s bend | 18.86 | Broke at the pin |
| PMI 8mm Nylon 14.3kN – double fisherman’s bend | 23.82 | Broke at the pin and the bend |
| PMI 8mm Nylon 14.3kN – figure-8 rethread bend | 20.34 | Broke at the pin and the bend |
| Nautilus 8mm Dyneema / Polyester + Kevlar 30kN – double fisherman’s bend | 34.23 | Broke at the pin and the bend |
| Nautilus 8mm Dyneema / Polyester + Kevlar 30kN – figure-8 rethread bend | 33.44 | Broke at the bend |
| PMI 10mm Classic Sport Nylon 27kN – double fisherman’s bend | 36.71 | Broke at the pin and the bend |
| Kordas 10mm Dana Nylon 27kN – double fisherman’s bend | 32.24 | Broke at the pin |
Rock thread testing
Slow pull tests (100mm/minute)
| Cord / Rope tested | Avg. kN 3.tests | Comment |
|---|---|---|
| Beal 5mm Dyneema 15kN – triple fisherman’s bend | 18.58 | Broke at the pin and the bend |
| Aspiring 5mm Dyneema 15kN – triple fisherman’s bend | 20.98 | Broke at the bend |
| Nautilus 5mm Dyneema / Polyester 10kN – triple fisherman’s bend | 12.90 | Broke at the bend |
| Beal 5.5mm Dyneema / Nylon 18kN – triple fisherman’s bend | 16.95 | Broke at the bend |
| Nautilus 6mm Dyneema / Polyester 14kN – double fisherman’s bend | 17.06 | Broke at the bend |
| PMI 7mm Nylon 11.9kN – double fisherman’s bend | 12.88 | Broke at the thread |
| PMI 8mm Nylon 14.3kN – double fisherman’s bend | 17.41 | Broke at the thread |
| Nautilus 8mm Dyneema / Polyester + Kevlar 30kN – double fisherman’s bend | 33.78 | Broke at the bend |
| PMI 10mm Classic Sport Nylon 27kN – double fisherman’s bend | 26.78 | Broke at the thread |
| Kordas 10mm Dana Nylon 27kN – double fisherman’s bend | 27.73 | Broke at the thread |
Rock V-thread testing
Slow pull tests (100mm/minute)
| Cord tested | Avg. kN 3.tests | Comment |
|---|---|---|
| Beal 5mm Dyneema 15kN – double fisherman’s bend | 18.58 | Broke at the thread |
| Aspiring 5mm Dyneema 15kN – double fisherman’s bend | 20.98 | Broke at the pin and the thread |
Analysis
Loop testing
When joining the loops with a bend to get above 15kN for recreational use:
- Triple fisherman’s: Beal 5mm Dyneema, Nautilus 5mm Dyneema/Polyester, Beal 5.5mm Dyneema/Nylon
- Double fisherman’s: Aspiring 5mm Dyneema, Nautilus 6mm Dyneema/Polyester, PMI 7mm Nylon
When joining the loops with a bend to get above 20kN for rescue use:
- Triple fisherman’s: Aspiring 5mm Dyneema/Polyester
- Double fisherman’s or figure-8 rethread: PMI 8mm Nylon, Nautilus 8mm Dyneema/Polyester+Kevlar
- Double fisherman’s: Kordas 10mm Dana Nylon, PMI 10mm Classic Sport Nylon
Rock thread testing
- The Beal 5mm Dyneema/Dyneema cord was over 18kN, and the Aspiring 5mm Dyneema/Dyneema cord was over 20kN on average. The Dyneema sheath had high resistance to abrasion during the tests, with only minor damage on all corners. Recommended as a rock thread.
- The Beal 5.5mm Dyneema/Nylon, Nautilus 6mm Dyneema/Polyester, and PMI 8mm Nylon/Nylon cords were over 15kN on average. The tests damaged the sheath, either a core shot or broke at the exit from the rock. Recommended as a rock thread for one-off use scenarios.
- The Nautilus 5mm Dyneema/Polyester and PMI 7mm Nylon/Nylon cords were under 15kN on average. The tests damaged the sheath with either a core shot or broke at the exit from the rock. Not recommended as a rock thread.
- The Nautilus 8mm Dyneema/Polyester+Kevlar cord was over 30kN on average. The tests caused moderate to major damage to the sheath with a core shot or broke at the exit from the rock. Recommended as a rock thread.
- The Nautilus 8mm Dyneema/Polyester+Kevlar cord was rigged as a thread to hold the tested rock in place. One length underwent 18 tests ranging from 12-18kN with only moderate wear to the sheath. Recommended as a rock thread to be reused multiple times.
- The PMI and Kordas 10mm Nylon/Nylon ropes were over 25kN in average strength. All tests broke at the exit of the rock with minor to major damage to the sheath. If you don’t have any suitable cord, the end of a rope will make an appropriate rock thread.
Rock V-thread testing
The Beal 5mm Dyneema/Dyneema cord (average 16kN) and Aspiring 5mm Dyneema/Dyneema cord (average 20kN), when tested with a 50-degree drill angle on the V, had sufficient strength for the rock type tested. Recommended as a rock V-thread.
Conclusions
- As a preference, for better abrasion resistance, use cords with either Dyneema or Kevlar in the sheath.
- Recommend using nylon or polyester sheathed cords for one-off descents (refer to analysis), but they may need to be replaced each time you use them.
- When comparing similar materials, the thicker the cord or rope, the better the performance.
- As you are working at the edges, the rock may be less robust, and you are recommended to join together a minimum of two drilled threads.
- I recommend keeping it simple and tie a full-strength loop of 15kN or more for a single thread. You may not be able to share the load between the two anchors equally, and if you choose to go down to one anchor, you know that the rigging is suitable.
- The test rocks used are weathered hard Greywacke river boulders. The rock thread had a 12mm hole drilled 75mm long and 75mm from the front edge. The boulder held 24 tests ranging from 12-33kN. This rock type was sufficiently strong with these dimensions.
- The rock V-thread had a 12mm hole drilled at 75mm centres to form a V of 50 degrees. This boulder held 6 tests ranging from 15-21kN. This rock type was sufficiently strong with these dimensions.
- Rock thread and V-thread anchors are part of the rigging toolbox for both recreational and rescue situations.
Disclaimer
SUMMARY: This post is not an instructional guide. Use at your own risk. We assume no responsibility or liability for any errors or omissions. Testing was under controlled conditions with a limited set of equipment. The views, information, or opinions expressed in the post are solely those of the author.
For the full disclaimer click HERE
