Lightweight systems – testing to the next level
Once you start testing you is realise there is more testing to do.
The testing aimed to push the limits of the belay for the lightweight rescue system. We decided on a 1.5m drop on 3m of rope with a 200kg load.
Back in 2017, we did some initial testing for tandem Prusiks and Grigri+ for a 1m drop on 3m of rope – Let’s lighten the load
Our baseline numbers for the 1m drop on 3m of rope with a 200kg load was an average of (over four tests each):
- 8.22kN and 171mm of slip for 7mm Tandem Prusiks and
- 9.35kN and 435mm of slip for the Grigri+.
Testing Setup
- Undertook a 1.5m drop on 3m of rope
- 200kg mass
- 10mm static/semi-static rope
- Belay device included 7mm Tandem Prusiks and the Grigri+
- Rock Exotica Enforcer load cell.
Testing Notes
- We used a rigid tower on Takaka Hill, Nelson, New Zealand
- New rope and cord used for testing.
- The 10mm rope was PMI Classic 10mm static nylon rope (26.5kN, CI1801) apart from test 6 which used Kordas Iris 10mm semi-static nylon rope (26kN, EN1891A).
- The rope used a bowline knot to attach at the load end.
- The 7mm Prusik cord was Edelrid 7mm Powerloc (14kN, EN564) and was tied as a loop with overhand rethread bend (aka water knot). We set the Prusiks up like this: Setting up your Prusik for lightweight rescue
- All knots and bends had hand tension.
- 200kg of weight in 20kg cast iron lots.
Testing results
Grigri+
Test 1
- Force: 2.83kN
- Slip: 2320mm (or 2.32m)
- Device: Remained intact
- Rope/sheath: Rope kinked/hour glassed, slight fuzzing and hardened/damaged internally with heat.
- Load Release: Yes
Test 2
- Force: 3.00kN
- Slip: 2570mm (or 2.57m)
- Device: Remained intact
- Rope/sheath: Rope kinked/hour glassed, slight fuzzing and hardened/damaged internally with heat.
- Load Release: Yes
Test 3
- Force: 5.00kN
- Slip: 3030mm (or 3.03m), load just touched the pads on the ground. However, the load was still hanging.
- Device: Remained intact
- Rope/sheath: Rope kinked/hour glassed, slight fuzzing and hardened/damaged internally with heat.
- Load Release: Yes
Overall
- Average Force: 3.61kN
- Average Slip: 2640mm (or 2.64m)
7mm Tandem Prusik
Test 4
- Force: 9.46kN
- Slip: 290mm
- Prusiks: Short Prusik sheath failure, severely damaged. Long Prusik welded on, less damage.
- Rope/sheath: Rope glazed/hardened in front and bunched sheath behind Prusiks.
- Load Release: No
Test 5
- Force: 4.26kN
- Slip: 320mm
- Prusiks: Short Prusik sheath failure, severely damaged. Long Prusik welded on, less damage.
- Rope/sheath: Rope glazed/hardened in front and bunched sheath behind Prusiks.
- Load Release: No
Test 6
- Force: 8.52kN
- Slip: 470mm
- Prusiks: Short Prusik sheath failure, severely damaged. Long Prusik welded on, less damage.
- Rope/sheath: Rope glazed/hardened in front and bunched sheath behind Prusiks.
- Load Release: No
Overall
- Average Force: 7.41kN
- Average Slip: 360mm
Analysis
| 1m drop on 3m rope 200kg load | 1.5m drop on 3m rope 200kg load | |||
| Force | Slip | Force | Slip | |
| 7mm Tandem Prusiks | 8.22kN | 171mm | 7.41kN | 360mm |
| Grigri+ | 9.35kN | 435mm | 3.61kN | 2640mm |
- The Grigri+ results were consistent, had a low force seen by the anchor, however, there was significant slippage of 2000-3000mm (or 2-3 metres).
- The Grigri+ compared to previous results for a 1m drop on 3m of rope it had 1/3 of the force however the slip was 6x as much.
- The Tandem Prusiks results were not consistent. Test 5 had a low force of 4.26kN compared to 9.46kN and 8.52kN for the other two tests. Having a look at the damage on the rope and to the Prusiks it was consistent with the other two tests.
- The Tandem Prusiks compared to previous results for a 1m drop on 3m of rope it had 0.8kN less force however the slip was 2x as much.
- From a 1m drop to 1.5m there is a general trend of decreased force with increased slip.
Final thoughts
I have to keep reminding myself that we are pushing lightweight equipment towards failure while undertaking significant drop testing with a 200kg load. As of yet, we haven’t been able to find this failure point, but I think we are not far away.
from the team at Over the Edge Rescue
Grant
