Lightweight systems – testing to the next level

By Grant Prattley
June 12, 2018

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

Anchors

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The post tackles a practical question for backcountry rescue teams: is 16mm tubular webbing strong enough for anchor rigging, given the appeal of reducing weight in a rescue kit? To find out, the team ran a series of pull tests comparing different wrap-and-pull configurations — Wrap 1 Pull 1, Wrap 2 Pull 2, Wrap 2 Pull 1, and Wrap 3 Pull 2 — across several real-world surfaces: pins, carabiners, smooth rock, sharp rock, and edge-protected sharp rock. A baseline was first established using 25mm webbing before switching to the thinner 16mm webbing to see how it held up.

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Friction

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Lightweight systems – testing to the next level