How much friction for your device?

How much friction for your device?

We were interested to know (as a guide) how much a lowering device can hold for rescue in particular but also personal use.

The testing is for practical use when out on a rescue, training or instructing a group about how much it can hold in relation to:

  • the particular device
  • the friction range minimum and maximum
  • for the friction setting mode

The keyword to think about here is ‘guide.’ We can’t give a definitive number and say that’s what your device will hold. Influences on friction include the actual load, grip strength, environmental conditions (wet, cold, dirt), new/old rope, size/type of rope, and contact with the terrain such as edge protection and pulleys. It’s a place to start and then adjust as necessary.

Context

We are looking at non-mechanical devices used for backcountry applications, including canyoning, caving, alpine, and rock climbing. For comparison, we have tested a lightweight rope rescue lowering device and the Munter/Italian Hitch.

For several years, we have been using a 9.5-10mm rope successfully. We can use standard equipment, operate with two tensioned ropes or single rope, and is suitable based on testing.

What do we want to know?

Friction testing the device (or hitch) involves:

  • Testing multiple friction settings from low to high, including standard and redirected in a carabiner.
  • Testing the minimum and maximum for each friction setting:
    • The minimum is the thumb and finger holding the rope.
    • The maximum is one gloved hand gripping onto the rope.

Materials used

Lowering devices

  • Conterra Scarab (rescue lowering device)
  • Aspiring Brakebar Rack (caving descent device)
  • Petzl Huit (figure-8 style device used in canyoning/sport mode)
  • Petzl Reverso (belay device)
  • Single and Double Munter/Italian Hitch

Rope

Korda’s Dana 10

  • Manufacturer: sacidkordas.com, Type: Canyoning rope semi-static A, Diameter: 10 mm
  • Weight: 68 g/m, Breaking strength: 27.80 kN, Static elongation: 2.7% (150kgs)
  • Materials: Core/Sheath – Nylon/ Nylon, Standards: EN 1891:1998, type A

PMI Classic Sport

  • Manufacturer: pmirope.com, Type: Static, Diameter: 10 mm
  • Weight: 66 g/m, Breaking strength: 27.00 kN, Static elongation: 1.9% (136kgs)
  • Materials: Core/Sheath – Nylon/ Nylon, Standards: Cordage Institute CI 1801 static rope

Sterling Canyon Tech

  • Manufacturer: sterlingrope.com, Type: Static, Diameter: 9.5 mm, 
  • Weight: 63 g/m, Breaking strength: 30 kN, Static elongation: 3.9% (136kgs)
  • Materials: Core/Sheath – Technora/ Nylon, Standards: Cordage Institute CI 1801 static rope

Testing procedure

A repeatable test procedure was set up.

Slow Pull

  • A 100kN vertical testbed was used at Aspiring Safety, Christchurch NZ.
  • A new rope was used for the start of testing. The same section of rope was reused between tests.
  • All tests were completed between 12mm pins and 12mm carabiners.
  • One test was undertaken on each variation by the same person with their dominant hand.
  • Testing was undertaken over several different days at least a week apart.
  • Testing speed was set at 100mm/minute. The sample rate of the testbed is 60Hz
Friction Testing
Friction Testing

How much friction do you need?

The critical thing with friction on your lowering device is getting the amount just right. A smooth lower that allows any attendant(s) to walk at a reasonable speed for the terrain and the rescuers (undertaking the lowering) to remain in control.

A balance between movement and control.

Too much friction

Too much friction is a real pain as the attendant(s)/stretcher move too slow with less control over their balance. When on a slope, the attendants have to pull against the lowering system putting more load onto the anchor than is needed. Often there is the associated loss of cognitive control as frustration sets in for all parties.

Other considerations:

  • For a top-down style rescue, you are often lowering a stretcher (litter) and attendant (bearer) without a patient thus only 100kg.
  • You need to know how to rig or change/adapt your system to get less friction at times. For example, if your ropes run over any edge protection, this will reduce the amount of friction you need.
  • With two evenly tensioned ropes lines and 2kN overall on the system, the load is only going to be around 1kN on each device.

Too little friction

Too little friction is not good as well. If we have to over-grip the rope, we can suffer from fatigue in the forearm (being pumped). You can lose control if you are not on it and stop and adjust things before this happens.

To avoid this situation:

  • Initially, start conservatively with more friction than we need and then subtract down to point where there is a balance between movement and control.
  • Once you have experience with the combination of device and the friction setting for the terrain and load, you develop a go-to friction setting.

Types of friction

When researching the information for this post, we found this graph and definitions (1) that made sense when you think about how friction works. The test results record limiting friction – the maximum value.

Definitions

Static friction:

Friction between two or more solid objects that are not moving relative to each other is called static friction.

Limiting friction:

When the body overcomes the force of static friction, it reaches a maximum value which is called limiting friction.

Kinetic friction:

After the body starts moving and friction decreases, the value is called kinetic friction.

Test data

Conterra Scarab

  • Tested with 9.5mm Sterling Canyon Tech
#Lowering DeviceThumb and Finger (kN)Hand (kN)
1Scarab 1 horn0.40.5
2Scarab 2 horns0.71.4
3Scarab 3 horns1.11.8
4Scarab 4 horns2.63.7
Scarab friction 1-4 horns
Scarab friction 1-4 horns
#Lowering DeviceThumb and Finger (kN)Hand (kN)
5Scarab 1 horn +carabiner1.01.2
6Scarab 1 horn +carabiner+ 1 horn1.11.8
7Scarab 3 horns +carabiner1.82.8
Scarab friction with redirect carabiner

Aspiring Brakebar Rack

  • Tested with 10mm PMI Classic Sport
#Lowering DeviceThumb and Finger (kN)Hand (kN)
8Brakebar rack low friction0.40.6
9Brakebar rack  low friction +
thumbed bar
0.81.0
10Brakebar rack  4 bars0.61.4
11Brakebar rack  5 bars1.32.2
Brakebar lowering friction
Brakebar rack friction
#Lowering DeviceThumb and Finger (kN)Hand (kN)
12Brakebar rack 2 bars + carabiner0.20.5
13Brakebar rack low friction + carabiner0.71.2
14Brakebar rack 5 bars + carabiner1.33.6
Brakebar lowering friction redirect carabiner
Brakebar friction with redirect carabiner

Figure-8 device

  • Tested with 10mm Kordas Dana
#Lowering DeviceThumb and Finger (kN)Hand (kN)
15Figure-8 device canyon style low friction0.30.6
16Figure-8 device canyon style high friction0.81.3
fig 8 lowering can style friction
Figure-8 device low and high friction
#Lowering DeviceThumb and Finger (kN)Hand (kN)
17Figure-8 device canyon style low friction + carabiner0.41.2
18Figure-8 device canyon style high friction + carabiner1.02.3
fig 8 lowering friction redirect carabiner
Figure-8 friction with redirect carabiner

Petzl Reverso

  • Tested with 9.5mm Sterling Canyon Tech
#Lowering DeviceThumb and Finger (kN)Hand (kN)
19Reverso low friction0.40.7
20Reverso high friction0.71.3
Plate belay friction
Reverso friction
#Lowering DeviceThumb and Finger (kN)Hand (kN)
21Reverso low friction + carabiner0.81.3
22Reverso high friction + carabiner1.12.4
23Reverso high friction + carabiner + carabiner2.03.6
Plate belay friction redirect carabiner
Reverso friction with redirect carabiner

Munter/Italian Hitch

  • Tested with 10mm PMI Classic Sport
#Lowering DeviceThumb and Finger (kN)Hand (kN)
24Munter / Italian0.51.4
25Double Munter / Italian1.43.9
Munter single double friction
Munter/Italian hitch friction with redirect carabiner
#Lowering DeviceThumb and Finger (kN)Hand (kN)
26Munter / Italian + carabiner0.71.3
27Double Munter / Italian + carabiner1.64.1
Munter single double friction redirect carabiner
Munter / Italian hitch friction with redirect carabiner

Conclusions

  • We found out, as a guide, the range of friction we could hold for the particular lowering device in various settings for rescue and personal use.
  • Think about the influencers of friction in your particular situation and then (if you have no prior experience) choose a conservative setting to start.
  • Reduce friction to get a balance between movement and control of the load.

Download the one page ‘Lowering Device Friction Summary’ below.

From the team at Over the Edge Rescue

Grant

Reference

  1. https://www.toppr.com/ask/question/distinguish-between-static-friction-limiting-friction-and-kinetic-frictionhow-do-they-vary-with-the-applied/

Lowering Device Friction Summary

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