Webbing anchors: efficient rigging and 16mm testing

What’s in this webbing anchors post?

  1. The basics for webbing anchors: So you know why you are using webbing anchors, what to use, set up and four ways of rigging.
  2. How to rig webbing anchors efficiently: Get the right (minimum) webbing length, rather than halfway through a rigging job finding out you are short and have to start again.
  3. 16mm webbing anchor testing: Answering the question “Does 16mm tubular webbing have sufficient strength for anchor rigging in backcountry rescue?” with tests around pins, carabiners and smooth rock, sharp rock and edge protectors.

The basics for webbing anchors

Using single or multiple wraps with webbing is a simple and effective way to rig an anchor. It is ideal for single point bombproof anchors such as rocks and trees. It is the best choice when you have a solid object that needs an anchor attachment. 

Features of webbing anchors

So you know why you are using webbing to wrap an anchor:

  • Equalising the load from almost any direction.
  • Loads equipment in line and doesn’t tri-load carabiners.
  • Webbing lies flat against objects, grips well and does not roll
  • Where you drop a leg against an object (W2P1 and W3P2);
    1. makes it easy to undo the tape bend as the load is onto the object rather than the bend and
    2. cinches down around the object to hold its position when loaded.
  • There is suitable strength for rescue situations of 20kN+ for single legs and 30kN+ plus double legs.

Materials

What to use and set up webbing for efficiency of use:

  • A length of tubular nylon webbing with open ends (not sewn) and (for a Wrap 3 Pull 2) at least three times the circumference of the object plus another metre (for the pull 2 legs and bend).
  • While 25mm has been used in the past, recent testing of 16mm webbing showed enough margin for lightweight rescue (20kN+)
  • If you have different webbing lengths, colour code for easy identification when rigging. For example, blue is 5m, and green is 7m
  • Mark the end of the sling with the length on one side and date into service on the other.
  • Cut at an angle and harden the end area with a hot knife as it assists with rethreading.
webbing date and length
Webbing ends: length and date into service

Rigging types

Four ways of rigging single and multiple wrap webbing anchors

  • Wrap 1 Pull 1 (loop)
  • Wrap 2 Pull 2 (double loop)
  • Wrap 2 Pull 1
  • Wrap 3 Pull 2
rigging types W1P1 W2P2 W2P1 W3P2

How to rig webbing anchors efficiently

Get the right (minimum) webbing length, rather than halfway through a rigging job finding out you are short and have to start again.

Estimate circumference

  1. To start, you need to work out the circumference of an anchor (aka a circle). Let’s do a little bit of geometry but not too much.
  2. The circumference is always Pi (π = 3.14 to 2 decimal places) times the circle’s diameter, no matter how large or small the circle is! In other words, in the example below, if the diameter is 1, the circumference is 3.14
estimate circumference webbing anchors
Reference: https://www.mathsisfun.com/numbers/pi.html
  1. While Pi is 3.14, for a simple field calculation we round down to 3.
  2. Therefore, for our purposes in estimating webbing length, use the formula:

circumference = 3 x diameter

Estimate diameter

An easy way to estimate diameter in the field is a hand span which is around 20cm.

estimate diameter hand span

Estimate webbing length

A practical example for a Wrap 3 Pull 2 (W3P2)

  1. Estimate the diameter (the tree is one hand span (20cm))
  2. Diameter x 3 to get the circumference (3 x 20cm = 60cm)
  3. The circumference x 3 for the 3 wraps of the webbing (3x 60cm=180cm)
  4. Round up to the nearest metre (200cm)
  5. Plus 100cm for the bend and extending legs on the pull 2 (200cm plus 100cm = 300cm)
  6. So for one hand-span tree, you need 3m of webbing to build a W3P2.
  7. Check out the video below

Field maths calculations for webbing length – Wrap 3 Pull 2

Using 3m as a base number for one hand span (20cm):

  • for every additional half a hand span diameter (10cm) for a W3P2, add another metre of webbing length OR
  • for every additional hand span diameter (20cm) for a W3P2, add another 2 metres of webbing length
Hand spans Circumference Circumference Round Up Add 1m Total
1.0 (20cm) 3 x 20cm=60cm 3 x 60cm=180cm 200cm (+)100cm 300cm (3m)
1.5 (30cm) 3 x 30cm=90cm 3 x 90cm=270cm 300cm (+)100cm 400cm (4m)
2.0 (40cm) 3 x 40cm=120cm 3 x 120cm=360cm 400cm (+)100cm 500cm (5m)
2.5 (50cm) 3 x 50cm=150cm 3 x 150cm=450cm 500cm (+)100cm 600cm (6m)
3.0 (60cm) 3 x 60cm=180cm 3 x 180cm=540cm 600cm (+)100cm 700cm (7m)
3.5 (70cm) 3 x 70cm=210cm 4 x 210cm=630cm 700cm (+)100cm 800cm (8m)
4.0 (80cm) 3 x 80cm=240cm 3 x 240cm=720cm 800cm (+)100cm 900cm (9m)
4.5 (90cm) 3 x 90cm=270cm 3 x 270cm=810cm 900cm (+)100cm 1000cm (10m)

Tips for rigging webbing anchors

  • Based on these numbers, webbing lengths can be 3m, 4m, 5m, 6m, 7m, 8m, 9m or 10m; however, you can choose what lengths suit your situation and specific uses.
  • We have found 5m and 7m as a couple of workable webbing lengths for field use (i.e. two hand spans and three hand spans).
  • For anything over 7m, we recommend using cord (e.g. 7mm x 10m cordalette) or a short rigging rope as webbing becomes messy – it’s hard to keep tidy and therefore rig efficiently.
  • This method works well for perfectly round anchors, however, this is not always the case. When sizing the anchor, you may need to look at the diameter from a couple of different aspects and then split the difference.

16mm webbing anchors testing

For backcountry rescue, the aim is to use lighter weight gear balanced with functionality and performance.
“Does 16mm tubular webbing have sufficient strength for anchor rigging in backcountry rescue?”
We undertook a series of functional tests around pins, carabiners and smooth rock, sharp rock and edge protectors to answer this question.
As a baseline for comparison, we started by testing 25mm webbing.

Edelrid X Tube 25mm tubular webbing

Between 30mm pin and 12mm pin/carabiner

Joined with a tape bend, average of 3 tests, 100mm/min

  • Wrap 1 Pull 1 = 27.98kN (70%)
  • Wrap 2 Pull 2 = 38.06kN (48%)
  • Wrap 2 Pull 1 = 33.36kN
  • Wrap 3 Pull 2 = 40.08kN
testing Wrap 2 Pull 1 30mm pin

Aspiring 16mm tubular webbing

Between 30mm and 12mm pins

Joined with a tape bend, average of 3 tests, 100mm/min

  • Wrap 1 Pull 1 = 20.16kN (81%)
  • Wrap 2 Pull 2 = 34.26kN (69%)
  • Wrap 2 Pull 1 = 20.80kN
  • Wrap 3 Pull 2 = 36.62kN
testing Wrap 2 Pull 2 30mm pin
Between Smooth Rock and 12mm pin

Joined with a tape bend, average of 3 tests, 100mm/min

  • Wrap 1 Pull 1 = 19.61kN (78%)
  • Wrap 2 Pull 1 = 29.69kN (59%)
  • Wrap 2 Pull 1 = 18.31kN
  • Wrap 3 Pull 2 = 33.52kN
testing Wrap 3 Pull 2 smooth rock
Between Sharp Rock and 12mm pin

Joined with a tape bend, average of 3 tests, 100mm/min

  • Wrap 1 Pull 1 = 9.76kN (39%)
  • Wrap 2 Pull 2 = 19.13kN (38%)
  • Wrap 2 Pull 1 = 9.31kN
  • Wrap 3 Pull 2 = 18.55kN
testing Wrap 2 Pull 2 sharp rock
Between Sharp Rock/Rope Protector and 12mm pin

Joined with a tape bend, average of 3 tests, 100mm/min

  • Wrap 1 Pull 1 = 18.73kN (75%)
  • Wrap 2 Pull 2 = 35.09kN (70%)
  • Wrap 2 Pull 1 = 20.20kN
  • Wrap 3 Pull 2 = 32.48kN
testing Wrap 3 Pull 2 sharp protector

Conclusions

The testing shows that the 16mm tubular webbing is suitable for lightweight rescue as:

  • Single strand variations (W1P1, W2P1) onto smooth objects break around the same minimum breaking strength as a 10mm static rope with a figure-8 on a bight (18kN).
  • Two strand variations (W2P2, W3P2) onto smooth objects break, on average, over 30kN, greater than commonly used lightweight HMS aluminium carabiners. For example, the CT Warlock HMS at 23kN.
  • Where sharp edges exist, edge protection needs to be used to bring minimum breaking strength back to similar values as smooth objects.

However, please carefully consider the information presented here and make your judgment in the context of where you operate, the team’s skill level, and if lighter weight webbing is the right way to go.

Note: This article is about technical rescue rigging. It relates to specific anchor rigging techniques that require lots of practice to master and judgment to use in the right place. This report does not constitute training of any sort.

This post is only a summary of the results. Check out the testing report below for more in-depth information and analysis.

Frequently Asked Questions

Question
  • We also use a rope to make these configurations. Can you do a similar test with an 8mm nylon cord?
Answer
  • We have done some testing with an 8mm cord around pins in the Canyon Rescue Rope Testing post.
  • We have done some testing for drilled threads using a nylon 8mm cord. The only material that survives around sharp edges is a cord with Dyneema or Kevlar in the sheath. See the post; Rock Thread and V-thread Testing 2021

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