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The Impact Forces when using Dynamic Rope vs. Static Rope vs. Spansets as Highline Anchors

Introduction

Recently we began to use large diameter Dynamic Rope as our anchoring material for highlines 40m (130 feet) and under in hopes that it would help lower the forces on both the body and on the line during dynamic events, such as leash falls and catches. In the field, it seems like this method of anchoring was quite effective in both of these regards, but there haven’t been any tests to conclusively say.

In this article, we will be taking a deeper look at this concept with a series of drop tests on our new drop test rig in the shop. We will be comparing peak forces on both the leash and the line during drop tests using an 80 kg (176 lbs) mass while using five different ropes and a set of spansets for anchors on a mock highline rigged in our shop.

We will be comparing three brand new ropes: a 10.5mm Static Rope (Sterling 10.5mm SafetyPro), a 9mm Static Rope (Sterling 9mm SafetyPro Static Rope), and an 11.2mm Dynamic Rope (Sterling 11.2mm Marathon Mega Dynamic Rope), and two very old and used ropes: a 10.5mm Dynamic Rope (brand and type unknown) and a 10.5mm Static Rope (Sterling 10.5mm SafetyPro), both of which are well over 7 years old and very heavily used. We will also be testing a pair of Green Spansets, that are lightly used, but several years old.

We will be conducting two tests using each of the new ropes as anchors: the first comparing the peak forces on the line and leash during the first leash fall of a session and the second comparing the peak forces on the line and leash after pre-loading both for 24 hours, to simulate forces near the end of a long session. We will perform the second test on both of the old ropes and the old spansets as well as the new ropes.

 

Description Of The Drop Test Rig

Before we dive into the procedures for the tests and their outcome, I would like to describe our drop test rig and how it works.

In our shop, we have two large metal pillars that are 14 feet (4.3m) apart and 14 feet (4.3m) tall. At the very top of these pillars, we have rigged two parallel lines on 6mm Amsteel, both of which are tensioned quite heavily. Attached to these Amsteel lines is a pulley. We also have an anchor in floor, positioned in the center between the pillars, but 20 feet (6m) to the side. From this anchor, we run a rope up to the pulley on the Amsteel lines and down to the floor. This rope is used for hoisting the drop mass.

The drop mass is an 80 kg kettlebell with a large handle on the top that we can easily attach things to. To attach the hoist line, we wrap a sewn prusik loop around the handle and attach it to a shackle. Then we attach a Snap Shackle to the rope and the normal shackle on the kettlebell. This Snap Shackle will allow us to easily release the test mass when it is time to test.

About 40 inches (1m) below the Amsteel lines, we have set a simple slackline, which can be changed in any fashion we’d like, depending on what we are testing. We can vary the anchors, the line, the hardware, whatever… This is the line that we will be dropping the test mass on. For most tests, we will have a dynamometer integrated somewhere in this line to measure peak forces of the line during the dynamic event.

On this line, we have threaded an additional dynamometer that is attached to a leash. This is for measuring the peak forces on the leash during a drop test. The other end of the leash is tied straight to the drop mass.

Lastly, at the same height as the Amsteel lines, we have rigged a backup static rope going through the dynamometer threaded onto the slackline. This is to prevent the drop mass from crashing into the ground in the event the slackline fails. We’ve rigged it so that it will not be engaged during tests, but only engage in the event of failure.

Checkout this video walk-through of our Test Rig for more info and a clearer picture of the setup:

 

Procedures

Test 1

Compare the impact force on both the line and the leash on the first leash fall of a session.

Materials

3 brand new rope samples, each 25 feet (7.6m) long:

10.5mm Sterling Safety PRO Static Rope

  • Weight: 4.73 lbs/100 ft (70.4 g/m)
  • Elongation @ 136 kg (300 lbs): 2.8%
  • Impact Force @ Fall Factor 0.3: 5.5 kN (1,236 lbf)
  • MBS: 27.2 kN (6,114 lbf)
  • More Info: https://sterlingrope.com/store/climb/ropes/static/safetypro/10-5mm-safetypro

9.0mm Sterling Safety PRO Static Rope

  • Weight: 4.3 lbs/100 ft (50.6 g/m)
  • Elongation @ 136 kg (300 lbs): 1.9%
  • Impact Force @ Fall Factor 0.3: 4.2 kN (1,236 lbf)
  • MBS: 19.0 kN (4,271 lbf)
  • More Info: https://sterlingrope.com/store/climb/ropes/static/safetypro/9mm-safetypro

11.2mm Sterling Marathon Mega Dynamic Rope

  • Weight: 5.3 lbs/100 ft (79 g/m)
  • Elongation @ 80 kg (176 lbs): 9.4%
  • Dynamic Elongation: 30.8%
  • Impact Force @ Fall Factor 1.77: 8.7 kN (1,966 lbf)
  • MBS: Unknown
  • More Info: https://sterlingrope.com/store/climb/ropes/static/safetypro/9mm-safetypro

- A length of high stretch slackline webbing that is at least 15 feet (4.8m) long with a sewn loop on one end. We used Lift for this.
- 3x Shackles
- 2x Dynamometers with readout capabilities (we used the ENFORCER from Rock Exotica)
- 1x Weblock
- 1x Threaded Highline, which was heavily used

 

Outline

For this test we rigged the anchors for the slackline with the same type of rope on each side of the line. We wrapped the rope around the metal pillars three times and joined the ends together with a double sheet-bend. We then tied a BFK with all the strands of the rope, resulting in the master-point being roughly 11 inches (28 cm) away from the pole.

On one end, we attached the first dynamometer to the BFK with a shackle. The other end of the dyno was attached to the sewn loop of the slackline webbing with a second shackle. On the other end, we attached a weblock to the BFK with a third shackle. The other end of the webbing was fed into the weblock.

We threaded a dynamometer onto the slackline to act as a leash ring. To this dyno, we tied a leash with a figure-8 knot. The other end of the leash was attached to the drop mass with another figure-8 knot. The unloaded leash was 35 inches (89 cm) long from tip of the knot to tip of the knot. This resulted in a 42 inch (107 cm) long unloaded leash distance, including the length of the dyno.

The resulting rigged slackline ended up being 11 feet (3.35m) long from sewn loop to weblock. Again, the distance from pole to pole is 14 feet (4.27m).

The drop mass was hoisted up to be 24 inches (61 cm) above the line prior to dropping. So a theoretical fall factor of:

Fall Factor = (42 inches + 24 inches) / 42 inches = 1.57

Of course, this is not actually the fall factor due to the attachment point moving during the dynamic event, but good to know anyway.

Before each drop, the anchor knots and leash knots were untied and retied, to simulate a fresh rig. The lengths of the anchors and leash remained constant from test to test. The slackline was then retensioned to roughly 1.4 kN (315 lbf) prior to each drop. This was about the max I could apply with a simple 3:1 Buckingham system. I tried to keep the tension as consistent as possible from test to test, but this proved to be very difficult. Minor differences in standing tension were noted.

Prior to each test, recording of both the line and leash dynamometers was initiated, capturing samples at 300hz and 500hz, respectively.

Each rope type received 5 drop tests.

 

Test 2

Compare the impact force on both the line and the leash after both have been preloaded for 24 hours, to simulate the forces at the end of a long session.

Materials

- 3 slightly used rope samples (same pieces from Test 1), each 25 feet (7.6m) long:
- 2 heavily used rope samples, each 25 feet (7.6m) long:

10.5mm Sterling Safety PRO Static Rope - about 8 years old, used on many high tension longlines as the pulley system rope. Has slight glazing and is extremely stiff.

  • Weight: 4.73 lbs/100 ft (70.4 g/m)
  • Elongation @ 136 kg (300 lbs): 2.8%
  • Impact Force @ Fall Factor 0.3: 5.5 kN (1,236 lbf)
  • MBS: 27.2 kN (6,114 lbf)
  • More Info: https://sterlingrope.com/store/climb/ropes/static/safetypro/10-5mm-safetypro

10.5mm Dynamic Rope (Make and Model unknown) - about 10 years old, used as the backup on many highlines and for a small number of climbs. Used as anchor material in shop slackline for ~6 months. Very stiff, very fuzzy, no core shots.
Specs: Unknown

- 2 lightly used, but very old Green Spansets
- A length of high stretch slackline webbing that is at least 15 feet (4.8m) long with a sewn loop on one end. We used Lift for this
- 3x Shackles
- 2x Dynamometers with readout capabilities (we use the ENFORCER from Rock Exotica)
- 1x Weblock
- 1x Threaded Highline, which was heavily used

Outline

This test has the same setup as Test 1, but instead of retying both the leash and anchor knots after each test, we left them cinched.

Prior to testing each rope, we did an initial drop to cinch both the anchor knots and the leash knots. Then we let the drop mass hang on the leash on the line for 24 hours. After this, we did 5 consecutive drops on the rig without altering the leash or anchor knots.

Prior to each drop, we would retension the slackline to roughly 1.4 kN (315 lbf).

 

Results

Test 1

10.5mm Safety PRO Static Rope

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 6.39 kN 7.15 kN 7.02 kN 6.79 kN 6.77 kN
Leash 5.21 kN 5.65 kN 5.82 kN 5.76 kN 6.04 kN

 

Average Line Peak Force = 6.82 kN
Standard Deviation = 0.29 kN

Average Leash Peak Force = 5.70 kN
Standard Deviation = 0.31 kN

10.5mm - Test 1 - Leash

10.5mm - Test 1 - Line

 

9.0mm Safety PRO Static Rope

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 6.44 kN 6.51 kN 6.33 kN 6.83 kN 7.00 kN
Leash NULL 5.52 kN 4.98 kN 5.43 kN 5.60 kN

 

Average Line Peak Force = 6.62 kN
Standard Deviation = 0.28 kN

Average Leash Peak Force = 5.38 kN
Standard Deviation = 0.28 kN

9mm Static - Test 1 - Leash

9mm Static - Test 1 - Line

 

11.2mm Marathon Mega Dynamic Rope

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 6.57 kN 6.65 kN 5.31 kN 6.83 kN 6.93 kN
Leash 5.32 kN 5.40 kN 5.64 kN 5.57 kN 5.60 kN

 

Average Line Peak Force = 6.75 kN
Standard Deviation = 0.16 kN

Average Leash Peak Force = 5.51 kN
Standard Deviation = 0.14 kN

11.2mm Dynamic - Test 1 - Leash

11.2mm Dynamic - Test 1 - Line

 

Test 2

10.5mm Safety PRO Static Rope - New

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 8.94 kN 9.90 kN 9.81 kN 10.02 kN 10.12 kN
Leash 6.51 kN 6.71 kN 6.62 kN 6.74 kN 6.79 kN

 

Average Line Peak Force = 9.76 kN
Standard Deviation = 0.47 kN

Average Leash Peak Force = 6.67 kN
Standard Deviation = 0.11 kN

10.5mm Static - Test 2 - Leash

10.5mm Static - Test 2 - Line

 

9.0mm Safety PRO Static Rope - New

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 9.67 kN 9.45 kN 9.75 kN 9.69 kN 10.38 kN
Leash 6.29 kN 6.43 kN 6.58 kN 6.52 kN 6.76 kN

 

Average Line Peak Force = 9.79 kN
Standard Deviation = 0.35 kN

Average Leash Peak Force = 6.52 kN
Standard Deviation = 0.17 kN

9mm Static - Test 2 - Leash

9mm Static - Test 2 - Line

 

11.2mm Marathon Mega Dynamic Rope - New

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 8.17 kN 8.19 kN 8.26 kN 8.72 kN 9.03 kN
Leash 5.84 kN 6.04 kN 5.99 kN 6.08 kN 6.15 kN

 

Average Line Peak Force = 8.47 kN
Standard Deviation = 0.38 kN

Average Leash Peak Force = 6.02 kN
Standard Deviation = 0.12 kN

11.2mm Dynamic - Test 2 - Leash

11.2mm Dynamic - Test 2 - Line

 

10.5mm Dynamic Rope - Old

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line NULL 9.83 kN 9.71 kN 10.33 kN 10.38 kN
Leash 6.20 kN 6.51 kN 6.50 kN 6.58 kN 6.71 kN

 

Average Line Peak Force = 10.06 kN
Standard Deviation = 0.34 kN

Average Leash Peak Force = 6.50 kN
Standard Deviation = 0.19 kN

Old Dynamic Rope - Test 2 - Leash

Old Dynamic Rope - Test 2 - Line

 

10.5mm Safety PRO Static Rope - Old

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 9.43 kN 9.84 kN 9.70 kN 9.99 kN 10.48 kN
Leash 6.50 kN 6.71 kN 6.52 kN 6.72 kN 6.88 kN

 

Average Line Peak Force = 9.94 kN
Standard Deviation = 0.39 kN

Average Leash Peak Force = 6.67 kN
Standard Deviation = 0.16 kN

Old Static Rope - Test 2 - Leash

Old Static Rope - Test 2 - Line

 

Green Spansets - Old

 

  Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Line 9.99 kN 10.48 kN NULL NULL 11.31 kN
Leash 6.90 kN 6.73 kN 6.70 kN 7.06 kN 7.23 kN

 

Average Line Peak Force = 10.57 kN
Standard Deviation = 0.55 kN

Average Leash Peak Force = 6.92 kN
Standard Deviation = 0.22 kN

Old Spansets - Test 2 - Leash

Old Spansets - Test 2 - Line

 

Line Stats (2 Samp. T) - Test 2

Below you will find the T values for the 2-sided, 2-sample T tests comparing each of the tested samples to the others. Any value above 0.95 or below 0.05 is statistically significant.

 

Line-Value Statistics

 

  10.5mm Static - New 9.0mm Static - New 11.2mm Dynamic - New 10.5mm Dynamic - Old 10.5mm Static - Old Green Spansets - Old
10.5mm Static - New NA 0.912163 0.001680 0.616073 0.648132 0.060067
9.0mm Static - New NA NA 0.000491 0.386363 0.680909 0.072310
11.2mm Dynamic - New NA NA NA 0.001273 0.000415 0.001006
10.5mm Dynamic - Old NA NA NA NA 0.811664 0.179988
11.2mm Dynamic - New NA NA NA NA NA 0.095694
10.5mm Dynamic - Old NA NA NA NA NA NA

 

Leash-Value Statistics

 

  10.5mm Static - New 9.0mm Static - New 11.2mm Dynamic - New 10.5mm Dynamic - Old 10.5mm Static - Old Green Spansets - Old
10.5mm Static - New NA 0.132800 0.001680 0.616073 0.648132 0.060067
9.0mm Static - New NA NA 0.001163 0.892443 0.192390 0.013364
11.2mm Dynamic - New NA NA NA 0.002081 0.000120 0.000199
10.5mm Dynamic - Old NA NA NA NA 0.169333 0.012256
11.2mm Dynamic - New NA NA NA NA NA 0.072154
10.5mm Dynamic - Old NA NA NA NA NA NA

 

All test data can be viewed and downloaded from this Google Sheet: https://docs.google.com/spreadsheets/d/1yLPC2Zol9hA7fOc2QK6u_RGKaByUk8ECcj1e2lfr4wU/edit?usp=sharing

Please note, the spreadsheet is quite resource intensive. Feel free to download and remove the charts for easier browsing and playing.
Also note, the raw test data is accessible in the hidden sheets. Please download the spreadsheet to enable these sheets if you would like to view them.

 

Discussion

First, I want to point out a few failed samples. These were all removed from the averages and statistical calculations done:

Test 1 - 9mm Static - Sample 1 - Leash

I forgot to turn on fast sampling on the Dyno and so no data was captured for this test on the leash.

 

Test 1 - 11.2 Dynamic - Sample 3 - Line

The backup caught on one side of the line, sharing some of the impact force with the line. This affected the output of this sample, causing it to be lower than the actual impact force.

 

Test 2 - 10.5 Static (Old) - Sample 1 - Line

I had issues with the Dyno and it only captured 2 seconds of data, missing the actual peak. It also only captured at 100 hz rather than 300 hz. Not sure why this happened.

 

Test 2 - Green Spansets (Old) - Sample 3 - Line

The dyno batteries died during the capturing of the data and so the data we have is not accurate. The CSV is just a copy of test 2.

 

Test 2 - Green Spansets (Old) - Sample 4 - Line

I forgot to turn on fast sampling after changing the batteries. No data captured.

 

Second, I want to point out some limitations of the drop test rig.

The distance between the poles is very small, exaggerating any forces we would see in real life circumstances. It’s hard to say if the results of these tests can be translated into longer lines. My gut says that these results are a worse case type of situation and that real life circumstances will be less than these results, but I cannot be sure until the same tests are done on different lengths of lines.

We are limited by height in the shop and so fall distances have to be kept shorter than real life situations.

 

Third, I want to point out some obvious flaws of this experiment.

We only tested one manufacturers rope, aside from the old dynamic rope.

The 10.5mm static new and old are from different batches, which may have had slightly different specs straight from the factory. We don’t have raw data from both of these batches to be able to draw meaningful conclusions.

Although we tried to make the tensions, fall distances, rope length measurements, leash length measurements, and fall angles the same from sample to sample, there were slight variations which could have caused some bias in the data.

As we tested multiple samples in a row while continuously retensioning the slackline, the webbing was loosing dynamics, causing the impact force to increase from sample to sample. You can see this in the data as the peak gets higher as we progress through the samples with each rope (sample 1 is the lowest and sample 5 is the highest in every case).

The lengths of ropes and spansets that we used are VERY short. In the field, the actual lengths of the anchor materials are typically MUCH longer, thus providing more room for shock absorption. It would be interesting to test different lengths of anchors on the same length line and compare impact forces there as well.

 

Alright, now to dive in to the results.

Going in to this experiment, I expected to see quite a large difference in impact force between dynamic and static rope during a leash fall, and even larger of a difference compared to spansets. If we look at the raw specs of each rope, it’s pretty clear that dynamic rope is built for fast, high force impacts, like a fall while lead climbing. However, since the numbers are given for different specifications for the two different types of ropes, it’s hard to compare them at face value.

If we take a look at Test 1, we see very little difference between the three ropes tested. There is no statistical significance comparing each of the ropes to the others. However, if we look at the differences between Test 1 and Test 2, we see a massive jump in impact force in Test 2. This tells me that a big portion of the impact force is absorbed by the cinching of both the anchor and leash knots as well as the settling of the highline rig. This is somewhat expected, but good information nonetheless.

However, watching the videos of each test, it’s clear that the backup rope was not loose enough and was actually loaded during each test during test 1. So, we cannot be sure if we captured the true peak impact force on the line. The leash data is unaffected by this though and we still see a large different there from Test 1 to Test 2

Diving deeper in to Test 2, we can see that there is a statistically significant difference between the new dynamic rope and all the other ropes and spansets, in both the leash and the line impact forces. However, the old dynamic rope was not significantly different from any of the static ropes, only the spansets on the leash impact. This is a bit disheartening as it tells me that the shock absorption feature that dynamic ropes have gets worse over time. Or this could be the result of the rope being a different make and model, we cannot be sure of this.

On the other hand, the old dynamic rope did not perform significantly worse than any of the static ropes, even the new ones. That is an excellent case for using dynamic rope as an anchor as we know it will provide at least the same amount of shock absorption as a static rope will.

Moving on, if we compare the old vs new 10.5mm static rope, we can see that there is no significant change in impact force between the two ropes. This is incredible as it means that we can count on static rope providing the same amount of absorption even later on in it’s life.

Lastly, taking a look at the spanset data, we see a lot of significant differences. The spanset had a significantly higher impact force on the leash compared to 9mm new static, 11.2mm new dynamic, and 10.5mm old static. I think if we had actually captured the data from sample 3 and 4 on the line, we would see significance on the line data as well.

That tells us that using static OR dynamic rope will decrease impact forces on the leash when compared to using spansets. This is good data. We can use this to make short highlines less painful to fall on. Simply swap out your spansets for a nice length of static or dynamic rope and you will significantly improve on the forces you receive on your body during dynamic events!

In general, I think the use of Dynamic Rope as a highline anchor is an acceptable practice and may lead to lower impact forces in both the anchor and the leash, particularly if using a new(er) dynamic rope. However, due to the increased complications of using dynamic rope, namely the higher elongation causing increased movements in your anchor, it should only be used in situations where impact force is a big concern.

Beyond that, I cannot yet make a meaningful recommendation on the use of Dynamic Ropes for highline anchors before the future research described below is performed. We can, however, recommend against the use of spansets for highlines 40m long and less.

 

Future Research

Unfortunately, after performing these tests I was left with more questions than answers. I really want Dynamic Rope to be a solution for a variety of problems in the highline rigging world. I cannot yet say if that’s the case because we do not have enough information. I would like to perform a few other tests that will help me make a better recommendation moving forward:

Perform Test 2 using a variety of aged ropes, all the same type, and preferably all from the same batch.

Was the aged Dynamic Rope that we used a fluke? Are “younger” aged ropes more helpful in reducing impact forces? Was the make and model of used dynamic rope already less dynamic?

 

Perform Test 2 using a variety of lengths of anchors.

Did the short length of our anchors reduce the difference in impact force we could have seen when using different materials?

 

Perform equalization comparison tests using static and dynamic rope to see if there is a meaningful gain in equalization using higher elongation materials.

Does a higher elongation rope used in a variety of anchoring configurations allow for better equalization between points?

 

That’s all we have for now on the topic. If you would like to checkout all the drop tests we did, we put together a video showing every sample. Check it out below (warning: long and boring).

As always, thanks for reading. If you have any questions, please feel free to comment below.



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