Prusik, Auto Blocks, and Klemheist Break Tests

The rule supposedly is that you want a friction hitch to be 3mm smaller than the diameter of rope you are trying to grab and to use 3 wraps. We did a bunch of tests and here are the numbers:

4MM PARACORD:
*Prusik 3.74kN
*Klemheist 3.34kN
*Auto Block 3 wraps - slips at 1.34kN, 4 wraps - slips at 5.32kn
*Paracord doubled twice 8.90kN
*Paracord in a loop 4.06kN

5MM ACCESSORY CORD:
*Prusik 8.16kN and 5.36kn
*Klemheist 7kN-ish Slips and locked off and broke at 11.62kN
*Auto Block: 3 wraps - 0.36kN Slips / 4 wraps - 3.62kn Slips

7MM ACCESSORY CORD:
*Prusik 7.9kN and 5.18kN
*Klemheist 3.3kN Slips
*Auto Block: 4 wraps - 0.8kN Slips

HOLLOW BLOCK 14KN MBS:
*Prusik 5.84kn
*Auto Block: 3 wraps - 0.42kN Slips / 4 wraps - 1.38kn Slips

00:00 What are friction Hitches
03:37 4MM Tests
05:08 5MM Tests
07:29 7MM Tests
08:53 10mm on 10mm Test
09:50 Hollow Block
10:53 Conclusion

[alexdematanecoursdekayak]

I'm a whitewater rescue instructor and your work is gold to me!!!
There is too much myth around rope and you debunk them and help making the rope sports a safer place.
Love from Montréal
Alex

[redpandason]

Ryan: Prusik knots don’t work when they’re the same diameter as the rope

Blake’s Hitch: Am I a joke to you

[nicholasricciuti]

There's no rule of only 3 wraps, that's just a starting point, when the diameter of the cord is closer to the size of the rope you need to have more wraps to create more friction. For rescue rigging a 8mm prusik is common and requires many more wraps against a single rope. The test of using 10.5mm prusik around a single 10.5mm rope will work just might need 15-20 wraps or more, haven't tried to know the exact number. Ryan should be testing how many wraps does it take to hold to be more accurate here. Also, autoblock is used with a belay device in the system, and more common around 2 ropes at the same time where there's a lot more surface area to create friction, and is more of a use case for the Hollowblock. That said, an autoblock is not intended to be directly loaded as an ascending device or progress capture. Hollowblock also comes in a longer length, probably needed for achieving more wraps when using on a single rope with friction hitches.

Overall should revise the test for number of wraps needed for diameter differences to achieve the same slipping strength, number of wraps needed to achieve MBS, and comparing application of different friction hitches when using the same materials. Not trying to give Ryan more work, but think the major point of number of wraps was missed...

[macengineering]

Adding here since I don't see this in the other comments. The Sterling Hollowblock is made from aramid fiber (hence the yellow color) and is much more heat resistant than common rope materials. This might matter in a friction hitch where things do get hot.

[dlingens]

Hello, actually it is not a fair comparison. If you read the Treeclimber's Knotbook, you will read, that the klemheist needs one more wrap, than the prusik to perform in a similar way. The autoblock (machard) needs some more wraps to be able to show its advantage. You need a longer cord and you have to make as many wraps as possible, making sure that the connecting-knot is in top of the autoblock. Than it does not slip. My results of my own tests with 6 mm cord: klemheist and prusik: 950 kg, autoblock 2400 kg (!!). Thanks for your video. Dirk from germany

[philbox]

What some may miss is the concept of fit for purpose. The Autoblock is fit for purpose when used below the device to as you say, "add friction" in an abseiling context. So in effect it doesn't need to hold all the weight, it merely needs to add enough friction so you stop if you let the Autoblock grab the rope to go hands free. Very comforting to me to see it slip and not break. As always though, test before you commit to any set up you use when abseiling or for that matter perform any transition when up in the air. Awesome set of tests. Will be using some of that data in future training sessions.

[GavynPendleton]

Good to know I’ve been rapping on the weakest slippyest friction hitch this whole time! The thing is it works well when used for the purpose of backing up an ATC.

[ThuTroothHurtz]

This has been a question in my head for more than 20 years. Your guys' channel officially wins the internet. Been watching a bunch of your videos. Subscribing.
Thumbs Up

[longshotpunk]

As a military mountaineer we are trained to use tubular webbing tied with a water knot and use that in the autoblock. I'd be curious to see the numbers on that combo.

[jima]

As a general note, when the ropes get wet, everything changes. The value of hollow block is that it takes higher temperatures compared to nylon. If it slips down the main rope, it will last longer than nylon will. Also, being small & sewn, with no large knot, you can attach it to a leg loop & have it be short enough to use as a third hand under a repel device that is attached directly to a belay loop

[OutdoorsWithChad]

This is so informative. I'm just getting into tree climbing and used two prusik loops with 1200 paracord (6mm) to ascend a single line (10mm). The prusiks worked great and were very secure.

It also gives me confidence that my line choice is "super good enough". Looking at the 550 paracord tests, my 1200 paracord prusiks should be at least 8kn.

I learn so much from this channel.

[justindunlap]

Thank you how not to highline team. I've been waiting for this break test for a while. Keep up the good work.

[Grethko]

Rad. People been asking me this for ages. Thanks lads

[yc__]

Finally, i was searching so long for a video on a prusic break test 👍

[niscent_]

personally i learned those three knots pretty early as i started mountain climbing, i use them as secondary safety for rappel and stuck with the prusik for purely practical reasons. prusik works both ways (which allows very comfortable details while getting in a rappel, like having it hold some slack in the rope for you), it stays on the rope even without a carabiner, and is vastly easier to get moving again after it locked tight.

[lindanilsson]

I really like this channel. I work as an arborist and sherrill, which is a american dealer for arborist gear, did some tests several years ago. Their conclution was that for maximum friction the friction cord has to be 5 7ths of the climbing rope. Thanks for great entertainment.

[miguelestebangaillour]

The friction hitches are really used on arborism. But always on double rope system. If u want to use in 1 line u got to add an extra friction device. Most used are rope wrench from ISC and chicane from petzl. Anyway, the knots that u tested is not common used. If you want to try the blakes hitch, distel, michoacan will be something nice to see. I like your vids! thanks for doing its!

[nicholaskarassavas]

Prusik still rules.. my camping and hammock goto.
Love your channels tempo and tests (have answered most of my knot and carabiner questions I had over the over the years)

[baileyhalliday]

I made my own adjustable lanyard with 10.2mm dynamic rope, initially I had one end tied in an 8 and clipped to me, the other end going through an ATC in guide mode. This worked and I had the benefit of being able to use this with an ascender to cinch onto my lanyard to un-weight my primary ascension device. However for positioning in a tree having the ATC clogged up my belay loop so I looked into friction hitches.

I didn't have any cord so I cut some older dynamic 9.5mm climbing rope and used this to make a friction hitch. I had both ends of my lanyard clipped into me and then used the friction hitch as a way to shorten this length (meaning if the hitch failed my I had a backup at the full length of my lanyard). I found two hitches that worked, the Blakes hitch and the Distel hitch. Ultimately I preferred the Distel for ease of tying and balance between grabbing and sliding.

[carlaitken]

I have a hollow block as a third hand (French hitch) as part of my abseiling kit. It’s comfortable to use, glides smoothly along the rope for Abseiling and can be used on different diameter ropes for different activities.

the benefit of it is it’s ability to hold well on a large variety of rope Diameters without the need to carry a different diameter prusik cords.

That said it is a pain in the backside to use for ascending a rope using it as a prusik (the knot becomes hard to loosen).

Great videos I be learnt loads from your channel and the knowledge gain gives me confidence in the equipment Keep it up mate 👍