Sorry for being late yet again. Loads of stuff has been going on and a lot of slackline related work needed to be done in the past weeks. You should go check out the last post on this website on webbing slippage, if you haven’t read that.
Now that this is out of the way, let us begin with a new article:
What is this?
Actually, I have no idea what to call it. Some people refer to it as a rope lashing tensioning system, some call it cord primitive, but most have never seen this before. Basically, it is a simple pulley system with neither pulleys nor a brake. Instead of bushings or bearings, the rope is bend around the bow side of a shackle or a ring or even a carabiner (carabiners are not recommended, due to their -4 weakness against triloading) and instead of using a brake device, this system relies on friction. In other words, it is a soft-release with cord instead of webbing.
What can it do?
Pretty much anything a soft-release can do and a little more. You can tension and detension up to 4kN of base tension. This is plenty for up to 40m and enough for lower stretch lines up to 60m and of course enough for every line up high (see limitations further down for highlines), if you like it on the looser end of the spectrum.
What can it not do?
Mhm. That question sounds a little odd. There is a limitation to this system, which isn’t intuitively obvious. You can’t rig it out of reach, since you need to tie it off after tensioning. This means you have to hold the tension of the line (more precisely a small portion of it) whilst tying it off, which can present some difficulties if your anchors are higher than you can reach without climbing.
There’s also the question of strength. The system uses very thin cord and although there are 9 strands of it, that does not mean the force is divided equally amongst them. Whenever I want to estimate the strength of the system, I use the following approximation:
50% of the load is on the first two strands.
25% of the load is on the next two strands.
12.5% of the load is on the next two strands.
6.25% of the load..
This is just a guideline and I have no quantifiable evidence for it. It is, however, important that you keep the unequal force distribution in mind and don’t forget that thin cord is not very strong. This is why I’ve switched to dyneema cord for lines that are more safety-sensitive, although the nylon accessory cord is much easier to handle and less expensive.
Do I need this?
If you rig your lines relatively loose and don’t have (or don’t want to carry) a pulley system, you might want to give this a shot. It has a little minimalist charme, if that is of any value to you.
How do I get one?
All you need is a little bit (9-12m) of cord (7mm nylon accessory cord or 5mm dyneema), some round connectors (circular profile and polished surface increases efficiency!!) like shackles, rings or lofrings (this is what we call low-friction-rings from now on, because it takes ages to say low-friction-ring) and a pulling aid (handled ascender for the accessory cord or another ring for the dyneema).
The cheap version:This is for the broke or minimalistic (or both) slackliner. 9m of 7mm accessory cord and one extra 12mm stainless steel shackle and a handled ascender. That is the entire rig. A double (or yosemite) bowline on the pin of the weblock-shackle, 4 full turns around both shackles (9:1 theoretical MA) and a slippery hitch as a tie-off with additional fisherman’s around the entire system to increase friction and keep everthing tidy.
The light version:
Adjustable anchor sling (I’ve integrated a second lofring into the sling for additional efficiency and weight saving), 9m of 5mm dyneema cord, and a lofring-ring linelocker. Since it is a pain to thread a linelocker with 2 closed rings, I leave it threaded permanently with enough tail for a back-up and use a weblock on the static side. You need some sort of pulling aid for the dyneema, since it is too slippery to hold on to. A carabiner or another ring work well. It would be optimal to splice the dyneema onto the lofring, but I haven’t had the time yet, so I just used a triple fisherman’s knot.
Been using this system for 3 months now and it works really well. The longest line we rigged so far was 60m, but mostly used it on 20-35m lines. It is the ideal travel kit, in my opinion. Also a fantastic option to bridge the dreaded 30-60m gap, which everyone encounters when progressing from a primitive to pulleys.
If you have ideas that need testing, material that needs a review or any sort of crazy idea, let us know!