Tuesday, April 22, 2014

There's more than one way to re-sling a cam!

That moment when you realize no one will be accidentally walking off with your custom climbing gear.

The thought process behind this setup:

Since I've gotten kind of promiscuous (in a non standard use of the term) with my selection of climbing partners. I am relying on my rack as the primary vs the box of chocolates that might show up. Therefore, I didn't want to be without my cams for 2 weeks while I send them off to Yates Gear for re-sling.

I considered the more popular, Blue Water Titan Cord, which is 5.5mm and rated to 3100lbs single strand. It's used to sling hexes and light weight cordelette, but it's slippery stuff, requiring a triple fisherman's with some tails to form a safe loop. 

The other option is Sterling Power Cord, which is also rated to 4800lbs, but with a standard nylon sheath it knots like standard perlon cord. The advantage of the nylon is once the double fisherman's sees a few anchor setups, it should be pretty permanently fixed and not require paranoia of constant knot rechecks. The downside, in double fisherman's configuration, the cord fails via sheath-core slippage. You can tie a triple fisherman's but it won't increase the failure strength by much, just change the mode of failure.

Looking at the single stem Black Diamond Camalot cams I own, it seemed like 6mm doubled over would fit in the stem, making Power Cord front runner.

Next I measured out the length I needed by doing a test run with some 5mm perlon I had lying around. It was more than 24 inches to make similar length loops as the original slings, so to make life simple for the guys at Rock and Snow (rockandsnow.com), I went with 36in. I didn't mind longer loops and this would give me more leeway to tie the double fisherman's, or even a triple fisherman's knot.

Strength wise, I'm not 100% sure on what I'll be getting. Single loop 6mm perlon on Rigid Stem Friends used in the common Gunks tie off is rated to about 8kn (per Wild Country). However, 6mm perlon is significantly less strong than Power Cord and my cord isn't single loop but double loop. Looking at various test of breaking points for the single loop double fisherman's, it seems like 50% is a fair conservative average. Using two loops should decrease force on the knot. As a very conservative guess, unless I'm completely disregarding a key variable, I expect this setup to exceed 12kN. It's very rare (though not impossible) for a top piece to see in excess of 10kN in real world use, but in excess of 12kN is pretty unlikely, and my cord failing might be the least of my concerns by 13kN.

Finally, as a finishing touch, I repurposed the old sling to maintain the color coding and also ensure I clip both strands. Finding my purple, green or yellow Camalot is as easy as the day I brought them home. 

Total cost to resling 4 cams was $15 (vs about $30), and I didn't need to part ways with them for two weeks. 

Please note, this will only work on this style Black Diamond Camalot. Do not try this on wired U stem cams. The reason is the cable can cut the cord or webbing. For those cams, such as my TCUs and Aliens, I will be having them re-slung professionally. 

Also, I do have some concerns with the long term use of Power Cord fatiguing over the edges of the stem hole, this wouldn't be an issue with Perlon. Eventually I'll mail them off, but probably not until the winter. For now I have a really unique and safe setup, that should get me through this rock season.

If you are a physics or materials science expert, feel free to send me a comment as to anything I might have missed about the safety of this setup.