6mm accessory cord?

cmqr9001 Black wrote:

I have a bit of a differing opinion on this. I use this New England 6mm nylon accessory cord bought from REI and it is by far my favorite cord to use because of how supple it is, easy to tie knots, and bites reall well as a prusik (better than 7mm in my opinion). The MBS is only 7.3kn, but assuming a typical 3-piece trad anchor, that’s 6 strands in the system for about a 44kn strength. Now the knot will probably reduce this by about 40% or so but that’s still puts it a around 26kn, and I tie in with the climbing rope. 

That is definitely not true. Modern research is showing that equalization doesn't distribute the load that way, and it's likely that in a fall only one piece will be loaded. This means that you could be in a situation where i.e. a 8kN fall would break one strand, then the next, then the next (if no force is dissipated between strands breaking). Of course, an 8kN fall is not likely, but put some wear on that cord and account for strength loss due to knots and you're easily down into the range of 3kN where breakage of all three strands one by one is very possible, especially in a factor > 1 fall.

I'm not saying don't use 6mm cord. If you want to take that risk, go for it. Just know what risks you're taking.

cmqr9001 Black wrote:

I have a bit of a differing opinion on this. I use this New England 6mm nylon accessory cord bought from REI and it is by far my favorite cord to use because of how supple it is, easy to tie knots, and bites reall well as a prusik (better than 7mm in my opinion). The MBS is only 7.3kn, but assuming a typical 3-piece trad anchor, that’s 6 strands in the system for about a 44kn strength. Now the knot will probably reduce this by about 40% or so but that’s still puts it a around 26kn, and I tie in with the climbing rope. That’s plenty strong for me. If I come close to 26kn I have bigger problems to worry about, like why is my hip bone separated from my spine etc etc. 

https://www.rei.com/product/767610/new-england-6mm-accessory-cord-package-of-30-ft?CAWELAID=120217890000791500&gclid=CjwKCAiApo3SBRA4EiwAty8i-j4y-icq7N7oqHyWWQHRTjh2kL8ACRVBuU1qqCvcZnENJPsWgEF2IhoCH_MQAvD_BwE

I´d be thinking differently when two of the pieces have failed and I knew the cord was a year or two old or maybe it was a bit longer and maybe I hadn´t actually taken as much care of it as I could and the week before it was used to hold my tarp up and the rating system for cord and tape doesn´t reflect it´s strength over the average karabiner and........

For a top rope anchor material, your primary concern should be durability.   A top rope anchor will be weighted and unweighted frequently as you and your friends work a problem.  This weighting & un-weighting causes the material to rub against rock edges, and can cause sheath damage.  On top rope, any potential damage will go unnoticed by the climber & belayer until the climber tops out (assuming the climber can/does top out).

This is in contrast to multipitch climbing, where the belayer can keep a constant eye on the anchor while he/she brings up the second.  if the belayer sees a problem with something rubbing, he/she can take care of it right then.  However, strength ends up being more significant in multi-pitch climbing because the primary purpose of a multipitch anchor is to protect against the worst case scenario of a factor 2 fall.

Mainly I just wanted to communicate the fact that just because a TR anchor isn't subjected to a high load doesn't mean they should be taken less seriously than other anchors.  In fact they should probably be taken more seriously. 

Personally, I either use 7mm nylon cordelette for my TR anchors, or I use an old 9mm rope.  I don't really know how durable smaller cords are, but I don't want to find out.

David Kerkeslager wrote:

That is definitely not true. Modern research is showing that equalization doesn't distribute the load that way, and it's likely that in a fall only one piece will be loaded. This means that you could be in a situation where i.e. a 8kN fall would break one strand, then the next, then the next (if no force is dissipated between strands breaking). Of course, an 8kN fall is not likely, but put some wear on that cord and account for strength loss due to knots and you're easily down into the range of 3kN where breakage of all three strands one by one is very possible, especially in a factor > 1 fall.

I'm not saying don't use 6mm cord. If you want to take that risk, go for it. Just know what risks you're taking.

Okay it seems I may have a misunderstanding of this then, if someone could help clear this up for me I’d appreciate it. 

In my understanding, even though the MBS is 7.3kn, you have two strands in each leg of th anchor. I realize that the bend radius at the carabiner will reduce this (anyone know how much??), but theoretically you should have somewhere around twice the strength of a single strand in each leg. 

It is also my current understanding (point it out if I’m wrong here please) that assuming relatively safe angles (<60*) between each leg that you should more or less have 3x the strength of each leg, but probably a little less from the angles. 

Then take into account the fig8 knot and reduce the whole system by 40-50% ish. 

This is the thought process I was using, I’d love for someone to point out where I’m incorrect. I understand that this is a super idealized setup, perfect equalization isn’t really applicable, and you have to consider the weakest piece in your system. 

*That being said*, at the very least wouldn’t it be safe to assume your anchor is as strong as a single leg, so in this case ~8.4kn ish for a 6mm 7.3kn MBS cord? (7kn X 2 strands) * (0.6 strength with knot). 

I’d love some feedback! Thanks!

cmqr9001 Black wrote: 

*That being said*, at the very least wouldn’t it be safe to assume your anchor is as strong as a single leg, so in this case ~8.4kn ish for a 6mm 7.3kn MBS cord? (7kn X 2 strands) * (0.6 strength with knot). 

This part is correct.

cmqr9001 Black wrote:

Okay it seems I may have a misunderstanding of this then, if someone could help clear this up for me I’d appreciate it. 

The biggest thing you are missing is that equalization is a "myth" - your three piece anchor is never really equalized. When weighted, one piece is taking the lion's share of the load, and typically no more than two pieces are taking a large share of it.  Read this: American Alpine Club anchors article

Mark Ra wrote:

I believe this just means not for use as a dynamic climbing rope. The Tendon 7mm accessory cord does appear to be rated to 13kn for static use. 

Yes. You’re right. 13kn rated. This means generally can be use as a quad anchor right?

Reviving this a bit. I have a mechanical engineering friend who works for ClimbTech and I’m going to have him break test my 6mm cord, one leg at a time in how it would be tied in a typical 3 piece trad anchor. From talking to him he suggests that the cord will probably break at the bend in the carabiner, which means the leg should break 80-90% of twice the strength of the cord, so with my 7.3kn cord we’re going to expect a ~11-13kn breaking strength for an individual leg of the anchor. He suggested it may break at the knot above the masterpoint instead first, but doubts it because of how many strands go into making the fig8 or overhand and increase the bend radius. I’ll post the results of the experiment when it’s all said and done on here. 

cmqr9001 Black wrote:

Reviving this a bit. I have a mechanical engineering friend who works for ClimbTech and I’m going to have him break test my 6mm cord, one leg at a time in how it would be tied in a typical 3 piece trad anchor. From talking to him he suggests that the cord will probably break at the bend in the carabiner, which means the leg should break 80-90% of twice the strength of the cord, so with my 7.3kn cord we’re going to expect a ~11-13kn breaking strength for an individual leg of the anchor. He suggested it may break at the knot above the masterpoint instead first, but doubts it because of how many strands go into making the fig8 or overhand and increase the bend radius. I’ll post the results of the experiment when it’s all said and done on here. 

Wow. That would be great man! Looking forward for the results. 

Auden Alsop wrote:

Should be fine, no way you should exert anything near 8.4kN toproping. I've used 4mm personally in the past, not necessarily recommended.

Oh god

I use 6mm nylon for my cordelette. Wouldn't make a TR anchor with it though just because it will wear out so fast it would be a waste of cord. I use static rope for my TR anchors because its cheap, very abrasion resistant. 

In all these threads related to this topic, what I fail to find is an objective number for minimum breaking strength at the master point.

Assuming for all other factors being ideal or near ideal.

almost as if there is a huge gap in research into this area.

when someone says 7 mm cordage is sufficient, what atleast one should hope to get is the recommended MBS for anchor building. 

Avery Angarshli wrote:

In all these threads related to this topic, what I fail to find is an objective number for minimum breaking strength at the master point.

Assuming for all other factors being ideal or near ideal.

almost as if there is a huge gap in research into this area.

when someone says 7 mm cordage is sufficient, what atleast one should hope to get is the recommended MBS for anchor building. 

That's because if anybody actually has those numbers, they aren't sharing. But there are thousands of climbers out there using 7mm cord so if it wasn't sufficient then we would have tons of climbers decking every day.

Additionally, it's impossible to estimate the force of a fall on any non-brand-new rope because all ropes lose their elasticity with use and (depending on who you ask) age.

I personally use 6mm cord for my cordalette and haven't had any issues, although I typically keep it pre-tied in a quad so maybe mine isn't the best example.

Avery Angarshli wrote:

In all these threads related to this topic, what I fail to find is an objective number for minimum breaking strength at the master point.

Assuming for all other factors being ideal or near ideal.

almost as if there is a huge gap in research into this area.

when someone says 7 mm cordage is sufficient, what atleast one should hope to get is the recommended MBS for anchor building. 

I was taught that your anchor should be able to withstand 5000lbs of force. I'mnot sure how scientific this number is, but if you do the math, you see that 6mm cord isn't quite strong enough, while 7mm cord is.  

jg fox wrote:

The AMGA recommends a 7mm cord due to it's strength and possible improvement on durability. In fact they only teach with 7mm cord and I bet the guy teaching was student of one of their courses.  Will Gadd recommends 8mm instead for ice climbing.

What was will gadds rational for 8mm in ice climbing(link by chance?)?  In general it is subjected to much less abrasion, though I guess being wet can cause some weakness.   I have never in my life seen anyone use 8mm though it happens I am sure.   Either way, people are not dying from their 7mm, or even 6mm anchors from what I can see........

Avery Angarshli wrote:

In all these threads related to this topic, what I fail to find is an objective number for minimum breaking strength at the master point.

Assuming for all other factors being ideal or near ideal.

almost as if there is a huge gap in research into this area.

when someone says 7 mm cordage is sufficient, what atleast one should hope to get is the recommended MBS for anchor building. 

That´s because the strength at the master point isn´t the relevant criteria, it´s just a by-product of whichever way you rig your anchor. It´s the strength at the individual points that matters and the various recommendations are around the 6-8kN level.

Nick Sweeney, your teacher may have been using the requirements of the arbor culture world for the 5000 lbs breaking strength.  The ANSI standards are 5000 lbs for gear and 5400 lbs for rope when doing tree work.

Nick Baker wrote:

What was will gadds rational for 8mm in ice climbing(link by chance?)?  In general it is subjected to much less abrasion, though I guess being wet can cause some weakness.   I have never in my life seen anyone use 8mm though it happens I am sure.   Either way, people are not dying from their 7mm, or even 6mm anchors from what I can see........

A quick google search isn't finding what I read several years ago.  I remember he preferred it for the strength holding because of the potential for high force falls on ice.  He said he desired to make anchors strong enough to hold his Chevrolet pick up.

FWIW for SPI they specified 7mm nylon cord for cordelletes.

jg fox wrote:

A quick google search isn't finding what I read several years ago.  I remember he preferred it for the strength holding because of the potential for high force falls on ice.  He said he desired to make anchors strong enough to hold his Chevrolet pick up.

Weird, I tried Googling before asking and wasn't able to find anything either. The idea that fall factors and forces are higher in ice climbing also does not make a whole lot of sense to me particularly as climbers are more likely to be using twin ropes on ice which have lower impact forces than normal climbing ropes.

Whateves.   I use sewn dyneema slings for everything but leaving rap thread usually anyways.   No water absorbtion and plenty of strength.