3:1 bend ratio acceptable?

[Boomslang]

I know a 4:1 ratio or better is recommended for a running rope, but does anyone have thoughts and opinions on how much extra stress or life shortening effect a 3:1 bend ratio would have on a rope? If it's simply a matter of adjusting the WLL how much should it be adjusted by?

 

[Treezybreez]

I imagine it depends on the rope construction. In theory a tighter braid would see more stress than a loose braid at a 3:1. Seems like I remember this topic from a while back. Might want to do some Buzz digging.

 

[Boomslang]

Nothing definitive, but I dug and I dug and found this little gem buried in the archives:

As far as bend ratio in rope; a 1 to 1 bend ratio has 40% strength loss, 2 to 1 30%, 3 to 1 20%, 4 to 1 15%, 5 to 1 12%, 6 to 1 10% and 8 to 1 5%.

I guess that will have to suffice.

 

[Treezybreez]

Those numbers look pretty significant. is there a reference for that? That is a gem.

 

[Boomslang]

No legit reference, which is why I say they aren't definitive, but they look reasonable enough so I'll use them.

The numbers came up a couple of times in this thread and no one disagreed with them: http://www.treebuzz.com/forum/threads/broke-a-biner.3250/

 

[JeffGu]

I found those numbers some time back from a source outside the forums, and I believe they were an average for several different rigging ropes.
Rope construction is a big factor in how much core fiber damage occurs for various ratios, so obviously a 16-strand climbing rope (cover dependent) will not be as affected as a kernmantle (more core dependent) and the double braid ropes will be somewhere in between.

Still, the accuracy of the chart or the ropes tested doesn't invalidate the figures entirely, because it gives us a good feel for the price we pay for bad ratios. For any given rope design, we're probably going to see similar jumps in fiber degradation for each jump in bend ratio. In other words, the ballpark figures given will probably be plenty close enough for us to decide how important the bend ratio is to our particular application.

For me, personally, it's important. I'm not worried about the rope breaking, because I've always got enough fudge factor in there... but I try to get as much life out of a rope as I can, so I try to avoid the three things I've found that are the hardest on the rope... excess friction, excess ultraviolet light exposure and horrible bend radius configurations. Not using natural crotch methods, not leaving ropes laying out in the sun, and using pulleys with large sheaves has made a huge difference in usable rope life, in my own experiences.

 

[frashdog]

Doesn't treestuff have a stuff breaker machine.
https://www.treestuff.com/news.asp?news_id=119

 

[JeffGu]

I think they sold it to monkeylove for a hundred bucks.

 

[miniwald]

Reference for other readers. The percentages posted above (#3) might originate in the forum thread with bend ratio chart.

P.S.: I joined this forum to post a bend ratio question. While researching the topic I discovered the chart.

 

[evo]

Since the dust is blown off, how about a 12-13mm climbing rope spliced for a carabiner? This is never the point of failure (or shouldn’t be) and is less than 1:1 ratio.

 

[ATH]

I bet if you send @yoyoman some rope, something to bend it around and cash money, he'll test it and post the video.

 

[KevinS]

For years I’ve done hundreds of trees and for branches tops etc that a guy with gloves or half a wrap can hold I carry a 1” loop sling and a steel biner and a 1/2” rigging line. I’m well below my swl and my bend ratio was 1:1 it was smooth, consistent from a worker point of view it was out of the dirt and sap etc. It’s below all recommendations and swl so I’m very comfortable and fine with it