Interesting rope drop test

[Burnham]

Black Diamond recently ran some drop tests to quantify to a degree a known characteristic of ropes...that is, a rope increasingly loses elasticity across a series of drops/falls that happen one closely following another. These guys were looking at it from the perspective of sport rock climbers, which doesn't translate to how we tree climbers use our lifelines...but it occurred to me that it does relate closely to how we use our rigging lines.

The bottom line is, repeated loads cause the rope to lose the ability to stretch unless it's given time to rest between the loads. Now we can't be putting our rigging lines down for a 2 hour nap after each catch , but we should be considering this phenomenon when we think about the loads we're putting on our rigging gear in the course of a removal.

Think about it...as we get further down the spar, blocking off nuggets with negative rigging, we tend to be increasing the loads as we get into bigger wood, all the while our bull rope is getting less stretchy with each subsequent catch.

Something to consider.

Here's a link to the BD test report.

http://www.blackdiamondequipment.co...tent=main+promo&utm_campaign=qc+lab-rope+rest

 

[MasterBlaster]

That's somethings my brain's never thought about. Very interesting!

 

[Husabud]

Since I started using the Porty and blocks to grab my chunks I have thought a rope would endure some "unknown" stresses during a removal. I have always had my groundie keep the chunk end when it goes down and send up the loose end to me. Just made sense to keep nobody waiting as well. I took one of Sherrill Tree's rigging seminars with Ed Carpenter last year and we drop tested, he has his own drop tower, a bunch of ropes and biners to get a feel of what we do to our ropes and equipment daily. Very intimidating to say the least. I guess I may have been right in my thinking to continuously flip my rigging line each drop. Thanks Burnham.

 

[sotc]

Less stretchy and also getting shorter which makes it more intense

 

[CurSedVoyce]

I have a tendency to switch my lines during a removal. Go to larger diameter lines as I move down the tree. If I have to take a large top, I will refrain from using the 1/2 line when I start. I mostly work from 1/2 up to 5/8ths as I progress. Of course I have a tendency to cut small as well

 

[Al Smith]

I have tried in vain to attempt to find the study of rope stress the coast guard did some 40 years ago where my ex wife worked as a research assistant .

 

[Husabud]

http://www.uscg.mil/directives/cim/16000-16999/CIM_16500_21.pdf

This may be related Al. I will ask a few friends if I can get ahold of it. It's nice to live on the coast sometimes, er uh most times.

 

[Al Smith]

That isn't it unfortunately although it is a wealth of info .I did see one item I kind of question where it mentions 3 strand nylon having a max elongation of 40 percent .Perhaps I was mislead to think 70 percent or perhaps that might have been an older figure which later proved to be unsafe .

The report I refered to was a research project which was assigned to two senior cadet honor students .It covered every known make and style of rope made at that time which was deemed fit to be in marine use .Although double braid was not a popular style of line at that period of time it too was covered .

 

[treesmith]

I have a tendency to switch my lines during a removal. Go to larger diameter lines as I move down the tree. If I have to take a large top, I will refrain from using the 1/2 line when I start. I mostly work from 1/2 up to 5/8ths as I progress. Of course I have a tendency to cut small as well

I tend to switch to larger lines as I get lower as well, Stephen. Another thing I do is use shorter lines. I have a couple of 5/8" Stable Braid that are ~100' long, and a couple of 3/4" lines that are ~75' long. My thinking is, why use a 150' or 200' line to lower chunks off a spar that's only 50' tall? Lotsa slack laying around in the way, and I'd rather ruin a 75-footer than a 150.

 

[CurSedVoyce]

Ditto... I try to use only as long a line as I really need with a little extra for a redirect or what not.

 

[SouthSoundTree]

With these things in mind, when rigging down a whole trunk, it can make sense to place a block at the bottom of the tree, and redirect to another tree for the lowering device to increase the rope in the system, until the proximity to objects below disallows the extra stretch.

I like switching ends, as it makes for less climber downtime and more even wear.

 

[Underwor]

I learned about the stretch of 3 strand nylon in Davey's climbing school in 1967. One of the instructors had a 120' chunk he climbed on. He let me try it. One hint after a 50' descent at just under free fall speed, be sure to let go of the tautline more than 3 or 4' off the ground. It hurts when your butt bounces off the ground and then back up a couple feet. The manila hemp we were using to learn on did not have near that stretch, just those great wisps of smoke coming off of it during a fast descent.

 

[treesmith]

Oh yeah...that's another reason I use short lines...easier/quicker to swap ends.

 

[MasterBlaster]

I climbed on manilla for a spell. I remember thinking "Damn! This is sure more flexible than the three strand esterlon I'd been climbing on!"

Kinda rough on bare hands, though...

 

[Al Smith]

Oh my you guys' got more ballz than me .I have a hard time trusting any rope let alone manilla .

 

[wiley_p]

Hysteresis. Though the larger issue is permanent elongation of rope fibers, thereby negating some of the elasticity of the rope.

 

[Climbinfool.]

All ropes have a drop (load cycle) I wish someone would come up with a chart that showed for example 1/2" double braid would take a 500lb shock load and how many times before it's done in.

 

[Peter]

Thats the point of having a safe working load set by a proper safety factor.

Never exceed the SWL= many Cycles To Failure, ie rope will wear out before you get anywhere near breaking it.

Exceed SWL even once, CFF is destroyed and its only a matter of time before premature failure, usually under a shock load.

I have first hand experience of breaking heavy double braids that have been abused. I used another contractor's rope to rig down a stem, and snapped it twice in a row taking relatively small sections, he told me afterwards that the rope had been used to pull a truck out with a large excavator.

 

[Climbinfool.]

Thats the point of having a safe working load set by a proper safety factor.

Never exceed the SWL= many Cycles To Failure, ie rope will wear out before you get anywhere near breaking it.

Exceed SWL even once, CFF is destroyed and its only a matter of time before premature failure, usually under a shock load.

I have first hand experience of breaking heavy double braids that have been abused. I used another contractor's rope to rig down a stem, and snapped it twice in a row taking relatively small sections, he told me afterwards that the rope had been used to pull a truck out with a large excavator.

I understand, but I don't think there is one person in here who hasn't gone over the SWL especially when negative blocking at the lower end of the trunk.

 

[gf beranek]

Yale was doing some drop load tests and TCI. 200 lbs dropped 12 feet. By the 4th drop the half inch climb lines broke almost every time, for sure on the fifth. In comparison the 3/8 high static exotic fiber, which was 3 times the breaking strength of the half inch polyester, broke on the first drop every time.

The half inch, by the third drop, was HOT to the touch.

Pretty interesting.

 

[Climbinfool.]

wow! that is interesting. I dont know if you remember Pier Tardiff. He came up one time and we did some shock loading with half inch double braid and his Dynamometer. 250lb log 12"x6' dropped at 6' equated to almost 1200lbs just over the SWL.