Why static SRT rope should not be used for DRT?

J

JMB6

Location
Cary
Newbie here.

I understand that using rope with high elongation at load is not optimal for SRT, because it will bounce.
On the other hand it's not clear to me why static rope with low elongation at load should not be used for DRT.
I read the argument is that it will not absorb impact at DRT climbing. But isn't there pretty much the same impact with SRT in case of a fall?

So why I should not be using static rope for DRT?
 
With two legs of line (DdRT or MRT), you are theoretically halving the rope’s elongation because the same weight is being distributed that would be on a single leg of line (SRT). This assumes you are comparing the two systems on the same anchor. Elongation or dynamic loading can be built into an SRT system with the use of basal anchors and redirects, and even more specifically through the choice of static, semi-static, or dynamic redirects. Your choice of anchors also affects a system’s ability to absorb loading, as the tree itself is designed to withstand shock, progressively, as your anchor choice moves up in the canopy (within structure safe enough to be considered for anchors).
In my opinion, there shouldn’t be a concern about using a more static line for DdRT (MRT) unless there is a concern that a climber will take a long, open fall on a very hard anchor (Even in this situation, there could be arguments made for force negation through “gear slippage”. Those concerns would be more experience based than situational for me, personally. At some point in my climbing career, I started using a very static line (yale 11.7) for everything. I train climbers on a nylon core 16-strand rope for both safety and hitch reaction.

Hope this helps.
 
I'm not 100% either but I'm pretty sure it's more in reference to the rope material construction, being less durable. Kernmantle and whatnot. I use marlow vega for the occasional ddrt and it is dreamy imo.
 
I’ve asked this question to manufacturer reps. They weren’t all that helpful.Here are the details you need to make a good decision-

Elongation is a moot point, as Yale 11.7 is more static than most kernmantles, yet has been marketed for mrs since before I joined the industry.

Construction is where things get weird, and I’ve received not so clear answers.

So, let’s start with natural crotch climbing, which is a focus on jackets. Some kernmantles handle it well, like htp. That jacket can take a beating! The teufelberger kernmantles I’ve tried have never handled it well. Yale kernmaster isn’t great for it either. They glaze easily.

As for cores, here’s the weirdness- the common explanation is that parallel strand cores lose strength at the bend in an mrs configuration. However, teufelberger sells drenaline as suitable for mrs, even though it has a parallel strand core. So....

Ultimately I think it’s up to you and your situation. Htp served me well as a dual system line, and handled mrs well in both natural crotches and friction savers. I still use xstatic in mrs, but only with a friction saver. If you’re still concerned about the issue, Samson hyperclimb/ivy or any Yale 11.7 will give you kernmantle performance while still being manufacturer recommended for mrs. Also, they won’t kink like the parallel core ropes will. You can see every point you’ve stopped along your descent on htp.

Hope that helps.
 
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Understanding the terms static...dynamic...stretch...is not easy. What arbos consider the words to mean are much different than what rock climbers consider.. How the rope makers determine those meanings for their ropes is not universal either.

As SRT was becoming established in arb work there was big concern about what might happen in case of a climber falling. What people didn't follow was that when the same rope is used in SRT the 'strength' and 'stretch' is an agreed upon unit of ONE. Now, take that same rope and use it DdRT. The strength of the system is TWO and the stretch is HALF. Forget about the fine details of decimal point calculations...this is conceptual.

When arb rope specs are compared to rock/rescue rope specs you'll see that most are in the semi-static place in the continuum.

Spending some time in the Treebuzz archives will bring up some long and indepth discussions from the past.

if there is concern that a TIP isn't strong enough to support a climber's fall then the TIP is too weak. Make a better choice of TIP. Don't choose a more dynamic rope. That is Stinkin' Thinkin' and is likely to lead to a failed TIP and injuries.
 
To me it is a moot point in regards to ropes unless very worn and theoretically should be replaced anyway if that worn.

what does matter is bridge/harness. A hard anchor with doubled static rope in a fall would put a very high load on a bridge that often isn’t replaced as often as it should be, and is so short there is no real absorption. I use a sequoia harness so it isn’t even a 1/2” line on the bridge and I must admit I don’t inspect the stitching as often as I should when busy.

but the occasions I am forced to ddrt on super static lines on trees where I could take a fall (generally when contracting on other people’s gear) I do choose a path in the tree so that if a fall occurred due to snap branch etc I will take a pendulum fall instead of a fall arrest type fall which would test the integrity of the bridge/harness...

I haven’t heard definitively about what caused the incident, but I believe there was a harness failure resulting in death only a few months ago, so I keep that as a healthy reminder to check the entire chain
Of life support equipment and what forces I am exposing it to...
 
JMB6 said:
So why I should not be using static rope for DRT?
Click to expand...
Before this goes any further its time to clean up the language. Are you asking about Double Rope Technique as in two separate TIPS and two independent climbing systems? Or...are you asking about DdRT which is the traditional arbo climbing system?

There is a very good reason I came up with DdRT over twenty five years ago. THe two systems are much different and the components are chosen for different purposes. The present use of SRS and MRS etc. is a better naming system
 
Chaplain242 said:
To me it is a moot point in regards to ropes unless very worn and theoretically should be replaced anyway if that worn.

what does matter is bridge/harness. A hard anchor with doubled static rope in a fall would put a very high load on a bridge that often isn’t replaced as often as it should be, and is so short there is no real absorption. I use a sequoia harness so it isn’t even a 1/2” line on the bridge and I must admit I don’t inspect the stitching as often as I should when busy.

but the occasions I am forced to ddrt on super static lines on trees where I could take a fall (generally when contracting on other people’s gear) I do choose a path in the tree so that if a fall occurred due to snap branch etc I will take a pendulum fall instead of a fall arrest type fall which would test the integrity of the bridge/harness...

I haven’t heard definitively about what caused the incident, but I believe there was a harness failure resulting in death only a few months ago, so I keep that as a healthy reminder to check the entire chain
Of life support equipment and what forces I am exposing it to...
Click to expand...
I’m curious- why are you climbing on other people’s gear when you contract?
 
Crimsonking said:
Gotcha. Man, that sketches me out. There are very few people whose gear I’d trust.
Click to expand...
I look at it in perspective that if there were an accident on my site (Me as groundy), or one nearby, that I would likely have to use someone else’s gear anyway to rescue, so may as well get used to the idea - but yes my own gear is preferable - especially since you need to inspect everything you are going to use and I know my own gear...
 
There is no real issue from an elongation standpoint. As we climb in work positioning systems and should not be exposing ourselves to falls with enough force to force elongation.

The issue comes more in “knotability“. Many low elongation ropes don’t hold knots well especially climbing hitches . This of course can be over come with a split tail, but them there is the issue of hand. Many low elongation ropes just don’t “feel” good to use in an MRS system.

Now going the other direction using a rope like a 16 strand arborist rope with ascenders is never a good plan.

Tony
 
I was reading a tcia book on rigging and something it talked about was the forces being applied when a rope is running over something in an MRS style:

It mentioned how when a rope runs over something creating a bend, with force applied, the fibers of the rope on the outside portion of the bend experience more of the load than the inside portion of the bend. This puts the load, more so, on the outside fibers of the rope potentially loading the sheath. The issue I see with this, is that with the construction of kernmantles, the load bearing core is encased by a non load bearing sheath. So the weakest part would be in the sheath.
24 strands on the other hand have both a load bearing core and sheath, meaning the outside fibers can take some abuse and loading.
I see that some Kernmantles are said to work for MRS and that makes me think that it has to do something with how the sheath is made or constructed. Idk though this is the only logical thing I've seen about it.
 
Tony said:
There is no real issue from an elongation standpoint. As we climb in work positioning systems and should not be exposing ourselves to falls with enough force to force elongation.

The issue comes more in “knotability“. Many low elongation ropes don’t hold knots well especially climbing hitches . This of course can be over come with a split tail, but them there is the issue of hand. Many low elongation ropes just don’t “feel” good to use in an MRS system.

Now going the other direction using a rope like a 16 strand arborist rope with ascenders is never a good plan.

Tony
Click to expand...
Tony's is the most practical answer, no one should be "taking a fall" on an arb line, if they do they're making bad decisions before the fall. In an MRS TIP blowout you're going to the ground, there's no dynamic loading happening to bridge or harness. Rope construction is not an issue there. Partial TIP blowout during base anchored SRS ascent is another matter and isn't related to the static kernmantle vs. semi-static double-braid for MRS question.

Second paragraph is also on point, it's the history of MRS climbing back to Tautline and Blake's where static kernmantles are a solid no go for those hitches. With split-tails it doesn't matter. Poor knotability with static kernmantles is an additional PIA beyond the hitch issue.

As far as durability goes, you will dramatically shorten the service life of any construction line climbing MRS without cambium/rope protection, it's just a matter of degree. I've wrecked a perfectly good 1/2" 16-strand in a gnarly black oak union/TIP climbing without cambium protection.

Sterling HTP does have an awesomely durable cover but as mentioned the core of the line is unfriendly to SRS multicenders so not a strong choice if you want versatility out of your line.
-AJ
 
moss said:
Tony's is the most practical answer, no one should be "taking a fall" on an arb line, if they do they're making bad decisions before the fall. In an MRS TIP blowout you're going to the ground, there's no dynamic loading happening to bridge or harness. Rope construction is not an issue there. Partial TIP blowout during base anchored SRS ascent is another matter and isn't related to the static kernmantle vs. semi-static double-braid for MRS question.

Second paragraph is also on point, it's the history of MRS climbing back to Tautline and Blake's where static kernmantles are a solid no go for those hitches. With split-tails it doesn't matter. Poor knotability with static kernmantles is an additional PIA beyond the hitch issue.

As far as durability goes, you will dramatically shorten the service life of any construction line climbing MRS without cambium/rope protection, it's just a matter of degree. I've wrecked a perfectly good 1/2" 16-strand in a gnarly black oak union/TIP climbing without cambium protection.

Sterling HTP does have an awesomely durable cover but as mentioned the core of the line is unfriendly to SRS multicenders so not a strong choice if you want versatility out of your line.
-AJ
Click to expand...
Htp is unfriendly to srs multicenders???

I've climbed on a HH for years on it. Just ordered more.
 
Sprucinator said:
I was reading a tcia book on rigging and something it talked about was the forces being applied when a rope is running over something in an MRS style:

It mentioned how when a rope runs over something creating a bend, with force applied, the fibers of the rope on the outside portion of the bend experience more of the load than the inside portion of the bend. This puts the load, more so, on the outside fibers of the rope potentially loading the sheath. The issue I see with this, is that with the construction of kernmantles, the load bearing core is encased by a non load bearing sheath. So the weakest part would be in the sheath.
24 strands on the other hand have both a load bearing core and sheath, meaning the outside fibers can take some abuse and loading.
I see that some Kernmantles are said to work for MRS and that makes me think that it has to do something with how the sheath is made or constructed. Idk though this is the only logical thing I've seen about it.
Click to expand...
You got the basic idea right, but some of the terminology used is muddied. A kernmantel has a load bearing core, can be parallel or braided, with a cover to protect it and also helps with the load some, on the outside of the eye like the core. Double braid might be a better term for the 24 strands term.

Since the parallel strands going around the eye are only being loaded around the outside, the lack of helping continues past the eye. With braided, the nonhelping strands on the inside of the eye are mixed with the outside strands of the eye that are being loaded.
 
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