Mechanical rope grabs for rigging

[Tom Dunlap]

There are arbos who use mechanical rope grabs in rigging systems and this has become an accepted practice. To me, this is completely wrong. The Gibbs ASCENDER and the CMI variation are meant to be used for ascending ropes or in controlled load situations. Using theses tools for rigging puts unknown, and generally, large loads on them. While the tools will probably not break, they will slip and grab possibly damaging the rope they are running on.

Using a rope tool for an attachment it a better idea. If the load causes the adjuster to slip and grab ther base rope will not be as likely to be damaged. In rescue rigging they use backups all of the time. Double and sometimes triple tensioners.

Having some Tenex eye on eye slings of various diameters to match up with your rigging lines would be a safer procedure. Besides being cheaper, they're easier to adjust than mechanicals too.

Tom

 

[Kneejerk Bombas]

Tom, you make good points. A gibbs can be replaced by an eye on eye piece of Tenex and a carabiner and a fair lead pulley. It will actually work better.

That being said I have used the Gibbs for years, in different applications. I think I have 3 of them. They don't wear out like those cheap tenex polyester ropes and they don't frey and become questionable after a few hours of work.
As far as slipping on the rope and damaging it, the same line of thinking could be applied for aluminum carabiners, I mean, they can break if overloaded. Does that mean that we should only use steel?

 

[Tom Dunlap]

I'm not talking about substituting tools, the point is that tools should be used for what the engineers designed them for.

If the slings are wearing and freying I have to wonder if they are sized right and used carefully. I've used several Tenex slings and they are in great shape after a lot of use.

Spend some time learning about the practices of other rope disciplines and you'll see how dangerous some of the accepted practices of arbos really are.

Just because a practice or a tool hasn't failed isn't a good measure of the correctness of its use. This is a converse application of this reasoning. I've been wearing seatbelts since my Dad had them installed on our brand new 1960 Plymouth but have never been in an accident where I needed a seat belt. Would I stop using a seat belt? Nope, its the right thing to do.

Somewhere in my reading about using a Gibbs as an anchor I came across a test where the slip/grab load was calculated. If I could find that data, I'd referance it but its out on the web somewhere.

Arbos can learn a lot from the rope disciplines that have a long heritage of testing and practice. We are great at going out and getting the tools but we don't always bring along the techniques that to with the use of the tools. I am really amazed that more arbos aren't hurt when I see and read about what is considered SOP. Many arbo SOPs would be laughed out of the room if you ever talked with other rope users.

Tom

 

[Kneejerk Bombas]

I shouldn't matter what a device's engineer had in mind at the design table. If any tool works, in it's load range, and is safe, It may have other applications.

What other commercial industries rely so much on their ropes and gear? Window washers, construction crews, rescue workers.

I'd say we may be the leaders, but there is very little arborist stuff made, so we may need to cross equipment from other disciplines.

Perhaps I misread you, can you give an example or two of SOP's that aborists commonly use, that would be considered laughable?

 

[TheTreeSpyder]

i think that putting rigging loads on mechanical rope grabs is improper technique also. I thing the fashion that they grab the line is meant for life support loads. i beleive some are rated to cut through a 1/2"line at 2000#; so 1000 # is accepted load; i think that is too much.

Eye saw an Arbomaster demonstration where 2 healthy guys pretightened a 1/2" line into the nose of a Portawrap with a 5/1; that was hitched to rigging line with a Gibbs. They said it wouldn't have any internal/invisible line damage; the beefier guy really impacted the 5/1 with what he had................

We use prusik chords when we need to grab a rigging line. i think that the spikes in the cam of my handled acsenders would do even more damage; even making removal of the instrument tricky after being loaded.

 

[John Paul Sanborn]

on friction anchors

http://www.technicalrescuemagazine.com/arti/be.html

http://www.pushdtp.com/trm/art/be.html


for good measure

 

[Tom Dunlap]

John,

Thanks for finding the article. Very good reading. In the article they mentioned that they used a RescueCender for tightening tyroleans. That is as close a use as I could find for loading a camming, shelled ascender for rigging. Since the Gibbs is in the same group, I would consider the two tools interchangeable.

Mike wrote: "...can you give an example or two of SOP's that aborists commonly use, that would be considered laughable?"

In rescue circles these two come to mind:

*not keeping a rope-use log
*subjecting anchors with unknown strength to unknown shock loads

and for good measure
*not retiring plastic helmets after four years use [take a look at this chart for more information: http://www.spelean.com.au/BW/TM/BWtechhel.html#helmets]

Tom

 

[Tom Dunlap]

AFter being out of town it takes me a few days to get caught up on my favorite discussion forums. Kind of like peeling layers. The first layer is the best and on to the less important. Guess which site I check first? A prize for the first correct answer

This AM I checked into a really good Rope Rescue site. Life dealt us a good hand this time. There is a thread about the use of Gibbs Ascenders. If anyone is interested in their proper use and limitations, read through this whole thread:

http://www.sarbc.org/cgi-bin/postit?login=sarbc&topic=rope&order=thread&article=2561

The SARBC forum is frequented by people who make their living dealing with lives not logs. Their industry standards are set and pretty high. For better insights into rigging, keep track of what this crew discusses, you'll learn a lot.

Tom

 

[Kneejerk Bombas]

Now I understand your concern about unsafe SOP's.
I thought you may have been refering to industry wide, accepted standards, for example, those laid out by ANSI.

The site you linked had a lot of talk about the Gibbs, it all boiled down to don't overload the Gibbs. That is sound advice. It could ruin your rope, or perhaps worse. I would go one step farther, and suggest you don't overload any of your gear.

In all the applications in which I have used my Gibbs, they have never slipped or damaged a rope. You need to know the safe loads any piece of equipment can handle.

As you may have guessed I am still not convinced to take them out of service for light rigging.

 

[Kneejerk Bombas]

One more point.

In an unrelated thread Tom noted:
"There has been a little research into the loads that are required to get sliding friction hitches [sfh] to slip or fail. There was a project done in Australia that showed some of the limitations of our SFH.I talked with a friend in Canada about other research. There are some knots that slip to failure and others that slip and grab but don't fail."

This is another problem with SFHs(I assume this includes the rope tools, mentioned in your first post), the variability in the ropes used for both the hitch and the main rope, lead to thousands of different outcomes in loading applications.

The gibbs is intensively tested and I know the safe working load range.

 

[John Paul Sanborn]

I was thinking the same thing, there is composition and then wear involved how they grab.
"I don't like XX when it's new, but after a little wear its my favorote for xx hitch."

I've heard that before.

Another one of those gut understandings you need whne "Pushing the limits".

 

[Kneejerk Bombas]

Good point John.
Another thing I've noticed is the prussic ropes have a memory. If switch climbing ropes, and the new rope is slightly smaller than the last, the prussic tends to need more attention.