my SRT rig

[Bounce]

When you use a prusik to back up an ascender, the prusik doesn't get tight (unless the ascender were to fail). It is tied onto the rope above the ascender, so the ascender advances it for you. If the prusik knot were to be loaded and tighten up and become difficult to move, you would be right - there would be no point in using ascenders then.

Regarding the potential for shock load, look at how the tether goes from the saddle, up to the handled ascender, and then down to the Croll. If the handled ascender fails, the person will fall until the tether is tight again pulling from the croll. This short free fall would generate a shock load. Otherwise, I agree - a Croll makes a great backup for the handled ascender instead of a prusik.

I understand that you are connecting the Croll directly to your harness with the keychain biner, but those things are not even rated. If you are considering the keychain biner to be what connects your backup ascender to your harness, maybe it should be a real rated carabiner?

 

[tophopper]

Except the Croll has some pissant little breaking strength rating...well less than 10kN if memory serves.

I use one, too...fwiw. But I don't really trust it as well as I'd like.

Show me any ascender that meets our minimum strength rating. Most are rated around 15kn

 

[PCTREE]

Wraptor

wont cut the rope at 700lbs force either....

I personally dont think those handled ascenders should be used in tree work as there is so much likelyhood of drops. 7 foot drop with toothed cam ascender can sever the rope (200lbs climber) and dont think that prussik backup is going to tighten up and grab that 2" stub of rope.

Obviously I might be a tad biased here

 

[tophopper]

I wasnt thinking about the wraptor Paul....

but since you mentioned it, I recently borrowed one for a few weeks from tnttree, and I dont remember seeing any rating information on it. Did I miss it or is not labeled on the unit? If not, dont you think it should be.

Great tool btw! Wish I could swing one.

 

[Burnham]

Show me any ascender that meets our minimum strength rating. Most are rated around 15kn

Agreed...but the Croll stands out as being rated really low...4.2kN to 6.5 kN, small diameter to large diameter ropes it accepts, which seems to be 8mm to 13mm.

It's a moot point, 'cause as we all know toothed ascender devices will shred the rope at dynamic loads lower than these.

 

[Bounce]

It's true that most ascenders have sub-par breaking strengths, but I feel like this is a smaller problem than the risk of the toothed cam cutting the rope, because that can happen before the breaking strength has been reached. If it breaks at 15 kN, but cuts your rope at 10 kN (just making #'s up here), then the breaking strength is a moot point.

You are absolutely right Paul - my prusik backup is probably not going to grab the 2" stub of line if the ascender chomps through the rope. I better rethink things. I decided to use a prusik to back up my ascender instead of another ascender because I thought that if the first ascender cut through the rope due to a fall, then wouldn't the 2nd one also do the same? It seemed to me like a prusik stood a better chance of actually being a backup, but not if it's only 2" above the handled ascender.

 

[Bounce]

Hey Paul - I was wondering the same thing about whether or not the Wraptor should have a breaking strength printed on it. It seems like it might slip before it broke so the breaking strength might not actually be achievable, but it would put some people's minds at ease. On the other hand, this could be construed as misleading advertising too, if it's impossible to achieve it's rated breaking strength. I can see arguments both for and against. What do you think?

 

[PCTREE]

We cannt afford to have them rated at this point, however I can tell you that we did a lot of drop tests with them and due to the stretch in the rope were not able to get one to fail. On my test bed we pulled till 4250 at which point the rope jacket was severed, we are required by ansi to hold 3100 so are good for that. We were originally quoted $12k to get ansi and CE stamps but now nobody will test them as they dont know what to test them as, as there are no specs for motorized rope ascenders. I need to get back on that I guess.

FWIW at 4250lbs of force with our harnesses your spine would snap anyway so I think we are good. The CMI Ropewalker is rated at 7500 but in my tests it severed the rope at 2000 so IMO this rating isnt very relevant. This was why we switched from a tear-away attachment for the backup lanyard to a solid one as we never want the CMI to see the force Unless of course the Wraptor pawl system malfunctions (which has never happened).

 

[tophopper]

It's true that most ascenders have sub-par breaking strengths, but I feel like this is a smaller problem than the risk of the toothed cam cutting the rope, because that can happen before the breaking strength has been reached. If it breaks at 15 kN, but cuts your rope at 10 kN (just making #'s up here), then the breaking strength is a moot point.

Not always the case.....

many people are rigging their Ddrt system to the handle or frame of the ascender to work off of after opening the cam and allowing a hitch above to secure everything to the line with a stopper knot below. This is all fine and dandy but essentially they are tied into the ascender handle, which could break from being overloaded during use (work climbing).

 

[PCTREE]

Sean, just saw your post. I guess we could wrap a cable around the hub and pull till it broke to get its breaking strength, however as I stated I see little relevance to this test as the rope cannt ever exert that force.

Thoughts anybody????

 

[tophopper]

We cannt afford to have them rated at this point, however I can tell you that we did a lot of drop tests with them and due to the stretch in the rope were not able to get one to fail. On my test bed we pulled till 4250 at which point the rope jacket was severed, we are required by ansi to hold 3100 so are good for that. We were originally quoted $12k to get ansi and CE stamps but now nobody will test them as they dont know what to test them as, as there are no specs for motorized rope ascenders. I need to get back on that I guess.

FWIW at 4250lbs of force with our harnesses your spine would snap anyway so I think we are good. The CMI Ropewalker is rated at 7500 but in my tests it severed the rope at 2000 so IMO this rating isnt very relevant. This was why we switched from a tear-away attachment for the backup lanyard to a solid one as we never want the CMI to see the force Unless of course the Wraptor pawl system malfunctions (which has never happened).

So its been tested, but is not rated. Doesn't that mean it isn't rated?

 

[PCTREE]

I need to look into this more. A lot of Co.s test their own gear and as long as you document it it is valid, however I still have yet to be told by any agency what standards they need to be tested to.

However after much inhouse testing I am confidant they are the safest "mechanical" ascender. I could see that a mere hitch may be safer still as it will slip insted of compromising the rope. My first design would slip at about 600lbs but that is not acceptable to the ansi standards for "Personnel hoists" which are only allowed to move 4" when loaded with 3100lbs (single person hoist)

 

[Bounce]

Personally as somebody who uses these products myself, I would want any tests to be done in a real world scenario with the unit hooked up and attached exactly as it would be in real life. I would want to know exactly what happens at what levels of force. The problem is that there are a bunch of stupid safety standards that say things like "minimum breaking strength must be at least 5000 lbs". These kinds of standards force the manufacturers to test it in a way that it would never be used. The CMI Ropewalker ascenders for example are the only ascender I know of that meets the 5000 lb ANSI Z133 breaking strength standard, but as you mentioned they cut the rope at 2000 lbs. It's completely absurd to even talk about a 7500 lb strength if they cut the rope at 2000 lbs.

Paul - I would say to test it in a real world scenario and then simply report what happens. While this would not satisfy ANSI, it's probably what end users want to see.

 

[DMc]

Show me any ascender that meets our minimum strength rating. Most are rated around 15kn

I notice you guys are pretty darn sharp about using the qualifiers "most" or "some" with regards to the ratings of mechanical ascenders. I pulled the following information from Bailey's site and is one of the reasons for my choice of this ascender.

"Note: A new Unicender slips on the rope at 1200 lbs, and less as it wears. This is a safety feature for the tool and the user. When exposed to a shock load such as a fall, the Unicender slips before it breaks. This slip also limits the shock to the user. The Unicender is not a fall arrest tool, and should be retired after a hard fall. The Unicender climbing tools ultimate breaking strength is 7,000 lbs. That is 2,000 lbs more than the industry standard."

Dave

 

[tophopper]

I wonder what a "hard fall" is defined as?

 

[PCTREE]

It occurred to me that the Unicender is safer to my knowledge as it slips like a hitch when dropped.

Sean, like this you mean

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Carl wondered why he got a "deal" on his unit....

 

[KentuckySawyer]

Regarding the potential for shock load, look at how the tether goes from the saddle, up to the handled ascender, and then down to the Croll. If the handled ascender fails, the person will fall until the tether is tight again pulling from the croll. This short free fall would generate a shock load. Otherwise, I agree - a Croll makes a great backup for the handled ascender instead of a prusik.

I understand that you are connecting the Croll directly to your harness with the keychain biner, but those things are not even rated. If you are considering the keychain biner to be what connects your backup ascender to your harness, maybe it should be a real rated carabiner?

Sean,
You are not understanding how the Croll attaches to my harness. The HMS Climbing Technology carabiner that I showed on the Croll goes directly to my bridge/ring. Similar to this setup:

The key biner is used for a non-life support purpose. Its what Taylor is using the bungee cord for in the above image. It just advances the Croll up the single line. There is little to no opportunity for shock loading. Do you understand now?

 

[Widow Shooter]

I like that set-up Cory, gonna try it out

 

[CurSedVoyce]

OK guys.. might as well post mine.. Still have to make that walker set up with bungees. This works fine for now as my "frog walker/tree frog"
Tear it up
The HC and VT are connected to the D on my saddles bridge via biner. The handled ascender has the foot loop. The Pantin is the other foot..
Sorry thee pics did not come out well

 

[Bounce]

Yep, I get it now. You are right - there is no potential for shock loading. That is a well thought out set up you have there!

 

[Burnham]

Here's a link to a nearly 3 year old thread...took me a while to find it, been looking off and on since this thread started.

http://gypoclimber.com/showthread.php?9950-B-s-version-of-Sherrill-s-Tree-Frog