Rack alternative for long drops?

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Re: Rack alternative for long drops?

Postby shibumi » Apr 9, 2012 11:12 am

Just datapointing here, but I've used a standard 6 bar rack on the longest drops I've done (1550'). Devices like the Simple and the Stop don't work well for me, I find it very hard to control my descent on longer (250'+) drops. I have 3 different 6 bar rack setups with different bar configurations and my favorite is an oversize top bar, steel second bar, and the last 4 aluminum. I have excellent control on any length drop and I keep the aluminum bars at about 1/8 to 1/4 worn which gives an optimal balance of control and heat dissipation. With gear I'm around 100kg.

What a lot of people fail to remember is that while some fraction of the friction of the descent is in the device, a large percentage of that friction is within the body of the rope itself (both inside the rope as well as the surface) and the configuration of the device affects that variable.

I general though, I agree with Allen Padgett, there's a lot that *can* be done with various devices, but that does not mean that is the best application for them.

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Re: Rack alternative for long drops?

Postby gdstorrick » Apr 10, 2012 4:58 pm

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Re: Rack alternative for long drops?

Postby Smeg » Apr 16, 2012 10:57 am

gdstorrick wrote:This thread reminded me of an exchange that I had about eight years ago, but it took me a little while to find it. Look on the ACA web site and search for the "Allp" - or try http://www.canyoneering.net/forums/showthread.php?1540-Racks-and-Trolls&highlight=Allp directly. You will find some discussions of people who preferred the Allp to the rack - "in fact, we prefer anything above a rack." Part of their problem was that they were using the Petzl rack, part seems to be technique, and part was that the Allp is also a capable long-drop device. I just reread the entire ACA "Racks and Trolls" thread and I still think it has some good comments.



What is wrong with the Petzl rack?
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Re: Rack alternative for long drops?

Postby gdstorrick » Apr 17, 2012 4:45 am

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Re: Rack alternative for long drops?

Postby ek » Apr 19, 2012 3:25 pm

Like LukeM, I've done Surprise Pit with a long-frame micro-rack, and I did not have any problems at any point. I did not have to feed the rope near the top, and I did not have trouble maintaining control as I got toward the bottom. I weighed about 140 pounds when I did that. I did not have to use the hyper-bar, but I wouldn't have had any problem using it. Unlike Luke, I did this on a 11 mm rope. (Not all 11 mm ropes are equally fast/slow though.) Anyway, I'm certainly not saying the long-frame micro-rack is as verstatile as a full (6 bar J-frame) rack, or as good as one for long drops.

LukeM wrote:
gdstorrick wrote:More precisely, AOTBE (&TNA), a longer rack can provide less friction. Rack length below the bars doesn't change friction, and one can push the bars together on a long rack. If you need more friction, changing to a shorter rack won't help (unless it is so short that there isn't room for the rope :big grin: ).

Thanks for clearing that up Gary. Looks like what I was taught about short micro racks being especially useful for heavier people (vs shorter) isn't necessarily correct. More like the longer version is especially helpful for lighter people and the shorter version is nice to save space/weight as long as you are heavy enough to rappel effectively without needing more bar spacing.

In my experience, some cavers have trouble pushing their bars up hard enough to get as much friction with a long-frame micro-rack (not using the hyperbar) as they would get with a short-frame micro-rack (not using the hyperbar). So on the one hand, I agree that the long-frame micro-rack is more versatile than the short-frame, and I'd be afraid to suggest the short-frame micro-rack for really long drops. I certainly would have had trouble with a short-frame micro-rack at Surprise Pit. On the other hand, I think that for shorter drops, the short-frame micro-rack really does provide more friction for some users than the long-frame micro-rack can provide for them.

Besides the weight of the user, another reason to use a short-frame micro-rack would be for thin ropes. But with a thinner rope, I would expect that pushing bars together would be easier, so this really would be solely a matter of weight/bulk/convenience. (I would want to try this out though, before assuming that pushing the bars together is easier for everyone with thin ropes.)
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Re: Rack alternative for long drops?

Postby eyecave » Apr 28, 2016 9:05 pm

kirk mcgregor did complete a rappel of thor using what he called a squeeze brake..... :shrug: ....the forces on the rope caused by mashing the threads of the rope resulted in a very significant (retire the rope) loss of rope strength from a single rappel... :yikes: ....the squeeze brake is a failed idea and will totally retire an otherwise new rope that it is used on in my opinion...kirk could research this if he hasn't already.....personally i don't think you can improve on a rack for long rappels....short repetitive stuff almost anything else is better, but the long ropes are best with racks...long racks... :banana: ....do not use any device that imparts stresses the rope is not designed to deal with!!!!. :boxing: ...the nylon threads that make up our rope are made for vertical weight and weighttransfer forces.....not squeezing lateral stresses coupled with vertical and weight transfer forces......i have 2000 plus feet of rope i have been told not to use by people whose opinions i respect.....squeezing the rope might never work.. :shrug: ....squeezing combined with conventional friction might do the job without the thread damage........ :shhh: ..we rely on friction for our devices...a new idea is needed....squeeze was a new idea; but not inlinewithropedesign......a way to attach something to lengthen a racks shaft and add a bar or three comes to mind..........someone could invent a suit that would fill up on descent and slow us down....a new sheath or core design that stopped the weakening effects of lateral nylon thread stress..... :shhh: ...something that would mechanically alter all or a portion of the forces involved into a more vertically centered "expression".....i am dangerously close or at the spot where my imagination becomes primary and practicality disappears. :big grin: ..and so i must stop...
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Re: Rack alternative for long drops?

Postby tncaver » Apr 29, 2016 7:56 pm

eyecave, it seems you have one heck of a LOT of rope that is perfect for pulling rocks out of cave digs, pulling stuck trucks out
of mud holes and pulling bushes up out of the yard. Maybe some of that rope is still suitable for short drops too, like 200 footers?
What do you think about that? I was lucky enough to rappel at White Side Mountain, North Carolina twice (650feet). We used a
brand new rope for both trips. That granite mountain is so abrasive that it made bad places on the ropes in just two days of rappelling. But those bad spots were only in a couple of places where the rope rubbed on the granite. The rope obviously could be
cut into shorter lengths that would still be adequate for most pits in TAG. It would be a terrible shame to have 2000 feet of rope go to waste. Maybe you could provide some of that rope for the Sewanee Cave Fest with a disclaimer that the rope has been used
on a long rappel. :grin:

I have another idea for you also. Why not have a section of your rope tested? I bet you have friends at PMI that could test your
rope for you to see how much strength your rope still has. You might be surprised how strong it still can be even after a compression
type rappel device has been used and also for older rope. I bet everyone on Cavechat who does vertical would like to know the results
of such testing. I know I would. :kewl:
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Re: Rack alternative for long drops?

Postby l lambert » Apr 29, 2016 9:43 pm

Descending the piece of rope eyecave is talking about after Kirk had traveled it I came across two suspect lumps in rope three hundred feet apart and nearly 2800 feet off the deck. I'm with eyecave, rack is the way to go and that rope is screwed. :doh:
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Re: Rack alternative for long drops?

Postby eyecave » Apr 29, 2016 9:59 pm

pmi tested the rope and found a significant change in the breaking strength of the rope that was great enough (i will try to refind the letter) that their advice was to retire the rope... :doh: ...which i did several years later... :shhh: ....what i want to do with the rope is send a shipment to the people of pangnirtung in nunavut, they use rope daily and generally don't have a lot of money.. :woohoo: ...my memory is that we ordered the rope with extra core strands and it tested...between 7000 and 7500 and afterwards at 6000......steve hudson studied the core strands with a microscope and believed the squeeze device deformed and weakened the core strands due to the lateral pressure and lateral deformity .. :down: .....the core is designed to withstand stretching in a linear fashion......severely bending or just bending a rope causes it to lose strength .......squeezing with enough force to be able to accomplish a rappel damages it just like a severe fall or too much weight will... :big grin: ..maybe more.........
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Re: Rack alternative for long drops?

Postby eyecave » Apr 29, 2016 10:08 pm

tn caver.......when rigging a big wall, specially on granite!........ever so often pull up ten feet or so and change those wear points.....or lower ten feet or so......can't avoid'em......cave rope spoils us with its toughness and we lower our guard.. :sadbanana: ...i dug a great big burr on my virgin first 300 doing a pendulum in neversink and i never did cut that rope...that burr spoke to me everytime i went past it...."be careful danny"..... :wink: ..
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Re: Rack alternative for long drops?

Postby CaverCarl » Nov 8, 2016 12:08 pm

I've tried a Scarab. It got very hot on a short rappel.


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Re: Rack alternative for long drops?

Postby CaverCarl » Nov 8, 2016 12:19 pm

I've tried the Scarab on a short rappel, (under 100').
It got very hot. I don't plan on using it again.


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Re: Rack alternative for long drops?

Postby snoboy » Nov 10, 2016 1:59 pm

I don't know if that is a picture of the Scarab as you used it, but it is rigged incorrectly. Have a look at the manual, and you will see that the rope is supposed to wrap over a horn away from the carabiner first. That could reduce the friction a little. The manufacturer even says you can damage the device by using it that way. :shrug:

The Scarab is the only device I am aware of that has actually had temperature testing done, where they pulled a lot of rope through it at 10m(33ft)/minute and measured the temperature... It did hit 100°C (212°F) which is hot enough to burn you obviously, but still well under melting point of nylon or polyester

One device was tested by pulling over a mile of dirty rope through it under rescue sized tension, with temperature reading thermocouples being monitored at several locations during pulls. At 2kN of tension, and a lowering speed of 10M per minute, the Scarab® maintained a frame temperature at about 100 degrees C. To our knowledge, the Scarab® is the only descent control device to have been tested to this degree.
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Re: Rack alternative for long drops?

Postby Tim White » Nov 14, 2016 8:52 am

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Re: Rack alternative for long drops?

Postby eyecave » Nov 14, 2016 9:15 pm

i have never seen (before) or used a scarab... :cavechat: ...but lifting a really long rope over the two upper ears could be a difficult problem.... :down: likewise rappelling with a heavy load?... maybe not possible without using a complex lifting designed thingy....simply taking the first bend and getting the bar on wouldn't be easy.... and....with a really long rope, not possible... :yikes: ..could be done with scarab off your seat and attached to you after getting the scarab bar on the rope...........but then a heavy rope awaits...and you gotta bend it over that first ear.......maybe a super strong person or when using a long rope that is more manageable and not too heavy to lift.. :down: ...then maybe one could twist and thread the device onto the rope... :question: ..at least ya couldn't drop it if you got the bar on..... :laughing: ....i wouldn't use this in place of a rack on a really long drop.........but for drops where the rope weight remains less than that the roperider can handle....looks like this would work.......certainly smaller and lighter and probably more compact....gotta use it.........look like a safe device to get on rope.....engage all four ears and the bar and just sit down....and then start taking the friction devices off......probably need to be aware of rope moisture and mud content.......don't forget ice........... :argue: ...in a loss of control situation rope management would be more complicated than a rack....another thing and keep in mind i know nothing about the device....we all know that it is possible to crater in with all bars engaged correctly in a rack used perfectly.....with all four ears in use is it possible to not have enough friction to slow down enough..i already know its probably very rare and caused by rope diameter or condition..probably the same stuff that cause other devices to fail....but what about other characteristics in accidents using this device...things like how easy it would be to get nylon rubbing across or against nylon........ :yikes: .......lets talk about its soul.. :doh: ....oh crap.....we all gotta buy one and use it for a while.... :sadbanana: .....
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