Thinnest rope for SRT?

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Thinnest rope for SRT?

Postby OpenTrackRacer » Jun 2, 2011 6:51 pm

We often have a need for rope deep inside a mine. This is usually to access a steep stope (area where ore has been removed) or winze (a vertical or inclined shaft). Most often the rope is used just as a safety handline on steep slopes. In rare cases one might want rappel or ascend a short distance with the rope as the only support.

We've been carrying around a 50' length of 11mm PMI Pit Rope. It works but it's very bulky. I'd like to find something smaller that would be easier to transport. I've seen some people just use accessory cord (rated somewhere around 1,600 pounds MBS) but that's obviously not an approved application. However, it's very convenient. This is sort of a Goldilocks problem and probably not very original (although I did search and didn't find anything).

So, I'd love to hear your thoughts and suggestions!

Thanks!

Mike
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Re: Thinnest rope for SRT?

Postby Extremeophile » Jun 2, 2011 6:59 pm

For exploration I often use 8mm, which is rated at 4,000 lbs - a resonable safety factor. You have to be more careful of edges and such. I would probably choose 10mm minimum for permanent rigging. I've heard of folks using 7mm, but I probably wouldn't use this for SRT (i.e. down and up)... I might use something like this for a pull-down where you're descending on a double strand, but you need a rappel device that will handle the smaller diameter.

Since rope volume and weight is a quadratic function of the diameter, 8mm is almost half the size and weight of 11 mm - a signficant savings.
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Re: Thinnest rope for SRT?

Postby NZcaver » Jun 2, 2011 9:03 pm

What Derek said. I've also used 8mm occasionally for in-cave drops, and it has worked well for me.
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Re: Thinnest rope for SRT?

Postby Tubo Longo » Jun 3, 2011 12:16 am

Mike, you haven't mentioned if you use rebelays and/or redirectional etc when rappelling/climbing on those mine drops. If you don't, and don't want to bother with PERFECT riggings and rebelays, I'd definitely reccomend to forget using any 8 mm, since is a diameter which asks for VERY careful riggings (4000 lbs seems a lot but actually I believe is less than most of the gear we use....) This is exp. true if you are used to 11 mm.
For the same reason I won't use a 9 mm: it still requires careful rigging.

I would rather suggest to use a 10 mm, which will give you a sensible advantage in bulkiness and weight but will keep the load limit still quite high.

About smaller diameter than 8 mm, the only (experimental) use I'm aware of was of tubular webbing and kewlar ropes (more than a decade ago, btw). In both cases there were issues with the mechanical gear, since no manufacturer still do not produce gear for use with rope diameter smaller than 8 mm.

Basically, don't throw away the safety for same weight saving.... :wink:
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Re: Thinnest rope for SRT?

Postby OpenTrackRacer » Jun 3, 2011 1:35 am

Thanks for the feedback. 8mm would be a huge improvement in both weight and volume over 11mm. We don't often use rebelays. If the rub point is rock we'll use a rope protector and if it's wood we usually don't need anything. We would not be using this rope to replace our 11mm Pit Rope on significant drops or in tricky rigging situations. It would be more for use on steep (but often climbable) slopes and short vertical drops that we might encounter deep in the mine. We all carry Black Diamond ATC's as backup rappel devices and those can be used with 8mm rope. Our Petzl ascenders are also compatible with 8mm rope so it seems like a good diameter for our needs.

Does anyone have a suggestion as to a brand of rope for this application?

Thanks (again)!

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Re: Thinnest rope for SRT?

Postby Tubo Longo » Jun 3, 2011 2:15 am

BW I'd say. If you plan any rappeling on 8 mm be aware of much increased speed unless extra friction is applied (like using a side brake biner): I'd definitely reccomend some external training beforehand.
Still, on any drop, even minor, if there's a rub point I'd suggest to use at least a redirectional vs. a rope protector while using an 8 mm.
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Re: Thinnest rope for SRT?

Postby Scott McCrea » Jun 3, 2011 5:34 am

8mm accessory cord is scary. It works and your rigging should be perfect, but it's still scary. It stretches a lot. A couple companies make 8mm caving rope. Cancord's is polyester so it doesn't stretch much. It sounds to me that 9mm might be a better option for you. You can get real caving rope in 9mm and it is a little more forgiving.

One big difference when you go smaller diameter is the thickness of the sheath. Smaller diameter=thinner sheath=less abrasion resistance.
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Re: Thinnest rope for SRT?

Postby Extremeophile » Jun 3, 2011 7:52 am

The rope I've used is from Imlay Canyon:

http://www.imlaycanyongear.com/ropes.php

These are 100% polyester (core and sheath), and they don't stretch as much as a full nylon rope would. They have a fairly tight and abrasion resistant sheath. You probably will only notice that there's more stretch than an 11mm on very long drops (>100'). They aren't considered "accesory cord" like other 8mm ropes made by Beal and the like. REI sells an 8mm cord that I would not recommend for caving. As for being "scary"... I think it's a matter of familiarity. Rappelling on 11mm might seem scary to someone who hasn't done it before. The warnings about reduced friction are absolutely correct and I would second the idea that you practice first in a controlled setting to get a feel for the friction needed. Using a braking biner with a bobbin or using all 6 bars or a hyperbar on a rack are good ideas. You will also probably see reduced life with 8mm rope, i.e. it doesn't take as many uses before the sheath becomes too worn, so expect to need to replace it more often. Also, I haven't had problems with ascenders gripping the rope but I've never had one coated with mud so YMMV.
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Re: Thinnest rope for SRT?

Postby LukeM » Jun 3, 2011 9:58 am

Isn't it commonly accepted that with 8mm rope (and even 9mm to some extent) you basically have very little to no allowance for letting the rope to rub against rock? Correct me if I'm wrong but aren't mines usually rigged using improvisation, i.e. not bolted for free hangs/optimal positioning? Rope pads aren't perfect and I've seen my fair share not staying under the rope. I guess what I'm saying is take what tubo longo said to heart and be careful. Unless using 9mm rope, for instance, would significantly make your trip more difficult what is the reason for going smaller, aka more dangerous?
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Re: Thinnest rope for SRT?

Postby GroundquestMSA » Jun 3, 2011 10:38 am

OpenTrackRacer wrote:We all carry Black Diamond ATC's as backup rappel devices and those can be used with 8mm rope. Our Petzl ascenders are also compatible with 8mm rope so it seems like a good diameter for our needs.


I use 8mm when I'm doing small drops deep in a cave. I always try to double it up even when I'm not pulling it down afterwards for the extra friction. I'm a tiny fellow but using a single 8mm line with an ATC is pretty quick. Of course if you are doing very small vertical drops I'm sure you can stay in control....It may not be worth the hassle to carry enough rope to double every drop.
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Re: Thinnest rope for SRT?

Postby wyandottecaver » Jun 3, 2011 6:34 pm

I think scott aluded to something that should be very much emphasized. There is a HUGE difference between CORD and ROPE. People seem hung up on diameter but thats a trap. There are 5mm escape lines that are safer than 9mm accessory cord for certain uses.

The other thing I see here is people equate slopes and small drops with less risk. WRONG. A fall is a fall is a fall. The recent rescue in sinking cove, where the caver had serious, potentially life-threatening injuries was on a 20-ish deep drop, and tumbling down a 200ft rock strewn slope aint no picnic either.

9mm ROPE is readily available and perfectly safe, and even has good wear resistance. You can't treat it like pit rope, but it is a huge difference from 11mm. You should also be aware that even among accessory cords of the same diameter there are big differences in feel and ruggedness.
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Re: Thinnest rope for SRT?

Postby Tubo Longo » Jun 3, 2011 6:38 pm

I may be wrong but I see some potential confusion. There're REAL caving 8 mm ropes and there're 8 mm accessory ropes. Of course anybody could cut a real rope to get accessory ones out of it, but I won't use an accessory rope to rappell/climb if not in a life/death situation.
Even with real rope, I agree with Derek that the sheath is usually way thinner, hence a significant shorter rope life and the need of careful rigging (in addition to the limited load limit). Instead I would be careful in using any rope specifically made for canyoning 'cause they usually are supposed to be used as double rope, not as single rope: using them as single may - may.. - change several parameter. I.e.: would be the load limit the same? What about stretching? etc.

As for Luke remark: there're 8 mm brands (personally I know of BW) with a significantly thicker sheath than others. But yes, 8 and 9 mm are associated with careful and knowledgeable rigging & rebelays tech: if you are not being either familiar and/or willing to get into those tech, better stick at least to a 9 mm or, even better, to a 10 mm. As for bulkiness, 8 vs. 9 doesn't make for much difference at all, while 10 mm does, both vs. 9 and vs. 11 mm. Still a 10 mm is a huge improvement over an 11 mm

GroundquestMSA, I'm not sure what you mean with "double it up": if it is what I think, then how do you climb back? And if you pull the rope down afterwards, how are you getting back at all? Are you may be talking of canyoning situation, not of caving ones?
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Re: Thinnest rope for SRT?

Postby LukeM » Jun 3, 2011 9:13 pm

wyandottecaver wrote:The other thing I see here is people equate slopes and small drops with less risk. WRONG. A fall is a fall is a fall.


I would like to point out that there is some potential difference in danger when using thin rope on long drops vs on short drops. One difference is the amount of stretch, which when climbing is proportional to the amount of sawing action on your rope if it is touching rock.

Also, on a slope you really can't generate the same level of force as you would if you were in free fall. Is this not worth factoring into the equation?
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Re: Thinnest rope for SRT?

Postby MUD » Jun 3, 2011 11:19 pm

From the Gonzo Guano Gear website....

You read it right. 8mm ROPE !

Cancord now makes 8mm rope. This is not an accessory cord construction, but Cancord's high-quality, extra-stiff, custom caving rope, designed specifically for use as push rope and in mini haul systems.

We do NOT recommend this rope for high-traffic rigging anywhere the integrity of anchors is questionable, or to inexperienced cavers of any sort. If you think your rigging is good enough to use this rope, you'd better be right. The safety margins with 8mm rope are very slim. That said, we know cavers who use accessory cord as push rope, You know who you are. Please consider 8mm rope.
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Re: Thinnest rope for SRT?

Postby GroundquestMSA » Jun 4, 2011 12:57 am

Tubo Longo wrote:GroundquestMSA, I'm not sure what you mean with "double it up": if it is what I think, then how do you climb back? And if you pull the rope down afterwards, how are you getting back at all? Are you may be talking of canyoning situation, not of caving ones?
wyandottecaver wrote:The other thing I see here is people equate slopes and small drops with less risk. WRONG. A fall is a fall is a fall.


Instead of setting up for a pull down I knot the rope to that I have two stationary lines. I only do this for added friction. It's nice to take it easy in an unfamiliar cave. I ascend on one rope as normal. I until recently used an ATC or a rescue 8. Now that I am using a rack I won't need to double rope.
If I am perceived as one of the "short falls don't hurt" offenders, let me say that my previous comments implied that a short drop gave less opportunity to lose control of descent (in this case using an ATC on small rope). An 18' rappel has little opportunity for dangerous heat/speed/fatigue acceleration even with unfavorable equipment.
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