Thinnest rope for SRT?

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Re: Thinnest rope for SRT?

Postby Tubo Longo » Jun 4, 2011 3:34 am

Luke, the point is that when using thin rope, either 8 or 9 mm, there should NOT be any friction point at all because of the reduced safety margins. For this reason such diameters are usually associated with rebelays tech. Should a rebelay fail, I believe the amount of force generated won't change much if you're in a free fall situation vs. a "touching the rock" one. May be the consequences. As for the amount of stretch/sawing, is the other way around: the sawing action is proportional to the amount of stretch, which is closely related to the lengh of the drop AND to how much dymanic a rope is. Infact pleae consider that the US caving ropes are usually way more static than say European one. Edelrid, a top brand in ropes in Europe, has a standard stretch of about 10% on its caving ropes. Hardly a number to be found on commonly used US caving ropes.

GroundquestMSA: so you are (were) rappeling/climbing on a rope "chocked" only by a knot of some sort..?? Boy.......... :yikes: As for the 18' drop, I won't bet a nickel on that. Thinks about going free fall from the very top, i.e. the lip of the drop: even a short caver (say 5') will fall 18+5= 23'. Trust me, landing on an hard surface after a free fall of 23' is more than enough to land you in a cemetery or in a wheel chair for the rest of your life. Even if I agree the descender won't barely get warm and the rope likely won't suffer any damage.
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Re: Thinnest rope for SRT?

Postby Cody JW » Jun 4, 2011 12:36 pm

This is not exactly SRT but I use half inch webbing for hand line use. I got some military issue for free from some Navy Seals and I can carry 50 feet in my pack and not even know it is there. I know it is not very abrasion resistant , but it is very compact and I have used it for years with no problem. I just tie a trusty bowline on bight and use a biner to tie off with. Any thing else I have tried is much more bulky.
It only takes one person to surrender a dog to a kill shelter ,but it takes many to rescue it.
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Re: Thinnest rope for SRT?

Postby Cody JW » Jun 4, 2011 12:45 pm

I use a figure eight on bight with my hand line, not a bowline.
It only takes one person to surrender a dog to a kill shelter ,but it takes many to rescue it.
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Re: Thinnest rope for SRT?

Postby GroundquestMSA » Jun 4, 2011 12:51 pm

Tubo Longo wrote:GroundquestMSA: so you are (were) rappeling/climbing on a rope "chocked" only by a knot of some sort..?? Boy.......... As for the 18' drop, I won't bet a nickel on that. Thinks about going free fall from the very top, i.e. the lip of the drop: even a short caver (say 5') will fall 18+5= 23'. Trust me, landing on an hard surface after a free fall of 23' is more than enough to land you in a cemetery or in a wheel chair for the rest of your life. Even if I agree the descender won't barely get warm and the rope likely won't suffer any damage.


Im afraid I don't have the vocabulary to make myself understood. I don't think I chock anything. I tie the middle of the rope around the anchor. I then have two equal halves of rope which are merrily tossed over the precipice and decended together.
I then ascend one or the other.
I don't think anyone would argue with the fact that a 23' fall will possibly make you dead and certainly make you disgruntled. I never mentioned a free fall. I simply meant that if you are rappelling with an ATC on 8mm rope (a bad idea) you will likely reach the bottom safely if you aren't going far.
Last edited by GroundquestMSA on Jun 4, 2011 10:09 pm, edited 1 time in total.
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Re: Thinnest rope for SRT?

Postby Marduke » Jun 4, 2011 8:04 pm

GroundquestMSA wrote: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.


Dirk might disagree. His "short" ~15ft fall lead to over a 30hr rescue last weekend.
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Re: Thinnest rope for SRT?

Postby Extremeophile » Jun 5, 2011 9:09 am

Are you saying that Dirk was descending thin rope using an ATC and lost control? I don't believe there's been an accident report issued yet, but I was under the impression that a block of some sort was used and he rigged to the wrong side of the block. Certainly this regrettable incident demonstrates short falls can be very serious and potentially fatal. I'm not sure there are enough details yet to conclude that this incident is an example of thin cord and ATCs being dangerous.
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Re: Thinnest rope for SRT?

Postby MUD » Jun 5, 2011 10:15 am

I think what he means is a short fall of any kind, rigged in or not, can be ugly!
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Re: Thinnest rope for SRT?

Postby Cavernuke » Jun 5, 2011 9:29 pm

My rwo cents worth:

Having been in the shipbuilding industry for over 30 years (which often involves climbing around in high places), I can report this: the most dangerous height you can work at is between 3 and 12 feet. That's where a majority of reportable injuries from falls take place. Why? Because you get sloppy and complacent.

Little falls can kill, too.

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Re: Thinnest rope for SRT?

Postby chh » Jun 6, 2011 9:11 am

GroundquestMSA, tying a knot in the middle of a skinny rope and descending on a double strand and ascending on a single is a perfectly suitable way to do it. However, the weight savings will really be moot. In order to do the same 50' pitch that you were doing with your 11mm, you need 100' of 8mm. You may even find that 100' of 8mm is heavier. If you are really looking to continue in familiar SRT territory a 9mm single is probably a better bet.

There are other advantages to doubling up on skinny ropes, but weight/bulk savings isn't really one of them.

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Re: Thinnest rope for SRT?

Postby Extremeophile » Jun 6, 2011 9:55 am

There are clearly a large number of people with a bias towards using nothing but 11 mm (e.g. PMI Pit Rope), but I suspect this is largely due to familiarity and inertia (i.e. if it's a system that works then why change). If I were caving only in TAG and driving up to entrance pits on the weekends then I would probably exclusively use 11 mm PMI or the like. It's reasonably priced, has a healthy safety margin. works well with most descenders, will last a long time, and won't be questioned by other cavers using it.

For push trips deep underground, where bulk and weight are critical, I believe rope as thin as 8 mm can be a safe alternative. It's true that when you take into account rope age, knots, carabiners, etc, the original rated strength is significantly reduced. Perhaps an 8 mm rope rated at 3,900 lbs is reduced to 2,000 lbs. A 200 lb caver is unlikely to generate forces exceeding 250 lbs during descent or ascent. This is still an 8x safety factor. The arguments for care on rub points should apply to any rope, regardless of diameter. I've read many stories about ropes being nearly cut through, but I've never read about a rope breaking from exceeding its tensile strength. I'm not advocating 8 mm rope for permanent rigging, rescue use, or for inexperienced vertical cavers, but I strongly believe it can be safe option for experienced cavers doing push climbs in remote areas. As with any new piece of equipment, practice under controlled conditions is wise.

Maybe the key point is that 8 mm can be very safe in the right hands and 11 mm can be extremely unsafe in the wrong hands. The overwhelming majority of vertical caving accidents are due to judgement error, not equipment failure. I'm not suggesting everyone switch to thin rope, but I don't think people should simply dismiss the use of light weight equipment as "unsafe". Being on a 20 hr trip with someone carrying 200' of 11 mm rope through crawlways and narrow canyons has its own safety risks before any rigging occurs.

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Re: Thinnest rope for SRT?

Postby chh » Jun 6, 2011 10:41 am

Derek, I agree with your standpoint completely save one (probably semantic) point. If you are using 8mm rope caving, you must be prepared to use that rope in a rescue situation. If you are truly pushing a cave to the point where smaller and smaller diameter ropes become a necessity, your own caving party IS your rescue team. I'm pretty sure you meant the use of 8mm ropes by an outside rescue team, but it is something that bears thinking about, particularly to someone like the OP who is new to thinner ropes.
I think it isn't so much the difference in MBS between 8 and 9mm ropes, for instance, that is the issue but rather the mindset required when your margins of error are reduced. Everyone defines their limits in different ways, hence the lack of a standard protocol. Really the answer to the OP's question is very simple. Using common ascenders and a tube style device, 8mm is usually the lower end of what the manufacturer states as an acceptable diameter. The rest of the equation, as I'm sure you and most people on the forum would agree with, happens just under your helmet :big grin:
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Re: Thinnest rope for SRT?

Postby Anonymous_Coward » Jun 6, 2011 10:48 am

Summary:

8mm rope is plenty strong but is easier to cut so should not be used in the same way as 11mm rope.

My personal view on it is that 8mm should be rebelayed or heavily padded in most cases. For this reason, it is not always appropriate as a "push" rope for descending unknown pits with unknown abrasion issues. If I'm just gonna chuck a rope down a pit and go, 11mm is more forgiving. However, as Derek stated it is much nicer to carry thin ropes around.

We ran into this dilemma in China with skinny rope. The rope was nice to carry, but on ledgy pits it would require so many rebelay bolts and bolting gear that the weight savings were greatly reduced. The time needed to hand-drill bolts and rig rebelays was exponentially more than the TAG "throw and go" method. This was especially frustrating in dead-bottom pits.

I feel comfortable climbing and rappelling on ropes down to 8mm as long as they are safely rigged. Sometimes this means multiple rebelays and/or rope pads. If you are using 8mm as a push rope, I would recommend the Imlay ropes as they have a greater sheath to core ratio than some other options.
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Re: Thinnest rope for SRT?

Postby wyandottecaver » Jun 6, 2011 6:26 pm

Andy's comment reminded me of a post I made somewhere else. I have used 9mm rope (and even 7mm "tech cord" once).....to do known drops. Using thinner ropes for unknown drops is a whole different ballgame.
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Re: Thinnest rope for SRT?

Postby OpenTrackRacer » Jun 7, 2011 6:44 pm

Thanks for all the great comments. I'm not opposed to 9mm rope versus 8mm. The difference in bulk and weight will likely be negligible. I have some Sterling 9.2mm Fusion that I obtained for making cows tails and just looking at that I can see how much more portable it is versus our 11mm Pit Rope.

All the comments about rub points is well taken. We'll be paying extra special attention to that if we end up using the smaller diameter rope.

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Re: Thinnest rope for SRT?

Postby OpenTrackRacer » Aug 9, 2011 8:32 pm

So, I still haven't gotten any new lightweight rope but I need to before an upcoming trip. Based on all the comments here I've decided to forgo 8mm rope. I think the margins are too tight for what we do and the weight savings isn't enough to make it worth it. With that in mind, I think 3/8" or 9mm rope will work for our needs. If anyone has a recommendation for their favorite rope in this diameter I'd love to hear it. Our requirements might be contradictory but we're looking for the lightest weight and best abrasion resistance. Cost, as always is also a factor.

Thanks!

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