Dropping a rope into a cave

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Re: Dropping a rope into a cave

Postby NZcaver » Jun 20, 2012 5:01 pm

Chads93GT wrote:While we may not all agree on how safe or unsafe it is, i think we can all agree that if you were at the bottom and you got hit by the rope bag with 10-30-50-100 feet of rope still in it, it is going to make you have a bad day.

Yep, but probably no worse than somebody being down the bottom as somebody rappels down "grooming" away loose rocks. I think the key difference here is I always knew there was nobody down the pit when I dropped the rope, not like TAG pits where you have dozens of different groups bouncing a pit on any given weekend.

Marlatt wrote:After dropping the pit, we discovered that the core was blown out through the side of the mantle a foot or so from the end of the rope!

Cool! Good thing it was only the last foot of the rope. I suspect the rope impacted something sharp-ish at high speed, then? Anybody take photos of the rope?
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Re: Dropping a rope into a cave

Postby tncaver » Jun 20, 2012 5:49 pm

Here is another story supporting my statement: I suggest NZCAVER and others pay attention.

Years ago, I asked my friend Larry Johnson to take me to the GOUFFRE HOLE in Cumberland County TN. He agreed to do it but had to be somewhere that evening, so the trip was very hurried. When we got to the pit entrance (241 foot drop), Larry decided to just toss the
rope down the pit since he was in a big hurry to go somewhere else. His decision cost him and me a LOT of extra time. I rappelled into the
pit only to discover a HUGE MESS of rope about 100 feet down. The tangle was horrendous. Also I noted many very sharp flutes of eroded limestone
rock. As I pulled the rope up and untangled it for over an hour while sitting in a harness 140 feet above the floor, I was cautiously examining every
foot of rope to be sure the sharp flutes had not severed the rope sheath to the core. Fortunately it had not. When I finally got the rope
untangled after dangling for an hour, I rappelled safely to the bottom of the pit and then immediately climbed back out without seeing any
of the cave so that Larry could leave for his obligation. This situation could have been much worse and was very unpleasant to say the least.

The flutes in that pit were very sharp. Had the rope been in a bag and slid down across one of those flutes, the rope, bag and all may have
sliced into a huge mass of permanently damaged rope. If you people continue tossing your rope down pits, eventually it will come back
and bite you in the butt or worse. I am telling you this for your own safety. Best of luck.
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Re: Dropping a rope into a cave

Postby tagkycaver » Jun 20, 2012 5:55 pm

Why would anyone WANT to drop a rope in a bag down a 100m pit? Always lower, never drop.
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Re: Dropping a rope into a cave

Postby NZcaver » Jun 20, 2012 6:18 pm

Yeah, yeah... pay attention, always/never, etc etc.

Yes, anybody choosing to recklessly toss a rope down a pit should be aware of possible dangers. Just like anything else involving ropes or caves.
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Re: Dropping a rope into a cave

Postby Anonymous_Coward » Jun 20, 2012 6:44 pm

NZcaver wrote:
Anonymous_Coward wrote:I have also heard when throwing a rigged rope down a deep pit, the end of the rope can whip at speeds approaching supersonic, creating forces that the rope was not designed to handle.


Call be a skeptic... but really dude? Supersonic?? :shock:


Yes, really. Did I stutter? PLEASE try to pay attention.
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Re: Dropping a rope into a cave

Postby NZcaver » Jun 20, 2012 8:24 pm

Anonymous_Coward wrote:Yes, really. Did I stutter? PLEASE try to pay attention.

Su..su..su..supersonic? My bad. Must be my ADD again.
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Re: Dropping a rope into a cave

Postby Stridergdm » Jun 20, 2012 10:21 pm

I've got to admit I've heard the same thing (lower, never toss) and I think to avoid hang-ups, etc that's good advice in general.

I have to admit that I'm still skeptical that the tip of a rope going supersonic by itself could do much. It going supersonic and hitting something, possibly. I suspect that someone is who far better at calculus than I am could figure out the forces on a rope falling to its end.

I can't imagine it's an easy problem.

On one hand, the end of the rope will be travelling very quickly, but have very little mass when it reaches "bottom".

On the other hand say you've got 100m free-hanging over the edge, I suspect the greatest force will be felt right at the edge since you've got 100m of rope below that.

Basically at t=1, you'd have 4.5m of rope hanging down and coming to a stop, the other 95.5 is in freefall so should transmit very little force.
At t=2 you'll have 19.6m of rope, but 4.5 has already come to a stop, the rest is coming to a stop, but the force is being dissipated over the full length, the remainder of the rope is still in freefall.

And so on.

(and yes, the tip of the rope will act like a bullwhip and go supersonic at some point most likely).

Hmm, the more I think about it, the more complex the math gets.

I think it would be interesting however to do some real-world testing.

Note I'm not advocating simply tossing the rope down the pit, but I'm far from convinced that rope damage is as likely as some think.

Hmm, I should see if I can get PMI to donate some rope to me for testing purposes. :-)
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Re: Dropping a rope into a cave

Postby driggs » Jun 20, 2012 11:05 pm

Chads93GT wrote:also, rappelling with the rope in a rope bag, tethered to your harness/rack should NEVER tangle up coming out, unless the person who stuffed the rope did it WRONG.


If the tether to the rope bag is too long, and especially if the rope still has twist in it from past coiling, the rope bag can spin causing the tether to wrap around the rope, and will quickly, annoyingly, and repeatedly bring your rappel to a halt, requiring you to untwist it to continue. I've found this to be worse the longer the tether, and especially bad with a single-line tether; it seems that a girth hitched loop of webbing attaching the rope bag resists spinning.

It should also be noted that you should never rappel feeding rope from a bag unless you've verified that there's a blocker knot in the end of the rope since you can't verify that it reaches the bottom until you're on the bottom (this is why your rope bag should have a grommet hole in the bottom, so you can see the knot).
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Re: Dropping a rope into a cave

Postby Jeff Bartlett » Jun 20, 2012 11:41 pm

NZcaver wrote:I think the key difference here is I always knew there was nobody down the pit when I dropped the rope, not like TAG pits where you have dozens of different groups bouncing a pit on any given weekend.


You're going to the wrong pits, Jansen! :)
"Although it pains me to say it, in this case Jeff is right. Plan accordingly." --Andy Armstrong
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Re: Dropping a rope into a cave

Postby NZcaver » Jun 21, 2012 12:46 am

Jeff Bartlett wrote:You're going to the wrong pits, Jansen! :)

Any pit where I can hide the bodies is a good pit, Jeff. :shhh:
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Re: Dropping a rope into a cave

Postby Chads93GT » Jun 21, 2012 12:55 am

Lotta "hide a dead body in a pit" pit's here in missouri. No one goes into the pits here but my friends and I, and we dont tell secrets ;)
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Re: Dropping a rope into a cave

Postby trogman » Jun 21, 2012 9:20 am

Considering that terminal velocity (~220 mph) is nowhere near the speed of sound, I don't see how the rope can attain anything close to supersonic speed- even in the deepest pits in the world. What am I missing here?

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Re: Dropping a rope into a cave

Postby Stridergdm » Jun 21, 2012 9:36 am

trogman wrote:Considering that terminal velocity (~220 mph) is nowhere near the speed of sound, I don't see how the rope can attain anything close to supersonic speed- even in the deepest pits in the world. What am I missing here?

Trogman :helmet:


The fact that it's not a rigid object.

Think of it like a bullwhip (which essentially it is). Your arm doesn't reach supersonic speeds, but as the energy from your arm motion is transmitted down the whip, the end will reach supersonic speeds.

In the case of the rope, since it's not rigid, much of the energy as it falls is going to get "concentrated" in the tip as the rope above comes to rest.

edited, added:

Also, terminal velocity depends on the shape, size and orientation of the object. If you think about it, the terminal velocity of a skydiver in a flat out position is I believe the 220mph you mention, but the terminal velocity of a skydiver under a parachute is FAR less.
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Re: Dropping a rope into a cave

Postby NZcaver » Jun 21, 2012 3:21 pm

Hmmm, apparently climbers are also known to ponder these Mysteries of the Universe...

Incident report - When the Whip Comes Down

Long followup discussion with lots of physics - Ropes @ Speed of Sound

And just for good measure, How to Toss Rappel Ropes
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Re: Dropping a rope into a cave

Postby chh » Jun 21, 2012 5:09 pm

[
driggs wrote:It should also be noted that you should never rappel feeding rope from a bag unless you've verified that there's a blocker knot in the end of the rope since you can't verify that it reaches the bottom until you're on the bottom (this is why your rope bag should have a grommet hole in the bottom, so you can see the knot).


You can also stuff your bag so both ends are on the top. Let the blocker knot hang out of the bag while you rap so you can still see it.

Also, you can also attach the bag directly to your rap device and then attach yourself to the device with a short tether. The bag stays pretty still this way if you are consciencious about how you attach it. Plus you can shout "ON PIG!", which I find infinitely more rewarding.
P.S. I don't normally do this. You'd have to have a metric buttload of rope and gear to get down the hole to warrant this in my opinion, but it's a fun trick.

By the way when caving or rock climbing, I normally rap with my rope or lower it. Sometimes I chuck it, but only when I can see the bottom (or next anchor) and can judge whether or not this is a good idea. If I can't suss it out than I just take it with me. Having said that though, I will say that I chuck ropes ALL THE TIME. Every working day as a matter of fact, but there's not sharp things for the rope to fall on and what not. Usually a rope gets smoked in the lowering device, nicked by a groundie, etc. I don't worry about throwing them most of the time. But this is usually under 200 feet and onto a forgiving surface. I think that's a good cutoff point though. More than a couple hundred feet? You outta think about lowering or or taking the rope with you to avoid the fustercluckage. :big grin:
Your words of caution are no match for my disaster style!
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