Author Topic: This looks like a nice abseil  (Read 2421 times)

Offline Pitlamp

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This looks like a nice abseil
« on: March 08, 2019, 08:58:56 pm »


I wonder how they stop the rope from glazing. Those hollow rack bars can't be the best for heat dissipation, surely?

Offline langcliffe

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Re: This looks like a nice abseil
« Reply #1 on: March 08, 2019, 09:57:09 pm »
Wouldn't a hollow bar have a reduced capacity for retaining heat, and a greater surface area for losing heat? He also abseiled very steadily, and didn't stop on the rope long enough to give it time to glaze.

Mind you, I'm probably stepping into the realms of ultracrepidarianism here...
« Last Edit: March 08, 2019, 10:19:33 pm by langcliffe »

Offline Fulk

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Re: This looks like a nice abseil
« Reply #2 on: March 08, 2019, 10:30:52 pm »
'''kin ''ell!!

Offline ObviousSpectre

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Re: This looks like a nice abseil
« Reply #3 on: March 08, 2019, 11:07:33 pm »
Imagine getting to the bottom and finding the rope a couple of meters too short  ;)
"Water is a third oxygen so we should be fine"

Offline Kenilworth

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Re: This looks like a nice abseil
« Reply #4 on: March 09, 2019, 01:00:15 am »
I believe Amy Hinkle, who used to post here a lot, has slid off of El Cap. Having stood on it, I don't feel interested in rappelling off. Seems exceptionally pointless, but no doubt it's some fun and something to boast about.

Offline langcliffe

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Re: This looks like a nice abseil
« Reply #5 on: March 09, 2019, 06:41:44 am »
Seems exceptionally pointless, but no doubt it's some fun....

Is having some fun in one's life pointless?

Offline Chocolate fireguard

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Re: This looks like a nice abseil
« Reply #6 on: March 09, 2019, 08:22:11 am »
Wouldn't a hollow bar have a reduced capacity for retaining heat, and a greater surface area for losing heat? He also abseiled very steadily, and didn't stop on the rope long enough to give it time to glaze.

Mind you, I'm probably stepping into the realms of ultracrepidarianism here...

Ultracrepidarianism eh?

I'm no expert on the language, but I'm sure there is no such word.

Offline mat

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Re: This looks like a nice abseil
« Reply #7 on: March 09, 2019, 08:45:09 am »
Wouldn't a hollow bar have a reduced capacity for retaining heat, and a greater surface area for losing heat? He also abseiled very steadily, and didn't stop on the rope long enough to give it time to glaze.

Mind you, I'm probably stepping into the realms of ultracrepidarianism here...

Ultracrepidarianism eh?

I'm no expert on the language, but I'm sure there is no such word.
Ultracrepidarianism is the habit of giving opinions and advice on matters outside of one's knowledge. The term ultracrepidarian was first publicly recorded in 1819 by the essayist William Hazlitt in an open Letter to William Gifford

Offline Chocolate fireguard

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Re: This looks like a nice abseil
« Reply #8 on: March 09, 2019, 08:48:24 am »
Wouldn't a hollow bar have a reduced capacity for retaining heat, and a greater surface area for losing heat? He also abseiled very steadily, and didn't stop on the rope long enough to give it time to glaze.

Mind you, I'm probably stepping into the realms of ultracrepidarianism here...

Ultracrepidarianism eh?

I'm no expert on the language, but I'm sure there is no such word.
Ultracrepidarianism is the habit of giving opinions and advice on matters outside of one's knowledge. The term ultracrepidarian was first publicly recorded in 1819 by the essayist William Hazlitt in an open Letter to William Gifford

I can't be bothered to look it up, but I'm sure that can't be right.

Online mikem

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Re: This looks like a nice abseil
« Reply #9 on: March 09, 2019, 09:00:26 am »
https://en.m.wikipedia.org/wiki/Ultracrepidarianism

It's actually bastardised Latin...

Offline ogofmole

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Re: This looks like a nice abseil
« Reply #10 on: March 09, 2019, 09:30:30 am »
Bet that tackle bag was heavy carrying the rope up that hill.

Offline Fulk

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Re: This looks like a nice abseil
« Reply #11 on: March 09, 2019, 09:58:20 am »
At 66 g/m, 2650 feet would weigh ~53 kg or 117 lb; I imagine they had at least two coils, carried by separate people*, to get it up there. Didn't the guy abbing say '3 and a half hours (or something) to get up, 7 minutes to get down'?

*Or maybe a dobbin.

Online mikem

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Re: This looks like a nice abseil
« Reply #12 on: March 09, 2019, 10:03:07 am »
800+m (half a mile) of rope, but take a longer one...

Wouldn't a hollow bar have a reduced capacity for retaining heat, and a greater surface area for losing heat?
You have almost doubled the surface area & halved the volume of the bars, so yes, they won't build up heat as much, but it will still get as hot if you go fast (same amount of friction).

On another thread from years ago Amata mentioned using hollow bars:
https://www.dailymail.co.uk/news/article-2403825/Into-void-Daredevils-complete-worlds-biggest-abseils-dropping-3-000ft-face-El-Capitan-Yosemite-National-Park.html

Mike
« Last Edit: March 09, 2019, 10:15:24 am by mikem »

Offline Fulk

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Re: This looks like a nice abseil
« Reply #13 on: March 09, 2019, 10:08:10 am »
If I heard correctly and he did indeed say 7 min to get down, that's nearly 400 ft / min – which I would say is quite fast (Jib Tunnel in 45 sec . . . ).

Offline Laurie

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Re: This looks like a nice abseil
« Reply #14 on: March 09, 2019, 10:21:32 am »
The weight of the rope below must have caused horrendous drag initially.
MNRC

Online mikem

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Re: This looks like a nice abseil
« Reply #15 on: March 09, 2019, 10:39:34 am »
That's why they used the jammer to take the weight off whilst threading the descender & passing the edge.

He passed the jammer at 2 mins 30 & reached the floor at 10 mins 30, so nearer 100 metres (330ft) per minute (although it must have been slower than that to start with & faster towards the end), Amy et al took twice that time. The question is whether the device was hot enough to melt through the rope if it had got stuck...

Offline mrodoc

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Re: This looks like a nice abseil
« Reply #16 on: March 09, 2019, 11:07:29 am »
The hard part is going back up the rope after the abseil. I was told if you are first on the rope it is rather disappointing when number two gets on it and you find yourself losing a considerable amount of height owing to the amount of stretch in the rope.  Also of course you bounce!

Online mikem

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Re: This looks like a nice abseil
« Reply #17 on: March 09, 2019, 11:44:42 am »
See Sirwang's post about setting up: 11mm rope in 5 loops & carried mile to bottom, 5.5mm in 2 loops to top so they could haul the main line up (other groups have used mules). 3 to 4 hours to prussik back up, but has been done in just over an hour...
https://www.google.com/amp/s/amp.reddit.com/r/climbing/comments/6h7q5l/mfw_ive_got_to_flake_out_a_3000_ft_rope/

Offline ogofmole

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Re: This looks like a nice abseil
« Reply #18 on: March 09, 2019, 01:48:42 pm »
Quote
3 to 4 hours to prussik back up, but has been done in just over an hour...

Now that would be a challange for the next Hidden Earth competition.

Offline langcliffe

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Re: This looks like a nice abseil
« Reply #19 on: March 09, 2019, 02:46:44 pm »

Ultracrepidarianism eh?

I'm no expert on the language, but I'm sure there is no such word.

What a wonderful example!

Offline Chocolate fireguard

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Re: This looks like a nice abseil
« Reply #20 on: March 09, 2019, 04:02:36 pm »

Ultracrepidarianism eh?

I'm no expert on the language, but I'm sure there is no such word.

What a wonderful example!

It's nice to know one's meager efforts to entertain are appreciated. By some.

Offline Fulk

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Re: This looks like a nice abseil
« Reply #21 on: March 09, 2019, 04:37:49 pm »
Is there such a word as meager?  ;D

Online mikem

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Re: This looks like a nice abseil
« Reply #22 on: March 09, 2019, 06:09:27 pm »
Well, it is a US film clip...

Offline Chocolate fireguard

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Re: This looks like a nice abseil
« Reply #23 on: March 09, 2019, 09:54:26 pm »
Is there such a word as meager?  ;D
Sorry. I typed meagre and changed it without checking when I saw the red underline.

Re the abseil: only two of those bars are hollow, the top two. The top one is thin-walled but No 2 is thick-walled and has the holes for the rack sides drilled such that they do not go through on a diameter - causing the rope to be diverted more, presumably to increase the friction if necessary. No 2 has a groove in it, presumably due to wear, as I don't see why they would want to decrease the above effect.

All of the other 6 bars are thin-walled and U-shaped. Somebody must have worked out that this gets heat away from the friction surface and into the moving air faster than conducting it away through a solid aluminium alloy bar.

Another feature is that short tubes have been fitted to one of the sides to stop the top 3 bars getting too close together. And a collar under the top bar means that the gap between 1&2 is a bit bigger than that between 2&3. These tubes slide off at the end of the clip when the rope is removed and all the bars except No 1 hang open. They had fitted a pair of tubes (rather than just one) between each pair of bars, so this seems to be a judgement they make beforehand.
I assume it's to share out the heat generation, stopping the ones at the top, mainly Nos 2&3 I think, doing all the work.

It all must work well as the heat generation runs to well over a kilowatt if the rate of descent is anything like has been said.

Hollow, as in tubular, bars are not a good idea. Perhaps they have to do it with the top bar with its extension and pin, but they have made sure it doesn't divert the rope much so heat generation will be less than in No 2. They made that one thick-walled.
Decreasing the mass to increase the surface area, without making sure that forced convection will always get to that area, will just cause the bar to get hotter for a given heat input.




Offline Fulk

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Re: This looks like a nice abseil
« Reply #24 on: March 09, 2019, 10:29:53 pm »
Quote
It all must work well as the heat generation runs to well over a kilowatt if the rate of descent is anything like has been said.

I worked it out as just over a kilowatt – still a lot of heat to get rid of. (And are you sure you didn't mean aluminum bars?)