Wet or Dry rope SRTing ???
- Thread starter Geoff R
- Start date
Quote from Graham:
Yeah, well, very nice to handle . . . but didn't you hear the story of the poor guy who was climbing the last pitch in Dale Head on this stuff (or so I believe), the sheath of which parted company from the core as he was prusiking up?
Anyway, he evidently slid down the rope until the knot in the end caused the sheath to bunch up, and he had ? very gingerly and slowly, pushing off from the wall ? to climb back up the exposed core . . . I think I'll stick to modern SRT rope! (Rumour has it that his underpants needed a good wash later.)
Yeah, well, very nice to handle . . . but didn't you hear the story of the poor guy who was climbing the last pitch in Dale Head on this stuff (or so I believe), the sheath of which parted company from the core as he was prusiking up?
Anyway, he evidently slid down the rope until the knot in the end caused the sheath to bunch up, and he had ? very gingerly and slowly, pushing off from the wall ? to climb back up the exposed core . . . I think I'll stick to modern SRT rope! (Rumour has it that his underpants needed a good wash later.)
JasonC
Well-known member
Bollox I am !Fulk said:
<waves antique Physics A-Level certificate in the air>Fulk said:
Yes indeedy, but the question is what sort of energy ? The point I was trying to make was that - assuming the potential energy is converted mainly into kinetic energy and heat from friction - descending slowly reduces the the KE (being proportional to velocity squared) and therefore increases the heat. Conversely, descending quickly increases the KE at the expense of frictional heat - as you rightly say, it all has to go somewhere.
So it follows that to reduce overall heating of the rope, you should descend as fast as possible - as fast as safely possible, I should say - which is perhaps counter-intuitive.
I admit this ignores any damage done to the small portion of rope in contact with the hot descender when you stop at the bottom - obviously it's best to unclip as fast as possible.
Peter Burgess
New member
Well the extreme is to drop the pitch with no rope at all. Then all your kinetic energy is converted into "something else" at the very bottom, apart from a small amount of heat and sound as you whizz through the air with the greatest of ease. I guess it would be your ultimate sacrifice in the noble cause of science.
TheBitterEnd
Well-known member
If understand Jason correctly, he is implying that the harder you hit the bottom, the less heat you generate. The difference being the amount of KE you absorb by bending you legs.
That said, I guess most of us will slow before landing ...
That said, I guess most of us will slow before landing ...
Peter Burgess
New member
There are some seriously bad misunderstandings of the concept of conservation of energy in this thread.
Peter Burgess
New member
And the one area that has hardly been touched yet is that concerning rates of heat transfer from rope to descender, descender to the air, etc. One thing that matters in terms of how hot something gets is how quickly the heat transfers to something else. The faster you put heat into it (determined by your rate of descent) the quicker you need to get rid of it to prevent the metal getting so hot it melts the rope. If you go slowly, the heat has a chance to escape before the temperature reaches a dangerous level. If you go fast, you will put energy into the descender at such a rate that it's temperature may rise to a dangerous level simply because the heat cannot transfer to the air or to the frame of the descender fast enough. As long as your rope is whizzing through the descender at a good old pace, you are spreading that heat along the length of the rope, but as soon as you slow down, you may be asking for trouble. I can't speak from experience, but would it be true that when ropes are found to be glazed, it is at points of slowing down such as rebelays, deviations, or the bottom?
It terms of heat transfer, I would estimate that heat will transfer to a wet rope faster than to a dry one, keeping the descender a bit cooler. Additionally, as has already been pointed out, the effect of evaporation of that water means that the rope temperature will not rise above 100 deg.C.
It terms of heat transfer, I would estimate that heat will transfer to a wet rope faster than to a dry one, keeping the descender a bit cooler. Additionally, as has already been pointed out, the effect of evaporation of that water means that the rope temperature will not rise above 100 deg.C.
Roger W
Well-known member
Oh dear! he said, trying to remember his A-level physics from the 1960's....
At the top of the shaft, our intrepid caver will have a quantity of potential energy depending on his weight (or, more correctly, his mass) and the depth of the shaft ( say, Titan, for example).
If he just steps off the edge, that potential energy will be converted into kinetic energy as he falls ever faster down the shaft.
That kinetic energy will be dissipated in a thoroughly unpleasant manner when he reaches the bottom.
If he makes use of a rope and descender, he will dissipate some of that energy as heat as he goes down and his descending device slows him up by friction with the rope. If he descends slowly, the heat will have more time to dissipate as he descends, and he will arrive gracefully at the bottom with only a little kinetic energy still to lose.
If he does an SAS abseil, dropping in free fall most of the way, he will arrive somewhere near the bottom with a whole lot of kinetic energy to get rid of. The violent braking necessary to slow him down to a suitable landing velocity will convert most of that kinetic energy to heat in a very short space of time, possibly resulting in a cherry-red stop and the fumes of vapourising nylon filling the air...
But the velocity gained due to gravity must be lost somewhere if you aren't going to make a hole in the floor when you land at the bottom. As Peter has just pointed out while I was typing this, it will be when you "slow down" - that is, brake more fiercely than you have been doing - that the temperature will go up.
At the top of the shaft, our intrepid caver will have a quantity of potential energy depending on his weight (or, more correctly, his mass) and the depth of the shaft ( say, Titan, for example).
If he just steps off the edge, that potential energy will be converted into kinetic energy as he falls ever faster down the shaft.
That kinetic energy will be dissipated in a thoroughly unpleasant manner when he reaches the bottom.
If he makes use of a rope and descender, he will dissipate some of that energy as heat as he goes down and his descending device slows him up by friction with the rope. If he descends slowly, the heat will have more time to dissipate as he descends, and he will arrive gracefully at the bottom with only a little kinetic energy still to lose.
If he does an SAS abseil, dropping in free fall most of the way, he will arrive somewhere near the bottom with a whole lot of kinetic energy to get rid of. The violent braking necessary to slow him down to a suitable landing velocity will convert most of that kinetic energy to heat in a very short space of time, possibly resulting in a cherry-red stop and the fumes of vapourising nylon filling the air...
But the velocity gained due to gravity must be lost somewhere if you aren't going to make a hole in the floor when you land at the bottom. As Peter has just pointed out while I was typing this, it will be when you "slow down" - that is, brake more fiercely than you have been doing - that the temperature will go up.
Peter Burgess
New member
How colourfully put.
All this talk of energy "absorbed", or "dissipated", in reality means something somewhere gets a bit warmer, whether its the rock, the rope, the rack or your entrails, depending on how you choose to reach the bottom of the 'ole.
And if you consider the simple physics, the same energy gets converted, "absorbed" or "dissipated" if you climb down a ladder. Hard to believe perhaps on the face of it, but true.
All this talk of energy "absorbed", or "dissipated", in reality means something somewhere gets a bit warmer, whether its the rock, the rope, the rack or your entrails, depending on how you choose to reach the bottom of the 'ole.
And if you consider the simple physics, the same energy gets converted, "absorbed" or "dissipated" if you climb down a ladder. Hard to believe perhaps on the face of it, but true.
JasonC
Well-known member
TheBitterEnd said:
That wasn't quite the point I was trying to make
In short, I was saying that descending quickly rather than slowly ought to result in less heat overall being transferred to the rope.
I may be wrong, but nothing in this thread so far has persuaded me that I am....
Anyway, it's all a bit OT, as has nothing to do with whether the rope's wet or dry, so I will cease and desist. Perhaps.
Peter Burgess
New member
The only thing that matters (when considering the energy equation) is the speed at which you hit the bottom. If you are barely moving when you touch down, then virtually all of your potential energy at the top will have been converted into heat somewhere along the line, either in the rock, your descender, or the air, and will transfer from one to either of the others depending on the temperature differences between them. If you have virtually no kinetic energy at the moment you reach the bottom of the rope, where else has all that potential energy gone?
It is sort of relevant to wet or dry ropes, as the heating effects will be different in each case.
It is sort of relevant to wet or dry ropes, as the heating effects will be different in each case.