cap n chris
Well-known member
ianball11 said:
What thickness rope do you routinely use?
Standardisation of some caving statements eg. i can do srt
- Thread starter hrock
- Start date
What thickness rope do you routinely use?
Leclused
Active member
Fulk said:
I think the risk is less with a simple. Just imagine that on a long pitch you are softing your grip on a stop due to hand or wricht-ache at this stage you will continue to descend with the stop causing extra rope friction and buring the rope. With a simple you'll probably stop and rest on the rope.
BR
Dagobert
Joe90
Member
If the Stop/Simple is hot enough to glaze a rope, then surely stopping will burn one section of rope far worse then if you slide over it briefly?
Not arguing either way here by the way just stating a point.
Personally I use a Stop but I and have an ID for anything bigger, I have not used a Simple before.
Not arguing either way here by the way just stating a point.
Personally I use a Stop but I and have an ID for anything bigger, I have not used a Simple before.
Leclused
Active member
Joe90 said:
I didn't say that the simple got hot engough. I said that with a simple you stop at the moment you start to have a hand or arm ache. With a stop you continue and then the heating builds up due the less pressure on the deadman handle.
That's my point of view of course
Dagobert
Wetting the rope is standard practice of course but sometimes it's not that easy, Eldon hole in summer, we asked the farmer if we could dunk our rope in his cattle drinking bath, he said no, because the lubricants in the rope weren't good for the water! (Took me by surprse that did, didn't think a farmer would know that)
And obviously wetting the rope once when you've 4 people coming down loses its effects after each person compresses the rope around the bobbin
CapnC - I own 10mm rope, the last few trips I've been on have been on 9mm and I get nervous about overheating irrespective of the rope diameter. Partly because it's not my rope.
I find the worst area is at the pitch bottom. People abseil down a bit too quickly then stand at the bottom with the stop on the same piece of rope, undoing the braking krab, or something other than getting the warm stop off the rope. I try to keep the rope moving through the stop whilst taking it off to dissipate the heat generated.
On a cold day, a warmed up stop is quite nice to hold.
And obviously wetting the rope once when you've 4 people coming down loses its effects after each person compresses the rope around the bobbin
CapnC - I own 10mm rope, the last few trips I've been on have been on 9mm and I get nervous about overheating irrespective of the rope diameter. Partly because it's not my rope.
I find the worst area is at the pitch bottom. People abseil down a bit too quickly then stand at the bottom with the stop on the same piece of rope, undoing the braking krab, or something other than getting the warm stop off the rope. I try to keep the rope moving through the stop whilst taking it off to dissipate the heat generated.
On a cold day, a warmed up stop is quite nice to hold.
langcliffe
Well-known member
I always pack my ropes the day before and dunk them in water. They then drain overnight, and next day are still moist enough to keep the descender cool but not heavier enough to be a pain.
Proper heat dissipation is a reason for a rack - they do a good job of it and wont burn through the rope on long rappels. 
I guess stops/simples could be used here, based on some of what you have said but I still have my doubts it wouldn't present a large array of problems based not only on what I have learned about them, but also what we here know of our ropes and our pits. The reason racks were invented were specifically for our long rappels. In fact they were invented right here in the same city which I live by John Cole, a NASA engineer! There's a reason no one uses stops and such here...they /suck/ for our caves and are considered unusable. To be honest especially if the trip is anything over 100-150ft I doubt a trip leader here would even let you bring one.
I guess stops/simples could be used here, based on some of what you have said but I still have my doubts it wouldn't present a large array of problems based not only on what I have learned about them, but also what we here know of our ropes and our pits. The reason racks were invented were specifically for our long rappels. In fact they were invented right here in the same city which I live by John Cole, a NASA engineer! There's a reason no one uses stops and such here...they /suck/ for our caves and are considered unusable. To be honest especially if the trip is anything over 100-150ft I doubt a trip leader here would even let you bring one.
Joe90
Member
Quote - Dagobert
"I didn't say that the simple got hot engough. I said that with a simple you stop at the moment you start to have a hand or arm ache. With a stop you continue and then the heating builds up due the less pressure on the deadman handle.
That's my point of view of course"
Sorry still not worked out the 'quote' thing.
I see your point, but presuming you have the dead end of the rope in your stronger hand. With a stop your weaker hand will be holding the handle, yes it will get tired faster, and probably yes resulting in you slackening your hold on the handle closing the cam, creating more friction. Now I might be wrong here, but using a Simple you still have the rope in the stronger hand. Allowing you to abseil much further before getting a sore hand/wrist..... surely this would also add to the heat of the device meaning by the time you feel the need to stop on your stronger hand it will also be damn hot.
"I didn't say that the simple got hot engough. I said that with a simple you stop at the moment you start to have a hand or arm ache. With a stop you continue and then the heating builds up due the less pressure on the deadman handle.
That's my point of view of course"
Sorry still not worked out the 'quote' thing.
I see your point, but presuming you have the dead end of the rope in your stronger hand. With a stop your weaker hand will be holding the handle, yes it will get tired faster, and probably yes resulting in you slackening your hold on the handle closing the cam, creating more friction. Now I might be wrong here, but using a Simple you still have the rope in the stronger hand. Allowing you to abseil much further before getting a sore hand/wrist..... surely this would also add to the heat of the device meaning by the time you feel the need to stop on your stronger hand it will also be damn hot.
1m/sec is considered appropriate speed of decent. Rope only glazes if you go too fast for the rack you are using. Do you not wear gloves there? Here you wear leather rappel gloves. And keep in mind there are a HUGE variety of them not just the 5bar Petzl with the red bars I see sold on the cavegear supplier's sites there (I realize you must have other versions but that's the one I see sold on sites there). The type of bars (design, thickness, composition of the material...), the length of the frame, etc all play into the equation.Ouan said:Amy said:Proper heat dissipation is a reason for a rack - they do a good job of it and wont burn through the rope on long rappels.
From personal experience racks can get hot enough to burn flesh and will glaze rope if you go fast enough.
jarvist
New member
It's all simple energy conservation - you must turn your potential (m*g*h) into heat (mass_of_heated_object * Specific Heat Capacity * Temperature Rise). For a short, quick drop (adiabatic limit), all this energy ends up as hot metalwork.
Racks don't have magic powers, they just weigh more and thus have greater heat capacity.
For a longer drop, you'd have to try and work out the loss of heat to the environment by the abseil device, which with wet rope will certainly be conduction (harmlessly) into the water of the rope.
Rebelays seem to take enough time to limit the temperature of a bobbin to a sane limit, it's only on long hangs that I've ever steamed rope, or noticed glazed rope. In steady state (i.e. a infinitely long hang) you'll reach the point where you are flashing to steam / melting the nylon sheath of the rope a constant amount per metre, irrespective of speed. Just don't stop, otherwise you may crimp through the rope
My understanding is that the motivation for a rack on a long hang is not just the increased thermal mass, but the ability to vary friction as you go down to compensate for the weight of the rope below varying. On a >60m hang on a bobbin, you end up having to haul yourself down the top half. It's really odd, you feel like you're on an upside down prussic setup, except taking the 'steps' is almost free.
cap n chris
Well-known member
Joe90 said:
Not debating the accuracy or relevance of this but just adding that when using a Simple (because it has no "dead man's handle") it might be a wise(r) plan to have both hands on the feeding rope just in case you take a significant unexpected hit to your controlling arm.
paul
Moderator
jarvist said:
However, I remember some investigations (sorry - I can't remember the source just now*) on heat generation when using a rack and the outcome was that they were not as good as they appear.
It seems that most heat is generated on the first or second bars (as may be indicated by the fact that these are worn at a faster rate) but because the bars are relatively isolated from each other, the heat isn't spread through the remaining bars as you would expect despite the relatively larger amount of metal to absorb the heat when compared to Bobbin-type descenders.
* found it:
See NYLON HIGHWAY NO. 9 - MAY 1978, Page 6 via http://www.caves.org/section/vertical/nhindex0115.html
jarvist
New member
paul said:
That's really interesting. I've previously burnt my thumb by touching the nut of my lower bobbin wheel on my simple when it was worn (beyond where it should have been replaced) after doing a fairly brisk abseil down about 15m.
I imagine that similarly with less contact area between the wheels and the plates, the wheels and the thread were pretty thermally isolated (+ low in mass), leading to a surprisingly high temperature for a relatively small abseil.
Incidentally, I've just calculated the 'worst case' scenario of an infinitely long abseil on 9mm dry rope at infinite speed at an ambient temperature of ~200C (descent into hell? 8~) ), and the result is that you end up fusing just under 4g of sheath per metre, which is only ~7% of the total mass of 9mm rope. So you'd survive it just fine, but the rope might be a write off.
Do the same calculation with vaporising water, and you just need .3ml per metre.
It's difficult to estimate the mass of a glaze on a rope, but this figure seems roughly correct order of magnitude for the worst ones I've seen.
jarvist said:
Yes most of the friction (and wear) is on the top two bars. We have special thick (they are almost solid!) bars for this which helps, and grooves will keep the rope traveling in the center rather than wiggling about and running against the frame. You have to remember we have a HUGE range of racks and bars here not just the Petzl 5bar no hyperbar standard thing I see for sale on all your caving sites. I'm sure some others trickle over but not sure how much ya'all are aware of just the variety. Basically quick run-down of benifits (and why we use) racks:paul said:
1) Good heat dispersion, yes you hit a max as you will with all things, but with the right setup for the drop you are fine, and should not glaze rope (if you glaze rope you're doin' it wrong!)
2) Excellent friction variability - smooth from top to bottom, no feeding rope, you can start at the top of a 2650ft rappel (El Cap!) or more and not feed rope, and as you loose the ropeweight beneath you increasing friction is easy and effortless to stay in control the entire rappel. Our ropes esp when wet and/or muddy figure 10pounds per 100ft. A typical drop is 200 or so min so even on "short" stuff you have easy 20ft of weight under you at the top, stiff so doesnt bend through the bars easy, and mud or dirt or anything gums things up and increases friction on the system making getting started even worse.
3) Easy to use and highly versitile
4) Good with thick rope, stiff rope, muddy rope, wet rope, dirty rope...all things that increase friction are easily managed for a smooth effortless ride.
I will say I hear from a lot of cavers out West that they use stops or simples, but they have short stuff. I do know both have a bad rep more from being missunderstood and not used as much in the US. When I started I actually wanted to get a stop (as I had to train myself to not let go of the rope...my reaction used to be to let go! i know I know...reverse!) but was told not to, so I went with a microrack for similar range but smaller without the bulk of a large rack instead.
HOWEVER with TAG region caving a rack is definitely a requirement not an option. Something short someone might let you use one but I doubt trip leaders in general would be comfortable with either on something over 150ft and would want you on a rack - 100/150 ft is considered the range of them from all I hear here. Although they might let you use it and then laugh if it doesn't work at all or tease forever about having to feed rope
... There's a reason they are called stops, they just stop and dont let you move! :tease: The view here is basically "wet/muddy/thick rope = rack. Thin rope *and* lots of rebelays = stop/simple" So...we have wet muddy thick dirty huge stiff rope and mostly single pitch drops through and through in TAG so there is just no place for the latter. I have heard simples are better at handling our ropes than stops so probably better luck that way.Whenever I come back over ya'all will have to show me simples and stops and I'll show you the amazing world of racks!
