spinoff post about the stop

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spinoff post about the stop

Postby chaz » Sep 10, 2005 3:26 pm

The main breaking mechanism on the stop is released by moving the lever closer to the body of the stop. Breaking is accomplished by pulling the lever out. In practice one often holds the stop and lever with one hand and releases the break by clenching the hand. The break lever can be released differently but this often seems to happen, especially with nasty rope.

The problem with this scenario for learning is that rappelling is scary and a beginners instincts are to grab the rope/device as hard as possible. On any device but the Stop(and one or two others I've never seen used caving) grabbing will slow you down or at the very least, not release the device.


A few years ago, my cousin was in town and wanted to go caving. After a training session we proceeded to drop several pits in the 40 foot range. He was doing great! We then progressed to something a little deeper, a 70 ft pit with a hole in the wall that leads to another 30 ft of depth (nicely decorated) Here we go... He got down in position to swing over and grab the hole, but he missed and in a panic grabbed the stop in front of him! I heard an OH and a THUD! I called down to him and he was thankfully alright. He said "I accidentally grabbed the red handle and dropped 15 ft real quick". We passed on the second drop but we did learn what can happen with a stop. Even after drilling him about it! Chaz
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Postby chaz » Sep 10, 2005 3:37 pm

APB---- looking for anyone with experience with the SRTE stop. I believe it is made in Austrailia. Very similar to the Petzl stop, but it has a double brake. If you let go it stops, if you squeeze tightly it also stops.
I was wondering how long a drop are folks doing with stops, either Petzl or SRTE.
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Postby filox1 » Sep 10, 2005 4:36 pm

Hey,

that last one is a good question, what will the friction of a bigun will do to all those moving parts...hummm? :roll:

Any way I am old school so in caves and pits I always use a 6 bar rack...
for cannoning I will use ATC - fig 8 or mountain hitch, and where I was in vertical rescue I use the rescue fig 8, I even use the pirana a couple of times.

Never liked the stop or any like it, too many moving parts for my taste but in fairnes I can't say is bad for this same reason, so, Can any of you convince me to try one?
:wink:


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Postby hank moon » Sep 10, 2005 7:15 pm

filox1 wrote:Never liked the stop or any like it, too many moving parts for my taste


If you like the rack, stick with it. Guessing you don't frog...? BTW a 6-bar rack has about 6 moving parts, whereas the STOP has 3 (not counting the springs). :wink:

Chaz: brake, man, brake, but try not to break!

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Postby filox1 » Sep 11, 2005 12:08 am

Hi Hank,

Sure I frog and sure there are moving parts on the ascender and such, and also aware of the six bars in my rack but this bars once I set them up they stay put and only apply friction to the rope alas the stop as I understood it has tree wheels whit some kind of bearings I guess.

I am an engineer and some years back was in charge of maintaining some machinery, any way we had to replace bearings as a routine in some of the machines and if you miss any the rotating part will either freeze or come apart. Also there are external factors like rust or grid between the moving parts.

So if you can explain how the stop works and why the moving parts wont fail with time I'll appreciated.
:?
also how hot will it get after a big drop... say over 150m?

Thanks
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Postby NZcaver » Sep 11, 2005 3:32 am

Ah, the evil stop descender... :twisted:
(Just kidding!)

I can't resist chiming in on this discussion. As a bit of a gear junkie, I've taken a few different descenders caving over the past couple of decades - the big U rack, big J rack with hyperbar, micro U rack with hyperbar, Kong Speleo, Petzl Stop, and Troll Allp. I might have even been spotted using a figure 8 or a Munter (Italian) hitch occasionally, but I don't make a habit of it.

Anyway, the descender I have used most over the years (by far) is the Petzl Stop. It's not perfect for all users in all situations, but then what is? I would not generally recommend it as the first descender for a novice. Any person using one for the first time needs to know that the handle is like a park brake in a car - NOT used for speed control. That's what your other hand is for, just like any normal descender. It you don't grip the rope before you grab the handle, you will end up doing what chaz mentioned in his post.

Actually, I saw the same thing happen years ago to a novice using a Kong Speleo (similar to a Stop). He did a knot pass (for practice) while rappelling down a cliff, then grabbed the handle to continue his rappel without first grabbing the rope below with his other hand. He sped down the last 10m/30ft of a rope and hit the ground, breaking his wrist while still trying to grab the rope below his descender. He was lucky.

As chaz stated, there are also double-action autostop descenders available which apply a brake if you either let go or squeeze too hard. SRTE and Anthron make two that spring to mind. I have borrowed and used an Anthron, but personally it didn't feel as comfortable to me as the Stop. I found that squeezing the handle half way to find the sweet spot took some getting used to. However, I have no doubt that this extra safety feature all but eliminates the risk of an out of control descent caused by "grab reflex". Despite my opinion the Anthron is a popular ascender - it's smaller, lighter, and at under US$100 much cheaper than the SRTE double stop.

For someone who mostly does longer drops (say 60m/200ft plus), I would suggest looking for something other than a Stop. A rack would be more suitable, particularly if is a J type or has a hyperbar - thereby allowing you to add or remove friction while on rappel. You can add some friction to a Stop by using a braking carabiner (I always use a Petzl Freino with my Stop), but I found it still doesn't have quite the same measure of control as a rack.

I also found that the action on earlier-version Stops was not as positive as it is on the current version - which probably led to the nickname Petzl "Slow". On my old one, I often had to tap the handle out to stop myself slowly sliding down the rope - but of course I would lock the descender off when sightseeing and snapping photos anyway. Just something to be aware of with those earlier Stops (the model that has the metal carabiner clip, rather than the newer plastic one.)

I will say that once you master the handle, the Stop is great for doing multiple drops and passing rebelays. It has a convenience and ease of handling that is hard to match. Plus it has less bulk and weight compared to most racks. The comments from filox1 about friction vs human bulk reminded me of something. In recent years, I seem to be (unintentionally) rappelling faster on my Stop that I used to. Perhaps I'm not as light as I used to be, or maybe I drag more stuff underground now. I especially notice this on newer ropes, or ropes less than 11mm (surprise, surprise.)

However, I don't think filox1 has anything to worry about when it comes to moving parts failing on a Stop. I'm not aware of any cases where that's happened, despite frequently being used in mud, grit, ice, and so forth. The lower stainless steel bobbin (connected to the handle) does rotate, but only about 30 degrees. This pinches the rope between the flattened top surface of the lower bobbin, and the round upper aluminum bobbin which is fixed to the backing plate. I strongly recommend filox1 borrows a Stop and tries it out - he might be pleasantly surprised! I'm always willing to lend one of mine to anyone who wants to play.

I tend mostly to teach first timers on a micro-rack or other U rack, often with a hyperbar. I introduce the Stop and larger J rack (if appropriate) once the basics are mastered. The Munter hitch, along with Prusik knots for personal ascending, are taught in the "backup techniques" category. I know many cavers descend on figure 8's, but they're not my choice for a few reasons. Firstly, the figure 8 was initially designed for descending a double rope - and SRT caving uses, by definition, a single rope. Secondly, it twists the rope. Thirdly, aluminum 8's deposit an awful lot of aluminum onto/into the rope. And lastly, I don't allow them to be used on my ropes. It's a personal thing.

For personal use, I have recently been rappelling more on my Troll Allp than my Stop. The Allp is also a bobbin-type descender, similar in size to a Stop, but it doesn't have a brake handle. It does however have a continuously variable friction adjustment, which is great for a smooth descent - short or long drop, light or heavy caver, big pack or not, one or two person load, etc. Unfortunately the Allp (also known as Alp with one "L") is expensive and a little hard to find, even in the UK where it's made.

I think the key thing here is that cavers should make informed choices about what fits their needs and their personal preferences - and periodically reassess those choices while keeping an open mind. True of many other things in caving and life in general, really.

Well, that's my 2 cents for tonight.

Cave Safe :waving:
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Postby chaz » Sep 11, 2005 8:58 am

Filox,
sounds like you are quite happy using the gear that you are using, but if you ever get the chance to check out a stop or even try it, I think as an engineer you will find it interesting and not as scary as you may think.
Thanks for your post.
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Postby chaz » Sep 11, 2005 9:08 am

NZ Caver,
Thank you for the info. I see you recommend the stop for up to 60 meters, What is the basis for this depth? Got any stories about longer drops and the difficulties or challenges involved? Thanks again! Chaz
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Postby NZcaver » Sep 11, 2005 3:00 pm

Hi chaz,

The 60m/200ft "depth limit" for using a Stop is just an estimate, and it's only my opinion. It could vary greatly with the type, diameter, and cleanliness of the rope, and the size and preferences of the user.

The reason I mentioned this is because the Stop is not a variable friction device like the J rack is. If you do a long drop, you will normally want to start with less friction at the top and add more as you descend. This compensates for the weight of the rope below you slowing you down. When you start a long descent you often need to pull up on the rope, which could weigh 4.5kg/10lbs for 60m/200ft of 11mm rope. (330m/1000ft of rope could weigh about 23kg/50lbs!) As you get further down you begin moving under your own weight, and eventually you probably want to add more friction to your descender before you go splat at the bottom.

This whole process would be more difficult with a Stop because you can't generally add/subtract friction, and because you need both hands to operate it (although the Stop is designed so you can deactivate the brake handle by clipping in a carabiner - not that I've ever seen anyone do it in a cave). The big drops are where the big J racks come in - I don't think there's any better device to use in this particular situation. Of course its bigger, heavier, and a little more complicated than a Stop for getting on/off rope or doing a changeover with, but that's the trade-off.

I think filox1 asked how hot the Stop gets - from a hands-on (non-scientific) standpoint I would have to say a big rack dissipates heat better than a Stop. But the Stop isn't too bad, and probably rates about even with a smaller rack and far better than a figure 8. The side plates on a Stop work as a kind of heat sink, not that I advise speeding down and glazing your rope. Someone else's rope perhaps... :wink:

Oh, there's something else I should mention. Before this thread split off, someone said you can't use a Stop for double rope rappelling. Actually you CAN use one on double rope, but it's not in any of the books (to my knowledge). I've done pull-down rappels several times like this and it works fine, although the brake handle doesn't properly function in this configuration. I've also rigged a Stop to provide less friction than normal on a single rope, but again the brake handle doesn't function when used this way. Before you ask, I would rather not describe (in open forum) how to mis-thread the Stop to achieve this - people might think I'm promoting bad habits. :roll:

Enjoy!
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STOP

Postby hunter » Sep 12, 2005 12:57 pm

Hmm, interesting posts. It was nice to see a few examples of the "grabbing" issue with a stop. I've discussed it but never actually seen someone fall due to this.
I have used a stop on a 100M drop with fairly clean rope and had no issue. My main concern is overheating. The stop gets toasty on a 100M drop, especially when the rope is dry.

Filox, it's worth taking a close look at a stop if you get the chance. There is so little movement in the stop I'm not certain it even has bearings. You rotate a "bobbin" in the stop to brake but otherwise nothing moves when you are rappeling. (so no wheel is rotating as you rappel)

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Postby NZcaver » Sep 12, 2005 1:31 pm

I wonder if anyone has ever done a temperature comparison between different descenders, either while being used or right after?

I can't imagine it being too difficult to set up an experiment. As long as the rope type/diameter, the weight of the load, and the speed of travel stay fairly constant, you could measure the average temperature of each device using some thermal gizmo.

Now that I think more about it, I might have to revise my earlier statement about the Stop's ability to dissipate heat. The Stop does have a lot of surface area that contacts the rope - most of both bobbins, and (depending on the rope diameter) a big chunk of both sideplates. I do recall mine getting very warm on longer drops, but usually I don't ascend straight back up and do it again on a rack just to compare... :D

So perhaps I was a little hasty comparing a Stop's heat dissipation to that of a smaller rack. Some food for thought.
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Postby hunter » Sep 12, 2005 3:51 pm

NZCaver,
Interesting thought. I think just going by weight most large racks will be better than a stop but I almost never use a large rack so I've never felt how hot they get. Seems like it will depend on metal as well. I seem to remember aluminum having a lower heat capacity but a higher thermal conductivity.
My usual method is to check the stop near the bolt holding the bobbin on. If I can't keep my hand there I figure it is to hot and slow down. No real justification for this method but it hasn't melted the rope yet...

I've glazed spots on a rope with an ATC after a couple rappels off a long climb and the ATC sizzled if I touched it with a wet finger so I figure that is way to hot.

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Postby Scott McCrea » Sep 13, 2005 2:23 pm

NZcaver wrote:I wonder if anyone has ever done a temperature comparison between different descenders, either while being used or right after?


There was a nice thread in the previous (crashed) DB that was started by Jim Thompson about heat produced by descenders. We actually did some testing at Convention in July. Jim has a IR (?) camera that can see heat. We tested a stainless steel rack, aluminum rack and a few other things, but not a bobbin or Stop. Last I heard, Jim was going to do some more testing, but he owns a disaster clean-up service and I'm sure he's working somewhere on the Gulf coast right now.
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Postby filox1 » Sep 14, 2005 1:30 pm

well, I guess I`ll try to find me a stop some where around here and check it out...

About the heating issue, I use a big J 6 bar steel rack for big drops and in places like Guaguas o Golondrinas I will spray it With water from time to time in my way down to cool it down.

Thanks all on for the input on the stop, as I say I never use it and though that it had some kind of wheels but from the posts i getter that the round things (bobbins?)are fix right

Any way thanks. :wink:
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Postby NZcaver » Sep 15, 2005 6:55 pm

Hi filox1,

Yes, the bobbins on the Stop are fixed. The top bobbin is fixed to one of the sideplates, and the bottom one is fixed to the handle - and rotates about 30 degrees relative to the sideplate as you operate it. All bobbin-type descenders I know of use "fixed" bobbins - otherwise you would freefall on them! You can download the user manual for the Stop at
http://www.petzl.com/ProduitsServices/D ... 9800-H.pdf

Try one out some time! :kaver:
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