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doogle
Nov 10, 2009, 10:17 AM
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According to Petzl, you can use a single rope down to 8.9 mm or a half rope down to 7.5 mm. Considering you can catch a fall on one half rope, why the discrepancy?
I notice the Black Diamond do not make this discrimination for the ATC Guide.
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I_do
Nov 10, 2009, 10:38 AM
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doogle wrote: According to Petzl, you can use a single rope down to 8.9 mm or a half rope down to 7.5 mm. Considering you can catch a fall on one half rope, why the discrepancy? I notice the Black Diamond do not make this discrimination for the ATC Guide.
Maybe because half's are more dynamic lowering peak force making it easier to arrest a fall? And the second rope is always there it will eventually chime in (most of the times). Or it might be due to being able to catch a fall when set up in auto-lock mode which is what my money is on.
But I'm sure someone will tell me I'm a retard and provide the right answer ;o)
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the_climber
Nov 10, 2009, 3:03 PM
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It has to do with the amount of friction provided by the device. The thinner your rope the less friction provided by the device (this is true with any belay device). So, taking that into consideration, there is a point at which the reduction in friction is such that holding a fall (or rappeling in many situations) isn't recommended. With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible.
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the_climber
Nov 10, 2009, 3:05 PM
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I_do wrote: *snip* But I'm sure someone will tell me I'm a retard and provide the right answer ;o)
Oh, and....
You're a retard! STFU nOOb!
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shoo
Nov 10, 2009, 3:16 PM
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the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible.
That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted.
Your argument is only valid for twin ropes.
Edited to add: I verified that this indeed what is stated in the instructions.
In reply to: Belay / rappel device for climbing and mountaineering. Compatible with CE (EN 892) and/or UIAA certified dynamic ropes (core + sheath): - half or twin ropes (2 x 1/2 ropes) >= 7.5 mm, - single rope >= 8.9 mm. This product is designed for rope diameters up to 10.5 mm (11 mm accepted). This product must not be loaded beyond its strength rating, nor be used for any purpose other than that for which it is designed.
http://www.petzl.com/...EVERSO3_D175000F.pdf
(This post was edited by shoo on Nov 10, 2009, 3:25 PM)
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doogle
Nov 10, 2009, 3:55 PM
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shoo wrote: the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible. That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted. Your argument is only valid for twin ropes.
Yes. This is my point exactly.
The twin rope case is obvious.
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shoo
Nov 10, 2009, 3:57 PM
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doogle wrote: shoo wrote: the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible. That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted. Your argument is only valid for twin ropes. Yes. This is my point exactly. The twin rope case is obvious.
Agreed. I'm actually going with a typo or poor editing on this one.
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the_climber
Nov 10, 2009, 4:06 PM
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shoo wrote: the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible. That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted. Your argument is only valid for twin ropes.
Shoo, how about you get some reading glasses.
Ie, 2 8.5mm half ropes, in independent slots on the devices, each giving aprox the same friction...as there is two of them (see my prevision post) you will get 2x the friction as you would only using 1 8.5mm rope.
(This post was edited by the_climber on Nov 10, 2009, 4:07 PM)
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doogle
Nov 10, 2009, 4:13 PM
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the_climber wrote: shoo wrote: the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible. That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted. Your argument is only valid for twin ropes. Shoo, how about you get some reading glasses. Ie, 2 8.5mm half ropes, in independent slots on the devices, each giving aprox the same friction...as there is two of them (see my prevision post) you will get 2x the friction as you would only using 1 8.5mm rope.
You seem to be missing the point that you can be caught on only ONE half rope. Not always two, as in twin ropes.
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the_climber
Nov 10, 2009, 4:24 PM
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doogle wrote: the_climber wrote: shoo wrote: the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible. That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted. Your argument is only valid for twin ropes. Shoo, how about you get some reading glasses. Ie, 2 8.5mm half ropes, in independent slots on the devices, each giving aprox the same friction...as there is two of them (see my prevision post) you will get 2x the friction as you would only using 1 8.5mm rope. You seem to be missing the point that you can be caught on only ONE half rope. Not always two, as in twin ropes.
No I get the point. The reverso is "RATED" for half and twins assuming both are in use.
That is the difference in ratings. "Use" and "ratings" are 2 different concepts.
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shoo
Nov 10, 2009, 4:26 PM
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the_climber wrote: shoo wrote: the_climber wrote: With double/half/twin ropes it is assumed you will be using 2 ropes. You get twice the friction from the device because you have 2 ropes threaded through. This allows it to be used with doubles/twins to a lesser diameter. However, even that has a point at which it becomes less recommended/feasible. That is absolutely false. You have 2 ropes threaded through 2 separate and independent slots. The two ropes have no real interaction with each other. In double/half rope technique, only one strand is being weighted. Your argument is only valid for twin ropes. Shoo, how about you get some reading glasses.
TC, how about you get a physics lesson.
As has been stated, when using DOUBLE/HALF technique, a fall results in ONLY ONE STRAND BEING WEIGHTED. If you are unclear how this works, please look up double / half technique. While you are holding 2 ropes, only one of them is actually being pulled through the device.
Since the two slots are independent (i.e. the ropes are going through separate channels, with no interaction between the ropes), this can be considered to be virtually the same frictional force applied to the rope system as if a single rope of the same diameter were being pulled through the belay device.
Now, you can say that there is some argument that there is some additional benefit from the friction coming from a person's hand due to the larger shape of two ropes rather than one. If you are making this argument, and it is very clear that you are not, then you make two possibly valid assumptions. First, a person's hand can put more total clamping force grabbing two small ropes than one. And second, the rope-on-rope frictional force is sufficient to transfer this additional force to the loaded strand. However, this says nothing about the braking properties of the belay device, and is instead the braking properties of your hand.
With TWIN technique, BOTH strands are weighted at the same time, therefore you get frictional benefit from both strands, effectively doubling the frictional force. In that case, there is clearly more friction for fewer ropes.
However, the instructions clearly specify a reduced diameter rating for both half/double and twin rope techniques. While it is clear that there is additional braking power when using twin technique, it is not at all clear for half/double.
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shoo
Nov 10, 2009, 4:30 PM
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I was right! It's a mistake in their manual.
In reply to: single 8.9 mm -> 11 mm double > 8.5 mm twin > 7.5 mm
http://www.petzl.com/...vices-descenders.pdf
This clearly shows that there is a different rating for double and twin ropes.
(This post was edited by shoo on Nov 10, 2009, 4:31 PM)
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doogle
Nov 10, 2009, 4:36 PM
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shoo wrote: I was right! It's a mistake in their manual. In reply to: single 8.9 mm -> 11 mm double > 8.5 mm twin > 7.5 mm This clearly shows that there is a different rating for double and twin ropes.
Well, that seems odd. Nice find.
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the_climber
Nov 10, 2009, 4:43 PM
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shoo wrote: That is absolutely.
Absolultely have to consider the friction from every souce... yes I paraphrased that one.
Doubles are independent.... (Not always BTW.)
Look, there are many techniques we can use climbing. Use of absolutes in climbing should be avoided.
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doogle
Nov 10, 2009, 4:48 PM
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the_climber wrote: No I get the point. The reverso is "RATED" for half and twins assuming both are in use. That is the difference in ratings. "Use" and "ratings" are 2 different concepts.
Of course, you can use your ropes how you like.
However, I would have thought the fundamental difference between halves and twins is that half ropes are designed to be clipped independently, and twin ropes through each piece. Is this not assumed knowledge?
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shoo
Nov 10, 2009, 5:03 PM
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the_climber wrote: shoo wrote: That is absolutely. That seems to be your catuch phrase lately shoo. Absolutely one one leader in a 3 person team. Absolultely have to consider the friction from every souce... yes I paraphrased that one. Doubles are independent.... (Not always BTW.) Look, there are many techniques we can use climbing. Use of absolutes in climbing should be avoided.
Your statement that the frictional force would be double is false in absolute terms. It is certainly not 2x the force and is most likely closer to 1x the force. I made no claim that it would be exactly 1x the force either, since there is rarely a such thing as truly independent systems.
However, I certainly accept your criticism of my general use of absolute terms. You're certainly right on that, and I apologize. I have made the same argument many times, including on this site, and should probably follow it more closely.
Always a good thing to have a little humility thrown at me, no?
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edm
Nov 10, 2009, 5:04 PM
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The rating discrepancy has nothing to do with the variation in friction.
There is no such thing as a single rope smaller than 8.9mm. Therefore the device cannot be rated for single ropes smaller than 8.9mm.
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doogle
Nov 10, 2009, 5:07 PM
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edm wrote: The rating discrepancy has nothing to do with the variation in friction. There is no such thing as a single rope smaller than 8.9mm. Therefore the device cannot be rated for single ropes smaller than 8.9mm.
Did you read any of this thread?
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edm
Nov 10, 2009, 5:16 PM
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I certainly did. I maintain that the discussion about the amount of friction obtained when a fall is taken on one or two strands is not relevant to the question in the original post.
The reason the Reverso 3 is rated down to 8.9mm for single ropes is because that is the smallest single rope there is.
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doogle
Nov 10, 2009, 5:24 PM
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edm wrote: I certainly did. I maintain that the discussion about the amount of friction obtained when a fall is taken on one or two strands is not relevant to the question in the original post. The reason the Reverso 3 is rated down to 8.9mm for single ropes is because that is the smallest single rope there is.
My apologies, I didn't think hard enough about your post.
Point taken, that seems like the likely explanation.
Still, seems a bit weird. Would you quote the top speed of your car as 100 km/h if that was the speed limit?
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edm
Nov 10, 2009, 5:34 PM
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No worries.
It seems to me that to rate the device for a sub-8.9mm single rope Petzl would need a sub-8.9mm single rope to do the tests with. There's no such thing, hence no lower diameter rating.
I suppose Petzl could do the testing using a half rope as a single rope, but I suspect providing a smaller single-rope diameter rating could be construed by some legal types as implicit encouragement to their customers to do the same in the field. It likely comes down to a legal issue rather than the performance limit of the device.
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doogle
Nov 10, 2009, 5:57 PM
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Good point
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shoo
Nov 10, 2009, 6:11 PM
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edm wrote: No worries. It seems to me that to rate the device for a sub-8.9mm single rope Petzl would need a sub-8.9mm single rope to do the tests with. There's no such thing, hence no lower diameter rating. I suppose Petzl could do the testing using a half rope as a single rope, but I suspect providing a smaller single-rope diameter rating could be construed by some legal types as implicit encouragement to their customers to do the same in the field. It likely comes down to a legal issue rather than the performance limit of the device.
I seem to remember Malcolm Daly from Trango stating somewhere on this site that the CE certification is the near equivalent of saying that the belay device passed some test from the manufacturer, whatever that test may be. The best part about Mal is that when you say his name, he tends to magically appear for comment. . .
In any case, the UIAA test for belay devices is quoted below:
In reply to: Strength Test 5.1. Manual Braking Device—device and rope breaking strength For each attachment point of the device: Place the device as shown in Figure 2 with an I/O angle of (30 ± 5) °, the rope is inserted as described in the manufacturer’s instructions. Test single rope or half rope (according to UIAA 101) of the minimum diameter acceptable according to manufacturer’s instructions. Twin rope shall be tested with 2 strands. The pulling speed shall be (100 ± 30) mm/min. Reach the load of [8(+0.5/-0)] kN. Maintain the load for (60 ± 10)s. The device shall not release the loaded rope, shall not show any visible damage, and shall continue to function properly. The rope shall not break. If more than one braking configuration is described in the manufacturer’s instructions, each configuration will be tested with a new rope specimen
http://www.theuiaa.org/...vice_2009%281%29.pdf
In other words, half/double ropes are tested in the same manner as singles, which makes sense.
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