Stop style bobbin question

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Re: Stop style bobbin question

Postby pub » Jul 17, 2012 12:03 am

TennEagle wrote:I do have the Petzl Stop manual, and it does have diagrams showing the addition of a carabiner for braking and an explanation of its use... http://wesspur.com/images/pdfs/petzl-stop.pdf "Additional Braking" is on Page 4, Figure 3A, with the description on Page 6.
That is the same Technical Notice: STOP D09 réf. : D09800-H (211004) that came with my Stop.

However, in the latest version, D09 STOP D098000I (250610), Petzl now recommends placing the braking carabiner directly on the Stop attaching carabiner and warns against placing the braking carabiner on the harness (See Fig 7A on Pg. 2).

http://www.petzl.com/files/all/technica ... 9-STOP.pdf

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Re: Stop style bobbin question

Postby NZcaver » Jul 17, 2012 12:57 am

pub wrote:... Petzl now recommends placing the braking carabiner directly on the Stop attaching carabiner and warns against placing the braking carabiner on the harness

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Well spotted. Also note Petzl's reasoning behind this recommendation is to prevent the upper end of the Stop from becoming trapped in the braking carabiner and significantly reducing friction. If you use a carabiner small enough not to cause problems (like a Raumer Handy), positioning shouldn't be an issue.
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Re: Stop style bobbin question

Postby Jeff Bartlett » Jul 17, 2012 8:57 am

NZcaver wrote:Well spotted. Also note Petzl's reasoning behind this recommendation is to prevent the upper end of the Stop from becoming trapped in the braking carabiner and significantly reducing friction. If you use a carabiner small enough not to cause problems (like a Raumer Handy), positioning shouldn't be an issue.


This is correct. If I may elaborate a bit here:

One thing of note about this particular failure mode is that it's only possible if there is a major shockload from below the rappeller, e.g. a failed rebelay directly below you where the sudden shockload on the lower rope pulls the rope taut below your descender. While I'm sure this has happened in the past, it seems exceedingly unlikely, and your mileage may vary based on how often you find yourself in this situation; while expedition cavers surely find themselves rappelling above a single-bolt rebelay, with another rappeller below that rebelay, frequently... many American cavers may never encounter this situation at all.

From Alpine Caving Techniques, 3rd ed:

Marbach & Tourte wrote:The problem of correctly placing the braking carabiner below the Simple descender deserves special attention here. This carabiner is practically indispensable for comfortably controlling your rappel speed, for effectively locking off, and for saving the right glove from excessive wear between the thumb and forefinger. Traditionally, this carabiner is placed in the harness maillon to the right
of the descender. However, experience has shown that in this position, an abrupt loading of the lower rope -- for example, when an anchor at a rebelay separating two climbers falls (fortunately, a rare event) -- could cause the upper end of the descender to jam in the braking carabiner. It remains stuck there while the sideplates separate under the lower spool without, however, causing it to fail or to become significantly distorted. If the pull on the lower rope is the result of a temporary and somewhat less brutal loading and is quickly rectified. The top of the descender still remains stuck In the carabiner; reducing the braking action practically to nil, presenting the risk of an uncontrolled descent and a very hard landing below.

To avoid this possibility. some cavers prefers to pass the lower rope directly back through the carabiner connected to the descender, which obviously requires repeated screwing and unscrewing of the gate. If the caver is using an auto-locking carabiner, some of these actions are simplified. However, one must be careful that the direction in which the rope passes through the carabiner does not rotate the locking sleeve open by rubbing against it. There IS another drawback to using this method, called the "Vertaco" method : if an anchor falls as described above, the sideplates on the descender could end up bending at right angles. possibly even breaking at the attachment hole... We therefore do not recommend this method.

Another group attaches the braking carabiner to the descender carabiner. The potential anchor rupture scenario does not result in any distortion or destruction of the descender, but effective braking will require the user to lift his right hand even higher, causing fatigue in the arm and more rapid wear on the right glove. We certainly do not recommend placing the carabiner in the hole of the descender's closure gate: the result is the same serious drawback of the second method, combined with the risk of losing the carabiner during the operation, which will then take longer to carry out. Finally and for the record, there are those who intend to avoid all of the above mentioned risks by systematically leaving a free length of line between any two climbers. This non-solution to the problem will lengthen the time it takes to complete the climbs and interrupt communication between team members, and fortunately has little hope of becoming widely accepted.


ACT goes on to recommend the Handy as a solution to all of the problems noted above.

One thing Petzl fails to mention is that attaching the braking carabiner directly to the attaching carabiner routes the rope in such a way that it will wear a groove in the front plate of the Stop. As noted previously, a Raumer Handy or a small carabiner like a Metolius FS Mini will also prevent this failure mode, even when attached to the harness. Please note: the Raumer Handy basically does not function on 11mm PMI; in fact, it's literally difficult to put the rope into the carabiner. I have an essentially new one that has been on rope once, and I'd be happy to sell it to a caver who finds themselves on 9mm or 10mm rope frequently... I sure don't!
"Although it pains me to say it, in this case Jeff is right. Plan accordingly." --Andy Armstrong
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Re: Stop style bobbin question

Postby snoboy » Aug 11, 2012 5:44 pm

Hey Jeff - If you are you using the funny little ring that comes with the Handy, you can flip it around, and use the rounded end of the carabiner for braking. Works great for larger/fuzzier/muddier ropes. Of course you have to be able to get the rope into the biner for it to work!
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