French Wrap Self-Belay

[NZcaver]

David - thanks for explaining that before Scott got to me...

I see what you mean. I will have to try that some time (without the unconscious bit!) Unfortunately I don't often get to play with my 6 bar rack, because it's in storage with all my other mothballed possessions.

[Cheryl Jones]

On a 6-bar, J-frame rack you can engage enough bars so that you will be having to hold the lower bars apart to move on the rope; if you let go then the bars will move together and add friction. At the least you won't hit the ground at near free-fall velocity as you would if let go while rapping on a fig-8.

Cavers who put spacers between the first two bars on their racks reduce this inherent stopping power.

Cheryl

[hunter]

Slight side issue, Buford would it be possible for you to post some of the information about used caving ropes in the report that you mentioned? I was in a cave this weekend that had a 20+ year old rope in it which we replaced but I would be really interested in data on how much the nylon actually degrades over that time period.

On the FW, I'm curious and will have to mess with this at my next vertical practice session, but has anyone here actually tried hanging from the leg loop on their harness? I understand that it should hold but it still seems like one might end up in a really bad position. Following up on this, why not use a longer backup attached to your harness properly? Seems like it should still be possible to control with one hand and you could then switch sides. It will get stuck in the device if you fall but that seems better than ending up hanging by your leg loop.

James Hunter

[ian mckenzie]

has anyone here actually tried hanging from the leg loop on their harness?

The FW is intended to replace your braking hand should you inadvertently let go. It was not developed in order to hold you if your descender comes off the rope. But its still an interesting question. You'd have to test it under shock conditions of course in order to get a reliable result, and that might hurt.

I tried the FW for a short time, but replaced it with a carabiner (as Petzl suggests - I use a Stop) which does NOT halt you if you inadvertently let go (and your Stop brake does not work, as is common), but would at least leave you sort of attached to the rope should your descender disengage, and has saved at least one life when that happened above a rebelay. You could put a wrap round the biner I suppose, tho that would probably add too much friction for normal use.

[hunter]

Ian,
I use a stop as well and almost never use a backup due to the hassle. I've used a shunt but was kind of curious when I saw the FW article. I'm headed to vertical practice in 4 hours so I think I will mess around a bit. I understand that the FW really isn't meant for a full catch but having read that article about someone's stop coming off so I wonder if a best of both worlds is possible.

I thought about the shock issue a bit. Seems like dynamic rope or a screamer as your backup attachment would be best. Of course more modifications just create a hassle which is why people like me don't use a backup in the first place...

James Hunter

[Buford Pruitt]

James,

There was a pretty good "used rope" thread on the previous NSS discussion board, and it's a pity it was lost when that board went down. If you want to resurrect that thread, I suggest you start it anew and see if its former posters will re-post.

Modern caving 11mm static ropes achieve tensile strengths approximating 7,000 lbs when new. A good rule of thumb is that these ropes lose 2-4% per year of their strength. If you want a safety factor of 10x (the industry standard for recreational use) and want your ropes to hold a 300 lb person, then the rope should be retired when its tensile strength drops to 3000 lbs. These ropes will have a theoretical tensile strength of 3058 lbs when they are 40 years old at a strength loss of 2% per year, and a theoretical tensile strength of 3094 lbs when 20 years old at a strength loss of 4% per annum. I understand most cavers retire their ropes at 20 years or sooner.

I feel that it is time for a full-length article on the subject to be published in the NSS News. Bruce Smith published an excellent article on the subject in the Nylon Highway long ago.

There are destructive testing results out there, Bruce's and others, but the ones I've seen are several to many years old. There are a lot of misconceptions about what you can do vs should not do to ropes. There are newer types of ropes being used by cavers that were not tested and published in comparison to the standard nylon-on-nylon kernmantle static ropes (to my knowledge).

I have tried in vain to convince one particular rope manufacturer to write the article; maybe if enough others cry out for help, he'll relent and publish a modern summary.

[hunter]

Buford,
Thanks for the info, I'd never heard the 2-4% average but it is a handy number to know (for webbing as well). I'll try to start a decent thread on used ropes once I get some more time.

James Hunter

[Scott McCrea]

The following thread was rescued from the cache of the NSS Discussion Board, version 1.0 at Archive.org. For more info on Rescued Threads, go here.



Euro prusik below decender self belay?

Posted by: Tiny Manke on June 08, 2000 at 19:46:21:
Where can I find more information on the European style self belay placing a prusik BELOW the rappel device. This was described by Bill Putnam in the ACA report editorial.

======

Re: Euro prusik below decender self belay?

Posted by: Van Bergen on June 12, 2000 at 10:53:12:
In Reply to: Euro prusik below decender self belay? posted by Tiny Manke on June 08, 2000 at 19:46:21:

I found out from the more experienced members of Dayton Underground Grotto, who have been using it for years. They didn't know its "real" name, only that it was French. It's not a prusik, but four simple wraps starting at the top; both ends have a loop and are attached to your seat harness with a biner (preferably to the leg loop on your contol hand side). The end loop, the size cord to use, its length, and the number of wraps are subject to experiment.

It rides just below your control hand, which is always gonna be right there anyway. If you panic, you grip the rope tighter. If you get knocked unconscious, the wrap grips the rope. Either way, you stop.

Your control hand on the knot keeps it loose. If it does lock, a slight downward push unlocks it, so it won't hang you up. Just make sure it's not so long that it can touch the rack when loaded! I just started using it, and it works perfectly when you let go, but the rest of the time you don't even know it's there. It's very little hassle, and it could save your life.

There is a downside: If you want to stop to take pictures or something, it makes locking off a little weird. You can just let the wraps hold you; it seems like a pretty solid lock, but it's a little uncomfortable with all your weight on one leg loop. Plus, I still get nervous with my hand away from the rope and the rope not tied off.

Another minor problem: If you need to change over, it's one more thing you have to remove.

If you have access to the Nylon Highway, the publication of the NSS Vertical Section, see the article "Rappel Safety Hitches Revisited" by Brady Robinson in issue #44. I didn't see this until after I started using the method, but I have since used the article to fine-tune my setup. According to the article, the single-strand-with-end-loops friction hitch is called a Penberthy, and the closed-loop version is called an auto-block.

Mr. Robinson provides excellent detailed instructions along with many helpful hints & tips.
With a safe place to experiment, this article should be all you need, although it would be better if you can find someone who already uses the method to demonstrate.

Ask around. If you are going to Convention, you're sure to find someone there who can demonstrate.

[NZcaver]

Time to start up this old thread again!

I just stumbled across some good information on rappel safeties here...
http://storrick.cnchost.com/VerticalDev ... yPost.html

This is on Gary Storrick's fantastic website, which I visit frequently. (Gary, I hope you don't mind my shameless advertising for your site. ) Although it's dated 1995, I think Gary's comments are still perfectly relevant today. There's also a bunch of references to support his opinions - opinions which I, for one, mostly agree with.

I have toyed with setting up a rappel safety once or twice myself - but I've never seriously considered actually using one. Despite Gordon's wonderful job of promoting the French Wrap, I just can't see the point of adding extra complexity to a rappel system - especially something so fickle. Using one means you can't position your control hand where you want to - it has to stay on the hitch or else you don't move. And if you panic and grab the hitch, it still won't arrest your descent.

Having said this, I normally use a stop descender. True, they also add a little complexity to the standard rappel system. I've accepted that, and I'm perfectly comfortable with having my left hand stuck to the stop lever during descent. I find stops are the most convenient descenders to use in a majority of caving situations, and are undeniably less fiddly than using a separate rappel safety. And if my Petzl Stop isn't ideal for one particular drop (because of rope diameter, depth, etc), I can always use my SRTE, Kong, or Troll ones instead.

I love Gary's last line on that webpage - "The Prusik safety may be highly contested among climbers. Among cavers, it is not. It is almost universally rejected."

Perhaps it should be...

[Buford Pruitt]

I see a lot of healthy controversy when reading through these threads on rappelling self belays and rope ageing strengths, but one thing is not at all controversial to me:

The books, "On Rope" and "Alpine Caving Techniques" do not adequately discuss those two subjects. They may indeed be more thoroughly researched and reported in "Nylon Highway" and in personal websites and grotto newsletters, but those are not readily availabile to most cavers.

This is a plea to the authors of the above-referenced excellent SRT caving books to incorporate these subjects into their next revisions, and to the NSS to put "Nylon Highway" online, someday, somebody.

Don't you just hate people who say, "What somebody oughta do is ___, but I don't have time to do it."

PS: Kudos and a tip of the helmet to Scott for his efforts to retrieve threads from the previous NSS Discussion Board. We all owe him a

[NZcaver]

The books, "On Rope" and "Alpine Caving Techniques" do not adequately discuss those two subjects.

Buford - I have to agree with you there.

On Rope (1996) [page 128] mentions using the Prusik hitch or a Gibbs as a spelean shunt above the descender, but the only reference to a French wrap style self-belay is this: "Some people try this (rappelling) with a short Prusik below a rappel device. In practice, the hitch always stretches into the device, rendering it useless."

Alpine Caving Techniques (2002) does not appear to mention separate rappel safeties at all. I would think this is because it has been discounted as a useful technique (at least in Europe - ironic with it being called a French wrap, isn't it? ). The authors may feel that mentioning something that's not recommended would only serve to confuse readers.

Vertical (1988) [page 79] talks briefly about using shunts while abseiling (aka rappelling, for those who don't know ). They are only mentioned being used above a descender, and again are discounted with comments like "A shunt can hardly be recommended as a safety device for a conscious caver" and "The Prusik knot can be tied above the descender as a psychological shunt."

I do think the French Wrap leg loop technique would do well to be included in future revisions, so rope users can make up their own mind about using one or not. I think my mind's already made up on the subject, but I guess opinions can change... 8)

PS - I think information on rope strength loss over time would also be very useful. However, this study would be a tough task. Firstly, by definition, it would take a long time. Secondly, multiple samples of all major types of caving rope would need to be tested. Thirdly, there are hundreds of different types of caving rope made around the world, and even testing multiple samples of each in different environments may not give conclusive results. And if used rope is included in the tests (for more realistic results), the complexity gets multiplied. Kudos to anyone who wants to try it, though!

[hank moon]

On Rope (1996) [page 128] ... the only reference to a French wrap style self-belay is this: "Some people try this (rappelling) with a short Prusik below a rappel device. In practice, the hitch always stretches into the device, rendering it useless."

A demonstrably false statement...easy to disprove. Was there more text? I don't have a copy of this book.

[NZcaver]

On Rope (1996) [page 128] ... the only reference to a French wrap style self-belay is this: "Some people try this (rappelling) with a short Prusik below a rappel device. In practice, the hitch always stretches into the device, rendering it useless."

A demonstrably false statement...easy to disprove. Was there more text? I don't have a copy of this book.

Hank - that was the only text I found describing the use of a rappel safety BELOW the descender.

You know you should really pick up a copy of that book... at least to "review"

[RescueMan]

I love Gary's last line on that webpage - "The Prusik safety may be highly contested among climbers. Among cavers, it is not. It is almost universally rejected."

Perhaps it should be...

Gary was refering in that article to the old prusik-above method which has been widely discredited for the following reasons:
1. it locks easily and is difficult to unlock
2. once loaded it can extend out of reach
3. it requires the "free" hand in order to tend it
4. in a panic, the almost universal (pre-conscious) reaction of even highly experience users is to grab the rope and hence the prusik, rendering it useless

What this thread has been about is the "French Wrap", more commonly called the autoblock, below the descender.

This backup system is widely used, very effective, and eliminates all four of the above problems with the prusik-above method.

BUT, it has its own limitations and caveats. Because it cannot extend into the descender, users often tie it off to a leg loop. This presents a number of issues which have been raised in this thread. Another, and perhaps more effective, way to use the autoblock is to extend the descender with a short sling. This allows the autoblock to be attached to the harness tie-in-point which makes it far safer and keeps body weight centered. It is also most suited to friction devices which require a downward pull of the brake hand to maximize friction, such as a fig-8 or Sticht plate-type device (ATC, Tuber, etc).

I agree with those who suggest that the autoblock is not well suited for use with a rack, which is a device requiring more freedom of movement of the brake hand and more user finesse.

As far as questions about "locking off" when using an autoblock, a hard lock off requires only that the rope be securely tied back to itself or to a piece of the hardware link (descender, biner, etc). The autoblock can be set onto the rope and the brake rope can be brought back up from below the autoblock and tied off. This serves the same function as cinching a rack's bars together with the tie-off, it puts additional brake friction onto the rope (the set autoblock) and creates a hard tie-off. Pulling up from below the autoblock keeps the autoblock in the set position.

As for those of you who claim to dislike the autoblock safety while admitting to having never tried it, isn't that a bit like thinking sex is gross before ever having enjoyed its benefits?

And, BTW, the RAPPEL SAFETY HITCHES REVISITED article By Brady Robinson is available here:
http://www.caves.org/section/vertical/nh/44/rshr.html

- Robert

[RescueMan]

I was in a cave this weekend that had a 20+ year old rope in it which we replaced but I would be really interested in data on how much the nylon actually degrades over that time period.

The 2-4% per year figure came from Bruce Smith's destructive testing of 100 samples of used caving rope. He found that lightly used ropes averaged a strength loss of 1.5 to 2 percent per year, and well used ropes 3 to 4 percent per year. Smith observed that "care of the rope has a far greater impact on a rope's life than age."

Other tests performed on old, stored, but un-used rope found no loss in either tensile strength or energy-absorption (Blue Water 12-year-old rope). This was in agreement with similar tests on unused rope, some of which tested higher than when new:

In June of 1990, Wellington Commercial Cordage tested samples of Rhino Rescue Rope stored for seven years by Bridger Coal's mine rescue team in Wyoming. The sample was 1/2-inch (12.7 mm) diameter, low-stretch kernmantle rope. The manufacturer's new rope tensile strength rating was 9,000 pounds (40.34 kN). For comparison, the independent lab tests on new Rhino Rescue Rope in 1983 averaged 10,495 pounds (47.04 kN). The test results from the Bridger Coal samples suggest minimal strength loss when the rope is properly stored.

Break #1 11,200 pounds (50.20 kN)
Break #2 10,600 pounds (47.51 kN)
Break #3 11,000 pounds (49.30 kN)
Average 10,933 pounds (49.00 kN)

(CMC Rescue Technical Report #1 November 1998)

On the other hand, tests performed by the UIAA in Italy on dynamic climbing ropes found that 60 cycles of top-roping reduced the number of falls the rope could hold by at least 50%.

http://www.alpineclubofcanada.ca/servic ... /#articles

And the UIAA found that after only 50 descents with a figure-eight, the dynamic resistance of a rope is reduced by one third (number of drops). The descents were undertaken with extreme care - slowly and without impact.

The UIAA also found that after climbing approximately 5000 meters, the dynamic resistance of the rope is reduced to half and after an additional 6000 meters it is down to 30 % (UIAA Bulletin # 146, June 1994, in German)

And exposure to sunlight caused a relatively low degradation of the mechanical properties of the filaments (approx. 10 % reduction in breaking strength and elongation), but corresponds to a notable reduction in the number of falls held (up to 50 %).

http://www.uiaa.ch/article.aspx?c=185&a=76

So, even though a new Blue Water II+ 11mm static rope can withstand 14 Fall factor 1 falls before failure, it seems the issue is not so much age, but use and exposure. Cave ropes don't, of course, suffer from UV exposure, but wet ropes have been shown to have about 30% less static resistance and as much as 66% less dynamic resistance.

http://www.alpineclubofcanada.ca/servic ... /#articles

The primary reasons for retiring of ropes are overuse, abuse, excessive exposure (sun, acids), and mechanical damage. But even normal and careful use degrades a rope's mechanical properties, particularly its dynamic energy-absorbing properties.

But, ultimately, it comes down to a judgement call unless it falls within an organization's SOPs.

- Robert