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curiosity kills the cat: rappelling off a thin cord
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Chris Jackson
(chris_jackson) - F
curiosity kills the cat: rappelling off a thin cord on 06/14/2006 23:47:42 MDT Print View

This is somewhat off-topic, but I am curious as to why high-strength cords such as 5 mm technora are not recommended for use as static (rappel) ropes? 5 mm technora is ultralight and has a 5,000 lb breaking strain. But it only seems to be used for emergencies (exiting from burning buildings etc), and presumably there is a good reason why! I'd rather not find out from direct experience, but I am curious...

David Bonn
(david_bonn) - F

Locale: North Cascades
Re: curiosity kills the cat: rappelling off a thin cord on 06/15/2006 01:20:11 MDT Print View

I can think of a couple of reasons.

One is that a thinner line would be more likely to cut or abrade in field conditions -- and a rope under tension (like when you are hanging from it) can be cut easily from a sharp rock. I'd also wonder if the sheath is up to the abrasion that comes with being ran through a rappel system. And maybe you could do that once or twice before you had substantially weakened the rope.

Another reason is that thinner ropes would likely require different rap devices than, say, the normal figure-8s most people use and possibly technique modifications.

Chris Jackson
(chris_jackson) - F
Re: Re: curiosity kills the cat: rappelling off a thin cord on 06/15/2006 23:25:29 MDT Print View

That makes sense. In a thinner rope, each fiber is under higher tension than in a thicker rope. A higher-tension fiber is more suspectible to being cut by abrasion.

You're undoubtedly also correct about the need for a different rappel device for thin ropes, though that problem could be solved.

Miguel Arboleda
(butuki) - MLife

Locale: Kanto Plain, Japan
Re: curiosity kills the cat: rappelling off a thin cord on 06/16/2006 00:22:32 MDT Print View

Climbing rope is made of a series of layers to add margins of safety for when the rope is subject to abrasion.

Also a very thin rope is hard to handle in the grip of a human hand. The fist can close only so tight.

And probably most important, climbing ropes are designed to stretch. This is vital for when you fall. If the rope didn't stretch, like dyneema core ropes tend to do, you would be yanked to a sudden stop that might break your back. It's the same stretching that occurs in bungee jumping; the stretch is what softens the fall.

Edited by butuki on 06/16/2006 00:24:47 MDT.

Douglas Frick
(Otter) - MLife

Locale: Wyoming
Re: Re: curiosity kills the cat: rappelling off a thin cord on 06/16/2006 10:17:38 MDT Print View

>And probably most important, climbing ropes are designed to stretch.

The original question was regarding a rap rope, not a climbing rope. Although a dynamic climbing rope often serves dual purpose as a rap rope, fixed ropes for ascending and descending (e.g., caving) are usually static because there is no expectation of a fall. A static rope is also less likely to wear because it doesn't stretch repeatedly against the rock. A sharp edge is still a problem, though.

Good thread. I'm considering replacing the dynamic twin rope (Beal Rando 8mm x 30m, 40.7 oz ) I occasionally carry with a lighter static rope since I mostly use the rope going down, not up.

Edited by Otter on 06/16/2006 10:44:15 MDT.

kevin davidson
(kdesign) - F

Locale: Mythical State of Jefferson
thin ropes--- to be or not to be on 06/16/2006 10:40:42 MDT Print View

You are right about the use of non-dynamic (static) ropes in certain situations, Douglas. I've sometimes have even combined the 2 for especially long rappels
( the static rope is brought along for hauling, primarily)---another app where stretch is a nuisance.

Miguel is right about one thing---- such a small diameter rope (5mm) would not be nearly, shall we say, ergonomic---- and the thinner rope would have a smaller window of safety ( edges, etc.). Smallest I use is 7mm.

Miguel Arboleda
(butuki) - MLife

Locale: Kanto Plain, Japan
Re: thin ropes--- to be or not to be on 06/16/2006 10:51:59 MDT Print View

Thanks for the corrections Douglas and Kevin. Makes sense when you think about it. I still have a lot to learn about ropes for climbing.

Interesting thread.

Douglas Frick
(Otter) - MLife

Locale: Wyoming
Re: Re: thin ropes--- to be or not to be on 06/16/2006 11:43:20 MDT Print View

>5 mm Technora

I looked at the specs on that rope: 5000lb average tensile strength. Subtract 15% to get Minimum Tensile Strength (MTS). Use a Safety Factor (SF) of 15 ("life lines"). Safe Working Load = MTS / SF = 283 pounds. That's not much more than 1X for me + heavy pack. I might assume that "working load" includes stopping a load's descent (2X or so), but that's cutting it a bit close to the bone considering that damage to a small number of threads in the thin rope could cut the MTS significantly.

Weight for 30m length is 27 oz. My 30m Beal Rando weighs about 14 ounces more, so that's significant if I'm carrying it "just in case." (I often carried a length of 1" tubular webbing in Hawaii because it gets slippery very quickly in rain, and a slip can be fatal.) I guess it would make sense to take a 5mm Technora if I wasn't planning to use it (not congruent with lightweight philosophy, I know), and consider it a single-use item. I don't think, given the specs and its vulnerability to damage, that I would rely on this rope for repeated use. The only price I could find for a 25m length was $105.

Edited by Otter on 06/16/2006 11:44:40 MDT.

Ron Bell
(mountainlaureldesigns) - F - M

Locale: USA
rap lines on 06/16/2006 12:54:53 MDT Print View

another possible mfgs reason is the aramid fiber ropes / runners will melt at lower temps. The polyester sheaths on static and dynamic ropes handle the heat of a hot rap device better than the nylon core. Perhaps the spectra/technora/kevlar(old school-remember the 5mm chouinard line for big hex runners?) spectra cores of the thin lines would also have a thin sheath. Another area to be wary of with any type thin rope for rapping, especially when used with a thicker line doubled for a rap is that the thin line will tend to run through the rap device faster than the thick one, possibly leaving you out of the thin rope half way down the line as the thin line slides though the anchor rather than the rap device...or god forbid you did not tie the ends together... off the end of the thin line and hurtling to the ground with the think one in the rap device. This was a problem when bluewater came out with the first thin 7mm X 200m static rap specific only line in the early 80's and folks were always used to using two fat 10.5-11 mm lead lines for a double rap. -Ron

Chris Jackson
(chris_jackson) - F
properties of 5 mm accessory cord on 06/16/2006 13:46:52 MDT Print View

Thankyou all for your excellent responses. I've learned a lot from this thread.

Melting point: Spectra has a low melting point which could be a real problem when rappelling on a thin cord. In contrast, technora has a melting point of 880 F and is used by firefighters as an emergency rap line for escaping burning buildings. Technora is also a bit stronger than spectra.

Rap device: As others have mentioned above, normal rap devices simply don't work with thin cord and the problem can't be remedied by using two biners. Presumably firefighters carry a descender specifically designed for these cords.

Stiffness: most of the thin cords are very stiff.

Knots: Some of these cords require special knots, and it seems that knots in thin cord may be much weaker than knots in normal rope.

Abrasion/Cutting: One might hope that high-tech thin cords would resist cutting better than standard ropes, but this doesn't seem to be the case. I suspect that abrasion is the 'killer' problem with using thin cords; the cord may be compromised after a single rappel.

Chris Jackson
(chris_jackson) - F
what is the lightest weight 'normal' static rope? on 06/16/2006 13:59:10 MDT Print View

Douglas, what's your impression of the Beal Rando rope? That's the lightest rope I've found (37 g/m). Like you, I would primarily (probably exclusively) be using it for rappelling (with two strands). I would be using it in alpine areas where the rocks can be very sharp.

You and Kevin both alluded to lighter options, and Kevin mentioned 7 mm. Are they CE rated, how much do they weigh, and can you provide a link to a website? Is the 7 mm a proper rope, or accessory cord?

kevin davidson
(kdesign) - F

Locale: Mythical State of Jefferson
It's 8mm rope on 06/16/2006 14:19:45 MDT Print View

Chris, I misspoke myself--- It is 8mm static that I use as a haulbag rope and have rapped with and used for non-technical glacier travel--although I have used 7mm cord ( not CE rated) as a handline and for a series of short rappels on a canyoneering trip.

New England Ropes has a good 8mm static rope.
Do not expect longterm usage w/ even 8mm. Inspect often.

Edited by kdesign on 06/16/2006 14:20:55 MDT.

Chris Jackson
(chris_jackson) - F
Re: It's 8mm rope on 06/16/2006 14:43:17 MDT Print View

Kevin, thanks for the clarification. The lightest ropes I've found so far weigh 37 g/m, eg the Beal Rando. There are a bunch of slightly heavier ropes at 41 or 42 g/m, and I haven't yet investigated how they compare for abrasion resistance. Some of the reports on the canyoneering websites reinforce your comment that 8 mm ropes have a short lifespan.

David Olsen

Locale: Steptoe Butte
Re: properties of 5 mm accessory cord on 06/16/2006 15:02:48 MDT Print View

It sounds like an aramid like Kevlar as its core, which firefighters use for
emergency rappels. Just loop the line over the handle of your axe, place the axe crossways in the
window and slide down using heavy turnout gloves and a special pre set rappel device. These ropes
are considered expendable.

Kevlar is like cable, high melting point but if flexed
enough looses much of its strength. Even running
it through a sewing machine as thread weakens it.

Spectra is a polyethelene like your water bottles,
but with the molecules lined up to increase the strength.
Very strong, probably more strong than aramid,
but a very low melting point. It is not effected by
flexing. Also very light, lighter than water so makes
good river rescue rope.

I think you would be best served by a 8 mm
static or dynamic rope for multiple rappels if
you are trying to go ultralight. Note again there
are special issues if used together with a larger
diameter rope.

Douglas Frick
(Otter) - MLife

Locale: Wyoming
Re: what is the lightest weight 'normal' static rope? on 06/16/2006 19:51:14 MDT Print View

> what's your impression of the Beal Rando rope?

It's a nice rope, if a bit slippery. Beal lists it as a "mountain walking" (randone'e) rope rather than a climbing rope, but it is rated technically as a dynamic twin (requiring a mate if it is to take falls). I bought it specifically because it's lightweight, cheap and available in a 30m length, which is just about right for my needs. I'm not a real climber, but I hate being stopped by a small section of wet class 3 or 4 with exposure (common in Hawaii). I'd be hesitant to use it as a single rope for technical climbing, but I've used it with a Dulfersitz and a Bowline On A Coil as a safety top-rope (tensioned), slung it around trees and rocks as a handline, and done some short raps with a Munter Hitch. I'm sure it would be fine for a running belay, although I haven't needed it for that yet. I'm still considering whether it would be technically acceptable as a single rope for glacier walking, but I really can't see why it wouldn't.

Edited by Otter on 06/16/2006 19:51:50 MDT.

carlos fernandez rivas
(pitagorin) - MLife

Locale: Galicia -Spain
other light rope options on 06/16/2006 23:22:59 MDT Print View

beal rando is a twin rope sold as a rando rope for "marketing reasons" (change a denomination is chaper than produce an especific rope)

mammut (swiss manufacturer has the twilight 7.5 mmm twin rope 38 gms/ m)

But maybe a better option is the 7.8 mm master rope (manufacturer claims 38 gms/m) if this weight is real this is a very interesting rope because the manufacturer claims that is certified both as a half and twin rope
chech the manufacturer (lanex)webpage

the climbing ropes series brand (lanex produce different ropes) is tendon

And for the same weight i feel safer with a double rope .....


Chris Jackson
(chris_jackson) - F
Re: other light rope options on 06/20/2006 23:46:43 MDT Print View

Carlos, thankyou for mentioning the Tendon Master 7.8 . As you say, it appears to be comparable in weight to the lightest Twin ropes, but offers the higher safety of a Double. It looks like a great option for European climbers, but it doesn't seem to be available in the US.

Edited by chris_jackson on 06/20/2006 23:47:23 MDT.

Chris Jackson
(chris_jackson) - F
Some hard data from the cutting edge on 06/20/2006 23:53:05 MDT Print View

There's some highly relevant data on the poor performance of high tech cords in real-world tests here (pdf)

Graham Williams
(cilo) - F
Re: Some hard data from the cutting edge on 06/21/2006 11:02:27 MDT Print View

I don't see how tom's paper on knots is relevant to a discussion on rappelling. Honestly, that has nothing to do with rappelling.

massive edit...please see below post...

I use a 7mm tag line all the time for rappelling. Obviously, ymmv.

Edited by cilo on 03/14/2008 09:55:22 MDT.

Chris Jackson
(chris_jackson) - F
Re: Re: Some hard data from the cutting edge on 06/21/2006 12:04:43 MDT Print View

Graham, in addition to the knot data, Tom's paper also contains results on rope strength after repeated flexing. The flexing data might provide some indication as to how the rope would perform after normal 'wear and tear' (poor choice of words!).

Nylon ropes have 90% knot strength, and flexing does not degrade them at all.

Technora and kevlar have 40% knot strength. They initially degrade very quickly under flexing, and the rope strength subsequently seems to plateau at 40% of the initial stength.

In real-world use, technora will have a 2,000 lb breaking strain (5,000 x 40%), and a poor knot strength. For comparison, the nylon rope tested had a 3,000 lb breaking strain and excellent knot strength, so the nylon rope is quite a bit stronger.

Re is technora used for rappelling? It seems to be used for emergency rappels by the military and possibly by firemen. Some himalayan mountaineers use 5 mm cord for rappelling, though I'm not sure whether that's technora, kevlar or spectra. Incidentally, I doubt that the NYFD uses spectra, because it has a very low melting point, lower than nylon (220 F?). For comparison, technora is around 800 or 900 F.

Re why not use 7 mm or 8 mm rope? 8 mm rope weighs 37 g/m , 7 mm weighs 31 g/m, 5 mm technora weighs 25 g/m . So 7 mm rope is similar in weight to 5 mm, while 8 mm is quite a bit heavier. I haven't seen any manufacturers endorse the use of 7 mm for rappelling, and I wasn't sure whether the sheath on 7 mm accessory cord was sufficiently robust. It seems that Edelrid will soon produce a '7 mm rap line', so that answers my question.

Re descender for thin cord: the Petzl Pirana provides a lot of grip, so it might be worth a try.

Edited by chris_jackson on 06/22/2006 18:13:37 MDT.