Rappelling Small Lines Safely - Considered

[David Yount]

 

jtulinsk

Differing sized rap lines will move through an ATC at different rates.

Not true if the joining knot is sufficiently large and jammed against a rap ring with the large line through the ring, or the joining knot is jammed through a twist of webbing, or sufficient extra friction is applied to the smaller line. Best way to introduce extra friction on the smaller line is to use a carabiner brake on the smaller line, up-rope from the ATC.

 

Willstrickland

I just take my shittiest racking 'biner and leave it. If they decide to filch it and rap the slings I don't care because it's their ass on those slings, not mine

It makes sense to consider carrying 2 or more lightweight inexpensive aluminum rap rings whenever you're descending by rapping a route without bolt+chain stations. They are less than 1/3 price of biners and less than 1/4 weight of biners. When a rap ring is left it usually stays at that rap station much much longer than a biner, meaning it benefits the public good much more. Though I do support Darwinism, I try not to hasten the demise of less critical thinking climbers, climbers that might filch leaver biners to bulk up their rack.

willstrickland

While you should always knot the ends of your rap ropes, it's super critical in this case. The feeding discrepancy is easy to remedy, just pay attention and brake a little harder on the skinny line to even out the feed rates.

Yes, always put sufficiently large knots with sufficient tales at the end of rap lines. A double overhand properly set with 6-inch tails is a good choice for lines 8.1mm and larger. But never tie the ends of the rap lines together; though this will definitely keep you from rapping off the ends, it will also offer great chances of hanging up when thrown down prior to rapping and will always create a huge snarl that will take significant time to unravel because it won't allow each line to freely unwind as the kinks and twists are ushered down the line from the rapping device. Oh, and if you're using accessory cord (7mm, 6mm or 5mm) then the stopper knot at the end of the cord should be bulkier than a double overhand, I just tested a double overhand in a 6mm cord and it pulled through an ATC with less than 50 pounds force and the 5mm cord with same knot slipped right through. Figure-Eight on a Bight in 6mm also pulls through an ATC. And if you're still using a Figure-8 belay/rap device then your concerns of the stopper knot slipping through are much more acute. For accessory lines the stopper knot I use and have recommended for years is a quad-thick overhand. With the final 4 feet of line fold in half to form a bight. With this 2 foot bight fold in half to form a double bight about 1 foot long. Now tie an overhand in the middle of this.

willstrickland

The feeding discrepancy is easy to remedy, just pay attention and brake a little harder on the skinny line to even out the feed rates.

Definitely pay attention to your lines while rapping, everytime. But if you're using lines of greatly different sizes then attempting to grab harder on the smaller line is challenging at best. Better to create extra friction on the smaller line with a carabiner brake on the smaller line up-rope from the ATC. I've also tried the Carabiner Wrap on the smaller line up-rope of the ATC but this never works up-rope of the ATC because the sling holding the upper biner just twists round and round the smaller line and begins to get shredded as I descend. And placing the Carabiner Wrap below the ATC was a bit of a cluster and it introduced endless twists into the smaller line. Neither satisfactory.

 

specialed

decide between a twin rope system (two 8mm's) or a 9.4 single rope and a 6mm trail line for alpine rock routes

Twins (7.5mm to 8.4mm) can twist on each other relentlessly while rappelling. In most alpine environments the raps are not in free space, quite the opposite, many low angle slabs are descended and wide ledges are walked across and down. And just after you reach the next rap station and unweight the lines…… all hell breaks loose, they seek each other out like oversexed incestuous Siamese twins. If they twist just 3 times about each other likely you cannot retrieve the lines, somebody has to prusik up (ascending 7.5mm lines is much more tricky than jumaring up 11mm, TiBloc with a thick stock biner is the best method I've found) to the twisting and get them to remain untwisted by separating them laterally with various features on the rock face. And when you pull the twins….. good luck. The chance that a falling line gets randomly stuck is in great part related to its size, because a (Sterling) 7.6mm twin flops about violently compared to an 11mm, the smaller line gets wrapped about stuff far more often and it fits into more places because of its smaller size too! The other setup is preferred, a single rope will almost never twist about a smaller line and the smaller line will not twist about the larger rope as long as you keep a little tension in the smaller line. So as the last climber to rap reaches the next rap station subtle tension should be applied to the smaller line by another climber, or the final climber can use a TiBloc on the smaller line up-rope of his ATC to apply tension to the smaller line. And ALWAYS pull the smaller line. ALWAYS. Twins wear out much more quickly than single ropes, but they EACH cost similar to a single rope. 7mm and 6mm cord wear out faster than twin ropes but are much cheaper to replace, $65 for 7mmx60m and $56 for 6mmx60m. A 7mm line is the way to go, at least the price vs. a 6mm is NOT a consideration.

 

Alex

I use a 6mm rap line combined with a 70m 9.4 single, strength isn't really an issue

If your smaller line is 7mm then tensile strength is not an issue, 2700pounds is a failure force as tested by Black Diamond on Sterling 7mm cord with a knot; it's impossible to generate twice this force (5400pounds) while rapping. And if you use 6mm line, rated 2000pounds single strand with a knot (2300pounds no knot), tensile strength is still not an issue cause you can't generate 4000pounds while rappelling. I don't know how much force can be generated, but I'll guess 1500pounds is a conservative upper limit if you're rappelling with some grace and style. To learn how to rap without safe style watch a recruitment commercial for the armed forces featuring rappelling. Basically, maximum rappelling forces are generated when decelerating - meaning that if you take huge leaps by shoving off the rock face and enjoy the acceleration down as you allow the ropes to fly quickly through your device and then as you swing back into the rock you prepare your feet to land by decelerating the descent….. it's _that_ deceleration that builds significant forces. Avoid it. Rap conservatively, smoothly, no leaps, and live long.

 

Matt Anderson

The non-rapping partner kept an eye on the knot (if he's the second one down) or held onto the seven mil (if he's the first one down.)

It is a nice idea for the second climber to watch the joining knot while the first climber descends…. But there's not much he can do if the knot does begin to move, besides observe it and communicate it, which is definitely a good thing. And when the last climber descends there's similarly nothing the first climber can do to prevent the smaller line from creeping, for if the line is held fast then the descender ceases descending because he is now held fast in place by the Fireman Belay. And if the joining knot moves and the descender attempts to reset its position (perhaps by holding fast to the small line and allowing the larger line to pay through the ATC) then both lines are being scraped hard where ever an edge is crossed and this is very very very bad for both lines… especially the small one. It's best to prevent the knot from moving by applying extra friction to the smaller line, a carabiner brake.

 

fishstick

I'd be very concerned about cutting a 6mm cord on rock edges or with rock fall.

Yes, me too. If you always feed the larger line through the rap rings (you are using rings right?) and your joining knot is sufficiently large to prevent it from crossing thru the rings then if your smaller line is chopped by rockfall or saws through rubbing on a sharp edge then you'll be held safely on the larger line (which is now considered a fixed line I prefer 7mm to 6mm because of the much greater tensile strength, greater abrasion resistance (related to its larger circumference), greater resistance to getting chopped by rockfall and last but not least… it's extra bulk helps to prevent the joining knot from slipping back through rap rings. But I'll tell you, a 10mm single and 7mm cord tied with an overhand can quickly slip thru rap rings. But if you make the joining knot bulky enough to prevent its migration, then you've got a liability of jamming in a crack when pulling. And if you've got a 9.7mm or 9.5mm or 9.4mm and you use 7mm or 6mm then there's really no chance of creating a joining knot to prevent migration without greatly increasing the common-enough-already risk of jamming in a crack when pulling. The more slings that go thru the rings the better, with enough slings present even a 9.4mm and 6mm combo won't creep backward. Incidentally, when joining dissimilar sized lines the common overhand knot can be greatly fortified by forming an overhand in the tail of the smaller line and snugging it up against the main overhand, and this does not create any greater bulk to get caught while pulling. Also used, and perhaps safer, is the square knot with overhands on either side backing it up, sometimes called a Square Fisherman.

fishstick

toss it via a throw bag or carry it in a fanny pack, feeding as you rap, otherwise the 5mm will tangle instantly

Feeding as you rap is the most sensible thing in most conditions with 6mm and 5mm lines. I usually feed my 7mm, unless it's a plum vertical rap on steep and unfeatured rock. The more experience I have with small lines the more I realize their affinity for wrapping about anything.

 

haireball

One question you might ask yourself is how you'd feel about twinning the 6mm low-stretch rope with your lead-rope in the event that the lead-rope were to be damaged and your best escape is continuing upward

If your lead rope is partially cut or severely abraded you can isolate that section of rope by tying a Butterfly and continue rappelling. This is almost always preferable than escaping by returning upward. As you rappel you will now have to "pass a knot" which is easier than passing a stone, but will slow the descent down quite a bit. And you now have to thread the smaller line through the rap rings because the Butterfly will not go through the rings or over the slings (if not using rings) if you were to pull on the smaller line. Now you will be pulling on the larger line, meaning your butt is depending 100% on that smaller line.... hopefully no dinner plates come your way. The Butterfly is commonly used by the middlemen in a rope team of glacier travelers to tie in to the rope.

 

willstrickland

New England's "Tech Cord" 5mm has tensile strength 5,000pounds 3.4pounds/200feet which uses "technora" and their "Spectra Cord" 5.5mm 4,000pounds 2.8pounds/200feet has spectra and kevlar. The "Spectra Cord" is 20% lighter and 25% weaker, I don't know about the prices. Though weaker than "Tech Cord", the 4,000pound "Spectra Cord" is certainly much much stronger than any 7mm or 6mm perlon (nylon) accessory cord! But this is only true as per manufacturers' specifications. Destructive tests performed by Black Diamond found that 7mm perlon (nylon) is much stronger in real world conditions than any of the 5.5mm high tech new fiber cords. In fact, a 6mm perlon cord is even stronger than most of the 5.5mm new fiber high tech cords - in real world condtions. Flexing and coiling and knotting and storing and stuffing and flaking those new fiber high tech cords permanently lowers their real world strength to the neighborhood of 6mm perlon. Maybe 7mm perlon is still the best overall choice for the smaller line (considering robustness, durability and price). http://www.neropes.com/maxim_climbing/default.htm

 

Pencil Pusher

you mean you'd rather rap off one rap ring than put the rope through all the slings?

Never trust your life to a single piece of gear if you can avoid it, always use two rap rings. If there are not rap rings at a rap station then I identify the best 3 pieces of webbing present, crack the knots by rolling them between my palms, thread my 2 rap rings and re-tie. If there are not 3 loops of adequate webbing then I choose the best 2 present and add another loop of my own webbing.

 

lambone

If you are using two ropes of different diameter, they will slip through webbing while you are rapping.

Different sized lines will not migrate at the anchor if adequate friction is applied to the smaller line, perhaps a carabiner brake.

lambone

P.S. For those of you who didn't know this, Rap rings should be used for body weight only, not as the main point on your anchor. They are not made to withstand high impact forces.

Rap rings are designed for rappelling anchors, they are bomber safe. Never trust your life to a single piece of gear if you can avoid it, always use two rap rings. Rap rings are not designed to be used as part of a running belay.

 

[This message has been edited by Idea Guy (edited 06-30-2001).]

[specialed]

the definitive answer.

[fishstick]

Related food for thought

http://www.xmission.com/~tmoyer/testing/High_Strength_Cord.pdf

[Guest]

Whoever plans to climb the Iron Horse at Index please get a *thick* quick-link and replace the rap ring hanging from the first set of pins. There are often fried slings there so we decided to add a rap ring, but now pins can't be clipped for pro!

Thanks!!!