Rapping on a single half rope

Is it safe to rappel on a single strand of a half rope (8mm)? For example, can I fix a line with this rope and rap on it? 

https://www.backcountry.com/mammut-phoenix-climbing-rope-8mm

I have done it many times.  Couple things to keep in mind:  you wont have as much friction so double up biners in ATC and don't use round stock biners.  Ones with flat sides give more friction. You can reverse asymmetrical biners to give more grab as well.  Then, expect lots of stretch so more wear over sharp or rough surfaces.  Doing this repeatedly could damage your rope. We used 8 mm for fixed lines on Shiprock, so we rappelled and ascended them.  Not the ideal choice but it was slabby there and the light weight was appreciated.

I spent a whole day with a couple guys trying different belay devices for rappel on an 8mm. We found that a munter hitch worked best. Ive hear that they make special belay devices for small ropes too, but I was gearing up for an alpine trip so I didnt want any specialized gear. I also tied up some new prusik slings. I think I used 5mm? It is pretty sketchy though. When you weight the rope it gets pretty skinny.

Two methods to add more friction:

- incorporate a Munter in-line with rap device
- build a Z rap system

Photos attached:

kemple sr. wrote: I have done it many times.  Couple things to keep in mind:  you wont have as much friction so double up biners in ATC and don't use round stock biners.  Ones with flat sides give more friction. You can reverse asymmetrical biners to give more grab as well.  

I also often ab on single half rope. However if one is using the a belay device designed to work with this thickness of rope (eg Pivot, ATC XP but not the original type ATC) then it should not be necessary to use extra krabs etc to increase friction....the system is designed to cope with leader falls and if it can't be trusted for plain bodyweight then it should never be used for belaying where the forces are potentially far greater. Apologies if I'm just stating the obvious.
That said I suppose using extra krabs wouldn't usually be a disadvantage either.

i shore wrote:

I also often ab on single half rope. However if one is using the a belay device designed to work with this thickness of rope (eg Pivot, ATC XP but not the original type ATC) then it should not be necessary to use extra krabs etc to increase friction....the system is designed to cope with leader falls and if it can't be trusted for plain bodyweight then it should never be used for belaying where the forces are potentially far greater. Apologies if I'm just stating the obvious.
That said I suppose using extra krabs wouldn't usually be a disadvantage either.

My personal experience,  confirmed by the majority of climbers I've asked, is that most rap devices provide inadequate friction at the lower end of their recommended rope ranges.  I agree that such devices shouldn't be used for belaying at those ranges either, and so the point is that one ought not to trust the manufacturer's ratings.  Add to that the fact that 8mm is below the manufacturer's rating for single ropes (ATC-XP is 9mm, Pivot is 8.7mm) and most people are going to find the friction to be inadequate for single-strand rappels, especially free-hanging ones.

So for rappelling on a single 8mm strand, doubling up the carabiners is going to be essential for most users.  If you aren't in the habit of extending the rappel connector, this is the time to do it, since you get more friction with an extended device.  As an additional safety measure, have the two carabiners for the z-system Marty C posted a picture of installed and ready to go in case you find you are still struggling to control the rappel. (The advantage of the z-system is that you easily can engage and disengage it in mid-rappel).  

At the risk of stating the obvious, one should test the rappel with the intended rope, device, and carabiner(s) in a safe setting before committing to it in a demanding climbing situation.  Make sure to test a free-hanging rappel, and make sure to test that at the end of the rappel when you don't have the advantage of much rope weight.  This is a situation in which one should not rely on what anyone else says they do---make sure the setup works for you!

Ok, that takes care of the friction issue.  The other issue is that 8mm ropes are pretty thin, and so are more liable to friction damage and slicing.  I think most people would say 8mm is too thin for heavy-duty fixed rope use.  For a light-duty fixed line that has been carefully situated away from flakes and sharp edges and will not be subjected to lateral motions that produce a sawing action at contact points, 8mm is ok.

You can look at a Petzl Pirhana or Sterling ATS.  Both devices allow you to add or remove friction to they system with ease. I got an ATS for canyoneering and use it for ski rappelling as well. I have used it on 8mm static canyon line and 8mm dynamic line.

https://m.youtube.com/watch?v=3Oa9Fqs0e8k

rgold wrote:

My personal experience,  confirmed by the majority of climbers I've asked, is that most rap devices provide inadequate friction at the lower end of their recommended rope ranges.  I agree that such devices shouldn't be used for belaying at those ranges either, and so the point is that one ought not to trust the manufacturer's ratings.  Add to that the fact that 8mm is below the manufacturer's rating for single ropes (ATC-XP is 9mm, Pivot is 8.7mm) and most people are going to find the friction to be inadequate for rappels, especially free-hanging ones.

So for rappelling on a single 8mm strand, doubling up the carabiners is going to be essential for most users.  If you aren't in the habit of extending the rappel connector, this is the time to do it, since you get more friction with an extended device.  As an additional safety measure, have the two carabiners for the z-system Marty C posted a picture of installed and ready to go in case you find you are still struggling to control the rappel. (The advantage of the z-system is that you easily can engage and disengage it in mid-rappel).  

At the risk of stating the obvious, one should test the rappel with the intended rope, device, and carabiner(s) in a safe setting before committing to it in a demanding climbing situation.  Make sure to test a free-hanging rappel, and make sure to test that at the end of the rappel when you don't have the advantage of much rope weight.  This is a situation in which one should not rely on what anyone else says they do---make sure the setup works for you!

Ok, that takes care of the friction issue.  The other issue is that 8mm ropes are pretty thin, and so are more liable to friction damage and slicing.  I think most people would say 8mm is too thin for heavy-duty fixed rope use.  For a light-duty fixed line that has been carefully situated away from flakes and sharp edges and will not be subjected to lateral motions that produce a sawing action at contact points, 8mm is ok.

Please listen to rgold. I have first hand experience with rapping on a sub-diameter tag line, and the scars from rope burns on my hands to prove it. We did a dual rap, or whatever it is called, where both climbers are rapping at the same time, counter balancing each other off a spire. I got the 8mm line and I would have let go about mid rappel if I didn't know the other guy would die as well...

Thanks for those very valid points especially that trying out a system in a safe setting is important. So Kemple Sr is right in that extra friction is often a good idea.
I almost had a bad accident using the original ATC abseiling on a new single sub 8mm rope some years ago (stupidly I hadn't tested it out first). However later I tried out the original  ATC XP in its higher friction mode with the same rope and it was fine.
I think you have pointed out before the apparently inexplicable specifications given by manufacturers of belay devices in that they claim thinner ropes work when used as double ropes but not as singles.....it is very possible that a only one rope in a double rope system will  take all the impact of a leader fall (eg if a runners on one rope is far above the last runner on the other rope) ie it is actually acting as a single rope.

i shore wrote:I think you have pointed out before the apparently inexplicable specifications given by manufacturers of belay devices in that they claim thinner ropes work when used as double ropes but not as singles.....it is very possible that a only one rope in a double rope system will  take all the impact of a leader fall (eg if a runners on one rope is far above the last runner on the other rope) ie it is actually acting as a single rope.

Yeah, I do find those rating a bit inscrutable. FWIW I've caught falls as high as FF=0.8 on 8.5mm halfs where only one piece was clipped, with the Pivot which is rated for 7.9mm halfs and 8.7mm singles and it worked fine.

I can't think of a situation with halfs where you could get a FF>1 where you could get completely dropped because only one rope engaged. In the worst case of a FF=2 fall with slack out one one rope, even you can't catch the person on one rope, the second rope will come under tension eventually. So your concern, that one of your doubles might be only acting as a single rope, won't happen in the worst falls. So this might be why they give a separate rating--half ropes might be subjected to lead falls as a single rope, but the falls will be at a lower fall factor in that case.

There's still the weird cases where someone takes a FF~1.5 onto one rope, which is a pretty serious fall, and then they could slide a very long ways before the second rope gets tension from the anchor and engages.

FWIW, and to each their own, but . . . . . .   I have rappeled many times with a DMM Bug, attached to a small locking biner on 7mm ropes. Even on  free-hanging raps. Nice to have one glove for the brake hand though.

YGD™ 

David Kerkeslager wrote:

Yeah, I do find those rating a bit inscrutable. FWIW I've caught falls as high as FF=0.8 on 8.5mm halfs where only one piece was clipped, with the Pivot which is rated for 7.9mm halfs and 8.7mm singles and it worked fine.

I can't think of a situation with halfs where you could get a FF>1 where you could get completely dropped because only one rope engaged. In the worst case of a FF=2 fall with slack out one one rope, even you can't catch the person on one rope, the second rope will come under tension eventually. So your concern, that one of your doubles might be only acting as a single rope, won't happen in the worst falls. So this might be why they give a separate rating--half ropes might be subjected to lead falls as a single rope, but the falls will be at a lower fall factor in that case.

There's still the weird cases where someone takes a FF~1.5 onto one rope, which is a pretty serious fall, and then they could slide a very long ways before the second rope gets tension from the anchor and engages.

I hadn't thought of that and it might indeed explain the lower rope diameters acceptable in the belay device manufacturers' specifications for double ropes compared to a single setup.

I think you are saying that one could get a high fall factor with double ropes eg with one runner on each rope if the runner on the second rope immediately fell out, or alternatively a runner had not been placed near/on the belay and the only runner was on one rope. The second rope would become involved after the first had stretched sufficiently and so both would play an additional part in stopping the fall.

Incidentally, being pedantic, I've just  looked at the makers' websites where the specs are: for half ropes 7.3mm-9.2mm for the Pivot and 8-11 for the ATC XP (incidentally in the latter case, if I haven't misinterpreted, in the instruction sheet the ATC appears to have the same specs as the ATC XP which I find hard to believe). These differences of a few mm are very small and are presumably rendered almost meaningless by variable factors such as new shiny ropes, dryrope treatment, and rope flexibility to say nothing of a belayer's grip strength.

I've never done it but wonder if this might be a situation where using a figure 8 descender might actually work better, since one would presumably have almost as much friction as with a fatter rope vs. an ATC type device where rope size matters more.
IDK, never tried it- just a thought.
And use autoblock

David Kerkeslager wrote:

Yeah, I do find those rating a bit inscrutable. FWIW I've caught falls as high as FF=0.8 on 8.5mm halfs where only one piece was clipped, with the Pivot which is rated for 7.9mm halfs and 8.7mm singles and it worked fine.

I can't think of a situation with halfs where you could get a FF>1 where you could get completely dropped because only one rope engaged. In the worst case of a FF=2 fall with slack out one one rope, even you can't catch the person on one rope, the second rope will come under tension eventually. So your concern, that one of your doubles might be only acting as a single rope, won't happen in the worst falls. So this might be why they give a separate rating--half ropes might be subjected to lead falls as a single rope, but the falls will be at a lower fall factor in that case.

There's still the weird cases where someone takes a FF~1.5 onto one rope, which is a pretty serious fall, and then they could slide a very long ways before the second rope gets tension from the anchor and engages.

Ignore Fall Factors, they are one of the stupidest things ever to be introduced to climbing. Effective FallFactors are slightly better but too complicated and variable to be of any real use.

That the other rope comes under tension eventually is may be true (or not) BUT if the rope has slid too far through the belayers hand then a) they will let go b) they have already been injured unless they are wearing gloves. When you design climbing equipment one requirement is that it does not harm or injure the user and rope-burns on the belayers hands are at least as serious as many injuries to the leader.

To know if a belay device is adequate you need to work out the force in the fall and measure whether this exceeds the force the belayer/device can provide. If the faller force is greater than the braking force then the rope must slide both through the device and the belayers hand. Then work out how much energy is left in the faller, how much will be dissapated in the protection pieces, the device and how much will go into the belayers hand, around 1600J or a bit under 2m of rope slip are considered the limits before the belayer is injured and will release the rope.

Jim Titt wrote:

Ignore Fall Factors, they are one of the stupidest things ever to be introduced to climbing. Effective FallFactors are slightly better but too complicated and variable to be of any real use.

That the other rope comes under tension eventually is may be true (or not) BUT if the rope has slid too far through the belayers hand then a) they will let go b) they have already been injured unless they are wearing gloves. When you design climbing equipment one requirement is that it does not harm or injure the user and rope-burns on the belayers hands are at least as serious as many injuries to the leader.

To know if a belay device is adequate you need to work out the force in the fall and measure whether this exceeds the force the belayer/device can provide. If the faller force is greater than the braking force then the rope must slide both through the device and the belayers hand. Then work out how much energy is left in the faller, how much will be dissapated in the protection pieces, the device and how much will go into the belayers hand, around 1600J or a bit under 2m of rope slip are considered the limits before the belayer is injured and will release the rope.

Cool, I was hoping you'd weigh in on this Jim. Do you know why manufacturers give separate ratings for single and half ropes, even though the fall might be only on one half rope?

Given what you're saying, it seems like falling on only one half rope is a real concern. It's not hard to imagine scenarios where a fall on one half rope results in greater than 2m slippage before the second half rope is tensioned.

The numbers are just a guess. Normally some "athlete" goes out and climbs one day and says it was okay then the advertising department get creative and extend the range to cover all the ropes the company sells. There´s no standardised test, most companies don´t test at all and the last published data from a manufacturer is well over twenty years ago (and completely distorted by the marketing guys as well). The last "good" published test results are from Salewa when they introduced the Sticht plate!
Th opinion from the CAI (who have done the most testing belay devices) and the DAV (who have done plenty) and myself is that no manual belay device (with the exception of the CT Alpne Up) is capable of stopping a worst-case fall and with half-ropes the problem is worse.
Luckily most of the time falls are far from worst case and we survive, accepting the odd rope-burn along the way!

I was top belaying a climb  I had led at  city of rocks this  summer.  Sitting down and belaying off my  harness with that lime  green  petzl thing. When Isa topped out she handed me a tag and then hiked off.  The next  climber to appear handed me a 6mm tag . One of the fossil  climbers was obviously skimping on weight.  I added a 2nd  biner as a matter of course.  The  climber  fell and I  caught him no  problem.  Very glad that I had  used the extra biner. 

Make America sketchy again yeeew!

Easy way (maybe best?) to add friction w a guide-style plaquette: Clip the ear back to your rap tether with a carabiner. Give that a shot...believe there’s a photo of the rigging in The Mountain Guide Manual...

coppolillo wrote: Easy way (maybe best?) to add friction w a guide-style plaquette: Clip the ear back to your rap tether with a carabiner. Give that a shot...believe there’s a photo of the rigging in The Mountain Guide Manual...

Page 123.  The method may not be as effective with certain other devices, eg the DMM pivot.  Whatever method you choose, make sure to test ahead of time in a safe situation to make sure you get enough friction.