UKC

Looking to do a bit of top-rope shunting but have a reasonably thin and slick rope so concerned it might not lock on a slow fall.

Been thinking of backing it up with a micro traxion on a short extender above the shunt (so the shunt pushes the traxion up the rope). Tried it at home and seems to work okay.

Anyone have any words of wisdom on the topic?

It'll be better still if you can double up your rope into two independent strands and have the shunt on one and the traxion on the other.

More generally, Petzl have some pretty good literature on the subject: https://www.petzl.com/GB/en/Sport/General-principles-for-solo-climbing-with...

Tie knots in the rope below you as you climb.

Micro traxions work well.

Some people tie a clove hitch as a back up and keep moving it up every few m.

For me a Shunt without any other device works fine top roping on a thin rope (9,6). 

I know others who use only a Micro Traxion top roping. 

The only drawback I experience is that I cannot lower myself to a point and repeat the sequence. May be you can lower yourself by putting in a gri-gri and lower yourself to the point of repetition, but it will be a lot of doing.

For long top ropes (± 60 meter, with traverses/swings) I sometimes use the combo of a Petzl Croll (top: attached with a Petal Torse) and a Micro Traxion (low: on the belay loop). But also then lowering will not be easy.

To answer your question: I wouldn’t put a Micro Traxion above the Shunt. 

Seconded. When I can I rig the two strands from separate placements with a bight between to make them as independent as possible. Even better with two ropes, of course. 

On a single line, be wary of placing the microtraxion above the shunt. Make sure it is extended enough such that if the toothed cam accidentally gets into the locked open position (has happened to me) the MT won't just roll onto the shunt below and perhaps stop it working properly. 

I use a shunt above the MT - MT on oval krab on belay loop, shunt extended and held in place with sling chest harness. This way the shunt is primary device as it catches first and is kinder on the rope as it doesn't have teeth. MT is there as backup and may catch if the shunt slides. I think the MT would still catch even if the shunt could physically run into it but I still prefer to ensure they can't interact at all. 

Someone else has said, if you can use two lines and have a device on each, this is probably best.

I don't climb anymore but used to use two independent strands, one I clove hitched into as a keep-me-alive backup of last resort, the other for the running belay (handled ascender in my case).

jk

I would be worried about the two devices interfering with each other, but admittedly I've never tried it. 

Micro traxions are great little devices, but the fact the teeth can lock in the open positions inadvertently (and visa versa which is normally just a pain) I would personally not be able to trust my life to it.  

I use a shunt on a semi regular basis and never had a problem with it slipping, you do have to make sure you fall in a clean way e.g. away from the rock and do not grab it. I will often leave overhands on a bite on the dead rope as I work up, or use a rolling clovehitch. 90% of the time though I just use the shunt. 

Dave Mcleod does a nice video on using a shunt for his projects.  Worth the time to watch it. 

youtube.com/watch?v=kd13IaWS8gQ&

Edit: It might be worth mentioning that you can modify the traxion so that the teeth cannot be held up by filing off the small nubbin, obviously this will void your warranty etc etc..

Problem with that (apart from being a faff) is that the shunt won’t run as well as the line won’t be weighted

Make sure the extender cant wrap around the shunt and stop it working.

I used to top rope on a shunt with extender. Extender looped over side of shunt one time and shunt failed.

Knott tying as you go or at least so you cant deck out.

I guess none of these systems are 100%.

How tall are you?! I just tried that at home and found that even with the shunt tight to my chest the micro-traxion can still touch it - and I would have thought worse this way around (something pushing up into a shunt more likely to release it than something pushing down into it).

Anyhow, think based on the consensus here I'm going for shunt and knots or 2 ropes depending on the situation. 

I just use a shunt with both strands and tie backup knots whenever I have the opportunity. Its never slipped and I trust it enough 

I'm 6ft though I don't think your height should be limiting.

I set the length by sitting on the MT so it is engaged then putting the shunt above with a small gap and connecting to it via sling and maillon. Set the required length of sling extender with a knot. That way I know that if the shunt slides it will not interact with the MT by the time the MT is fully engaged. I'm probably making it sound more complicated than it is.

I'm not sure what you mean by something pushing up on the shunt. When you are climbing, the MT is dragging downwards as low as it will go while the shunt is held chest height with the chest harness. There is more gap between the devices when climbing than when sitting on the rope. They never touch each other.

I don't like tying backup knots as it is faff. Also, I mainly climb sea cliffs where I abseil down the line I climb up. When I'm finished I don't like the possibility that I pull up my rope with lots of knots that could get caught in cracks etc. I have also read that a high factor fall of a shunt onto a knot can cause the shunt to deform, potentially enough for the rope to come out. If using knots as your backup, make them fairly regular. I prefer the MT as backup.

You can have the devices either way around (I have), I just prefer toothed device below. Just bare in mind the risks and limitations of both in whichever configuration you choose.

In the end this is just the way I do it, and there are many ways people achieve the same thing. It may not suit everyone. You just have to be comfortable with whatever method you use, otherwise you won't climb freely and I'd argue that if you don't trust your fall protection you might end up trying to grab the rope or device, or otherwise hesitating in a way that could be dangerous.

Take from that what you will. Be safe and have fun!

If you have a trax then just use a trax. You can use a chest harness and suspend the trax between belay loop and chest harness if you're really worried about loading it dynamically (but you really don't need to be). 

If you want a backup aside from your backup knot tied lower down, you can trail a maillon on short rope leash (I use a petzl connect but you could use any old bit of rope). The maillon will then block on the knot. 

If you're working a bunch of routes then buy yourself a length of static rope which is more robust and thicker. 

Hope this helps! 

I tried today to shunt on no so steep ground and to fall. The shunt catches perfect. Every time I had fallen or slipped I had to release the shunt; so no worries about rope slippage. I used a Mammut Infinity 9.5 mm. Not a really thin (slick) rope. (I can try the same on a really skinny rope 7.6 mm if you like.)

For the Micro Traxion & Croll set-up I use a Beal Unicore rope (100 m/10 mm). Unicore just in case because I am "worried" of skinning. I pull the rope up (on a ledge, etc) as I progress every 15 meters, but so there is still enough weight on the rope to let the traxion work smoothly. 

Hope this is of any use.

I decided to get a new semi-static rope anyhow as was more concerned about wear on it if I end up having to climb up it (and don't want to trash my lead rope) so think it'll be fine but thanks for the offer and advice thus far.