I'm just looking at using a Shunt for self belay. My question is let's say you get stuck half way up the route and need to descend. Now do you get your weight off the Shunt to unclip it from your harness?
When shunting make sure you always have a belay device, along with a prusic loop (or an ascender if you have one). The prusic either needs to be 2.5 metres long (a 2.5m loop of 5mm or 6mm perlon joined with a double fishermans knot), or a short prusic (1.5m) extended with a sling (60mm or 120mm). The beauty of a Shunt over an ascender for self lining (the correct term for this type of soloing) is that - unlike an toothed ascender (Croll etc) - it allows you to climb both up and down a rope, but if you can’t climb down or up here’s a step by step way to descend:
1.Hang from the Shunt (this will probably be attached direct to your belay loop with a 10mm mailon).
2.First you need to set up a back up.
3.Pull up the rope below you.
4.Tie a loose clove hitch about six feet from the shunt.
5.Clip a screwgate into it (don’t tighten the knot).
6.Clip this screwgate into your belay loop.
7.You now have a loop formed between your shunt and the clove hitch. This is your primary back up.
8.Take your belay device and thread it into this into the loop and attach to your harness, getting it as close to the Shunt as possible.
9.Now tie off your belay device (you should have enough slack between your device and the clove hitch back up.
10.Take your prusic and attach this just above the shunt with a Klemheist knot.
11.Step into the prusic and take your weight off the shunt.
12.Detach yourself from the shunt and let your belay device take your weight.
13.You should now be hanging from your belay device.
14.Clip a quickdraw from your belay loop to the shunt.
15.Remove the prusic.
16.Unclip the clove hitch.
17.Release the rope from your belay device.
18.Using one hand to stop the shut locking and the other controlling your belay device descent to the ground.
On the subject of self lining it’s worth looking at what petzl have to say about it here (includes recommended devices and set up).
Also check out the video near the end if you want a little educational scare!