In reply to dvidg:
bueno
It has the interesting advantage that it would be a neat setup for two experienced climbers to swing leads in a party of 3 without any of the associated rope faff that normally comes with this kind of thing.
Personally I would recommend that the central person was tied in with a double figure of 8 (double over the rope and then tie in with a figure of 8 as you normally would and you end up with a figure of 8 with 4 strands rather than the normal 2 strands of rope), this would dispense with the screwgate and would be a safer, though also a relatively bulky knot which could be a minor annoyance.
Real world limitations:
- You'd have to be really very sure that all the pitches were short.
- Reclipping gear to the rope isn't habitual for most climbers so there is probably a higher likelihood of gear getting left in the rock because the middle person forgets to reclip a piece and the last person does not see it to remove it.
- There might be changes you would need to make to how you deal with situations where the leader gets into trouble, or the second swings off the line or etc. etc. other problems. But I can't really think of any in a simple thought-experiment of the situation. Even if he leader falls the middle person can just clip to the belay and untie if you need more rope to lower the leader back to the belay.