Y-Hang or a Bowline on a bight?

[MSD]

I agree that sometimes it can be useful to be able to prussik up "half" of a Y-hang, particularly at an awkward pitch head - the fig-8 plus butterfly combo is useful here. However, a disadvantage of this combo is that for a really big Y-hang, you can be forced to do this in order to reach the traverse line. Going down is even more awkward in this situation. With a "bunny ears" Y-hang the traverse line goes to the middle of the knot, which can be a lot more convenient, depending on the situation.

It's horses for courses. Rigging a pitch requires reading the cave and the available belays and selecting the appropriate techniques and knots from the toolbox.

Mark

 

[cap n chris]

However, a disadvantage of this combo is that for a really big Y-hang, you can be forced to do this in order to reach the traverse line. Going down is even more awkward in this situation. With a "bunny ears" Y-hang the traverse line goes to the middle of the knot, which can be a lot more convenient, depending on the situation.

Damn good point, MSD! Thanks.

 

[SamT]

ey - touch 'im and you'll bleed he's that sharp.

 

[potholer]

One definite point in favour of a bowline-on-the-bight is that it's extremely easy to untie, even after numerous descents and ascents by jerky abseilers and prusikkers, though it does require a little more attention paid to really tightening up before use than some other knots.

 

[sidewinder]

Have you tried a bowline-on-the-bight at single bolt re-belays instead of the figure 8?
Again extremely easy to untie.

I think you have to think about what knot and how to rig each pitch for no rub points, ease of getting on and off at pitch heads and what would happen if a bolt failed.

I have seen people rig using alpines on very large y-hangs which could result in a serious fall factor within the belay loop if a bolt failed. If they had used a bowline-on-the-bight and clipped into both loops a bolt failure would not result in a serious fall factor

 

[potholer]

I occasionally use a bowline-on-the-bight on single bolt rebelays - usually on longish pitches and/or where the particular rope has a tendency to make knots difficult to undo, though I usually rig with maillons, and getting two loops in can be a bit messy.

In your alpines-at-pitchheads example, presumably you're talking about the situation of someone being clipped in to one or other side while manouvring, and the belay failing on the side they were clipped into?
I'd guess bolt failures in that situation would tend to be unlikely (though possibly a dodgy natural might pul off), and even with a double-loop knot, someone would still need to have approached the knot somehow and clipped in to both loops to be secure.

If the knot really was well below both belays, there'd be a significant difference in the layout between a butterfly-based layout, (tight traverse line going along (or up) to one bolt, then taught line way down to the second knot), and a double-loop layout, with a traverse line leading down (or along) to the knot itself. A lot would depend on the terrain the caver had to cross to reach a point where they could access the knot.
In that situation, protection of the caver and ease of access while getting to the knot *may* be a more important factor in choosing a rigging arrangement than potential belay failure while belays are likely to be largely unloaded.