Anchors and the bunny ears knot

[mick]

Sometimes I use the double fig8 knot (aka the bunny ears) to extend an anchor over an edge for toproping. I am fond of this knot because it provides redundancy with one piece of cordalette, but I remember someone telling me that it was suboptimal, for a reason I cannot recall. Thoughts?

Scenario is as follows:
1. Monster tree is far back from edge. Use cordalette tied with figure8 (or figure 9) around tree to build a bomber anchor.
2. Two lockers (opposite&opposed) thru said loops.
3. Tie bunny ears on a bight on 2nd cordalette, clip both loops to lockers.
4. Tie bunny ears on a bight on the other end of 2nd cordalette, clip two lockers (opposite&opposed) thru these bunny ears.
5. Middle of rope thru 2nd set of lockers, now the biners and climbing rope are lowered down past edge.
6. Toprope super hardcore like a champion.

The two issues that come to mind are:
1. Getting on rappel after building anchor is awkward -> Typically I will back up my atc with a prussik, then put another prussik on the two strands of 2nd cordalette as I lower myself hand-over-hand over the edge to weight the climbing rope. Is there a better way?
2. 2nd extended cordalette still rubs on the edge if toprope wanders side to side -> Has anyone tried feeding tubular webbing over top of cord or rope to protect it from an edge? Does it work well or just slide around and off the abrasion point?

A final note is that the bunny ears knot must be dressed properly or it tends to shift unsettlingly when weighted and can cause the ears to end up different lengths and no longer semi-equalized. Barring this, is there any other flaw in this knot to worry about?

Bunny ears photo for reference:

[*Chris*]

1) Your setup - as described - is bomber.

2) The bunny ears really aren't adding much over a fig-8 on a bight or an alpine butterfly. You're really not trying to equalize two distinct points as you've described.

3) If an edge is sharp enough to worry than your probably shouldn't top-rope it... otherwise it's just wear and tear. There are two schools of thought:

a) power point before edge - the rope runs over the sharp part. The pros: Minimizes the exposure of any one piece of soft gear to the edge since the contact point is always moving. Ropes are designed to handle edge abuse. The Cons: Ropes wear out and are expensive.

b) power point below edge - the slings/cord/webbing whatever runs over the sharp part. Pros: the inexpensive stuff suffers the abuse and is easy to replace. The rope runs with less friction. Cons: Soft gear needs to be replaced often.

It's preference between the two.


Finally, related to bunny ears... the only complaint that I've ever heard is that they give a false sense of redundancy. If you snip the rope at the point indicated below the whole thing falls apart. That's a bunk arguement since single ropes are considered redundant by default and the same arguement applies to your tie in knot, your lead line, etc. When ropes start exploding that's when I'll seriously take a look at bouldering.

[mick]

I agree that the spot you pointed out is a potential single failure point. However, I think there's still a bit more "insurance" with the bunny ears as seen here: