We hate to use the term "safer" in climbing, but here's a method to manage risk a little more appropriately.
Using this method, we'll never be off belay, and we'll never be trusting our life to a single piece
Evaluate your last point of attachment.
We're looking for the best anchor that we can make. Realistically, that's likely to be the newest, shiniest looking bolt, because we're unlikely to have much else in this situation. In a perfect world, we find a tree or horn or thread to sling.
However, let's assume we're the simplest, most common, likely situation, we're just on a bolt, not incredibly trustworthy.
Call down to you partner to lower
We're 35m in, and we've got a 50m rope. That's 50 feet of rope that we've got to work with. In this situation, lowering is going to be safer than rappelling, because we-
- aren't trusting our life to a single piece. If the top bolt blows, we take a fall which isn't fun, but is to a piece which is ≈ only 8 feet lower, which is a 16 foot + rope-stretch fall, at most.
- are still attached to our partner. That's going to be most ideal, because it's a useful method of redundancy
As we lower, we're trying to find a better spot to anchor
Your belayer has 15m of rope left with which they can lower you. Once we've been lowered 10m, we'll be only half the rope length above the last anchor. As we lower, evaluate bolts. In a "perfect" world, you'd be able to replace the second highest quickdraw with a bail biner, then clean the rest of the draws on you way down to your destination. They key here is to have clear communication with your belayer regarding your intentions, so they can let you know how much rope is left.
As you approach the end of the rope, transition back to the end of the rope
- Once your belayer runs out of rope, pull on their strand to haul yourself back to the closest bolt
- Swap the quickdraw at your "new" anchor for a larger basket biner if possible, if not, we'll assume the bolt-side carabiner of the quickdraw is what we're going to refer to as the bail biner.
- Clip yourself to the bail biner with your tether, or another quickdraw (to your belay loop)
- Ask for slack, weight the attachment to the bolt.
- Pull a loop of the belayer's side of the rope through the bail biner.
- Tie a figure eight on a bight (or any other mid rope loop knot), clip it to your belay loop. (You are now on belay via this strand)
- Untie your rope-end tie-in knot
- Pull rope end through and down, pass it through the bail biner.
- Tie in at the end of the rope.
- CHECK YOUR SYSTEM
- Unclip and untie your mid rope loop knot, ask your belayer to take up all slack.
- Pull up on the anchor so that your tether/quickdraw attachment to the bail biner isn't tensioned, and your tie-in is.
- Unclip, lower.
Using this system, we can stay safely redundant with our attachment, and end up leaving (probably) 4 carabiners behind. You can get more carabiners. Depending on your level of comfort, you can leave more or fewer.
Once down to our partner, we can rig our system to rap the rest of the cliff
Either you or your partner has the other rope. Let's assume it is merely a tag-line. If it's a rated rope, this would still work, but you'll have more options.
- Rated rope goes through rings
- Join the two strands with an EDK (with several feet of tail/backed up, no need to be stingy)
- Tie a mid rope loop knot between the EDK and the rings in the rated rope (Clove is fine), clip a carabiner to it and then also clip it around the rated rope (A "carabiner block")
- Pull tag line
- Rinse and repeat