I attempted to summarize the above posts.
This is a discussion thread about techniques for climbing on Double (aka Half Ropes). There is a lot of literature of WHY to climb on Doubles/Half Ropes, but no really information on HOW. This is about HOW. A work in progress...
Double or Half-Ropes: Half (or double) ropes generally have a little "(1/2)" symbol on them. With halves, generally speaking, as you lead up, you alternate clipping one rope or the other at least until the route starts to traverse or zigzag, then you need to plan clips to keep the ropes running straight as possible. So for example, you might lead up, put in a piece, clip blue, lead up a bit more, put in another piece, clip red, and so on. When you take a fall, you're caught by just one of the ropes.
Twin Ropes: ‘are generally marked with a little sideways "8", as in the mathematical symbol for infinity. The idea with twins is that you treat them like a single, and always clip both ropes through every piece. When you fall, you very much want to be caught by both ropes.’ http://www.chockstone.org/TechTips/TwoRopes.htm
Best Practices to Consider:
1/ Do not clip the two ropes into the same piece of pro as the two ropes (during a fall) may move at different rates and damage each other.[This may be negligible in reality, but a best practice none the less].
2/ For the same same reason as above, do not twist the ropes around each other.
3/ Consider that the first pieces of pro on each half rope could be subject to an upward and outward force in the event of a fall.
4/ Ensure you have a ‘clean’ rope system (no twists, knots, etc) before leaving the ground, this will help avoid on the wall issues. If you find the ropes twisted for some reason, consider tying off to the belay and fixing it.
5/ Be clear on who is climbing what pitch is useful. Are you leading in blocks? How will this affect your anchor and flaking choices?
6/ As belaying doubles takes more practice, take time to review the route with the belayer. IE: "Once I'm over the little roof above us it traverses right for 20ft. and then angles back left. Then comes the slab and I'll likely run it out a bit there. The anchor is just after that but it's natural and kind of hard to frig together so it may take a few." You can highlight sections where you want a tight belay, a looser belay, and so on…
7/ Plan out your rope paths and gear choices when possible. Think, "How would the ropes run in Freedom of the Hills?" and try to repliacte that.
8/ Doubles are designed to be clipped independently of each other. Where rope drag is not an issue, clip the ropes in an alternating fashion. Where rope drag is a cosideration, clip in a manner which reduces drag. Ropes should generally run in as straight a line as possible to reduce drag.
Other Tips to Consider:
1/ Consider rapping only 30m at a time (on only one of the ropes) to keep the other as back up (for stuck ropes), reducing tangles on varried terrain.
2/ When belaying two seconds, have them climb at similar rates as the ropes will be more easily be paid out on the next lead.
3/ Set up a regular system for which rope colour will be on your left or right to avoid confusion on the wall. IE: bLue = Left side, oRange = Right side.
4/ Practice untangling rope twists from your harness tie-ins before starting a multi-pitch. This will avoid untying from the ropes mid climb.
5/ Be patient when dealing with dbl or twins. They offer some real advantages if you take your time and flake them and stack them cleanly. Fastest way to have a birds nest is get pissed and try to violently shake out a tangle.
6/Communication. Dial this and doubles life will be easier. What are your calls? ‘Clipping Red!” “Clipping Blue!” “Take Red” “Slack Blue”. Ensure you have communication system that makes sense and works in the wind or other hard to hear situations [this goes for all climbing really].
7/ Brits have historically used them (each climbing partner bought one half rope. This may not be so practical. Manufacturers recommend climbing with the same two halves equally so that they stretch and wear equally.
8/ Your belayer, if not experienced with Doubles, may be your greatest ‘danger’.
9/ RE: Double clipping pro.
*Can reduce rope stretch in the event of a fall (could prevent a decking [could be negligeble). It also increase impact force on the pro (concern for gear pro, but less of a concern on a good bolt).
* Double clipping can also provide a psychological edge.
Avoiding the issue
* Rope manufacturers recommend using 2 biners (or the pros biner and a draw to ensure the ropes run separately) when clipping both doubles to a piece.
*You can [possibly] start off clipping doubles as twins and switch to doubles (alternating) but you should avoid switching to twin after clipping as doubles. [This seems dubious]
* When using doubles with 2 seconds you often have to clip both ropes in order to protect both followers.
* Instead of clipping two skinny ropes through one biner, double up pro. put in two pieces of pro close together and clip one skinny rope to each one. That's how the Brits do it.
10/Feeding out rope:
-On Easy terrain: Just feed out both ropes as one to eliminate uneven rope feeding.
-On more challenging terrain:
-A: where gear is ‘bomber’: feed the clipping rope, while maintaining belay with the non clipping rope. After clipping rope is clipped, pull out a comparable amount of non clipping rope to what you just had. Now, as climber climbs past the pro, you can just bealy both ropes simultaneously again.
-B: Where gear is questionable: If you are genunienly worried about the quality of highest pro, and want to minimize the distance one would fall if the top piece blew, then by all means belay both ropes quasi-independently.
11/Belaying requires extra finger and hand work, like when paying out and taking rope in on separate ropes. Some situation may not lend themselves to this. IE: Belaying with gloves in cold conditions.
12/ Highly recommended: belay second with an autoblock type belaydevice. Reverso, Reversino, or Black Diamond ATC Guide Belay Device are some products. Of course know how to use them too.
13/ If you're swapping leads, just anchor yourself in with clove hitches on the anchor with each rope you are tied into. After adjusting the cloves to keep you tight and provide enough room, you stack each rope on its anchor strand. Or simply flake the two rope together over your ‘daisy chains’.
14/ Be conscious of how much rope stretch there is on such skinny ropes; it can work for you (less impact), or against you (like falling from an overhanging route).
15/ On routes with lots of rope-cutting threats, you can use burly 9mm+ double ropes.