What are some pros and cons of climbing with double ropes versus a single rope and a tagline on a long alpine rock route?
There are trade offs with each system. The nice thing is that the weight is about the same for each, depending on what you use for your tagline and how skinny you go on your main line.
For me, the main upside of going with a tagline is that there is less rope to deal with at each belay. I can put the tagline in my pack and not pull it out until the descent. Many of the routes in the U.S. are set up for single 60-meter ropes (30-meter rappels) so most of the time I can leave the tagline at home. Long rappels are sweet when the pulls are super clean but oftentimes in the alpine there are more things that the rope can snag on, and shorter rappels (less than 30 meters) might be a good idea.
The other benefit of using a tagline is that you can use it like a tagline. Instead of putting it in your pack you can trail it behind you and tag up any additional gear that you need or haul a pack. Since it’s not running through any of the gear it makes this process much easier than trying to pull that off with a double rope system.
The upsides of using a twin or half rope system is that you don’t have that extra weight of a rope in your pack while climbing. You also have a “real” rope that you can lead on if the ropes get stuck when pulling them on rappel. To safely use a tagline it’s recommended that you thread the fat rope through the anchor. That means you are pulling the skinny rope. If for some reason the ropes get stuck you might be hanging there with just a skinny accessory cord in your hand.
There are a few manufactures out there selling skinny taglines that can hold one or two leader falls (using it as a twin). If you are going to be using your tagline a lot it is probably worth looking into one of those ropes.
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