How to safely use 7mm Rope

Recently setting out on a mountaineering adventure, my partner thought the dry treatment on my 9.8mm rope was no longer adequate. We quickly turned around back into town to a reputable mountain shop where I was talked into buying a 7.7mm rope from Petzl. Rather than purchasing a 9.1mm/30m rope, a 50m seemed like the right length. However taking the advice of the sale, I later realized none of my belay devices are rated for 7.7mm and am regretting the decision.

So the question is, how do I safely mountaineer with a single guide rope?
Does anyone rappel with a single 7.7mm rope? I bought an Edelrid microJul and have yet to test it (though now I need smaller cord for a backup). 

A microtraxion (or other pulley) nor ascender aren’t rated for this size, so how is anyone safely performing crevasse rescue?

My partner would also have to modify their belay gear.
Do I need to store the rope until the technology gets smaller? Is it imperative to use twin ropes when using 7.7mm? Now the advantage of less weight is nullified by needed to carry 2 ropes. 

How do I properly use a 7.7mm rope?

Jeffy P wrote:

Recently setting out on a mountaineering adventure, my partner thought the dry treatment on my 9.8mm rope was no longer adequate. We quickly turned around back into town to a reputable mountain shop where I was talked into buying a 7.7mm rope from Petzl. Rather than purchasing a 9.1mm/30m rope, a 50m seemed like the right length. However taking the advice of the sale, I later realized none of my belay devices are rated for 7.7mm and am regretting the decision.

So the question is, how do I safely mountaineer with a single guide rope?

Pretty much the same as a normal sized rope. 

Does anyone rappel with a single 7.7mm rope? I bought an Edelrid microJul and have yet to test it (though now I need smaller cord for a backup). 

Use an atc and add another biner or two to increase friction. 

A microtraxion (or other pulley) nor ascender aren’t rated for this size, so how is anyone safely performing crevasse rescue?

You use it anyway and it works fine, but if you really care that much about if it's rated to it or not, the edelrid spoc is rated down to 7mm.

My partner would also have to modify their belay gear.

No

Do I need to store the rope until the technology gets smaller?

No

 Is it imperative to use twin ropes when using 7.7mm? Now the advantage of less weight is nullified by needed to carry 2 ropes. 

You're mountaineering not taking multiple FF1.7 falls, a single twin or half is completely fine. Weight benefits of using a half vs a single have never been real,  the difference between a 50m 9.2 and a 50m 7.7 is, 750g once you add the second half and a tag line the single rope system is still quite a bit lighter. 

How do I properly use a 7.7mm rope?

You use it pretty much the same as you would a normal rope, I add another biner to increase friction when I'm using my 7.1mm skimmer ropes. In mountaineering I would be less concerned about how well a belay device functions as everyone uses gloves and falls are generally smaller and on lower angled terrain. 

Double it up for the 5th class

Also if traveling ultralight with few belayed pitches use a munter, leave the device at home.

What they said; Extra biner clipped through the rope to add friction on rappel or belay. There's also the super munter if a regular munter isnt enough.  Also test your prusiks, I use 5mm prusik cord when on skinny rope, as opposed to 6mm on thicker rope.  For mechanical rope clamps, my Kong Duck is technically rated down to 8mm but i've found it grabs my 7.5mm just fine, so I just use it.

What are you trying to accomplish/what rope system(s) will you be employing?

Rapping on the rope doubled should be pretty chill with any device. 

Half/twin use for leader and follower should be straightforward. This is what they are made for, the manufacturers tell you how to do it.

Petzl has testing data for using a single half rope for glacier travel, as well as break test data in Microtrax and other rope grabs.

Belaying a follower on a single half rope is normal and allowed by the manufacturer. Many ways to do this.

Belaying a leader on a single half is sketchy if the leader falls. People have died doing this. That said, I will absolutely do this at some point in the future. 

Simulclimbing-- far less sketchy if you double over your rope and use it as a twin. Probably not worth the cluster of double ropes plus rope grabs to isolate a fall from the second. 

Anchoring with the rope around rock horns-- be careful really sharp edges, and prevent any movement.

Tyrolean traverses-- really nice if you can be belayed on another strand if the length allows.

Top rope soloing-- I've used a 7.5 mm rope a bit for top rope soloing a specific route with a very long approach for a single pitch of climbing. I recommend not falling. There are ways to make this reasonable, as long as you aren't falling on it. Not gonna recommend this.

Lead soloing-- can only recommend a knot system for this. Revo is promising for thinner ropes, but not sure I'd use it for 7.7 mm. This is kinda something you do because you're already in a committed spot on a mountain somewhere and it's better to sketchfest your way up half a pitch rather than bail.

Highline leash-- BITD before highliners knew what they were doing, I heard of people using two half ropes as a leash, for redundancy. They would sleeve them together, but tie separate knots to each one. Not really done anymore.

I think that covers most of the ways I'd use a rope.

Oh yeah Kong Duck is cool for thin ropes; on my 7.5 mm, two strands fit in it. Great for reascending a rappel rope when you miss the rap station.

J C wrote:

Oh yeah Kong Duck is cool for thin ropes; on my 7.5 mm, two strands fit in it. Great for reascending a rappel rope when you miss the rap station.

I had actually never tried that until now- they just barely fit side to side so both strands are clamped by the cam. I'm sure that is outside the manufacturers specified use but good to know it could be done in a pinch

When I got a pair of 7.9mm ropes a couple years ago, I also bought 3 belay devices to go with them.   One Micro Jul and a pair of BD Aline ATC XP's is what they were.  I figure 3 is the most that will climb on these at a time, and I don't want anyone in the situation where they would try and use a device not suitable for these ropes.  The ATC is one just about everyone knows how to use.  

I also keep a few pair of Mechanics gloves for belaying and rappelling, which I rarely do for normal diameter ropes.  

On a recent Devil's Tower climb, I ended up using someone's full diameter rope for one of the rappels down.  Since all I had were the skinny rope belay devices, I had to build a carabiner brake.  Good trick to know.   

Use your microjul, it will be fine