Studies of rappel forces, sponsored by the AAC, concluded that typical rappels could easily generate forces equal to twice the weight of the rappeler. You are probably wearing your pack, and odd bits of gear and clothing as well. Most climbers want a 5:1 or 7:1 safety ratio, at a minimum (at least those who have survived to discuss their practices).

There is also the question of abrasion and wear of the rope, which can happen very rapidly, reaching dangerous proportions even during the duration of a single rappel.

I would really prefer to carry a thicker rope - the extra weight is well worth the increased weight.

6mm prusik (the UIAA rate stuff) is plenty strong to support body weight. Have used 5 and 6mm plenty of times to prussik up and to make haul systems. I even learned to use 6mm cord to escape a sport climb route. Having only the main rope connected to the bolt by a 6mm prussik and rappeling of. (NEVER lower off a prussik or sling, failure is almost guaranteed) I do prefer to leave gear, than doing that.

I never learned to double or triple wrap a figure of eight. So can't comment on that. Haven't tried to use the eight upside down either. Just seamed really tricky to me.

As for carabiners strenght. It's should be printed/stamped/forged/lasered on them. I only carry 2 big HMS biners, the rest are all small lockers. As long as you can fit a proper clove hitch in it, it will be big enough to do most jobs.

"They also now make mini non locking carabiners. I have about 6 of them and they are fun to use and very practical. before you scoff, they are as stong if not stronger than the full sized ones, the only difrence is that they are not good at handeling mutiple lines, or a lot of rope."

Source?

I bought them at REI.

http://www.rei.com/product/733586

Thanks.

I found these as well looking online:

http://www.camp-usa.com/products/carabiners/nano-23-orange-118903.asp

I have and use four of the nano's - they are fully rated and are excellent carabiners.

6mm is fine for prussick slings - that is typically about the size I use, but I would rather not use that size for a main rope. On the REI website the 6mm and 5 mm cords are listed as accessory cordage. Doesn't that say something?

Cavers, who do some of the most sophisticated ropework anywhere, in exploring deep and vertical caves, often use thinner ropes because of the weight savings involved. I wouldn't be surprised if stronger ropes become available in thin ropes, but there is a limit because smaller diameters are susceptible to more rapid and dangerous rope abrasion. Perhaps new materials will get around that limitation.

It has to be noted that the thinner ropes eliminate any realistic opportunity to use any sort of body rappel, hasty rappel, dulfersitz. As a hasty rappel becomes more vertical any rope will attempt to fold you in half horizontally. A single 7/16" rope tries hard to saw you in half vertically. Thinner ropes could be expected to saw more aggressively. It pretty much makes a harness and belay device a requirement.

It also makes some sorts of handling more difficult. You aren't going to be pulling on the line without heavy gloves or ascender/s.

The practical requirement for a harness, belay device and some way to grip the line complicate the issue.

There are other methods that are modified munter hitches that use multiple wraps around one leg of the biner to increase friction. In fact, that is what the multiple holes in the commercial descender are made for; tailoring friction just like a rappel rack. I'm thinking try this out in the back yard and tune it until it works properly.

Bill

Speaking to the consequences of abraision. One of my Vertical Rope instructors would take a pice of webbing and a prusick cord of 6mil. He would then have someone hold the webbing and using the prucsic cord literaly saw through the webbing. This would happen fast, VERY fast. A prusic cord under load can chew through webbing in about 30 seconds, if that long.

You are absoluty correct when you say that the thinner rope requires more gear and thought. When I orginaly posted about using 6mm line it was intended to be in a doubled form and for a one way trip. If you wanted to go back up the doubled 6mm cord, you could do that using a prusic loop. Heck you could even cut the material for the loop of the end of the rope you just rappeled on. They do that technique on Purcell systems.

Remember, almost all sub 8mm cord is static cord. Even a short
fall on a piece of webbing or static cord without a dynamic
rope somewhere in the line of connection to absorb force, can be fatal either by rope failure or injury to the person.

Also-

Testing by a university at Calgary showed that in extreme cases, a rappel can generate forces exceeding 1000 lbs.