I understand the designations for ropes and the corresponding limitations for their use, but am confused about double (half) ropes. I get that they are supposed to be clipped individually into your pro, never together, yada-yada. Here's my problem: you're on a route that has a big traverse and you're clipping the same rope (of your two doubles) into your gear. After a couple of placements clipped into the same rope, aren't you essentially using your double rope as a single? If you fall, and you've only clipped one of your doubles to your last piece of pro, all your force is on the one rope. What gives?
If you alternate clips, it defeats the rope-drag purpose the doubles are so helpful at reducing, but that's what I've been doing. It's also a pain with rope management, always checking to see if your ropes are crossed.
Pat Seay | via rockandice.com
I've always wondered that very thing and now have the perfect opportunity to use you as my stooge to get an answer. According to Jim Ewing, the product engineer for Sterling Rope, the old UIAA half-rope standard was to drop test it with an 80 kg weight. If the rope withstood that drop, it passed. But some smart guy later determined that the 80-kg weight, which was the same used to test single ropes, didn't produce enough rope data to be accurate -- they needed more drop tests to produce more data to provide better numbers. So, they reduced the weight to 55-kg and raised the drop-test standard to five.
The critical bit of knowledge is that five drops with a 55-kg weight has the same overall mass value as one drop with an 80-kg weight. In essence, says Ewing, a certified half rope is rated as a one-fall single rope. Don't, however, believe that a double rope can be used as a single -- take one hard fall on a single strand and it's time to retire it.
Ewing also notes other considerations. A fall from a traverse generally yields a very low fall factor. If you placed pro at the beginning of the traverse, you'll simply swing. If you fall onto gear placed before the traverse, you'll have a lot of rope out relative to the distance you'll fall vertically, netting the low fall factor. Impact forces resulting from a fall from a traverse will be well south of the rating of the [half] rope, says Ewing.
How you choose to clip and arrange the ropes while traversing is your call. Every situation is different and requires some craftiness to keep everything running smoothly and safely. Always watch out for sharp edges when you are traversing, as ropes are more likely to be cut in swinging falls than straight-down plunges.