Combining double and twin technique within a pitch

I've been thinking about a potential issue when double ropes are initially used as doubles and then recombined as twins within a pitch. (There was a discussion here on concerns about friction and heat as the ropes run at different speeds through a single carabiner; this is a different concern).

I'm concerned about the nature of the forces generated on the carabiner of the first piece after doubles are re-combined as twins. Consider the following picture:

doubles-twins sketch 1

Here the climber has been clipping the red rope on the left and the blue on the right. She decides to recombine them at a good pink nut (perhaps to reduce rope stretch, fearing ledgefall), and then climbs up past a green fixed pin. The ovals represent the rope-side carabiners.

She then falls. What happens?

doubles-twin sketch 2

Each rope will become taught and attempt to take the shortest path between the pin and the corresponding piece before the nut -- the dashed lines in the picture. And each piece will exert a force on the nut's rope-end carabiner as shown by the block arrows, outward and slightly upward. The vector sum of those two forces is straight up. We can expect the carabiner to run up the twinned ropes as they are pulled apart, until it reaches the limits of the sling. At that point, direct upward force will be applied to the piece. This is similar to the sideways pull that can be applied to the middle piece when three pieces are not colinear, and it's similar to the "zippering" from below that can happen when the belayer stands away from the wall and the first piece is not good against an outward pull. In this case, it's even more extreme as the net force can be straight upward.

Conclusion #1: If you're going to recombine doubles and begin using them as twins, the first recombined piece should be multi-directional.

Ok, let's say that it was a cam instead of a nut and it holds upward force just fine ... but the pin wasn't good. What happens?

doubles-twins sketch 3

Here I've drawn the carabiner in the orientation it's likely to end up in after running up the twinned ropes: the outward forces from the tensioned ropes will pull the long axis of the carabiner to be horizontal. Now there's a moment of freefall as the climber/ropes/carabiner/sling all fall below the piece, and maybe we can hope that the biner will reorient itself so as to take the forces on the long axis; but it seems reasonably likely to end up cross-loaded, perhaps with one rope through each carabiner end and the sling pulling directly upward on the gate.

Conclusion #2: If you're going to recombine doubles and begin using them as twins, each rope should get its own biner (and sling?) on the first recombined piece.

Thoughts?

I'll see you " the resultant vector forces" and raise you "the tension and tangent function".

Do you worry about things a lot generally?

I "combined" clipping like that on a couple occasions and each time got really tangled up and a worse rope drag than using a single line. I don't understand that technique. Maybe it is useful in some cases, or maybe it requires practice. For me it's either double or twin technique, not a combination of the two.

kcradford wrote:Do not recombine doubles. Why would you ever clip the ropes the way you are showing themin the drawing? double ropes are desiged to have one rope through each pice of gear,and are not intended to be used as twins. you are increacing the forces on the pices that have both ropes cliped to them.

Some ropes are rated for both double and twin use, though I imagine the fall will be jarring when both clipped (I hate falling anyway so not really a difference to me). I think the reasons to clip both would be a situation where an emphasis would be on the using twins in the first place. Somewhere you have a higher expectation of cutting a rope perhaps. It's an edge case for sure.

The upward force will be pretty negligible unless that angle is very wide, but yes it could slide pieces upward. If you insist on going to twin and you're concerned place two pieces. The first in the direction of the fall, the second in the expected direction of pull due to rope separation. However, I think your better plan if you're in this situation debating is to pause and ask MP, but this time please include a photograph of your setup. MP currently sucks at hypotheticals but should be better at a current position, bear with them in the meantime.

Haven't finished the morning coffee yet, so most of the verbiage is over my non-caffeinated head.

But... your artwork is stunning. Definitey put a legit smile on my face.

Thanks for sharing.

kcradford wrote: Why would you ever clip the ropes the way you are showing themin the drawing?

Reducing rope stretch = ledgefall potential is the main reason. I've done it, and I know lots of other climbers have as well. The conclusion of the previous thread was that it was generally safe (including email from a Mammut rep); but that thread was mainly concerned with friction and heating as ropes run at different speeds.

Your diagram shows the two independent ropes clipped into carabiners roughly in the same horizontal plane. Also, they are shown fairly close vertically to the carabiner where they are both clipped together. Both of these maximize the angle that they enter that carabiner.

I don't see that as a very realistic scenario. I usually clip one rope, climb up a bit, clip the other rope. Rinse and repeat. Of course, sometimes I clip the same rope several times in a row.

But, in the rare case if I were to clip each rope into a seperate piece on the same horizontal plane, they would likely be very close to each other - like an arms length because I'd be placing gear at the same stance. And that would minimize your upward force vector angle.

I just don't see it as much of a problem.

The last pieces clipped separately don't have to be at the same height in this scenario, that was just a convenient way to draw it. They do need to be separated left and right of the recombined piece for these concerns, so that the tensioning ropes will pull outwards in opposite directions.

kevin neville wrote:The last pieces clipped separately don't have to be at the same height in this scenario, that was just a convenient way to draw it. They do need to be separated left and right of the recombined piece for these concerns, so that the tensioning ropes will pull outwards in opposite directions.

Then draw it again and I think you'll see you're worried about nothing.

you mean use half rope technique as half rope technique, and use twin technique as twin technique?

Whoa..

That

is

EARTH SHATTERING!!!

mind, blown.

Draw it with the ledge and the last good stance from which she placed the last piece. It may make more sense. ...

I think the general idea is: It depends on the situation. In rarely encountered circumstances the rope system you are describing has a use. In most, you shouldn't do that.

It sounds like a lot of trad climbing. "X works well 90% of the time, but occasionally I have to do Y because bad shit will happen." Only you can make the call at the time of the climb. Having said that, it defeats the purpose of double ropes if you use them as twin ropes.

Were I in that situation I would look for pro "off route" and way away from the ledge, traverse over and place pro and a double length runner. That's all I can say from an MS paint picture.

On a climb with multiple ledges the last thing I would wanna do it to create more friction. As it is its already a huge pia. The rope drag will be so you will not be able to progress up the route because of it and will need to back clean.

I don't mean so far out that a double length runner creates that much rope drag. Just enough that if you were to fall, you would swing away from the ledge. If that's not possible, and you think you might hit the ledge then chalk it up in the no fall category.

And this is kinda what I think when he mentions many ledges. Some that size or larger. Up to being able to lay down on.

FAIL! Zippy, I was saying combining twin and doubles rope technique is PIA. ...and so is your so called wit. DOUBLE FAIL!

Zippy then don't interact with me, simple as that. Some people are just always on different pages. If you live long enough and pay attention you will see for yourself. So go amaze folks who get you.

Zippy you are right for once. I don't like you. I don't like your style. I think you are dick. So do I care that you are a dick? No. Why do you feel so obligated to start threads about me, tell me how you hate my guts and what kind of anguish I'm causing you by being so annoying to you. Let it go. Take some pills smoke some weed and let it ghhoooo..