Twin ropes physics

I climbed recently with twin 8mm ropes and I liked them a lot. However, I have some questions regarding the physics of falling and the stress placed on gear.

Say I place a piece and clip rope A. I then climb 10 feet higher and place a piece and clip rope B. I climb above my last piece a few feet and take a fall. Now, I know most of the stress will be placed on rope B, but will anything be placed on rope A being that the last piece it's clipped into is 10 feet below where I fell? If there is any stress placed on rope A, it will most likely be upward and/or outward, yes?

Also, I know that it makes a difference depending on where rope A is clipped compared to rope B - i.e. is rope A clipped into a piece that is way to the left and then is rope B clipped into a piece that is way to the right. But what if the pieces are pretty straight in line? Should you just clip both ropes into the pieces then?

You're doing it wrong if you're climbing on twins.

Good explanations here. supertopo.com/climbing/thre…;tn=165

It's the internet so take what you will.

Yep, twins are not the same as doubles. The technique you are referring to is used with doubles, not twins. This is important obviously when making sure you have the correct rope for the job.

It's basically a single rope small lead fall on B to answer one of your questions.

Brian Stevens wrote: Also, I know that it makes a difference depending on where rope A is clipped compared to rope B - i.e. is rope A clipped into a piece that is way to the left and then is rope B clipped into a piece that is way to the right. But what if the pieces are pretty straight in line? Should you just clip both ropes into the pieces then?

Twin ropes should both be clipped into every piece. A single twin rope is not rated to catch your fall!

Half (aka double) ropes should be alternated. If you clip them both to one piece there will not be enough stretch and the fall could be hard enough to hurt you.

Some ropes are rated to be used as both twin and double.

It sounds like you either don't know what kind of ropes you are using or you are using them wrong. You should research the difference between twin and double ropes.

As others have said, you should not be using twin ropes in the way that you are describing. Twins - both ropes are clipped to every piece of pro, always.
Doubles - clip one rope to each piece of pro, sometimes alternating and sometimes switching after two or three pieces

Some ropes are rated as both doubles AND twins, in which case you can do either of the above.

I had been using ropes that were rated as both doubles and twins.

Figure your plumb line is a y-axis.

When you run the Half-technique, unless you can get the two independent protection placements relatively close in relation to the vertical climb high point x-axis, it's pretty much a single strand lead fall catch.

I think you're basically fine. Even a twenty footer in free-space with these ropes isn't that big a deal; they are made for really soft catch and can certainly catch more than that. Although, what you really want to think about is not falling; most of the time when you use these systems, you are in terrain where falling is not an option and you have to move fast. You are just giving yourself a chance that maybe you don't get your ass kicked too much.

The reality of a climb is that it actually is pretty difficult to get a half-technique to distribute a fall between independent pro placements. It's certainly possible, maybe pulling through an overhang, keep yourself from smacking a curtain/pillar as well as the inner wall.

So one thought, the half-technique can allow you to control your fall/plumb line with alternating pro on traverse, overhang sections, or otherwise wide but comparable x-spacing along your y.

(draw out some quick and dirty vector examples and you'll see how this works. It may be that the x/y axis labels I'm thinking need to be transposed to get a good eye-ball on the situation. Try x=0 as plumbline which would be the y-axis I'm thinking.)

Another thought, if you alternate, you can limit your fall distance somewhat if you go for those top-rope type clips by using your off-strand.

Most of what I use half-technique for is to allow a little more leader freedom in movement by reducing rope drag on wandering stuff, and bring up two seconding climbers/working as a three person team on the mountain. That doesn't mean I don't plan the system out and gauge acceptable risk. I still do in case of a fall, but realize the situation can be inherently more dangerous than the typical single rope outing at the sport or trad crag where you plan to take all kinds of whippers.

So maybe don't push the system too much in route selection and pro spacing until you get some more miles.

Twin technique is basically using the two strands together to act as a single rope. Sure you increase the force on yourself and the pro, but it's nowhere near catastrophic when looking at just the energy in the system itself, and should be (will be) more in line with the single-rope rating anyway.

Either system allows you the obvious splitting up the rope between partners on the approach hike, and greater distance for a rap. Given the risks, the rewards of using these flexible systems are well justified. As a climbing team, you will be able to enjoy the most breathtaking climbs by attacking them alpine-style and in amazingly remote settings.

Some other things I think are important are:

Keep with either one technique or the other during a given pitch. On critical mid-pitch directionals, if going with the half-technique, then separate the strands with different length slings to keep the rope systems operating independent.

Manage the rope system with your alpine slings not to catch/trap a rock edge if you fall;

Realize you have greater elongation to plan for so don't get complacent and deck yourself on a ledge system; and

Use a belay device capable to catch given smaller strand diameters.

Short answer: Nearly all the stress of your fall will be on the highest gear placement.

Long answer:

You would not want to clip your doubles into the same gear for two main reasons:

1) If two ropes catch your fall, neither one will stretch very much. This will increase the impact and shear forces on your gear, the rock (more important for sandstone...), and your body.

2) The whole purpose of using doubles is to reduce ropedrag by limiting the bends in each rope over the length of your route. If you clipped the same rope two times in a row, then that rope wouldn't "skip" bending for that placement, your ropes would rub together in that placement, and your rope drag would be the same or greater than if you had just used one rope.

To answer your question, though, nearly all the stress associated with catching your fall would be on your highest placement. I say nearly all because the stress is dissipated through all your placements if the rope direction changes enough (if the quickdraws/streamers on your lower placements are taught, if the rope drags on the rock... pretty much anytime the rope changes direction.) The stress on each placement is proportional to the angle that the rope changes direction and the contact area on each surface.