Why do you want to climb on two diffrent size ropes? If you really wanted to redirect you could just take a sling and knot it in the middle in such a way to have a biner on ether side and than the sling cant move and you have your ropes in diffent biners, since your just belaying the follower with this system the knot isnt going to screw with any load issues that you may have.

Why not just use an autoblock off the anchor? Is this set up for that you want for transion speed at the anchor when swinging leads? If it is than mabey you could just have 2 quick draws than for your redirect and not worry about the weight/space for a redirect sling.

Yo. Before I get flamed, just gotta say that while new to a double rope system, I have considerable experiance belaying on multipitch climbs and am aware of the pros and cons of a redirect vs. a belay off the anchor (ex: munter or reverso) as well as direct off the harness...blah blah blah.

My question is...When climbing on a double rope system and belaying the second off the harness, through a redirect at the anchor, is it common (safe) practice to clip both strands through the same biner at the redirect?

In other threads (and elsewhere) it has been confirmed that double/half ropes, when clipped as twins (two strands, one biner) create a potentially dangerous situation w/ higher impact forces and melting ropes when catching a lead fall...

I am planning on climbing on a 9.1 and an 8.6 together as doubles and am curious as to others' opinions on clipping both strands together into a redirect biner at the anchor...or would you ALWAYS use and autoblocking device such as the Reverso...? Will the impact force significanly increase? What do YOU do on multipitch alpine routes w/ doubles?

Vic

3) Lower impact force. Double strands means double the impact force.

Yo. Before I get flamed, just gotta say that while new to a double rope system, I have considerable experiance belaying on multipitch climbs and am aware of the pros and cons of a redirect vs. a belay off the anchor (ex: munter or reverso) as well as direct off the harness...blah blah blah.

My question is...When climbing on a double rope system and belaying the second off the harness, through a redirect at the anchor, is it common (safe) practice to clip both strands through the same biner at the redirect?

In other threads (and elsewhere) it has been confirmed that double/half ropes, when clipped as twins (two strands, one biner) create a potentially dangerous situation w/ higher impact forces and melting ropes when catching a lead fall...

I am planning on climbing on a 9.1 and an 8.6 together as doubles and am curious as to others' opinions on clipping both strands together into a redirect biner at the anchor...or would you ALWAYS use and autoblocking device such as the Reverso...? Will the impact force significanly increase? What do YOU do on multipitch alpine routes w/ doubles?

Vic

We should harness your force doubling machine to power the world. Sorry, but this statement is just wrong.

Two strands means that the force from each strand is applied to the pro. HOWEVER, the weight of the climber will be split between the two strands. So, the force from each strand is half as large. If one strand is clipped, then one strand will hold all of the weight of the climber. This implies that that one strand would be applying the full equivalent load to the pro.

The force felt by the piece would be the same with one or two strands.

Actually, you are completely wrong here. You would be right if the ropes were completely static (zero elasticity). With dynamic ropes, they stretch to absorb most of the impact of the fall. Two strands will stretch half as much thus placing double the impact on the point. To be more precise, by clipping two strands into a single point you are reducing "elasticity" of the system by a factor of two. That translates into double impact force.

--Misha

no

You could have a point that the ropes would act as springs in parallel, but the biner DOES NOT impart a pinned end condition. Your assumptions are incorrect

Sorry, but you are wrong. I think you are confusing weight with force. Let me simplify. Remember F=ma? Well, when you are falling, just before the rope "engages" you have a velocity V. It pretty quickly goes to 0 as you decelerate. That's the acceleration parameter "a". The faster you decelerate, the higher that value is. When the rope is very elastic, the acceleration (deceleration in this case) value is smaller. That makes for a lower value of force. When you double up both strands of the rope, the elasticity decreases, so the acceleration and therefore the force increases. (using absolute numbers here)
Just imagine falling on a very soft elastic rope compared to a very stiff 11+mm rope. When do you think the force on the point will be higher?

--Misha

PS. Draw a diagram with forces.

No no

I understand what you are saying, and you are still wrong. When I have more time I will try to write out why.

Vic, to go back to your original post - I think the key ingredient is who you're belaying - the second. They won't generate a fraction of the force in a well-belayed TR fall as a leader, and I don't believe the concern of force impact on the gear - in this case a redirect off of the anchor - is as great as if we were talking about belaying a leader. I'd be cool with it.

P.S. I still think you'd be better off belaying directly off the anchor in every possible circumstance - buy an ATC Guide!

Please do! New discoveries in physics are always exciting!

--Misha

this thread is a good example why you shouldn't get technical data from this site. don't be lazy and actually look up the research. call the companies that have ACTUALLY conducted these kinds of tests (BD, Petzel, etc). get THEIR opinions. it is VERY dangerous to get this kind of info from the site. most people here don't have a clue. just because someone says their are a "physicist", doesn't mean they know what they are talking about. ask the REAL experts......the guys who do this for a living.