75m or 65m tagline?

I have a 75m 7mm tag line. It likes to tangle itself into knots. Since the probability of tangling seems to be a non-linear function of the cord's length, I'm considering chopping 10m off. It's not much, but maybe it will help...and it will be a little lighter too. Obviously, if it's shorter, then I'd have to make shorter raps. But I don't think there's too many places where you'd need to make 70m instead of 60m raps. Or is there? And of course if I chopped it, then there would be less remaining if I had to further chop it in the event of it getting caught. Any other thoughts about this?

Is there any need for a tag line longer than your lead line?

Bob Johnson wrote:Since the probability of tangling seems to be a non-linear function of the cord's length...

I'm curious if/why this is the case

that guy named seb wrote:Is there any need for a tag line longer than your lead line?

Tag lines are static while the lead line isn't. To account for stretch in the lead line while rapping on the lead line/tag line combo, you can get a tag line about 5m longer than the lead line.

Bob Johnson wrote: Tag lines are static while the lead line isn't. To account for stretch in the lead line while rapping on the lead line/tag line combo, you can get a tag line about 5m longer than the lead line.

What length rope do you have? If it's a 70 meter line i definitely wouldn't cut it, If you have a 60 meter lead line i would definitely cut it down.

Nathanael wrote: I'm curious if/why this is the case

Well I haven't done any research on it, but it is plausible that tangling would scale at a faster rate than linear. Let's just say that each little segment of the cord can get tangled with a probability x that is completely independent of all the other segments' (not the case, but not a bad model for a really long cord). Let's say there are N such segments in the rope. The probability of the rope not developing any tangles whatsoever would then be proportional to (1-x)^N, which is a ridiculously small number for large N. This also shows that the probability of developing a snag grows exponentially (not linearly) as the number of segments increases.

Anyway, the physics of ropes is not simple and there are much better models out there, but this provides a rough idea of the complexity.

Don't forget the exponential rate of tangles which is counter relative to the diameter of said cord.
There's also the Belayer/Leader factor and the less correlated gender factor.

Luc wrote:Don't forget the exponential rate of tangles which is counter relative to the diameter of said cord. There's also the Belayer/Leader factor and the less correlated gender factor.

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Actually, I recall some controlled testing where it was shown that tangles correlated with diameter. Smaller diameter's resulted in more tangles. Length was kept the same during the testing.

So the smaller diameter is at least part of the problem with tangles.

I have a fair amount of experience with rappelling with the 60 m rope and a tagline. Tangles are part of the game. I have had some doozies.

I believe the trick is learning how to control the tagline so that it does not get tangled. I would suggest finding your favorite way to do that. There are two ways that I have tried that seem to work OK.

One way is to pre-stuff the tagline in a bag and hang it from the first to rap.. Be sure to tie the free end off to something in or with the bag so it does not create a mess in there. And be wary of tangles anyways as the rope pays out of the bag.

The other way I have tried is the first to rap attaches one end of the tagline to their harness. As they rap, their partner pays out the tagline from a stack at the rap station. This also is kind of tricky because the person rappelling can't be wanting to go down while his partner is up above dealing with a tangle. So the tagline also needs to be stacked in this case at the rap ledge. And the first rap is a fixed line wrap. For this option DO NOT get smart and throw a munter on the tag line as a quasi belay - can pump all kinds of coils into the system.

Whatever you do to get control, you are not going to rap as fast as with the single rope or double ropes. Well, your mileage may vary.