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Information on Tyrolean Traverses

Tyrolean Traverses - A Synthesis of Available Information

Please note this information isn't all attributable to the Gearshack. Much of it is from experience, backed up by examples from:

Petzl

The Mountain Skills Training Handbook by Pete Hill and Stuart Johnston; David & Charles 2004; ISBN 0 7153 1848 9

PLEASE NOTE: This information is not intended to give you advice on how to set up a Tyrolean Traverse. It is aimed at professionals and is a synthesis of publicly available information, presented to help and give guidance on current professional practice and the purchase of suitable equipment. Do not attempt these activities without professional training and guidance.

Tyrolean traverses should be used as a temporary activity when constructed with rope. Leaving them up for long periods or over tensioning can lead to rope failure; please see this article from the BMC: https://www.thebmc.co.uk/media/files/Gear/TCM11_01_Low%20stretch.pdf

Introduction
Generally Tyrolean Traverses are simple to set up in principle, but there are always concerns about the forces acting on the ropes and anchors. This is because the rope is tensioned and horizontal. This takes out the stretch which normally absorbs forces acting on the rope - and the horizontal nature of a Tyrolean greatly increases forces acting on the anchors.

The first principle of a Tyrolean is: always choose absolutely bomber anchors. Strain on the anchors will be high.

When the rope is hanging, it forms a curved shape which many call a parabola (it isn’t, but anyway it sags). When you put a load on the rope it’ll be a triangle. Your load will always want to slide to the middle, so forces are always calculated from there anyway.

The calculation of forces is very complicated, as there is a huge range of factors. Rope stretch (in itself very complex), whether the anchors are at the same height, whether a rope is used to pull the weight to the end, and so on. You don’t have a hope of getting a correct answer, so bear in mind the fundamental principles for reducing the forces.

a) Don’t tension the rope too much. It’s easier for instructors to work if the rope is really horizontal, but this is the worst thing for increasing stress on the system. To achieve this, only use a 1:3 system as illustrated to get tension into the rope - that way you can’t over-tension it.
b) Also consider just how horizontal it needs to be in reality. If you can put up with hauling people uphill a bit at the end of their traverse (or they can do it for themselves), then the system will be less tensioned.
The forces will be the same horizontally as the person/load crosses the rope - however they will vary vertically, as the angle of the rope changes. This doesn’t ordinarily affect operation much in our case.
c) Ideally the sag should be 15 degrees or more - this way the load on the end will never exceed 2 x the weight of the person/load (approximately of course!).
d) If one end is higher than the other, the horizontal forces are still the same - but the vertical force is greater at the top end of your traverse. In this case put any tensioning equipment and/or pulling ropes at the bottom end if possible so it stresses the end which has the easiest job!

What Kit and Which Method to Use?

Traditionally this has been done using bits of string  and old rope (perhaps I exaggerate). However there is some commonly used kit now. This is often not manufactured specifically with this is mind, but is climbing or Work at Height/Rescue kit which can be adapted safely.
Always use low stretch rope ('abseiling' type rope) for Tyroleans for the main ropes. Climbers setting up a Tyrolean will of course not have one handy; this refers to adventure exercises or rescues.

Method 1
Here’s one system for tensioning, borrowed from Petzl. This has the advantages of simplicity and using a device which is easily locked or released. 

https://www.petzl.com/US/EN/Professional/Tensioning-a-rope-for-a-Tyrolean?ActivityName=Technical-rescue#.V9QZ8pMrIk4

Method 2
The system recommended by Pete Hill and Stuart Johnston in their excellent book can be found at:

http://books.google.co.uk/books?id=zP8GuBEtirAC&pg=PT230&lpg=PT230&dq=technical+info+tyrolean+traverse&source=bl&ots=H_-CYCD7MM&sig=CWVdmEaK9U789INNeGRuvF4twF4&hl=en&ei=8Zk8Td7vLcPPhAfJ5vmLCg&sa=X&oi=book_result&ct=result&resnum=7&ved=0CEAQ6AEwBjgK#v=onepage&q&f=false

This uses slightly different kit and isn’t quite as easily managed, although is better for climbers and instructors who are unlikely to be carrying around the expensive and large Petzl I’D.
Basically: tension the rope using a pulley system with an ascender attached to the rope. The ascender grips the rope to pull it into tension. Behind the ascender is the end of the rope, tied off with a locked Italian Hitch. As the rope is tensioned it is taken in, the Italian Hitch is locked off, the ascender moved along the rope again, and the whole process repeated.

However, please remember that rope manufacturers and Petzl recommend only using a 1:3 ratio so you don’t tighten the rope excessively.

 
Attachment
Generally it is accepted that (except for climbing situations) a pulley will be used to attach the load/person. This is often a Petzl Tandem, or a Petzl Tandem Speed, ideally suited to the purpose. Most pulleys need an oval karabiner so that strain is even on both flanges.
Some situations of regular use demand that the pulley is backed up on to a cable by a second karabiner, but this is more common on ropes courses than on Tyrolean Traverses.
Backup
Most people use a parallel rope if the Tyrolean is either an adventure exercise or a rescue. They are not always used in climbing situations or escapes as carrying extra kit for this eventuality will not be practicable.
The safety (parallel) rope must be secured to a similar standard to the original, as the same strains will come onto it in the event of a failure of the main rope. In fact the safety system will receive a shock or a dynamic load (depending on how the failure manifests itself) – and therefore could be said to need even better anchors.
The load/person attached to the Tyrolean would therefore have a second attachment from them to another pulley which runs along the parallel rope.