No.16 Anchor Options
Before the throwline has been set a Risk Assessment should made and climbing methodology considered carefully.
There certainly is more than one way to set a tree climbing system and a creative and systematic approach must be taken when choosing which system to use.
Each tree and job specification differs and so should the climbing system.
When the throwline has been set a plan for works is already underway and choice of system should have been made.
A 2:1 system may be set from the ground to enable instant Work Positioning.
With a Rope Wrench a 1:1 may be set and used as an Access and Work Positioning system.
The 2:1 and 1:1 may be initially installed for Access and a climber may choose to enter the tree and install a second rope to use as their Work Positioning system.
Accessing the tree to the uppermost Anchor Point before work begins gives a close-up arboreal Risk Assessment of hidden cavities, weak attachment points and potential mammal or insect disturbance.
The high point anchor will experience greater force than it is accustomed to.
A tree grows for itself and not the benefit of a tree climber!
We must enter the structure with respect for its inherent strength and weakness.
We must be aware of leverage forces and always try to set the anchor on an upright branch.
As a tree is organic an anchor may be weakened by rodent or fungal attack, among other things.
A closed system (2:1) places a force equal to the climbers mass upon the high point anchor.
As their mass begins to move it will create higher forces.
An open system (trunk anchor) places a weight up to twice that of the climbers mass.
As they begin to move the high point anchor will experience more than double the climbers weight.
Anchor Setting
The Choke
A Running Bowline http://vimeo.com/85393662 can cinch the working end to an isolated branch. It leaves a non-retrievable 1:1 rope system and can be used for fast and ergonomic access with a Rope Walking System.
Teufelberger ‘Fimble Saver’
The Fimble Saver https://honeybros.com/Item/Teufelberger_fimblSAVER offers
i) zero cambium damage
ii) zero rope wear
iii) retreivability
iv) control of the working end (splice)
v) options for rigging 1:1 and 3:1 systems.
The 2:1 system is the most common arborist system but we shouldn’t be constricted by it.
It sets a platform where a climber may move between 1:1, 2:1 and 3:1 systems.
ART - Rope Guide
The pulley style frictionless anchor gives smooth and efficient Up, Down and Sideways movement.
The Rope Guide is designed for 2:1 technique.
It is described here (in English) http://www.youtube.com/watch?v=kKK3omXV1Lk.
The Running Bowline and Fimble Saver can cinch on to a stem with no branch unions but the Rope Guide does it in such a way as to make retrieving consistently successful.
As the retrieval ball catches the Trapeze Link(5) it drags the Camming Device(4) down the remaining length of the rope(3) and creates space for flicking the Pulley(2) out of the ring.
With a Double Snapper(1) installed manipulation of the ring makes this even easier and the guide is lowered gently to the ground.
It’s a real boon and ART has designed each part so functionally that you only need worry about giving it a slow and soft retrieval as installation, work time and un-installation are close to perfect.
Energy Absorption in the Anchor
Rock Climbing and Industrial Access have in-built shock absorbency in their ropes and component design.
Rock Climbing ropes are fully dynamic and easily absorb impact forces.
Industrial Access workers use a semi-static kernmantle rope with slight in-built stretch (3% at 20% elongation)and and the toothed ascenders will rip the thin outer cover in a Fall Arrest situation, dissipating the energy.
As arborists we move in and out of Fall Arrest and we use different rope design so one part of our energy absorbency system is to manually manage slack.
As a rule no more than 50cm of slack should enter our system.
Vigilant slack management and careful component configuration area positive way to create in-built energy absorption.
Device and Rope knowledge are key, Shop K run splicing workshops and it is a good chance to learn about rope construction and best use.
Treemagineers/Teufelberger have certified a Footlocking System that consists of a Polyester covered/Dyneema cored access rope and a fully Dynamic Footlocking prussik.
Dyneema is akin to steel in terms of energy absorbency but the careful configuration with the dynamic prussik ensures that loads are kept low enough for safe use.
It is an interesting step in the right direction of component configuration.
Scientific tests show that our body will begin to suffer great internal damage with impact forces over 600kg.
A 70kg climber can generate forces up to 1000kg and I encourage new climbers to read simple physics theory to understand force multiplication and implication.
Seek help when designing your systems!
The Trunk Anchor
When the climb line has been spread over many branches and tied off at the bottom with a trunk anchor, the Tree can be a great ally for energy absorption .
When set like this a climber must be aware that their mass when applied to the rope will exert greater forces at the highest branch point than a closed system.
This can be managed and turned into a powerful systematic approach by LOADING the branches in certain ways.
I encourage new climbers to study about rope angles and load forces.
It is key knowledge for setting climbing and tree removal systems.
There are many ways to tie a trunk anchor, here is my favourite http://vimeo.com/85415643
A belay device may be attached to the rigging hub in a rescue situation but climbers must be aware that the connecting karabiner link may crossload, notice how the video example has no crossloadable elements.
The belay device can form a small part of a rescue system.
Upon injury a trained aerial rescue climber will need to climb to the victim because:
i a climber would most likely have a lanyard to tree connection upon injury that will need removing.
ii the climber will be lowered in an inverted position (head bent underneath back) and the chances of lowering an injured/unconcious climber and their equipment to the ground without getting caught on lower branches is unlikely.
iii from the ground it is difficult to assess if the victims rope has been cut.
Only after these 3 points have been addressed a Trunk Belay should be considered.
Urban Forestry run monthly Aerial Rescue workshops and I encourage all to attend.
Trunk Belay’s are useful if an access system has no in-built descent, ie. Footlocking and Cammed Ascender access need a change of equipment to descend.
There have been instances where a conscious climber have been lowered from a wasp attack when climbing on these systems.
Tying/Setting the Self-Belay Anchor
If a mechanical device is chosen then follow manufacturers instruction for correct rope choice and installation of the device.
A rope on rope system presents the climber with an overwhelming choice. Here is the favourite of most: Valdotain Tresse (VT)
i Begin by wrapping the hitch 3 or 4 times around the climbing rope.
ii The top leg passes underneath the bottom leg.
iii Braid the two legs around the rope until the hitch runs out.
iv Attach a pulley and karabiner.
The climber can attach the Working End (splice) to the pulley which makes a 2:1 system or install a Rope Wrench and tie the working end to a trunk anchor making a 1:1 system.
Changing the amount of wraps and braids alters friction and as this is the sole means of safety when aloft a climber should be highly aware that it is tied and operates correctly.
It is the sole responsibility of the climber to manage their hitch correctly, please seek advice and training.