Technical Tree Rigging

Balancing out on dead limbs rigging over a shed into a little, tiny drop zone. Yes, things can get technical.

One of the services that we offer at Ascents Tree is technical rigging of limbs, required when large and heavy wood is over any type of structure that you do NOT want damaged. Frankly, when you are paying for a tree service, there shouldn't be any amount of damage that a customer should be happy with.

The key to good, technical rigging is:

Have a rigging plan. It doesn't have to be a detailed and exhaustive document, but climber and groundman should identify drop zone, hazards and challenges, likely rigging points, and lowering/lifting devices, which ropes are to be used, and who is responsible for what duties in the operation.

Identify the limits and hazards of the tree in question. How high can we establish a rigging block, and how likely is that Rigging-Point to fail under the forces applied to it (it should be near zero). What kind of forces are going to be applied- compression or leverage? We want all rigging to use as much compression force, as possible, to support the rigging. Our rigging plan should reflect that. How strong is the tree, what species are you dealing with, how healthy is the wood around the rigging point, and how far out on a limb is your rigging point if it is on a lateral limb?

Identify the parts of the tree to be removed, and if it is a total tree removal, identify the sequence in which each major part of the tree will come down. Removing a tree is a balance between providing lower clearance to remove upper limbs, without stripping the tree too cleanly as to eliminate good rigging points, or create a 'stripped pole' situation where the tree lacks the stabilzation provided by lateral limbs until after the most dangerous, highest force-and-leverage limbs are removed.

I use a Figure-8 in the tree when lowering small pieces, and if we're short on crew. In this job, we used span rigging or V-Rig technique, whereby we transferred load to the main anchor point in order to avoid lowering pieces onto the shed roof.

Ensure you have a good idea of specific log weights you will be dealing with. This is very important- and the use of log density wheels for determining the weight of pieces will allow the climber to more safely determine rigging point and rope strength. A good knowledge of weights (and lowering device adjustments) gives the crew the ability to better control the lowering of pieces. If too much friction is applied at the lowering devices, the shock load of falling pieces can stress the tree structure and rigging equipment. Too little friction, and you can have an uncontrolled piece rip down that can cause damage, or injure workers below.

On a related note, understand the capacity of all the equipment you will be using. Ensure that you have adequate rope strength for the loads. Understand that a rigging Figure-8 cannot hold nearly the load of a Port-a-Wrap, and that as rule the Port-a-Wrap has a specific comfortable weight capacity per wrap. So, while a Figure-8 can hold about 250-300 lbs maximum, it has very smooth control in the range of 30lbs to it's maximum. A Port-a-Wrap holds about 300-330lbs per wrap, but it definitely can be annoying with smaller loads (sub 80lbs, or so). Use adequate rigging blocks or rings, and if using snatch blocks (like a Rock Exotica Omni Bloc, or a Petzl SPIN L1), absolutely ensure that the face plate is fully closed.

So, here are a few considerations that we look at before quoting a tree. Rigging is a big part of what we do, and synchronizing both safe rigging, and safe climbing, is a big factor when quoting a complex tree. Arboriculture is a dangerous and challenging discipline of rope access, and our fatality rate speaks for itself. Untrained 'tree cutters' are risking their life for your deal, so if your arborist shows up with a chainsaw and a ladder, you might want to reconsider that quote.