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Reverse thinking: top of the tree rigging friction

Richard Tregoweth - Tuesday, July 12, 2016

Top of the tree friction tools are relatively new to arboriculture. David Driver of X-Rigging fame introduced the concept, and Kevin Bingham further expanded the idea with the Rig'n Wrench (DMM Pinto Rig attached to a Rope Wrench used for light rigging).

The Safebloc, marketed by SHERRILLtree, is a derivative of the X-Rigging Rings.

Treetools asked Jed Copsey, the lead climber with Oakwood Treecare in Auckland, to put the SHERRILLtree Safebloc through its paces. Below is Jed's summation:

SafeBloc… A new concept to rigging

Since the introduction of pulleys and arborist blocks (also known as impact blocks) to the tree care market, their use is considered standard practice for lowering cut branches and sections of wood out of a tree.

There are numerous styles of blocks and pulleys designed to best suit particular tree rigging jobs. While these devices are terrific for handling large weights and capable of withstanding excessive force, they also have limitations.

The traditional way of adding friction to control the speed of lowered sections of timber is using base-anchored lowering devices such as the Port-a-Wrap, GRCS and other fixed bollards.

While this has become the norm for many arborists, it also means that by using a 'close to a frictionless' pulley at the top we are multiplying the forces on the rigging points. The anchor point, arborist block and sling take all the forces generated by controlling the speed of the falling timber.

Doubling the load at the top

Once the weight of a removed section has passed through the hardware to the lowering device at the base, it has created roughly double its weight on the rigging point. Extra factors such as potential shock loading, and oscillating forces also come into play.

An experienced arborist will (in extreme cases or wherever feasible) attempt to bring more of the rigging line into play, allowing the rope to 'elongate' or stretch, thereby absorbing the forces generated by controlling the speed of the falling weight.

A relatively new alternative to the traditional arborist block or pulley at the top combined with a base anchored lowering device is the introduction of the X-Rigging rings by David Driver.

David is also the innovator behind the SafeBloc, marketed by SHERRILLtree in the USA.

Like the X-Rigging Rings the SafeBloc concept applies friction at the top lowering point to help reduce forces and minimise the impact on the rigging point. The result, in theory, should be a smoother and safer tree dismantle operation.

I'll skip discussing the X-Rigging rings at this point and move straight onto the SafeBloc.

Recently arriving onto the arborist market the SafeBloc is a triple hole 'thimble' that applies friction at the top rigging point. The setting up of the SafeBloc is the same as a traditional pulley or blocks, in the sense that a dead-eye, loopie or whoopie sling connects the SafeBloc to the rigging point.

Immediately after hearing about the SafeBloc, like all arborists I was picking away at it.

How much friction did the device generate? How easy it is to operate? What weight is the device?

Questions like these immediately sprang to my mind.

Lightweight yet strong

On receiving the SafeBloc (courtesy of Treetools New Zealand), I was impressed by the compact dimensions and overall weight.

The SafeBloc is only 40mm thick and weighs in at 1kg (not including the added weight of a sling). The SafeBloc is ideal for hauling up a climbing/rigging line and securing it to the rigging point.

Another visual feature I was impressed with was the smooth, slick finish to the hardware. The product certainly looks like it was built to endure the hard life inflicted by arborists.

Next up was to see how quickly the rigging line can be retrieved once it passed through all three thimble holes. For this, another arborist and I used a 50m length of 14mm rigging line from Donaghy.

The groundsman retrieved the rigging line without too much effort eliminating my doubt retrieval could be accomplished by one person pulling on the rigging line.

However, this gave way to another question; how could much weight and resulting force be safely managed with the SafeBloc without the need for a lowering device secured to the base of the tree?

It's important to note; the SafeBloc IS NOT retrievable (unlike some hardware on the market, natural re-directs and natural crotch rigging). And, the SafeBloc cannot be attached mid-line.

Such factors play a significant role when an arborist decides which rigging hardware to invest in. With the constant innovation in the arborist industry, I believe it will only be a matter of time before the introduction of some form of a retrievable sling (similar to the X-Rigging rings).

The Whoopie sling supplied with the SafeBloc, however, does not allow for the SafeBloc's retrieval from the ground.

Too much friction

The removal of a Lawson’s Cypress with a confined drop-zone was the first job on which I used the SafeBloc. The groundsman and I configured the SafeBloc with the rigging line running through all three holes, but we had little idea of how much weight this would safely handle, so, as a cautionary measure, we also used the base anchored Port-a-Wrap in addition to the SafeBloc to lower each section.

Each piece weighed approximately 150-200kg.

After lowering the first section, we realised that using all three holes and the Port-a-Wrap produced too much friction.

So we decided not to use the port-a-wrap for the next section. This time, the piece was lowered in a much more controlled manner.

Using all three holes of the SafeBloc at the top anchor meant that a respectable amount of weight could be dropped safely using the SafeBloc alone.

The SafeBloc design has one major drawback. Because the smooth side of the SafeBloc sits flush against the trunk at the top rigging point and the way the rope threads through the holes on the SafeBloc, there a high probability of rope-on-rope friction occurring.

There is potential for rope-on-rope contact

In complex rigging situations, the heat from rope-on-rope friction could potentially glaze or melt the rope if overused.

Lowering lines are designed to withstand the heat generated during a typical lowering operation, but users need to be constantly monitoring their gear in situations when rope-on-rope friction can occur.

Arborists should not be complacent with the equipment and should always update and replace gear that is no longer fit for purpose.

The next day was the removal of a Silver Dollar Gum. Due the nature of the work, the SafeBloc was employed as the primary rigging anchor point with a small ISC Arborist Block used as a redirect at the base and to also help distribute the weight of the loads.

I was surprised to find, after several cuts, that dropping quite a considerable amount of weight produced minimal stress at the top anchor. It was also surprising to see that my grounds crew were quite happy to take 200-250kg sections without the use of a base anchored lowering device.

In short, I am extremely impressed with this concept and the craftsmanship that has gone into the production of the SafeBloc.

As the SafeBloc starts to become noticed and purchased within the arboriculture community, I will be interested to see what other arborists have to say.

Thanks again to Treetools New Zealand for giving me the opportunity to test the SafeBloc in a work environment.

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