It not an exact science, just adding support where it’s most needed.
Almost all of the other lifts were balanced with but 2 slings placed next to one another, for my own convenience….obviously it takes experience to recognize the balance/attachment points. However, the limb at 5.30 in the vid was the longest and required the furthest extension of the crane….I left it till the end to make sure the operator was well groomed by that stage as I’ve only ever worked with the individual once previously which was a couple of years earlier.
Anyway, a little sideways roll on a horizontal is usually nothing of great concern but this one was weighted in such a way that would have resulted in a considerable jolt on the crane….all things considered i.e. the weight, momentum, multiplying of forces, the crane at full stretch….extra measures were definitely needed.
4 dead-eye slings were used to cradle (often referred to as spider-legs) the limb. http://www.honeybros.com/gbu0-prodshow/HB91PA.html
Countering the seesaw (butt to tips) effect is relatively easy, but the sideways roll can be a little more challenging to stabilize. In this instance the crane/hook was positioned slightly favoring the most weighted side of the limb but just beyond where its spine ended thus splitting off into several sub-laterals.
The slings were appropriately positioned to counter the opposing sides but because the hook had now over-run the longitudinal-balance-point then a sling also had to be set further towards the butt to compensate for this. The slings were attached using up any excess with half-hitches and then finished with a running bowline or timber-hitch.
When multi-slinging, its important that the hook remains in its original position when you tie off the slings i.e. if, when attaching the first one you pull the hook off-centre, the others can become somewhat redundant because their support of the load will be diminished due to the changed positioning of the hook. Also, for any lift, one should always allow the crane-op to position the hook before attaching the slings…..never grab/attach the slings until the hook has settled where you want it, or chances are it’ll be in the wrong position and you wont know until the cut has been made, after which the load can dramatically shift in any which way or direction.
About 6-10in of lift was applied to that limb before it was cut, I checked that the tension on each sling was equal as far as I could tell.
The cut was made from two opposing directions, first the top then the bottom, meeting somewhere in the middle. I watched each cut carefully for signs of compression so I'd know which one to finish with, or/and incase the tension needed further adjustment, I finished with the undercut and it actually came off pretty good.
I hope that helps Craig
While crane work might look like fun, and it can be for sure….there’s a very serious side to it where just a slight mis-judgment can lead to catastrophic and fatal consequences. One should be a proficient rigger before taking the plunge. And there’s no better place to practice/build up to crane work than during day-to-day rigging practices….many of the same principles apply, only, for the best part, branches are heading in the opposite direction….although the Hobbs and GRCS etc add yet a further dimension this.
Been at the dentist this morning so I’m glad I only had to write this lot as opposed to speak it.
Thanks again