Hey Dan. Yeah the top of the dead zipline fir was always going to be the potential deal-breaker. Didn’t have the slightest concern about the lower limbs on the way up but I knew that higher up it was all a lot more fragile. Thankfully I have the gift of blankness for such moments.
I used to favour setting the block as high as possible also for the reasons you mentioned....but as you know other considerations often come into play. More often than not nowdays I’ll favour setting my lanyard and climb-line above the block, and to do so I like to maintain a good safety margin (at least 12 in) between the block and the cut.
I know what you’re saying about the fall factor but consider also the parachute effect of falling a top i.e. is not really the equal in acceleration of a falling log, so that extra foot you mentioned probably doesn’t figure too much....especially on a top in full leaf or the conifers in the video.
If you remember the conifer right at the end, and I think another bigger one there abouts in the middle of the video, we had on both instances over 100ft below us to slow the tops down. Notice also the retention of limbs on the backside to act as a ballast, and I think even considering how much more springy conifers are the hardwoods then they didn’t turn out half bad.
Furthermore, I’ve worked on lots of dead and compromised hardwoods in the past, and especially on leaners I’ve set the block as much as 15 ft below the cut on occasion. The reason obviously being that the higher the block the greater the leverage on the tree....and in the case where the tree itself is the weakest link (and not the rigging), I’ve made that call and was satisfied thereafter it was the right one.
Remember though, this is not advice to anyone....I’m merely pointing out that the rule-book doesn’t cover all situations or in fact the overall best means for risk management. That ever popular publication ‘the art and science of practical rigging’ was part written by a guy who was killed either during or shortly after( I cant remember which)....rigging a tree. Who woulda figured that, not him obviously, poor guy, RIP. But it just goes to show. A healthy knowledge in physics is one thing, but you can’t beat experience, the right experience. If I get taken one day it won’t be through ignorance though.
I have the 5/8 polydyne, but it only comes out for best. Definitely notice the difference in the shock reduction on a spar etc. I would recommend it to anyone for that kind of work. Thanks again.