I don't know why, but this job from 15 years ago popped into my head, kind of a similar situation, I think. It was a Saturday job for a friend, too. Just had him and my wife for groundies, but we did good and had it down by beer thirty... my wife was great on a Porta wrap. There was another pine off the driveway that I set a block right about even with the first cut, and then ran down to a Porta wrap at the base. I would rig the pick off of a loop runner and pull on the bull rope, and then they would tighten it up and put a few wraps on it. When I made the cut, it would ride the line clear of the roof, and then they could just lower it clear of the house, unhook, and then we would reset for the next pick. By rigging it that way, when the pick released, all the energy was transferred to the bull rope, and it would just slide down the line until it came to a stop at the low point on the "sag line", as we called it. F=MA, so the felt force in the tree was fairly minimal, and there just wasn't really any bouncing or oscillation up in the tree. There was a bit of shock as the slack in the loop runner absorbed the fall, but it was more rotational as the pick ran down the line, and was really pretty smooth... never felt like I was going to get bucked out of the tree, so to speak, and as you can see, we took some fairly decent sized pieces off. If you are at 80', you will have more room to work with over the garage, but the other advantage of a sag line over a regular speed line is the piece just kind of finds it's own point on the line and you don't have much in the way of deceleration forces. I was fortunate because in this case I had that nice vertical limb for a lifeline, but all in all I remember it as a pretty smooth ride... hope this helps.
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