apcoble

....and I'm asking these questions because I want to access canopies above this cable, using two single ropes attached to different anchor points. sorry if that was confusing.

The line is choked through a double-hitch figure 8 knot and a separate rope is tied to the hitch using a fisherman's knot. Pulling on the retrieval rope allows us to get the knot down.

You explained that well in the 2nd paragraph of your response. That is essentially what we're doing, where we have a separate rope (retrieving rope) to pull down ascending rope at the end of the day. I think you make a good point about not being able to be belayed from the ground. The only problem is that I was considering having two anchor points. We currently have a horizontal cable that were operating off of. The cables were installed to trees about 15 m in the air. Below the cable, we're ascending from an anchor point that is the double-tandem pully attached to the cable. This may sound strange, but I'm conducting tree physiology research. That is why we had cables installed, they are essentially our research plots in the tree canopies.

Yes, I mean the tail is near the branch or anchor point. It makes more sense to use a ground anchor. What does it mean to have a 60-80M to haul about the crown?

When setting an anchor up for a single rope technique, is there a downside with respect to safety for tying a figure eight on a single hitch and feeding line through the hitch so that we maximize rope length? In other words, the anchor point is one end of a rope tied off on a large branch. We're ascending up the rope using Petzl ascenders, foot-grabs and gri-gri for self belaying.