A tip that might help people, and a new idea which I haven't tried yet, not dreamt up in an armchair, but while mentally examining the forces on the willow from the zipline, and keeping an eye on my rope lanyard, if I had to make a panic-cut and swing, if something went south...
Nearby to Will, at his 10:00 position roughly, I had him anchor an orange piece of short, multipurpose rigging rope and large biner to the deciduous tree, and had him operate from out of the crash zone and shatter area. It is simply attached to the tree with a RB, then the large biner is clove-hitched on and ready to serve as either solely a redirect with a small amount of useful friction bending around the biner, or its quickly switched to a munter-hitch. This biner-to-anchor distance is fully adjustable. I wanted zipped pieces to clear the other willow trunk (other co-dominant leader) that was nearly in-line with zipline. Easy, just adjust the biner on the clove hitch to the desired location. I wanted piece to crash away from the sprinkler system (heads marked with cones), as well.
There is a Garta Heart/ Garta hitch
https://www.google.com/search?q=gar...e=univ&ei=aJu6VMT1Mob4yQSt4YLIDQ&ved=0CCYQsAQ
that is used to advance rope well one direction, and lock the other direction.
When I was getting to the small top, above the rotten, hollow trunk, I moved the zipline top-anchor point from my trunk (to be topped) to the other willow trunk (left intact to be felled into the woods) for less shock on my lanyarded-into rotten/ hollow trunk. This resulted in slack in the zipline system, as the anchor trunk was closer to the ground anchor, and the working piece coming from the far/ outside. I barely grazed the roof with a small tip already on the last zipped piece, oops. You know that sound a gutter makes when kissed by a tip.
This is where you need rapid slack removal, like on a GRCS, with a little, up to lot of friction to resist the shockloading of the zipped piece when it loads the line.
I was thinking that a 90* bend around the biner was too little slack, and a munter, if Will held too hard, might be too shocking (likely deadwood above could fall out of the crown onto me).
I was thinking about a double clip through the biner to get a 'round turn' around it. Might work, sorta like that ox block device. In my head, this seems like it could lock up if easily clipped in the wrong orientation between the loaded zipline side of the rope, and the brake-hand side of the rope. This will need hands on testing.
The garda hitch might be useful when you need rapid slack removal, and don't need to release it.
I'm going to take a couple pics and post from my phone.
