the above is a string of cursing becasue i just spent a long time on a thorough explanation and then hit the backspace key!!! damned page went back and i lost everything i said.

as with many of my suggestions, i feel it's necessary to state the obvious first: climbing (and ESPECIALLY rappelling) is an inherently dangerous activity and you take your life in YOUR OWN hands. i can not be held responsible for anyone who may read this making ill use or application of the advice given, or anyone who sustains some injury or death from engaging in climbing/rappelling. that being said, on we go with the suggestions...

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as far as my suggestion for your setup goes, it's possible if you switch the trees, but it's really not necessary IF your tree is as large as it appears to be in the drawing AND is well rooted. if that's the case, the tree will more than hold your weight applied during a rappel (or other scenarios for that matter).

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i'm a little confused about something here though: you don't want to climb, just rap on a static line? and then your going to walk back up and either rap again or just collect your fixed rope? recreational rapping is by no means my area of expertise, because when i rap, it's because a walk-off is out of the question and i intend on leaving so i try to leave as little gear as possible, and i CERTAINLY don't fix the rope.

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if it were me, then i wouldn't just be rapping, i'd be rapping down and leaving, so i would do one of two things:

1) in the interest of leaving no gear behind, and dependent on the type of tree and conditions, i'd simply sling the rope around the tree and rap off using both strands, then pull the rope and be gone

2) wrap some webbing (wrap-3-pull-2) and attach some biners/rap rings and thread the rope through, rapping off of both strands and then pulling the rope and leaving the webbing + rings/biners behind

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it sounds to me like you just want to have a fixed single line to rap though... to be honest i wouldn't use your setup at all (the redundancy achieved is both complex and unnecessary if your first tree is big enough). what you're concerned about is not your rope failing (if it does, it's either because of misuse/abuse or it was just your day to go). what you're concerned about is your knot failing, so all you really have to do it take your knot out of the weighted system. the easiest way to do that, provided that your tree is big enough, is to simply tie a -not-a-knot around the tree. to do this you take a section toward one end of your rope and wrap it around the tree 3-4 times. this will cause the strands to bite down on the tree and themselves, which will actually hold your weight on it's own. but because we want to be safe, to finish the not-a-knot setup we tie a running bowline over the load strand with the remaining tail. the running bowline is key, because it provides a measure of safety for slippage (which really won't happen anyway) AND the running part keeps the knot out of the loaded system, because you're not actually tying your load strand into the bowline.

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if your first tree (the one closest to the edge) is tiny and the one in the back is big, then just skip the first tree entirely and rap off of the second in that same single tree anchor manner.

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if BOTH trees are skimpy then you'll want to have them backed up (or find another anchor method). in that case, i would suggest webbing to equalize the trees. if you're REALLY opposed to spending the extra $20 on some webbing (and the stuff is pretty cheap so i don't see why you wouldn't pony up for better protection), then just switch your configuration so the load strand comes off of the first tree.

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