A few weeks ago a friend and I were experimenting with hanging multiple hammocks between two trees from the same structural ridgeline.
The trees were a hair past 30' apart from each other.
We used 11 or 12mm climbing rope as the main line and used a tensioning system similar to what people use for slacklines. We had tied 4 lineman's knots ten feet apart with a two foot overlap (so the second knot was 8feet from the first, the third was 2' from the second and the last was 8' from the third, if that makes sense).
After the tension was appropriate we simply hung our hammocks from the main line and were good to go.
Surprisingly, the sag that came from the main line was easily compensated when adjusting the suspension between our hammocks and the main line.
It was a pretty comfortable night as far as our set-up was concerned. Now it getting down to 18 degrees and this being our first attempt at an overnight hang in the cold... that's a different story.
Has anybody else tried this or something similar?