I did a little experiment hanging from some buried posts today and had a few surprises.
I tried to go cheap and bought a couple 8 foot "cherry tone landscape timbers" that are basically 3-1/2" peeler poles with two sides slabbed-- $2.99 each vs $15 each for 4"x4"x10' treated timbers.
So I sunk each one 2 feet deep at diagonal corners of my 12 foot square patio, giving me a 16 foot hang. I know 2 feet is weak, but one edge is up against the patio concrete and they are in glacial clay hardpan soil.
I hung my Grand Trunk Ultralight with tree straps at the top of each pole, so just under 6 feet high. I set it for what I normally use for a hang on big trees in the yard and sat down on the edge, to find it sagging right down to the ground. The poles had enough flex to close the gap between what is normally 18" off the ground to zero.
So I tightened up the suspension a little more and climbed in. The GTUL ripped in half across the middle, dropping me on the patio-- with no harm. This is a nearly brand new hammock with no known damage and several unremarkable hangs. I used 6' whoopie slings with a lark's head in the end channel, and a Dynaglide ridgeline. The ridgeline was not super tight when I climbed in, so I was very surprised.
The only thing I can imagine is that the spring in the poles put some peak stress on the cloth. FYI, I'm 5'10" and an honest 220 pounds.
So I got out the Hennessy Expedition and went through the same drill. I need to set the Hennessy flat at with the ridge line at shoulder height to compensate for the spring in the poles and end up a decent hang and my butt 10" or so off the ground. I can still flex the ridge line a few degrees and the hang is comfortable enough, so I don't think there is undue stress on the hammock, but I had an idea that there is a point of higher stress as I slowly add my weight and the hammock drops as the poles flex. I can bounce a bit, flexing the poles while I am in the hammock. I'm not too worried about the poles breaking as I don't hear anything like cracking or other indicators of stress. The poles are free of large knots or splits.
I think I should beef things up a bit. Aside from possible stresses on the hammock body, the flex makes it impossible to get a taut pitch on the tarp. I'm wondering if full 4"x4" posts are enough. I would go to 10' length and bury them 3 feet for a 7 foot reveal. Does anyone use a setup like that? Should I go heavier, like 4"x6" ?
Any ideas what happened with the GTUL? The only thing that comes to mind is the 16 foot span was too much for it. I would think the structural ridge line would have taken that stress. Am I wrong?