Yep, when I built my lanai in Fl I went with one 6x6 set 4' deep in concrete. I have a very nice tree for the other hammock attachment spot.
I know it was over build but I no confidence in 4x4 posts to handle that kind of stress even with the lanai built over it. The 6x6 has been in place now 3 years and I hang in it all winter. My nieces and their children will also take it as the first of choice of bed when they come to visit.
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