The corkscrew anchors I have are 17 inches long with spirals on the bottom 7 inches and a big D-type handle. I use them for my 10x20 canopy.
Late last spring when I was testing it was very wet here. I used two anchors attached to a pole for hanging one end with the other end attached to my deck. I had screwed the anchors straight down into my grass. When the hammock was loaded, the shaft first bent and then it pulled out. YMMV