Originally Posted by bowl-maker
If you are really concerned about the load on the joist, you can hang "in line" with the joist...that is to say, both ends of the hammock connect to the same joist. That way you are not providing any sideways forces to your joists.
Or if that's not an option, he could put a cross-brace between two joists (on each end of the hammock) and hang from them. Eliminates torque, spreads load between two joists on each end, and you can drill, screw, nail, and modify all you want, without touching the joists (except to fasten the two braces).
By "cross-brace," I mean a board cut to fit perfectly between two joists and fastened in at 90 degrees to them.