Not being able to balance a checkbook, I thought I needed some help understanding the load vectors descirbed here. The guy I sent this too has taught graduate level physics and has real world engineering experience. I sent him a link to this thread (starting on page 5) and got this response...
This is an engineering problem. You don't want the hammock to fall, right?
The weakest link I see is the eye bolts pulling out of the studs in the ceilings. The strongest way to rig this is to have the force pulling on the eye bolt perpendicular to the shaft of the bolt.
The picture shown puts the majority of the force on the ceiling eye bolts parallel to the shaft, exactly what you don't want. It might hold if you have a big eye bolt screwed in really well, but the chances of pulling or wiggling out are maximized.
You might as well just use two eyebolts, screw them into the wall and attach the hammock to those two points. If you really want to get fancy, then screw two eye bolts into the wall, one high and one low, and none into the ceiling. The bottom one acts like a pulley, and does apply a force vector that tends to pull the eye bolt out, but the top one has the force pulling directly down, perpendicular to the shaft which is what you want. Of course, you have to have strong steel eye bolts that can't shear.
The odds that you will have a steel bolt shearing from a perpendicular force are much much less that pulling the bolt directly out of the wood studs with a parallel force. Think of a claw hammer pulling a nail out of some wood versus hitting the nail sideways and trying to break in in half.
If you really want to keep is simple and strong, then why not screw the eye bolt into the wall at an angle, like the nail on a picture hanger? Ideally, the shaft of the bolt and the rope that hangs from it would be at a 90 degree angle.
Boy, it sure makes sense to simply put the eye bolt in at an angle as opposed to going through all of this other stuff.... any other big brains out there who wish to refute or verify this?
-jeff
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