Originally Posted by willk
Both those look like joke fittings - suitable for use while stationary but hopeless for a seat underway. I note they call them table supports...
A hinge is a hinge. It's all about the engineering of the part. Clearly, the limitation is the two crossbars. On the 500 lb version, there are stampings to increase the rigidity of the component.
Even if we assumed Seadog built to a 2:1 safety ratio (which is on the low side, most manufacturers chase a 3:1 or 5:1), that would put even the light duty hinges at 600 lb capacity. Then, we'll assume the load is divided evenly amongst both hinges, so we'll times this by two. Meaning, the hinges would have had to seen in excess of 1200 lb of loading to fail.
I'm a geek though. I like simple math. And overbuilding things.
We COULD take the kg weight of his passengers, total cubic centimeters occupied by their butts, approximate seating position (sitting close to the edge will act like a lever to multiply the forces involved), and the approximate height in which the passengers jammed their butts down on the seat to calculate the total dynamic loading on the hinges...