Don’t try this at home

Floating placidly in Vancouver harbour is this ocean-going freighter with a monstsrous gantry crane perched across the deck.  It looks like an arrangement dreamt up by engineers and performed by acrobats. Gantry cranes are used for unloading (and loading I guess) container ships.  There are a lineup of these cranes at the dock facilities just east of downtown, and clearly there must be room for one more.

How the heck does this thing not tip over?