These are offshore drilling rig platforms - the ones that look for new wells. And they're tied up close to shore because they're not exploring with the price of oil so low. At least they're being tended, unlike most other things in the harbor.
These cranes sit on the Ilha side of the harbor and, to me, look like a bunch of daleks invading the water. Andreas says I'm silly for imagining it so.
The breakers break old ships apart. This is their complex at the mouth of the harbor. It's sad in a way, but at least they're recycling. You can see they live out there, too. It's only a mile or so to shore.