have fuel tanks there. Wing tanks they are called. Double bottoms are used for ballast. The advantage of putting fuel tanks there is that it does not reduce cargo space, they are somewhat neutral to stability, relatively simple piping system. The only problem is a collision like this. A double hull would not have helped this situation much because penetration was too deep.

The number of fuel tanks would probably be about a dozen per side. That limits the spillage.

Hitting an anchored ship is like running into a parked car (almost).

how do you ram an anchored ship in fair weather?

asleep at the wheel might explain a ramming in open seas, but the ramming ship supposedly had only just left port.

Notice that the radar antenna on the Cotunav ship is still rotating. I guess the helmsman or radar operator were not paying attention. The side of a container ship is about as big a radar target one can expect. To not see it is probably a criminal violation of some maritime law.

But it does take time.

...for years and years and years and....