There constructed from Mega blocks, which are then welded together, the Mega blocks can be built anywhere (for example, we have some mega blocks being built in japan, then shipped to Brasil for assembly into drill ships).
Usualy major components are installed in the Mega blocks during assembly such as Gen-sets, motors, thrusters, switchboards, pumps, major pipe runs etc etc.
Once the mega blocks are assembled, major wiring, control systems, finishing and fitting is done once the hull is floating.
This keeps time in the dry dock to a minimum (dry dock is the major capital asset and bottle neck as a general rule).
The mightly ships thing on the assembly of the container ship was miss leading as many of the mega blocks were being constructed at many sites so all you actualy viewed was the final assembly in dry dock....which when its lego is quick