In my opinion we should not generally ban offshore structures and vehicles.
Offshore structures should be handled as towers, as building offshore structures is a challenge of engineering. An offshore HVDC inverter plant is more remarkable as a 15-story building in a town!
In fact, each structure with a basement in a body of water can be considered as offshore in strict way and so even many bridges belong in this category.
Concerning vehicles my opinion is the following:
- trains: no - too low
- ships & aircraft: if taller than 50 metres, then yes
- cranes: permanent cranes should be added. Also Emporis has such objects in the database (
http://www.emporis.com/building/cont...amburg-germany )
- rockets: yes, if taller than 10 metres
- large excavators and other big machines: yes, if taller than 30 metres.