more like , a big ship or something like a retired oil rig. It needs to go in deep waters (>200 miles off the coast) and stay there for extended periods of time

more like , a big ship or something like a retired oil rig. It needs to go in deep waters (>200 miles off the coast) and stay there for extended periods of time (and weather). A cruise ship would be ideal as it can be relatively self-sustaining. A bunch of cruise ships would be enough to start a big city.