China is estimated to be four years behind South Korea in terms of its shipbuilding technology, a report said Wednesday, suggesting South Korea maintains the advantage over its fast-growing rival. Shanghai Shipyard, which is owned by the China State Shipbuilding Corporation, recently inked a deal with Singaporean firm Opus Offshore to build drillships. The vessels, which require a higher level of technology than standard ships, will be the first of their kind to be constructed by Chinese shipbuilders.