Nikkei press reported 2015 shipbuilding market share in Japan. According to it, the top supplier was Imabari Shipbuilding (24%).
Figure: 2015 Shipbuilding Market Share in Japan
|Manufacturer||Market share (%)|
|Japan Marine United||16.8|
|Mitsui Engineering & Shipbuilding||4.6|
Source is Nikkei Sangyo Shimbun newspaper, the article on 2016 July 25th.