Several anti-freezing systems, such as heating coil system, hot air spray system, ballast water circulation system and air bubbling system, have been applied to the water ballast tanks for the vessels, operating in cold sea. In this study, numerical simulations were performed to investigate effectiveness of the air bubbling system used for winterization design concept for water ballast tank. Through the results of this study, it became clear that the air bubbling system equipped in each frame of water ballast tanks was effective to prevent freezing along the outer surface by promoting convective heat transfer.