Converting existing ships is not an easy matter and its very cost-intensive. Oceangoing ships are built with a holistic concept planning. Every piece is in its place for a reason to give the vessel good balance and good marine capabilities. Change weights of tanks and engines and the whole vessel integrity suffers from it. You don’t do those things because you had a fun day. This means that the pressure to go for LNG must be rather high now.
China's Huarun Dadong yard has started retrofitting Hapag-Lloyd's ultra-large containership Sajir to use LNG as fuel, world's first such conversion.