As was discussed earlier, LNG currently has a very high overhead for compression and liquification.
The ship has lower CO2 emissions in itself, but that does not account for the production emissions. It may make things worse. There is also some slippage of methane though the engine and that is a significant issue. However it will reduce other emissions like sulphur, which has been a problem for a long time in the shipping industry.
There is no easy answer.
