Abstract.A project to import a large amount of liquid hydrogen (LH2) from Australia by a cargo carrier, which is equipped with two 1250 m 3 tanks, is underway in Japan. It is important to understand sloshing and boil-off characteristics inside the LH2 tank during marine transportation. However, the LH2 sloshing and boil-off characteristics on the sea have not yet been clarified. First experiment on the LH2 transportation of 20 liter with magnesium diboride (MgB2) level sensors by the training ship "Fukae-maru", which has 50 m long and 449 ton gross weight, was carried out successfully inside Osaka bay on February 2, 2017. In the experiment, synchronous measurements of liquid level, temperature, pressure, ship motions, and accelerations as well as the rapid depressurization test were done. The increase rate of the temperature and the pressure inside the LH2 tank were discussed under the rolling and the pitching conditions.

To establish the worldwide storage and marine transportation of hydrogen, it is important to develop liquid hydrogen tanks/carriers as well as a long level sensor such as a superconducting magnesium diboride (MgB2) level sensor. An external-heating-type MgB2 level sensor is expected to be an excellent choice for liquid hydrogen because of its high linearity, resolution, and reproducibility. The dynamic level-detecting characteristics of three 500-mm-long MgB2 level sensors have been evaluated under conditions of oscillating liquid level using an optical cryostat and a high-speed microscope. The response time to variations of the liquid hydrogen level is about 0.1 s, and the difference between the level read optically and that detected by the MgB2 level sensors is about 5 mm under these conditions. Thus, the MgB2 level sensors have superior response performance for the sloshing measurement of liquid hydrogen.