If hydrogen can be stored in 600 bar tanks in vehicles, it can be transported in ships. PNG ships transport gas at 250 bar. When produced by electrolyzers situated at a depth of 1000 meters hydrogen would arrive at the surface pressurized to 100 bar.
High-pressure electrolysis is the most efficient way to do the job.
Compressed or liquified isn't the only way hydrogen can be transported. The Japan-based classification society ClassNK, has granted Approval in Principle (AIP) to a new H2/CO2 FPSO (floating production, storage and offloading) design developed by Mitsubishi Heavy Industries (MHI) and Chiyoda Corporation. It uses a new organic chemical hydride method to convert hydrogen into highly stable methylcyclohexane (MCH), which can be stored in liquid form at an ambient temperature and pressure.
This is probably not the last word on this problem either, considering the effort being put forth by the auto industry to transition to hydrogen.