Before getting all warm and squishy about hydrogen (or any other kind of) fuel cells go back and read my post showing the volume of fuel required to provide a given amount of power. Consider that volume along with the volume of the fuel cells - the complete system, cells, cooling pumps, heat exchangers, controllers, power management components, propulsion controllers and propulsion hardware and in my opinion we end up with a 100 TEU ship the size of a cruise ship if it is expected to enter the liner trades.
I won’t even begin to think about the cost per ton mile of the tiny payload left over after fuel tanks and propulsion systems are installed. Build humongous megaships? Sure, just multiply the potential problems and add the cost of having to offload offshore and use a fleet of robotic feeders to transfer cargo?
I think we are a very long way away from seeing hydrogen fuel cell powered, fully automated vessels in much of any use where the vessel is out of view of human overseers for more than a few minutes n a voyage more than a few miles with ground support at each end - as in crossing fjords.
Maybe someday but look at the volume of current plants, look carefully at the power produced per unit of volume and add that to the fuel storage requirements for a seagoing ship: