tl;dr:
Using hydrogen as an energy carrier is a scam, it is stupid and it is wasteful.
Unless you have a very specialized use case.
Let's say you have 1 standard m3 of LNG. That is ~11 MWh of energy.
Spent in a ship engine with 50% efficiency, you get ~5.5 MWh of net propulsion.
Convert the samme Sm3 of LNG to hydrogen via steam reforming, and you get 250kg of hydrogen. Burn that in an engine (at 50% efficiency), and you get ~3.6 MWh net propulsion.
Use 7 MWh of electricity and create 100kg hydrogen via electrolysis, and get 1.5MWh of propulsion.
See a pattern here?
Converting any energy to hydrogen is a lossy process. Then lossy *again* when you spend the hydrogen. The lost energy is lost as heat. *May* be partially recovered via some machinery (requiring space, construction, maintenance, resources and recycling) for *potential* use in some process.
Say you get 80% efficent electrolysis and 65% efficient fuel cells. I believe that is pretty rad tech these days. If what you need in the end is electricity for driving an engine, you just started out by converting half of the energy to heat. Which you need to recover and find use for.
And at the same time: if what you *had* initially was electricity (wind, solar, hydro, nuclear) and what you wanted was heat, a heatpump will return 5x the energy you put into it.
Put 7 MWh (not 11) in a battery, and you get 6,5 MWh of propulsion in an electric engine.
Battery technology is here today providing >6000 cycles, before the battery is down to 90% efficiency.
Hydrogen as an energy carrier does not make the slightest common sense. And I have not even mentioned distribution and storage, for which none of the hydrocarbon infrastructure is reusable. (Apart from drivers and roads.)