This is the boring but correct answer, particularly as diesel engines can be refitted to burn ammonia until fuel cells are ready to take over.
However, to make it geeky and exciting again you could have autonomous floating wind and solar farms generating the hydrogen and converting it to ammonia.
The ships could then refuel at multiple points in the middle of the ocean (ideally without stopping) and so carry less fuel and save on the costs of fuel burnt transporting the fuel.
However, to make it geeky and exciting again you could have autonomous floating wind and solar farms generating the hydrogen and converting it to ammonia.
The ships could then refuel at multiple points in the middle of the ocean (ideally without stopping) and so carry less fuel and save on the costs of fuel burnt transporting the fuel.