Most newer ships has free fall lifeboats so the problem with control wires that has been discussed here is a thing of the past. (Except on old ships, that is)
Ammonia is a way of storing Hydrogen in liquid form without the need for deep refrigeration:
Ammonia can be used for Fuel Cells as well as in conventional marine engines:
Nobody are talking about just putting new types of fuel on old ships without changing much, incl. the education and training of the personnel that is going to crew or service the ships of the future.