Ammonia tankers seem a good test bed for this tech as they already carry Ammonia and dock in places that handle it. Other fuel cell based technologies seem to

Ammonia tankers seem a good test bed for this tech as they already carry Ammonia and dock in places that handle it. Other fuel cell based technologies seem to be working on scaling up, they can supplement electrical generation for crew before working with the existing generators with the aim to eventually replace them. Like trains, ships get technical benefits from being hybrid. This makes it relatively easy then to be made more hybrid, plug into shore power when available, add some batteries and, solar panels etc. There's no one easy fix but lots of little ones. The most interesting one I saw discussed is contracts that share the blame when delays happen. Previously ships would race to their destination and then wait around because if they missed a connection they would be held responsible. Now they can all go at slower, more efficient just-in-time speeds and the costs of the occasional missed deadline are amortized. With fuel savings they all come out ahead so it's a win-win.