Without additional regulation, burning ammonia in ship engines could cause serious impacts on air quality that could result in more than 600,000 additional premature deaths per year, according to new MIT research.
Technically not green, but I thought you guys would be interested
China claim to have one: https://electrek.co/2024/05/02/fully-electric-10000-ton-container-ship-begun-service50000-kwh-batteries/
It looks like it only manages to do 300 miles in a river.
Good… But not the bulk of all shipping.
Getting river boats to go green is a good step though.