[bt848]

There's always sailing, although it's a bit laborious, and fission has a good record at sea :-)

[blunte]

There is some progress in applying wind power to shipping (other than the traditional fixed sails) - https://www.ship-technology.com/projects/msbelugaskysails/

The German company SkySails has been working for years on kites that can reduce fuel use on large ships. I think at some point we'll see alternative (renewable) energy taking over shipping as it is gradually taking over other domains.