My dream ship would be a sailing ship that uses only renewable energy for propulsion. It would be sleek and fast, like the big clippers back in the day of the sailing age but more modern, and would have either old fashioned sails or maybe something a bit more modern like Flettner sails:
What would be even cooler, would be if we could make flexible solar panels and use them to make the sails.
The ship will still need a propeller and bowthruster for maneuvering in ports and harbours. They could be powered with electric motors or hydrogen.
I think in the future such ships will be built for carbon neutral transport at sea.