apparently we ARE working on replacing shipping ships with "renewables" powered variants, i saw a thing for a wind generator ship on here a month or so back i think
there are turbines you could use to propel a ship, if you use nuclear power to power them; those have a few problems though: 1) the words nuclear power scares people, 2) if you want to coast you'll have to let the turbines dip into an oceanic current, which means you're also going to have to turn that nuclear engine on and off which is it's own can of worms... and 3) a minority of people will complain that the turbines kill fish and shit when that's absolutely not true and not how any of this actually works as the turbines themselves would rotate slower than a propellers that are already on what we currently use and would be stretched long enough nothing could actually get near one as the sheer pressure exerted would just sort of toss anything away that comes near them.
oh and 4) it would be a massive money sink building one... so it's like... why not abuse what we already have rather than change. That last part is a fucking idiotic argument, but it will be used as the last line of defense against change.
Nuclear powered; like a submarine... and then the turbines that churn the water are on the side of the ship and it's balanced with ballasts. I'll happily draw you a picture if you want; I mean that sincerely, not as like an insult or anything... plz don't misinterpret my tone.
Pay attention.