Moving through the water is very efficient - if you go slowly enough. If ships travel slower than the hull displacement speed, they could travel on electric motors and solar power today.
The challenge is convincing global markets that slow shipping is worthwhile, when everything is moving in the opposite direction (faster and faster).
Check your math here... it doesn't work out. Most large ships DO travel at less than displacement speed, going faster would take more energy than their engines produce.
Even covering an entire ship's deck with present solar panel technology, the ship couldn't run on the panels... they would have to charge a battery bank, then when full the ship sails a certain distance, stops, recharges, and repeats.
The only practical means of powering modern ocean going vessels given their range and size are fossil fuels or nuclear reactors.
If you can get by with sails for some things, that's great, but unless someone starts building massive numbers of sailing vessels, there's not going to be enough of them to replace motorized shipping, and even then some routes and cargoes won't be able to ship that way. Some cargoes are perishable, for instance.
Any plan anyone comes up with for fighting climate change will fail if it requires a significant portion of humanity to change its behavior all at once.