The US Navy did run a number of nuclear powered cruisers up through the California class. Originally the idea was to keep up with the carriers whose range was limited by their fossil fueled escorts. Still the nuclear powered surface ships other than carriers fell out of favor as more efficient fossil fueled ships came about which also had much lower man power requirements.
Considering the large surface area of many cargo and passenger ships it would seem to indicate the possibility of some usage of solar power. The big issue being efficient enough panel construction in the face of the harsh conditions they would face.
Ah yes. I'd forgotten about those. I was thinking mostly of the ocean liner Savannah, and a few other nuclear-powered ships, one of which was built and operated by the Germans (the Otto Hahn, later retrofitted with conventional powerplant), and another by the Japanese, Mutsu. All three have been decommissioned.
The Soviets built, and Russia continues to operate a fleet of nuclear-powered icebreakers.
The US nuclear cruisers were the Long Beach (CGN-9), Bainbridge (CGN-25), California (CGN-36), South Carolina (CGN-37), Truxtun (CGN-35), the Virgian-class ships: Arkansas (CGN-41), Mississippi (CGN-40), Texas (CGN-39), and Virginia (CGN-38). All were decommissioned in the 1990s.
As for solar power: the power requirements for marine propulsion are simply too great. You're much better off with wind (or a wind + powered) design.
The Tûranor PlanetSolar is a 100% solar-powered ship. Virtually its entire topside surface is covered with solar panels, with portions of the deck cantelevering out when at sea to increase surface area. Despite a very high-efficiency hull design, the ship's cruising speed is 8 knots (it can double that for short periods). Its solar output is 90 kW, or roughly 120 horsepower. You'll often find rather larger motors as outboard engines.
The Maltese Falcon yacht discussed above has two 1,800 HP diesel engines -- that's 1,300 kW. The freighter Emma Maersk has an 80 MW (109,000 HP) powerplant. The engine and specs themselves are impressive. You could stand inside an engine cylinder:
The Emma'selectrical capacity alone is 29 MW. Note that for a containership you've got the added complication that you're stacking containers on the deck itself -- solar cells would be covere, unless they could be unfurled above the containers, which would be complicated and likely not particularly robust in a marine and port environment. And at 60W/m^2 net solar PV potential, the 22,232 m^2 surface area of the Emma is nearly 22 times too small to provide adequate electrical power alone to the ship.
As for fuel consumption, at a cruise speed of 25.5 kt and 3,600 gallons of fuel per hour, she gets about 0.008 mpg, or 43 feet per gallon. Or 122 gallons per mile.
The freighter Emma Maersk has an 80 MW (109,000 HP) powerplant. The engine and specs themselves are impressive. You could stand inside an engine cylinder:
I visited Lars Maersk when she/he (I never know what to do with male-named ships) came back from sea trials. That was my second thought(1) when entering the engineroom. The cylinders were open for inspection and I suddenly realized "that piston is actually big enough for me to stand on."
I haven't been in a modern liner's engine room, though I've seen some smaller and older ship's machinery, and it's impressive stuff.
My thought when encountering a steamship's works (the design was late 19th century), all covered in grease an gunk and pipes and stuff all over the place was "y'know, I write and work on software systems, and if you could physically instantiate them, this is probably what they'd look like".
The tour guide, also the engine wiper, turned out to be a DBA in her day job, and absolutely loved the image.
First off: fossil fuels are going away. They're going to be too costly to extract, to rare to utilize, and/or too harmful to the environment. Take your pick. It's not as if there's a choice.
Secondly: the question isn't "how much fossil fuels", but "how much energy" EROEI (energy returned on energy invested) is what makes the economy tick, and it's almost certainly the most significant factor in the economic growth and expansion of the past 250 years or so.
Absent the energy surpluses provided by fossil fuels, yeah, we'll likely be doing less.
As for what it takes to make ships -- electrical energy (from renewable sources) can substitute for much fossil fuel use. Coking for steel is an exception, though that can come from where it did initially: charcoal. Or synthesized coke. Mind that exhaustion of forests for both lumber and fuel was among the key reasons England turned to, first seacoal, shortly after mined coal, as its energy needs grew.
And there's no guarantee that the Universe is going to provide humans with the energy we've become accustomed to.
The Emma Maersk, a monster among cargo ships at 11,000 TEU. During the Panamax era, 3,000 - 5,000 TEU was more common. Max weight for a 20 foot container is 14 tons. This gives the Emma a capacity of 154,000 tons, or 38.5x the capacity of the Red Jacket.
The largest cargo ships are the Maersk's Triple E class class, such as the Mærsk Mc-Kinney Møller, with a capacity of 18,270 TEU, or nearly 64x the Red Jacket.
The more common Panamax hull would be 10-17.5 clipper cargoes.
I'm not sufficiently versed in shipbuilding research to know what size ships are being considered for sail (or sail-hybrid) propulsion, but it seems likely that designs larger than the best clipper technologies of 1853 might be possible some 160+ years later.
Considering the large surface area of many cargo and passenger ships it would seem to indicate the possibility of some usage of solar power. The big issue being efficient enough panel construction in the face of the harsh conditions they would face.