[tialaramex]

Yup. The other number that came to mind was the alternative that would actually work on big ships - big nukes. US carriers are nuclear powered, but most of the power produced is NOT electricity, it can only be used for propulsion.

I'm sure cruise passengers are more wasteful than the average person at home or in an office, but the tremendous amount of power needed to drive a huge lump through the ocean at any reasonable pace dwarfs the pumps in the infinity pool and the blaring music and all the rest. And that's going to have to come from somewhere.

[darkpuma]

Slightly tangential, but a good opportunity to mention the NS Savannah, probably the closest we've ever come to nuclear cruise ships: https://en.wikipedia.org/wiki/NS_Savannah

[dredmorbius]

There were actually several other nuclear-powered commercial ships, none of which proved economical, though there's also the small problem that about 200 major cargo ships are lost at sea every decade. That's roughly the number of all present marine nuclear propulsion systems (within a factor of two).

The others were the German Otto Hahn (https://en.wikipedia.org/wiki/Otto_Hahn_(ship)), Japanese Mutsu (https://en.wikipedia.org/wiki/Mutsu_(nuclear_ship), and the Russian Sevmorput (https://en.wikipedia.org/wiki/Sevmorput). There is also a fleet of six Soviet/Russian icebreakers, still in service, the lone regime in which nonmilitary nuclear marine propulsion has proved viable.