Fossil fuel powered ships are worse, because the carbon emissions of running a hotel at sea are high and ships use very low grade fuel with all sorts of nasty byproducts. And electric or renewable long distance ships run into the exact same problems as electric or renewable planes, namely the poor energy density.
Transatlantic cruises don’t have to be luxurious. If you’re comparing air freight to shipping by sea, it’s very clear ships are far more efficient. We just need to become better at containerising people :)
You mean? Yes.
Yes, you'll need to have a crew and you'll need to need to ship the necessities, which eats into the efficiency of this mode of transport. However, a plane will create 40 times more CO2 for the same amount of cargo transported than a ship. I'd say we can figure out how to fit a larger crew and more supplies in that margin.