So if you're talking freight, ships are unparalleled in their energy efficiency, even when you look at the disgusting dirty fuel they use. They're SLOW, which reduces friction with water, and have economies of scale.

However, planes are more efficient for passengers due to the volume (of people). People take up a lot of space, much moreso than cargo, which makes giant boats really not the most efficient choice for human transport because you end up using a giant hull with tons of overhead to move all these lightweight people across the ocean. Once planes get up to cruising altitude they hit a sweet spot where their fuel efficiency improves drastically, but it's still not nearly as good as trains.... But I have no idea how to calculate how expensive or environmentally damaging it would be to build and maintain a set of trans-continental railways. I can only imagine the insane amounts of marine destruction needed for any amount of transport bandwidth...

And none of this is taking into account time, which is another important factor. A container ship takes 10-14 days to get from New York to London; a direct flight takes about seven hours.