This is a bit of an oversimplification though. The duration of moving people by ship means that people need to be given food and water. People also aren't going

This is a bit of an oversimplification though. The duration of moving people by ship means that people need to be given food and water. People also aren't going to be spending the entirety of a weeks long voyage in a seat - they'll need beds and recreation facilities to stay sane. You're also less likely to find large numbers of people who all want to depart and arrive at the same time, so filling a large ship to capacity is more difficult and the ship will be running partially empty much of the time. All these things lead to lower net efficiency. The reality is, people aren't going to give up air travel. The best bet to make air travel more sustainable is to develop hydrogen powered planes. The Soviets demonstrated this concept [1]. 1. https://en.wikipedia.org/wiki/Tupolev_Tu-155 https://en.wikipedia.org/wiki/Tupolev_Tu-155