How much fuel does a cruise ship use?

A client asked me the other day how much fuel a cruise ship uses on an average voyage compared to his car. I wasn’t sure what to tell him as it wasn’t a question I’d ever been asked before but I went away and did some rough, (very rough), maths work to try and calculate it for him.

You can check out the results below, (the maths is very rough so feel free to correct me if you can).