Today's post in by request. A bronzed goddess I know who's recently traveled aboard a Caribbean cruise wanted to know if cruising takes more or less fuel than a transatlantic airplane trip to Europe. Here's my take.
Fuel Cost of Flying
According to this chart from Nova, a typical transatlantic flight aboard a 747-100 will consume 57.7 gallons of fuel per passenger, or 115.4 gallons round-trip. (I'm not sure why they include three significant figures; I'm sure the variation is at least a few percent.) Incidentally, if you could drive solo all the way to Europe you would burn about five times as much, so flying isn't that bad in terms of mileage relative to driving a car alone.
Fuel Cost of Cruising
On the other hand, taking a one-week Caribbean cruise will burn about 140 gallons of fuel per passenger. (Here I assumed fuel efficiency of about 20 feet per gallon on a modern cruise ship - inspired by the QE II's mileage of 29 feet per gallon; a cruising speed of 22 knots, 3500 passengers and 3 days of full-speed cruising of the 7 total days.) The per-capita mileage of a cruise is then about 13 miles per gallon: about the same as driving alone; perhaps a little worse.
A transatlantic flight and a one-week cruise consume about the same amount of fuel. You're not exactly doing Gaia a great favor by vacationing on either, but the occasional vacation isn't going to outweigh habitual energy usage either. If you have a 2-hour commute in your own car, you'd burn roughly 25 gallons per week, so cruising once a year isn't going to overwhelm your daily habits.
Who knows; maybe the next generation of cruisers will like fuel-saving tech like this too? (Personally I would love a nuclear cruise ship as much for its silence as for its eco-friendliness, but I don't think that's in the cards.)