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When one pictures a cruise liner, one probably pictures a great behemoth chugging its way across the ocean, transporting thousands of passengers in accommodations at the height of luxury. It would seem like cruise ship gas mileage would be quite low, then. To a degree this is true. However, when some other factors than straight gas mileage, such as gas per mile per person, are taken into account, cruise ships' fuel efficiency doesn't look so bad. In fact, as I'll show later, cruise liners aren't bad at all when compared to jumbo jets.
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Fuel Efficiency for a Large Cruise Ship
Just as with cars, larger cruise ships tend to have lower fuel efficiency, at least in gross terms. To give the reader an idea of the fuel efficiency of large cruise ships, I'd like to use the world's largest cruise liner as an example. The MS Oasis of the Seas, completed in 2010, has a total length of 361.8 meters, a height of 72 meters above the sea line, and room in its 16 passenger decks for 6,296 passengers. At its cruising speed of 22.6 knots (26 mph), the Oasis of the Seas burns 11361 gallons of fuel each hour. The fuel efficiency, then, is 0.0023 mpg, or 12.08 feet per gallon!
This figure seems very low, especially in comparison with mpg ratings for cars. However, keep in mind that a cruise ship carries many more people than does a Honda Civic. The Oasis of the seas, when fully occupied, gets 14.40 mpg per passenger, or 19.36 mpg per person including the crew. This is still a low figure, but not quite as absurd as the overall miles per gallon number.
Image: Wikimedia Commons - Oasis of the Seas
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Small Cruise Ship Fuel Efficiency
It is difficult to find precise mpg figures for smaller cruise ships, but it's possible to get a rough estimate based on engine outputs. Cruise ships in the Voyager class are about 311 meters in length, but have a tonnage of "just" 138,000 Tons (compare that to the Oasis of the Seas, which comes in with 225,282 gross Tons). The Voyager class boats use diesel engines, which combined have a total output of 75,600 kW. Assuming an efficiency of about 30% means the boat is burning roughly 1.84 gallons of fuel per second, or 6640 gallons per hour. Since the ship's cruising speed is 23.7 knots, or 27.3 mph, the cruise ship's fuel efficiency is roughly 0.004 mpg. Since the ship carries 3114 passengers, its gas mileage is 12.79 mpg/passenger, or 17.65 mpg/person including crew. This isn't too different from the much larger Oasis of the Seas, surprisingly enough.
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Cruise Ship Gas Mileage Compared to Jetliner
To put these figures into perspective, consider a typical jetliner. The Boeing 747-400 seats 624, cruises at 567 mph, and has a range of 8357 miles. With a total fuel capacity of 57,285 gallons, the 747-400 has a gas mileage of about 0.15 mpg. Taking passengers into account, the figure is 91 mpg/passenger! A fully loaded jetliner is actually pretty fuel efficient - about the same per person as an SUV. It's true, then that cruise ships don't have very good gas mileage. But it helps to put things in perspective: true, the ships burn a gallon of fuel every 50 feet, but they're moving 5000+ people! Viewed in this light, cruise ships are just a little bit wasteful.
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