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The World's Largest Cruise Ship and Its Supersized Pollution Problem (theguardian.com)
An anonymous reader cites a report on the Guardian: When the gargantuan Harmony of the Seas slips out of Southampton docks on Sunday afternoon on its first commercial voyage, the 16-deck-high floating city will switch off its auxiliary engines, fire up its three giant diesels and head to the open sea. But while the 6,780 passengers and 2,100 crew on the largest cruise ship in the world wave goodbye to England, many people left behind in Southampton say they will be glad to see it go. They complain that air pollution from such nautical behemoths is getting worse every year as cruising becomes the fastest growing sector of the mass tourism industry and as ships get bigger and bigger. According to its owners, Royal Caribbean, each of the Harmony's three four-storey high 16-cylinder Wartsila engines will, at full power, burn 1,377 US gallons of fuel an hour, or about 96,000 gallons a day of some of the most polluting diesel fuel in the world.
This is a first world problem, and it has a first world solution. There's a reason commercial mega-ships are so much worse than even larger military mega-ships: nuclear power. There's no reason at all a ship of this size shouldn't have a reactor for its fuel. There are no safety precautions that aren't acceptable for the loss of a reactor that are acceptable for the loss of 8000 souls, so safety shouldn't be an issue.
We can run reactors in the confines of a submarine, in aircraft carriers, and on large combat ships, and it's arguable that a military ship is more at risk than a commercial ship, since it will be actively engaged in combat! When anti-nuclear pundits win, the environment loses. And so does the company, since it would be cheaper in the long run, certainly in a period time for which this ship will operate.
Those ships burn the bottom products of the oil stack after refining. The fuel is closer to tar or asphalt that diesel. On a cold day you can actually walk on that fuel as if it is a road. And yes, using such fuels needs to be made very illegal. Anyone can do the math. Those ships could never exist if they had to use real diesel fuel as the price of passenger tickets would not equal the fuel burned on a cruise.
The drawback I see with thorium is that it is currently only *researched* by the military navies.
I.E.: if gargantuan civilian "floating cities" ships decide to adopt it, it will be completely new technology. It won't have been tested and proven since long time, with all the drawbacks and caveat very well known, and the whole design perfected over several revision like current maritime nuclear generator used by navies.
I'm not sure that these kind of companies will be able to spend as much as government/military to perfect the technology. They'll probably spare on the R&D side of things. To avoid nuclear catastrophes, it might be better to re-use older/proven/known reactors for the cruise ships, and let those with deeper pocket manage to bring thorium reactors to reality.
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The actual figures are here if you spend 30 seconds to look them up. There are three 16-cylinder engines AND three 12-cylinder engines. The fuel consumption is actually 3x1377 + 3x1033 gallons per hour, so a total of 173,520 gallons per day. With a capacity of 6360 passengers, that's 27.3 gallons per passenger per day, or 1.14 gallons per passenger per hour. The cruising speed is 22.6 knots, which is 26.0 mph.
So it works out to 0.0438 gallons per passenger per mile, or 22.8 mpg per passenger. That's a hell of a lot less fuel efficiency than a jetliner or passenger car at capacity, let alone a motorbus. I believe that's the point people are (clumsily) making.
There's no reason at all a ship of this size shouldn't have a reactor for its fuel.
Liability.
The insurance cost(if they could get it) would be prohibitive.
Many of the ports that cruise ships visit would ban them.
That's a hell of a lot less fuel efficiency than a jetliner or passenger car at capacity, let alone a motorbus. I believe that's the point people are (clumsily) making.
Which is not an appropriate comparison, as jetliners/cars are used for transportation with (especially jetliners...) habitation as an afterthought. Cruise ships serve primarily for (luxury) habitation. To get at the actual mileage one should probably deduct the energy consumption per guest of a luxury hotel. This seems to come in at roughly 200-300 MJ per guest and night, maybe more on a ship with usually all artificial lighting. Source: http://www.lincoln.ac.nz/PageFiles/6834/909_sbaccom_s3364.pdf
Bunker C fuel seems to run at 40MJ a gallon, which turns out to about 8-10 gallons per day for habitation alone (large fudge factor applied for unknown energy conversion efficiency).
Still gives a surprisingly inefficient 30mpg for transportation.
"That's a hell of a lot less fuel efficiency than a jetliner or passenger car at capacity, let alone a motorbus. I believe that's the point people are (clumsily) making."
Another point that people are making is that these large ships use the cheapest, dirtiest, most polluting fuel there is. They do cause pollution problems in the port cities where they anchor.
Generally, ships use a generator to provide power and heating while the ship is docked. For a large cruise ship this generator needs to be substantial. It also runs on the same fuel as the main engines, and there are no emissions regulations for these ships.
So everyone downwind of the docks (i.e. most of Southampton, in this case) gets to sit in a column of smoke for the entire time the ship's docked.
The obvious solution would be to connect the ship to the shore electric grid. This is being worked on (example) but conversion takes time.