Cruise ships were once called floating hotels, but that hardly covers the behemoths on today's seas. They are more like floating cities faced with some of the same public health and safety issues that confront municipalities.
At least cities have a mayor, a single authority in charge. A cruise ship is more like a city with 10 mayors scattered across the globe, each responsible for a different piece of the action.
The result was on display this month with the misery on board the Carnival Triumph and more tragically last year when the Costa Concordia capsized off the coast of Italy.
Cruising is still relatively safe, but the rash of recent incidents suggests that the industry's explosive growth may be inviting disaster, or at least deprivation.
The stranding of the Triumph in the Gulf of Mexico after an engine fire -- which left its 3,100 passengers enduring five days with limited food, scarce electricity and toilets overflowing onto decks and shower floors -- might have been written off as an aberration, if not for similar accidents. This was the fourth time in 27 months that a cruise ship, all of them owned by the industry's two largest operators, has been stranded at sea, crippled by some sort of fire.
In 2010, the Carnival Splendor was adrift for days in the Gulf of Mexico with 3,300 passengers on board after an explosion in a diesel generator. Last year, the Costa Allegra, also owned by Carnival's parent, was stranded in the Indian Ocean, towed to shore by a fishing vessel. A smaller ship, owned by Royal Caribbean, suffered a fire last year in its engine room and was temporarily disabled off the coast of Borneo.
While the industry insists that ships are built with redundant systems, and Carnival says all its ships have "redundant engine rooms," clearly something wasn't redundant enough on these ships to allow them to limp to shore under their own power.
All but the smaller Royal Caribbean ship had to be towed in.
After the Splendor stranding, you'd think the industry would have done more to ensure backup power, or at least more effective ways to feed passengers and provide adequate toilets. And how would these powerless ships have fared if they'd been caught far out to sea in turbulent waters or a storm? That's unclear.
Other safety issues -- training deficiencies and the difficulties of getting thousands of passengers off a sinking ship -- were underscored last year, when the Costa Concordia, owned by Carnival's parent, ran aground and capsized of the coast of Tuscany, killing 32 people.
One impediment to fixing problems is fragmented authority. Cruise ships are governed by standards adopted by an international organization affiliated with the United Nations. Enforcement is splintered. The U.S. Coast Guard has authority for ships that stop in U.S. ports. But that authority vanishes when the ships get 12 nautical miles from shore.
Investigations of problems are led by the country where the ship is registered. Hardly any are flagged in the U.S. Italy is investigating the Costa Concordia sinking. Splendor's stranding is being probed by Panama and the Coast Guard. More than two years later, no report has come out.
Sen. Jay Rockefeller, D-W.Va., who held hearings last year into cruise line safety, says cruise ships "seem to have two lives," one in port where the Coast Guard can monitor them, and one at sea, "where the world is theirs."
And that increasingly appears to be a problem -- one that needs closer scrutiny than it has received.