SAN FRANCISCO - The cruise ship Carnival Triumph limped into port at Mobile, Ala., Thursday night, four days after losing propulsion and power to run even basic systems.
That vacation disaster echoed the Carnival Splendor's stranding 27 months ago off the coast of Baja and Carnival-owned Costa Allegra going adrift a year ago off Somalia.
If they had been airplanes, U.S. officials might have grounded an entire fleet. But the cruise ship industry is largely unregulated. Companies purposefully register their ships in just about any country other than the United States to avoid U.S. oversight, taxes and labor laws.
When ships visit U.S. ports, they are subject to regulations and inspections by individual agencies, including the U.S. Coast Guard and the Centers for Disease Control and Prevention.
However, in international waters only the International Maritime Organization, an agency of the United Nations, has authority over safety and operational standards. It has never ordered the docking of multiple ships based on safety concerns, and it's unclear if it even has that authority.
Nearly half of the large cruise ships at sea belong to Carnival Corp, which owns several other cruise lines, including Princess Cruises.
Because of its size, statistically Carnival Corp. is likely to experience more accidents than rival companies. It could be a coincidence that the company has had three major incidents in 27 months.
So the questions aren't so much why it keeps happening to Carnival-owned ships, but why it keeps happening at all and why no governing body has been able to prevent such incidents.
Companies such as Carnival Corp. and Royal Caribbean International, the two largest cruise companies, are listed on the New York Stock Exchange and have corporate headquarters in Florida. Yet their ships are registered in other countries, predominantly Panama, Liberia, the Bahamas, Bermuda and Malta.
The ships are required to meet the standards of the registry country and, in general, don't pay taxes on the money they make from U.S. passengers because everything related to the ship is consider an export.
There is a perception that the cruise industry is beset with problems. But that is a misperception, said Carolyn Spencer Brown, editor of Cruise Critic (cruisecritic.com). She disagrees with critics who say the industry seems to hope for the best without preparing for the worst.
The International Maritime Organization "sets the basic standards for any cruise ship operating in the world," she said.
The IMO has established some measures aimed at preventing accidents, as well as dealing with accidents when they occur. In 2009, the IMO required new ships of about 400 feet or longer to have dual engine rooms and a redundant electrical system, features that might have prevented the three recent Carnival incidents.
But that requirement applies only to new ships, which are often added when older ones are retired -- a practice that may be delayed because of the cost of complying with the new requirements.
The strandings of the Carnival Splendor and Triumph were in relatively harmless waters, but the passengers on Costa Allegra probably didn't love being powerless off the coast of Somalia in pirate-rich waters.
PHOTO GALLERY: Cruise ship stranded at sea (http://bit.ly/VUyOUl)
A big concern is what could happen if a cruise liner has an engine fire and loses propulsion in Alaska's popular Glacier Bay, where it could drift into a glacier or run aground.
A true disaster would be a ship that runs aground, as the Costa Concordia -- another Carnival-owned ship -- did in Italy in January 2012, and tip over in the icy Alaskan waters, where assistance would be hundreds of miles away.
The Concordia, incidentally, remains wedged on a rock off the Tuscan coast, and it's not expected to be removed for several more months. Thirty-two people died in that crash.
It's unclear to what extent the IMO, which also sets rules that cover liability for and compensation of passengers at sea, will play a role in the Carnival Triumph aftermath.
While there are specific international guidelines about loss or damage of luggage and canceled voyages, much of the compensation that Triumph passengers get might rely on public relations -- and on the standard cruise contract that greatly limits the cruise lines liability in nearly every situation possible.