This would make a lot of sense to me. It wouldn't matter what the primary target was. If the victims can't receive medical treatment, many more people would die.
(You scared me bad enough -- now I'm scaring myself!)
"Ridership on cruise ships has increased exponentially over the past ten years. Ten years ago, a cruise ship of 70,000 gross tons was the largest in the world. Today, we have an entire class of cruise ships that exceed 140,000 gross tons. These new mega-ships carry upwards of 5000 passengers and crewmembers. A successful terrorist attack on any one of these ships could result in a catastrophic number of casualties, and threaten the economic viability of the entire industry.
"Just last week, Coast Guard units in Miami, along with the FBI, responded to a bomb threat against a cruise ship capable of carrying approximately 3,000 passengers and 1,000 crewmembers. The ship implemented their security plan a plan required by the Passenger Vessel Safety Act - to prevent the threat from being realized. We successfully ensured the safety of the passengers, crew, vessel, and port as a whole."
Maybe just like the WTC, they have tried it before?