These ships have redundent steering systems. For a rudder to go hard over like that, a steering rod would have to snap, or the rudder post would have to fail. I investigated a 36 inch rudder post failure on a super tanker once. But, on a new vessel, I don't think that was the issue. These vessels have gyro-stablizers, stabilizer fins, and I believe quick ballast water movement to provide passengers with a puke free enviornment. My best guess at this point is that the stabilizers may have malfunctioned, not the steering system.
I read one passenger report saying that she noticed a persistent tilt before the incident, which would point to the stabilizers it would seem. Also, I don't recall any mention of a turn in the initial reports.
Reuters quotes a Carnival statement, "Crown Princess experienced an unexpected list to the port side as she began sailing north toward her final port of New York." But then in the same statement, "... some passengers were injured as the ship sharply turned ...", and the article goes on to say, " U.S. Coast Guard Petty Officer Donnie Brzuska said the ship listed because of a problem in the steering mechanism."
But what about that passenger report? Here it is - 20 Seriously Hurt When Cruise Ship Tips to Side Off Florida Coast (AP) :
"Some passengers said the ship was already tilting Tuesday morning, even before the sudden roll to the side. Martha Lynn George said she at first thought something was wrong with her bed when she awoke but then realized the whole ship was slightly tilted."