The Triumph is still being repaired at a shipyard in Mobile, Alabama, Carnival spokeswoman Joyce Oliva said.
"We are now focused on the lessons we can learn from the incident and also what additional operational redundancies might be available," Cahill, the Carnival president, said this week.
Another ship, the Carnival Splendor, had a fire in 2010 due to "a catastrophic failure of a diesel generator," he said.
In a Friday news release, Carnival said total advance bookings for 2013 are behind 2012 levels, but since January, booking volume for the rest of the year has been "running significantly higher than last year," despite "slightly higher prices."
"Despite considerable attention surrounding the Carnival Triumph, we had been encouraged to see booking volumes for Carnival Cruise Lines recover significantly in recent weeks," said Micky Arison, chief executive officer of Carnival Corp.
"Attractive pricing promotions, combined with strong support from the travel agent community and consumers who recognize the company's well-established reputation and quality product offering," were the reason, he said.
Nevertheless, Carnival stock sank Friday after a weak forecast for sales and profits this year.
Sen. Jay Rockefeller, chairman of the Senate Commerce, Science and Transportation Committee, sent a letter Wednesday to Arison.
"The Coast Guard has responded to a string of 90 marine casualty incidents with passengers onboard Carnival ships in the last five years," the West Virginia Democrat wrote. "It seems that Carnival has failed to take any meaningful course of corrective action after these continual incidents. This needs to change."
Despite all the recent problems, Donahue doesn't see any long-term negative effects for Carnival or its competitors.
"I don't necessarily see this week's events, or even combined with the Triumph event, as casting a pall on the cruise industry," he said, noting that several colleagues and friends who have recently gone on cruises, including on Carnival, enjoyed their vacations.
"People generally accept that complex pieces of equipment can encounter challenges. That's not the hurdle. I don't think anybody considering the cruise would be unforgiving of an unforeseen event, because those types of events occur with complex systems. People are far less forgiving (when) communications around the events seem to be lacking," he said.