“Our product is very fun in the sun,” Antorcha said. “Our guests want to be in the pool and in the sun.” So Carnival beefed up the experience around the pool deck with Fun Ship 2.0 , expanding the water park, adding outdoor seating on a lower deck, bars and eateries, including Guy Fieri’s Burger Joint, interactive Hasbro game shows and new entertainment. The line is also retrofitting more than a dozen older ships with some of the amenities.

Or consider the Celebrity Solstice-class ships, a design so popular that most of the line’s older ships have been retrofitted — “Solsticized” — with some of its features, including spa staterooms, several new bars and restaurants, and the iLounge, a computer center. Even within the Solstice class, the ships continued to evolve. On the last two, the Lawn Club Grill was added in space formerly occupied by the Corning glass-blowing shop, and cabana-like alcoves were added to the Lawn Club.

Celebrity wanted more high-end suites on its newest ship, said Harri Kulovaara, executive vice president of Maritime & Newbuilding, so it added a deck. That allowed the company to add 42 suites, including 34 AquaClass spa suites (a new category) and Celebrity’s first two-bedroom suite, which also has a glass-enclosed shower cantilevered out from Deck 14 and a tub on the veranda.

But there’s not necessarily consensus about the changes. One of next year’s two new ships, the Royal Princess, will have a larger, three-deck atrium that will hold a pizzeria, wine bar, coffee bar and other features designed to turn it into the ship’s central hangout. Norwegian’s new Breakaway, on the other hand, will put its hangout space outside on new promenades that have waterfront restaurant seating intended to increase the passengers’ connection with the sea, said Kevin Sheehan, Norwegian’s CEO.

The line will continue to build cabins for singles that were introduced on the Norwegian Epic — smaller inside cabins designed for one, with portholes looking out on the corridor and access to a lounge exclusively for guests in those cabins.

“To me that [solo stateroom] was a very important thing,” Sheehan. “As in the rest of the industry .. there is a large market of people who want to travel alone and we didn’t have an alternative for them.”

Now, he said, Norwegian is adding solo cabins on the Pride of America while it’s in dry dock and will add them to other ships, although older ships won’t have the lounge.

At the same time, he said, the standard balcony stateroom that debuted on Norwegian Epic has been redesigned after widespread complaints about the bathroom, which had been deconstructed into separate parts — toilet, shower, sink — and offered minimal privacy.

The company has already done away with another feature that debuted on Norwegian Epic, a faux ice skating rink that no one used, but that took a lot of labor to set up and take down every day. Sheehan learned about the problem from a co-worker who didn’t recognize him when he spent two weeks posing as a crew member for the CBS reality TV series, Undercover Boss. He immediately got rid of the rink.

Del Rio said Oceania also made mistakes. Designers didn’t anticipate the popularity of the Barista coffee bar — which, unlike most ships, offers free specialty coffee drinks — or the Bon Appetit Culinary Center, which offers hands-on cooking classes for a fee. And he’s disappointed that a 10-person private dining room, Privee, initially available for $1,000 a night but knocked down to $250, did not get much use. On the next ship, he said, the culinary center and the coffee bar will be larger, and Privee will be eliminated.

An earlier version of this article gave an incorrect history of the Lawn Club on Celebrity Cruises ships.