Above Deck 17 on the Norwegian Getaway, a father and young son wearing safety harnesses work their way around a ropes course, taking careful steps on a web of narrow beams, winding their fingers through a rope net for balance.
Up ahead, a woman is walking The Plank, the most extreme element of the course - a beam six inches wide that extends eight feet over the edge of the ship, 180 feet above the water. Connected by a harness to an overhead line, she looks down, grinning, asks someone to take her photo, and kicks her leg out to the side, clearly undisturbed by any fear of heights.
Water slides with free falls and 360-degree spirals. A rock-climbing wall, bungee trampoline, miniature golf. They're all part of the Norwegian Getaway, the new Miami-based cruise ship. And they're another round in the cruise industry's version of an escalating arms race - each line trying to outdo the others with ever-more-exciting recreational features.
Next up is Royal Caribbean's Quantum of the Seas, with simulated skydiving, bumper cars, circus school and a Ferris-wheel-inspired capsule that raises passengers hundreds of feet.
Travel agents and cruise line executives say it's rare that a passenger chooses a particular cruise specifically because she wants to walk The Plank or surf FlowRider on Oasis of the Seas or whoosh down Carnival Breeze's DrainPipe slide. But these features do contribute to the overall perception of how much fun one might have on a new ship.
Increasingly, however, these features are competing with the ports where the ships call: Would it be more fun to spend the day exploring the port city? Or to stay on the ship and not have to fight crowds for space in the surf pool, flume ride, zip line, bowling alley, water slide, miniature golf course, rock-climbing wall, bungee trampoline, The Plank - or whatever the newest recreational feature is?
It's becoming a happy dilemma for the cruise passenger sailing on a ship topped with a playground at sea.
It's also a bit of a dilemma for the cruise lines, which want passengers to buy and experience the shore excursions they organise. But they also know that when people stay on the ship in port, their money stays with them - and they spend it in the bars, the shops, maybe the spa or a specialty restaurant.
Kevin Sheehan, CEO of Norwegian Cruise Line, says he has seen more passengers choosing to play on the ship rather than get off in some ports. "We have the stuff to keep them excited when they stay on the ship," he said.
Royal Caribbean, citing comments by guests on its biggest ships that they don't have time to explore all the features, schedules only three port calls on seven-day Caribbean cruises by Oasis and Allure of the Seas, compared to the usual four.
"When you build ships like this, the sea days are as special as the port days. ... One of the major reasons is all the fabulous features the two ships offer. We're trying to balance the time our guests get to see the ports and these features," said Lisa Lutoff-Perlo, Royal Caribbean's executive vice president of operations.
"Clearly we hope they shop in the shops and eat in the specialty restaurants, but we also want them to enjoy the ports, the shore excursions."
Carnival hasn't seen a significant change in the number of people staying on board during port calls, said Mark Tamis, that line's senior vice president of guest operations. Like Lutoff-Perlo, Tamis says Carnival tries to strike a balance.
"We continue to program onboard activities, so the ship is never quiet," Tamis said. Guests love WaterWorks, Carnival's pool compex and water park, he said. "It's not only the people who use it, who want to go down these amazing water slides, but people love to watch.
"It's important. It just comes down to variety, the feeling that you have so much to do."
Most stage entertainment takes place at night, while the ship is at sea. The new Carnival Live! concert series, however, which will take place evenings while the ship is in Nassau, Cozumel or Catalina Island, the port stays have been extended and guests will be able to choose - concert or an evening in the destination?
Bob Zweig, a travel agent with Cruise Planners, said lines are building completely different ships today from when he joined the travel industry in 1977. There are more restaurants, more shows, more recreational amenities. "The ships have become entertainment centres," he said.
He also sees a trend of more people staying on ships in port, and says that benefits the cruise lines. "I truly believe part of their goal is to keep people on the ships. That's where they make their money."
The race is mostly among the cruise lines in what the industry calls the mainstream category - Norwegian, Carnival and Royal Caribbean - although the premium lines are also building signature, if more sedate, recreational features: Celebrity with its top-deck lawns; Princess with its over-the-water SeaWalk on its new Royal Princess. And Disney, which doesn't fit into the usual classifications, has expanded its water park and put an elevated flume ride atop its newer ships.
"For someone who has never cruised before, I don't know that the ship's features are the main draw," Zweig said. "They're interested in the destination and the price. I tell them that the ships in a lot of cases have become a part of the destination; that's why ships these days have more sea days."
Repeat customers are more likely to take the ship itself into consideration, he said. They want to go on the ships they've heard about - the biggest or the newest or the ones with the gee-whiz features.
"They might not surf on FlowRider, but it sets a tone, a personality, for the brand that attracts people. It talks about fun, about multigenerational travel, about being in a place on vacation that is unique, that offers things for so many people," said Lutoff-Perlo. "Innovation and these types of features are really important because they talk about who we are, and who we are is more important than the actual features."
For that reason, the lines try to retrofit older ships with the most successful features from new ships when it is technologically possible. Norwegian is looking at which popular features from Norwegian Getaway and Norwegian Epic it can add to older ships.
Carnival has upgraded many of its older ships with the bigger, splashier elements of WaterWorks as well as its 2.0 Fun Ship program of bars, eateries and entertainment. Royal Caribbean has started retrofitting its Voyager-class ships with FlowRider - Navigator of the Seas emerged from dry dock just a few weeks ago with a newly installed surf pool.
"We have to study the engineering ... some things are not as easily retrofitted," Lutoff-Perlo said. "When we introduced FlowRider on our Freedom-class ships, we never thought we would put them on the other classes. But we just did."