The Oasis of the Seas, the world's largest and newest cruise ship, navigates through a ship channel to a cheering crowd at Florida park in Dania Beach as it heads for its home port nearby in Port Everglades in Fort Lauderdale, Florida November 13, 2009.

FORT LAUDERDALE, Fla., Nov. 25 (Reuters) – Royal Caribbean's new Oasis of the Seas is the largest, widest, tallest, most expensive cruise ship afloat, a cornucopia of amusements aimed at quashing the notion that cruising is a sedentary vacation, said chief executive Richard Fain. Then he donned swim trunks, jumped on a boogie board and challenged fellow executives to a contest in one of the Oasis' two FlowRider pools that simulate surfing.

''I've never been a believer in building it big just for size's sake. We build large because we've had so many ideas they simply don't fit in a smaller hull,'' Fain said.

The $1.4-billion Oasis of the Seas, the world's biggest cruise ship, enters service during the industry's worst year in decades but is so exuberantly excessive that Fain predicts it will be profitable from day one.

Oasis is a floating resort that eclipses the condo towers it sails past at its new home, Port Everglades in southeast Florida. The 225,282-grosston ship has 16 passenger decks and can carry 6,292 passengers plus 2,165 crew.

It has rock-climbing walls, a basketball court, an ice skating rink, a carousel with hand-carved wooden animals, a shopping promenade lined with cafés and bars, cantilevered whirlpools overlooking the sea and a Central Park with 12,000 live plants and trees.

An amphitheater surrounds a deep-diving pool on the stern, where high-divers and synchronized swimmers perform. Passengers can harness themselves onto the ''zip line'' and soar across the ship above an open-air atrium nine decks high and lined with balconied cabins.

One of its many bars, the Rising Tide, floats up and down between three decks, while a touring company performs the Broadway musical ''Hairspray'' in the 1,380-seat theater.

The Oasis, which starts its inaugural voyage on Dec. 5, was six years in the making and arrives at a time when cruise lines are cutting rates to fill berths.

Net yields, a measure of revenue generated per bed per day, were down 16 percent during the first nine months of 2009 for the major companies, Carnival, Royal Caribbean and Norwegian Cruise Line, said Rod McLeod, a vacation management consultant who has held senior management posts at all three lines.

''Over the last 20 years, that's the steepest level of year-over-year declines in yields, which is understandable given what's happened in the worldwide economy,'' said McLeod, now with McLeod/Applebaum Partners in Miami.

The cruise lines are cautiously predicting 2010 will be less awful, with yields down by only 7 or 8 percent. Generally the farther ahead passengers book cruises, the more the lines can charge. The window has begun to widen, with passengers now booking an average of three months ahead, compared with just six weeks in early 2009, McLeod said.

But a wave of new ships ordered during the boom times are now coming on line and that will put pressure on rates, a boon for bargain-hunting passengers but not so much for cruise line earnings.