If you like your cruise ships big, you're going to love what Royal Caribbean (NYSE:RCL) has sailing over for 2009. The company announced that it has ordered what will be the world's largest cruise ship.

More than a thousand feet long, 154 feet wide and 240 feet high, the monstrous floating vessel will be able to take on 5,400 passengers. The gargantuan ship trumps recent orders for huge additions by Carnival (NYSE:CCL) and Royal Caribbean itself.

This isn't an arms race. We're not waiting for a cruise line to announce a fleet addition that is four football fields long, instead of a mere three. In fact, bigger isn't necessarily better when marketing cruise ships; some seafaring tourists prefer the intimacy of smaller boats.

The decision to go big is mostly about economies of scale. Staffing and operating costs naturally rise with larger ships, but not at the same dramatic rate as the potential revenue of incremental berth bookings. That's good news for Royal Caribbean. It's also good for a company like Motley Fool Rule Breakers newsletter recommendation Steiner Leisure (NASDAQ:STNR). Steiner runs most of the Royal Caribbean onboard spas, and it's likely to lend its soothing touch on the new RCL behemoth as well.

More ships -- and bigger ships -- have opened up cruising to new demographic groups. Disney (NYSE:DIS) has ramped up the family market, and it's just a matter of time before it adds a third ship to its fleet. Norwegian Cruise Lines revolutionized the stodgy tiered dining routine by introducing freestyle cruising, where folks dine at the restaurant they want, whenever they want. That kind of newfound flexibility is enticing more landlubbers to give cruising a shot.

Yes, Royal Caribbean is likely to take full advantage of its larger ships by adding more features. All of the RCL boats include the signature rock walls, but its newest ships also include ice skating rinks and a more varied selection of live entertainment. In that sense, size does matter; keeping as many as 5,400 travelers happy means offering something to interest everybody.

I was fortunate enough to grow up in a family that loved taking summer cruises. I remember when the pinnacle of onboard excitement was skeet shooting, shuffleboard, and frigid salt-water pools. In contrast, today's activity-packed cruise ships keep getting bigger -- and so does their potential to command a heftier chunk of the travel-market dollar.

Shares of Steiner Leisure have soared 93% higher since being recommended in the Rule Breakers newsletter service 16 months ago.

Longtime Fool contributor Rick Munarriz went on a less ambitious three-night Royal Caribbean cruise last year. He owns shares in Disney. The Fool has a disclosure policy. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.