A cruise ship or cruise liner is a passenger ship used for pleasure voyages, where the voyage itself and the ship’s amenities are a part of the experience, as well as the different destinations along the way. Transportation is not the prime purpose, as cruise ships operate mostly on routes that return passengers to their originating port, so the ports of call are usually in a specified region of a continent. There are even “cruises to nowhere” or “nowhere voyages” where the ship makes 2-3 night round trips without any ports of call. By contrast, dedicated transport oriented ocean liners do “line voyages” and typically transport passengers from one point to another, rather than on round trips. Traditionally, an ocean liner for the transoceanic trade will be built to a higher standard than a typical cruise ship, including high freeboard and stronger plating to withstand rough seas and adverse conditions encountered in the open ocean, such as the North Atlantic. Ocean liners also usually have larger capacities for fuel, victuals, and other stores for consumption on long voyages, compared to dedicated cruise ships. Although often luxurious, ocean liners had characteristics that made them unsuitable for cruising, such as high fuel consumption, deep draught that prevented them from entering shallow ports, enclosed weatherproof decks that were not appropriate for tropical weather, and cabins designed to maximize passenger numbers rather than comfort (such as a high proportion of windowless suites). The gradual evolution of passenger ship design from ocean liners to cruise ships has seen passenger cabins shifted from inside the hull to the superstructure with private verandas. The modern cruise ships, while sacrificing qualities of seaworthiness, have added amenities to cater to water tourists, and recent vessels have been described as “balcony-laden floating condominiums”. The distinction between ocean liners and cruise ships has blurred, particularly with respect to deployment. Differences in construction remain. Larger cruise ships have also engaged in longer trips such as transoceanic voyages which may not return to the same port for months (longer round trips). Some former ocean liners operate as cruise ships, such as Marco Polo. This number is diminishing. The only dedicated transatlantic ocean liner in operation as a liner (as of December 2013) is the Queen Mary 2 of the Cunard fleet. She also has the amenities of contemporary cruise ships and sees significant service on cruises. Cruising has become a major part of the tourism industry, accounting for U.S.$29.4 billion with over 19 million passengers carried worldwide in 2011. The industry’s rapid growth has seen nine or more newly built ships catering to a North American clientele added every year since 2001, as well as others servicing European clientele. Smaller markets, such as the Asia-Pacific region, are generally serviced by older ships. These are displaced by new ships in the high growth areas. The world’s largest cruise ship is currently Royal Caribbean International’s Allure of the Seas beating its sister ship (the Oasis of the Seas) by 5 centimeters.