Vessel Types

Merchant ships are classified as passenger carriers, cargo ships, and tankers. During the height of passenger travel by ship, the largest as well as the most glamorous ships afloat were the famed liners of the North Atlantic, which, beginning in the mid-19th century, sailed regular schedules between the Americas and Europe. Competing in speed as well as in size and appointments, such ships as the Mauretania, the Queen Mary, the Queen Elizabeth, the United States, and the France gradually reduced the time for the North Atlantic crossing to less than four days. Their size, from about 45,000 to 75,000 metric tons and up to 300 m (1,000 ft) in length, was gigantic by the standards of the first half of the 20th century, but they have been dwarfed by the oil tankers of the 1970s and '80s. Today's passenger liners operate principally in the cruise trade.

Cargo Ships
Cargo ships carry packaged goods, unitized cargo (cargo in which a number of items are consolidated into one large shipping unit for easier handling), and limited amounts of grain, ore, and liquids such as latex and edible oils. A few passengers are accepted on some cargo liners. Specialized ships are designed and built to carry certain types of cargo, for example, automobiles or grain.

Container Ships
In the late 1950s container ships set the pattern for technological change in cargo handling and linked the trucking industry to deep-Sea shipping. These highly specialized ships carry large truck bodies and can discharge and load in one day, in contrast to the ten days required by conventional ships of the same size. The rapid development of the container ship began in 1956, when Sea-Land Service commenced operations between New York City and Houston, Texas. Barge-aboard, or lighter-aboard, ships, also called seabees (sea barges) or LASH (lighter-aboard ships), resulted from an evolutionary development of the container ship. They are capable of carrying about 38 barges, or up to 1,600 containers, or a combination of containers and barges. Their design enables them to deliver cargo to developed or undeveloped ports, without the need for berthing.

Tankers
Tankers, designed specifically to carry liquid cargoes, usually petroleum, have grown to many-compartmented giants of a million metric tons and more. Despite their great size, their construction is simple, as is, for the most part, their operation. A major problem with the giant tankers is the severe environmental damage of oil spills, resulting from collision, storm damage, or leakage from other causes.

Specialized tankers transport liquefied natural gas (LNG), liquid chemicals, wine, molasses, and refrigerated products.

Treaties and Conventions
Many treaties and conventions have been adopted over the years with the objective of increasing the safety of life at sea. One of the most important agreements provided for the establishment of the International Iceberg Patrol in 1913, after the Titanic disaster. Under the International Load-Line Convention of 1930, ship loading was regulated on the basis of size, cargo, and route of the vessel. The International Convention for the Safety of Life at Sea, which governs ship construction, was ratified by most maritime nations in 1936, and updated in 1948, and again in 1960 and 1974.