Cargo ship A cargo ship or freighter is any sort of ship or vessel that carries cargo , goods , and materials from one port to another . Thousands of cargo carriers ply the world ' s seas and oceans each year ; they handle the bulk of international trade . Cargo ships are usually specially designed for the task , often being equipped with cranes and other mechanisms to load and unload , and come in all sizes . Today , they are almost always built of welded steel , and with some exceptions generally have a life expectancy of 25 to 30 years before being scrapped . Types . Cargo ships / freighters can be divided into five groups , according to the type of cargo they carry . These groups are : General Cargo Vessels carry packaged items like chemicals , foods , furniture , machinery , motor - and military vehicles , footwear , garments , etc . Tankers carry petroleum products or other liquid cargo . Dry Bulk Carriers carry coal , grain , ore and other similar products in loose form . Multi - purpose Vessels , as the name suggests , carry different classes of cargo – e . g . liquid and general cargo – at the same time . A Reefer ( or Refrigerated ) ship is specifically designed and used for shipping perishable commodities which require temperature - controlled , mostly fruits , meat , fish , vegetables , dairy product s and other foodstuff s . Specialized types of cargo vessels include container ships and bulk carrier s ( technically tankers of all sizes are cargo ships , although they are routinely thought of as a separate category ) . Cargo ships fall into two further categories that reflect the services they offer to industry : liner and tramp services . Those on a fixed published schedule and fixed tariff rates are cargo liners . Tramp ships do not have fixed schedules . Users charter them to haul loads . Generally , the smaller shipping companies and private individuals operate tramp ships . Cargo liners run on fixed schedules published by the shipping companies . Each trip a liner takes is called a voyage . Liners mostly carry general cargo . However , some cargo liners may carry passengers also . A cargo liner that carries 12 or more passengers is called a combination or passenger - cum - cargo line . History . The earliest records of waterborne activity mention the carriage of items for trade ; the evidence of history and archaeology shows the practice to be widespread by the beginning of the 1st millennium BC , and as early as the 14th and 15th centuries BC small Mediterranean cargo ships like those of the 50 foot long ( 15 - 16 metre ) Uluburun ship were carrying 20 tons of exotic cargo ; 11 tons of raw copper , jars , glass , ivory , gold , spices , and treasures from Canaan , Greece , Egypt , and Africa . The desire to operate trade routes over longer distances , and throughout more seasons of the year , motivated improvements in ship design during the Middle Ages . Before the middle of the 19th century , the incidence of piracy resulted in most cargo ships being armed , sometimes quite heavily , as in the case of the Manila galleon s and East Indiamen . They were also sometimes escorted by warships . Piracy . Piracy is still quite common in some waters , particularly in the Malacca Straits , a narrow channel between Indonesia and Singapore / Malaysia , and cargo ships are still commonly targeted . In 2004 , the governments of those three nations agreed to provide better protection for the ships passing through the Straits . The waters off Somalia and Nigeria are also prone to piracy , while smaller vessels are also in danger along parts of the South American , Southeast Asia n coasts and near the Caribbean Sea . Definitions . The words " cargo " and " freight " have become interchangeable in casual usage . Technically , " cargo " refers to the goods carried aboard the ship for hire , while " freight " refers to the compensation the ship or charterer receives for carrying the cargo . Generally , the modern ocean shipping business is divided into two classes : Larger cargo ships are generally operated by shipping line s : companies that specialize in the handling of cargo in general . Smaller vessels , such as coasters , are often owned by their operators . Vessel prefixes . A category designation appears before the vessel ' s name . A few examples of prefixes for naval ships are " USS " ( United States Ship ) , " HMS " ( Her / His Majesty ' s Ship ) , " HMCS " ( Her / His majesty ' s Canadian Ship ) and " HTMS " ( His Thai Majesty ' s Ship ) , while a few examples for prefixes for merchant ships are " RMS " ( Royal Mail Ship , usually a passenger liner ) , " MV " ( Motor Vessel , powered by Diesel ) , " MT " ( Motor Tanker , powered vessel carrying liquids only ) " FV " Fishing Vessel and " SS " ( Steam Ship , now seldom seen , powered by steam ) . " TS " , sometimes found in first position before a merchant ship ' s prefix , denotes that it is a " T " urbine " S " teamer . ( For further discussion , see Ship prefixes . ) Famous cargo ships . Famous cargo ships include the Liberty ships of World War II , partly based on a British design . Liberty ship sections were prefabricated in locations across the USA and then assembled by shipbuilders in an average of six weeks , with the record being just over four days . These ships allowed the Allies to replace sunken cargo vessels at a rate greater than the Kriegsmarine ' s U - boat s could sink them , and contributed significantly to the war effort , the delivery of supplies , and eventual victory over the Axis powers . Lake freighters built for the Great Lakes in North America differ in design from " salties " because of the difference in wave size and frequency in the lakes . A number of these boats are so large that they cannot leave the lakes because they do not fit into the locks on the Saint Lawrence Seaway . Sizes of cargo ships . Cargo ships are categorized partly by capacity , partly by weight , and partly by dimensions ( often with reference to the various canals and canal locks they fit through ) . Common categories include : Controversies . Due to its low cost , most large cargo vessels are powered by bunker fuel also known as Heavy Fuel Oil which contains higher sulphur levels than diesel . This level of pollution is accelerating : with bunker fuel consumption at 278 million tonnes per year in 2001 , it is projected to be at 500 million tonnes per year in 2020 . International standards to dramatically reduce sulphur content in marine fuels and nitrogen oxide emissions have been put in place . Among some of the solutions offered is changing over the fuel intake to clean diesel or marine gas oil , while in restricted waters and Cold Ironing the ship while it is in port . If the various requirements are enforced , the International Maritime Organization ' s marine fuel requirement will mean a 90 % reduction in sulphur oxide emissions ; whilst the European Union is planning stricter controls on emissions .