DWT Ships are specifically cargo vessels with a maximum permissible deadweight. DWT Ships have a point of submersion known as Plimsoll line. However, Plimsoll line may also indicate the actual DWT of a ship not loaded to its fullest capacity. DWT is the acronym of Dead Weight Tonnage which is used to measure how much weight(applicable for cargo) a ship is carrying or can safely carry. DWT is also called dwt, d.w.t, DWT or D.W.T. DWT is calculated on the summation of the weights of shipments or cargo, crew, passenger, provisions, fuel, fresh water, and ballast water. DWT Ships or freighters are used to transport goods, cargo, materials from one port to another. Each year thousands of DWT Ships ply the world's seas and oceans. DWT Ships handle a huge bulk of shipments of international trade. They come in different sizes are specially equipped with cranes and other automatic mechanisms to load and unload cargo or shipments. Today, DWT Ships are almost always made of welded steel, and generally have a life expectancy of 25 to 30 years. After 25-30 years these giants are scrapped.
DWT Ships or Bulk carriers were developed from general cargo ships. Until 1911, bulk freighters were operated by steam pressure. In 1911, the the first bulker with diesel propulsion came into action. The demand for DWT Ships was pretty low until the 1950s. Later with growth in international bulk trade between industrialized nations including European countries, the United States and Japan, bulkers became larger, sophisticated and more specialized.Today, it is the Asian countries that dominate the DWT Ships construction industry. Over 82% of bulkers afloat comes from Japan, China, Taiwan and Korea. Of the world's total DWT Ships , almost 62% are built in Japan at different shipyards such as Sanoyas, Oshima, Hishino and Meisho. South Korea ranks second in DWT Ships building and has notable shipyards like Daewoo and Hyundai Heavy Industries.The People's Republic of China ranks third and has prominent shipyards such as Chengxi, Dalian Shipyard, and Shanghai Waigaoqiao. Taiwan ranks fourth with major shipyards such as China Shipbuilding Corporation.
There are a numerous classification societies round the world. Some of the largest societies are : Lloyd's Register(Great Britain), Det Norske Veritas(Norway), Polski Rejestr Statkow (Poland), Hellenic Register of Shipping (Greece), China Classification Society (CCS), Indian Register of Shipping (India) , Bureau Veritas(France), Nippon Kaiji Kyokai(Japan), Germanischer Lloyd(Germany), Registro Italiano Navale(Italy), Russian Register of Shipping( Russia) and the American Bureau of Shipping(United States of America). Each classification society employ material engineers, ship surveyors mechanical engineers, piping engineers, chemical engineers and electrical engineers based at different ports and corporate office around the world.
These classification societies publish stringent rules and regulations regarding the strength of the DWT Ships, the provision for adequate equipments, and the reliability of the machinery implemented. DWT Ships built in any country have to abide by the particular classification society’s rules. DWT Ships are not restricted to follow rules of the relevant society of the country where the vessels are built. However, classification for a DWT Ship is not compulsory. A ship-owner with an un-classed DWT Ship has to compulsorily satisfy governmental regulating bodies for the issuance of a safety construction certificate.
Steel DWT Ships built in accordance with classification societies standards or equivalent rules, are assigned a particular class in their Register Book. DWT Ships are continued to be classed in the same category till they are maintained in accordance with the rules.
DWT ships or freighters are generally divided into three classes: Bulk Carriers, Tankers, Crude Oil Carriers.
Bulk Carriers: A Bulk carrier, bulker or bulk freighter is a merchant liner designed to transport both dry and wet unpackaged bulk cargo such as grains, cements, preserved meat, fruits, vegetables, coal, ore, fertilizers, bulk liquids such as refined petroleum products, and chemicals as well.
Tankers: These vessels are used for transportation of wet products such as refined petroleum products in numerous bulk tanks for safety. These vessels specialize in carrying different products in a single voyage. They have a capacity less than 100,000 dwt are classified as "clean" or "dirty". Clean tankers carry different chemicals or refined petroleum products ( gasoline, kerosene, jet fuels). Dirty vessels transport heavy fuel oils or crude oil.
Crude Oil Carriers : These specialized vessels used to carry bulk crude oil in tanks.
Panamax: These maximum sized ships have cargo carrying capacity between 50,001 - 80,000 dwt. They can pass through the locks of the Panama Canal.