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a vessel for transporting liquid cargoes in bulk. Tanker cargoes include petroleum and petroleum products, liquefied gases, food products (vegetable oil, milk, starch syrup, whale oil, and wine), chemicals (acids and alcohol), molten sulfur, asphalt, and fresh water.
In the second half of the 19th century, petroleum and petroleum products were first shipped in bulk in hold boxes (inset tanks) or directly in the hull; earlier, petroleum had been shipped in barrels. The first bulk shipment was accomplished in Russia on the Caspian Sea in 1873 by the Artem’ev brothers, owners of the wooden sailing schooner Aleksandr. Wooden and metal tanker barges were later built to carry petroleum on the Caspian Sea and the Volga. The first Russian iron steam tanker, the Zoroastr, was built in 1878. Its eight inset cylindrical tanks had a capacity of 250 tons; the tanks were later removed and the petroleum was loaded directly into the holds. The Russian steam tanker Spasitel, with a capacity of 670 tons, served as a prototype for modern tankers. Built in 1882, four years earlier than the British steam tanker Glückauf, the Spasitel had a deadweight capacity of approximately 3,000 tons and was virtually of the same design as the Russian vessel.
By mid-1974, the tanker fleet constituted almost half of the volume of the world merchant fleet. At that time, Lloyd’s Register of Shipping had registered a total of 7,855 tankers with a gross tonnage of approximately 155 million register tons (counting ships with gross tonnages of at least 100 register tons). By the beginning of 1975, the total deadweight capacity of the 1,268 tankers under construction or ordered with deadweight capacities of at least 2,000 tons was 168 million tons, almost 82 percent by volume of all ships on order in the world.
The tanker is a single-deck, self-propelled vessel with an engine room, crew quarters and service areas in the stern and a longitudinal (sometimes transverse on the sides) system of framing the ship’s hull, usually without a double bottom in the cargo tanks. The cargo areas are divided into tanks by several transverse bulkheads and one to three longitudinal bulkheads, depending on the size of the tanker; several of the tanks are used only for taking on water ballast. Access to the tanks is through small deck openings with sealed covers. The tanker is loaded with one or several types of cargo by shore equipment and unloaded by ship pumps through pipes laid along the deck and in the tanks. The tanks are equipped with heat exchangers—coiled piping through which steam passes—which heat congealing cargoes, such as paraffin-base petroleum, mazut, and bitumen.
Tankers have equipment to prevent and fight fires, for example, devices to fill the tanks with inert gas and devices for extinguishing surface and regular fires with vapors, foam, and water spray. In order to improve seaworthiness, tankers traveling unloaded take on water in ballast and cargo tanks; the cargo tanks are equipped with apparatus for washing the tanks with hot water under pressure and for removing petroleum contaminants from the water. The inner surfaces of the tanks are protected with anti-corrosion coatings, and the tanks of chemical tankers are sometimes made of corrosion-resistant materials.
Petroleum tankers are among the largest transport ships. A typical large tanker built in 1975 has a deadweight capacity of approximately 550,000 tons, a length of 400 m, a width of 63 m, sides 35 m high, and a draft of 28.5 m. The main engines are two steam turbines rated at 26,800 kilowatts (32,400 hp) each. Small and medium tankers usually have diesel power plants, while steam-turbine units are most common on large tankers.
E. G. LOGVINOVICH
ii. To carry excess fuel to avoid unavailability or having to purchase it at a higher price.