Tankers are ships designed for the carriage of liquid cargoes in bulk. As liquids fill the compartment entirely, minimizing structural encroachment is not much of a priority in their design (although swedged or corrugated bulkheads may be used to ease tank cleaning). Tankers are considered Type A vessels for loadlines and freeboard calculations, being designed for the carriage of liquids, they are essentially designed to be flooded and lack the large deck openings of cargo or container vessels.
The first form of bulk liquid transport appeared in 1861 with the Elizabeth Watts carrying 224 tones of petroleum in large barrels. Not much is known about the vessel except that it serviced several ports around England on a 45 day voyage. It was not until twenty years later in 1886 the British realized that the transport of bulk petroleum products was economically viable. This spawned the construction of the GLUCKAUF, a 2,700 ton tanker with segregated tanks integrated directly into the hull of the ship, in addition it was the first commercial vessel with the engine room placed aft to optimize cargo volume and ease the construction of the tanks.
Up until the early 1890’s tanker design differed seldom, every tanker had to have a void space (coffer dam) sometimes filled with water to cool the oil that was being pumped into the holds. Each hold was approximately 25 feet deep with a 5 foot square expansion tank just below the main deck, this allowed the tank to be pressed full reducing the free surface effect while the vessel is out to sea. At this point there were approximately seventy operating tankers many of which were converted passenger liners, the average passenger liner could be converted to a 2,000 to 3,000 gross ton tanker were a purpose built tanker could carry 3,000 to 4,000 gross tonnes.
1897 saw a revolution to the marine industry, the coming of the diesel engine meant that instead of having to have valuable deck space taken up by masses of coal they can create a tank much like the tanks that are used to hold the cargo but smaller to power there own vessel. In addition the diesel engine is much smaller and slower moving than a steam engine this allowed for smaller engine rooms and less maintenance on the slower moving diesel engine. By 1927 approximately 28% of the global commercial fleet have been fitted with diesel engines.
During the Second World War the need to produce a supply chain became crucial for success in Europe. Several tankers at this point were riveted this was a timely procedure often taking more than a year to construct one vessel. The T2 series were the first tankers to be fully welded, much like the liberty ships.
Before the 1950’s it was not uncommon to locate refineries close to the oil wells and than ship refined petroleum to the markets. However the fifties saw that through technical advancements, being able to build ships larger and changes in political ideals of developed countries sparked the growth of the crude oil tanker. These tankers offered less financial loss should the vessel be pirated or lost at sea and by the late 1950’s 50% of the world’s tonnage were crude oil and product tankers.
Throughout the 1960’s there had been several groundings, explosions and structural failures and there had been a couple of disasters involving very large crude carriers (VLCC) that have been brought to the political forefront and forced the International Maritime Organization (IMO) to form The Convention for the Prevention of Pollution from Ships 1973 (refereed to as MARPOL 73). A few years later in 1978, the Amoco Cadiz lost steering and ran aground releasing 1.6 million barrels of oil in the sea. This sparked the amendments to Safety of Life at Sea (SOLAS) for redundancy in steering gears and the development of MARPOL 73/78 which introduced the concept of protectively located (PL) spaces. PL spaces are specially designated areas extending down the side shell and a given percentage of the bottom plate this helps in the prevention of cargo loss should rounding occur.
In 1989 the Exxon Valdez ran aground in Prince William Sound releasing 1.4 million barrels of thick crude in the environmentally protected area. This forced the United States Government to pass The Oil Pollution Act of 1990 which states that all tankers that enter US costal waters must be double hulled. Later in 1992 IMO revised MARPOL 73/78 for actual dimensions, piping arrangement and ballast distributions according to the deadweight of the vessel. SOLAS and MARPOL 73/78 with all amendments to this date is the current regulating body in conjunction with flag state rules and classification societies.