Oil in barrels
When the modern oil industry began in the mid-19th century, particularly with the Pennsylvania oil boom of the 1860s, there was no sensible way to move large quantities by sea. Oil was shipped in wooden barrels, loaded and unloaded like any other general cargo. Barrels leaked, took up space and were costly to handle. The cargo was also flammable, and the volatile vapours made it dangerous aboard sailing ships and early steamers.
Shipowners were reluctant to carry it, and early attempts to pump oil into tanks built into ordinary iron ships were not encouraged by insurers or by the experience of explosions and fires. Another obstacle was that liquid cargoes in partly filled tanks shift as the ship moves, which can affect stability.
Barges and the Caspian
The first steps towards bulk carriage came on inland waters. On the Caspian Sea, the oil fields around Baku produced large quantities, and the Nobel brothers’ company, Branobel, used tank vessels to carry it across the sea and up the Volga. The Zoroaster, built in 1878 for this trade, is commonly regarded as the first successful purpose-built oil tanker. The Caspian had its own distinct pattern of shipping, which is explored in the account of Caspian shipping. In the United States, oil was also carried on river and canal barges.
The Glückauf and the modern layout
In 1886 the Glückauf, built at Newcastle by Armstrong Mitchell for a German owner, entered service and is widely seen as the prototype of the ocean-going tanker. Her tanks were formed by the hull itself, subdivided by bulkheads, instead of being separate containers set inside it. Her machinery was placed aft, away from the cargo, which reduced the risk of fire from engine heat and sparks. Pipes and pumps allowed the cargo to be loaded and discharged in a short time.
Most tankers since have followed that basic pattern: cargo tanks forward and amidships, with the engine room and crew accommodation at the stern. Expansion tanks and separate compartments for ballast, together with systems for venting vapour, became features of later vessels.
Companies, canals and larger ships
Once the Glückauf type was proven, tanker fleets grew with the trade in kerosene, for lighting, and then in fuel oil and petrol. Marcus Samuel’s firm, which became Shell, used tankers to carry oil from the Black Sea to the Far East, and an early tanker is recorded as passing through the Suez Canal in 1892 after the canal’s regulations were adapted to allow it. The question of access to canals shaped tanker design from the beginning.
In the early 20th century, builders developed the longitudinal framing system associated with the engineer Joseph Isherwood, which made long hulls stronger with less steel. Tankers grew in length and capacity, and the switch of warships and merchant ships from coal to oil fuel increased demand.
The wartime tanker fleets
Tankers were vital in both world wars, because modern fleets, aircraft and armies ran on oil, and they were attacked accordingly. The struggle to keep oil flowing across the Atlantic was a major part of the Atlantic convoy battle. The United States built large numbers of standardised T2 tankers during the Second World War, and these simple, mass-produced ships were sold into commercial use afterwards, helping to build postwar fleets.
Supertankers
After the war, the growth of oil use in Europe and Japan, together with the shift in production to the Middle East, encouraged bigger ships. Larger tankers have lower costs per tonne carried. The closure of the Suez Canal in 1956 and again from 1967 to 1975 pushed owners to carry crude oil around the Cape instead, which favoured ships too large for the canal. Terms such as VLCC (very large crude carrier) and ULCC (ultra large crude carrier) came into use for the biggest classes.
By the 1960s and 1970s, tankers of several hundred thousand deadweight tons were being built. The Seawise Giant, completed in Japan in the late 1970s and later lengthened, exceeded 400,000 deadweight tons and is generally listed among the largest ships ever built. Such ships were so large that few ports could take them, so cargo was transferred at offshore terminals or by smaller vessels.
Accidents and regulation
Size brought risk. The grounding of the Torrey Canyon off Cornwall in 1967 was the first major tanker oil spill to attract worldwide attention and led to new international conventions on pollution. The Exxon Valdez ran aground in Alaska in 1989, and the United States passed the Oil Pollution Act in 1990. Rules requiring double hulls, which add a second layer of protection around cargo tanks, were gradually introduced for new tankers under both US law and international agreements.
Tanker losses have also been historical turning points for how maritime disasters are investigated and remembered, a theme in the discussion of famous shipwrecks.
A quiet but vital trade
Oil tankers rarely attract the attention given to liners, but they carry a very large share of the world’s seaborne cargo by weight. Their development shows how the needs of a single commodity can shape ship design, canal planning and international law.