Oil tanker

The Knock Nevis. Formerly known as the Seawise Giant and later renamed as the Jahre Viking, it was the largest ship in the world. It has now converted to a floating oil storage terminal

Petroleum tankers, also known as oil tankers, tankers, or oilers, are ships of varying sizes designed for the bulk transport of petroleum. The largest are up to 650,000 tons. Since the creation of the first oil tanker back in 1878, crude oil has normally been transported by ship from near the point of extraction closer to consuming markets where the crude oil is then refined into a variety of products or materials used in further manufacture. Tankers can roughly be divided into two types - naval and merchant - and these can be divided into further subtypes.

History

The first successful oil tanker was the Zoroaster, which plied the Caspian Sea from the Aspheron peninsula, near Baku, in what was then the Russian Empire, in 1878. Ludwig Nobel, brother of Alfred Nobel, was the first to conceive of an oil tanker. Ludwig Nobel's idea owed to the problems and costs of shipping oil in wooden barrels. He thought to ship oil in bulk tanks and the oil tanker was created. The original oil tanker had ballast and safety problems. As the tanker pitched and heaved in the sea, the oil would move more quickly than the water, tipping or forcing the vessel. This is an example of the free surface effect of liquids in ships, and it wrecked several early vessels. When Nobel solved these problems, the Zoroaster was built. By the mid-1880s, Ludwig's tanker had proved itself on the much rougher Atlantic ocean and his basic concept revolutionised the transport of oil. It was the first step towards tanker designs seen today.

Naval tankers

Naval tankers carry a liquid cargo of petroleum, or fuel to other naval ships steaming at sea, and can transfer the fuel during replenishment at sea. They may also carry small quantities of ammunition and cargo. The U.S. Navy’s first diesel-powered surface ship, the oiler USS Maumee, was a good-sized ship for her time at 14,500 tons, and her engines were very large, developing 2,500 horsepower each. Her Captain, CDR Henry C. Dinger, and his Executive Officer Chester Nimitz worked out the first procedures for transferring fuel oil at sea. Initially, refueling with oil followed the same pattern as coaling – done at anchor in a protected roadstead with the receiving ships moored alongside. In less than six months, Dinger and Nimitz had worked out a mechanism for underway replenishment (UNREP) by towing the receiving ship alongside. When the United States joined the Allies in World War I, Maumee was the oiler that made it possible for the U.S. Navy to deploy destroyers across the Atlantic. During World War II, the transport of petroleum and its products was a critical strategic activity since shortages had a paralysing impact on mechanised nations. The destruction and defense of these ships was therefore of prime concern.

Merchant tankers

Merchant tankers carry a wide range of hydrocarbon liquids from crude oil to refined petroleum products. They vary in size from roughly 55,000 deadweight (a measure of cargo-carrying capacity) of the Panamax crude carriers to over 300,000 for the Very Large Crude Carriers (VLCCs). A 300,000dwt tanker is designed to load 2 million barrels of crude oil, usually about 285,000 tonnes, but has the extra capacity to load lighter, higher volume crude oils if necessary. Suezmaxes load about one million barrels while Aframaxes load 650,000 - 800,000 bbls. Note: definitions of what size of tanker constitute what type e.g. whether a 320,000dwt tanker is VLCC or a ULCC, varies from broker to broker, lawyer to lawyer and ship owner to ship owner. As there is no set, standard, classification, there is no one 'correct' answer. All descriptions of X-size being an X-tanker should be treated with caution.

Class	Tonnage (dwt)
Aframax	80,000-120,000
Suezmax	130,000-160,000
VLCC	200,000-320,000
ULCC	over 320,000
V Plus	over 440,000

Supertankers

Commercial crude oil supertanker AbQaiq.

The term supertanker usually refers to the world's largest ships, those tanker ships above 250,000 in deadweight tonnes (dwt) (i.e. carrying capacity) and capable of transporting two million barrels of oil. By way of comparison, the oil consumption of Spain and the UK combined is about 3.2 million barrels of oil a day.

"Supertanker" is an unofficial term. In the shipping industry, it is standard practice to refer to supertankers using size designations such as Very-Large Crude Carriers (VLCC) and Ultra-Large Crude Carriers (ULCC). Supertankers are capable of transporting vast quantities of liquids, and in practice are used to move crude oil.

The largest supertanker—indeed the world's largest ship ever —was the Jahre Viking or Seawise Giant (now the permanently moored storage tanker Knock Nevis), weighing in at 564,763 deadweight tonnes. In the 1950s, tankers with only a tenth of that capacity would have been called supertankers.

The four largest supertankers, built circa 2002, carry the designation (V Plus), although the term ULCC has not been assigned a maximum dwt. Smaller classes of tanker, such as Aframax or Suezmax, are no longer regarded as "supertankers".

Until the 1960s, international maritime trade relied heavily on the Suez Canal, the width and depth of which effectively placed a limit on the size of merchant vessels; it was rare for oil tankers to exceed 45,000 tonnes in displacement. This was changed drastically by the Six-Day War, with the Suez Canal being closed from 1967 to 1975. Being forced to make the longer and costlier detour through the Cape of Good Hope, shipping companies opted for the next-best option, that was to build very large tankers, free from the constraint of the Suezmax, that offer better economies of scale than that of older, smaller vessels.

When first introduced, their size and draft prevented them from docking at many existing docks, requiring them to discharge their cargo into smaller tankers offshore. Some ports have developed special deep-water off-loading facilities connected to the land by pipelines (such as the Louisiana Offshore Oil Port). Supertankers are also very efficient ships, mostly relying on a single propeller for propulsion, and therefore supertanker transport costs typically account for only US $0.02 per gallon of gas at the pump.

Pollution

From time to time there have been accidents that have led to serious and catastrophic pollution. Another concern has been the pollution caused by careless cleaning of ships' tanks. According to the U.S. Coast Guard, fewer than 67 barrels (about 2,800 gallons) were spilled out of more than 4.2 billion barrels of petroleum delivered by tankers to the U.S. in 2005. The total volume of petroleum spilled from tankers annually in the U.S. has averaged fewer than 4,000 barrels annually from 1996-2005, including no marine incidents during 2005's record hurricane season. In fact, far more oil enters the oceans from natural sources and other incidents than from tanker spills.

The Exxon Valdez incident was indeed a big let off for the coast of Alaska and for Exxon. Current media reports suggest that some 11 million gallons of oil was dumped on the coast. This equates to some 35,000 mts of cargo - the Exxon Valdez had the capacity to load about 215,000 mts, so the result of the spillage could have been much worse.

Anti pollution control and measures

Following the Exxon Valdez incident, the United States passed the Oil Pollution Act of 1990 (OPA-90), which included a stipulation that all tankers entering its waters be double-hulled by 2015. Following the sinkings of the Erika (1999) and Prestige (2002), the European Union passed its own stringent anti-pollution packages (known as Erika I, II, and III), which also require all tankers entering its waters to be double-hulled by 2010. The Erika packages are controversial because they introduced the new legal concept of "serious negligence". [1]

Double hulled tankers

In "single-hulled" tankers, the hull is also the wall of the oil tanks, and any breach will result in an oil spill. Newer tankers are "double-hulled", with a space between the hull and the storage tanks to reduce the risk of a spill if the outer hull is breached. This space carries water ballast when the ship is not carrying an oil cargo.

Safety controversy

In theory the addition of an extra hull should prevent such a ship from suffering a catastrophic breach of the hull. A double-hull tanker is said to be safer than a single-hull in a grounding incident, especially when the shore is not very rocky. But some commentators have questioned whether double hulls are actually any safer than single hulls. The proposition has been put forward double hulls could be more dangerous than single hulls. Collisions at a low speed won't necessarily damage a vessel. Collisions at a greater force would still have to rupture the internal oil tanks and cause the oil to spill. There is a physical force called hydrostatic balance which refers to the (strong) tendency of oil and water to repel each other. Expert opinion (see The Tankship Tromedy by Jack Devanny, ISBN 0-9776479-0-0, http://www.bookmasters.com/marktplc/01558.htm) points out that hydrostatic pressure within tankers is more than adequate to contain an oil spill in the event of a low impact collision, especially if the internal tanks are set in an elevated position.

The case against double hulls can be found, for instance, in the article "Double, double toil and trouble" in Fairplay International Shipping Weekly, 23 Jun 2005. The essence of the case against double hulls is as follows. A single hull is more easily inspected and maintained than are double hulls. Plus the struts between the skins of a double hull are subject to hogging and sagging forces (the tendency to make metal bend down at the ends and up in the middle (hogging) and down in the middle and up at the ends (sagging)), racking and twisting, whereas these forces are non-existent in the case of a single hull tanker. Double hulls also carry a greater risk of explosion than a single hull. Gas from crude oil is flammable and double hulls have void spaces between their skins, whereas single hulls do not (because they don't have two skins). Gas collects within the void spaces and so must be pumped full of inert gas to prevent explosion. For single hull ships, empty ballast tanks would also have to be inserted as there is possibility of gas leakage from oil tanks into empty ballast tanks as well.

Several groundings and collisions show that the double hull provides adequate protection against oils spills. This supports the results from advanced structural ultimate strength calculations where carried out for various tank arrangements for impact speeds of 5 and 10 knots respectively in connection with the OPA90(US National Research Council: Tanker spills. Prevention by Design 1991). These calculations show, that the oil spills from double hull tankers are reduced to one third for reasonable double hull designs compared with conventional SBT tankers.

The biggest oil spills come from a few cases of high energy collisions (http://www.earthtoys.com/emagazine.php?issue_number=07.02.01&article=green_ships). The potential for such spills cannot singly be used as an argument against the merits of double hulls reducing the oil spill potential in case of groundings and collisions. Other measures than tank arrangement and structural strength must be considered in order to reduce the risk of such incidents.

A very significant danger posed by double hulls is the free surface water effect. "A double-hulled tanker doesn't need longitudinal bulkheads for longitudinal strength, as the inner hull already provides this. This results in much wider tanks, significantly increasing the free surface effect," writes Earthtoys Emagazine. The free surface effect is a very dangerous phenomenon that occurs when a liquid, or any mass bulk like grain, seeds or powder which can replicate the motion of water,is able to flow freely from side to side, or from fore to aft, along with the pitch and heave motion of the sea. When a vessel tilts, the free water rushes from one side of the ship to the other. The sudden rush of water to one side can cause the ship to suddenly list dangerously, even causing it to tip and sink. The free surface water effect, caused by the crew trying to put out a fire, was a significant factor in the sinking of the roll-on, roll-off Red Sea Ferry, the Al-Salam Boccachio '98, which caused the deaths of over 1,000 people. In single hull tankers swash bulkheads are used to reduce the risk for sloshing, which may occur in wide cargo center tanks and side ballast tanks.

In this section the author is talking about Oil Tankers, but cites an example of a Ro-Ro Ferry which is a completely different kind of vessel, and by its characteristics the free surface effect has a much greater impact. If you remember the Herald of Free Enterprise disaster, it is within that context that the free surface effect is more pronounced. Problems as cited in this article with respect to Double Hulled vessels have in the main been proved to be incorrect and speculative in nature.

Owing to the greater use of materials involved, greater hogging and sagging forces, greater likelihood of explosive gas/air mixture building and greater difficulty of inspecting and maintaining double hulls when compared to single hulls, some commentators believe that double hulls are more dangerous than single hulls. Further criticisms of double hulls can be found in "Double Hull Tankers: High Level Panel of Experts Report" (2005) at http://www.emsa.eu.int.

A full investigation of the pros and cons of single v double hulls can be found in an article on green shipping by C. G. (Chuck) Steiner President and CEO WaterSmart Environmental, Inc. The article can be accessed at http://www.earthtoys.com/emagazine.php?issue_number=07.02.01&article=green_ships.

List Of Notable Supertankers

• Knock Nevis, permanently moored since 2004
• Batillus class supertankers
  • Battilus, scrapped 1985
  • Bellamya, scrapped 1986
  • Pierre Guillaumat, scrapped 1983
  • Prairial, formerly Hella Fos, Sea Giant, scrapped 2003
• TI Asia, formerly Hellespont Alhambra
• TI Europe, formerly Hellespont Tara
• TI Oceania, formerly Hellespont Fairfax
• TI Africa, formerly Hellespont Metropolis
• Esso Atlantica, two ships in class, both scrapped
• Esso Pacific, scrapped
• Torrey Canyon, first supertanker, wrecked in 1967

• Former supertankers converted into Mercy class hospital ships
  • USNS Mercy
  • USNS Comfort (T-AH-20)

Further reading

• Sullivan, George (1978). Supertanker!: The Story of the World's Biggest Ships. Dodd, Mead. ISBN 0396075274.
• Mitchell, William Harry (1987). Sailing Ship to Supertanker: The Hundred-Year Story of British Esso and Its Ships. Terence Dalton. ISBN 086138055X. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
• Double double, toil and trouble. Fairplay International Shipping Magazine. 23 Jun 2005.{{cite book}}: CS1 maint: year (link)
• Devanny, Jack (2006). The Tankship Tromedy: the impending disaster in tankers. ISBN 0-9776479-0-0.
• European Commission / European Maritime Safety Agency (2005). Double Hull Tankers: High Level Panel of Experts Report.

External links

• Bill Willis. Supertankers
• Intertanko - the society of International Tanker Operators
• The International Maritime Organization - Tanker Safety (for double-hulls)

See also

• Replenishment oiler
• Tanker (ship)