Oil tankers are often classified by their size as well as their occupation. Tankers move approximately 2,,, metric tons 2. Some specialized types of oil tankers have evolved. One of these is the naval replenishment oiler , a tanker which can fuel a moving vessel. Combination ore-bulk-oil carriers and permanently moored floating storage units are two other variations on the standard oil tanker design.
Oil tankers have been involved in a number of damaging and high-profile oil spills. As a result, they are subject to stringent design and operational regulations. The technology of oil transportation has evolved alongside the oil industry. Although human use of oil reaches to prehistory, the first modern commercial exploitation dates back to James Young 's manufacture of paraffin in The oil was moved in earthenware vessels to the river bank where it was then poured into boat holds for transportation to Britain. In the s, Pennsylvania oil fields became a major supplier of oil, and a center of innovation after Edwin Drake had struck oil near Titusville, Pennsylvania.
The expense was significant: for example, in the early years of the Russian oil industry, barrels accounted for half the cost of petroleum production. In , two sail-driven tankers were built on England's River Tyne. The modern oil tanker was developed in the period from to It was, during the late 19th century, one of the largest oil companies in the world.
Ludvig was a pioneer in the development of early oil tankers. He first experimented with carrying oil in bulk on single-hulled barges. A primary concern was to keep the cargo and fumes well away from the engine room to avoid fires. The first successful oil tanker was Zoroaster , which carried its long tons of kerosene cargo in two iron tanks joined by pipes.
In , oil tanker design took a large step forward. Swan designed a set of three Nobel tankers. It adopted the best practices from previous oil tanker designs to create the prototype for all subsequent vessels of the type. It was the first dedicated steam-driven ocean-going tanker in the world and was the first ship in which oil could be pumped directly into the vessel hull instead of being loaded in barrels or drums.
The s also saw the beginnings of the Asian oil trade. Until , tankers were designed to be able to navigate the Suez Canal. Hostilities in the Middle East which interrupted traffic through the Suez Canal contributed, as did nationalization of Middle East oil refineries.
In United States shipping magnate Daniel K. Ludwig broke the record of , long tons of heavy displacement. The world's largest supertanker was built in at the Oppama shipyard by Sumitomo Heavy Industries, Ltd. Seawise Giant was renamed Happy Giant in , Jahre Viking in ,  and Knock Nevis in when she was converted into a permanently moored storage tanker.
With the exception of the pipeline, the tanker is the most cost-effective way to move oil today. In Shell Oil developed the average freight rate assessment AFRA system which classifies tankers of different sizes.
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The ships became larger during the s, which prompted rescaling. The system was developed for tax reasons as the tax authorities wanted evidence that the internal billing records were correct. Before the New York Mercantile Exchange started trading crude oil futures in , it was difficult to determine the exact price of oil, which could change with every contract.
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However, the system is still used today. Merchant oil tankers carry a wide range of hydrocarbon liquids ranging from crude oil to refined petroleum products. By only a few ULCCs remain in service, none of which are more than meters long. Because of their great size, supertankers often cannot enter port fully loaded. The act of hiring a ship to carry cargo is called chartering.
Tankers are hired by four types of charter agreements: the voyage charter, the time charter, the bareboat charter , and contract of affreightment. One of the key aspects of any charter party is the freight rate , or the price specified for carriage of cargo. As of [update] , the chartering market is persistently volatile across all tanker sectors. Some particular variables include winter temperatures, excess tanker tonnage, supply fluctuations in the Persian Gulf , and interruptions in refinery services.
In , the sustained rise in oil prices had only a limited impact on demand. In , time-charters tended towards long term. The first half of was relatively strong, but in the second half rates dropped significantly. A sudden rise in oil production, longer transport routes, and slow steaming because of high bunker prices led to a shortage in tonnage towards the end of the year. From , the demand for new ships started to grow, resulting in in a record breaking order backlog for shipyards, exceeding their capacity with rising newbuilding prices as a result.
Prices rose significantly in and early , but delivery of new tankers was projected to keep prices in check. In , oil tankers made up In , 2. By comparison, in 1. The United Nations also keeps statistics about oil tanker productivity, stated in terms of metric tons carried per metric ton of deadweight as well as metric-ton-miles of carriage per metric ton of deadweight.
International law requires that every merchant ship be registered in a country, called its flag state.
In , the average age of oil tankers worldwide was 10 years. Ships are generally removed from the fleet through a process known as scrapping. Oil tankers are often sold second-hand.
In , Oil tankers generally have from 8 to 12 tanks. Individual compartments are referred to by the tank number and the athwartships position, such as "one port", "three starboard", or "six center. A cofferdam is a small space left open between two bulkheads, to give protection from heat, fire, or collision.
A major component of tanker architecture is the design of the hull or outer structure. A tanker with a single outer shell between the product and the ocean is said to be "single-hulled". In , the Marine Board of the National Academy of Science conducted a survey of industry experts regarding the pros and cons of double-hull design.
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Some of the advantages of the double-hull design that were mentioned include ease of ballasting in emergency situations,  reduced practice of saltwater ballasting in cargo tanks decreases corrosion,  increased environmental protection,  cargo discharge is quicker, more complete and easier,  tank washing is more efficient,  and better protection in low-impact collisions and grounding.
The same report lists the following as some drawbacks to the double-hull design, including higher build costs,  greater operating expenses e. In all, double-hull tankers are said to be safer than a single-hull in a grounding incident, especially when the shore is not very rocky.
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Although double-hull design is superior in low energy casualties and prevents spillage in small casualties, in high energy casualties where both hulls are breached, oil can spill through the double-hull and into the sea and spills from a double-hull tanker can be significantly higher than designs like the mid-deck tanker , the Coulombi egg tanker and even a pre-MARPOL tanker, as the last one has a lower oil column and reaches hydrostatic balance sooner.
An oil tanker's inert gas system is one of the most important parts of its design. As inert gas is introduced into a mixture of hydrocarbon vapors and air, it increases the lower flammable limit or lowest concentration at which the vapors can be ignited. Operations aboard oil tankers are governed by an established body of best practices and a large body of international law. One method is for the ship to moor alongside a pier, connect with cargo hoses or marine loading arms.
Another method involves mooring to offshore buoys , such as a single point mooring, and making a cargo connection via underwater cargo hoses. In this method, two ships come alongside in open sea and oil is transferred manifold to manifold via flexible hoses. Prior to any transfer of cargo, the chief officer must develop a transfer plan detailing specifics of the operation such as how much cargo will be moved, which tanks will be cleaned, and how the ship's ballasting will change. After the conference is complete, the person in charge on the ship and the person in charge of the shore installation go over a final inspection checklist.
Loading an oil tanker consists primarily of pumping cargo into the ship's tanks. Loading starts slowly at a low pressure to ensure that equipment is working correctly and that connections are secure. The process of moving oil off of a tanker is similar to loading, but has some key differences. Tanks must be cleaned from time to time for various reasons. One reason is to change the type of product carried inside a tank.