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Oil tankers generally have from 8 to 12 tanks. Each tank is split into two or three independent compartments by fore-and-aft bulkheads. The tanks are numbered with tank one being the forwardmost. 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. Tankers generally have cofferdams forward and aft of the cargo tanks, and sometimes between individual tanks. A pumproom houses all the pumps connected to a tanker's cargo lines. Some larger tankers have two pumprooms. A pumproom generally spans the total breadth of the ship. | |
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. Most newer tankers are double-hulled, with an extra space between the hull and the storage tanks. Hybrid designs such as double-bottom and double-sided combine aspects of single and double-hull designs. All single-hulled tankers around the world will be phased out by 2026, in accordance with amendments to Annex I of the MARPOL Convention. IMO distinguishes three categories of tankers that will be phased out: • Category 1 - oil tankers of 20,000 tonnes deadweight and above carrying crude oil, fuel oil, heavy diesel oil or lubricating oil as cargo, and of 30,000 tonnes deadweight and above carrying other oils, which do not comply with the requirements for protectively located segregated ballast tanks (commonly known as Pre-MARPOL tankers) • Category 2 - as category 1, but complying with protectively located segregated ballast tank requirements (MARPOL tankers), and • Category 3 - oil tankers of 5,000 tonnes deadweight and above but less than the tonnage specified for Category 1 and 2 tankers Phased out types
Category 1 tankers have been phased out in 2005. These so-called preMARPOL tankers were single hull with only some segregated ballast tanks. Around one third of the cargo tanks also acted as ballast tank. During ballast discharge oil was released in the environment. These tankers did not extent high above the water line, allowing Hydrostatically Balanced Loading (HBL), so relatively little oil was spilled in case of bottom damage. [pic]
30 percent of the side shell in way of the tanks of a MARPOL tanker should be non-cargo. MARPOL tanker
Category 2 tankers will be phased out in 2010 the latest, depending on the year of delivery. With MARPOL tankers, it is not allowed to use ballast tanks as cargo tanks. This has reduced operational spillage drastically. The downside is designs based on MARPOL spill more oil when damaged then a preMARPOL tankers. This is due to several factors: 1. as ballast tanks could not be used as cargo tanks anymore, cargo space was lost. To compensate for this, tanks were made taller, which means that more oil is spilled before hydrostatic balance is reached, 2. a MARPOL rule is that 30 percent of the side shell in way of the tanks of a MARPOL tanker should be non-cargo. The cheapest way to reach this, is by making these tanks as narrow as possible. This means that centre tanks became extremely large, so in case of damage, the amount of spillage increased, 3. in a preMARPOL tanker ballast tanks were also filled with inert gas, as these were also used as cargo tanks, which reduced corrosion. Ballast tanks of MARPOL tankers are not protective this way, causing structural failure by corrosion on the Erika, Castor and Prestige, 4. the painted area tripled, increasing required maintenance and corrosion in case this maintenance is done poorly. Category 3
These small tanker will also be...