Tanker

Tankers move the world's liquid cargoes (crude oil, refined petroleum products, chemicals and liquefied gases) in large integral tanks that form part of the hull. They are distinguished from dry-cargo ships by their piping and pumping systems, which load and discharge cargo through a network of lines, pumps and a manifold rather than through hatches and cranes. A modern tanker's cargo operations are run from a control room and involve careful management of tank pressures, temperatures and the ship's stability as liquids move.

The main types reflect the cargo. Crude oil tankers are the largest, ranging up to the Very Large and Ultra Large Crude Carriers that serve long-haul export routes. Product tankers carry refined fuels such as gasoline, diesel and jet fuel, and are usually coated internally so different clean products can be carried without contamination. Chemical tankers, governed by the IMO's IBC Code, have stainless steel or specially coated tanks, sophisticated segregation and heating, and carry a wide variety of often hazardous liquids. Gas carriers transport LNG and LPG in insulated or pressurised tanks at very low temperatures.

Because their cargoes are polluting and often flammable, tankers carry safety and pollution-prevention systems that other ships do not. Segregated ballast tanks keep ballast water entirely separate from cargo, an inert gas system fills the space above the cargo with oxygen-poor gas to prevent explosion, and crude oil washing cleans tanks using the cargo itself to reduce residues. Double hulls, now mandatory for oil tankers under MARPOL, provide a second barrier against spills in a grounding or collision. Tanker operations, from loading through the loaded passage to discharge and tank cleaning, are among the most tightly regulated and procedure-driven in the industry.