Tankers can range in size of capacity from several hundred
tons, which includes vessels for servicing small harbours and coastal settlements, to several hundred thousand tons, for long-range haulage. Besides ocean- or seagoing tankers there are also specialized inland-waterway tankers which operate on rivers and canals with an average
cargo capacity up to some thousand tons. A wide range of products are carried by tankers, including: •
Hydrocarbon products such as
oil,
liquefied petroleum gas (LPG), and
liquefied natural gas (LNG) •
Chemicals, such as
ammonia,
chlorine, and
styrene monomer •
Fresh water •
Wine •
Molasses •
Citrus juice '' (1902), converted in 1906 into the world's first sailing tanker. Tankers primarily date from the later years of the 19th century. Before this, technology had simply not supported the idea of carrying bulk liquids. The market was also not geared towards transporting or selling cargo in bulk, therefore most ships carried a wide range of different products in different holds and traded outside fixed routes. Liquids were usually loaded in casks—hence the term "
tonnage", which refers to the volume of the holds in terms of how many
tuns or casks of wine could be carried. Even potable water, vital for the survival of the crew, was stowed in casks. Carrying bulk liquids in earlier ships posed several problems: • The holds: on timber ships the holds were not sufficiently water, oil or air-tight to prevent a liquid cargo from spoiling or leaking. The development of iron and steel hulls solved this problem. • Loading and discharging: Bulk liquids must be pumped - the development of efficient pumps and piping systems was vital to the development of the tanker. Steam engines were developed as prime-movers for early pumping systems. Dedicated cargo handling facilities were now required ashore too - as was a market for receiving a product in that quantity. Casks could be unloaded using ordinary cranes, and the awkward nature of the casks meant that the volume of liquid was always relatively small - therefore keeping the market more stable. •
Free surface effect: a large body of liquid carried aboard a ship will affect the ship's stability, particularly when the liquid is flowing around the hold or tank in response to the ship's movements. The effect was negligible in casks, but could cause capsizing if the tank extended the width of the ship; a problem solved by extensive subdivision of the tanks. Tankers were first used by the
oil industry to transfer refined fuel in bulk from refineries to customers. This would then be stored in large tanks ashore, and subdivided for delivery to individual locations. The use of tankers caught on because other liquids were also cheaper to transport in bulk, store in dedicated terminals, then subdivide. Even the
Guinness brewery used tankers to transport the stout across the
Irish Sea.
T2 tanker in 1943 Different products require different handling and transport, with specialised variants such as "
chemical tankers", "
oil tankers", and "
LNG carriers" developed to handle dangerous chemicals, oil and oil-derived products, and
liquefied natural gas respectively. These broad variants may be further differentiated with respect to ability to carry only a single product or simultaneously transport mixed cargoes such as several different chemicals or refined petroleum products. Among oil tankers,
supertankers are designed for transporting oil around the
Horn of Africa from the
Middle East. The supertanker
Seawise Giant, scrapped in 2010, was in length and wide. Supertankers are one of the three preferred methods for transporting large quantities of oil, along with
pipeline transport and
rail. ==Regulations==