Tanker (ship)
A 'tanker (or tank ship or tankship) is a merchant vessel designed to transport liquids or gases in bulk. Major types of tankship include the oil tanker, the chemical tanker, and gas carrier. In the United States Navy and Military Sealift Command, any type of tanker used to refuel other ships is called an oiler
Background
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
Tankers are a relatively new concept, dating 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:
