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. 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. Tighter regulation means that tankers now cause fewer environmental disasters resulting from oil spills than in the 1970s. Amoco Cadiz, , Erika, Exxon Valdez, Prestige and were examples of accidents. Oil spills from tankers amounted to around 1,000 tonnes in 2020 from three incidents (an all-time low), down from 636,000 tonnes from 92 incidents in 1979 - a fall of 99.8%. Design considerations Many modern tankers are designed for a specific cargo and a specific route. Draft is typically limited by the depth of water in loading and unloading harbors; and may be limited by the depth of straits or canals along the preferred shipping route. Cargoes