Ship & Naval

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. 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

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 the amount of tuns of wine (casks) that
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 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: Describes the effect a
  large surface area of liquid in a ship will have on the stability of that ship.
  See Naval Architecture. Liquids in casks posed
  no problem, but one tank across the beam of a ship could pose a stablity
  problem. Extensive sub-division of tanks solved this problem.

In the end, the tanker had its beginnings in the oil industry, as oil companies sought cheaper ways to
transport their refinery product to their customers. The Oil Tanker was born.
Today most liquids are cheaper to transport in bulk and dedicated terminals
exist for each product. Large storage tanks ashore are used to store the product
until it can be subdivided into smaller volumes for delivery to smaller
customers.

Even the Guinness brewery company
in Dublin had a tanker fleet to export
the famous stout to the UK.

Different products require different handling and transport. Thus special
types of tankers have been built, such as "chemical tankers" and "oil tankers". "LNG carriers", as they are typically known, are a
relatively rare tanker designed to carry liquefied natural gas.

Among oil tankers, supertankers are designed for transporting oil
around the Horn of
Africa from the Middle
East. The floating storage and
offloading unit (FSO) Knock Nevis, formerly the ULCC Jahre
Viking, is the largest vessel in the world. The supertanker is 458 metres (1504 feet)
in length and 69 m (226 ft) wide.

Supertankers are one of the three preferred methods for transporting large
quantities of oil, along with pipeline transport and rail. However such
tankers can create environmental disasters from oil spills especially if an accident causes the ship
to sink. See Exxon
Valdez, Braer, Prestige oil spill, Torrey Canyon, and Erika for
examples of coastal accidents

Reza & Sintha