Ballast tank

A ballast tank is a compartment within a boat, ship or other floating structure that holds water, which is used as ballast to provide stability for a vessel. Using water in a tank allows for easier adjustment of weight than stone or iron ballast as was used in older vessels. It also allows for ballast to be pumped out to temporarily reduce the draft of the vessel when required to enter shallower water.

The basic concept behind the ballast tank can be seen in many forms of aquatic life, such as the blowfish or argonaut octopus, and the concept has been invented and reinvented many times by humans to serve a variety of purposes. For example, in 1849 Abraham Lincoln, then an Illinois attorney, patented a ballast-tank system to enable cargo vessels to pass over shoals in North American rivers.

In order to provide adequate stability to vessels at sea, ballast is used to weigh the ship down and lower its centre of gravity. International agreements under the Safety Of Life At Sea (SOLAS) Convention require cargo vessels and passenger ships to be constructed so as to withstand certain kinds of damage. The criteria specify the separation of compartments within the vessel and also the subdivision of those compartments. The International agreements rely upon the states which have signed the agreement to implement the regulations within their waters and on vessels which are entitled to fly their flag. The ballast is generally seawater which is pumped into tanks known as ballast tanks. Depending on the type of vessel, the tanks can be double bottom (extending across the breadth of the vessel), wing tanks (located on the outboard area from keel to deck) or hopper tanks (occupying the upper corner section between hull and main deck). These ballast tanks are connected to pumps which can pump water in or out. These tanks are filled in order to add weight to the ship once cargo has been discharged, and improve its stability. In some extreme conditions, ballast water may be introduced to dedicated cargo spaces in order to add extra weight during heavy weather or to pass under low bridges.

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Wikipedia