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A ship at sea is a massive structure which though floatable, requires stability to sail through the waters. As water is easily and abundantly available, it is used for providing the required stability and trim to the ship. This water is known as ballast water and process of taking ballast water into the ship is known as “ballasting". The tanks on ships wherein the ballast water is filled are known as ballast tanks.
Also, all the ships are supplied with a system that can take-in and discharge ballast water. Ships have a dedicated ballast water system and tanks for this purpose. The ballast tanks are located at the lowermost region of the ship and below the machinery room. Ballasting is important for ship’s own safety and thus special attention is given to this process. When the ship is loaded with cargo, it already has weight and thus ballasting is not very important. However, when the ship discharges cargo and is not carrying any weight, it easily gets affected by the sea condition. It is then that the ship requires ballasting the most.
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Ballast tanks provided in the ship’s lower-most region hold the ballast water. The number of ballast tanks in a ship depends on the ship’s size, design, and requirement. For e.g. a ship might have one large single ballast tank at the center or multiple tanks on either side. Moreover, larger the ship, more the number of ballast tanks. A typical large vessel will have several ballast tanks, along with the double bottom tanks, wing tanks, and fore-aft peak tanks.
A particular ballast tank on a ship is filled depending on the position of the cargo loaded on the ship. This means that that if more of cargo is loaded on the starboard side than the ort side of the ship, then the port side ballast tanks will be more filled with more ballast water to balance the cargo weight and gain overall stability of the ship. The filling of ballast tanks also depends on various other factors such as the draft required by vessel, depth at ports, capacity of ballast tanks etc.
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How is Ballasting Done?
Ballasting on a ship is done through openings provided at the lower most portion of the ship’s hull. The openings are connected to a ballast system through piping. Ship ballast system has dedicated ballast pumps for the ballasting process. For safety purpose, non return valves are provided in the pipelines near the openings to prevent sea water from entering the ship and vice-verse. The Ship’s ballast system, along with the pumps, is located at the lower most regions of the engine room and below the sea-water line, to provide the necessary suction head to the ballast pumps. Various factors such as ship’s external and interior layout, loading capacity, ballast tanks capacity, time taken for ballasting and de-ballasting etc are taken into account before starting the ballasting process. Continuous watch is also kept on all ballast tank levels through the ship’s automation system until the whole process is over.
Without proper ballasting of all tanks, no ship can sail safely. Good ballasting not only helps in providing adequate stability and trims to the ship but also reduces stresses on hull, helps in smooth maneuvering process, and reduces rolling and pitching.
The ballasting and de-ballasting process generally occurs at the ports before the cargo is loaded onto the ships. The process takes place simultaneously with the cargo loading or unloading process. However, ballasting and de-ballasting can also occur while the ship is in transit, especially during rough sea, change in wind conditions, and several internal factors.