What Is a Ballast Water System?
A ballast water system allows a ship to pump water in and out of very large tanks to compensate for a change in cargo load, shallow draft conditions, or weather.
The capacity of ballast water tanks might be millions of gallons on a large vessel. This allows vessels to carry a light or heavy load while maintaining ideal buoyancy and handling conditions in all situations.
A ship might discharge all ballast water tanks to pass a shallow area or forward tanks only to raise the bow in rough open seas.
Physical components of the system include; raw water intakes, large and small strainers, pumps, distribution pipes, ballast water tanks, treatment system, discharge system, and all the valves, sensors, and controls to run the equipment.
Ballast and de-ballast operations on ship must be carried out by an experienced and responsible officer as it is directly related to the stability factor of the ship. A ballast system may differ from ship to ship but the basics of all ballast systems remain same; filling, removing, and transferring water from one tank to other to get the required stability for a ship.
Invasive Species in Ballast Water
Invasive species are a significant threat to ecosystems and the economies of the affected areas. Researchers think that about one-third of all documented invasive plants and animals are able to travel in the ballast water tanks of ships.
Zebra Mussels were introduced into Lake Saint Clair in 1988 when a ship emptied ballast water into the Great Lakes System. The Great Lakes hold nearly twenty percent of the earth’s fresh surface water in a watershed system. The non-native mussels eliminated native varieties once used by industry and have caused an estimated 7 billion dollars (US) in damage by encrusting or clogging underwater equipment essential to industrial and recreational activities.
Sea Lamprey and Spiny Water Fleas are organisms which feed off of host fish or compete with young fish for food. Many species of fish impacted by these invasive species have significant commercial or sporting value. These animals and others can live in fresh or salt water and may spread into inland waterways from saline ports and harbors.
Plants can also travel long distances in ballast water. Eurasian Milfoil is a surface plant which can clog equipment and deter recreation where it forms thick mats. Eurasian Milfoil was introduced to the United States in the 1940s. Because the plant can produce large colonies from only one small fragment it is likely the plant was introduced in the ballast water of a ship.
Getting Familiar with the System
All valves in the ballast system are normally hydraulically operated from the remote operator station in the ship’s control centre or in the ECR in manual mode or in automatic sequence.
The ballast pump suction and discharge valves, along with other valves, have their fail safe in the OPEN position so that if any valve malfunction or get stuck, still remains open to carry out ballast operation.
Different Forms of Ballasting and De-ballasting
Ballasting or De-ballasting can be done in five following ways :
- Transferring water between tanks using gravity.
- Ballasting or De-ballasting tanks from sea using gravity.
- Ballasting the tanks using the ballast pump/pumps.
- De-ballasting the tanks using the ballast pump/pumps.
- De-ballasting the tanks using the stripping ejectors.
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Important Points to Consider while Operating Ship’s Ballast System
Care should be taken to ensure that the tank is not over filled; as this will damage the tanks because the pressure vacuum valves have lower capacity than that of the pump. The filling valves will close automatically when the tanks reach their set point level, which have been pre-set.
Also care has to be taken not to run the pump dry or run the pump with discharge valves closed. This can be taken care by automated system, which ensures that the pump will not start until all the necessary valves are opened.
Valves can be put in auto mode, which ensures that the valve closes automatically once ballast tank is filled with required amount of water or once the set point is reached.
Port and starboard sides are considered two separate systems, each having their own automatic sequence for ballast /de-ballasting.
When filling ballast tanks with ballast pumps it should be observed that the motors are not overloaded (check current in ammeter). If this occurs, the number of opened valves to ballast tanks shall immediately be reduced (closed) until current is within allowable limit. Ballast pump motor overload alarm is given for the safety of ballast pump.
Some times during sea voyage one can get an alarm on the ballast pumps suction pressure high. At that time just open the suction valve to the sea chest and close them when the pressure is reduced.
The water in the heeling tanks should always be half of their total capacity. But if required the heeling tanks can be used as ballast tanks. Ballast pump is used to empty or fill the heeling tank.
Also in some ports the port authorities may ask for a sample of the ballast that the ship is carrying. In this case the sample has to be taken from the sounding pipe connection. The locations of all the sounding pipes are provided on the ballast system plan of the ship.