We need to exchange ballast water on board to maintain the ship’s stability and keep the cargo safe. Proper Ballasting and Deballasting can significantly reduce the rolling and pitching of the vessel.
Where can the Exchange of ballast take place?
Ballast water exchange cannot be carried out anywhere at sea. Following are the requirements.
- Conduct ballast water exchange at least 200 nautical miles from the nearest land and in the water of at least 200 meters in depth.
- When a ship cannot meet the above criteria due to reasons such as short voyage duration or enclosed waters, the exchange is to be conducted as far from the nearest land as possible, but at least 50 nautical miles from the nearest land and in a water depth of at least 200 meters.
The ballast water exchange methods are
Sequential method – In this method of ballast water exchange, The tank is emptied completely or to at least 95% and then refilled with replacement ballast water.
Emptying of tanks can be done individually or in pairs.
Flow-through method-
The flow-through method is a process by which replacement ballast water is pumped into a ballast tank intended for the carriage of ballast water, allowing water to flow through overflow or other arrangements in order to achieve at least 95 percent volumetric exchange of ballast water. Pumping through three times the volume of each ballast water tank shall be considered to meet the standard.
Dilution method-
The dilution method is a process by which replacement ballast water is filled through the top of the ballast tank intended for the carriage of ballast water with simultaneous discharge from the bottom at the same flow rate and maintaining a constant level in the tank throughout the ballast exchange operation.