Methods of Ballast Exchange
There are three methods of ballast water exchange which have been evaluated and accepted by the IMO. The three methods are the sequential method, the flow-through method and the dilution method.
- Sequential method – A process by which a ballast tank is first emptied and then refilled with replacement ballast water to achieve at least a 95% volumetric exchange.
- Flow-through method – A process by which replacement ballast water is pumped into a ballast tank, allowing existing ballast water to overflow from the tank (see figure below). For effective ballast exchange, the volume of flow through water should be at least 3 times the volume of the water in the tanks.
- Dilution method – A process by which replacement ballast water is supplied through the top of the ballast tank with simultaneous discharge from the bottom at the same flow rate and maintaining a constant level in the tank throughout the ballast exchange operation (MariEMS 2017).