What is Flow-through Method of ballast water exchange and factors taken into account?

The flow-through method involves pumping replacement ballast water into the bottom of a full ballast tank, forcing existing ballast water out through an overflow or other arrangement. Ballast water equal to approximately three times the tank capacity must be pumped through the tank to achieve 95% effectiveness in eliminating aquatic organisms.

The flow-through method does not typically alter stability, hull girder stress and vessel attitude. It therefore eliminates concerns of exceeding shear force and bending moment limits and concerns related to shallow forward and aft drafts and extreme trims. As with all methods, the Ballast Water Reporting Form provided in Appendix 1 is to be completed and transmitted to the next port where ballast water is discharged.

In those instances where the flow-through method alters stability, hull girder stress or vessel attitude, a ballast water summary sequence table is to be submitted demonstrating that adequate strength and stability has been maintained.
As the flow-through method is not suitable for all tanks, in addition to the design requirements , the following items are to be evaluated on those vessels utilizing the flow-through method:

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