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Encyclopedia of Marine Technology


Any solid or liquid weight placed in a ship to increase the draught, to change the trim, or to regulate the stability. Ballast water is allocated during the voyage to accommodate changes in the distribution of cargo and consumables, and in response to operational requirements such as draught limitations.

- Clean ballast – The ballast in a tank which, since oil was last carried therein, has been so cleaned that effluent there from if it were discharged from a ship which is stationary into clean calm water on a clear day would not produce visible traces of oil on the surface of the water or on adjoining shorelines or cause a sludge or emulsion to be deposited beneath the surface of water or upon adjoining shorelines. If the ballast is discharged through an oil discharge monitoring and control system approved by the Administration, evidence based on such a system to the effect that the oil content of the effluent did not exceed 15 parts per million shall be determinative that the ballast was clean, notwithstanding the presence of visible traces (MARPOL).

- Segregated ballast – The ballast water introduced into a tank which is completely separated from the cargo oil and oil fuel system and which is permanently allocated to the carriage of ballast or to the carriage of ballast or cargoes other than oil or noxious substances (MARPOL).

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