FIGURE 2-2 Typical ballast system.

organisms is unlikely to be practicable for existing vessels but could be an attractive option if incorporated in new ship designs.

As was noted earlier, some unpumpable ballast water always remains on board.2 This unpumpable water may form a virtually permanent layer on the bottom of a dedicated ballast tank, with the concomitant capability of supporting


 The amount of unpumpable ballast water remaining on board varies greatly because of vessel diversity. One report notes that vessels claiming to have only unpumpable ballast on board were carrying, on average, 157.7 metric tons of water and sediment (Weathers and Reeves, 1996).

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