Vessels and Ballast Water - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 18

Fig. 7 Discharge of ballast water below the water level from a container vessel
It is absolutely critical to know how much ballast is in each tank to be able to
provide for the vessels seaworthiness. On older vessels these measurements are
done via sounding pipes (see Fig. 6 ), and then by means of sounding tables, the
quantity of ballast water can be calculated. Most modern ships are equipped with
instruments that enable automatic measurements of the quantity of ballast water in
ballast tanks, while these still need to be equipped with sounding pipes to allow
direct measurements in the case of automatic system failure.
Ballast water is discharged through the overboard discharge, which is on most ves-
sels situated below the water level (see Fig. 7 ). On some vessels ballast water discharge
is situated above the water level, and mainly on bulk-carriers ballast water can be dis-
charged directly from the topside tanks high above the water level (e.g., see chapter
“ Ballast Water Sampling and Sample Analysis for Compliance Control ”, Fig. 4 ) .
Vessel Ballast Capacity
The vessel ballast capacity is mainly determined by the vessel cargo capacity in
terms of cargo weight, and the speed at which the cargo operations may be
conducted. Generally, the more tonnes of cargo a vessel is capable to carry, the more
ballast may be needed when sailing without cargo on board, and if the cargo opera-
tions on a vessel are very fast, then the ballast uptake or discharge has to be corre-
spondingly fast. The ballast water capacity of a vessel is given in terms of volume
of spaces that are available for ballasting expressed in m 3 , and in terms of the ballast
pumps capacity expressed in m 3 /h.