Vessels and Ballast Water - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 21

sonal communication) and an experienced crane driver can handle also up to 30
containers per hour (Chief Offi cer Guy Mali personal communication). The number
of gantry-cranes that can be employed at a time depends on the vessel size, port/
terminal and priority of vessel. The number of container operations is also very
much related to the capacity of containers handling at the terminal. There are usu-
ally several, e.g., three to fi ve, cranes in operation at the same time., e.g., in average
the container vessel Hamburg Express when in the Port of Rotterdam handles
4,100 containers in ~24 h, what results in approx. 46,000 tonnes of cargo loaded or
discharged (Chief Offi cer Guy Mali personal communication.). In general container
vessels manage to be served by ballast water pump capacities in the range of
1.000-3.000 m 3 /h, i.e., two pumps, each 500-1,500 m 3 /h.
As the port cargo loading and unloading capacities are increasing through time
mainly with the use of newer technologies supporting faster cargo operations, newer
vessels of similar cargo capacities in general have ballast water systems of higher
capacity. An increase in ballast water capacities of new vessels can be expected also
in the future.

Ballasting and Deballasting Process

Vessels conduct ballast water operations usually in the port as opposite to the cargo
operations, i.e., when a vessel would load cargo, ballast water would be discharged,
and when more or heavier cargo is loaded on one side, ballast water would be dis-
charged from that side or loaded/moved to the other side. Ballasting and deballast-
ing may also be conducted during navigation or at the anchorage, depending on the
vessel type, weather and sea conditions, and vessel operations.
Ballast water is taken onboard by:

- gravity through opening valves which enables a vessel to take on water into bal-

last tanks (or cargo holds used for ballast) below the water line;

- pumping water into ballast tanks (or cargo holds used for ballast) above the water

line.

Nevertheless, all the water may be taken on board by pumping, instead of using
the gravity method.
The tanks are fi lled according to a predetermined sequence, depending on the
type of the vessel and current cargo operation. The ballast tanks are usually fi lled
up to maximum capacity in order to prevent the free surface effects. 4 This “rule”,

4 i.e., movements of water in the tank from side to side and hence changing centres of gravity as
well having dynamic side effects, and with this negatively impacting the transversal stability of the
vessel; this is especially important for cargo holds and wider ballast tanks; e.g., double bottom,
topside.