7.5 FACTORS DETERMINING QUANTITY OF BALLAST DISCHARGED

7.5.1 Ballast capacity of vessels

The differences in ballast capacity between vessel types is considerable. Table 11 shows the average ballast tank capacity as percentage of dwt for different vessel types.

Vessel dwt of commercial vessels can range from 30,000 to 250,000 dwt. The average dwt of vessels entering Victoria's four main ports ranges from about 25,000 dwt for Port of Melbourne to 100,000 dwt for the Port of Hastings³⁶¹

Vessel type is also indicative of the types of cargoes carried and vessel ballasting practices.

TABLE 11
Vessel type and ballast tank capacity

Vessel Type	Average Ballast Tank Capacity as a percentage of dwt
Roll on, roll off vessel	38%
Bulk Carrier	41%
Tanker	26%
Container	30%
General Cargo	35%

Source: Walters, S. (1996), Ballast Water, Hull Fouling and Exotic Marine Organism Introductions via Ships - A Victorian Study, Publication 494, Environment Protection Authority (Victoria), p47.

7.5.2 Vessel type and loading activity

The Committee notes that although there is a clear relationship between vessel type and ballast discharged for example, roll on, roll off vessels commonly both load and unload cargo during a single visit and do not need to discharge ballast - the most significant determining factor for quantity of ballast discharged is whether a ship loads or unloads cargo, or both. The amount of cargo loaded or unloaded will also influence the quantities of ballast discharged. Table 12 shows total vessel visits by various vessel types to Victorian ports. This information is also useful when considering ballast management plans and the ability of various types of vessels to undertake ballast management measures.

TABLE 12

Total vessel visits by vessel types to Victorian ports for 12 months, July 1994 to August 1995

Vessel Type	Melbourne	Geelong	Hastings	Portland
Roll on, roll off	942	2	67	-
Container	906	-	1	-
Tanker	225	158	151	9
General Cargo	243	37	5	-
Bulk Carrier	181	145	27	156
Other	154	-	7	-
Totals	2651	342	258	165

Source: Walters, S. (1996), Ballast Water, Hull Fouling and Exotic Marine Organism Introductions via Ships - A Victorian Study, Publication 494, Environment Protection Authority (Victoria), p. 119.

7.5.3 Number of vessels visiting Victorian ports

Ostensibly, the amount of ballast water discharged into respective Victorian ports is influenced by total ship visits to each port. Figure 6 and Table 10 show, however, that the quantity of ballast discharged into each port is in fact not determined in the main by vessel visits. Rather, the loading activity : ballast ratio is the determining factor. Indeed, a comparison of Figure 5 with Figure 6 illustrates the relationship between loading activity (reflecting port trading patterns) and ballast discharged. Thus, the Port of Melbourne receives the greatest number of vessel visits, yet the Port of Hastings receives the greatest volume of ballast water.

Notwithstanding the importance of the loading activity : ballast ratio, the Committee emphasises that the number of ship visits is an important contributing factor to the risk of organism transfer via hull/marine fouling³⁶²

The contribution of hull fouling to the introduction of exotic organisms into Victorian coastal waters is significant, and may be a more effective vector for organism transfer than ballast water itself³⁶³ Hull fouling and organism transfer is discussed more fully in Chapter 3.

7.5.4 Individual vessel ballasting practices

Ships do not necessarily empty all their ballast tanks upon berthing. The quantity of ballast discharged will depend on such factors as:

· whether the vessel is loading or unloading cargo, or both;
· weight of cargo;
· cargo distribution on-board the vessel;
· weather conditions; and
· other factors affecting trim and list³⁶⁴

7.5.5 Summary

The Committee finds that port trading patterns ultimately determine both the likelihood, and quantities, of ballast discharge. In general, port trading patterns are determined by whether the port imports or exports cargo and the types of cargo handled (which influences vessel type and dwt). In addition, the Committee notes that the size of vessels entering port and therefore the ballast capacity of vessels - is also determined by individual port receiving facilities and draft allowance of port channels.

FIGURE 6
Ship visits and estimated ballast water received by Victorian Ports, August 1994 to July 1995

Source: Walters, S. (1996), Ballast Water, Hull Fouling and Exotic Marine Organism Introductions via Ships - A Victorian Study, Publication 494, Environment Protection Authority (Victoria).

The number of vessels needing to discharge ballast as a proportion of total vessels visiting therefore differs from port to port. The majority of ships, for example, which enter the ports of Hastings and Portland load cargo. Ships which load cargo are more likely to discharge ballast than those which unload cargo or both load and unload cargo³⁶⁵ It follows, therefore, that a greater proportion of the ships visiting Hastings and Portland discharge ballast, than those visiting the Port of Melbourne where most vessels both load and unload cargo.

The Committee finds that the number of vessels needing to discharge ballast upon arrival in a Victorian port will not constitute every ship visit to Victoria. In addition, for those ships which do discharge ballast, not all ballast tanks are necessarily filled and every filled tank is not necessarily emptied. The Committee observes that in a number of submissions to the Inquiry, the assumption has been made (or is implicit) that every ship visiting Victoria discharges ballast water. This may give a distorted view of the magnitude of the task of ballast water management and monitoring.

The Committee finds that the number of ships needing to take remedial action as part of a port ballast management plan upon entry to Victorian ports is likely to be relatively small if the following vessels are eliminated from management calculations:

· ships which do not intend to discharge ballast,
· ships carrying ballast which (following rudimentary risk assessment) are deemed not to pose a high risk to Victoria, and
· ships which have properly exchanged their ballast at sea.