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BOX 2-1Ballast Defined Ballast is any solid or liquid placed in a ship to increase the draft, to change the trim, to regulate the stability, or to maintain stress loads within acceptable limits. For the purposes of this study, the term ballast includes the sediment that accumulates in ballast tanks, which may be discharged with ballast water.
configuration, and requirements of the ship and on the complexity of its pumping and piping systems. Ballast capacity can range from several cubic meters in sailing boats and fishing boats to hundreds of thousands of cubic meters in large cargo carriers. Large tankers can carry in excess of 200,000 m3 of ballast. Ballasting rates can be as high as 15,000 to 20,000 m3/h (see Table 2-1).
Piping is sized so that flow velocities do not exceed about 2.6 to 3m/s, with ballast pump capacities ranging up to 5,000 m3/h. There is no international standard unit of measurement for ballast; quantities of ballast are variously recorded in metric tons, long tons, cubic meters, U.S. gallons, Imperial gallons, and barrels. In this report cubic meters is used as the unit of measurement; conversion factors are given in the glossary.
Typical vessel types and their ballast needs can be broadly classified as shown in Table 2-1. There is a wide range of ballast tank locations and configurations, as illustrated schematically in Figure 2-1. The capacity, location, and flexibility of use of ballast tanks is a focal point in ship design. Consideration of required drafts and trim, hull loading limitations, and required vertical center of gravity establishes the necessary ballast volume and location. Because of different cargo distributions or fuel and water quantities on board, sister ships can have different ballast needs, even though the locations and sizes of the ballast tanks are identical.
Ideally, ship owners prefer to complete all voyages with cargo. However, many trades and voyages require passage without cargo or in a light-cargo condition. For example, a crude oil tanker or iron ore carrier typically transports a single cargo load between two ports, then returns to its point of origin or another port without cargo. In this empty condition the vessel requires ballast to operate safely—a condition referred to as being "in ballast."1 In contrast, a container ship may be fully loaded between two ports but may then proceed with only a partial load between the next two ports. This vessel, therefore, sails with some cargo and some ballast, that is, "with ballast." Since fuel costs usually increase with
Definitions of ballast-related terms are provided in the glossary.