Liquids in bulk
Ore-bulk-oil carriers
Tankers and bulk carriers almost invariably carry cargoes one way only, and the return voyage to the loading port is made in ballast, earning no money. These ships are also vulnerable in times of a recession in their particular trade, as they are not flexible enough to carry other types of cargo. The combination ore-bulk-oil (or OBO) carrier was developed in answer to both these problems. The OBO has gas-tight holds which can load either bulk cargoes such as ore and coal or crude oil. These ships can be recognised because on deck they carry a row of hatches to load and discharge the bulk cargo and also have smaller hatches and the associated pipe work to load oil. Equipping a ship for two types of cargo inevitably means that OBOs are more expensive to build and maintain than pure bulk carriers or tankers, and a compromise cannot be as efficient as a dedicated design. In addition, flows of ore or coal and oil are rarely complimentary to each other, so OBOs tend to specialise in one or the other. Being able to switch to whichever trade is more profitable is useful, but the availability of many OBOs means that ships switching rapidly depressed freight rates in the alternative trade. For these reasons, building OBOs has become less popular of late.
|
