Which of the following is NOT a concern for an OBO vessel?

An OBO (Oil/Bulk/Ore) vessel is designed for the transportation of various types of cargo, specifically oil, bulk materials, and ore, which means versatility is actually a key feature of such vessels. Therefore, versatility cannot be considered a concern for an OBO vessel. Instead, the design and operational flexibility to switch between different cargo types is one of its fundamental advantages.

The other options relate to specific operational challenges and considerations in the management of an OBO vessel. Carrying different types of cargo can complicate operations, particularly in terms of contamination risks and the necessity for adequate cleaning procedures. Ballasting involves managing the weight and stability of the vessel, which is critical for safe navigation, especially when changing between cargo types. Tank cleanliness is essential to prevent contamination when carrying oil, bulk materials, and ore successively. Thus, while versatility is a valuable attribute of OBO vessels, the other concerns are critical in ensuring safe and efficient operation.