What is the term for a vessel that runs on demand without a fixed schedule?

The term "tramp" refers to a type of vessel that operates on a flexible schedule, transporting cargo as required rather than adhering to a set route or timetable. Tramp vessels are often employed in the shipping industry to deliver cargo to various ports based on demand, making them versatile and adaptable to the needs of different clients. They typically take advantage of fluctuating market conditions, which allows them to optimize their routes and cargo loads according to current shipping requirements.

The other vessel types listed serve more specific purposes. For example, container ships are specifically designed to carry standardized cargo containers on fixed routes and schedules. Barges are flat-bottomed boats primarily used for transporting goods on rivers and canals, often lacking their own means of propulsion. Ferries operate on established routes, regularly transporting passengers and sometimes vehicles between two points. Understanding these distinctions clarifies why "tramp" is the correct choice for a vessel that runs on demand without a fixed schedule.