This involves ships without a fixed schedule or published ports of call picking up cargoes as they become available. They usually carry bulk raw or low-value materials like grain, ore, or coal, for wh [..]

Tramp shipping refers to the unfixed transportation of mostly cargoes over the water, without a fixed route, a fixed timetable and according to demand to any port

irregular sailing schedules (IE# Bulk ship)

An ocean carrier company operating vessels not on regular runs or schedules. They call at any port where cargo may be available. Sometimes used for bulk cargo shipping.