bulkheads. On a designated voyage between scheduled ports, the ballast water loaded in a port might be able to be held on board and discharged again at its origin. If ballast water loading were necessary in one port, the ballast could be retained on board until the next visit to that port. However, the inventory control requirements of such an operation, coupled with unpredictable cargo and weather-related ballast requirements, would probably render this approach impractical in most cases.