● Barges, which are towed behind ocean-going tugs. These are used for shorter routes where
sea conditions are fairly reliable, such as between the USA and Puerto Rico. They have the
advantage of being cheaper to run than normal ships.
● Combination ships. In addition to the specialised ships, many other designs are used, often
to allow for dominant patterns of trade. Examples of such combination ships are the RO-
RO/container ships that carry vehicles imported into the USA and return with bulk grain
to Japan, and the oil-bulk vessels that carry oil from the Middle East and return carrying
ores. One useful combination is passenger/container, as the passengers are ensured
priority treatment in ports.