Various classes of cargo ships are used for the worldwide transport of goods needed in production and sold in shops. Each ship type is suitable for different sorts of cargo, sized to meet the demands of the open sea, of shallow water transit, highly specialised or general purpose.
The ships can roughly be divided into the following types:
- Dry bulk
- Liquid bulk / tanker
- Container ships
- General cargo ships
- Reefer ships
Bulk carries: These carry unpacked bulk cargo in their large holds. Dry bulk carriers hold dry goods such as ore and grains. Liquid bulk carriers are designed to carry things like oil, chemicals, and liquefied natural gas. Oil tankers are a specialised form of liquid bulk carrier. There are also combination ships that have holds to carry both dry and liquid bulk.
Container ships: They are specially built to hold compartmentalised containers. Their use has dramatically transformed sea-borne transportation, and they’ve become a favourite mode of carriage. They’re enormous vessels, and their growing size has forced ports to transform their infrastructure to accommodate both their size and their special form of loading and unloading. Their cargo includes finished products. On-board cargo is measured by Twenty-foot Equivalent Units (TEU). This unit measures the rough volume taken up by the metal boxes, or containers, that are placed within the ships, or moved to trucks and trains.
General cargo ships: These can carry a variety packaged goods, such as food, garments, chemicals, machinery, appliances, vehicles, etc. This cargo is not bundled into common containers but packaged according to need. Roll-on roll-off (ro-ro) cargo is often included in this category. Ro-ro vessels carry wheeled cargo, such as loading transport trucks that themselves carry a supply of goods.
Reefer ships: These are refrigerated ships that carry perishable goods such as meats, vegetables, and fruits.
According to a report, Review of Maritime Transport 2018, by the UNCTAD: China, the Republic of Korea and Japan together delivered 90.5% of new ships in 2017.
Dry bulk carriers, which carry iron ore, coal, grain and similar cargo, account for the largest share of the world fleet in dead-weight tonnage and the largest share of total cargo-carrying capacity, at 42.5 per cent. They are followed by oil tankers, which carry crude oil and its products, and account for 29.2 per cent of total dead-weight tonnage. The third largest fleet is container ships, which account for 13.1 per cent of the total. As container ships carry goods of higher unit value than dry and liquid bulk ships and usually travel at higher speeds, they effectively carry more than half of total seaborne trade by monetary value.United Nations Conference on Trade and Development, Review of Maritime Transport: 2018, United Nations Publications, 2018, (UNCTAD/RMT/2018), p. 23.
Dead-weight tonnage is the sum of all weight that a ship may carry: including cargo, crew, passengers, fuel, provisions, fresh water and ballast water.
All ship types have been steadily growing in dead-weight tonnage, except for general cargo, which has seen a long-term decline. This declining class of ships is aging and there are less new orders for their construction since UNCTAD began to keep such records.
Container vessels are increasingly preferred over their general cargo counterparts. According to the Review of Maritime Transport 2018, ” [i]n 1980, container ships had one tenth the total tonnage of general cargo ships; at present, container ships have 3.4 times more total dead-weight tonnage”.
Containers are often favoured because they provide certain logistical and technical advantages. Each container holds a standard volume of goods and they can be moved between various modes of transportation: from shipping, to rail, and truck hauling. This intermodal system allows for each container to be packed at the point of departure and moved from the back of a truck, to train, to ship on its way to a final destination where it will be opened for final distribution. Also, specialised containers can be refrigerated in order to transport items, such as vegetables that require temperate control. This means that the vehicle that transports containers doesn’t itself need to be specialised for the purpose of refrigeration, allowing for a broader range of cargo to be moved.
The administrative and technical arrangements surrounding the supply and value chains that span oceans and continents are remarkable. There’s been a progressive tendency toward technical complexity in tracking, planning, machinery, and intermodal compatibility that conversely eases the timely worldwide supply of time-sensitive and distributed networks of supply, production, and commercialisation.