Classifying cargo ships

Considering the diversity of cargoes that are carried across the world every day, one would expect there to be a wide variety of different types of cargo ships and that is indeed the case. Generally speaking, there are different ways of classifying cargo ships based on types, whether they sail regular schedules or not and their size. We discuss these different classifications in this section.

Types of cargo ships

The following the different types of cargo ships you are likely to encounter in international trade:

Tankers
These ships are designed to carry liquid cargos such as oil, petroleum, certain types of chemicals and other types of viscous cargoes (even wine). Those that carry oil cargos are commonly termed ‘oil tankers’ and if they are big enough, they are also called ‘supertankers’. Tankers can range in size from several hundred tons, designed for servicing small harbours and coastal settlements, to several hundred thousand tons, with these being designed for long-range haulage. A wide range of products are carried by tankers, including: Oil tankers take long to load and offload their cargos and the larger ones can only enter special ports designed to deal with their enormous size.

Container ships
Perhaps one of the most common type of merchant vessel you will encounter is the container ship which has been specially designed to carry containers. The may sometimes be termed ‘box ships’ because they carry boxes (i.e. ‘containers’). Some container ships are equipped with their own container cranes and can therefore load and offload their own containers, while others don’t. Container ships can be load/offloaded quite quickly and most ports today are equipped with container-handling facilities. These vessels are seldom small ships and are quite large.

Click here to learn more about containerisation.

Ro-Ro
So called because they are roll-on/roll-off ships where cars and trucks are driven directly into the hold of this vessel across a ramp usually at the back or stern of the ship. These ships have very high sides and look somewhat ungainly in the water (almost as though they are top-heavy). The design is intended to protect the cars that these ships carry from countries such as car-producing countries such  as Japan, Korea, France, Germany, the US, etc. to their markets around the world. Notwithstanding the large numbers of cars these vessels carry, they can be loaded and offloaded quite quickly.

General cargo ships
Common in the early part of the last century before the advent of the container, general cargo ships still ply the seas today. These are ships that have holds for carrying general and break-bulk (non-containerised) cargos and for this reason they may also be referred to as break-bulk ships. These ships are often equipped with their own gantry cranes and are capable of loading and offloading their cargos themselves. They complement container ships by carrying cargo that won’t fit a container, as well as cargos that are too small for a full container load (referred to as less-than full container load or LCL). Palletised cargos may also be carried aboard such general cargo ships and, of course, there is nothing stopping them from carrying containers as well. They take longer to load because the varying nature of their cargos and one can expect longer port times with this type of vessel.

Bulk carriers
As the names suggests, these types of vessels are designed to carry bulky cargos, usually grains (such as maize) and ores (such as coal). They generally do not have their own cranes, but some do. They can also be recognised by the large box-like, raised hatches on their deck, designed to slide outboard for loading. Bulk carriers can be quite big ships and they take some time to load/offload. Bulk carriers can be wet or dry. The cargo in a wet bulk carrier is open to the elements.

Reefer ships
These are ships designed to carry perishable cargos  that require refrigeration or some form of temperature control such as fruits, meat, fish, vegetables, dairy products and other foodstuffs. They may be split into two categories; those with side doors that are lowered to the quay and serve as loading and discharging ramps for forklifts; and those that have a traditional cargo operation with hatches and cranes/derricks well suited for the handling of palletised and loose cargo. In the rear of the side door there is a double pallet elevator, which brings the cargo to the respective decks. This special design makes the vessels particularly well suited for short distance trade.

Chemical carriers
Some chemicals need to be transported in specially vessels specifically designed to handle the chemical in question (such as natural gas). These types of ships are very specialised and are not that common.

Mail and supply ships
These are not very common and they are designed to deliver mail, supplies and sometimes people to remote locations. Perhaps the best-known of these is the RMS St Helena that takes cargo/mail/supplies from the UK and South Africa to the island of St Helena.

Liner versus tramp ships

A (freight or cargo or ocean) liner is a cargo ship sailing on a regular schedule, as opposed to a tramp ship which does not have a fixed schedule or published ports of call. Tramp ships (also called tramp freighters or sometimes even tramps steamers although steam ships are seldom seen today) trade on an ad hoc basis depending on whatever cargo is required to be shipped wherever.

Ship sizes
Cargo ships are categorised partly by their capacity, partly by their weight, and partly by their dimensions (often with reference to the various canals and canal locks through which they can travel). Some common categories include:

• Handysize refers to a dry bulk vessel or product tanker with deadweight of 15,000–50,000 tons. Handysize is the most widespread size of bulk carrier, with nearly 2000 units in service for a total of 43 million tons of carriage. Very flexible, they also tend to be the oldest of the bulk carriers. Sometimes the smaller of these vessels carrying 20 000-28 000 deadweight tonnage are referred to as ‘Small Handysize’.
• Handymax is a naval term for a bulk carrier, typically between 35 000 and 60 000 deadweight tonnage (DWT). A handymax is typically 150-200 meters (492-656 feet) in length, though certain bulk terminal restrictions such as those in Japan mean that many handymax ships are just under 190 meters in overall length. Modern handymax designs are typically 52 000-58 000 deadweight tonnage in size, have five cargo holds and four cranes of 30 metric ton lifting capacity.
• Seawaymax refers to vessels which are the maximum size that can fit through the canal locks of the St Lawrence Seaway that link the Great Lakes with the Atlantic Ocean. Seawaymax vessels are 740 feet in length, 78 feet wide, (maximum 226 m length, 24 m beam) and have a draft of 26 feet (7.92 m).
• An Aframax ship is an oil tanker with capacity between 75 000 and 120 000 deadweight tonnage. Aframax tankers are mostly employed in the intra-regional trade of the North Sea, the Caribbean, the Far East and the Mediterranean. The term is based on the Average Freight Rate Assessment (AFRA) tanker rate system.
• Malaccamax is a naval term for the largest ships capable of fitting through the Straits of Malacca between Singapore and Indonesia. A Malaccamax ship is defined to be, with 18 000 TEUs, of 300 000 deadweight tonnage, 470 m long, 60 m wide, and 20 m of draft. The restriction is caused by the shallow point on the Strait, where minimum depth is 25 m.
• Suezmax is a naval term for the largest ships capable of fitting through the Suez Canal fully loaded, and is almost exclusively used in reference to tankers. Since the canal has no locks, the only serious limiting factor is draft (maximum depth below waterline). The current channel on the canal allows for 16 m (53 ft) of draft (or depth), meaning many supertankers are of too deep to fit through. Currently, the canal is being deepened to 18 - 20 m. The typical displacement of a Suezmax ship is 150 000 tons. Of note is the head room limit of 68 meters by the Suez Canal bridge. There is also a width limitation of 70.1 meters, but only a handful of tankers exceed this size, and they are excluded from Suez by their draft in any case.
• Panamax ships are of the maximum dimensions that will fit through the locks of the Panama Canal. This size is determined by the dimensions of the lock chambers, and the depth of the water in the canal. Panamax is a significant factor in the design of cargo ships, with many ships being built to exactly the maximum allowable size, which is length: 294.1 metres (965 ft); width: 32.3 metres (106 ft); draft (depth): 12.0 metres (39.5 ft) in tropical fresh water (the salinity and temperature of water affect its density, and hence how deeply a ship will sit in the water); and height: 57.91 metres (190 ft) measured from the waterline to the vessel's highest point. A Panamax cargo ship would typically have a displacement of around 65 000 tons.
• Capesize ships are cargo ships too large to traverse either the Suez Canal or Panama Canal (i.e., larger than both panamax and suezmax vessels). To travel between oceans, such vessels must round the Cape of Good Hope (South Africa) and Cape Horn (South America). Capesize vessels are typically above 150,000 deadweight tons, and ships in this class include VLCC and ULCC supertankers (see below) and bulk carriers transporting coal, ore, and other commodity raw materials. The term is most commonly used to describe bulk carriers rather than tankers, however.
• VLCC (Very Large Crude Carrier), supertankers between 150 000 and 320 000 deadweight tonnage
• ULCC (Ultra Large Crude Carrier), enormous supertankers between 320 000 and 550 000 deadweight tonnage.

Other shipping facts

You should note that ‘tonnage’ is a measure of the size or cargo capacity of a ship, while deadweight tonnage (often abbreviated as DWT or dwt for deadweight tonnes) is the displacement at any loaded condition minus the lightship weight. It includes the crew, passengers, cargo, fuel, water, and stores. It is often expressed in long tons or (more commonly) in metric tons.

Merchant ships are any seagoing ships that are commercially exploited and include cargo ships, passenger ships, dredging vessels, pontoons, drilling rigs, etc. A merchant ship is not just a cargo ship, therefore, and you need to distinguish be more specific by referring to cargo or freight ships.

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