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:
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
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.
|Did you know: The largest tankers can carry over
300,000 tonnes of oil, enough to heat an entire city for a year?
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
|Did you know: The latest generation
of container ships can carry the equivalent of
10,000 heavy trucks?
Click here to learn more about containerisation.
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.
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.
|Did you know: The largest bulk
carriers can transport enough grain to feed nearly
four million people for a month?
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
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
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.
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
- 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
- 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.