There are many different sizes and types of containers in the world today. The two most basic and common are the 20 foot and 40 foot. One 20ft until equals 1 TEU (Twenty Foot Equivalent Unit) and one 40ft until equals 2 TEU. This is important to know as vessels sizes are described based on the maximum number of TEU they can carry.
The standard height for containers is 8’6” but there are variations called 40ft High Cubes that are 9’6” high. The standard width for containers is 8’0”. 45 foot containers are always 9’6” high (diagram bottom left). Overleaf is a list of the new ISO codes in use and the different types of containers.
As container shipping evolved, containers began to be developed for specific cargos or trades. Thus the standard 20 and 40ft units are just the tip of the iceberg when it comes to container types.
This wider range of container types also allowed shipping lines to charge additional premiums based on the container used. For example, a refrigerated (Reefer) container is much more profitable than a container holding only dry cargo.
Containers have to be loaded onboard a vessel in a specific sequence in order to maintain their structural integrity. Below are examples of how containers cannot be loaded without risk of the stacks on deck collapsing.
The correct manner of on deck stowage is shown in this diagram. Containers maintain their structural integrity through the corner posts. There is very little strength in the walls or roof of the containers.
The pattern of container stowage on deck also depends on the construction of the hatch cover. Some vessels have the ability to stow 40ft units on top of 20ft units on deck, this is known as Russian Stowage. Other vessels cannot do this. In the latter case, it is important for the stowage coordinator to stow as many of the 20ft units underdeck as possible, otherwise this will start to reduce the possible cargo intake of the vessel since 20ft units can be stowed much higher underdeck than they can on deck.
Other Container Examples
Refrigerated containers (Reefers) container cargo that has to be maintained at a specific, and constant, temperature (often foodstuffs). The container itself is fitted with its own motor that maintains the containers internal temperature.
These motors have to be connected to the vessels power supply in order to run. Each vessel will have a number of reefer dedicated bays that are fitted with power connections. Not every slot onboard will have this power connection so each vessel has a limit as to how many reefers can be loaded.
Reefer containers have a very high profit margin for the shipping line so it is very important for the stowage coordinator to be able to stow as many of these units onboard as is practical. On some trades (such as from South America) it is the reefers that drive the trade and thus the stowage. Often, the carriage of reefer containers is a seasonal thing as it is dictated by the various fruit growing seasons.
Due to the fact that the containers are connected to a power supply, the reefer motor is considered an “ignition source” and this must be taken into account when loading Hazardous Containers in close proximity. (See Hazardous Cargo notes).