Containers of various sizes are used in the industry and we shall now understand how they are utilised for cargoes of various sizes and types.
Size of containers
The standard containers consist of the following size: –
- 20 ft ´ 8 ft ´ 8ft,
- 20 ft ´ 8`00” ´ 8’06”
- 40 ft ´ 8ft ´ 8ft,
- 40 ft ´ 8”00” ´ 8”06”
Hi-cube containers have the dimensions of 20’/40’x8’00”x9’00”or9’06”.
In addition you will find 35 ft, 45ft and 52 ft containers. Even 57 feet containers are being tried out. Construction of the containers is explained elsewhere in these modules.
The 20 feet container is commonly known as TEU. (Twenty Equivalent Units) 40 Feet container is known as FEU (Forty Equivalent Units).
Dimensions of Containers
The container has 3 dimensions, width, height and length. Each of these is determined by various factors. There is a tendency among seafarers to think that since a ship carries a large number of containers, it is the ship that finally determines the container, but it is the other way around. The ships are adapted to fit the containers. The dimensions of the container are determined by other considerations, such as rail and road facilities etc.
Width
The width of the container is 8 ft. This is due to the fact that carriage widths on roads are between 8 ft. and 8.5 ft. with all US roads being 8 ft. This has not changed from Roman days when 8 ft. was the space required by two horses pulling a carriage. The width of the container therefore has remained constant.
Height
Container heights started with 8 ft. and have gradually risen to 9.5 ft. World over the maximum height of permitted on road transport has ranged from 3.5 m to 4m which brought about the height restriction of 8 ft. Later developments in transportation especially the lowering of rail carriages have allowed the increase of height to 8.5 ft. and then to 9.5 ft.
Length
Containers come in varying lengths ranging from 10 ft. to 45 ft. The first container was a converted trailer, which was 20 ft., and hence the 20-ft. length became the common size. Matsons (one of the earlier container companies) started with 24-ft. containers because of California regulation allowed 2 x 24-ft. trailers as one unit. This size is still current in the Alaska trade. Sea-land started with 35-ft. containers but has slowly switched over to the standard ISO 20-ft. size. The next size that has come about is the double of 20 ft. the 40-ft. and thence the 45-ft. 52-ft. and 57-ft container are under consideration by the International Standards Organisation in draft stage. These changes have come about as road regulations permitted such increase in trailer lengths on account of the advances in road transport technology.
Types of containers
The GP or general purpose container accounts for the large majority of the fleet and is used for most general cargo commodities. The containers are 20 ft or 40 ft in length with a limited stock of 45 ft.
The standard external height of GP containers is 8 ft 6 inches although high cube containers at 9 ft 6 inches in height are becoming common.
Special containers are provided for specific carriage requirements and examples are listed below.
| Type | Sizes (In feet) | Characteristics | Typical uses |
| Open Tops | 20/40 | Soft detachable roof tarpaulin or tilt | Machinery requiring top loading and overheight cargo. |
| Half Heights | 20/40 | Soft detachable roof tarpaulin or tilt, half height | High density cargoes such as ingots, heavy steelwork, drums. |
| Flatracks | 20/40 | No sidewalls or roof (and ends may be collapsible) | For out of gauge cargoes and restricted loading situations. |
| Platforms | 20/40 | Flatbed with corner castings. Limited numbers of high rated equipment | Over-length cargoes and special projects. |
| Fantainers | 20/40 | Extractor fan fitted | Agricultural products requiring ventilation e.g. onions, potatoes. Also used as a normal GP container. |
| Highly Ventilated | 20 | Side vents along top and bottom rails | Hygroscopic cargoes such as coffee, cocoa, tobacco and seeds. |
| Top Ventilated | 20 | Side vents along top rail | Hygroscopic cargoes such as coffee, cocoa, tobacco and seeds. |
| Open Sides | 20 | Side gates and side curtains | Agricultural products requiring ventilation, livestock and side loading. |
| Bulk | 20 | Top loading ports and door discharge shoot | Dry cargoes in bulk e.g. malt, sugar also used as a normal GP container. |
| Tank Containers | 20 | Tank within an ISO frame of various types | Liquid cargoes in bulks including foodstuffs and hazardous. |
| Refrigerated – Integral | 20/40 | Refrigerated Integral | 8’6″ and 9’6″ |
| Refrigerated – Insulated | 20, (8’ and 8’6”) | Top & bottom end ports and connects to ships refrigeration system | Reefer cargoes on specialised ships operating in ANZ and SAF Trades. |
Markings on a container
The most visible markings on a container are the company name/logo. In addition the following are required by law and the practice of the trade:
- Name of the Owner or Shipowner with number.
- Tare weight, Gross weight, Net weight and Cubic capacity.
- Dimensions.
- Date of Survey.
- Date of Manufacture and Manufacturing Number
- Refurbishing Date wherever applicable.
Other than this, the important markings are:
- the identification number (BIC code)
- the allowable weights and cubic capacity.
- the safety approval plate (see annex I), and
- the customs approval plate.
The ISO code
The ISO 2176 provides for a marking code for international identification of containers. The markings give information of the owner, the number, size and type of container. The National Registration Organisations and The International container Bureau have developed the BIC code, which identifies a container through Owner code and serial Number. These can be verified by check digit and are registered with the Bureau.
The ISO standard has a four-alphabet code for the owner, the BIC code uses 3 alphabets to identify the owner and the fourth alphabet is U, which means a registered owner. Others can use other alphabets as the fourth one. Today nearly all owners are registered and hence all owner identification ends in a ‘U’. The container number consists of 6 digits followed by a seventh digit in a square called the check digit. This check digit is the verification of the identification. The check digit is computer calculated in data processing.
The next is a 2-alphabet code denoting the country of certification and a 4-figure code, which gives the size, & type of the container.
A B C U X X X X X X X
D E X X X X
Allowable Weights and cubic capacity
All containers are marked with the tare weight and maximum gross weight of the container in both kilograms and pounds. The internal cubic volume available for loading in both m3 and ft3 is also marked. This is as per ISO standards.
Safety approval plate
This is as per the CSC convention. It includes the BIC code markings. Additionally every container has to carry a CSC SAFETY APPROVAL PLATE as shown in the diagram. The plate size is 200 x 100 mm. and contains 9 lines of markings.
Customs approval plate
This is plate certifies that the container is permitted to be carried under customs seal.
Materials used in manufacture of containers
Containers are built on a steel frame, the cladding may be constructed either of steel or aluminium or Glass fibre reinforced plywood. A majority of the containers are steel cladding with aluminium cladding a close second. GRP clad containers are few in number.
Steel
This is very widely used because of its easy availability and cheap price. Containers of steel are easy to construct as steel is easily welded. The other advantages of steel containers are less susceptibility to damage, & ease of maintenance. The disadvantages of steel are that it is prone to corrosion and hence requires to be regularly painted. Its tare weight is high and life of the container is short, about 10 to 15 years. The use of special alloys like CORTEN steel has reduced the disadvantages. Corten steel is less susceptible to corrosion than ordinary mild steel. It is high tensile steel and hence permits lower scantlings thus reducing the tare weight. It compares quite well with the tare weight of Aluminium. Cost wise, a steel container is the cheapest and most leasing companies uses steel containers.
Aluminium
It is the lightest container due to low weight of aluminium. Aluminium also does not corrode easily in a marine environment and therefore maintenance is not required so frequently. Its disadvantages are that it is easily damaged. (An impact, which will only dent a steel container, will probably create a hole in an aluminium container). The repairs of aluminium containers are expensive as it cannot be welded and repairs are by riveting. Riveting is expensive and not available worldwide. United States is the only place where riveting is cheaper. Aluminium containers are more expensive than steel but have a longer life, proximately 15 to 20 years.
GRP
These are containers where the panels are made of GRP. These containers are practically corrosion free, offer better use of internal space. The disadvantages are that their tare weight is the highest, Repairs are costly as any damage means replacing the whole panel. They are the costliest containers. They are generally used for thermal containers as they provide good thermal insulation. Life of a GRP container is the longest among the three, about 25 years.
Types of containers
Over the years containers have evolved into various types depending on their use. The first container was a basic closed box. This is called the ‘dry box’ and majority of the containers available today is of this type. Some cargoes are such that loading them through the door is not practicable and to accommodate such cargoes as well as to containerise cargoes whose height exceeds the standard container height, the roof of the container has been omitted and these are called ‘open top’ containers. The problem with open tops is that on the return leg they can not be used as dry boxes. To overcome this and to make optimum use of the container a canvas top was developed. This is sometimes called a soft-top and can be used as both a dry box as well as an open top. To containerise other cargoes, which exceed athwartship dimensions, open sided containers are also available. Containers are also available with side doors for loading cargo of long lengths that can be loaded in the containers. Thus it is possible to have a container with only the floor and the end frames, such frames are generally made collapsible and this is called a collapsible flat rack (COFLAT). It can be used both with the frames up and as a flat rack with the end frames down. Flat racks without the end frames are also available and are called artificial tween decks (ATD). These are used for carrying large bulky pieces, which require more than one container space, like project cargoes and machinery. The topmost tier loaded either under deck or on deck is used for this purpose. The ATDs are placed on top of the last tier to create a deck and this cargo is loaded over two or more rows as required. The ATDs ensure that the weight of the cargo is divided over all the rows used. These are variations of the basic box.
The other types of containers available are those used for specific purposes or cargoes. Here we have reefers, tank containers, and even garment containers or hangertainers where garments are carried hung on rails at the top of the container. The dry box is also available with ventilation and is called a ventilated dry box. Special containers are also available for bulk cargoes; these have loading openings in the roof and discharge chutes either at the bottom or sides.
The four corner pillars of the container take the entire weight of the container & the cargoes stowed inside. The container should always be lifted with the help of a spreader. The spreader is placed on the container with its corner on the top of the corner pillars of the container and locked. This lock is called as Twist lock operated either manually or automatically.