Various cargo handling techniques for seagoing general cargo ships

Various cargo handling techniques for seagoing general cargo ships

Planning and control of cargo handling

The techniques of cargo handling have, at least in ocean transport, developed considerably over the last decades. This is particularly due to:

(a) Technological advances in ship design and lifting equipment

(b) Rapid development and increase in the tonnages of bulk cargo

(c) The impact of unitisation, and

(d) The new and modern techniques of refrigeration, particularly with container carriage.

It is shippers, as a group, which have been influencing these developments. The requirements for efficient transport have led the transport industry, port authorities, shipowners etc., to develop new concepts for ship technology and cargo handling. It is up to the individual shipper to utilise the available methods of transport and cargo handling, in order to be competitive in the international markets. As a minimum, requirements must be properly defined by shippers so that the most appropriate services may be made available by the carrier.

The shipper will have to prepare consignments for transport. The handling and storage of cargo is not his immediate responsibility, but as it will influence the total transport cost and quality, shippers' will have to ascertain that the best available methods are provided and used. While in transit, commodities are represented by documents. It is in the shipper's interest to see to that the paper work is handled efficiently.

Cargo preparations

Some sort of packaging will normally be a prerequisite for carrying commodities as general cargo, especially in break bulk. Packaging has at least three functions:

(a) To protect the goods;

(b) To keep a consignment together;

(c) To prevent the goods from damaging the environment.

Transport usually subjects the cargo to mechanical forces (shocks, vibrations, pressures) and/or climatical forces (temperature, moisture). At least for a conventional shipment, the packaging needs to be strong enough to withstand the rigours of stowage and multiple handling.

Goods which are not packed properly may damage other goods in the same transport. In such cases the shipper may be liable. Paper and carton are traditionally mostly used in local transport, where the risk of damage is usually smaller. Plastic and especially jute are used to produce bags. Bags are commonly used to pack traditional bulk commodities in small quantities, like cement, sugar or grain. Wood is still common to make cases or crates. Drums and barrels are made of metal or plastics and are used for transport of liquids in small lots.

The shipper has to follow procedures laid down by public authorities as well as commercial practice with regard to packaging, marking and declarations of contents.

The marking should embrace at least the following:

(a) Destination: Address of the end receiver, transhipment, order-number.

(b) Handling instructions: Especially with fragile commodities it is important to mark the package with handling directions to avoid breakage and other damages. To avoid language difficulties a set of internationally recognised signs are developed for cargo marking.

(c) Dangerous goods: Some goods are classified as dangerous. In general, goods are regarded as dangerous if they have chemical or physical properties which can damage other goods, materials or the environment. Examples are explosives, flammable liquids or gases and poisons.

IMO, the International Maritime Organisation, has worked out rules for the handling of dangerous goods at sea in conventions which have been ratified by most member countries. These rules incorporated in the IMDG code contain regulations regarding packaging, marking and labelling, stowage requirements, etc. for various types of explosives, gases, and various types of inflammable materials.

Cargo loading and discharging The rate at which cargo is loaded aboard or discharged from a ship has a significant bearing upon the overall cost of transport. Excessive time in port deprives consignees of the use of their goods, and ship operators of the use of their vessels. Therefore, the improvement of cargo handling methods has been a constant aim of many of those concerned in the operation of ships.

Every cargo handling or transfer system consists of a number of identifiable elements. Goods are moved from one place to another, such as a quayside storage area and a ship's hold. Then there is the commodity itself, which may take many forms, as already described.

Finally, there is the medium by which the cargo is transferred, which may be manual labour, specially designed equipment or some combination of the two. In an efficient system, these four elements must be properly matched. This implies a certain cooperation between the port authority, the shipowner, the shipper, and the possible stevedoring company engaging the port labour.

The earliest efforts to increase cargo handling rates were concentrated mainly on the transfer medium, and led to the development of a wide range of mechanical equipment, such as cranes, conveyors etc., which has substantially improved loading and discharging rates, especially for bulk cargoes. General cargo handling has, however, not benefited to such a great extent from such developments.

In liner shipping, the principal restriction to high handling rates has always been the large variety of packagings used for general cargo, so that significant improvements have only become possible by reducing the number of different forms in which goods are presented for shipment.

Thus it is only with the adoption of unitisation that general cargo carriers have achieved high transfer rates and been able to take advantage of handling techniques similar to those which have been developed for homogeneous cargoes. It is customary to distinguish between vertical and horizontal loading of ships as well as other means of transport. With vertical loading, the cargo must pass over the rail of the ship and into holds through hatches in the deck.

Derricks, cranes and conveyor belts are commonly used for the transfer of dry commodities. Liquids and gases are moved through pipelines. This traditional method is very useful for the handling of bulk cargoes.

Horizontal loading of cargo is done through openings in the bow, side or stern of a ship. These ships are commonly referred to as roll-on/roll-off (Ro/Ro) ships as the cargo can be accepted on wheeled vehicles. Flexibility and fast port turnarounds are the essential feature of Ro-Ro operations, and cargo handling rates can be significantly increased.

Discharging door of a Ro/Ro ship

Fig: Discharging of a train coach via the stern door of a Ro/Ro ship

Not all horizontal loading ships are strictly Ro-Ro ships. Pallet carriers may, for example, have side doors only and the cargo is loaded or discharged by fork-lift trucks operating on the quayside.

Summarized below some more details on general cargo ship cargo handling procedure and operational info:

Cargo handling procedure for heavy indivisible loads

Various cargo handling techniques for seagoing general cargo ships

Machinery system main info pages