TT Talk - Growing convergence of interests

It can be difficult to have relevant perspective when developments inevitably take time to come to fruition, but the last six months has been quite remarkable in the maturing of safety awareness in the unit load industry. This is most welcome, since the Club has regularly, over the last decade and more, raised concerns from its claims experience relating to the correct stowage and securing within 'cargo transport units' (CTU), and declaration of weight and contents.

One immediate catalyst for the current debate has been the publication of the ‘Lashing@Sea’ report by the Maritime Research Institute Netherlands (MARIN), which was the conclusion of a three year research project initiated in 2006. The primary focus of the report - as its name suggests - was a review of lashing and securing on board ships (ro-ro and heavy lift as well as container ships). The findings of the research demonstrated that otherwise sound securing practices are vulnerable to conditions beyond the design parameters. Key among the causes of stow instability were the unreliability of container weight information and vertical weight distribution errors due to inappropriate stow sequence. These lead to extreme GM load conditions that additionally challenge bottom tier container integrity, where information and monitoring systems available to the ship's crew need improvement.

One of the recommendations, therefore, was that gross mass should be measured and used in ship planning. The benefits that could be derived by the international supply chain ensuring that what is put into the chain is accurately known are incontrovertible. The maritime legal infrastructure has long existed that is capable ofbeing used, with little modification but appropriate policing, to achieve enhanced compliance for that mode. This is likely to lead to greater adherence to good practice in related issues in cargo management, improving both safety and security throughout the supply chain.

Furthermore, one of the chief benefits of the unit load concept is that the cargo being carried is not handled individually throughout its transit. Thus, if a change in law or culture can ensure that cargo is accurately weighed when it reaches the maritime mode, it is likely to be effectively measured at the point of stuffing the unit.

This edition of TT Talk therefore focuses on some of the important developments. However, first, it is worth offering some definitions to improve the differentiation of terminology and concerns.

(i) Misdeclaration of gross mass, over or under, can erode or even compromise the safety of the conveyance on land, impact stack stability, both ashore and at sea, and impact the stability of the ship itself. Containers may be stacked too high or too low for their correct mass, or inappropriate decisions taken in relation to other CTUs in the supply chain.

(ii) An overweight CTU is one where the gross mass exceeds the permitted maximum axle loading for road and rail systems in individual countries. Where the CTU enters the supply chain and reaches a transport system that has known maximum gross mass limitation below that of the laden unit, it is correctly stated as 'overweight'.

(iii) Where the payload of a laden CTU is such that the mass exceeds the rated maximum gross mass of the unit, it is overloaded. This relates to 'safe working loads' and may impact equipment other than the CTU itself. The issues discussed here relate primarily to 'misdeclaration' of gross mass at the point at which a CTU is entered into the supply chain. While such a unit may, rarely, also be 'overloaded' in relation to the capacity of the unit or 'overweight' in relation to one or more parts of an intermodal movement, this is not the focus of this edition of TT Talk.

The term 'CTU' is used to mean 'Cargo Transport Unit', comprising in this context both freight containers, as well as road/rail freight vehicles used in ro-ro operations. It is also technically necessary to draw a distinction between 'weight' and 'mass'. 'Mass' relates to the property of object regardless of its environment. 'Weight' denotes either mass or the force of gravity acting on it. Thus, the forces involved during an ocean voyage (particularly pitch or surge) will materially change weight, although the mass will be consistent. However, this TT Talk will use the two words synonymously but relating to the meaning of 'mass'.

Staff Author

TT Club