Boxes in boxes

This is a serious matter for a business which is characterised by tight time schedules and complex logistics chains, where delays often have a direct impact – not only on financial results and reputations but also on the entire transportation network which brings goods from the point of production to the point of sale. Hence, more efficient cargo handling is indeed worth striving for.
‘Boxes in boxes’ concept
Det Norske Veritas (DNV) has designed a lightweight, open-top frame structure, capable of carrying up to eight containers, which can be loaded on the quay and lifted on-board in one move. This will save valuable time in port, something which is of utmost importance to shipping companies as well as shippers and terminals. Additionally, this ‘boxes in boxes’ concept can reduce the need for container lashing and increase cargo safety. This proposed concept, which reduces the number of crane lifts and the need for lashing, could be a significant step towards efficient cargo handling. While waiting for the ship to arrive in port, the containers are loaded into an open-frame structure which is equipped with built-in stacking cones and cell guides. The loaded frame is then lifted on board onto two adjacent container stacks, to which it is secured by means of twistlocks. In addition to reducing the number of crane lifts, this has the benefit of locking two stacks together so that the deck reaction loads – and consequently the lashing requirements – are significantly reduced. A frame dimensioned for empty containers would only weigh approximately three tonnes. The decision to design it for empty containers was based on several considerations. Firstly, lifting up to eight loaded containers would be beyond the capacity of today’s cranes. Secondly, reinforcing the frame for the carriage of loaded containers would lead to increases in size and weight. Lastly, on many trades a large number of the carried containers are empty on parts of the loop. These empty containers are typically stowed in the top tiers, which corresponds well with the proposed use of the frame. Because the frame has an open top, once it is on-board, single containers can be unloaded just as easily as from an ordinary stack. Similarly, single containers can be loaded from the quay into a partially filled frame. This means that the improved efficiency can be obtained without sacrificing cargo handling flexibility. The only additional planning involved to allow for the use of frames is the planning of the pairs of stacks on top of which the frames are to be stowed. The stacks in each pair have to be of equal height, meaning that care must be taken to ensure an equal number of high cubes in those particular stacks. However, should unforeseen circumstances make this impossible the containers that were planned to be stowed in a frame can be lifted on-board individually. The empty frame left on the quay can be folded for convenient storage. Another advantage of the concept is that it does not require any modifications to terminal facilities, lashing equipment or the existing fleet; it can be lifted by existing cranes, secured by means of ordinary twistlocks and carried on any container vessel. This is an important feature of any innovative measure aimed at improving container handling efficiency. Container transportation was introduced more than half a century ago, and the highly standardised infrastructure which supports it is truly enormous and thus very costly to replace.
Considerations
Apart from the ‘boxes in boxes’ concept, a number of other measures were evaluated in terms of efficiency and safety gains as well as cost, reliability and technical feasibility. Some of these were aimed at reducing the amount of lashing. One such method was transverse container stowage; however, it was found that the amount of transverse lashing would not be dramatically reduced and some additional longitudinal lashing might be necessary. Other possible methods included constant-tension wire lashing, electro-magnetic container securing and cell guides on deck. These were abandoned mainly because they involve the introduction of new components which would require maintenance and which could cause delays if they failed. Lastly, various ways of improving cargo loading efficiency were proposed and investigated. One of the most promising ones was the side-loading of holds, which would allow the simultaneous loading of decks and holds. However, such a concept would most likely require some form of on-board cargo handling system to carry each container to its slot. Since it would be impossible to access the containers below deck by means of shore cranes, failures in the on-board system would inevitably cause delays. The conclusion was thus that the benefits would come at a higher cost, in terms of possible adverse consequences, compared to the ‘boxes in boxes’ concept.