Mitigating the loss of containers overboard

Photo: © Ruslan Gilmanshin | Dreamstime.com

While the volumes of containers lost at sea fluctuates year on year, typically influenced by the more severe of weather conditions, the challenge of reducing the numbers remains.  TT Club’s Peregrine Storrs-Fox outlines the various attempts by agencies around the world in the cause of prevention, including his own organisation’s on-going efforts.

Understanding the circumstances that lead to collapse of stow-and-loss-overboard incidents is important to mitigate the risks. In this context, TT has been involved from conception in the MARIN[1] TopTier Joint Industry Project, drawing together a group of more than 40 stakeholders in identifying and resolving the circumstances that lead to such incidents.

The TopTier project has created a number of working groups focused on the wide range of relevant factors, which illustrates the complexities involved.

TT’s own analysis of historic incidents clearly shows that weather is the single most influential factor, but the data demonstrate that this is far more complex a challenge, involving a wide range of interconnected operations.

The process starts with the consignor who typically places a transport order, including making a declaration about the cargo being shipped. Accuracy is of course vital – cargo type, nature and characteristics etc – but in the context of loss overboard, the declared weight or verified gross mass is pivotal. It should also be noted that poor load distribution when packing cargo will erode safety margins.

At the ship/port interface, the terminal operating system (TOS) will support appropriate stowage on board the ship, alongside stow planning software, influenced by declarations of cargo type and gross mass. Where these systems in essence seek to load heavier containers lower in any given deck stack, TopTier studies identified discrepancies up to 20% between planned stow versus the actual final stow on board. If representative of all operations, this is itself alarming.

This is significant, particularly where a heavy container is erroneously stowed towards the top of a stack. In any adverse sea statethere is increased risk of stack collapse under the physical forces exerted. Furthermore, if that stack is in the middle of the stow, further collapses in adjacent stacks are more probable.

Following the experience of winter 2020/21, TT undertook certain analyses. Accessing geospatial data sourced from Geollect it was possible to identify potential commonalities across several incidents, albeit such data were inconclusive in isolation. Wave height was among the more obvious attributes, but wave length and period appeared to be of even greater importance.

Working with Brookes Bell, it was recognised that wave period is responsible for resonant phenomena, such as parametric roll and synchronous rolling, behaviours that are problematic and can give rise to losses overboard. As wave height increases, so does the wave period, which is a factor in synchronic roll response. In storm conditions, wave groups and wave steepness can vary significantly too and may also influence the combined motions (pitch, heave and even roll) of some ship types. Advice on parametric rolling was one of the early deliverables from the TopTier project.

From a mariner’s perspective there are further factors to consider. The loss of a container stack is affected by other aspects beyond simply the wave height, such as sea and swell from different directions, rapidly changing conditions, and lack of information to ship’s crew about swell which could be predicted ahead of time. For larger container ships, other factors also affect the loss of containers, including excessive metacentric height (GM), whipping and bottom contact in shallow water.

Furthermore, container stack calculations effectively do not take full account of all the constituent components under dynamic force in defining design margins. Lashings have a safe working load at 50% of maximum break load, but the ISO container tests for stacking and racking set the forces at the certified strength. Thus, these cannot be used in isolation when considering the container stack forces. Taken together, the developed combined forces of compression and racking, which should be used in ships’ planning models, may be higher than the certified strength values of individual containers. This may be particularly pertinent for stacks 10/11 high.

Appreciating all the factors that may erode safety at sea is vital and TT looks forward to the finalisation of the TopTier research and the opportunity to continue to be involved in the ensuing debates, particularly at the IMO. However, ships will never be able to avoid the impact of heavy seas entirely. Consequently, TT, in furtherance of its mission to make the global logistics industry safer, more secure and more sustainable, is currently involved in two other innovation initiatives.

The first, being profiled in the latest TT Club Innovation in Safety award, organised by ICHCA, is the development of two complementary digital and engineering solutions to mitigate the risk of container loss overboard from Trendsetter Vulcan Offshore (TVO), applying well-established systems from the offshore industry.

Their Janus system’s monitoring capabilities include both predicting and detecting parametric roll, allowing evasive action to be taken before ship and stack dynamics enter a destructive range.

The second TVO element, an engineering solution called ‘next-generation lashing’ (NGL), fundamentally overhauls the current deck lashing regime. The system reduces container motion and controls the dynamics of container stacks. By tethering the top of the outermost stacks, NGL creates a wing wall that stabilises the containers in the bay via enhanced tension stability, providing additional restraint at the top of the stack, thus eliminating the dynamic twist lock tensions that have the potential to be the initiating cause of many container stack failures.

TT’s second innovation engagement is with the LR Safetytech Accelerator Cargo Fire and Loss Innovation Initiative (CLFII). Within a broader technology scope, is onboard cargo control, including whether cargo has been properly loaded, secured and monitored during transit.

Conventional wisdom remains that heavy storms should be avoided where possible to minimise the risk of loss of containers. Nevertheless, deployment of innovative technology can assist in building greater safety margins, including leveraging data capture to improve understanding and predictions in changing sea conditions.

[1] Marine Research Institute Netherlands