‘Best opportunities to reduce risk of container stow collapse lie upstream’
2020 looks to have been an exceptional year in terms of container losses. But why do stows collapse and how do you prevent this from happening? Simon Burthem, Chief Operating Officer at TMC Marine, explains the causes through ‘supply chain chronology’ and says mitigating the risk requires ‘all parties to jointly share responsibility’.
Burthem presented his view on the complex issue of container losses during a Brittannia P&I webinar on the topic held on 28 January.
‘When compared to the number of boxes shipped, less than one thousandth of a per cent is lost. Based on these numbers one could conclude that there is no real problem,’ says Burthem. ‘Does this mean ship operators and owners should not concern themselves with the safety of the cargo? Obviously no.’
He estimates 3000 boxes were lost in the nine months from May 2020. An exceptionally high number. Yet, in addition to the frequency of such incidents apparently increasing, lost containers are now ofthen requested to be found and recovered. Burthem: ‘And this results in a very large bill that far outweighs the lost cargo.’ This makes the need to mitigate this risk all the more urgent.
And this results in a very large bill that far outweighs the lost cargo
Why do stows fall?
So why do container stows fall? Burthem: ‘Either the lashing system is too weak or otherwise it is overloaded. Which is obviously an oversimplification. To properly understand the causes of these instances it is necessary to look deeper into the mechanisms at play, to see where the root causes and contributory factors occur.’
‘Practical experience is that there is frequently an error chain which starts when the container is packed,’ he adds.
Principles of container securing
‘A ship in a seaway moves in six degrees of freedom. The ship’s hull responds by bending and twisting and the pontoon hatch covers move relative to the hatch openings. Container stacks move as the clearances in the lashings are taken up and outer stacks are exposed to wind loading. All this results in applied forces acting on the containers. It is the lashing system of which the structural strength of the containers themselves is an integral part that resists the applied forces and secures the stacks,’ explains Burthem.
Burthem: ‘However, there will always come a point where the loading exceeds the ultimate strength of the system and components will start to fail. The failure of one component often causes a consequential overloading and failure in another part of the system. And experience tells us that the entire sequence of collapse can progress rapidly.’
Supply chain chronology
According to Burthem, the best way to categorise the causes of container stow collapse is by means of ‘supply chain chronology’. ‘This is to say that the return of TMC’s experience is that the root cause of a stow collapse can frequently be back up the chain long before any box has been loaded on the ship. Taking packing issues for example. This is about what is inside the boxes, how it is secured and what the accuracy of the declared contents, condition and weight is.’
About twenty per cent of containers at any given time are misdeclared
‘Some estimates are that about twenty per cent of containers at any given time are misdeclared,’ states Burthem. ‘And upwards of two thirds of all cargo claims may be attributed to misdeclaration and poor container packing. The net outcome is an unpredictable and potentially excessive loading on the container shell and securing system. If the problem is significant enough, a stow collapse may result.’
Improper distribution of weights
Burthem continues: ‘If packing issues are an upstream issue over which carriers have little control, for a long time the real elephant in the room has been the improper distribution of weights in the container stack, which whilst possibly resulting from misdeclared container weights, can also arise due to problems in the planning process. In my opinion, weight distribution issues have a larger downstream impact on a more frequent basis than any other root cause.’
‘An essential part of the planning process is the confirmation that the allowable stack weights are not exceeded. Clearly the plan is only as good as the information it is based upon. So if the inputs are wrong, the output will also be unreliable.’
In my opinion, weight distribution issues have a larger downstream impact on a more frequent basis than any other root cause.
‘The basis of limiting container weights in combined stack loads is primarily to not overload the lashing system and container frames,’ he says. ‘Real world stowage inevitably departs from standardised stowage arrangements. The use of other stowage patterns is not prohibited, but caution needs to be exercised to ensure that the actual arrangement of normal and high cube boxes, weights, lashings and vessel GM (metacentric height, Ed.) does not result in a condition whereby the stow is unsuitable for the anticipated rigours of the sea.’
Also read: Are container ships overloaded?
He adds: ‘It is not always easy to adhere to good practice such as maintaining a block stow and properly tapered weights from top to bottom, but a failure to do so can result in excessive loads being placed on the containers and the lashing systems.’
Proper inspections of lashing gear
Allowing the lashing system to work as it was designed, requires ‘a robust system of control and record keeping’. Loose lashing gear needs to be inspected promptly, maintained periodically and changed as required, according to Burthem.
‘Some fixed lashing gear, in particular sockets, can be difficult to properly inspect due to lack of time and accessibility issues. Sockets are often found to corrode from the inside necessitating close inspection to identify any problems. A socket that has thinned due to corrosion will have a reduced buckling strength.’
Crew and stowage regulations
A stow which differs from the container securing arrangement (CSA) in terms of weight distribution, GM and even stack weight does not necessarily equal an unsafe stow, according to Burthem. ‘But at what point should the crew become concerned? This is not always clear.’
Burthem adds: ‘Shipboard loading computers may also not provide the capability to analyse lashing forces, meaning that the sole means available to the crew to ensure that a proposed stow is safe, is by strict adherence to the CSA. Even where a lashing programme is available, time constraints and cultural issues have been known to affect the crew’s perceived empowerments to request changes to a stow.’
Time constraints and cultural issues have been known to affect the crew’s perceived empowerments to request changes to a stow
‘Some large terminal operators are now not sending a planner on board meaning that it is often so much harder for the crew to raise concerns or to affect change. And of course late changes in ballast or miscommunications as to the ship’s condition can obviously result in a larger GM than the stowage plan envisages and should always be avoided.’
Best practices at sea
Burthem stresses lashings also need to be monitored throughout the voyage with the crew retightening loose lashings as appropriate. ‘Loose lashings can permit a container stack to move as the ship rolls and bear on the adjacent stacks in turn putting those lashings under additional load.’
Weather routing sometimes is prescriptive and sometimes masters have the flexibility to take independent decisions. ‘Whichever approach is taken, it is important to note the difference between significant and maximum wave heights. Good practice is to consider both,’ says Burthem. ‘Similarly, ballast changes at any stage of the voyage need to be carefully considered and the appropriate tools used to assess the impact before doing so.’
Sometimes the crew fails to properly prepare or respond to bad weather. ‘There will inevitably come a point when extreme weather genuinely exceeds vessel capability, but experience dictates that stow collapses most often occur in bad, but not extreme weather.’
Because big ships tend to roll less than small ships, crew may respond late to worsening weather. At which point the window to mitigate risk has already closed, according to Burthem.
He adds: ‘The limiting roll angle is not always clear from the class rules, and it is perhaps unreasonable to expect a ship’s crew to have a detailed appreciation of what it is or how it is derived. Some crews do have the benefit of more advanced decision making tools, which allows motions to be assessed and changes to heading or speed to be analysed before committing. Changes to both heading and speed simultaneously run the risk of making matters worse rather than better. Good practice is to change only one parameter at a time.’
By the time the problem has reached the ship, it is already too late, the team has failed.
Opportunities lie upstream
Burthem concludes by saying that ‘the best opportunities to mitigate the risk of stow collapse lie upstream. The management of downstream shipping stresses may provide some easy wins for a carrier, but effective loss prevention requires all parties to jointly share responsibility. You can see the ship as the goalkeeper. By the time the problem has reached the ship, it is already too late, the team has failed.’