Container lashing: taking the strain for a bigger problem
The Naval Architect Jul/Aug 2020
On 28 May, APL England, a 5,510TEU container ship, was detained by AMSA inspectors at the port of Brisbane. En route from Ningbo to Sydney on 24 May it had suffered a temporary loss of propulsion during heavy seas and the resultant rolling caused several stacks to collapse and somewhere in the region of 40 to 50 containers to be lost overboard.
Upon boarding, it was found, in contravention of SOLAS requirements, that lashing arrangements for cargo were inadequate, while the securing points for containers on the deck of the 2001-built ship had been heavily corroded.
Lashing failures are regularly cited in container ship incidents and ship insurers send out regular reminders to members to ensure that cargo, be it containers or other equipment, are well secured while at sea. But are they really the cause? Not directly, according to John Southam, a former master mariner and now loss prevention executive for P&I club North.
He says: “Rarely, from a technical point of view, is it a single failure of lashings. As with most things it’s a combination of problems and when you boil it down lashings usually fail because of weight distribution.”
Gillian Clark, North’s senior executive for claims, agrees: “When you look at the majority of container casualties that have stow collapses you’ll see that stows generally tend to go en masse. That suggests that lashings aren’t so bad overall but it has more to do with general issues.”
IMO’s Verified Gross Mass (VGM) certification, introduced in July 2016, made it a SOLAS requirement for containers to be weighed prior to boarding and has helped to alleviate the problem, but much still depends on the diligence of cargo planning.
The weight distribution of a container ship is, of course, contingent upon its design. Every vessel’s cargo securing manual will show the maximum allowable weight distribution, bay by bay, tier by tier and row by row. Heavier boxes should ideally be stacked towards the middle and each bay and stack will have a maximum GM.
Southam compares it to the ‘Swiss cheese’ model: “Most of the time when we get to look at the plans you can immediately see that a heavy box sat quite high up the stack. So if I can see it, there’s no way that others wouldn’t have been able to if that plan had been checked thoroughly.
He adds: “Shipowners and operators don’t want to do restows because they cost money. You start to avoid moving weight around because you don’t want to take a box off and put it back on again because it’s not for this port.”
The SOLAS VGM requirements, which stipulate the master should be provided with the verified container weight “sufficiently in advance”, is ambiguous enough so as to have limited impact on last-minute loading.
Clark notes: “By the operator accepting to load it’s almost vindicating that there was indeed ample time because they’ve taken the box. Ideally, you want to take away those pressures and make sure people stick to the cutoff times, but you’re talking about major stakeholders and the pressure is huge on those lines.
Class societies have been attempting to address the commercial aspect with some of their products and services. As well as updating its rules and calculation methods, DNV GL’s StowLash3D free software enables the user to reproduce a real lashing case without conservative simplifications. LR’s LashRight tool provides a similar function, consistent with its own rule requirements.
But the first, simple steps that can be taken is for all parties to be checking the stowage plan against the Cargo Securing Manual and working within the boundaries of the ship’s design. “It won’t cure things 100% because, as we’ve discussed, there are so many layers to this problem, but that’s not a bad start,” says Southam.