The threat and effect of dynamic separation

Ship classification society Class NK and Rio Tinto have released a report entitled “Safe Shipping of Solid Bulk Cargoes – Dynamic Separation & resulting Free Slurry Surface Effect”, covering dynamic separation of solid bulk cargoes and the resulting free surface effect.

Research by the Global Bauxite Working Group identified the moisture-related cargo failure of “Dynamic Separation”. The new report shows how cargoes can undergo this process.

Rio Tinto said that since 2011 it had been “deeply involved” in understanding how solid bulk cargoes behaved during ocean transportation, especially identifying any cargo instability due to moisture.

The work first started with an investigation into the behaviour of iron ore fines, conducted via the Iron Ore Fines Technical Working Group (IOF TWG). This work was submitted to the International Maritime Organisation (IMO) to assist with policy formulation for the carriage of iron ore fines.

Following this work the Australian coal industry embarked on a study to understand the behaviour of coal during shipping, again leading to assisting the IMO with policy on the safe shipping of coal.

Recently, bauxite has also been investigated via the Global Bauxite Working Group (GBWG), with the outcomes utilized by the IMO to develop policy to ensure the safe shipping of bauxite.

ClassNK and RT entered into a Collaboration Agreement in 2013, under which they undertook a joint study into the behaviour of solid bulk cargoes during shipping. The collaboration included dynamic centrifuge physical modelling, where the impact of the ship’s rolling motions and cargo properties on the stability of the solid bulk cargoes was investigated. The outcome of the joint study has contributed to IMO policy formulation for bauxite in 2017.

The researchers said that, under the traditional cargo liquefaction model, only by ensuring compliance before the cargo was loaded could any risks due to cargo liquefaction be mitigated. If a cargo was misdeclared and the vessel sailed, the Master and crew had no recourse and the cargo might liquefy, causing the cargo to shift and the vessel to capsize.

Under a dynamic separation model of cargo instability, ensuring compliance before the cargo is loaded would still mitigate the risk. However, if the cargo was misdeclared and the vessel sailed, and the Master and crew understood the potential signs of cargo dynamic separation and its influence on a vessel’s behaviour, the Master and crew could develop mitigation strategies after the vessel was en route.

At the first sign of unusual vessel rolling motions, crews now know that something is wrong with the cargo’s stability.

        They can act to firstly reduce vessel motions and input forces to the cargo to prevent further cargo separation.

        The crew can get ready to abandon ship early as they know what is happening.

·       They can seek refuge if possible or let others know they have issues and may need assistance.

        They could potentially start with measures to increase the vessels GM and regain stability and prevent a list from developing.

RT and ClassNK said that this new understanding of cargo instability due to moisture and how it affected vessel stability needed to be circulated to the maritime community, as it was paramount to ensuring the safety of all mariners regardless of the cargo declaration (Group A, B or C).