Dynamic separation of cargoes
In January 2015, a Bahamas-flagged bulk carrier called the Bulk Jupiter sank off the coast of Vietnam with a cargo of 46,000 tonnes of bauxite and a crew of 19 men. Only one survived the tragic incident, which was thought to have been the result of classic cargo liquefaction.
Based on research conducted by the Global Bauxite Working Group and endorsed by the fourth session of the International Maritime Organisation’s Sub-Committee on Carriage of Cargoes and Containers (CCC-4), it is probable that a different phenomenon dubbed ‘dynamic separation’ was responsible for this tragedy.
What is dynamic separation?
Dynamic separation occurs during a voyage where the moisture in the cargo migrates to the surface of a hold as the cargo compacts from underneath due to vibration and vessel movement. This occurs when the cargo contains enough small particles that stop the moisture draining from the cargo.
As a slurry of water and fine particles collects on the top of the cargo it creates a free surface effect in the hold. Over time, the sloshing motion of the slurry can deposit loose cargo unevenly in the hold. The research also shows that different wave periods of the slurry in different holds results in the ship having a peculiar motion rather than a regular roll period in a seaway.
Modelling shows that over time, cargo collects on one side of the holds. As this occurs in adjacent holds, the ship’s weight distribution and stability become affected. The result in more extreme circumstances is the ship progressively listing to one side. As this list increases, so does the action of the free surface water, potentially undermining the surface of the cargo, resulting in a shift and capsize.
Mitigating the risk
To reduce the risk of dynamic separation occurring, bauxite fines will be reclassified from being a Group C—no known risks—cargo to a Group A cargo. This means that under certain conditions the cargo may present a risk due to moisture. It will be adopted to the International Maritime Solid Bulk Cargoes (IMSBC) Code in May 2019. You will be required to:
- test the particle size distribution of cargo and determine its transportable moisture limit before loading
- load and carry the tested cargo with a moisture content below the transportable moisture limit
- IMSBC Cargo moisture management processes will apply.
If the cargo contains a moisture content beyond the threshold identified in the CCC-4 report, loading is not permitted.
Pending adoption of changes into the IMSBC Code, we have determined that the test and schedules adopted by CCC-4 should be applied to BAUXITE when shipped from Australia in solid form in bulk. We have issued by approval AP5456 to allow the test and schedules to be used.
Contact us for more information.