The liquefaction of some bulk cargoes on passage is an old problem
The liquefaction of some bulk cargoes on passage is an old problem that has regrettably not gone away. The loss of three modern ships, with heavy loss of life in 2010, was a brutal reminder of this. All were carrying Indonesian nickel ore; cargo, which by its very nature and the fact that it is mined in an area of excessively high rainfall, is recognised as hazardous and highly prone to hygroscopic effects.
It would be easy to suggest that it was inadequate testing to determine the water content that was the problem, or that prudent operators should reject such charters out of hand. But the fact is that these cargoes are of increasing value, so that the demand for them by steelmakers is high and growing.
It is also a fact that there is a distinct lack of expert advice available in many of these areas, and a notable shortage of science in the determination of water content. There is also often a great deal of commercial pressure on shipmasters to accept the assurances given by the cargo owner, anxious only to get the cargo loaded and the ship on its way. Can the Master place any trust on such assurances, when he sees that the cargo is lying uncovered and that samples have been taken from part of the stack that the cargo owner has chosen, and that the methods chosen for testing that it is below the transportable moisture limit are crude and possibly suspect?
This cargo, despite its risks, is not going to go away and indeed is likely to increase in volume, which suggests that owners wishing to take advantage of its availability need to think of defensive measures. The Italian classification society RINA suggests that a permanent solution would be to fit strong longitudinal bulkheads under the hatch coamings to port and starboard in alternate holds, restricting the cargo to the space under the hatches and leaving it less area into which it may flow, or produce a dangerous free surface.
The society now offers a special notation which indicates that the ship is fitted to carry cargo which may liquefy during the voyage. Such a vessel would, when thus converted, resemble the traditional ore carrier, with the cargo carried filling a greater volume of the available space. With the space for cargo in alternate holds under the whole of the hatches, it will also be possible to use the loading spout to spread the cargo more evenly, rather than leaving it as a pyramid shape in the bottom of the hold which is obviously more susceptible to a shift should the cargo start to liquefy.
It is, however, likely that conventionally strengthened bulk carriers, without these special features, will find themselves fixed to load these potentially difficult or dangerous cargoes. In such cases it is recommended that expert cargo surveyors with experience are employed to thoroughly examine the cargo, and that all available guidelines for its safe carriage, notably those contained in the International Maritime Solid Bulk Cargoes Code are scrupulously followed. It might also be prudent for care to be taken during the loaded voyage to avoid, where possible, heavy weather that might produce motion and vibration likely to liquefy the cargo.
Source: BIMCO, Watchkeeper