High-Density Solid Bulk Cargo: The 0.56 m3/t Threshold

A high-density solid bulk cargo is one with a stowage factor of 0.56 cubic metres per tonne or less, and the threshold matters because it marks the point at which an evenly distributed cargo can still overstress the tank top. It is a free-standing definition, in IMSBC Code section 1.7: “High-density solid bulk cargo means a solid bulk cargo with a stowage factor of 0.56 m3/t or less.” The same 0.56 figure is also written into the loading provisions of several individual schedules, in the form “When the stowage factor of this cargo is equal to or less than 0.56 m3/t, the tank top may be overstressed”, which is why it is often taken for a threshold that exists only in the schedules. Barytes , at a stowage factor of 0.34 cubic metres per tonne, sits far inside the threshold, though its schedule states the tank top warning in its own terms rather than by quoting the 0.56 formula.

The full article will cover where the threshold is invoked in the Code, what it requires by way of cargo distribution, and the structural reasoning behind it. A dense cargo reaches full deadweight in a small volume, so it concentrates load over a limited area of the double bottom, and the constraint that binds is permissible tank top loading rather than grain capacity.

It will also set out which cargoes sit either side of the line, since that is the practical question. Iron ore and concentrates sit well below it, brown fused alumina straddles it, and cargoes such as alumina and coal are nowhere near it despite often being described loosely as dense.