Cubic Capacity

It should be immediately obvious that the ship is limited by her deadweight to a maximum cargo of iron ore of 55,000 tonnes, which will fill only approximately a third of available hold space, whereas all hold spaces will be full if loading coke, but only about half of the available deadweight will have been used. This is a fairly extreme example to illustrate the relationship of cargo stowage factor versus ship cubic capacity and deadweight that a dry cargo chartering person must constantly bear in mind. Nevertheless, the freight rate per tonne for 25,000 tonnes of coke must be around double that for 55,000 tonnes iron ore to provide the same approximate return to the shipowner. With certain ship types, the amount of bulk cargo that can be loaded will be greater or lesser than for a different ship type with an equivalent cubic capacity. For example, tweendeckers might suffer from a restricted tonnage intake compared with a self trimming bulkcarrier, because the ‘overhang’ created by fixed tweendecks will interfere with the stowing of cargo in the lower holds, creating unusable, wasted space (illustrations on page 13 ‘Cargoes’). But not all cargo, of course, is carried in bulk. Much cargo is carried in ‘packages’ of one kind or another, from traditional bags through to modern pallets. Whereas many bulk commodities will ‘flow’ into the sides and corners of a ship’s cargo compartments, bagged or palletised goods must be stowed and often cannot fit between hold frames and, indeed, may be intentionally kept clear of hold sides by devices such as ‘cargo-battens’, in order to encourage cargo ventilation. Thus, as explained earlier dry cargo ships have two cubic capacities – ‘grain’ (for measurement of bulk commodities), and ‘bale’ for ‘non-bulk’ goods. Finally it should be emphasized that while stowage reference books will provide comprehensive guidance there are several ways in which the stowage factors of some cargoes can change significantly. For example, roundwood floated down river and therefore very wet, the density of pressed bales etc. It is always worth investigating the experience of others in a trade when new cargoes/commodities or sources are being worked.