Cargo load and Stowage Factor for bulk cargo
Generally, a ship using more of its capacity during transportation will be more energy efficient when measured in terms of fuel used per tonne of cargo transported. Thus ship capacity utilization becomes an important element of overall ship/fleet energy management. Ships may operate without utilizing their full cargo loading capacity. This may be for a number or reasons from the poor design of the ship to lack of transport demand but the ship manager should look at all options to increase the ship load factor if there is spare cargo capacity. If the load factor of the ships in a fleet is increased, then the gross emissions of these ships will also increase (assuming everything else remains as before). However, it is very simple to show that energy efficiency of the ship in terms of gFuel/tonne*mile or gCO2/tonne*mile will reduce. Savings can also be obtained by using fewer ships for the same operation that would outweigh any increase due to the increased cargo carried on an individual ship. To remove unused cargo carrying capacity, there must be the right ships in the right place at the right time. This means that it may not be possible to fill the space cargo capacity all the time even with a large fleet. If the cargo carrying capacity can be increased for certain voyages, this would have the effect of improving the overall efficiency of the ship as calculated for example by the EEOI. To achieve a better ship load factor, the whole issue of fleet planning and working relationship with shippers, ports and charterers will play a role. It is not necessarily a simple thing to do but it is quite rewarding in terms of energy efficiency and in emission reduction (MariEMS 2017).
If a cargo is light for its volume, then the holds may be full but the ship may not be down to its load line marks. The ratio of the volumetric area to the weight of a cargo is called the “stowage factor” and is a very important factor when loading bulk cargos. If the ship’s master and chief officer get their calculations wrong and either the ship is not full or they have to leave cargo that they have ordered behind, it may become an expensive operation for the ship-owner. In such cases, the ship-owners may be required to pay compensation to either the charterer or port operator. This also means that the ship will run less efficiently due to lower load factor and produce more GHG emissions (MariEMS 2017).