Stowage Factor (SF) is the volume occupied by one unit of mass (weight) when stowed in a cargo space.
Stowage factor1 is the numeral, which expresses the volume (space) in cubic metres or cubic feet occupied by a unit mass of cargo, i.e., 1 tonne (1 metric ton) when stowed. It is an empirical figure reached by experience of previous stowage and takes into account “broken stowage” and dunnaging. For example, the actual volume occupied by 1 tonne of a piece of cargo may be 2.5 cu. in. but because of its awkward shape and the need to separate it from other, adjacent cargo, it will occupy 2.73 cu. m. The SF is then said to be 2.73.
Before general metrication, stowage factors were given in cubic feet per ton (of 2,240 pounds). Indeed, these figures were easier to remember. For example, jute in bales stowed at about 65 (ft3 /ton). The metric SF is about 1.81.
It must be stressed that SFs are always quite approximate values and the actual space taken up by a parcel of cargo will depend on the care taken in stowing it, the shape of the compartment, the type of dunnage used, the form of packing, the need for a greater or lesser segregation from other cargo in the same compartment and even the season in which the cargo is loaded. SFs are therefore useful at the planning stages before a cargo is loaded so that it can be considered how best to load the cargo on board the vessel or in a container to maximise the space used with the greatest safety.
In the case of bulk liquids, SF is replaced by SG – the “specific gravity” – which is the mass (tonne) per unit volume (m3). This is because bulk liquids will fill the compartment into which they are loaded.
Stowage Factor2 is a unit of measurement, which indicates how much space (volume) a particular weight quantity of cargo will occupy in ships’ cargo compartment. The stowage factor is not actual cubic measurement of one tonne of a commodity. The SF may be different from the actual cubic measurement of one tonne of the commodity because of the method of packing or nature of the commodity. The unit of measurement is usually given without any reference to the units of volume or weight but these can sometimes be used. The SF is the ratio of volume to one unit of weight, for example, the number of cubic feet per ton or cubic metres per tonne. In modern days, with metrication, it is probably logical to use a SF based on cubic metres per tonne but in the shipping business it is difficult to change something people have been familiar with for many years. Therefore, while the SF of wheat in bulk may be said to vary between 1.25 and 1.39 (cubic metres per tonne) which can be converted to 44.85 and 49.87 cubic feet per ton, shipping people still use the older numbers because these seem to be easier to express without decimals. Therefore the S.F. of a wheat cargo may be described as varying from 45 to 50.