Stowage Factors (SF) of coal vary depending on:
- Size of Coal
- Wet or Dry
- Ship Type
- Trimming Process
1- Size of Coal: coal is screened and graded by size. Smaller the coal the less stowage space required by one metric ton. Care must be taken to avoid undue breakage of pieces of the larger coal sizes which lessens coal value.
2- Wet or Dry: wet or dry condition not only affect the stowage factor (SF), but also wet coal dry-off during voyage and is therefore likely to substantially reduce the tonnage of cargo discharged as much as 4%.
3- Ship Type: like many other bulk cargoes, ships without self-trimming facilities lift less coal for a given cubic capacity. Today, most coal is transported in bulk carriers which are highly suitable for the carriage of this commodity.
4- Trimming Process: trimming is crucial because the angle of repose of coal exceeds 35°. Today, most modern bulk carriers have self-trimming facilities, but certain ship types particularly small, general-purpose ships operating in coastal waters, are unlikely to be equipped with such self-trimming facilities. Thus, these type of old ships need careful trimming to secure the cargo.
Today, much coal business is fixed on the basis that the cargo be loaded, trimmed as necessary and discharged free of expense to shipowners, but the AMWELSH charter-party stipulates in line 20 that loading, dumping and trimming costs are to be for shipowners to bear. Loading and trimming costs are self-explanatory. Dumping costs apply usually to certain loading ports of the United States. Dumping costs are charges to cover the expenses of unloading railway wagons that fetch the coal from mines to the dockside.
5- Origin: stowage factors of coal loaded in suitable bulk carriers from certain areas:
- Australia Coal 38/44
- Australia Coal Briquettes 54
- Continent Coal Briquettes 54/55
- Poland Coal 42/45
- Poland Coal Briquettes 55/60
- South Africa Coal 40/44
- United States Coal 41/48
- United States Coal Low Ash 55
- West Africa Coal 50/56