Stowage - what and why
Dry Bulk vessels can carry a variety of commodities unlike specialized vessels, which are designed for a more limited number of cargoes. This gives dry bulk vessels more flexibility.
Port and berth restrictions set limitations to how much cargo a vessel can carry, however the specifications or the stowage of the commodity can also be a ruling factor.
The various commodities have different stowage factors. The stowage factor of the cargo indicates how many cubic metres of space one metric tonne will occupy in a hold. Since freight rates often are agreed on the basis of per ton loaded, it will be essential to know the estimated intake.
Imagine a cargo of cotton
Note that cotton is only used in this example for visualisation purposes, since cotton fiber will be compressed into bales before being shipped. Anyway if you visualise a free flowing cargo of cotton. This will take up much of the space in the holds, however the weight of the cargo when you have filled up the vessel's holds will not be as high as if you had a solid heavy cargo of iron ore in your holds. The total area of a vessel's hold might therefore be a limiting factor instead of the deadweight for some cargoes. Cargos with a high stowage will cube out before the vessel reaches its maximum deadweight carrying capacity.
Grain vs bale
Vessel capacity is listed with a grain and bale capacity. The grain capacity is used for “free flowing” cargoes, whilst bale capacity is used for packed cargo or cargoes with other substances than free flowing.
When you know the stowage factor of your commodity, which is given as a number of cubic feet per ton (cuft/t) or cubic meters per ton (m3/t), your estimated intake can be determined by dividing the hold cubic by an assumed stowage factor.
Remember to check if the vessel's cubic capacity is given as cubic feet or cubic meters.
Keep this conversion in mind:
1 cubic meter = 35.315 cubic feet
The stowage of the cargo will also assist the master when planning the loading of the cargo to keep the vessel in safe trim.
Various commodities have different stowage factors
Some of the major dry bulk commodities and stowage factors are:
A kamsarmax with a description as follows:
82.500 mt dwat on 14.5 ssw - TPC 72
loa/beam: 229 m / 32.2 m
Grain cap 3.400.00 cuft
Cargo of bauxite with a stowage of 33 cubic feet/ton.
2000 mt is deducted as allowance for bunkers and stores, thus the vessel has a cargo carrying capacity of 80.500 mt. The vessel does not have any draft restrictions at the load nor discharge port, and the total grain cubic capacity is 3.400.000 cubic feet.
Based on the stowage of the bauxite, this vessel has room for about 103.000 mt
3.400.000 : 33 = 103.000 mt
However since the vessel has a carrying capacity of 80.500 mt, it is her deadweight in this example that is the limiting factor.
What if the vessel carries soybeans with a stowage of 53 cubic feet per ton instead?
With the same information as before and no restrictions in port / berths, the vessel can load about 64000 mt of cargo.
3.400.000 : 53 = about 64.000
In this case, the limiting factor is the space in the vessel's hold, and not her deadweight. Even though this vessel has a carrying capacity of 80.500 mt, her cargo space only has room for about 64.000 mt of soybeans.
What are the different commodities in the list above?
Grains include many different products like; barley, corn, oats, soybeans, wheat, maize, canola and soybean meals. Some of the products shipped will be seeds whilst other products have been further processed into meals or pellets.
Most of what is being shipped is destined for animal or human consumption.
Some major exporters are Argentina, Brazil, Uruguay, Russia, North America, Canada, Australia and New Zealand.
Bauxite is a brownish clay-like mineral of which the majority is used to produce aluminium metal, while smaller parts goes towards chemical and refractory materials.
Some of the largest deposits can be found in Guinea, Brazil, Australia and Jamaica.
Iron ore is a raw material. It is used to make pig iron, which is the main material used in the production of steel. Steel is primarily used in structures, automobiles, machinery and ships.
Iron ore is mined in around 50 countries, with some of the largest producing countries being Australia, China, Brazil, Russia, India.
Phosrock (short for phosphate rock) is the primary source of all phosphate based fertilizer products. It is an important mineral resource which is considered the most economical fertilizer with numerous uses and applications in agriculture. It is also used as a raw material for animal feed supplements and for industrial applications.
Large producing nations are China, Morocco, Russia, United States and Jordan.
Coal - usually coking coal or steam coal.
- Coking coal (or metallurgical coal) is used for the production of coke, which is an important fuel in the blast furnace used for the production of steel.
- Steam coal (or thermal coal) is used in generating power and central heating.
Australia, Indonesia, Russia, US and South Africa are some of the major countries exporting coal.
Cement is a grey dusty cargo mainly used as a binder in concrete. This is the basic material for all types of constructions.
Major exporting countries are Vietnam, Turkey, Thailand, Canada, Germany and Spain.
Timber is a valuable product with little waste, thus even chippings of woods are utilized.
Wood chips are the raw material for paper and in recent years wood chips are also used in biomass power generation.
Wood chips will often be carried in special wood chip carriers which offer a high deadweight/cubic ratio for this high-stowing product.
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