Stowage Factor (SF)

Stowage Factor (SF) is the density of the cargo in the ship’s hold. In the shipping business, Stowage Factor (SF) is a very important piece of information.

Due to the ship’s cubic capacity, a ship has only a limited volume (space) in her holds. In some cases:

  • Light Cargo: the ship’s holds are full before all the ship’s deadweight cargo capacity is utilized
  • Heavy Cargo: full deadweight capacity can be reached with space still available in holds, but that space is unusable

In the shipping business, some historic measurement systems are still in use, for example, variations of the old English system (imperial system) of weights and measures are still frequently used for Stowage Factor (SF) – cubic feet to one ton (ft3/ton).

Stowage Factor (SF) Example 1: Ship A
Deadweight Cargo Capacity (DWCC): 55,000 tons
Grain Cubic Capacity: 70,000 m3 (2,470,000 ft3)
Cargo: 55,000 tons of Bulk Phosphate
Bulk Phosphate Stowage Factor (SF) about 0.90 m3/ton (32 ft3/ton)

In fact, Ship A has space for 77,000 tons on her holds.
70,000/0.90 = 77,000 mtons or 2,470,000/32 = 77,000 mtons (rounded)
However, Ship A can only take 55,000 mtons in weight of Bulk Phosphate before Ship A loadline is submerged

Stowage Factor (SF) Example 2: Ship B
Deadweight Cargo Capacity (DWCC): 55,000 mtons
Grain Cubic Capacity: 70,000 m3 (2,470,000 ft3)
Cargo: 55,000 mtons of Barley
Barley Stowage Factor (SF) about 1.47 m3/ton (52 ft3/ton)
 
In fact, Ship B can lift 55,000 tons.
70,000/1.47= 47,500 mtons or 2,470,000/52 = 47,500 mtons (rounded)
However, Ship B can only take 47,500 tons in weight of Barley before Ship B is full and no more space is available in the Ship B’s holds

In ship chartering, the Stowage Factor (SF) of the cargo is of crucial importance. In order to obtain the same income, a higher freight rate per tonne have to be negotiated for a lighter cargo than for heavy cargo. The Master (captain) must have to have the full information of the cargo so that the master (captain) can arrange the loading sequence in order to keep the ship in a safe trim. Furthermore, the master (captain) must be informed about if the cargo consists of two or more different commodities with different Stowage Factors (SF), so that master (captain) can arrange the stowage in such a way as to keep the ship in trim.

Stowage Factor (SF): the amount of space occupied by a given quantity of any dry commodity in whatever mode of transport (eg: grain in bags or in bulk) is said to be its stowage factor – best expressed for ease of remembering in terms of cubic feet per long ton or per metric tonne, but often described as cubic meters per tonne. The difference between long tons and metric tonnes is slight, only 1.6%, and for practical purposes can be disregarded. The trend is to quote tonnages in metric units and thus it will usually be found convenient to work in metric tonnes rather than in imperial units. There is, however, considerable ‘market’ resistance to working in units other than cubic feet when describing stowage factors.

Not only are stowage factors expressed in cubic feet easier for most people to remember – dispensing with the fractions required when utilizing cubic meters – they are the traditional method of describing cargo-space requirements and unlikely to be abandoned for a long time, if at all. Consequently, it behooves all involved in trading goods at sea, whether they prefer to work in cubic feet or in cubic meters, to bear in mind that 1 Cubic Metre equals 35.3148 Cubic Feet, for undoubtedly the need will arise to convert one to another. Whether in cubic feet or in cubic meters, the lighter a commodity, the more space it will occupy, and therefore, the higher its stowage factor. Thus corn stows around 50 cubic feet (1.42 cubic meters) per tonne in bulk condition, whilst much heavier iron ore occupies 15 (0.42) or less.

As a result, a ship with a “poor cubic” – that is to say with a low ratio of cubic cargo space in relation to available deadweight, would have difficulty in loading a full deadweight cargo of corn, because of insufficient space in her holds. Furthermore, awkward or squared shapes cannot usually fit into every nook and cranny in a ship’s holds, thus losing valuable space through what is known as broken stowage (the term also used to describe spaces between packages, and indeed, any commodity remaining unfilled). Moreover, with many non-bulk commodities shipped, for example, in bags or in bales, the necessity of keeping them away from ship’s sides and other metal areas so as to avoid ‘sweating’ and associated damages, and to create ventilation channels, causes more loss of cubic capacity. Consequently, ships are measured for two sets of cubic capacity.

Grain Capacity describing the total volumetric space available for all bulk cargoes (not just for grain); and Bale Capacity recording unobstructed space available for non-bulk cargoes. It. follows that a ship’s bale capacity should normally be smaller than its grain capacity, although, with some modern “box-type” hold designs used principally in the short-seat trades, the grain and bale capacities are similar, the holds being clear, regular-shaped and unobstructed. Another method of assessing cargo space requirements is that termed Bulk Density, whereby a small amount of bulk cargo is closely packed into a box and thereafter accorded a “stowage factor” expressed in terms of pounds (lbs) per cubic foot, or kilograms per cubic meter, depending on the box dimensions. This figure, however, must be treated with a degree of caution, as it fails to take into account the shape or characteristic of the carrying vessel. Furthermore, densely packed material does not necessarily recreate the lay of cargo in a ship’s hold.

Stowage factors based on bulk density, therefore, are liable to be lower than the actual stowage factor of the commodity in a ship’s cargo compartment. Carriers running a regularly scheduled service between certain ports (a liner service) normally charge freight on the basis of USD per cargo ton. But where the goods involved are light and occupy a large amount of space, such a system would restrict carriers’ income. Accordingly, as a general rule, most operators levy carriage charges on a volume basis for articles stowing at more than 40 cubic feet or, if charging on a metric basis, more than one cubic meter. Thus has arisen the term, Measurement Ton. whereby operators elect to levy freight on a tonnage basis if the goods involved stow at less than 40 cubic feet; or on a volume basis per every 40 cubic feet, for cargo stowing above that figure; or if they work in metric units, per metric tonne or per cubic meter.

Stowage Factor (SF) is a vital subject as much of the structure of commercial ship trading depends on the amount of cargo a ship can carry, and the ‘freight’ a carrier will receive or a shipper pay for the transportation of that cargo. Constantly, the international shipping market has moved away from traditional methods of cargo measurement-based heavily on ‘imperial’ or ‘local’ units, towards the all-embracing metric system. Nowadays it is more usual to encounter ‘metric tonnes’ rather than ‘long tons’ or ‘short tons’ to describe the weight of a bulk commodity or measurement in ‘meters’ rather than in ‘feet’. 

Long Tons are tons of 2,240 pounds. Short Tons are tons of 2,000 pounds. Metric tons, or tonnes, are 1,000 kilos (kg). Bill of Lading (B/L) tons are the tons on which the revenue is earned for shipment. If the cargo is more than 40 cubic feet per ton (or 1 cubic meter per tonne) shipment is charged on measurement; that is, every 40 cubic feet is charged as 1 ton. This is known as a measurement ton. If it is less than 40 cubic feet per ton the shipper is charged on weight. For example, a typical liner ship with 9,802 bills of lading tons onboard has, in fact, only 3,857 tons of 2,240 pounds.

The one exception to this trend towards metrication is that of ‘stowage factors’ (SF), which is the amount of space occupied by a given quantity of any dry commodity whatever its mode of carriage, whether it be ‘loose’ (e.g. ‘in bulk’) or ‘contained’ (e.g. in bags or on pallets). Nowadays, it is usual to describe the stowage factor (SF) of a commodity as ‘per metric tonne’ rather than as ‘per long ton’, but the stowage factor itself is usually described in terms of ‘cubic feet per tonne’ instead of ‘cubic meters per tonne’, mainly because it is so much easier for practitioners to remember stowage factors of particular commodities in terms of cubic feet rather than in terms of cubic meters. Some cargoes (like iron ore) stow heavily and others (like coke) stow lightly. Reference to ‘cargoes’ will reveal that iron ore will stow around 13 cubic feet per tonne, whilst coke requires around 80 cubic feet per tonne. That means that a given space can contain around six times more tonnes of iron ore than of coke. In terms of ships, imagine you are operating a bulk carrier of 55,000 tonnes deadweight cargo capacity (DWCC), with a cubic capacity in her cargo holds of two (2) million cubic feet.

 

Freight payment may be on:

  • Weight
  • Measurement
  • Lump-Sum
  • Ad Valorem (used in the liner trades, usually is based on a percentage of declared value)

The most common in dry cargo voyage chartering is US$ per tonne. Be careful as some trades describe the quantity of cargo in metric tons and freight in long tons. 

  • Tonne (metric ton): 1,000 kg 
  • Long ton (2,240 lb) : 1,016 kg (approx.) 
  • Short ton (2,000Ib): 907 kg

Shor ton is rarely used, mostly seen in trades involving the United States. 

Measurement: In general cargo liner trades the calculation of freight may be described as weight or measurement in shipowners’ option: 

  1. If Stowage Factor (SF) below 40 CUFT per tonne – freight paid on a weight basis
  2. If Stowage Factor (SF) above 40 CUFT per tonne – freight paid on a measurement basis.

Lump-sum: is used in certain trades where, for example, Stowage Factor (SF) is not known accurately. When, loadable quantity is unknown at the time of fixing, for example, due to high Stowage Factor (SF) preferred for a specific trade route. Furthermore, the lump-sum freight rate is used if various ports in a discharge range, a trader wants one rate to apply for any port. When fixing a lump-sum freight rate, the shipowner must ensure that the maximum number of local discharge ports is specified; and rotation of the ports, for example in geographical rotation.