Vessel experience factor (VEF): how it is built and used

A vessel experience factor (VEF) is the average ratio between a tanker's own cargo figure and the shore figure over earlier voyages. It shows whether today's difference between ship and shore is normal for that ship. It does not change the quantity on the bill of lading.

How a vessel experience factor is built

For each voyage, the ship's figure is divided by the shore figure. The UK P&I Club (2015) describes the vessel load ratio (VLR): the quantity received as measured on board, which is the total calculated volume (TCV) less the on-board quantity (OBQ) at the loading port, divided by the bill of lading figure. The vessel discharge ratio (VDR) works the same way at discharge, with the quantity remaining on board (ROB) and the outturn figure. The mean of the qualifying ratios over several voyages is the VEF, calculated for loading and for discharge separately.

Both sides are compared as volumes at standard temperature, so both must be corrected in the same way: see volume correction factor and density at 15 °C. The ship's side starts from ullages and the tank tables, covered in ullage reports and sounding tables.

The club prefers loading data. At discharge, cargo left in ship and shore lines and uncertain shore tank figures make an accurate VDR hard to obtain. At loading, calibrated shore tanks and the shipper's declared figures can be set directly beside the volume received on board.

Not every voyage qualifies. The club lists voyages that are normally left out: the maiden voyage and voyages before a structural change to the cargo tanks, the first voyage after dry-docking (not necessarily in the clean products trade), voyages without shore measurements, voyages after a non-liquid cargo, and voyages whose ratio suggests a significant error. It also counts only voyages within a set margin of the average ratio of all voyages listed.

The recommended practice is API MPMS Chapter 17.9, Vessel Experience Factor (VEF), 3rd edition, July 2019. According to API's 2025 catalogue it covers data compilation, maintenance and validation, the appropriate use of a VEF, parcel tankers, compartmental VEFs and vessel-to-vessel transfers, for liquid bulk cargoes including crude oil, petroleum products, chemicals and liquid petroleum gases. Vegetable oils are not named in that scope. Its guidelines for data validation, which decide which voyages count, are not reproduced here: the document is sold by API.

Worked example: nine loadings, one outlier

A fictitious tanker with nine loadings. Volumes are in cubic metres at 15 °C; the ship's figure is TCV less OBQ. Each ratio is rounded to five decimals, averages are taken over those rounded ratios, and the VEF is rounded to four decimals.

Voyage	Shore (B/L), m³	Ship, m³	Ratio ship/shore	Note
1	28,450.000	28,391.000	0.99793	first loading after dry-docking
2	30,210.500	30,168.200	0.99860
3	29,875.000	29,826.300	0.99837
4	31,020.000	30,982.800	0.99880
5	30,540.000	30,747.700	1.00680
6	29,990.000	29,943.000	0.99843
7	30,760.000	30,718.500	0.99865
8	31,105.000	31,054.000	0.99836
9	30,330.000	30,290.000	0.99868

1. Voyage 1 is left out on the dry-docking criterion, before any averaging.
2. The mean of voyages 2 to 9 is 0.99958625.
3. Each ratio is compared with that mean. Voyage 5 lies 0.007214 above it; the other seven lie between 0.000786 and 0.001226 below it. In this example we reject a ratio more than 0.0050 from the mean. That limit is our own choice for the illustration, not the API figure.
4. The VEF is the mean of the seven remaining ratios: 0.99855571, rounded to 0.9986.

Kept in, voyage 5 would lift the VEF to 0.9996. A ratio like that usually has a cause worth finding. Britannia P&I (2026) lists causes of ship–shore differences such as calculation errors, incorrect shore tank calibration, a wrong line displacement figure and flow meter calibration errors. Rejecting the voyage statistically does not explain it.

Applying the VEF to a new loading

On the next loading the shore figure is 32,540.000 m³ and the ship measures 32,410.000 m³. The raw difference is −130.000 m³, or −0.400%.

Because the VEF is ship over shore, dividing the ship's figure by it puts that figure on the shore's footing, based on this ship's history: 32,410.000 / 0.9986 = 32,455.438 m³. The remaining difference is −84.562 m³, or −0.260%. With voyage 5 left in (VEF 0.9996) it would be −117.031 m³, or −0.360%.

So one voyage decides on which side of a common allowance this loading falls. Britannia calls ±0.3% a commonly quoted allowance for signing the bill of lading, and says that on oil tankers the difference between the ship's figure and the B/L figure should be less than 0.3% after applying the VEF. Above that, it advises the master not to sign until the source of the discrepancy is found, and to require re-gauging. Below it, the master may sign under protest with a letter of protest. Britannia adds that some jurisdictions recognise no allowance at all.

A short example from the quay

A cargo of vegetable oil is measured at 1,000 t in the shore tank, and the ship's own figure on board comes to 990 t: 10 t short. That is odd enough to check. The ship's earlier voyages show how its own figure compares with the bill of lading figure: it may always come out a little lower or a little higher, and the ship often applies a correction of its own. If it does, your figure has to be corrected the same way before the two are compared. The VEF is used for that check only. If the earlier voyages show the same gap, the surveyor can tell the client that the difference looks normal for this ship and that the cargo is probably on board. But nobody knows for certain, so the surveyor remains responsible, and the factor alone is worth little.

What a vessel experience factor is not

Not a correction of the cargo quantity. The bill of lading carries the reference figure for the quantity shipped (Britannia). The VEF moves only the ship's figure, and only for the comparison. In the example the B/L stays at 32,540.000 m³.

Not proof of what happened on this voyage. A VEF is a statistic about earlier voyages, built from the ship's own records. The UK P&I Club calls a properly developed VEF a first line of defence against spurious paper shortage claims. For the surveyor it is a control tool and nothing more: it does not take the surveyor's responsibility for a shortage away. It also warns that discharge ratios in particular are not impervious to error or external manipulation as a basis for that historical figure, which is why it prefers loading data. Each ratio compares the ship with a shore figure, so a systematic error at the terminals where the ship usually loads ends up in the VEF as well. A difference that looks normal after the VEF makes a paper loss plausible; it does not show which figure is right. For the claim itself, see the outturn report and cargo claims in bulk shipping.

Not valid for every operation. The UK P&I Club treats a VEF as relevant only to full cargo transfers. In a ship-to-ship transfer there is no shore figure, both ships may apply their own VEF, and a mother vessel doing a part discharge cannot rely on hers.

Keeping a VEF you can defend

Based on the working practice of our sector specialist: 25 years in the port, 20 of them as a cargo surveyor. A vessel experience factor is a control tool: it does not relieve the surveyor of responsibility for a shortage, and the client is told.

General advice: ask for the voyage list behind a VEF, not only the factor. A list that holds up shows, per voyage, the shore and ship figures, the OBQ or ROB, the reason for every exclusion, and the point from which the list was restarted after a change to the tanks. Reading that list against the ullage report is part of what an independent cargo surveyor does.

FOSS

FOSS is software for inspection companies and the port, with a sector specialist at the table. Measurements are entered once, offline on board if need be, and nine report types come from that input. The outturn per receiving medium is set against the bill of lading weight, and a shortfall of more than 0.5% flags a protest automatically.