1. Why a Vessel Experience Factor?
Marine cargo measurement is inherently uncertain: a ship's tanks are calibrated capacity tables read under list, trim, sloshing and temperature stratification, while shore measurement uses meters or shore tanks of differing accuracy. Any single voyage's ship-vs-shore difference is mostly noise. But across many voyages a persistent tendency emerges — a given vessel may consistently read slightly more or less than shore. The VEF distils that persistent tendency into one factor, so the vessel's figure can be compared to, or reconciled against, shore on a known footing.
2. VEFL vs VEFD
VEFL (Load)
Vessel vs Shore B/L
Built from loading voyages: vessel load TCV against shore bill-of-lading TCV. Used to compare shore-delivered to vessel-received.
VEFD (Discharge)
Vessel vs Shore Outturn
Built from discharge voyages: vessel TCV against shore outturn TCV. Used to compare vessel-sent to shore-received.
Same Math
Identical Algorithm
VEFL and VEFD use the same §9 procedure — only the source of the voyage ratio differs.
3. The Calculation (API MPMS 17.9 §9)
Note that the mean used for qualifying is the ratio of summed volumes (not the average of individual ratios), and the final VEF is likewise a ratio of sums — but over the narrower set of qualifying voyages.
4. The Two Qualifying Filters
Two filters protect the VEF from bad data without letting an operator cherry-pick favourable voyages:
Filter 1 — Major Error
0.98 – 1.02
Ship capacity tables carry up to ~2% error; a ratio beyond ±2% signals a measurement blunder and is removed before the mean.
Filter 2 — ±0.30%
mean × (1 ± 0.003)
After the mean is known, voyages whose ratio sits more than 0.30% from it do not qualify — they are outliers within the normal band.
Floor
5 voyages
Fewer than five qualifying voyages → no valid VEF. Other exclusions (post-drydock, onboard-only) come from §8.3.
5. Worked Example (Appendix C — M/T CONSENSUS)
Thirteen recorded voyages. One (Cusiana, ratio 1.04702) is a major error and is dropped. The mean of the remaining twelve is 1.00105, giving a qualifying window of 0.99805–1.00405. Two more voyages fall outside that window (1.00414 and 0.99644) and do not qualify, leaving ten:
This calculator reproduces the standard's published result of 1.0011 exactly. Applied as a VEFL, a vessel reporting a load TCV would be compared to shore on the basis that it tends to read about 0.11% high.
6. Standards & References
| Standard | Scope |
|---|---|
| API MPMS Ch. 17.9 / IP HM 49 | Vessel Experience Factor (VEF) — §8 qualification, §9 calculation, App. C form/example |
| API MPMS Ch. 17 | Marine Measurement (vessel gauging, OBQ/ROB, cargo measurement) |
| API MPMS Ch. 12 | Calculation of Petroleum Quantities (TCV basis) |