A bunker quantity survey gauges every fuel tank before and after transfer, takes temperature at multiple depths, corrects observed volume to 15 °C using the product’s correction table, applies density from a representative sample, and calculates the wedge in partly filled tanks. The report states vessel, barge and surveyor figures separately.
The procedure
- Initial gauging of every bunker tank — ullage or sounding — with trim and list corrections from the vessel’s own tables.
- Temperature at three depths per tank. Heated fuel oil stratifies, and a single reading misstates the volume.
- Wedge calculation where a tank is partly filled and trim prevents the liquid reaching the sounding point.
- Transfer observed, with the barge’s own figures recorded independently.
- Representative drip or line sample taken, sealed and split three ways — vessel, supplier, surveyor.
- Final gauging repeated identically, volume corrected to 15 °C, density applied to give mass.
- Report shows vessel figure, barge figure and surveyor figure side by side, with the difference stated plainly.
The wedge, in plain terms
When a tank is not full and the vessel is trimmed by the stern, the fuel lies as a wedge that may not reach the forward sounding pipe. Sounding gives zero, the tank is recorded as empty, and a real quantity of fuel vanishes from the calculation. The wedge formula reconstructs that volume from the trim, the tank geometry and the actual sounding. On a vessel with several partly filled tanks it is regularly the largest single disputed figure in the survey.
The three disputes that come up every time
| Dispute | Root cause | How it is settled |
|---|---|---|
| Quantity short against the delivery note | Barge meter versus vessel tank gauging; temperature and density differences; the wedge | Independent gauging both ends, corrected to 15 °C, with the working shown |
| Density different from the bunker delivery note | Sample not representative, or taken from the wrong point | Continuous drip sample at the manifold, sealed and split three ways |
| Quality off-specification after delivery | Contamination, commingling with existing stock, or a genuinely off-spec parcel | Retained sealed samples analysed by an accredited laboratory |
On-hire and off-hire bunkers
The same method applies at charter delivery and redelivery, where the quantity remaining on board is a payment item. Doing this properly at both ends removes an entire category of charter dispute — see the on-hire and off-hire guide.
Frequently asked questions
What is included in a bunker survey?
Tank-by-tank gauging before and after with temperature profiles, volume correction to 15 °C, density from a representative sample, the wedge calculation, sampling and sealing, and a three-way figure comparison.
Who pays for the bunker survey?
Whoever is exposed to the quantity: the buyer of the bunkers, the charterer, or the owner under a charterparty. Suppliers occasionally instruct their own.
How long does a bunker survey take?
Two to six hours depending on tank count and transfer duration, plus the report within one to two working days.