A bunker dispute rarely starts in the boardroom or over an invoice.
It often starts on deck — sometimes at 02:00 AM, in heavy rain, when the sounding tape comes up from a tank and the reading simply does not reconcile with the neat figure printed on the Bunker Delivery Note (BDN).
The BDN records the quantity declared by the supplier. It is an important commercial document, but it is not, by itself, an independent measurement of what the vessel has received.
After 20 years in marine surveying, one lesson remains constant:
When the numbers do not agree, go back to the tank, the measurements, the timing and the evidence.
That is where a professional Bunker Survey begins.
- QUANTITY: NEVER RELY ON ONE NUMBER
A bunker quantity survey is not about checking a BDN and signing a form.
It starts with establishing the vessel’s ROB (Remaining On Board) before delivery and ends with reconciling the post-delivery condition against the quantity declared.
The surveyor considers:
- ROB Before Bunkering: Physical measurements of the relevant fuel tanks before delivery.
- Pre- and Post-Delivery Soundings/Ullages: Measurements taken under comparable conditions wherever practicable.
- Tank Calibration Tables: Correct application of tank capacities and vessel trim/list corrections.
- Delivery Records: Pumping times, interruptions, quantities and operational records from the vessel and delivery unit.
- Temperature & Density: Observed data and applicable correction factors used in the quantity calculation.
And sometimes the difference is not where people first expect it.
A surveyor must look at lines, valves, tank configuration, measurement timing and the actual sequence of the transfer.
The question is simple:
Can the quantity stated on the BDN be independently reconciled with what was physically observed?
- FIELD MEASUREMENT: EXPERIENCE MATTERS
On paper, bunker calculation is mathematics.
On board, it is mathematics combined with judgement.
A few centimetres on a sounding tape can represent tonnes of fuel. A vessel changing trim during transfer can alter readings. Freshly pumped fuel may be turbulent or contain entrained air. Temperature can vary between tanks and measurement points.
The experienced surveyor therefore watches the operation, not just the figures.
| Field Variable | What the Surveyor Watches For |
| Measurement Timing | Stabilisation, foam, turbulence and entrained air before final readings. |
| Trim & List | Changes in vessel condition affecting tank readings and calibration. |
| Temperature | Differences between observed fuel temperature and the basis used for calculation. |
| Tank Geometry | Calibration limitations, inaccessible spaces and unusual tank configurations. |
| Free Water / Residues | Water or sediment that may affect the determination of net fuel quantity. |
A good survey report therefore records more than what was measured.
It records when, where, how and under what conditions it was measured.
That field context is often what makes the difference when the figures are later challenged.
- SAMPLING: THE CHAIN OF CUSTODY STARTS AT THE MANIFOLD
Where sampling is within the agreed scope, sample integrity is critical.
The normal sequence is:
Continuous Manifold Sampling → Sealing → Identification → Chain of Custody → Laboratory Testing
The surveyor observes the sampling operation, verifies identification and seal numbers, records the relevant details and maintains traceability through handover.
The laboratory determines whether the fuel complies with the applicable specification.
The surveyor’s role is different:
to document how the sample was collected, sealed, identified and transferred.
When a quality claim arises days or weeks later, that chain of custody can become as important as the laboratory result itself.
- NUMBERS ARE EASY. EVIDENCE IS HARDER.
Anyone can copy numbers from a bunker receipt.
A professional surveyor builds the contemporaneous record behind those numbers.
Depending on the agreed scope, this may include:
- Original field measurement records and calculation sheets;
- Density, temperature and correction data;
- Key operational timestamps;
- Photographs of relevant measurements, interfaces and seals;
- Records of interruptions, abnormalities or disputed observations;
- Letters of Protest or other contemporaneous records where circumstances warrant.
This creates a traceable sequence:
ROB Before → Delivery → ROB After → Calculated Quantity → BDN Reconciliation
When a discrepancy appears, the surveyor can go back through the sequence and identify where the numbers stopped telling the same story.
- WHY INDEPENDENT VERIFICATION MATTERS
Most bunker deliveries finish without a dispute.
But when a discrepancy does arise, arguments made days later are rarely as valuable as evidence recorded at the time and at the place where the event occurred.
An independent bunker survey does not replace the BDN or the contractual arrangements between the parties. It provides an independent technical record of the measurements, observations and calculations made during the operation.
That record can help Shipowners, Charterers, Insurers and P&I Clubs assess quantity or quality claims on the basis of evidence rather than assumption.
VM CONTROL INSIGHT
A bunker survey is not about proving the supplier wrong or the BDN right.
It is about going to the tanks, checking the measurements, understanding the operation and documenting what actually happened.
Because after 20 years on board, one thing is clear: when bunker figures are disputed, experience tells you where to look — but evidence tells you what happened.