Bunker survey guide: how a chief engineer verifies the fuel actually delivered

Fuel is usually the largest single item in a vessel’s operating cost, and almost all of it is bought in a handful of operations a year, each settled in a few hours alongside. The bunker survey is the only moment where the paper figure and the physical fuel meet. Handle it with discipline and the invoice matches reality. Handle it casually and the difference disappears into a tank, with nobody able to prove anything a week later.

I write this from the engine side of the operation. As a chief engineer I have gauged barge tanks in the rain with a torch held in my teeth, argued density figures in a barge office the size of a wardrobe, and signed bunker delivery notes with a hand still smelling of fuel oil. None of what follows is theory. It is the sequence I would expect any of my engineers to be able to run without me standing behind them.

Scope. This is an independent working guide to the quantity side of bunkering, written for ships’ officers and the shore staff who read their figures. It does not replace your SMS bunkering procedure, the charter party’s bunker clauses, or the current editions of MARPOL Annex VI and ISO 8217 — where they differ from anything here, they govern.

What the survey actually is

A bunker quantity survey answers one question: how much fuel moved from the barge to the ship? Everything in the procedure exists to defend that answer. Two independent measurements are available — the barge’s tanks and the ship’s tanks — and a delivered figure claimed on the bunker delivery note (BDN). The survey’s job is to make the ship’s own measurement strong enough to stand against the other two.

On many ships the chief engineer runs this alone. On larger stems, or where the operator has been burned before, an independent bunker surveyor attends. Either way the method is the same, and the ship should never outsource its understanding of the figures: the surveyor leaves, the fuel and the invoice stay.

Before the hose is connected

The survey is mostly won or lost before any fuel moves.

Agree the plan. Which ship’s tanks receive, in what order, to what final soundings or ullages. The plan is agreed between the chief engineer and the barge, temperatures and stop signals included, before anything else happens.

Gauge the ship — all tanks, not just the receiving ones. Every fuel tank on board gets an opening sounding or ullage, including tanks nominally “not involved”. An unexplained rise in a tank that was supposed to be idle is one of the oldest tricks in the book, and the only defence is an opening figure for everything. Record the trim and list at the time of gauging; the calibration tables are entered with them, and a half-metre of trim can move the figure noticeably in a long, shallow tank.

Gauge the barge. Go on board the barge and witness its opening ullages yourself, tank by tank, with its own calibration tables open. Check the temperature in each barge tank while you are there — fuel expands with heat, and a warm cargo reads more volume for the same mass. Note the density and the temperature stated for the delivery; you will test both against reality later.

Dip for water. Water-finding paste on the sounding tape costs nothing and answers a question you cannot answer later. Free water found in a barge tank before delivery is a conversation to have at the manifold, not in an office three weeks on.

Rig the sampler. The representative sample is drawn continuously at the receiving ship’s manifold, throughout the delivery — a drip sampler filling slowly as the fuel passes. A sample handed over pre-filled from the barge, however politely, is not your sample. Decline it as the primary and take your own.

During the transfer

Once fuel is moving, the officer’s job is to watch for the ways a figure gets inflated.

The cappuccino effect is the famous one, and the name is accurate: air entrained into the fuel — from compressed-air blowing of lines, enthusiastic stripping, or pumping arrangements designed for the purpose — turns the surface of the fuel into foam. A sounding tape or ullage reading taken through foam reads liquid that is not there. The signs are recognisable once you have seen them: frothy, aerated samples at the manifold; sounding readings that will not settle; the hiss of air in the barge’s lines; a barge unusually eager to have closing gauging done quickly. The defence is patience. Let the tanks stand, re-gauge after the foam has collapsed, and compare against the barge’s closing figures. Air collapses; the discrepancy it created does not.

Watch the temperature. The delivered temperature should track what was declared. A higher temperature than declared means more observed volume for the same mass, and the difference does not belong to the ship.

Keep a timeline. Start and stop times, rate changes, any interruption and its stated reason, every re-connection. A quantity dispute is reconstructed from exactly this kind of contemporaneous note, and the side with the better notes usually wins.

After delivery: the arithmetic

Closing gauging mirrors the opening: all ship’s tanks, the barge’s tanks witnessed, trim and list recorded, temperatures taken. Then the numbers, in order, each written down:

1. Observed volume from the calibration tables, entered with the actual trim and list at gauging time.
2. Volume corrected to 15°C. The observed volume at the measured temperature is corrected with the volume correction factor (VCF) for the fuel’s density class — the standard petroleum measurement tables familiar to every tanker officer (the ASTM/ISO tables; Table 54B covers fuel oils). This step exists because volume is a function of temperature and mass is not.
3. Mass. Corrected volume multiplied by the density at 15°C from the BDN, with the standard weight-in-air correction applied. The result is metric tonnes — the figure the invoice is written in. Our bunker quantity calculator runs this same observed-volume → VCF → mass chain in the browser, which is a quick way to check a barge’s figure at the manifold before anyone signs.
4. Comparison. Ship’s delivered figure against the barge’s delivered figure against the BDN. Small differences are the nature of tank measurement. Differences beyond that need a decision at the manifold, not a shrug.

The discipline that matters: every line of this is written, signed and kept. An arithmetic trail that a stranger could re-run six months later is what turns “the chief says” into evidence.

Sampling and the legal layer

Quantity is commercial; the sample is regulatory as well. From the continuous drip sample at the manifold come the sealed bottles: the MARPOL delivered sample retained on board under MARPOL Annex VI, the ship’s commercial sample, the supplier’s, and the one that goes to the laboratory. Every bottle sealed, every seal number recorded on the BDN or the sampling record, every label countersigned by both sides. The BDN itself is retained on board for the period MARPOL Annex VI requires, and port state control officers do ask for it — bunkering paperwork is standard PSC territory, which is one reason it belongs in the same disciplined state as everything else a PSC preparation walk would touch.

Quality is the sample’s other job. The fuel is bought against ISO 8217, and the laboratory result against that specification is the ship’s protection if the fuel later misbehaves in the purifiers or the engine. Until the result is back, the prudent chief keeps the new fuel segregated rather than blending it over a known good bunker — a practice older than any standard and still the cheapest insurance on board.

When the figures do not agree

Disagreement is not a crisis; it is a procedure.

First, re-run the arithmetic on both sides — an entered trim correction or a transposed density solves more disputes than anyone admits. If the discrepancy stands, re-gauge together, barge and ship, and let the foam settle before anyone reads a tape. If it still stands, the ship documents rather than argues: a letter of protest stating the ship’s figure, the barge’s figure and the measurements behind the ship’s; the BDN signed for receipt only, with the quantity noted as disputed where that is the case; photographs of the soundings and gauges where practical; and the whole file — calculations, temperatures, seal numbers, timeline — kept together. The commercial follow-up belongs to the owner and the charterer. The evidence belongs to the ship, and it is built in those few hours or never.

Where the figures go next

A bunker figure does not retire when the barge lets go. It feeds the voyage economics — bunkers are the deduction that turns a freight figure into an earnings figure, which is exactly the arithmetic our voyage true-profit calculator walks through. And under the compliance regimes now pricing carbon, the same delivered tonnes drive the exposure: the EU ETS voyage cost follows the fuel burned, the FuelEU compliance balance follows its GHG intensity, and the year’s accumulated tonnes decide the ship’s CII rating band. A quantity figure sloppily established alongside becomes a compliance figure sloppily reported a year later — one more reason the few hours of the survey deserve the discipline this guide describes.

The bunker survey is not glamorous work. It is standing on a barge with a tape, writing numbers down and refusing to be hurried. But it is one of the few places on a ship where a single officer’s care translates directly, measurably, into money and legal protection — and where the habits of evidence a vessel keeps every day decide how strong its position is on the day something is challenged.