Bunkers: Quantity and Quality

Ask what a ship bought last night and the answer comes off the delivery note: 1,162 tonnes, ISO 8217, signed at the manifold, filed. Every number in that sentence is somebody else's arithmetic. Nothing was weighed: a depth of liquid was read against a barge's own tank table, corrected for a temperature nobody on your side took, and multiplied by a declared density the seller wrote down. The standard has no year on it, so it is whichever of seven editions the contract silently defaults to. And the fuel it describes was analysed ashore before that barge was loaded. The stem is not documented. It is asserted, and the assertions are worth several thousand dollars each.

So the course prices them. Lesson 1 rebuilds the delivery note out of its three claims and puts a figure on each: the sounding, the missing temperature correction, the declared-versus-tested density gap, and what the residual then does to the ROB ledger. Lesson 2 asks what a Coriolis mass flow meter actually removes, why Singapore made it compulsory in 2017 and Rotterdam and Antwerp-Bruges in 2026, and why the unauthorised alterations it later found were in the pipework rather than the instrument. Lesson 3 is the ten minutes at the manifold that decide a dispute two years later: the delivered sample MARPOL requires, the commercial samples a claim is really built on, the seal number that has to reach the delivery note, and why a barge-drawn bottle keeps losing cases. Lesson 4 converts the invoice into dollars per gigajoule, because on-specification VLSFO varies by three per cent in energy and the cheapest tonne is routinely the dearest gigajoule. Lesson 5 reads ISO 8217:2024 as a purchasing menu, including the viscosity floor that arrived with the 2024 edition and the sulphur figure three of its four tables now leave to the buyer. Lesson 6 is the arithmetic that decides whether a laboratory result is a claim at all, the recipient's limit of specification plus 0.59R, and the Clause 5 cases where every number was inside its limit and the fuel still wrecked injection systems. Lesson 7 prices the mass that was never hydrocarbon and turns storage life into a rule about how much to lift. Lesson 8 starts the clock: seven days on many supplier terms, against thirty on the balanced contract, and the costed choice between de-bunkering, blending down and burning with mitigation.

Four required exercises run on one Excel workbook, the bunker stem calculator, on lessons 2, 4, 6 and 8. It builds a delivery note from soundings and a tank table and prices the density argument inside it, ranks three on-specification offers per gigajoule and finds the break-even premium, applies the recipient's limit to six parameters of a laboratory report, and normalises two months of daily consumption to one reference calorific value so that an apparent deterioration can be handed back to the bunker that caused it.

Three subjects are deliberately not taught here, and each is named where it belongs. Our course Marine Engineering & Main Engines owns what this fuel does to machinery: the grade families, viscosity as a heating instruction, the density ceiling, the separators and the cat fines, along with the corrected-SFOC drift and the engine-versus-hull attribution that a consumption figure eventually runs into. Our free course Alternative Fuels for Shipping owns FAME chemistry, which is why the specific-energy formula here stops at the bio grades. And our free course Maritime Regulations, Explained owns the regulations, which matters more than it sounds: the tested calorific value you are about to learn to calculate never enters DCS, CII, the EU ETS or FuelEU at all. It changes the invoice, and nothing else.

The opening lesson is free to read as a sample. By the end you should be able to take one delivery note and one laboratory report, say which lines on them are claims and which are noise, price each in dollars, name the clock each one runs on, and write the four lines into the next nomination that would have prevented the argument.