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Tankers

Tanker cargo operations

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A tanker fixture looks like a dry cargo fixture with different words. But the differences go deeper. The cargo is pumped, not lifted, so a different party is responsible for delays at each end of the voyage. The charterer must approve the ship before it can be fixed at all. And the quantity is measured by two methods that almost always disagree.

Vetting comes before the fixture, not after

With a dry cargo ship, a charterer accepts the vessel’s description and fixes it. With a tanker, most serious cargoes are moved by or for oil majors and traders. They will not load a ship that their own inspection system has not cleared. So offers are made subject to the charterer’s vetting approval, and that condition is not a formality. If a ship’s inspection report is old, or its operator has an open finding, the charterer can refuse it without giving a reason.

The industry system is OCIMF’s Ship Inspection Report Programme. Its current form, SIRE 2.0, went live on 2 September 2024 and fully replaced the older questionnaire. It is digital and based on risk. The inspector completes a questionnaire built for that ship on that day, not a fixed list. So two ships of the same age and type do not get the same inspection.

For a broker, the result is about timing: vetting can be the slowest part of a tanker fixture. Ask about the ship’s vetting status before you offer it, not after the charterer asks.

The atmosphere in the tank is the safety system

An empty oil tank is more dangerous than a full one. A full tank has no room for a flammable mixture of air and vapour, but an empty tank is mostly vapour. The answer is inert gas. The air in the tank is kept below the oxygen level that allows burning, so the mixture inside stays outside the range in which it can burn.

That is why an inert gas system counts as cargo equipment, not firefighting equipment. If it fails, cargo work stops. It is not a defect that can wait until later. Next to it are the rules for gas freeing, tank entry and hot work (welding and similar work). All are set out in ISGOTT, the International Safety Guide for Oil Tankers and Terminals. OCIMF, the International Chamber of Shipping and the International Association of Ports and Harbors publish it together. The sixth edition, 2020, is the current one.

ISGOTT also contains the ship/shore safety checklist. The ship and the terminal complete it together before the transfer starts. Afterwards, it shows what each side agreed was true at the start.

The last three cargoes

If a tank carried the wrong product on the last voyage, it will contaminate this cargo. The contamination is often invisible and always expensive. So the standard question on a clean petroleum or chemical enquiry is: what were the last three cargoes? The answer decides whether the ship can be offered at all, before anyone discusses the rate.

Behind this question is tank cleaning. Cleaning between grades takes time, water, slop tank space (for dirty wash water) and sometimes a set cleaning order. A ship that must clean for two days to load the cargo earns for two days less. If the last cargo leaves residues that cannot be washed out, the ship cannot be offered for this cargo. Coated tanks let a ship carry more kinds of cargo and change how it is cleaned. Whether a ship is coated, and with what, is a chartering fact that no general vessel register holds.

On crude oil, cleaning works the other way round. Crude oil washing uses the cargo itself to clean the tanks during discharge. It removes oil stuck to the tank walls that would otherwise stay on board. MARPOL Annex I requires this equipment on crude carriers. It reduces pollution and increases the cargo delivered at the same time: oil washed off the tank walls is oil that gets delivered.

15,458

Tankers in the Neptune Atlas register. Of these, 13,540 have a deadweight, with a mean of 57,332. That is everything a register knows. Coating, segregated ballast, pump capacity, heating coils and vetting status are not in it, and these are what really decide a tanker fixture. A product that claimed otherwise would be filling those gaps with guesses.

Whose pump it is decides who is responsible for the delay

The terminal does the loading, from the shore. The ship does the discharging, with its own pumps. The charterparty (the charter contract) reflects this difference in a pumping warranty. The owner usually promises a discharge rate, or a pressure at the ship’s manifold (the pipe connection to the shore), kept up for the whole operation. If the ship fails to meet it, the lost time counts against the owner, not the charterer.

The details matter. If the ship keeps up the agreed pressure, it has performed, even if a limit on the shore side made the operation slow. That difference is at the centre of many tanker demurrage disputes.

Laytime (the time allowed for cargo work) is counted differently from dry cargo in one way. A tanker voyage charter often allows a fixed number of running hours for the whole operation, for all purposes, instead of a separate allowance at each end. Demurrage is paid at a daily rate from the moment those hours are used up. Otherwise it works like laytime and demurrage anywhere else.

Two measurements of one quantity

The bill of lading figure comes from the shore tanks. The ship’s figure comes from measuring the empty space in its own tanks (ullaging), correcting for temperature and trim, and using the calibration tables. The two figures differ almost every time. On a cargo of 100,000 tonnes, a difference of a fraction of a per cent is hundreds of tonnes of oil that either side may believe is theirs.

The trade’s answer is the vessel experience factor. This is the ship’s past ratio between its own figures and the shore figures. It is used to judge whether today’s difference is the ship’s normal gap or a real loss. It is used as evidence. It does not give either side a right. A letter of protest that records the difference is routine and is not an accusation.

Temperature is easy to overlook. Oil expands when warm, so a quantity in cubic metres means nothing without the temperature at which it was measured. Cargo is agreed either in standard volume at a reference temperature, or in weight in air or in vacuum. If you use the wrong basis, the figures show a shortage that did not really happen.

Chemicals and gas follow different rules again

Everything above is about oil. Chemical tankers work under the IBC Code and MARPOL Annex II. These group noxious liquid substances (harmful liquid chemicals) into categories and set the ship type, tank materials and discharge rules. A chemical parcel tanker carries a dozen grades that must be kept apart, so the work is about keeping many parcels separate, not handling one cargo. Gas carriers are different again. The chartering words look similar across all of them, but the operating limits are not the same.

References

Tanker sizesHandy to ULCC: where the tanker size bands sit, and why the coating and the last three cargoes decide suitability, not the deadweight. Dangerous goods and the IMDG CodeFour pieces of information turn a hazardous cargo into one that can be shipped. An enquiry without them is not yet an enquiry. How to calculate laytime and demurrageWhen the clock starts, what stops it, how the demurrage figure is worked out, and why most claims fail on the paperwork, not on whether they were right. Bunkers and fuel gradesTwo fuel grades, sometimes three, each with its own price. The largest number on a voyage estimate is also the one nobody guarantees.

Neptune Atlas

Neptune Atlas holds the register particulars that a tanker enquiry starts from and shows clearly where the register has no information. Coating, pump capacity and vetting status are not fields any commercial register holds, so they remain questions for the owner and are not filled in with guesses. Every paid plan starts with 7 free days. A card is needed to start them, and cancelling before they end costs nothing.

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