Neptune Atlas

Tankers

Tanker cargo operations

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A tanker fixture looks like a dry cargo fixture with different words in it, and the differences are structural. The cargo is pumped rather than lifted, so the two ends of the voyage have different owners of the delay. The ship has to be approved by the charterer before she can be fixed at all. And the quantity is measured by two methods that reliably disagree.

Vetting comes before the fixture, not after

On a dry cargo ship, a charterer takes the vessel’s description and fixes. On a tanker, most serious cargoes are moved by or for oil majors and traders who will not load a ship their own inspection regime has not cleared. Offers are made subject to charterer’s vetting approval, and that subject is real: a ship whose inspection report is stale, or whose operator has an open finding, can be declined without a reason being given.

The industry mechanism is OCIMF’s Ship Inspection Report Programme. Its current form, SIRE 2.0, went live on 2 September 2024 and replaced the older questionnaire entirely. It is risk-based and digital: the inspector completes a questionnaire compiled for that ship on that day rather than a fixed list, which means two ships of the same age and type do not get the same inspection.

For a broker the consequence is scheduling: a vetting can be the long pole in a tanker fixture. Ask about the vetting position before offering, not after the charterer does.

The atmosphere in the tank is the safety system

An empty oil tank is more dangerous than a full one, because a full tank has no room for a flammable mixture and an empty one is mostly vapour. The answer is inert gas: the tank atmosphere is kept below the oxygen concentration that will support combustion, so the mixture inside is outside the flammable range at all times.

That is why an inert gas system is a piece of cargo equipment rather than a fire-fighting one, and why its failure stops cargo operations rather than merely being a defect. Alongside it sit the regimes for gas freeing, tank entry and hot work, all of which are laid out in ISGOTT, the International Safety Guide for Oil Tankers and Terminals, published jointly by OCIMF, the International Chamber of Shipping and the International Association of Ports and Harbors. The sixth edition, 2020, is the current one.

ISGOTT is also where the ship/shore safety checklist lives. That checklist is completed jointly before transfer begins, and it is the document that shows, afterwards, what each side agreed was true at the start.

The last three cargoes

A tank that carried the wrong thing last voyage contaminates this one, and the contamination is frequently invisible and always expensive. So the standard question on a clean petroleum or chemical enquiry is the last three cargoes, and the answer decides whether the ship is offerable before any discussion of the rate.

Behind it sits the cleaning. Tank cleaning between grades takes time, water, slop capacity and sometimes a specific cleaning sequence, and a ship that must clean for two days to lift the cargo has two days less earning. Where the previous cargo leaves residues that cannot be washed out, the ship is simply not a candidate. Coated tanks widen what a ship can carry and change how she is cleaned; whether a ship is coated, and with what, is a chartering fact that no general vessel register carries.

On crude, the equivalent mechanism runs the other way. Crude oil washing uses the cargo itself as the cleaning medium during discharge, removing clingage that would otherwise stay aboard as residue. It is required equipment on crude carriers under MARPOL Annex I and it is a pollution measure and a cargo outturn measure at the same time: oil washed off the bulkheads is oil that gets delivered.

15,458

Tankers in the Neptune Atlas register, of which 13,540 carry a deadweight, at a mean of 57,332. That is the whole of what a register knows. Coating, segregated ballast, pump capacity, heating coils and vetting status are not in it, and they are what actually decide a tanker fixture. A product that pretended otherwise would be filling those gaps with assumptions.

Who owns the pump decides who owns the delay

Loading is done by the terminal, from the shore. Discharge is done by the ship, with her own pumps. That asymmetry is written into the charterparty as a pumping warranty: the owner typically warrants a discharge rate or a pressure at the ship’s manifold, sustained for the operation, and failure to meet it is the owner’s time rather than the charterer’s.

The alternatives matter. A ship that maintains the agreed pressure has performed even if the shore’s restriction made the operation slow, and that distinction is the substance of a large share of tanker demurrage arguments.

Laytime itself is counted differently from dry cargo in one respect worth knowing: a voyage charter of a tanker commonly allows a fixed number of running hours for the whole operation, all purposes, rather than separate allowances at each end, and demurrage runs at a daily rate from the moment it is exhausted. The mechanics are the same as 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 ullaging her own tanks, correcting for temperature and trim, and applying the calibration tables. They differ almost every time, and a difference of a fraction of a per cent on a cargo of 100,000 tonnes is hundreds of tonnes of oil that either side may believe is theirs.

The trade’s answer is the vessel experience factor: the ship’s historical ratio between her own figures and shore figures, used to judge whether today’s discrepancy is her normal offset or an actual loss. It is an evidential tool, not an entitlement. A letter of protest recording the difference is routine and is not an accusation.

Temperature is the quiet part. Oil expands, so a quantity in cubic metres is meaningless without the temperature it was measured at, and cargo is contracted in standard volume at a reference temperature or in weight in air or in vacuum. Getting the basis wrong produces a shortage that never happened.

Chemicals and gas are different regimes again

Everything above describes oil. Chemical tankers work under the IBC Code and MARPOL Annex II, which categorise noxious liquid substances and dictate ship type, tank materials and discharge requirements, and a chemical parcel tanker is a coordination problem with a dozen grades and segregations rather than a single cargo. Gas carriers are different again. The chartering vocabulary looks similar across all of them; the operating constraints do not transfer.

References

Tanker sizesHandy to ULCC: where the tanker 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 a shippable one. An enquiry without them is not yet an enquiry. How to calculate laytime and demurrageWhere the clock starts, what stops it, how the demurrage figure is actually worked out, and why most claims are lost on the paperwork rather than the merits. Bunkers and fuel gradesTwo grades and sometimes three, priced apart. The largest number on a voyage estimate is also the one nobody warrants.

Neptune Atlas

Neptune Atlas carries the register particulars a tanker enquiry starts from and shows plainly where the register is silent. Coating, pump capacity and vetting status are not fields any commercial register holds, so they stay questions for the owner rather than gaps filled by assumption. 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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