Class certifies the ship against the society's own technical rules. Flag state certification makes it legal for the ship to trade under international conventions. Port State Control is the spot check that verifies both in a foreign port. Vetting is the charterer's private judgement on whether to risk cargo on the vessel. Only vetting decides the fixture.
What does each inspection regime actually check?
Each regime asks a different question about the same ship.
Class checks the ship as a physical object. Lloyd's Register describes classification as rules that define standards of quality, safety and reliability, assessed against the structural strength and integrity of the hull and the reliability of the propulsion and steering systems. Surveys run on a fixed cycle: annual surveys, intermediates, and the special survey, typically every five years.
Flag state certification checks legal compliance. The flag administration confirms the vessel meets the conventions it has ratified, SOLAS, MARPOL, STCW and the MLC among them, and issues the statutory certificates the ship must carry. In practice most flags delegate the survey work to a classification society acting as a recognised organisation.
PSC checks that the paper matches the ship. A Port State Control officer boards a foreign-flagged vessel in port, verifies the certificates, and samples the ship's actual condition and the crew's ability to operate it. PSC exists precisely because flag oversight varies: the Paris MoU's stated mission is to eliminate the operation of sub-standard ships through a harmonised system of port State control.
Vetting checks everything the other three produce, and then the management behind it. A vetting department reads the SIRE, RISQ or CDI inspection report, the operator's TMSA submission, the PSC history, class status, incident record and crew matrix, and forms a view about risk. It is the only regime that looks at the whole picture, because it is the only one whose money is on the line. How that process runs from questionnaire to fixture is covered in charterer vetting explained.
Who conducts each one, and under what authority?
| Regime | Run by | Basis | Output | Consequence of failure |
|---|---|---|---|---|
| Class survey | Classification society (private body) | The society's own rules; statutory work delegated by the flag | Class certificate; conditions of class | Suspension or withdrawal of class; P&I cover ceases; ship effectively cannot trade |
| Flag state survey | Flag administration, often delegated to class as a recognised organisation | UNCLOS and the IMO and ILO conventions the flag has ratified | Statutory certificates | Certificates lapse; the ship cannot legally sail |
| PSC inspection | Port state authorities under a regional MoU (Paris, Tokyo and others) | Conventions enforced on foreign ships in port | Inspection report with deficiencies; detention where warranted | Detention; refusal of access after repeat detentions |
| Charterer vetting | The charterer's vetting team, informed by SIRE, RightShip or CDI | The charterer's own risk criteria; contract, not statute | Acceptance or rejection for a fixture | Lost cargo; no appeal |
The four rows rest on different kinds of authority. A flag state acts as a sovereign: under UNCLOS Article 94, every state must effectively exercise jurisdiction and control over ships flying its flag, and the IMO's enforcement model relies primarily on that jurisdiction. A port state acts under a regional agreement: the Paris MoU coordinates 28 maritime administrations. A class society acts as a private rule-maker whose certificates carry weight because flags and insurers demand them. A charterer acts under no authority at all beyond the right to say no.
Which are regulatory and which are commercial?
Flag and PSC are regulatory. Both enforce international conventions, one from inside the ship's registry, one from the quayside of a foreign port. Their sanctions are legal ones: invalid certificates, detention, refusal of access.
Class sits between the two camps. It is a private body, but its certificate has quasi-regulatory force for two reasons. Flags authorise societies to conduct mandatory surveys and issue international certificates on their behalf, so a class surveyor is often also the statutory surveyor. And insurers hard-wire class into cover: Gard's Rule 8 requires the ship to be and remain classed with an approved society throughout the period of entry, with cover ceasing automatically if it is not.
Vetting is purely commercial. No convention requires it, no authority runs it, and no tribunal reviews it. The thresholds are the charterer's own and are mostly unpublished. That is what makes it both the least accountable regime and the most demanding one: a regulator must show cause; a charterer only has to prefer another ship.
Does a clean PSC record mean a ship will pass vetting?
No. PSC verifies minimum convention standards on a sampling basis; vetting judges acceptability against the charterer's own criteria, which start where the conventions stop. A ship can hold every certificate, carry a clean PSC history, and still be turned down on age, on the recency of its last SIRE or RightShip inspection, on the operator's management record, or on a single observation the charterer happens to weigh heavily.
The P&I club Skuld puts it plainly in its vetting guidance: you do not pass or fail a vetting inspection. The report gives the charterer information; the decision is theirs, made against thresholds they do not publish. A clean PSC record helps, because inspection history feeds the risk picture, but it answers a different question. The full comparison of what a PSC officer and a SIRE inspector each look for is drawn out in SIRE vs PSC.
Can class or flag findings affect a vetting outcome?
Yes, directly and sometimes mechanically. Vetting departments read conditions of class, overdue surveys and class withdrawals as management signals. RightShip's Safety Score model counts class among its inputs, and classification with a non-IACS society triggers one of its safety rules outright. Flag choice matters too: the Paris MoU publishes flag performance lists, and a ship flying a black-listed flag is banned from the entire region after three detentions in 36 months, 24 months for a grey-listed flag. Detentions also escalate the vessel's Ship Risk Profile, which raises inspection frequency and is visible to every vetting department that looks; how that profile is calculated is explained in the Paris MoU Ship Risk Profile.
The hardest link runs through insurance. Lose class and P&I cover ceases automatically under rules like Gard's Rule 8. An uninsured ship does not need to fail vetting; it never reaches it.
Which regime decides whether you get the cargo?
Vetting. Class, flag and PSC decide whether the ship may trade. The charterer decides whether it will, and that decision is made fresh each time. Oil majors state that express approvals are given only for specific voyages, not for a period of time, and RightShip's own methodology says a vetting recommendation is valid only for the nominated vessel and voyage under consideration. There is no approved list to get onto and stay on.
That per-fixture logic changes what preparation means. A statutory certificate is renewed on a cycle; a vetting file has to be current whenever the next cargo appears. Operators who treat vetting as one more periodic inspection fall behind the ones who keep their evidence continuously ready; how to prepare for charterer vetting covers that routine. For pooled tankers the same logic sets earnings directly, as pool points explained shows.