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Which State has primary responsibility?
Under the international law of the sea, the flag State has key duties of administrative, technical and social control over ships flying its flag. Port State control (PSC) is a supplementary mechanism for inspecting foreign ships in port; it does not replace the flag State’s duty of oversight. Both must act on the basis of the applicable instruments, the limits of their jurisdiction and the principle of proportionality.
What does the inspector assess?
PSC usually begins with a check of documents, certificates and the visible condition of the ship. Where there are clear grounds, a more detailed inspection may be carried out. Serious deficiencies can lead to corrective actions or detention. But not every administrative deficiency is a ground for detention; the decision must be proportionate to the risk, documented and based on the applicable procedures. The guidance on PSC procedures, including the current Resolution A.1206(34) (Procedures for Port State Control, 2025), is important for managers in the inspection field.
Institutional risk beyond a single ship
A rise in similar findings across several ships can be a sign of weak flag State oversight, crew training, the quality of ISM audits or the performance of delegated organisations. PSC data should therefore feed back into the flag State’s risk dashboard. Treating each detention purely as a single case throws away the opportunity for structural correction.
Suggested decision
Create a loop linking PSC data, flag oversight, periodic surveys and corrective action. Interpret indicators as rates and trends, taking account of fleet size and changes in the risk mix. Provide a clear review mechanism for complaints about undue delay or unjustified detention as well.
Practical checklist
- Document the difference between primary responsibility and supplementary oversight
- Keep a reasoned file for every detention or release
- Link recurring findings to reform of the flag system
- Measure trends against a suitable statistical denominator
Frequently asked questions
Does every deficiency on a ship lead to detention?
No. The type and severity of the deficiency and its effect on safety, security or the environment under the applicable rules are what matter.
Related advisory area: Regulación marítima internacional y asuntos de la OMI
Editorial note: this article is written for awareness and management decision-making. Applying any rule depends on the authentic current text, the legal position of the State concerned and the facts of the case. The content is independent and implies no endorsement by, or affiliation with, IMO.