A carrier tells you a booked vessel has been "detained by Port State Control" and gives no further detail. That single word covers two very different situations: a minor paperwork finding fixed in an afternoon, or a ship held in port for weeks until its fire safety system is rebuilt. Knowing which one you are dealing with, and what Port State Control actually is, changes how you judge the delay and what you ask the carrier for.
Port State Control is not flag State control
Every ship flies a flag, and its flag State (the country where it is registered) carries the primary legal responsibility for making sure the ship is built, equipped, crewed and operated to international standards. That is flag State control, and it applies wherever in the world the ship happens to be.
Port State Control (PSC) is a separate, second check. It is the right of the country a ship is visiting, the port State, to board a foreign-flagged ship calling at one of its ports and verify for itself that the ship complies with the international conventions its flag was supposed to have already secured. The International Maritime Organization (IMO) describes the relationship directly: flag State control is the primary line of defense, and "port State control provides a safety net to catch substandard ships." PSC does not replace flag State responsibility. It exists because a flag State's own oversight is not always enough, particularly for older ships or flags with a thin inspection record, and a port State has a direct interest in not letting an unsafe ship sail from its own harbor.
The IMO's own procedural framework, Resolution A.1185(33), Procedures for Port State Control, 2023, lists the conventions a PSC inspection checks a ship against: SOLAS (safety of life at sea), the Load Lines Convention, MARPOL (pollution prevention), STCW (crew training and certification), the Tonnage Convention, the Anti-fouling Systems Convention, COLREG (collision regulations), the civil liability conventions for oil and bunker pollution, the Ballast Water Management Convention and the Nairobi Wreck Removal Convention. Many PSC regimes also inspect against the International Labour Organization's Maritime Labour Convention, 2006 (MLC), which covers crew wages, hours of rest and living conditions, under a separate ILO framework referenced in the same IMO procedures.
The regional MOU system
No single body runs Port State Control worldwide. Instead, groups of neighboring maritime administrations coordinate their inspection regimes through a regional Memorandum of Understanding (MOU), so a ship is not boarded on a different, uncoordinated basis at every port in the region. The IMO's own page on the subject lists nine regional PSC MOUs plus the separate United States Coast Guard PSC programme, which functions as a tenth regime.
The two largest, and the ones most relevant to container and bulk trades, are:
- Paris MoU, covering the European coastal states and the North Atlantic basin from North America to Europe. As of September 2026 it has 28 member maritime administrations, from Belgium and France to Canada and the United Kingdom (Russia's membership has been suspended). It began operating in 1982.
- Tokyo MoU, covering the Asia-Pacific region, with 22 member Authorities as of September 2026, aimed at eliminating substandard shipping and promoting maritime safety across the region.
These MOUs are not isolated from each other. A ship's inspection and detention history in one region is visible to inspectors in another: results feed into the IMO's Global Integrated Shipping Information System (GISIS) and the public Equasis database, which aggregates PSC history across the regional MOUs and the US Coast Guard programme into one per-ship record. IMO renewed its data-exchange agreement with Paris MoU on this basis on 26 February 2026, the sixth such agreement following similar ones signed with the Abuja, Indian Ocean, Tokyo, Mediterranean and Riyadh MOU secretariats in 2025. In practice, a poor inspection record built up calling at European ports does not stay hidden when the same ship later calls in Asia-Pacific, because it feeds the same shared risk picture.
Deficiency vs detention: what the words actually mean
These two terms get used loosely, but the IMO's own procedures define them precisely, and the distinction matters for how long a delay might run.
| Term | IMO definition (paraphrased) | What it means in practice |
|---|---|---|
| Deficiency | A condition found not to be in compliance with the requirements of the relevant convention. | A finding that must be corrected, sometimes before departure, sometimes at the next port or within a set period. The ship can often still sail. |
| Detention | Intervention action taken by the port State when the ship or its crew does not correspond substantially with the relevant conventions, to ensure the ship will not sail until it can proceed to sea safely, whether or not that affects its normal departure schedule. | The ship is formally prevented from sailing until the underlying deficiencies are rectified and the port State control officer (PSCO) is satisfied it is safe to proceed. |
Not every deficiency triggers a detention. The IMO's own guidelines for PSCOs (Appendix 2 of the 2023 Procedures) direct the officer to use professional judgement, weighing whether the ship can still safely navigate, fight a fire, maintain stability, communicate in an emergency and carry its cargo safely for the intended voyage. If any of that assessment comes back negative, the ship "should be strongly considered for detention," and a combination of less serious deficiencies can add up to the same outcome even when no single one would. Where deficiencies genuinely cannot be fixed at the port of inspection, the PSCO may instead let the ship proceed to another port under specific conditions, with the next port's authority and the flag State notified in advance.
A detention is not the end of the process. The company or its representative has a right of appeal against a detention (the appeal does not suspend it), and the IMO's procedures state plainly that "if a ship is unduly detained or delayed, it should be entitled to compensation for any loss or damage suffered."
How ships get selected for inspection
Port States cannot board every foreign ship that calls, so both Paris MoU and Tokyo MoU use a risk-based targeting system built around a Ship Risk Profile, rather than random or purely quota-based selection. Under the Paris MoU's New Inspection Regime, the profile is calculated from a set of factors drawn from a ship's inspection history in the region over roughly the previous three years: the ship's type and age, its number of deficiencies, its number of detentions, the performance record of its flag, the performance record of its recognized organization (classification society acting on the flag's behalf), and the performance ranking of the company responsible for its safety management. The profile sorts ships into three categories, each with its own inspection window:
| Risk category | Inspection window |
|---|---|
| High Risk Ship | 5 to 6 months after the last inspection |
| Standard Risk Ship | 10 to 12 months after the last inspection |
| Low Risk Ship | 24 to 36 months after the last inspection |
A ship that has not been inspected within its window becomes a mandatory priority for inspection the next time it calls. Outside that scheduled cycle, an "overriding factor" (such as a collision or a pollution discharge) or an "unexpected factor" (such as reported cargo problems or a failure to report arrival times correctly) can push a ship forward for inspection regardless of where it sits in its normal window. This structure is periodically refined. As of September 2026, coordinated work is under way to revise how flag and recognized-organization performance feed the profile and to add environmental criteria, so treat the specific weighting as something that moves rather than a fixed formula.
The scale of enforcement is real. Under its 2025 Annual Report, published 1 July 2026, Paris MoU recorded 16,474 inspections, of which 9,879 turned up at least one deficiency, resulting in 688 detentions and 19 refusals of access. That works out to a detention rate of 4.18 percent, up from 4.03 percent in 2024 and the fourth consecutive year above pre-pandemic levels. Fire safety, structural and electrical faults, and seafarer welfare issues under the MLC accounted for close to 40 percent of all deficiencies recorded that year.
What happens to the cargo aboard a detained vessel
A detention is a judgment about the ship, not the cargo. Nothing in the IMO's detention framework authorizes a PSCO to seize, unload or otherwise take control of cargo, and a detained ship's containers or bulk cargo generally stay exactly where they were stowed. One factor a PSCO does weigh when deciding whether to detain is whether the crew can "safely handle, carry and monitor the condition of the cargo" for the rest of the voyage, so cargo-handling safety is part of the underlying seaworthiness question, but the detention itself targets the vessel's fitness to sail, not the goods on board.
That does not make the delay harmless. The ship, and everything loaded on it, stays in port until the deficiencies are rectified and the detention is lifted, which can run from a day or two for a straightforward fix to several weeks for a major structural or fire-safety rebuild. Every piece of cargo aboard is delayed by exactly as long as the ship is, and so is anything downstream that was connecting through that vessel's next port call.
It is worth keeping this separate from a different, much more common use of the word "detention" in freight: container detention (also called per diem), the daily charge a carrier bills for holding onto its container past the free time allowed. That is a commercial billing dispute over equipment return, not a Port State Control action, and our guide to demurrage and detention invoices under the FMC rules covers it in full. The two uses of "detention" describe unrelated problems, and it is easy to assume a carrier's detention notice means the vessel when it actually means the box.
Classification societies do not do PSC's job
A classification society verifies that a ship's hull, machinery and equipment meet its own technical class rules, and issues a class certificate as evidence. Many classification societies also act as a "recognized organization" (RO), authorized by a flag State to carry out statutory surveys and issue certificates on the flag's behalf, a role the IMO's procedures define specifically in those terms. Both of these are checks against the flag State's own standards, whether performed directly or delegated to the RO.
Port State Control is a different, government-run check by a country the ship is visiting, and a valid class certificate does not exempt a ship from PSC inspection. The two systems are connected only in that a recognized organization's own detention and deficiency record feeds into the flag performance and RO performance factors used to calculate a ship's risk profile. A ship can hold a fully valid class certificate and still be detained by a PSCO who finds the vessel does not, in practice, correspond with what that certificate says on paper. The IMO's procedures go further and require PSC inspectors to be independent of ROs and classification societies entirely, with no commercial relationship to either, precisely so the two checks do not collapse into one.
What a shipper or forwarder can actually do
If a carrier tells you a vessel is PSC-detained, there is very little you can do directly. The detention is a matter between the port State, the flag State and the ship's operator, and rectifying it is the carrier's problem to solve, not yours. That said, a few things are worth doing:
- Ask whether it is actually a detention, or a deficiency the ship sailed with. The two carry very different timelines, and carriers sometimes use "detained" loosely for any PSC finding.
- Ask for the underlying reason category (structural, fire safety, crew certification, MLC) if the carrier will share it. A structural or fire-safety detention historically runs longer than a documentation or minor equipment finding.
- Request the detention and release documentation for a delay claim. Under the IMO's own procedures, a ship that is unduly detained is entitled to compensation, and if your contract of carriage or insurance depends on documenting the cause of a delay, the port State's detention and release notices (and the flag State's response) are the paper trail that supports it.
- Do not assume the cargo has been touched. A detention is about the vessel, not an inspection or hold on your goods, so there is usually no separate customs or cargo process to chase in parallel unless the carrier or terminal tells you otherwise.
If a lane you rely on runs through a chokepoint or region where disruption already compounds delay risk, our coverage of the Strait of Hormuz disruption and general average, the mechanism that spreads the cost of a ship's own emergency across everyone's cargo on board, are both worth reading alongside this one. For cargo that moves by RoRo rather than container, where seaworthiness findings can affect a different set of deck and lashing equipment, see our guide to RoRo vs container shipping for vehicles and machinery.
Find a forwarder who can talk you through it
A forwarder who has actually handled a PSC delay before can usually tell within a few questions whether a carrier's "detained" means a two-day fix or a three-week one. CargoLinked's directory lists freight forwarders by country and service, all self-published by the companies themselves, so check a company's own track record and credentials before relying on it for a time-sensitive lane. If you would rather describe your shipment and let forwarders respond, you can also post it to the public requests board, where eligible forwarders can quote against a validity date you set.
Regulatory detail changes: PSC risk-profile methodology, MOU membership and detention statistics are updated periodically by Paris MoU, Tokyo MoU and the IMO. Confirm current figures directly with the relevant MOU before relying on them for a specific shipment or claim.
