A ship arrives in port. Cargo comes off, cargo goes on, and a few days later it leaves. That's the visible part — the part you can photograph from a pier in Rotterdam or Singapore.

But somewhere on that ship, often within hours of arrival, a stranger in steel-toed boots and a hi-vis vest has climbed the gangway with a clipboard. They are not from the shipping company. They are not from the cargo owner. They work for the country the ship is currently floating next to, and they have the legal authority to keep that ship from leaving.

This is port state control. The paper trail it generates is one of the most underused datasets in maritime — partly because, until recently, you basically had to scrape it out of regional government websites one PDF at a time.

The thing you think it is

If you've heard of port state control at all, you probably think of it as a kind of safety check. A maritime MOT. The ship shows up, someone confirms the lifeboats work and the fire extinguishers haven't expired, and everyone moves on.

That's the surface. What's actually happening is a globally coordinated, regionally enforced, statistically targeted enforcement regime designed around one uncomfortable assumption: that flag states — the countries whose flags ships fly — cannot always be trusted to police their own vessels.

This is not a paranoid view. It's the foundational premise of the entire system. After the Amoco Cadiz ran aground off Portsall on the Brittany coast in March 1978 and discharged roughly 223,000 tonnes of crude into the sea, European maritime authorities were forced to ask the question nobody had really wanted to ask out loud: if a ship is registered in Liberia, inspected by a classification society contracted by its Liberian owners, and crewed under Liberian labor rules — who exactly is checking that any of it is real?

The answer they arrived at was: whoever the ship happens to be visiting. That country. Right now. With as little notice as possible — though which ships get boarded, and how thoroughly, is anything but random.

The Paris MOU didn't spring fully formed from the wreck. The Hague Memorandum had already been signed two months before the Cadiz grounded; the disaster accelerated and politically widened a process that was quietly underway. By 1982 it had become the Paris Memorandum of Understanding, and the cascade followed — Tokyo, Caribbean, Mediterranean, Indian Ocean, Black Sea, Abuja, Viña del Mar, the Riyadh MOU covering the Gulf. Nine regional MOUs depending on who's counting and which year you look, plus the US Coast Guard running its own parallel program entirely outside the MOU framework. Each operates a shared database. Each targets ships based on a risk profile. Each can detain a vessel that fails badly enough.

What an inspection actually generates

When an inspector boards a ship, they're not just looking. They're filling out a structured report against a known taxonomy. Every finding gets coded. Not "the lifeboat looked rusty" but a specific deficiency code in the life-saving appliances category, paired with an action code that tells the ship what they have to do about it.

The action codes are the part with real teeth. Broadly, a deficiency can be noted and rectified on the spot, flagged for rectification before departure, formally passed to the next port of call for follow-up inspection, or — at the serious end — used as grounds for detention, where the ship is physically not allowed to leave until the problem is fixed. Each MOU has its own numeric scheme for these (Paris MOU code 30 means detention; Tokyo's classification looks different; the Black Sea and Indian Ocean MOUs use their own variants). The concepts line up. The code numbers do not. Anyone consuming this data across regions learns quickly that "action code 17" is not a universal noun.

A single inspection can generate zero deficiencies or fifty. Most generate a handful. A commercial vessel on busy multi-region trades can accumulate well over a hundred inspections in its operational life — each one a snapshot of how that ship was actually being maintained on a particular Tuesday in Algeciras or Yokohama.

Query our /vessel/{imo}/inspections endpoint — keyed on the IMO number, because it's the only identifier that survives a rename — for an older bulk carrier and you'll often see sixty, eighty, sometimes well into three figures of inspection records stretching back years. Each one an independent look inside the same hull, by a different inspector, in a different port, rendered as structured data: date, port, MOU region, deficiencies found, action codes, detention flag.

That is not a safety check. That is a longitudinal medical record.

Why this is hard to get at

All of this data is public. Every MOU publishes inspection results. Most have searchable web interfaces. Detention lists are released monthly, sometimes weekly. In principle, anyone can look up any ship.

In practice, it's fragmented across ten-odd separate authorities, each with its own schema, its own search interface, its own quirks about how vessel identifiers are formatted, its own approach to historical retention. The Paris MOU exposes things one way. Tokyo exposes them differently. Some regional databases have inconsistent historical coverage; some go back decades cleanly; some pre-2000s records from regional bodies weren't keyed on IMO number at all and have to be re-linked by triangulating vessel name, port, and date — which is exactly as fun as it sounds, and not always recoverable. IMO numbers persist by regulation across a vessel's entire lifetime, and for five years after scrapping, which means the database occasionally contains ghosts: clean inspection histories on hulls that no longer exist.

So the data is "public" in the same way that a library is public if the books are in eleven different buildings in eleven different cities and each librarian has different opening hours and a different cataloguing system. And one of the librarians has thrown away everything before 1998.

This is the gap a port state control API exists to close. Not by inventing new data — the inspectors are still doing the work, the MOUs are still publishing the results — but by normalizing what can be normalized and being honest about what can't. One vessel identifier. One output schema. Top-level fields — date, port, detention status — line up cleanly across regions. Deficiency codes are preserved with their source MOU intact, because there is no universal crosswalk between them and pretending otherwise produces lossy categorization that quietly misleads downstream consumers. A detention in Rotterdam and a detention in Yokohama become comparable as detentions. The individual deficiencies underneath stay in their native vocabulary.

What this is actually for

The use case that pays for the infrastructure is chartering.

A fixture takes minutes on the phone and commits a ship to weeks of employment on terms worth millions, against cargo that may be worth significantly more. "I looked it up and it seemed fine" is not really adequate due diligence. Until recently, the alternative meant a frantic afternoon with nine browser tabs open and a colleague who could read French port reports.

Now it's a single call that returns a structured history all the way back. Chartering teams run this as a last check before confirming. Sometimes the check changes the answer. A ship with three detentions in the last two years is not the same commercial proposition as a ship with zero, regardless of what the broker says about it.

Insurers, financiers, journalists chasing sub-standard operators — they all use the same underlying records. But chartering is the case that demonstrates the real point: the difference between data being technically accessible and data being usable inside a decision that has to be made before lunch.

The thing that should bother you

A clean inspection record doesn't mean a well-maintained ship. It means a ship that hasn't yet been caught being poorly maintained.

The two are not the same, and you can fool yourself with this data quite easily if you forget the difference. Ships have passed inspections in one port and broken down in catastrophic ways shortly afterwards. Whole categories of deficiency — fatigue, falsified rest hours, structural problems behind fresh paint — are systematically under-detected because they're hard to see from a one-day visit. The reason port state control exists at all is that the people responsible for a ship's safety, when left to their own devices, sometimes don't keep it safe. Every detention in the database is a small piece of evidence that this judgment was correct. Every clean inspection is, at best, evidence that on one particular day, in one particular port, nothing visibly wrong was found.

Every inspection is a roll of the dice — a chance that an outside party with no commercial interest in the answer takes a hard look at reality. A hundred of those rolls, across a vessel's lifetime, in ports around the world, is about as close as the maritime industry gets to ground truth.

That's what's actually inside the API response. Not a compliance score. A long, structured record of every time the world checked.