Boardings, seizures and detentions: what a state may actually do

Four zones, four sets of powers

Almost every confused report about a tanker being “seized” comes from ignoring where the encounter happened. The law of the sea gives states quite different powers in four places.

In port, the coastal state is in the strongest position. Port state control lets inspectors board, examine certificates, machinery and crewing, and detain a ship that is unsafe until deficiencies are corrected. Detention here is routine and has nothing to do with sanctions; it is a safety regime, coordinated regionally through arrangements such as the Paris Memorandum. A state’s sanctions measures also apply in full to a vessel in its port.

In the territorial sea, a foreign ship enjoys the right of innocent passage. Passage that is not innocent, because it prejudices peace, good order or security, may be dealt with, but the coastal state’s criminal jurisdiction over a passing ship is limited.

In the exclusive economic zone, freedom of navigation applies. The coastal state’s rights concern resources and the marine environment. It is not a general policing zone, which surprises people who assume a two-hundred-mile enforcement belt.

On the high seas, the flag state has jurisdiction. Another state’s warship may board only with consent, or on a specific legal basis: a treaty, a Security Council authorisation, or one of the narrow grounds set out in the law of the sea. The ground that matters in this subject is reasonable suspicion that the vessel is without nationality.

Why the flag question became the tool

That last ground is the reason European states shifted the conversation toward registration.

If a vessel’s claimed flag turns out to be fraudulent, or if it sails under two flags as convenience dictates, its legal position changes fundamentally. A ship without nationality has no state to assert jurisdiction on its behalf and no state obliged to protect it, and it may be boarded on that basis.

Asking a passing tanker which state it is registered with, and who insures it, is therefore not an interdiction at all. It is a question that a properly registered vessel answers in seconds and a fraudulently registered one cannot answer well. The answer, or the silence, tells the coastal state which category it is dealing with, and only in the second case do stronger powers open up. The mechanics of fraudulent registration are covered in fraudulent registries and false flags.

What a sanctions listing does not do

A designation is a prohibition on dealings. In US practice it blocks property that comes within US jurisdiction. In the EU and UK vessel regimes it closes ports and prohibits services.

None of that is a power to take a ship at sea. Physically seizing a vessel or its cargo requires a domestic legal basis, usually a court process, customs or criminal law, or a specific statutory power, and it requires jurisdiction over the vessel at the moment of the act. That is why so many encounters described as seizures are, on examination, either port detentions for safety deficiencies or cargo actions taken once a vessel entered a state’s waters voluntarily.

The practical sequence

A state that wants to act against a specific hull generally has to wait for it to come within reach, then use the most ordinary power available.

Port state control finds deficiencies on an old, poorly maintained ship without much difficulty, and detention on safety grounds is legally straightforward. Insurance documentation can be demanded, and a certificate from an insurer that cannot be verified is itself a problem. Customs and revenue powers apply to cargo. Sanctions measures apply to any transaction touching the state’s persons or financial system.

The result is that enforcement concentrates at chokepoints and in ports, and that vessels in this trade avoid both. That avoidance is itself the cost the measures impose: longer voyages, fewer places to bunker, no access to the ports where repairs are cheap.

What this site records, and what it does not

Incidents are part of the data model here, with a kind field that includes seizure, boarding and detention, and each requires a dated primary or major-outlet source before it appears.

What this site will not publish is anything that helps locate a vessel now. No positions, no tracks, no last-known port. The reasoning is set out in AIS: going dark and spoofing: a hull on this list has a crew aboard, and a public dataset that makes a specific ship easy to find at sea serves interception as readily as compliance.