Why Vessels 'Go Dark': AIS Manipulations and How to Detect Them

Why Vessels “Go Dark”

In recent years “shadow fleets” of tankers have emerged, bringing new masking tactics. The main tracking tool is AIS (Automatic Identification System). Under the SOLAS Convention almost all commercial vessels must continuously broadcast their location and course to avoid collisions and enable rescue. But violators exploit this system: they can falsify it—or simply turn it off.

AIS in Simple Terms

An onboard transmitter sends position, speed, route, ship name, and IMO number every few seconds.

• Class A – for large commercial vessels, more frequent and detailed updates.
• Class B – for small vessels, simpler and less frequent.

When AIS was designed in the 1990s no one imagined thousands of satellites and web services would monitor it. In crowded areas (e.g., Singapore Strait) signals can “choke,” and in the open ocean VHF range (20–40 nautical miles) means a ship may vanish until a satellite catches the signal again.

Common AIS Manipulations

• Signal Shutdown – the vessel simply “goes dark.”
• Spoofing – falsifying identity, route, or destination.
• Provocative Messages – since late 2023 some ships in the Suez Canal broadcast notes like “no ties with Israel, USA, UK” to avoid attacks by Yemeni Houthis.

There are legitimate reasons to disable or alter AIS (piracy protection, military missions, classified cargo, technical maintenance), but every blackout must be documented. Unexplained gaps raise alarms.

Red Flags for Regulators

OFAC (US) and OFSI (UK) highlight warning signs such as:

• Frequent AIS “dark” periods
• Regular ship-to-ship (STS) transfers to hide cargo
• Sudden route or flag changes
• Complex, opaque ownership chains
• Poor inspection records

Suspicion increases when several indicators coincide.

How Businesses Can Avoid the Trap

• Check Vessel History – Platforms like Windward, Lloyd’s List Intelligence, Kpler, and Polestar reveal past AIS gaps and suspicious routes.
• Write It into Contracts – Require that unauthorized AIS shutdowns constitute grounds for termination.
• Verify IMO Numbers – Cross-check against sanctions lists.
• Examine Ownership – Complicated offshore structures warrant deeper due diligence.

Any company shipping goods by sea—from grain to oil—risks entanglement with a “shadow fleet.” Even if you don’t handle sanctioned cargo, a counterparty might—and penalties or reputational damage can reach you too.