Ship Tracking OSINT: IMO, MMSI, AIS and the Shadow Fleet

Most of the world’s trade moves by sea, and ships leave far more traces than you might think: position broadcasts, registration numbers, port calls, satellite images. Maritime OSINT combines these traces to establish who a ship is, where it is and what it is doing. This guide covers the core concepts and the free tools.

A ship’s ID card: IMO, MMSI, call sign

• IMO number: a 7-digit number that never changes during the ship’s life. Even if the ship is sold or its name or flag changes, the IMO stays the same. It is the most reliable way to identify a ship with certainty.
• MMSI: a 9-digit radio identity. Its first three digits show the flag state. When the flag changes, the MMSI changes too, so on its own it is not enough to identify a ship.
• Call sign and name: These change easily. Dozens of ships can share the same name; searching by name and trusting the first result is the most common mistake.

AIS: the position ships broadcast themselves

AIS (Automatic Identification System) is the system through which ships broadcast their position, speed, course and identity by radio. These broadcasts are collected by coastal receivers and satellites, and sites such as VesselFinder and MarineTraffic show them on a map.

But AIS is a statement from the ship, not hard truth. Ships can switch AIS off (“going dark”), broadcast false positions (spoofing) or enter wrong identity data. These behaviours are common among ships evading sanctions.

Identifying a ship step by step

1. Collect your clues: name, hull colour, type (tanker, container ship, bulk carrier), approximate length, location and date.
2. Find candidates: Search AIS sites by name or area; note ships with the same name separately.
3. Verify with the IMO: Do the length, type and build year match your clues? Check former names and flag history on Equasis.
4. Build a timeline: Use news, port records and AIS history to order the ship’s movements before and after the event.
5. Record your sources: Note where and when each finding came from; ship data changes often.

Ships on satellite imagery

Large ships are easy to see on free satellite imagery such as Sentinel-2. In a true-colour image each pixel is about 10 metres; count the pixels from bow to stern to estimate the length. A 250–280 metre ship is a large tanker or bulk carrier; a 30 metre boat is only a few pixels.

Where AIS goes quiet, satellite imagery speaks: you can check where a ship with its AIS off really is, or whether two ships met at sea to move cargo (ship-to-ship transfer).

The shadow fleet and sanctions

The “shadow fleet” is the name given to ships used to get around sanctions: mostly old, frequently changing name and flag, with ownership hidden behind shell companies. These ships also carry a high risk of accidents and pollution.

• Name and flag changed several times in a short period
• Single-ship owning companies set up recently
• Long AIS gaps and ship-to-ship transfers at sea
• An IMO number that appears on sanctions lists

By searching an IMO number in free databases such as OpenSanctions, you can see which countries’ sanctions lists a ship is on and the records about it. Some of these records rest on a single source; always cite the source in your report.

Ethical limits

AIS data of commercial ships is public, but there are real people behind small boats and private yachts. Do not use ship data to track individuals’ movements; keep your research to organisations, trade and the public interest.

Try what you have learned in our maritime missions: start from a satellite tile and find the ship, the date and its history.