How to Find a Ship Using IMO Number

Ship names change. Flags change. Owners change. The IMO number does not. That is why, when you need to identify a vessel with certainty, the most reliable method is to find a ship by IMO number. This guide explains what the number is, where to find it, how to check it, and how to run an IMO vessel search to see where the ship is right now.

What is a vessel IMO number?

An IMO number is a unique seven-digit identifier assigned to a ship for its entire life. It is written as the letters "IMO" followed by seven digits, for example IMO 9074729.

The scheme was introduced by the International Maritime Organization in 1987 and made mandatory under SOLAS Chapter XI-1, Regulation 3. It applies to passenger ships of 100 gross tonnage and above and cargo ships of 300 GT and above. Numbers are issued by S&P Global on behalf of the IMO, when a ship is built or first registered.

Because a vessel IMO number stays with the hull from construction to scrapping, it is the best way to trace a ship's history, even if it has been renamed or reflagged several times.

Where to find a ship's IMO number

If you do not already have the number, look in these places:

  • The hull. SOLAS requires the IMO number to be permanently marked on the stern or hull sides and on an internal bulkhead.
  • Ship certificates. The Certificate of Registry, Safety Management Certificate, class certificates and P&I entries all carry it.
  • Shipping documents. Bills of lading, charter parties, fixture recaps and port clearance papers usually quote it.
  • AIS data. Class A transponders broadcast the IMO number as part of their static data, so it appears on most vessel tracking platforms.

How to check an IMO number is valid

The last digit of an IMO number is a check digit, so you can catch typos before you search:

  1. Take the first six digits.
  2. Multiply them by 7, 6, 5, 4, 3 and 2 respectively.
  3. Add the results together.
  4. The last digit of that total should match the seventh digit.

For IMO 9074729: (9×7) + (0×6) + (7×5) + (4×4) + (7×3) + (2×2) = 63 + 0 + 35 + 16 + 21 + 4 = 139. The last digit is 9, which matches the seventh digit, so the number is valid.

Note that the IMO also issues seven-digit numbers to shipping companies and registered owners. If a ship IMO lookup returns nothing, check that you have not been given a company number instead.

How to find a ship by IMO number: step by step

  1. Confirm the number. Run the check digit test above.
  2. Open a vessel search tool. Use an AIS tracking platform such as Navtrac, or IMO's free GISIS database for official ship particulars.
  3. Enter the seven digits. Most tools accept the number with or without the "IMO" prefix.
  4. Verify the match. Check the returned name, ship type, flag, gross tonnage and year built against your documents. A mismatch suggests a wrong number or a renamed vessel.
  5. View the live position. On a tracking platform, open the vessel page to see its current position, speed, course, destination and recent port calls.

Why track vessel by IMO rather than by name?

Searching by name sounds easier, but it causes problems. Dozens of ships can share a popular name, and a ship can change its name several times in its life. An IMO vessel search returns exactly one ship.

IMO numbers also beat MMSI numbers for long-term identification. An MMSI is a radio identifier tied to the flag state, so it changes whenever a ship is reflagged. The IMO number never changes. If you need to track vessel by IMO across years of history, sales and reflagging, it is the identifier to rely on.

Common uses for an IMO number lookup

  • Chartering and fixtures: confirming the nominated vessel before signing
  • Compliance and sanctions screening: checking a ship's ownership, flag and history
  • Port operations: preparing for arrivals and clearances
  • Insurance and claims: linking a casualty or claim to the right hull
  • Cargo visibility: following the ship that is carrying your goods

Run an IMO number lookup with Navtrac

Navtrac combines real-time AIS data with an interactive map, so a single IMO number lookup takes you from identification to live tracking. Find the vessel, see where it is now, follow its route and monitor its port calls in one place.

Search for a vessel on Navtrac and start tracking in seconds.