The IMO Ship Identification Number Scheme
“With the aim of strengthening maritime security and pollution prevention, and contributing to the prevention of maritime fraud,” the IMO initiated a ship identification number system in 1987 through Resolution A.600(15). This system involves assigning a permanent identification number to ships (passenger ships of 100 gross tonnage and above, and all cargo ships of 300 gross tonnage and above). This number remains unchanged even if the ship changes flag and must appear on all certificates issued to the ship.
The IMO ship identification number system was mandated under Regulation XI/3 of the SOLAS Convention (adopted in 1994) and became mandatory on January 1, 1996. Its voluntary application to fishing vessels of 100 gross tonnage and above was adopted by the IMO in 2013 through Resolution A.1078(28).
Regulation XI-1/3 of the SOLAS Convention requires that ship identification numbers be permanently marked in a visible location either on the hull or on the superstructure of the ship. Passenger ships should bear this marking on a horizontal surface visible from the air. The identification number should also be displayed inside the ship.
A ship’s IMO identification number is never reassigned to another vessel. It consists of the three-letter prefix “IMO” followed by seven digits (e.g., IMO 8712345). These seven digits are assigned to each ship by the Information Handling Services Maritime & Trade (IHS M&T) (formerly known as Lloyd’s Register-Fairplay) at the time of its construction, to the section of the hull that houses the engine room. It is the determining factor if additional sections are to be added to the ship.
This unique number is indeed assigned to ocean-going, propelled merchant ships of 100 gross tonnage or more at the time of keel laying, except in the case of the following ships:
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Ships without mechanical propulsion
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Pleasure yachts
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Vessels engaged on special services (e.g., lightships and SAR vessels)
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Hopper barges
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Hydrofoils and air-cushion vehicles
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Floating docks and structures of similar type
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Warships and troop transports
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Wooden ships
For new ships, the IMO number is assigned at the time of registration. For existing ships, the IMO number is assigned prior to the renewal of any of the ship’s international safety certificates.
The integrity of an IMO number can be verified using its check digit. This is done by multiplying each of the first six digits by a factor from two to seven, corresponding to their position from right to left. If this number is represented by “ABCDEFG”, “G” must be equal to the unit digit of the sum (A × 7) + (B × 6) + (C × 5) + (D × 4) + (E × 3) + (F × 2). The rightmost digit of this sum (the units digit) is the check digit. For example, for IMO 9074729: (9 × 7) + (0 × 6) + (7 × 5) + (4 × 4) + (7 × 3) + (2 × 2) = 139.
References :
https://www.imo.org/fr/ourwork/msas/pages/imo-identification-number-scheme.aspx
https://fr.qwe.wiki/wiki/IMO_number
https://www.fao.org/fi/static-media/MeetingDocuments/GlobalRecord/GRWG4/A30Res1117f.pdf
https://www.rif.mer.developpement-durable.gouv.fr/attribution-du-numero-d-identification-des-navires-r162.html
