The IMO NO., more specifically the IMO ship identification number, is a unique identifier that was originally introduced to register and manage ships flying flags of the contracting parties. The recent OFAC sanction programs targeting DPRK, Iran and Venezuela have brought to light the importance of these numbers in monitoring and tracking ships. Here are some basics about it.

I.    History of Vessel Identification Numbers

The earliest record of ship registration number has been lost, but the identification number scheme can be tracked back to 1960s when all ships listed by the formerly Lloyd’s Register were assigned a number every year. LR later decided to use a unique 6-digit number that does not alter with the change of ship’s name as the all-time identifier of a ship for easier management. In early 1970s, with the consent of shipowners and shipbuilders, the number was assigned to a hull during construction for new vessels.

As a measure to enhance maritime safety, security and environmental protection, and to facilitate the prevention of maritime fraud, in November 1987 at its fifteenth session, the IMO adopted LR’s existing identification number scheme and promoted it among all contracting govenments. It is not intended to prejudice matters of liability, civil law or other commercial considerations in the operation of a ship. The implementation of the IMO scheme was made mandatory in 1996 through SOLAS regulation XI-1.

II.  IMO Identification Number Schemes

The IMO number is assigned to ships by HIS Maritime & Trade when constructed free of charge. It is made of the three letters of “IMO” followed by seven decimal digits (six information digits followed by a seventh check digit). The six information digits to be checked are weighed from left to right by 7, 6, 5, 4, 3, and 2. Add the products up and divide the sum by 10, the remainder is the check digit.

III.   Requiremens in the SOLAS Convention

In SOLAS Chapter XI-1-Special measures to enhance maritime safety, rules about ship identification number are established through Regulation 3:

1.      This regulation applies to all passenger ships of 100 gross tonnage and upwards and to all cargo ships of 300 gross tonnage and upwards.

2.      Every ship shall be provided with an identification number which conforms to the IMO ship identification number scheme adopted by the Organization.

3.      The ship’s identification number shall be inserted on the certificates and certified copies.

4.      The ship’s identification number shall be permanently marked in a visible and easily accessible place – on one of the end transverse bulkheads of the machinery spaces, or on one of the hatchways, or in the case of passenger ships, on a horizontal surface visible from the air.

5.      The permanent marking shall be plainly visible, clear of any other markings on the hull and shall be painted in a contrasting color.

6.      The permanent marking may be made by raised lettering or by cutting it in or by centre punching it or by any other equivalent method of marking the ship identification number which ensures that the marking is not easily expunged.

IV.   Eligibility Criteria

SOLAS regulation XI-1/3 provided that passenger ships of 100 gross tonnage and upwards and cargo ships of 300 gross tonnage and upwards are eligible for an IMO number. In 2017, the IMO Assembly adopted Resolution A.1117 (30) to include in the eligibility criteria:

1.      All ships of 100 gross tonnage and above (including fishing vessels with steel or non-steel hull construction);

2.      Passenger ships of less than 100 gross tonnage;

3.      High-speed passenger craft and mobile offshore drilling units engaged on international voyages (SOLAS regulation V/19-1);

4.      All motorized inboard fishing vessels of less than 100 gross tonnage down to a size limit of 12 meters in LOA, authorized to operate outside waters under the national jurisdiction of the flag State.

And the following types of ships are excluded:

1.      Ships without mechanical means of propulsion;

2.      Pleasure yachts;

3.      Ships engaged on special service;

4.      Hopper barges;

5.      Floating docks and structures classified in a similar manner;

6.      Ships of war and troop ships; and

7.      Wooden ships, other than fishing vessels.

V.  Further Application

Permanently displaying the IMO number in a visible place, as required by the SOLAS convention, and inserting the number in the ship’s certificates have significantly improved information accuracy. Through MSC/Circ.1142 and MEPC/Circ.425, the number was included in ship’s plans, manuals and other documents carried on board, which has since then facilitated ship surveys, inspections and maintenance. Its application in an increasing number of commercial certificates has also provided access to ship operation and law-breaking records.

The unique identifier has also been inserted in AIS, LRIT and other devices. In the case of vessel name duplication or changes, researching a vessel by its IMO number can effectively prevent the obfuscation. For example, search only by vessel name “Ocean Harmony”, and you will get four different ships, but if search by its IMO number, you will be able to identify the exact vessel.

 For more information, please contact your manager at the Club.