The International Maritime Organization number is a unique identifier for ships, registered ship owners and management companies. IMO numbers were introduced to improve maritime safety and security and to reduce maritime fraud. They consist of the three letters "IMO" followed by unique seven-digit numbers, assigned under the International Convention for the Safety of Life at Sea. The IMO number scheme has been mandatory for all ships since 1 January 1996. The number identifies a ship and does not change when the ship's owner, country of registry or name changes. The ship's certificates must also bear the IMO number. Since 1 July 2004, passenger ships are also required to carry the marking on a horizontal surface visible from the air.
History
IMO resolution (1987)
In 1987 the IMO adopted resolution A.600 to create the IMO number scheme aimed at the "enhancement of maritime safety and pollution prevention and the prevention of maritime fraud" by assigning to each ship a unique permanent identification number. The IMO number remains linked to the hull of a ship for its lifetime, regardless of changes of names, flags, or owners. Lloyd's Register had already introduced permanent numbers for all the ships in their published register in 1963, and these were modified to 7-digit numbers in 1969. It is this number series that was adopted as the basis for IMO numbers in 1987.
SOLAS regulation (1994)
SOLAS regulation XI/3 was adopted in 1994 and came into force on 1 January 1996, making IMO numbers mandatory. It was applied to cargo vessels that are at least 300 gross tons and passenger vessels of at least 100 gt. In the SOLAS Convention, "cargo ships" means "ships which are not passenger ships". The IMO scheme does not apply to:
floating docks and structures classified in a similar manner
ships of war and troopships
wooden ships.
Security enhancements 2002
In December 2002, the Diplomatic Conference on Maritime Security adopted a number of measures aimed at enhancing security of ships and port facilities. This included a modification to SOLAS Regulation XI-1/3 to require the IMO numbers to be permanently marked in a visible place either on the ship's hull or superstructure as well as internally and on the ship's certificates. Passenger ships should also carry the marking on a horizontal surface visible from the air. The enhanced regulations came into effect on 1 July 2004.
is the manager of the scheme and, as such, identifies and assigns IMO numbers without charge. The organization was previously known as Lloyd's Register-Fairplay and IHS Fairplay. For new vessels, the IMO number is assigned to a hull during construction, generally upon keel laying. Many vessels which fall outside the mandatory requirements of SOLAS have numbers allocated by Lloyd's Register or IHS Markit in the same numerical series, including fishing vessels and commercial yachts.
Structure
An IMO number is made of the three letters "IMO" followed by a seven-digit number. This consists of a six-digit sequential unique number followed by a check digit. 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 of 2 to 7 corresponding to their position from right to left. The rightmost digit of this sum is the check digit. For example, for IMO 9074729: + + + + + = 139.
