IMO number

The IMO number of the International Maritime Organization is a generic term covering two distinct meanings.

[1] In 1987 the IMO adopted Resolution A.600(15) to create the IMO ship identification 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.

[1] Unique and permanent numbers are needed due to the frequent changes in ships' names or other details.

As one example, the vessel with IMO ship number "IMO 9176187" was built in Japan, has been through the names Asia Melody, Cornelie Oldendorff, Maxima, Jaydee M, Evangelia, Evangeli, Shinsung Dream and Orange Dream, has operated under the flags of Panama, Liberia, Marshall Islands, the Republic of Korea and Sierra Leone, with numerous different owners/operators, and has had home ports of Majuro, Freetown and Cheju, but its IMO number has remained unchanged throughout.

That in turn was revoked in 2017 and replaced by Resolution A.1117(30), which allows its application to ships of 100 gt and above, "including fishing vessels of steel and non-steel hull construction; passenger ships of less than 100 gt, high-speed passenger craft and mobile offshore drilling units [...]; and all motorized inboard fishing vessels of less than 100 gt down to a size limit of 12 metres in length overall (LOA), authorized to operate outside waters under the national jurisdiction of the flag State".

In May 2005, IMO adopted a new SOLAS regulation XI-1/3-1 on the mandatory company and registered owner identification number scheme, with entry into force on 1 January 2009.

For new vessels, the IMO ship number is assigned to a hull during construction, generally upon keel laying.

The checksum of an IMO ship identification number is calculated by multiplying each of the first six digits by a factor of 7 to 2 corresponding to their position from right to left.