IMO Number
An IMO number is a permanent ship identifier assigned under the IMO identification scheme. It normally consists of “IMO” plus seven digits and remains unchanged when a vessel changes name, owner, or flag. Ships within the scheme display it on certificates and hull markings, supporting reliable safety, compliance, and anti-fraud records throughout the ship's life.
Definition
IMO number is the permanent seven-digit vessel identifier that stays with the vessel for its operational life regardless of flag or owner change and is used for compliance tracking by Port State Control and flag states.
What an IMO Number Is
An IMO number is a permanent seven-digit vessel identification number prefixed with IMO, for example IMO 1234567. It is assigned by S&P Global, formerly IHS Markit, on behalf of the IMO. The ship identification number scheme was first adopted in 1987 by IMO resolution A.600(15) and has since been revised; it is now set out in resolution A.1215(34), the integrated scheme that also covers company numbers. The scheme was created to uniquely and permanently identify ships, reduce fraud, support accurate records across name and flag changes, and improve Port State Control tracking. Unlike a yacht name, call sign, or MMSI, the IMO number is designed to stay with the hull for life. In due diligence, it is usually the most reliable key for finding inspection history, casualty records, ownership changes, flag changes, and statutory certificate references.
Which Vessels Get an IMO Number
The IMO ship identification scheme covers propelled sea-going merchant ships of 100 GT and above, and SOLAS regulation XI-1/3 makes the number mandatory for passenger ships of 100 GT and upwards and cargo ships of 300 GT and upwards. Pleasure yachts are among the ship types excluded from the scheme's general coverage, so private yachts may receive an IMO number voluntarily or because a flag state, size threshold, commercial use, or certificate regime requires one. The number may be assigned at keel-laying or when the vessel first enters convention coverage. For large yachts, obtaining an IMO number early simplifies builder records, class documentation, radio licensing, insurance, finance, and later sale due diligence. It also avoids confusion when the yacht changes name before delivery.
Permanence and Uniqueness
The defining feature of an IMO number is permanence. Vessel names can change at any time. MMSI numbers are assigned by radio authorities and can change with flag or radio licensing. Call signs can also change. The IMO number does not change when the vessel is sold, renamed, reflagged, converted, transferred between managers, or moved between registries. It is never reused for another vessel. When a vessel is scrapped, the number is retired permanently. This permanence is why databases use the IMO number as the primary vessel key. For buyers and managers, it prevents a vessel with a poor inspection or detention history from hiding behind a new name, new owner, or new flag.
Where the IMO Number Appears
An IMO number appears on statutory certificates, class records, the International Tonnage Certificate, safety certificates, ISM certificates, MLC certificates where applicable, pollution certificates, and many insurance and finance documents. Ships within marking requirements must display the number permanently on the hull or superstructure in a clearly visible position, using painting, engraving, or other permanent marking accepted by the rules. It is also the primary search key in Port State Control databases such as Paris MOU THETIS and Tokyo MOU systems, the IMO GISIS database, S&P Global ship records, class records, and many maritime intelligence tools. When certificate names differ slightly or a yacht has been renamed, the IMO number ties the record together.
IMO Number and Vessel History
The IMO number is valuable because vessel history follows it. A buyer, charterer, insurer, or manager can search the IMO number to review Port State Control inspections, detentions, deficiencies, flag history, ownership records, management changes, casualty reports, and certificate anomalies. This is especially important for yachts that have operated commercially, changed flags, or passed through multiple managers. A clean-looking certificate file is useful, but independent database history can reveal repeated deficiencies, overdue surveys, security issues, or name changes that deserve questions. Management companies should verify the IMO number during take-on due diligence and reconcile it against hull markings, class records, flag documents, radio licence, and insurance schedules.
IMO Numbers for Companies and Managers
Separate from ship IMO numbers, the IMO also operates a company and registered owner identification number scheme, first adopted by resolution MSC.160(78) in 2004 and now part of the integrated scheme in resolution A.1215(34). Companies managing ISM-certified vessels are assigned a Company Identification Number, and registered owner entities may also be identified. This creates a database link between the DOC-holding company, registered owner, and managed vessels. In yacht operations, this matters when a professional manager holds the DOC and supports multiple vessels under one Safety Management System. Company identification improves transparency for Port State Control, flag states, insurers, and due diligence teams. Owners should understand that the vessel IMO number identifies the yacht, while the company number identifies the legal or management entity connected to ISM and ownership records.
Frequently Asked Questions
Manage IMO Number in HelmOps
Yacht expenses, maintenance, tasks and trips in one place. Records you add offline sync when the connection returns.
Track vessel certificates and their expiry dates
Store the DOC, SMC and other vessel documents. HelmOps reminds the captain and owner 90, 60 and 30 days before each one expires.
No credit card required.
Verified reference
https://www.imo.org/en/ourwork/iiis/pages/imo-identification-number-schemes.aspx(opens in new tab)
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