Maritime glossary · International Maritime Organization Number
IMO Number
The seven-digit identifier permanently assigned to a ship — never reused, never changed, even on resale or reflag.
Definition
The IMO number is the maritime equivalent of a chassis number. Assigned by S&P Global (formerly IHS Markit) on behalf of the International Maritime Organization, it sticks to the hull for life — through ownership changes, name changes, flag changes, even conversions. It is the only identifier that lets you reliably link an AIS broadcast to historical records like inspections, casualty reports, dry-dock visits, and class society surveys. The check digit at the end is computed from the first six digits, which is why a typo in any single digit always fails validation.
Worked example
A handysize tanker built in 2012, sold three times, reflagged twice, and renamed once still carries the same IMO number. That is how Vessel Hunter ties a 2019 detention in Rotterdam to a 2024 inspection in Houston, even though the ship has had two different names in between.
How Vessel Hunter uses IMO Number
Every record in the Vessel Hunter dossier — specs, ownership, inspections, dry dock, casualty, class — is keyed on the IMO number so the history travels with the hull, not the name.
Related terms
- MMSIMaritime Mobile Service Identity
The nine-digit identifier broadcast by a vessel’s AIS and used to route VHF radio calls.
- AISAutomatic Identification System
The VHF radio system every commercial vessel uses to broadcast its position, course, and identity.
- Flag State
The country under whose laws a ship is registered — sets the regulatory standard for the vessel.
- Classification Society
An independent body that certifies a vessel’s structural integrity, machinery, and equipment against published rules.
The bigger picture
IMO Number is one piece of the commercial maritime picture Vessel Hunter pulls together for shipyards, port agents, and service providers. Every vessel record bundles AIS, ownership, inspections, dry-dock history, casualty record, classification status, and a verified contact for the operator decision-maker behind the ship — so the team that reaches out first wins the work.
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