An IMO number is a permanent seven-digit identifier assigned to a ship under the International Maritime Organization’s identification scheme. It stays with the hull for life regardless of changes to name, flag, or owner, which makes it the reliable key for identifying a vessel across databases.
Ship names are reused and repainted; flags and owners change with sales. The IMO number does not, which is why safety inspections, casualty records, sanctions screening, and tracking systems all key vessels by it. The scheme is mandatory for most seagoing merchant ships above small-tonnage thresholds.
The seventh digit is a check digit: multiply the first six digits by weights seven down to two, sum, and the last digit of the sum must match. Alongside the IMO number, ships also broadcast an MMSI, which unlike the IMO number can change with flag.
Container events name a vessel and voyage; resolving that vessel to its IMO number is what lets a tracking system join carrier events with AIS positions and port calls. When TrackingMCP shows the ship carrying your box and its progress toward the port of discharge, the IMO number is the join underneath; the visible layer is the timeline in tracking.
An IMO number is a permanent seven-digit identifier assigned to a ship under the International Maritime Organization’s identification scheme. It stays with the hull for life regardless of changes to name, flag, or owner, which makes it the reliable key for identifying a vessel across databases.
Most seagoing merchant vessels of consequence do; the scheme is mandatory for passenger and cargo ships above modest size thresholds. Small craft, fishing vessels in some regions, and inland vessels may fall outside it.
The IMO number is permanent to the hull; the MMSI is a radio identity programmed into the ship’s transceivers and changes when the ship reflags. Tracking systems use both: MMSI for live AIS, IMO for identity over time.
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More in Identifiers & codes: Container number (ISO 6346) · Container check digit · Container prefix (owner code) · Booking number · SCAC code · UN/LOCODE · MMSI · TEU & FEU · Browse all 106 terms →