Maritime glossary
The terminology behind every vessel record.
AIS, IMO, MMSI, DWT, GT, PSC, ISM Code, charter party, demurrage — commercial maritime runs on a tight vocabulary, and every term has a specific operational meaning. This glossary defines the twenty-five most-used terms in plain language, with a worked example and a note on how Vessel Hunter surfaces each one in the platform.
Vessel identification
- AISAutomatic Identification System
The VHF radio system every commercial vessel uses to broadcast its position, course, and identity.
- IMO NumberInternational Maritime Organization Number
The seven-digit identifier permanently assigned to a ship — never reused, never changed, even on resale or reflag.
- MMSIMaritime Mobile Service Identity
The nine-digit identifier broadcast by a vessel’s AIS and used to route VHF radio calls.
Dimensions & tonnage
- DWTDeadweight Tonnage
The maximum weight in tonnes a vessel can carry — cargo, fuel, ballast, crew, stores — without exceeding its load line.
- GTGross Tonnage
A unitless measure of a vessel’s total enclosed volume — used for port dues, pilotage fees, and SOLAS thresholds.
- NTNet Tonnage
Gross Tonnage minus the volume of spaces not available for cargo — used for canal tolls and certain port dues.
- LOALength Overall
The maximum length of a vessel from the foremost to the aftmost point, including any fixed projections.
- Beam
The widest point of a vessel — the constraining dimension for lock chambers, dry docks, and some terminals.
- Draught
The vertical distance from the waterline to the deepest point of the hull — the constraint that decides which ports a loaded vessel can enter.
Operations
- ETAEstimated Time of Arrival
The forecast time at which a vessel is expected to arrive at its next port or waypoint.
- ETDEstimated Time of Departure
The forecast time at which a vessel is expected to leave a port.
- Bunker
Marine fuel oil — colloquially named after the coal bunkers steamships used to carry.
- Master
The captain of a merchant vessel — has overall command, signs the bill of lading, and represents the owner on board.
Safety & compliance
- PSCPort State Control
Inspections of foreign-flagged vessels in a port’s waters, run under regional MoUs to enforce international maritime conventions.
- ISM CodeInternational Safety Management Code
The mandatory IMO framework for safe management and operation of ships — basis of the Document of Compliance and the Safety Management Certificate.
- SOLASSafety of Life at Sea
The principal IMO convention on the safety of merchant ships — covers construction, fire protection, life-saving, navigation, and more.
- MARPOLMarine Pollution Convention
The IMO convention preventing pollution from ships — oil, chemicals, garbage, sewage, air emissions, sulphur.
- Classification Society
An independent body that certifies a vessel’s structural integrity, machinery, and equipment against published rules.
- Flag State
The country under whose laws a ship is registered — sets the regulatory standard for the vessel.
Commercial / chartering
- Demurrage
A daily fee paid by the charterer to the owner when cargo operations exceed the agreed laytime.
- Laytime
The time agreed in the charter party for cargo loading or discharge — once exceeded, demurrage starts.
- Charter Party
The contract under which a vessel is hired to a charterer — voyage, time, or bareboat.
- Voyage Charter
A charter for one or more specific voyages, priced per tonne of cargo or as a lumpsum freight.
- Time Charter
A charter for a fixed period, paid as a daily hire rate, with the owner providing the crew.
- Bareboat Charter
A lease of the vessel without crew — the charterer takes on management, crewing, and operational risk.
Need the data, not just the definitions?
Vessel Hunter ships the full dossier per IMO — specs, ownership, inspections, dry dock, casualty, class — and pairs every vessel with the verified operator contact. See the live demo or read up on every feature in the platform.