Maritime & AIS Glossary

A transponder-based system that broadcasts vessel identity, position, speed, and course over VHF radio, allowing ships and shore stations to track maritime traffic in real time.

One of 27 standardised AIS packet formats, each carrying different data — from position reports (types 1–3) to static voyage data (type 5) and binary messages.

The onboard device that transmits and receives AIS signals over VHF, automatically broadcasting vessel data to other ships and coastal stations every few seconds.

A secret token passed in the x-api-key request header to authenticate API calls. Each key is tied to an account and its associated credit balance and rate limits.

A designated area where vessels drop anchor to wait for berth availability, tide, weather, or customs clearance before proceeding into a port or terminal.

AIS message types 6, 8, 12, and 14 that carry application-specific payloads such as meteorological data, tidal heights, or notices to mariners.

A designated space at a quay or pier where a vessel can moor for loading, discharging, bunkering, or repairs. Assigned by port authorities based on vessel size and cargo type.

A list of vessels denied entry to ports or flagged by maritime authorities due to repeated PSC deficiencies, sanctions, or safety violations.

Mandatory AIS equipment for SOLAS vessels (300 GT+ on international voyages). Transmits position every 2–10 seconds underway and every 3 minutes at anchor.

Voluntary or nationally mandated AIS for smaller and recreational vessels. Uses a less frequent transmission protocol with lower power and reduced data fields.

A unique radio identifier assigned to a vessel by its flag state telecommunications authority, used for voice and data communications on maritime radio channels.

The actual direction of a vessel's movement relative to the seabed, measured in degrees (0–359°). May differ from heading due to wind, current, or leeway.

The unit of consumption deducted from an account balance on each billable API request. Different endpoints cost different credit amounts per call.

The total weight in metric tonnes a vessel can carry, including cargo, fuel, fresh water, ballast, crew, and provisions — a key measure of cargo capacity.

The intended port or anchorage as manually entered by the crew into the AIS transponder. Accuracy varies; the field is advisory rather than authoritative.

The vertical distance between the waterline and the lowest point of the hull in metres. Determines whether a vessel can safely navigate a particular channel or port.

A shortcoming identified during a PSC inspection where a vessel fails to meet international convention requirements. Deficiencies are recorded and may trigger follow-up inspections.

The action taken by port state control when a vessel's deficiencies are serious enough to pose a danger to safety, health, or the environment — the ship is held in port.

The crew-entered estimated arrival time broadcast in AIS static voyage data, expressed in UTC. Accuracy depends on whether the crew updates it during the voyage.

A specific URL path in the API that performs a discrete function, such as /vessel-location or /vessel-particulars. Each endpoint has its own parameters and credit cost.

The country under whose laws a vessel is registered and whose flag it flies. The flag state is responsible for ensuring the ship meets international maritime conventions.

Inspections and enforcement of international maritime conventions carried out by the country where a vessel is registered, as distinct from port state control.

A dimensionless measure of a vessel's overall internal volume, calculated per the International Tonnage Convention. Used to determine registration fees, port dues, and SOLAS applicability.

The direction the bow of the vessel is pointing, in degrees (0–359°). Reported directly from the ship's gyrocompass via the AIS transponder.

A permanent seven-digit identifier assigned to a ship by the International Maritime Organization. Unlike MMSI, it never changes — surviving reflagging, sale, or name changes.

The structured data format returned by the API. All endpoints return JSON objects containing a res field with the requested maritime data.

An indicator of how fully loaded a vessel is, derived by comparing current draught to maximum design draught. Classified as ballast (0–49%), partial (50–75%), or laden (76–100%).

The north–south geographic coordinate of a vessel's position, expressed in decimal degrees. Positive values indicate north of the equator, negative values south.

The east–west geographic coordinate of a vessel's position, expressed in decimal degrees. Positive values indicate east of the prime meridian, negative values west.

UN/LOCODE — a five-character code (two-letter country + three-letter location) identifying ports, terminals, and logistics hubs worldwide. E.g. NLRTM for Rotterdam.

Maritime Mobile Service Identity — a nine-digit number that uniquely identifies an AIS transponder. Used in distress calls and as the primary lookup key in vessel tracking APIs.

A regional agreement between port state authorities to coordinate PSC inspections. Major MOUs include Paris, Tokyo, and US Coast Guard, each covering a geographic zone.

An AIS field (0–15) set manually by the crew indicating the vessel's current operational state, such as under way using engine, at anchor, moored, or aground.

AIS message types 1, 2, and 3 that carry dynamic data: MMSI, position, SOG, COG, heading, navigational status, and timestamp, broadcast at regular intervals.

Splitting large result sets across multiple API responses using page or offset parameters, preventing oversized payloads and enabling incremental data retrieval.

A coastal or inland facility with infrastructure for vessels to load and discharge cargo, take on fuel and provisions, and undergo maintenance. A key node in global supply chains.

A recorded visit by a vessel to a port, including arrival and departure timestamps, berth assignment, and cargo operations. Historical port calls are available via the API.

The inspection regime by which a port country verifies that foreign vessels comply with international maritime conventions, independent of the flag state.

An on-board examination of a foreign vessel by port state control officers to verify compliance with SOLAS, MARPOL, STCW, and other international conventions.

A mobile AIS receiver installed on vessels that relays AIS signals from nearby ships to a central server, extending coverage beyond fixed terrestrial stations.

How quickly a vessel is changing its heading, measured in degrees per minute. Positive values indicate a turn to starboard, negative to port. Reported in AIS position messages.

The process of calculating an optimal maritime path between two positions, accounting for waypoints, currents, weather, depth constraints, and traffic separation schemes.

A per-endpoint cap on the number of requests per minute. Exceeding the limit returns a 429 error. Limits range from 15 req/min (historical) to 100 req/min (vessel location).

Representational State Transfer — the architectural style used by this API. Clients send HTTP GET requests to resource-oriented URLs and receive JSON responses.

The process of refreshing cached API response data after a defined period. Setting appropriate revalidation intervals reduces credit usage while keeping data fresh.

A single HTTP call made to an API endpoint. Each successful, billable request deducts a fixed number of credits from the account balance.

AIS signals collected by low-earth-orbit satellites, providing global coverage in open ocean where terrestrial shore stations cannot reach.

AIS message type 5 carrying information that changes rarely or per voyage: IMO number, call sign, vessel name, dimensions, vessel type, destination, ETA, and draught.

The actual speed of a vessel relative to the seabed, reported in knots via AIS. Differs from speed through water when significant currents are present.

A credit variant consumed when retrieving vessel positions sourced from satellite AIS receivers, as opposed to terrestrial receivers. Required for open-ocean tracking.

Restrictions imposed by governments or international bodies on vessels, owners, or operators — prohibiting transactions, port access, or trade with designated parties.

Safety of Life at Sea — the principal international maritime safety treaty, mandating requirements for vessel construction, equipment, and operational procedures including AIS carriage.

AIS signals received by fixed shore-based VHF antenna stations, typically covering up to 50 km from the coastline with high-frequency position updates every 2–10 seconds.

A credit variant consumed when retrieving vessel positions from shore-based AIS receivers. Used for coastal and port-area vessel tracking within ~50 km of land.

AIS transponders synchronise their transmission slots to Coordinated Universal Time (UTC) to avoid collisions between simultaneous broadcasts on the shared VHF channel.

Very High Frequency radio spectrum (156–174 MHz) used by AIS to broadcast vessel data. AIS uses channels 87B (161.975 MHz) and 88B (162.025 MHz).

The overall length and breadth (beam) of a vessel in metres as transmitted in AIS static data messages. Used for berth planning and bridge clearance calculations.

The name a vessel is registered under and broadcasts via AIS. Names can change on sale; the IMO number provides a more reliable permanent identifier.

A numeric AIS code (20–99) classifying a vessel by function — e.g. tanker, cargo, passenger, fishing — as defined in ITU-R M.1371. Used for filtering and analytics.

A shore-based system — similar to air traffic control — that monitors and guides vessel movements within port approaches, harbours, and restricted waterways.

The year a vessel's hull was completed and launched, sourced from IMO registration records. Indicates vessel age for maintenance, insurance, and compliance assessments.