When only 50% of vessels arrive on their predicted ETA, relying on carrier updates alone can lead to costly delays and detention fees. The difference between a vessel being ‘Anchored’ offshore and ‘Discharged’ at the terminal is a critical gap where supply chain plans fall apart. Effective container tracking isn’t just about finding a dot on a map; it’s about getting accurate, timely data to manage your logistics.

This guide explains the tools and terminology for real-time container tracking. We’ll look at how AIS technology works for all ships over 300 gross tons and compare the features of popular free platforms like MarineTraffic and VesselFinder. You will also learn to interpret key port statuses and see how automated alerts can help you move from reactive problem-solving to proactive management.

How AIS Vessel Tracking Works

AIS works by having vessels automatically broadcast their identity, position, course, and speed using VHF radio transponders. Other ships, shore-based stations, and satellites receive these signals, allowing for real-time tracking, collision avoidance, and maritime traffic management.

Core Components: Transponders and Frequencies

At the heart of the AIS system is a VHF transponder that each vessel uses to automatically broadcast its data. This communication happens on two dedicated VHF frequencies, 161.975 MHz (Channel A) and 162.025 MHz (Channel B). The system uses two main types of transceivers. Class A transceivers are mandatory for all ships over 300 gross tons and transmit with a power of 12.5 watts to ensure maximum range and signal reliability. For smaller commercial and recreational craft, Class B transceivers provide a lower-power alternative, typically operating at 2 or 5 watts.

Data Transmission: Static vs. Dynamic Information

AIS broadcasts two distinct types of information. Static data includes information that rarely changes, such as the vessel’s unique 9-digit MMSI number, its IMO number, name, call sign, and dimensions. This data packet is typically transmitted every six minutes. In contrast, dynamic data consists of real-time information that changes as the vessel moves. This includes its precise position, speed over ground (with a resolution of 0.1 knots), course over ground, and rate of turn. To gather this information, AIS integrates directly with a ship’s onboard systems, primarily its GNSS (like GPS) for position data and its gyrocompass for heading. Dynamic updates are sent much more frequently, often every few seconds, to provide an accurate, live picture of the vessel’s activity.

Top Free Tools: MarineTraffic, VesselFinder

MarineTraffic and VesselFinder are the top free tools for tracking ships using AIS data. Both offer live maps and 24-hour track history. MarineTraffic focuses on core navigation data, while VesselFinder’s free tier includes more commercial details like vessel tonnage, build year, and recent port calls.

Shared AIS Foundation and Core Free Features

Both MarineTraffic and VesselFinder build their platforms on the same public Automatic Identification System (AIS) technology. They track SOLAS-compliant vessels over 300 Gross Tonnage by processing signals broadcast over standard VHF maritime channels (161.975 MHz and 162.025 MHz). Data is collected from a global network of terrestrial receivers and augmented with optional satellite feeds.

The free versions of both tools provide a similar core experience. Users get live maps showing a vessel’s current position, speed, course, and basic identification like its IMO number and dimensions. Both platforms also allow you to view a vessel’s 24-hour track history on their web and mobile applications.

Key Differences: Data Depth and Upgrade Paths

The main distinction in their free offerings is the depth of commercial data. VesselFinder’s free tier includes more specific details, such as a ship’s gross tonnage, year of build, summer deadweight, and a list of its last five port calls. MarineTraffic’s free version focuses more on real-time navigational data, like the vessel’s current draught and its destination ETA, without providing the same level of historical commercial information.

For users needing more capability, both platforms reserve advanced features for their paid plans. Full satellite tracking, extended history, API access, and fleet management tools are all part of their subscriber and enterprise services. VesselFinder has clearly priced tiers for adding satellite coverage and longer track histories, while both services offer customized enterprise plans for advanced fleet monitoring.

Interpreting Status: “Berth”, “Anchored”, “Discharged”

A vessel is ‘Anchored’ when waiting offshore for a dock space, ‘Berth’ when moored at the terminal for operations, and ‘Discharged’ after its cargo has been fully unloaded. This sequence tracks a vessel’s progress from arrival in port waters to cargo handover.

Waiting Offshore (Anchored) vs. Docking (Berth)

A vessel’s status changes to ‘Anchored’ when it arrives at a designated offshore anchorage area within port limits. Ships wait here when their assigned berth is not yet available. Once the dock space is free, the vessel moves to its ‘Berth,’ which is the specific mooring spot at the terminal where it will be secured for cargo operations.

After mooring lines are fully secured, the vessel’s status becomes ‘All Fast.’ This signals that the ship is safely docked and ready for work to begin. The “All Fast” declaration is a key milestone because it allows the ship’s master to tender a Notice of Readiness (NOR). The NOR officially starts the contractual countdown, or laytime, allocated for loading or unloading cargo.

Cargo Operations and Completion (Discharged)

The ‘Discharged’ status indicates that all specified containers have been successfully unloaded from the vessel. This process uses large ship-to-shore cranes to transfer containers from the ship’s hold and deck onto the terminal’s yard for temporary storage.

Once the last container is offloaded, a completion report is sent to the shipping agent, marking the end of the vessel’s primary port task. Terminal operators must complete all discharge activities within the laytime period established by the NOR. Failing to meet this deadline results in demurrage, which are penalties paid to the shipping line for the delay.

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ETA vs. ATA (Estimated vs. Actual)

ETA (Estimated Time of Arrival) is a dynamic forecast used for planning logistics, but it often changes due to weather or port congestion. ATA (Actual Time of Arrival) is the confirmed, unchangeable timestamp when a vessel docks, triggering customs and unloading. The gap between them creates operational risks.

ETA: The Dynamic Forecast for Planning

The Estimated Time of Arrival (ETA) is a predictive timestamp based on variables like sailing schedules, port congestion, weather, and other operational factors. This forecast is not static and can update multiple times during a vessel’s transit, providing a running estimate for shippers and consignees. Logistics coordinators rely on the ETA to tentatively schedule downstream activities, including customs brokerage, trucking appointments, and warehouse labor.

ATA: The Final Timestamp for Execution

The Actual Time of Arrival (ATA) is the confirmed, unchangeable timestamp recorded by port systems when a vessel officially docks. This timestamp triggers the start of physical processes like cargo unloading, customs clearance, and container pickup availability. The ATA is the true metric for measuring on-time performance, especially since only around 50% of vessels arrive on their predicted ETA.

The ATA follows another key milestone, the Actual Time of Departure (ATD). Once a vessel’s ATD is confirmed, it signals the voyage has started and allows for a more accurate recalculation of the ETA. A close alignment between the final ETA and the ATA indicates an efficient, predictable supply chain, while a significant gap highlights operational risks and potential delays.

Getting Automated Updates

Automated updates are near-real-time notifications about a container’s status, sent via email, SMS, or API webhooks. They are triggered by predefined events like vessel arrival, customs clearance, or delays, using data from carriers, AIS, and GPS to help avoid penalties like demurrage.

How Update Triggers and Alerts Work

Automated updates operate on an event-driven model. The system sends notifications when a container’s journey meets a predefined condition. This approach provides timely information for proactive management, which helps logistics teams avoid costly demurrage and detention fees. Common triggers include major milestones like vessel departure, port arrival, and customs clearance. The system also flags significant changes to the estimated time of arrival (ETA).

Alerts are delivered through channels like email, SMS, or API webhooks. Webhooks can push data directly into a company’s Transportation Management System (TMS) or other business software. Systems can also generate exception alerts for anomalies detected by sensors, such as a temperature change in a refrigerated container or an unexpected deviation from the planned route.

Data Sources and Technical Payloads

To provide accurate, timely updates, tracking platforms combine data from several sources. They ingest information from carrier EDI and API feeds, Automatic Identification System (AIS) vessel data, GPS or IoT sensors attached to containers, and port community systems. This data fusion creates a single, reliable source of truth with near-real-time latency between a physical event and its corresponding notification.

For software integration, these updates are typically packaged as a JSON payload and sent via an API webhook. A standard payload contains essential identifiers, including the container ID, its ISO size/type code (e.g., “45G1”), the vessel’s IMO/MMSI numbers, and UN/LOCODEs to specify port locations. The data also includes event timestamps and a summary of the container’s route.

Final Thoughts

Tracking your shipment effectively means understanding the technology behind it, from the AIS data that powers live maps to the specific port terminology that defines a vessel’s status. Free tools like MarineTraffic and VesselFinder provide an excellent starting point for visualizing a ship’s journey, but they focus on different types of data. Getting the full picture requires knowing the difference between an estimated arrival (ETA) and the actual arrival (ATA), as this gap is where most supply chain disruptions happen.

The real advantage of modern tracking systems is the shift from reactive problem-solving to proactive logistics management. Automated updates, triggered by real-time events, give you the information needed to anticipate delays and make adjustments before they become costly problems. By using this data, you can better coordinate drayage, customs, and warehousing, ultimately reducing the risk of expensive fees like demurrage and detention.

Frequently Asked Questions