Neither app is universally more accurate. MarineTraffic and VesselFinder both display Automatic Identification System (AIS) data, so the more trustworthy position is usually the one with the newer timestamp and the better source for that vessel and location. Near a coast or in port, terrestrial receiver coverage and update age dominate. Far offshore, satellite availability and latency dominate. A faulty, switched-off, misconfigured or spoofed transponder can make either service wrong.
For general consumer map coverage, MarineTraffic is a strong choice and documents a path to satellite AIS. For developers and data teams, VesselFinder is attractive because its API exposes source labels, timestamps, credit-based terrestrial and satellite access, and voyage and port-call datasets. Those are use-case advantages, not proof of a head-to-head accuracy winner.
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The short answer: compare the position age and source, not just the app name
An AIS icon is not a live GPS feed from the vessel. It is a report transmitted by the vessel’s onboard equipment and received by a network operated or supplied to the tracking service. Two apps can show different locations for the same ship because they received different reports, used different receiver networks, or refreshed their maps at different times.
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- Last-received time: how old the displayed report is.
- Source: terrestrial, satellite or roaming.
- Transmission quality: whether the ship’s AIS equipment is sending complete and plausible data.
A newer terrestrial report is normally more useful for a ship near shore than an older satellite report. In the open ocean, a recent satellite report may be the only available position. If the two apps disagree, the record with the newer timestamp and a source appropriate to the vessel’s location is usually the better situational estimate.
How AIS accuracy actually works
AIS is a maritime radio system. The International Maritime Organization requires it to exchange a vessel’s identity, type, position, course, speed and navigational status. The system does not independently verify every field. The IMO’s revised guidance captures the fundamental limitation: “The accuracy of AIS information received is only as good as the accuracy of the AIS information transmitted.”
That means an app can accurately receive an inaccurate report. A ship may transmit a stale position because its GPS, transponder, antenna or power supply has a problem. The crew may leave a destination or navigational status unchanged. In other cases, reception is interrupted, the vessel is outside a receiver’s range, or the signal is deliberately manipulated.
Terrestrial AIS near coasts
Terrestrial AIS uses shore-based receiving stations listening to VHF transmissions. A vessel must be within radio range, and the signal can be affected by geography, antenna height, weather conditions and local network density. Port approaches and busy coastlines often have frequent updates because many receivers can hear the same transmission.
MarineTraffic says its coastal receiving network picks up AIS transmissions “provided that the vessel is within its range.” It also states that terrestrial coverage does not reach 100% of the world’s seas. Terrestrial positions are generally refreshed more often than satellite positions, but a quiet or poorly covered coastline can still produce gaps.
VesselFinder documents thousands of terrestrial AIS stations. Its API identifies a terrestrial record with the source label TER. The presence of a terrestrial label tells you how the record was received; it does not guarantee that the underlying ship data is correct.
Satellite AIS offshore
Satellite AIS receivers listen from orbit, extending coverage beyond the horizon of coastal stations. Satellite reception is essential for remote and open-ocean areas, but satellites see many transmissions at once and may deliver reports less frequently than shore stations. A ship can therefore appear to jump a considerable distance between two satellite updates even when it has been moving normally.
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Roaming and mixed coverage
A service may receive a vessel through more than one network type as it moves. MarineTraffic describes roaming as a source category. A vessel can be seen frequently by coastal stations, then switch to satellite-derived positions after leaving coverage, and later return to terrestrial reception. Comparing a recent terrestrial report in one app with an older satellite report in another is not a fair accuracy test.
MarineTraffic and VesselFinder compared by use case
| Reader need | Likely better fit | What determines the result |
|---|---|---|
| Watching ships in a port or along a coast | Either | Local receiver density and the age of each position matter more than the brand. |
| Following a vessel in the open ocean | The service showing the newer satellite position | Satellite visibility, collection timing and latency are decisive. |
| Consumer map and general ship lookup | MarineTraffic | Its published help material explains terrestrial, satellite, roaming, station attribution and paid satellite access. |
| API integration and data engineering | VesselFinder | Its documentation exposes JSON and XML APIs, source labels, credit pricing, voyage and port-call data, and terrestrial/satellite selection. |
This table is a fit guide, not an accuracy ranking. A VesselFinder satellite record can be fresher than a MarineTraffic satellite record for one ship, while MarineTraffic can be fresher for another ship in the same region.
Which is more accurate in coastal waters?
For a harbor, river mouth or coastal route, start with the app that shows the more recent terrestrial report for the target vessel. Receiver placement is highly local: one service may have excellent coverage on one side of a bay while another has a better station on the opposite shore.
Look for a position received within the last few minutes, then compare the ship’s reported speed and course with its apparent movement. A position that is newer but inconsistent with the vessel’s speed may reflect a bad transmission or a map refresh issue. If both apps show recent terrestrial reports that are close together, the difference between them is unlikely to be operationally significant for casual watching.
MarineTraffic documents server downsampling of overlapping coverage to one position per MMSI per minute, as stated in material dated June 4, 2025. MMSI is the vessel’s Maritime Mobile Service Identity. This means several receivers may hear the same transmission while the service still presents one selected report per minute; it should not be interpreted as a position being generated every minute by the vessel.
Which is more accurate offshore?
Offshore, the key question is not which logo is on the map but when either service last received a satellite report. Open the vessel’s details, note the source and timestamp, and calculate how far the ship could have traveled since that report. A cargo ship moving at 15 knots covers about 7.5 nautical miles in 30 minutes; an icon based on a two-hour-old report can therefore be many miles from the ship’s present location.
VesselFinder’s published average of 90% of satellite positions arriving with less than one hour of latency provides useful context, but individual vessels can fall outside that average. Satellite collection can be delayed by satellite geometry, congestion, the ship’s antenna and the service’s processing pipeline. MarineTraffic’s satellite options similarly extend reach without turning AIS into continuous real-time tracking.
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Is MarineTraffic live?
MarineTraffic is near-real-time when a vessel is transmitting and a receiver can hear it, but “live” does not mean continuous or guaranteed. Terrestrial coverage normally updates more often near shore. Satellite positions can be separated by longer intervals. MarineTraffic also says a vessel can be removed from its Live Map after 24 hours without a fresh position.
A missing icon therefore does not prove that a ship has stopped, sunk or left the area. It may be outside terrestrial range, waiting for a satellite collection, transmitting faulty data, or temporarily absent from the service’s active display. Check the vessel’s last-known position and timestamp before drawing a conclusion.
Why a ship is missing or appears in the wrong place
1. The vessel is outside terrestrial range
Coastal AIS is line-of-sight radio. Mountains, headlands, distance from shore and sparse station coverage can create gaps. A vessel may disappear after rounding a cape and reappear when it reaches another receiver’s footprint.
2. Satellite reception is delayed or unavailable
Remote waters depend on satellite AIS. The next report may not arrive for a while, and the service may not display a vessel if no fresh position has been received. Compare the last-received time rather than relying on the icon’s apparent location.
3. The transponder is off, faulty or poorly installed
AIS equipment can lose power, have a damaged antenna or provide an incorrect GPS input. The IMO limitation applies here: the tracking service cannot correct an erroneous transmission it successfully receives.
4. The vessel is not required or configured to transmit in the way you expect
AIS carriage requirements vary by vessel type, size and jurisdiction, and a master can sometimes make a safety-related decision to limit transmission. Small craft may use different equipment or no AIS at all. Do not assume every object on the water will appear.
5. The data is stale or manually maintained
Destination, estimated time of arrival and navigational status are reported fields. They can be entered manually and left unchanged after plans change. Treat them as operational hints, not independently verified facts.
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6. The report is spoofed or otherwise anomalous
VesselFinder’s terms warn that AIS data may be incomplete, delayed, inaccurate or unavailable because of equipment problems, reception gaps, spoofing and third-party source limitations. A position that conflicts sharply with the vessel’s speed, course or known route deserves skepticism.
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How to perform a fair personal accuracy test
No independent, controlled benchmark establishes that one service is universally more accurate. You can still make a useful local comparison by controlling the variables.
- Choose several known vessels. Include ships in a port, near a coast and, if possible, one offshore target. Use vessels with stable MMSI identities.
- Open both services at the same time. Avoid comparing a screenshot from one hour with a current view in the other.
- Record the source. Write down whether each record is terrestrial, satellite or roaming. In VesselFinder API data, note
TERorSAT. - Record the timestamp. Capture the last-received time, not merely the time your browser loaded the map.
- Capture the position and movement fields. Note latitude, longitude, course, speed and heading where available.
- Repeat the sample. Take observations at several times and on different days. One delayed satellite report cannot establish a service-wide pattern.
- Separate freshness from positional correctness. A newer report is fresher, but only an independent reference such as a verified local receiver or official navigation system can establish whether its coordinates are correct.
This method tells you which service is more useful in your operating area. It does not create a universal accuracy score because receiver coverage and vessel transmissions change from place to place.
What the API data tells you
VesselFinder’s documented API can return JSON or XML records containing coordinates, course, speed, heading and timestamps. The explicit source field is valuable in automated systems because a data pipeline can treat terrestrial and satellite records differently, calculate age, and flag stale observations.
Its credit model also distinguishes source cost: one credit per terrestrial AIS position and 10 credits per satellite AIS position, according to the current API documentation accessed in 2026. Those are API consumption units, not measures of accuracy. Satellite access costs more because it extends coverage; a higher credit charge does not mean the coordinate is more precise.
VesselFinder documents datasets for voyages, masters and port calls in addition to position feeds. These can support historical analysis and arrival/departure workflows, but a port-call record should not be mistaken for a continuously updated location. MarineTraffic’s published material is more oriented toward map users and explains station attribution and satellite plan options.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to read the fields without overtrusting them
- Position: the coordinates in the latest received AIS report, not necessarily the vessel’s current coordinates.
- Timestamp: the most important field for judging freshness. Always display it with the position.
- Course over ground: direction of movement over the ground; it can differ from the ship’s heading.
- Speed over ground: useful for estimating how far a stale position may have drifted from reality.
- Heading: the vessel’s bow direction, which can differ from its course while turning or in current.
- Destination and ETA: reported operational fields that may be manually entered or outdated.
- Navigational status: a transmitted status value that can remain unchanged if the crew does not update it.
Use several fields together. A timestamp that is only two minutes old, a plausible speed and a course matching the track is more reassuring than a very recent record with an impossible jump or an unchanged destination from days earlier.
MarineTraffic versus VesselFinder for common tasks
Watching a ferry commute
Either app can work well if it has dense terrestrial coverage along the route. Choose the one with the shorter last-received interval in your local harbor. If one map shows a satellite badge for a ferry that is plainly near shore while the other shows a fresh terrestrial report, prefer the terrestrial report for short-term movement.
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Use the latest position, speed and course to understand movement, then treat the displayed ETA as a report rather than a promise. Weather, traffic separation schemes, pilotage and port congestion can change an arrival after the AIS record was transmitted.
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Following a transoceanic voyage
Expect gaps. Record the age of every satellite position and estimate the vessel’s possible travel since that observation. For a continuous operational picture, public tracking apps are not a substitute for the carrier’s own updates or professional maritime systems.
Building an application
VesselFinder is the clearer fit when your integration needs source labels, explicit terrestrial/satellite selection, structured API responses and port-call or voyage datasets. Design the application to store the source and timestamp with every coordinate, reject implausibly old records, and show users when a position is stale.
Can a local AIS receiver improve coastal tracking?
A local receiver can provide direct terrestrial AIS reception in the area around its antenna, independent of a public map’s choice of station. It is most useful for technically minded users who need frequent local updates and can install an appropriate antenna, cabling and network connection. Range depends on antenna height, terrain, radio conditions and the transmitting vessel.
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MarineTraffic says contributors can apply for a free pre-programmed AIS receiver. Availability and eligibility can change, so confirm the current terms before planning an installation. A receiver improves local visibility; it does not provide satellite coverage, repair a vessel’s faulty transmission or make every ship detectable.
Safety and operational limits
Public AIS apps are awareness tools. Do not use either service as the sole source for collision avoidance, navigation, search-and-rescue decisions or confirmation that a channel is clear. For safety-critical decisions, use the vessel’s approved bridge equipment, radar, visual observations, official notices and the instructions of the relevant maritime authority.
Even a position with a fresh timestamp can be wrong if the transmitted coordinates are wrong. Conversely, an old position may still be useful for understanding a vessel’s last known route, provided its age is obvious to everyone using it.
A practical decision framework
Choose MarineTraffic when
- You want a general-purpose consumer map and ship lookup.
- You value published explanations of terrestrial, satellite, roaming and station attribution.
- You may need a documented upgrade path to satellite AIS.
Choose VesselFinder when
- You are integrating AIS into software or a data pipeline.
- You need source labels such as
TERandSATattached to records. - You need structured JSON/XML access, credit-based usage or voyage and port-call datasets.
Use both when the decision matters
For a high-interest vessel, compare the newest reports in both services, record source and age, and investigate discrepancies against an independent official or onboard source. The two apps can complement each other because their receiver networks and processing paths may differ.
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Bottom line
MarineTraffic and VesselFinder are only as accurate as the AIS reports they receive and the coverage available at that moment. In coastal waters, choose the service with the freshest terrestrial position for your area. Offshore, choose the one with the newer satellite report and account for the vessel’s possible movement since that timestamp. MarineTraffic is a sensible general consumer choice; VesselFinder has a strong advantage for API-driven work. Neither deserves a blanket claim of being the most accurate everywhere.
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