🛰️ Why is the AIS position of my vessel not up to date?
If a vessel’s AIS position is not current, it is usually related to signal availability, transmission behavior, or technical limitations of AIS data collection. This article explains the most common causes and why gaps can occur.
🔌 1. No AIS signal transmission
- AIS transponder switched off
- Technical issue onboard
- Power supply interrupted
👉 Check: Confirm with the vessel if AIS is active.
🗺️ 2. Limited AIS reception (coverage gaps)
- Satellite coverage is not continuous
- Coastal stations only work near shore
- Remote ocean areas = fewer updates
👉 Typical: Less frequent updates mid-ocean.
💡 Side note:
Fleettracker combines terrestrial, dynamic, and satellite AIS data sources to provide the best possible global coverage. Despite this, temporary gaps can still occur.
🛰️ 3. Satellite AIS limitations (how it works)
- Vessels share communication time slots (SOTDMA)
- Signals are sent in shared communication cells
- Multiple vessels may transmit simultaneously
⚠️ Result:
- Signal collisions
- Corrupted or incomplete messages
- Not every transmission is received
📡 4. Signal strength & vessel type
- Class A: strong signal → better detection
- Class B: weaker signal → less reliable
Additional factors:
- Older AIS devices
- Low power mode
- Long distance to satellite (~800 km)
👉 Impact: Fewer valid position updates.
🚢 5. High traffic density (signal collisions)
- Many vessels transmitting at the same time
- Signals may overlap or overwrite
👉 Result: Missing or delayed positions.
⏱️ 6. Transmission frequency (normal behavior)
- Moving vessels → frequent updates
- At anchor/port → fewer updates
👉 This is expected AIS behavior.
🔄 7. Data provider & filtering
- AIS data is received from external providers
- Invalid or incomplete messages are filtered out
👉 This can create visible gaps in tracking.
⚙️ 8. Vessel data issues
- Incorrect MMSI / IMO
- Duplicate vessel entries
👉 Check: Verify vessel settings in Fleettracker.
⚠️ Why gaps in AIS tracking are normal
Even though vessels may transmit multiple signals per minute:
➡️ Only a portion of these signals are successfully received and validated
This can result in:
- Irregular update intervals
- Missing positions
- “Jumping” vessel tracks
🧹 Data quality improvement in Fleettracker
Fleettracker helps improve track quality by automatically identifying implausible AIS positions.
- Incorrect or unrealistic positions can be detected and removed
- This ensures a cleaner and more reliable vessel track history
- Helps avoid misinterpretation caused by faulty AIS data
👉 Learn more:
🔍 When should you take action?
Investigate if:
- No updates for an unusually long time
- Vessel is near shore but no signal
- Other systems show newer data
✅ Recommended next steps
- Contact vessel to confirm AIS status
- Verify MMSI / IMO
- Compare with other AIS tools
- Wait for next satellite update
- Contact Swiss Climate Support