AIS Spoofing: 10 Bridge Red Flags

Simple Summary

An AIS target suddenly appears tens of miles away with no intermediate track, or “snaps” into a port. Radar/visual don’t support the jump, and the ECDIS trail looks broken. Treat the AIS position as untrusted until you confirm with independent sensors.

Quick checks

• Compare ARPA trail and EBL/VRM to the AIS vector.
• Toggle radar overlay ON/OFF on ECDIS to verify the echo.
• Scan CPA/TCPA for other ships’ tracks of the same target.

Solutions

• Navigate using radar and visual; do not rely on suspect AIS for collision avoidance.
• Manual plot the contact until the picture stabilizes.
• Log the anomaly and brief the Master if persistent.

Simple Summary

Dozens of AIS tracks form neat rings or “flowers” around a fixed point on the chart, often near shore. It can coincide with regional GNSS interference, so your own position may also drift. Switch to independent references until the pattern clears.

Quick checks

• Zoom out on ECDIS to see the full ring pattern.
• Check bridge GNSS alarms (pos lost / HDOP high).
• Ask nearby ships if they observe the same behavior.

Solutions

• Navigate on radar ranges/bearings and visual references.
• Use DR and parallel indexing; avoid GNSS-dependent legs.
• Report to VTS if it affects traffic flow.

Radar/ECDIS settings (quick)

• Radar overlay: toggle OFF/ON to confirm echoes.
• Trails ON (short): verify movement vs circular artefacts.
• Vector length: reduce to 3–6 min to avoid clutter.
• Guard zones: widen slightly to catch real contacts.

Simple Summary

AIS says the ship sits on land or inside a terminal, but you see it under way offshore. This points to spoofed or faulty position data. Trust your independent sensors first.

Quick checks

• Radar overlay + visual bearings to fixed marks.
• Second GNSS receiver (if fitted) to compare position.
• Ask nearby traffic if they see the target where you do.

Solutions

• Navigate by radar/visual; discount suspect AIS for CPA.
• Adjust CPA alarms based on radar target, not AIS symbol.
• Report to VTS if safety of navigation is affected.

Simple Summary

Two AIS targets share the same MMSI/name/IMO in different places at once. One track is likely synthetic or misconfigured. This can mislead CPA decisions if you follow the wrong symbol.

Quick checks

• Compare AIS particulars (type, length/beam, call sign) to the hull you see.
• Call the nearer contact on VHF using MMSI/name.
• Cross-check with radar echo and relative motion.

Solutions

• Treat the more credible (radar/visual) contact as real for CPA.
• Record the duplicate ID and time; brief the Master.
• Inform VTS if it affects traffic handling.

Evidence to keep

• Screenshots of both targets showing identical MMSI/IMO.
• Deck-log entry with UTC, range/bearing, and remarks.
• ARPA plot or ECDIS trail snippet if policy allows.

Simple Summary

AIS particulars (type, dimensions, call sign, flag) don’t fit the ship in view or known registry info. Repeated mid-voyage edits to destination/draft also raise suspicion. Assume identity uncertainty and cross-verify before acting on the data.

Quick checks

• Eyeball length/beam vs AIS dimensions.
• Cross-check IMO/name against a trusted registry per company procedures.
• Query the vessel on VHF if safe and appropriate.

Solutions

• Treat AIS identity as unverified; use radar/visual for CPA.
• Record discrepancies and pass in watch handover.
• Inform VTS if identity confusion impacts traffic decisions.

Simple Summary

The target reports “at anchor” or “not under command” while making steady speed, or shows 0 kn while clearly moving. Either the AIS status field is wrong or the whole position/velocity is suspect. Prioritize independent sensors.

Quick checks

• Compare ARPA speed/track with AIS SOG/COG.
• Look for wheel-over points or course changes on the echo.
• Ask on VHF if the vessel confirms its status when safe to do so.

Solutions

• Base CPA/TCPA on radar tracking and visual bearings.
• Reduce reliance on AIS collision-avoidance vectors until aligned.
• Log the inconsistency and brief the Master if traffic is affected.

Legit reasons to rule out

• Strong current or wind set while drifting with engines stopped.
• Manual status not updated after heaving anchor or clearing pilotage.
• Sensor selection mismatch (wrong GPS source feeding AIS).

Simple Summary

The target’s heading and course over ground differ by a large, persistent angle without wind/current or maneuvering to explain it. Consider the AIS vector unreliable until it matches radar and visual movement.

Quick checks

• Check wind and current set; small differences can be normal.
• Confirm the target’s echo and relative motion on ARPA.
• Shorten vector length on ECDIS to reduce misleading tails.

Solutions

• Use radar vectors and manual bearings for CPA decisions.
• Delay course alterations based on AIS-only cues.
• Monitor for convergence of heading and COG before trusting AIS again.

Radar/ECDIS settings (quick)

• Trails ON (short) to see true motion.
• Vector length 3–6 min to match near-term movement.
• Radar overlay toggle to verify echo alignment with AIS.

Simple Summary

ARPA plot, EBL/VRM, or visual bearings agree on where the contact is, but the AIS symbol sits offset or points elsewhere. Until sensors align, treat AIS as advisory only, not the basis for maneuvers.

Quick checks

• Confirm target acquisition and lock on radar.
• Check ECDIS sensor input priority and overlays.
• Compare bearings to fixed marks for sanity.

Solutions

• Navigate by radar vectors and visual bearings.
• Note the offset and monitor for convergence.
• Inform VTS if the mismatch disrupts traffic flow.

Evidence to keep

• Screenshot with radar overlay ON and AIS symbol visible.
• Deck-log entry with UTC, bearing/range, and remarks.
• ARPA plot details (vector, CPA/TCPA) if policy allows.

Simple Summary

ECDIS or GPS receivers show “position lost,” “HDOP high,” or “initialising,” and other ships report issues too. Expect AIS positions to drift or jump. Shift navigation to references that don’t rely on GNSS.

Quick checks

• Verify alarms on multiple receivers if fitted.
• Ask nearby ships/VTS if they see the same problem.
• Check company notices or local advisories if available.

Solutions

• Navigate by radar ranges/bearings, visual marks, and DR.
• Delay GNSS-dependent wheel-overs and recheck clearing bearings.
• Log the event and adjust passage plan margins if required.

Simple Summary

Unfamiliar stations on VHF imitate authorities and direct a course change while your AIS picture looks wrong. Treat this as a combined deception risk and verify before complying with any instructions.

Quick checks

• Ask the caller to confirm identity, channel, and position.
• Cross-check with published VTS/authority call signs.
• Verify traffic picture on radar and visually.

Solutions

• Do not alter course solely on an unverified VHF request.
• If in doubt, contact the published VTS number or call sign directly.
• Record details and escalate to the Master immediately.