Using AIS VDR and VTS Evidence in Maritime Cases
Modern collision and allision cases turn on electronic records. Automatic Identification System data, voyage data recorders, and vessel traffic service logs often reconstruct the minutes before impact. Lawyers who preserve those sources early have a clearer fact pattern.
AIS broadcasts a ship’s identity, position, course, and speed. Other vessels and shore stations receive the signal. Plotting those points shows meeting, crossing, or overtaking geometry. Gaps and jump points matter. A missing burst can mean equipment failure, poor antenna placement, or a later edit of a commercial feed.
AIS is not a complete navigation record. Update rates vary. The displayed heading may lag. A tug and tow may not match a single clean track. Counsel should compare raw shore data with the vessel’s own unit and with radar overlays when they exist.
The voyage data recorder is closer to an aircraft black box.
It can store radar images, bridge audio, heading, speed, and alarm history. Immediate notice after a casualty is critical. The unit overwrites on a cycle. If nobody saves the file, the best evidence disappears.
Bridge audio can decide fault. It may capture helm orders, pilot exchanges, and alarm reactions. Transcripts need context. Background noise and language mix can create disputes. A navigation expert should interpret radar screenshots with the audio, not in isolation.
Vessel traffic services add a shore view.
In a busy waterway such as the Houston Ship Channel, VTS radio logs and traffic-image records show what controllers saw and said. Those records can confirm or contradict a pilot’s memory. They also show whether a vessel followed local reporting rules.
Authentication is the next step. Parties must show the data came from the unit in ordinary use. Chain of custody, download reports, and vendor software versions help. Courts may exclude a polished animation if the underlying points are incomplete.
Privacy and regulation also appear. Crew voices are on the VDR. Commercial AIS aggregators may not match official feeds. Coast Guard or port requests can secure official copies faster than a later subpoena.
Good practice is simple. Send a preservation letter the same day. Ask for the VDR save, the AIS log, and VTS recordings. Inspect the wheelhouse before equipment is reset. Then build one timeline from all three sources.
AIS shows where the ship reported it was. The VDR shows what the bridge saw and said. VTS shows how the waterway was managed. Together they often decide a Houston maritime case more reliably than memory alone.