Three distinct IMO tracking + data instruments together provide the technical basis for casualty investigation, flag/coastal-state monitoring, and merchant-ship security-alert response. Each has its own SOLAS regulation, retention rule, and data-request procedure. All three are routinely audited at PSC inspection + play a central role in casualty investigation.
Voyage Data Recorder (VDR) — SOLAS V/20
A shipborne recorder capturing ship data (position, heading, speed, engine parameters, watertight door status, bridge audio, radar image, ECDIS image) continuously to a protected memory. Function is analogous to an aircraft "black box". Required on all passenger ships + cargo ships > 3,000 GT constructed on or after 1 July 2002 (subsequently amended to include existing ships).
Retention. Minimum 48 hours in the protected float-free capsule; longer in the primary recorder + optional back-up.
Simplified VDR (S-VDR). Reduced data-capture version for cargo ships > 3,000 GT constructed before 2002 + retrofitted.
Post-incident data retrieval. After a casualty, the VDR is preserved intact + data downloaded by casualty investigators. Regular VDR data may be pulled for post-voyage analysis or training.
Annual performance test required by IMO Res. A.861(20).
Investigation use. Cases where VDR data has been central: Costa Concordia, El Faro (recovered from wreck), MV Grande America, Ever Given.
Long Range Identification and Tracking (LRIT) — SOLAS V/19-1
A global vessel-position reporting system introduced 1 January 2008 in the wake of enhanced maritime security concerns. Required for all passenger ships + cargo ships > 300 GT operating in Areas A2, A3, or A4 (i.e. most SOLAS commercial tonnage). Ship-side equipment reports position via satellite to a national or regional LRIT Data Centre.
Reporting frequency. Every 6 hours minimum by default; more frequent when the vessel is in a specific coastal-state area.
Data content. Vessel ID, position, date/time of report. NOT cargo, crew, or destination.
Access rules. Flag state has full access. Coastal states can access vessels within 1,000 nm of their coast. Port states can access vessels intending to enter their port. Search + Rescue authorities have global access.
Confidentiality. Not public data. The LRIT International Data Exchange (IDE) hub is operated by EMSA on behalf of IMO.
Comparison with AIS. AIS is short-range VHF broadcast used for collision avoidance + regional monitoring; LRIT is long-range satellite reporting for security + tracking. Both are complementary.
Ship Security Alert System (SSAS) — SOLAS XI-2/6
A covert distress-alert system by which the ship can send a security alert (e.g. under piracy or terrorist attack) to the flag state administration + designated Company Security Officer, without alerting the attackers on board. Required on passenger ships + all cargo ships > 500 GT.
Activation. By a "panic-button" located discreetly on the bridge + typically a second in a hidden location. Activation must not produce any audible or visible signal on board.
Recipient. Flag state + designated Company Security Officer (from ISPS Code). NOT MRCCs (that's the DSC or SART role).
Data transmitted. Vessel ID, position, date/time. NOT audio or additional detail.
Test rules. Test alerts are permitted but must be coordinated with the flag state + Company to avoid false-alert response.
Real-world use. SSAS activation was used in Somali piracy incidents 2008-2013 + Houthi seizure of Galaxy Leader (2023).
Data-request procedure after casualty
Casualty investigators (typically the flag state Marine Casualty Investigation Board) can request:
VDR data. Directly from the vessel or the recovered capsule. Chain of custody must be preserved.
LRIT position history. From the flag-state LRIT Data Centre; typically the full voyage history.
SSAS activation records. From the flag state + Company records.
Any Master, DPA, or SSO should ensure the SMS documents the procedure for each — including who has authority to authorise data release.
See also
· AIS — short-range broadcast counterpart to LRIT.