What to check on a Simplified VDR (S-VDR).
A full Voyage Data Recorder logs a wide set of bridge parameters: radar video, ECDIS data, speed and depth, rudder and engine orders, wind, hull stress on some ships, and bridge audio from several microphones. The Simplified VDR (S-VDR) was created so that older cargo ships did not have to be rewired to collect data their original bridge instruments never produced. It still captures the core evidence needed after a casualty — date and time, ship's position, speed, heading, bridge audio, radio communications audio, radar data and AIS data —…
What makes the simplified version different
A full Voyage Data Recorder logs a wide set of bridge parameters: radar video, ECDIS data, speed and depth, rudder and engine orders, wind, hull stress on some ships, and bridge audio from several microphones. The Simplified VDR (S-VDR) was created so that older cargo ships did not have to be rewired to collect data their original bridge instruments never produced. It still captures the core evidence needed after a casualty — date and time, ship's position, speed, heading, bridge audio, radio communications audio, radar data and AIS data — but drops parameters such as full ECDIS chart data, wind and hull stress that a full VDR carries. It is accepted only as a retrofit on existing cargo ships; new cargo ships must fit a full VDR.
Main components
Data acquisition unit
Collects and time-stamps signals from the gyro or heading sensor, GPS, radar, AIS transponder, echo sounder and bridge microphones, compresses the audio and radar image, and passes the combined stream to the recording capsule.
Final recording medium (capsule)
A fixed or float-free protective capsule, built to survive fire, shock and deep submersion, stores at minimum the last 48 hours of data in a continuous loop. Float-free capsules carry a locating beacon and release automatically if the ship sinks.
Bridge microphones and interface unit
At least one microphone covers the main conning position; the interface unit multiplexes sensor signals and provides the playback interface used by investigators, normally accessed by an authorised technician rather than the crew.
Selection and retrofit considerations
Because an S-VDR is fitted to an existing bridge, the deciding factors are compatibility rather than raw capacity:
- Availability of a suitable NMEA or serial output from the existing gyro, GPS and echo sounder, since older instruments may need an interface converter.
- Capsule type, fixed or float-free, and hull location clear of interference with existing structure.
- Whether the ship's AIS unit already outputs the data fields the S-VDR needs to log without modification.
- Power supply arrangement, since the capsule must run from an uninterruptible source that survives a main power failure for at least two hours.
Regulations and class
SOLAS Chapter V Regulation 20 sets the carriage requirement; cargo ships of 3,000 gross tonnage and upwards constructed before 1 July 2002 were permitted to fit an S-VDR instead of a full VDR. IMO Resolution MSC.163(78) and the related performance standard set the minimum data set and the 48-hour recording capacity. Class requires an annual performance test by an approved technician, checking that all required data channels are actually being recorded and that the capsule can be recovered and played back, with the results recorded in the ship's certificate.
Typical faults
| Fault | Consequence |
|---|---|
| Microphone gain drifted or channel dead | Bridge audio missing or unintelligible in the recording, a common annual test failure |
| Interface converter fault on an old sensor feed | One or more required data channels stop recording without an obvious alarm |
| Capsule battery for the locating beacon expired | Float-free capsule will not transmit its position if released after a casualty |
| Data overwritten before retrieval after an incident | Evidence lost because the continuous loop recorded over the event before the capsule was saved |
| UPS battery failed | Recording stops during the power failure that is often exactly when it is needed most |
What to look for in a supplier
- Technician certified by the VDR manufacturer to carry out the annual performance test, not a general electronics contractor.
- Experience integrating older bridge instruments typical of pre-2002 tonnage, since the interfacing work is where most S-VDR problems originate.
- Stock of replacement capsules and beacons compatible with the installed model, given these units are eventually discontinued by the maker.
- A clear procedure for securing the data after an incident, including how quickly the capsule can be downloaded before the loop recording overwrites it.
Test the bridge audio channel by talking normally from the actual conning position, not next to the microphone; annual tests have been passed on a system that could not pick up a watch officer's voice from where he actually stands.