Eighteen hours without MSI: diagnosing NAVTEX silence and a SafetyNET receiver on the wrong ocean
MV Brahmaputra Star, 12,000 GT tanker, is on passage from Chennai to Singapore in sea area A3. At 0400 the master asks why the bridge has printed no maritime safety information for eighteen hours, although a cyclone warning for the south Bay of Bengal was broadcast at 0300. The NAVTEX receiver is powered, tuned to 518 kHz, and its display shows 'no message received' with a valid UTC clock. Message-type selection is set to 1, 2, 3, 4, A, B, D, E and L. The Inmarsat-C terminal is logged in and displays 'IOR', but the EGC printer is producing messages addressed to the AOR-E region and the LES ID is one the previous owners used. The vessel's GPS is feeding the Inmarsat-C, but the NAVTEX has no position input and no station list selected. An HF SSB with NBDP is installed, but the operator says he has never used it.
1. Diagnose the NAVTEX silence. Give at least four plausible causes, ranked, with the check you would make for each.
Read the worked answer
Ranked causes and checks
- Outside NAVTEX coverage. Indian NAVTEX is a coastal service, typically useful to about 200-400 nm depending on transmitter power and time of day. Eighteen hours out of Chennai towards Singapore, the ship may simply be beyond it. Check: plot the position against the published coverage diagram and look at where and when the last message was printed.
- No station selected, or a station set not in range. With an empty station list the receiver hears the signal and prints nothing. Check: the station-selection menu; select all stations or the ones in range.
- Message-type filter. The set is on 1, 2, 3, 4, A, B, D, E, L, which includes navigational and meteorological warnings, so this is probably not the cause - but confirm that types 1 and 2 are not inhibited and that the printer or display itself is working.
- Antenna, coaxial cable or earth fault. A corroded connector or a broken centre conductor produces 'no message' with no error message. Check: signal or field-strength indication, substitute a spare antenna or a length of wire, inspect the coax and the earth.
- No time-share synchronisation. NAVTEX needs the station's time signal to lock; without a lock, nothing prints. Check: the receiver's UTC source and any 'synchronised' flag.
- Receiver in test or local mode, or out of paper. Cheap to check first.
Start with 1 and 6 - they cost nothing and they are the most common. Note that whatever the cause, the ship has also been in A3 with no working MSI source, which is the more serious finding.
2. How should the SafetyNET/EGC side be configured, and why is reception on the wrong ocean region more dangerous than no reception at all?
Read the worked answer
Correct configuration
- The Inmarsat-C must be logged in to the satellite for the ocean region the ship is in - IOR for the Indian Ocean - with the antenna in clear view.
- EGC must be enabled, with the message categories the ship is required to receive not filtered out: distress, urgency, safety, SAR, navigational (NAVAREA), meteorological (METAREA) and piracy.
- The terminal's position input must be correct and current, because EGC messages are addressed by NAVAREA, METAREA and circular areas. A wrong position means the right messages go somewhere else.
- The LES configuration must be current and not a leftover from another owner or another ocean region.
Why AOR-E printing is worse than silence: the terminal is receiving Atlantic MSI and missing the Indian Ocean messages - including the 0300 cyclone warning for the south Bay of Bengal, and any SAR traffic or distress relay for the ship's own area. It gives the illusion of a working MSI service while the content is for the wrong ocean. A dead printer gets investigated; a printer producing plausible-looking warnings in the wrong ocean does not. The watchkeeper reads a gale warning for the North Atlantic, assumes MSI is being received, and sails on into the cyclone.
3. If both MSI paths fail, what alternatives exist and what must be recorded?
Read the worked answer
Fallback sources, in order
- HF NBDP on the MSI broadcast frequencies (4210, 6314, 8416.5, 12579 and 16806.5 kHz). The set is fitted, so the ROC holder should use it rather than say it has never been used: tune, select the published mode, and copy the scheduled broadcast. This is exactly why the fitting is carried.
- Ask for it. A DSC individual call or Inmarsat-C message to the nearest MRCC or coast station, or plain radiotelephony on VHF channel 16 near the coast, requesting the latest gale or cyclone warning and NAVAREA warnings for the position.
- Inmarsat-C safety priority message to the RCC, if the terminal can still transmit even though EGC is misconfigured.
- Prudence meanwhile: with no MSI the area has unknown hazards. Slow down, keep well clear of the likely cyclone track, and put the reasoning to the master in writing rather than pressing on at full speed.
Recording: the radio log must show the time the failure was noticed, the checks made, the alternative source used, the MSI actually received and copied, and the defect report to the company and to the next port. An eighteen-hour MSI gap with no log entry is itself an inspection finding. When the equipment is restored, record the reception test - a known NAVAREA VIII or METAREA VIII message printed correctly - so there is evidence the fix worked.