A4 Voyage with Inmarsat at the Edge
MV Northwind is a 1,600 GT US-flag SOLAS cargo ship on charter to a seismic survey in the Chukchi Sea. She will spend 14 hours at 72°N 165°W, well inside Sea Area A4, before returning south. The GMDSS installation includes an Inmarsat Fleet 77 terminal, an MF/HF radio with DSC and NBDP, a NAVTEX receiver, a float-free 406 MHz EPIRB, two SARTs, three portable VHF radios, and a reserve battery. At 0300 UTC the Inmarsat terminal displays "no service"; the 8 MHz HF DSC watch receives no acknowledgment to a routine DSC test, and the last NAVTEX message is nine hours old. The third mate, newly certified, asks whether the ship is compliant in A4 and whether the Inmarsat outage is a reportable failure. The master wants to know which communication paths remain and how the reserve battery should be managed.
1. Is the vessel compliant for the A4 portion? Identify the required GMDSS functions and any shortfall.
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A4 is the sea area outside Inmarsat coverage and outside MF/HF coverage of coast stations. The required GMDSS functions there include HF radiotelephony, HF DSC, and HF NBDP for distress alerting, distress traffic, and MSI reception. Inmarsat is not the primary A4 system.
On paper the vessel has the right core equipment: MF/HF with DSC and NBDP, 406 MHz EPIRB, SARTs, portable VHF, and reserve power. The likely shortfall is operational. NAVTEX is a coastal service and is not a reliable A4 MSI source, so the vessel must use HF NBDP for MSI; a nine-hour-old NAVTEX message suggests the bridge has not established an HF NBDP MSI watch. The crew also appears to be treating Inmarsat as primary when it is not part of A4. Before entering A4 the vessel should verify HF DSC on several bands, confirm the NBDP MSI schedule and frequencies, test the reserve battery, and brief the watch on the fact that Inmarsat may be unavailable. If the HF installation cannot provide those functions, the vessel is not compliant.
2. Why does Inmarsat show no service, and how do sea area boundaries affect the answer?
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The vessel is at 72°N, outside the nominal geostationary Inmarsat coverage that defines A3, which extends roughly to 70°N and 70°S. At that latitude the satellite elevation is too low or below the horizon for the terminal, so "no service" is expected in A4. Even near the edge of A3, low elevation, antenna blocking, or heavy weather can interrupt service, so A3 does not guarantee continuous Inmarsat coverage everywhere.
A3 is the area within Inmarsat coverage; A4 is outside it. The vessel must therefore plan for HF as the primary distress and MSI path and treat Inmarsat as supplementary. The Inmarsat outage alone is not a distress situation, but it should be logged and reported to the company and, if it degrades the required GMDSS capability, brought to the flag administration's attention. If both Inmarsat and HF become unavailable, the vessel has lost its primary A4 distress capability and should consider diverting or requesting assistance through any remaining means.
3. What immediate actions should the radio officer take, and how should the reserve battery be managed?
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The radio officer should first shift the DSC watch to other HF bands, such as 4, 6, 8, 12, and 16 MHz, rather than remaining on 8 MHz alone, because propagation at high latitude is variable. Use HF radiotelephony and NBDP to request MSI and to establish contact with a coast station; try a different band if calls go unanswered. Keep the Inmarsat terminal on and monitor for service restoration, but do not rely on it.
Reserve power should be treated as a finite emergency supply. Confirm the battery is fully charged, test it under load, and avoid nonessential loads. The reserve source must be capable of operating the GMDSS installation for the period required by SOLAS and FCC rules, typically one hour when an emergency generator is available and six hours when it is not, with the VHF reserve included. If the battery voltage falls or the load test fails, start the emergency generator or charge immediately and inform the master. Log every failure and action taken.