Power Supplies, Batteries, Maintenance, Fault-Finding and Testing
Power sources
GMDSS equipment is supplied from the ship's main and emergency sources, with a reserve source (usually a battery) independent of the generators, capable of supplying the distress and safety functions for the required period. Know that the reserve source must be able to supply the required load and that its capacity is tested regularly.
Batteries
Batteries must be kept charged, ventilated and clean, with terminals protected against corrosion. Know the difference between types and the need to avoid overcharging and deep discharge. Specific gravity and voltage checks indicate condition. Traps include assuming a battery that shows voltage is fully serviceable, and forgetting that battery capacity must be demonstrated by test.
Maintenance and fault-finding
Routine checks include self-tests on DSC, EPIRB and SART, antenna inspection, and checking that equipment is switched on and correctly programmed. Fault-finding follows a logical path: check power, then antenna and connections, then settings, then the equipment itself. Keep records of tests and faults. A trap is testing a distress function in a way that transmits a live alert.
Testing
Tests must not generate false alerts. DSC test calls should use the appropriate test facility or a non-distress format. EPIRB and SART self-tests are designed for this purpose. Any accidental transmission must be cancelled and reported.
Worked example
A VHF DSC set fails to transmit. Check the power supply and fuse, then the antenna and coaxial connection, then the MMSI programming and channel selection. If the set passes self-test but no acknowledgement is received, the fault may be at the coast station or in propagation, not necessarily the vessel's equipment.
Regulatory Framework, Licensing, Watchkeeping and Radio Records
The framework
The GMDSS sits within the international regulatory framework of the SOLAS Convention, the Radio Regulations of the ITU, and national implementing rules. SOLAS Chapter IV sets carriage requirements; the Radio Regulations govern frequencies, distress procedures and licensing. Certificates of competency for GMDSS operators are issued under the STCW Convention. Traps include mixing up which instrument covers what: SOLAS for carriage, Radio Regulations for frequencies and procedures, STCW for operator certification.
Licensing and documents
A ship radio station requires a licence issued by the flag administration, and the vessel is identified by its MMSI. The radio log, certificates and equipment manuals must be available on board. Know that the MMSI is linked to the vessel and used in DSC and AIS, and that a change of ownership or flag may require updating.
Watchkeeping
Vessels at sea must maintain a continuous radio watch appropriate to their sea area and equipment: VHF channel 70 DSC and channel 16, MF DSC and 2182 kHz, and HF DSC frequencies, plus satellite services where fitted. NAVTEX and EGC receivers should be monitored. Traps include assuming a single watch satisfies all requirements, and forgetting that the watch must be maintained while the vessel is at sea.
Radio records
Keep a radio log recording distress, urgency and safety communications, tests, and significant events. Records must be accurate and retained as required. False alerts and their cancellation should be recorded.
Worked example
An inspector finds a vessel in A2 with VHF and MF DSC but no continuous watch on the MF DSC frequency. The deficiency is a watchkeeping failure: the required watch must be maintained, and the radio log should show it.