4.4 Radio Logbooks, Watchkeeping Requirements, & Routine Maintenance

Radio Logbooks, Watchkeeping Requirements, & Routine Maintenance

Operational discipline at sea relies on continuous watchkeeping, meticulous record-keeping in radio logbooks, and rigorous preventive maintenance of emergency battery power supplies.

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Mandatory GMDSS Watchkeeping Standards

Under International Maritime Organization (IMO) GMDSS standards and UK MCA regulations, every vessel fitted with a marine VHF DSC station must maintain specific radio watches while at sea.

Mandatory Watchkeeping Channels

1. VHF Channel 70 (156.525 MHz - DSC Watch): Mandatory Continuous Watch. Every DSC-equipped vessel must maintain an automated continuous watch on Channel 70 at all times while underway. Modern VHF DSC radios feature an internal, independent secondary receiver dedicated exclusively to scanning Channel 70 without interrupting voice operations on working channels.
2. VHF Channel 16 (156.800 MHz - Voice Watch): Where practicable, vessels should maintain a continuous voice listening watch on Channel 16 for distress, urgency, and safety broadcasts from Coastguard MRCCs or nearby craft. Dual-watch mode (monitoring Channel 16 and a selected working channel) is standard operating procedure.

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Radio Logbook Requirements and Legal Evidentiary Status

A GMDSS Radio Logbook is an official legal record of all radio operations, equipment checks, and safety communications. In the event of a collision, grounding, or distress incident, the radio logbook is impounded by the Marine Accident Investigation Branch (MAIB) and serves as primary evidence in maritime courts and coroner inquests.

Statutory Logbook Entries

Official radio logbook entries must include:

• Station Details: Vessel name, Call Sign, MMSI, and Ofcom license reference.
• Operator Details: Names and SRC certificate details of designated radio operators.
• Distress & Safety Traffic: Time (in UTC), frequency/channel, and full summary of any distress, urgency, or safety messages transmitted, received, or intercepted.
• Incident Logs: Position, nature of distress, and actions taken during SAR operations.
• Maintenance Logs: Results of daily power checks, weekly DSC test calls, and monthly EPIRB/SART self-tests.

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Preventive Maintenance Schedules (Daily, Weekly, Monthly)

To ensure radio stations remain operational during emergency conditions, GMDSS regulations mandate structured preventive maintenance routines:

┌────────────────────────────────────────────────────────────────────────┐
│                   GMDSS PREVENTIVE MAINTENANCE SCHEDULE                │
├────────────────────────────────────────────────────────────────────────┤
│ DAILY:   - Verify battery resting & charging voltage under load.      │
│          - Check GPS position input feed to VHF DSC console.          │
│ WEEKLY:  - Perform routine DSC test call to shore station or vessel.  │
│          - Check emergency battery physical security & connections.   │
│ MONTHLY: - Perform EPIRB built-in self-test & HRU expiry check.       │
│          - Perform SART built-in self-test (check on radar screen).   │
│          - Clean & inspect battery terminals for corrosion/sulfation.  │
└────────────────────────────────────────────────────────────────────────┘

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Emergency Power Systems & Battery Chemistries

GMDSS regulations require that marine radio stations be equipped with a dedicated emergency reserve source of electrical energy capable of powering the radio for at least 1 hour on vessels with emergency generators, or 6 hours on vessels without emergency generators.

Comparison of Battery Technologies

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Battery State-of-Charge & Voltage Thresholds

For a nominal 12-Volt Lead-Acid Battery System, voltage measurements must be taken after the battery has rested for 2 to 4 hours with all chargers and loads disconnected.

• 12.6V to 12.8V: 100% Fully Charged (resting open-circuit voltage).
• 13.8V to 14.4V: Active Charging Voltage (float or bulk charge from alternator/charger).
• 12.2V: 50% Discharged (minimum acceptable state before mandatory recharge).
• 10.5V: 0% Fully Discharged (Critical Cut-off Threshold). Below 10.5V, the VHF radio will fail during a 25W transmission due to voltage drop, and irreversible battery plate sulfation occurs.

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Specific Gravity Testing & Maintenance Hazards

For flooded lead-acid batteries, electrolyte density is measured using a hydrometer:

• Fully Charged Specific Gravity: 1.265 to 1.280 at 20°C.
• Discharged Specific Gravity: 1.150 or below.

Safety Warning: Hydrometer testing must NEVER be performed on sealed AGM or Gel batteries, as attempting to open sealed cell valves destroys the battery and voids its marine safety certification.

Statutory Watchkeeping Obligations Under GMDSS

To ensure that distress and safety signals are never missed at sea, the IMO GMDSS regulations and Ofcom Ship Radio License conditions mandate continuous radio watchkeeping while at sea.

Every vessel fitted with a marine VHF DSC radio station must maintain:

1. Continuous DSC Watch on Channel 70: A continuous digital watch on 156.525 MHz (Channel 70) using an integrated dual-receiver or dedicated DSC watch receiver.
2. Continuous Voice Watch on Channel 16: Where practicable and safe, a continuous listening watch on 156.800 MHz (Channel 16) radiotelephony while under way.

Mandatory GMDSS Radio Logbook Records

The GMDSS Radio Logbook is an official legal document. In the event of a maritime collision, grounding, or search and rescue operation, the logbook is seized by maritime accident investigation branches (such as the UK MAIB) as primary legal evidence.

The master or designated radio operator must record:

• Daily Entries: Summary of distress, urgency, and safety communications intercepted or transmitted; results of daily battery voltage tests; current vessel position.
• Weekly Entries: Record of weekly DSC test calls conducted with coast stations or companion vessels; inspection of antenna mounts and cabling.
• Monthly Entries: Inspection of emergency power supplies, hydrometer specific gravity checks on flooded batteries, and HRU expiration dates on EPIRBs and SARTs.

Emergency Power Systems & Battery Maintenance

Under GMDSS rules, marine VHF radio stations must be capable of operating from an emergency source of electrical energy (batteries) independent of the vessel's main engine generators.

• Battery Types: Sealed AGM (Absorbed Glass Mat) or Gel batteries are preferred over flooded lead-acid batteries due to spill prevention and low gassing during charging.
• Voltage Thresholds:
  • 12.6V – 12.8V: Fully charged battery (at rest).
  • 13.8V – 14.4V: Active engine alternator or shore charger voltage.
  • 12.2V: 50% discharged (requires immediate recharge).
  • 10.5V: Critical cut-off threshold (radio transmission power drops severely, distortion occurs).
• Specific Gravity Testing: For flooded lead-acid batteries, a hydrometer is used to measure electrolyte specific gravity. A reading of 1.265 – 1.280 indicates a fully charged cell, while readings below 1.200 indicate a discharged state requiring replacement or equalization charging.