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Navigation & Communication
Emergency Communication (GMDSS)
Global Maritime Distress and Safety System (GMDSS) equipment raises distress alerts, handles search and rescue traffic and receives safety broadcasts. SOLAS chapter IV and chapter 11 of the 2009 MODU Code set the fit by sea area. The sub-Category covers VHF, MF and MF/HF DSC radios, satellite terminals, NAVTEX receivers, EPIRBs, SARTs, AIS-SARTs and portable GMDSS VHF radios.
Sea areas and the equipment each needs
The GMDSS fit depends on where the unit works.
| Sea area | Coverage | Added equipment |
|---|---|---|
| A1 | VHF DSC range of a coast station | VHF DSC, EPIRB |
| A2 | MF DSC range of a coast station | MF DSC radio |
| A3 | Recognised mobile satellite service | Satellite terminal or MF/HF DSC |
| A4 | Any area outside A1, A2 and A3 | MF/HF DSC radio |
Every unit also carries NAVTEX for maritime safety information, a 406 MHz satellite EPIRB, a radar SART or AIS-SART and portable VHF radios. The DSC frequencies are channel 70 on VHF and 2187.5 kHz on MF.
The modernised GMDSS from 2024
IMO amendments to SOLAS chapter IV came into force on 1 January 2024. They replaced Inmarsat-specific wording with a recognised mobile satellite service, which lets Iridium and Inmarsat both serve sea area A3. They dropped narrow-band direct printing (radio telex) as a carriage requirement and moved the survival craft radio equipment into chapter IV. The MODU Code's chapter 11 was rewritten in line, through resolution MSC.506(105). Before you buy a used item, confirm its model is still accepted under the new rules and by your flag state.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Sea areas covered | Fit to your operating area | A1 to A4 |
| Satellite service | A3 acceptance | Inmarsat or Iridium |
| EPIRB type | Float-free, GNSS position | 406 MHz with 121.5 MHz homing |
| SART type | Detection by radar or AIS | 9 GHz radar SART or AIS-SART |
| Battery and HRU expiry | Survey acceptance | Date printed on the item |
Standards and what a used unit must show
The IEC 61097 series sets the test standard for each GMDSS item, alongside IEC 60945. On EU-flagged units the wheel mark is mandatory. SOLAS chapter IV requires availability through duplication of equipment, shore-based maintenance or at-sea maintenance, with two of these methods in sea areas A3 and A4. The reserve source of energy must run the radios for one hour, or six hours where the emergency generator does not supply them. EPIRBs are tested annually, following MSC/Circ.1040, and get shore-based maintenance at intervals not exceeding five years.
Failure modes and inspection
- Reserve batteries lose capacity, which a discharge test shows.
- MF/HF antenna insulators and couplers corrode, and the transmit power drops.
- EPIRB and SART batteries and hydrostatic release units expire on their printed dates.
- EPIRB seals and lanyards degrade in sunlight.
A radio surveyor or approved service agent runs DSC test calls, checks transmit power and antenna current, tests the EPIRB in self-test mode and with a 406 MHz tester, checks the SART response, and confirms position input from GNSS.
Documentation
- Type-approval certificate or wheel mark declaration for each item.
- Last radio survey report and annual EPIRB test record.
- EPIRB shore-based maintenance certificate with date.
- Battery and HRU expiry dates.
- Programming record for MMSI and EPIRB identity.
Integration with your unit
Each DSC radio, satellite terminal and EPIRB holds the previous unit's identity. An authorised agent reprograms the MMSI and EPIRB coding, and you register the beacon with your flag state. Radios need GNSS position, a reserve power supply and an alarm panel on the bridge. Satellite terminals need your own service activation.
Refurbishment, used or surplus
Fixed DSC radios of a model already on board make good used spares. EPIRBs and SARTs are cheap next to a failed survey, so buy them new or unused surplus with long battery life left, or have an approved service agent service them first. Equipment that needs shore-based maintenance is best bought with fresh service paperwork.
Related equipment
Routine radio traffic runs on VHF and UHF radio systems, and GMDSS radios take position from GNSS receivers. Naventr can collect battery and HRU dates from the Seller before you decide.
FAQ
Frequently asked questions
Can I buy a used EPIRB for my unit?
Yes, if it is a type-approved 406 MHz model with an in-date battery and release unit. An authorised agent must recode it with your unit's identity, you register it with your flag state, and it needs annual testing and shore-based maintenance at intervals not exceeding five years.
Is Iridium accepted for GMDSS?
Yes, since 1 January 2024 SOLAS chapter IV refers to a recognised mobile satellite service, and IMO recognises Iridium alongside Inmarsat. Your flag state decides how it accepts each service on its units, so check its circulars before you fit an Iridium terminal.
What GMDSS equipment does a unit in sea area A3 need?
A unit in sea area A3 needs VHF DSC plus either MF DSC with a recognised satellite terminal or an MF/HF DSC radio, plus NAVTEX, a 406 MHz EPIRB, a SART or AIS-SART and portable VHF radios. Your flag state and the MODU Code set the exact fit.
What changed in GMDSS in 2024?
The modernised GMDSS came into force on 1 January 2024, opening sea area A3 to any recognised satellite service and dropping radio telex as a carriage requirement. It also moved survival craft radio equipment into SOLAS chapter IV, and MSC.506(105) rewrote MODU Code chapter 11 to match.
Who can reprogram the MMSI on a used DSC radio?
On many models only the OEM or an authorised dealer can clear an MMSI once it is entered. Ask the Seller whether the identity has been cleared, and budget for an authorised agent to program your MMSI before the radio survey.
Looking for emergency communication (GMDSS)?
Tell us what you need and we will find out what is available. We reply within one business day.