Entry & progression
Governing: SOLAS chapter IV as amended by MSC.496(105); MSN 1864 (M) Amendment 1; STCW Code A-IV/2. Leads to: OOW (Yachts) <3000 GT and above (MSN 1858 A2 section 6).
The system in one paragraph
The GMDSS ensures that a ship in distress can alert rescue authorities ashore by at least two independent means, wherever she is; that the shore can alert ships near the casualty; that ships, aircraft and rescue centres can coordinate; that survivors can be located; and that every ship receives maritime safety information. It does this through VHF, MF and HF radio, satellite services and beacons, sized to the ship's sea areas.
Functions
The REG Yacht Code 16.1 list follows SOLAS IV: ship-to-shore alerting by two separate and independent means using different services; shore-to-ship and ship-to-ship alerting; SAR coordinating communications; on-scene communications; locating signals; MSI; general radiocommunications; and bridge-to-bridge communications.
Sea areas
| Area | Defined by |
|---|---|
| A1 | VHF coast station coverage with continuous DSC alerting (Ch 70) |
| A2 | MF coast station coverage with continuous DSC (2187.5 kHz), outside A1 |
| A3 | Coverage of a recognised mobile satellite service (RMSS), outside A1 and A2 |
| A4 | Everywhere else |
Before 2024, A3 meant Inmarsat geostationary coverage (MIN 643 describes it as roughly 70°N to 70°S, often working to 76°). Revised SOLAS makes A3 depend on the RMSS the ship uses. Iridium's constellation is global, so for an Iridium-fitted ship A3 extends over the poles; for an Inmarsat ship it stops at the edge of geostationary coverage.
What changed on 1 January 2024
Resolution MSC.496(105) and related performance standards:
| Change | Effect |
|---|---|
| NBDP no longer required | HF telex transmission not mandatory; the NBDP marking is removed from certificates issued or renewed after 1 January 2024 |
| A3 by MF/HF alone | The "VHF + MF/HF (DSC, RT, NBDP) + secondary means" option is no longer acceptable; A3 ships relying on it must fit at least one satellite ship earth station |
| RMSS | Inmarsat and Iridium both recognised; choice of Iridium in place of Inmarsat is subject to flag acceptance |
| MSI receivers | One requirement: receiver(s) capable of receiving MSI and SAR-related information (IV/7.1.1.4) |
| VHF and SARTs | Moved from chapter III to chapter IV |
| A1 EPIRB | VHF-EPIRB no longer accepted in place of a satellite EPIRB |
Existing ships generally did not need immediate re-certification; certificates update at renewal unless the ship is modified or her sea areas change.
The operator's competence
STCW A-IV/2 sets two competences: transmit and receive information using GMDSS subsystems and equipment and provide radio services in emergencies. The GOC is the certificate that proves both for all sea areas; MSN 1864 A1 (2.3) makes it the standard GMDSS certificate for UK deck officer CoCs.
CAUTION — Codes lag conventions The REG Yacht Code 2019 edition still lists Inmarsat C and NBDP-era equipment. Yachts are surveyed against their flag's current instructions; read your yacht's Record of Equipment.
TIP — Think in functions When the examiner asks "how would you alert the shore from mid-Atlantic if the satellite terminal failed?", answer in functions: second independent means (HF DSC, EPIRB), then procedure.