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Chapter 7A of 8
GMDSS Fundamentals and Sea Areas
What GMDSS Is
The Global Maritime Distress and Safety System (GMDSS) is an internationally agreed set of satellite and terrestrial radio systems, plus the procedures for using them. It handles distress alerting, search and rescue coordination and safety communications.
GMDSS replaced the old system of continuous Morse code (CW) watchkeeping. Alerting is now automated and mostly digital, so it no longer depends on a radio operator listening to one frequency around the clock.
The Nine Functional Requirements
A GMDSS vessel has to be able to do all of these:
- 1.Send ship-to-shore distress alerts by at least two independent means, each using a different radio service.
- 2.Receive shore-to-ship distress alert relays.
- 3.Send and receive ship-to-ship distress alerts.
- 4.Send and receive search and rescue coordinating communications.
- 5.Send and receive on-scene communications.
- 6.Send and receive locating signals.
- 7.Send and receive Maritime Safety Information (MSI): navigational and weather warnings and urgent safety information.
- 8.Send and receive general radio communications with shore-based radio systems or networks.
- 9.Send and receive bridge-to-bridge communications.
⚠️ "At least two independent means" is a core GMDSS principle. No single failure should be able to stop a vessel from getting a distress alert out. That's why carriage requirements always give a vessel backup alerting paths suited to its sea area.
Sea Areas A1 to A4
What equipment a vessel has to carry depends on the sea area(s) it sails in. Sea areas are defined by radio coverage, not just by distance from shore:
| Sea Area | Coverage | Typical Range |
|---|---|---|
| A1 | Within range of at least one VHF shore station with continuous DSC alerting | Usually about 20 to 30 nm from that station |
| A2 | Outside A1, but within range of at least one MF shore station with continuous DSC alerting | Usually out to roughly 100 to 150 nm |
| A3 | Outside A1 and A2, but inside INMARSAT geostationary satellite coverage | Roughly 76°N to 76°S |
| A4 | Everywhere outside A1, A2 and A3 (the polar regions) | Distress alerting relies on HF, because satellite coverage doesn't reach |
A vessel has to carry equipment for the highest-numbered sea area it will enter. A vessel that never leaves A1 doesn't need A3 or A4 equipment. One that sails from A1 into A3 needs equipment that covers both.
License Requirements
You need the right commercial operator license to run GMDSS equipment:
- •The GMDSS Radio Operator's License (DO) gives full operating privileges. It requires both FCC Element 1 and Element 7.
- •The Restricted GMDSS Radio Operator's License (RG) is for vessels limited to voyages within 20 nautical miles of shore. It has its own shorter exam, Element 7R.
GMDSS operators have to be trained and licensed for GMDSS specifically. A standard MROP on its own, without the GMDSS element, doesn't let you operate GMDSS equipment.
Sample Questions
10 questions drawn from across the course. Pick an answer for each, then check your score.
1.What replaced continuous Morse code (CW) watchkeeping as the primary means of maritime distress alerting under GMDSS?
2.What is the international VHF voice distress, safety, and calling frequency?
3.What is an MMSI?
4.What language is used for international NAVTEX broadcasts on 518 kHz?
5.What area of coverage do INMARSAT geostationary satellites provide, corresponding to Sea Area A3?
6.Which proword indicates a distress condition — grave and imminent danger requiring immediate assistance?
7.What frequency does a 406 MHz EPIRB use for final homing by search-and-rescue aircraft, in addition to its primary satellite distress frequency?
8.What is the correct procedure for correcting an error in the GMDSS radio log?
9.How many independent means must a GMDSS-equipped vessel be capable of using to transmit a ship-to-shore distress alert?
10.Is voice transmission permitted on VHF Channel 70?
Answer all 10 questions to see your score.
What's in the full course
- 📖 All 8 study chapters
- ✏️ All 63 questions, with answers and references
- ⏱️ Timed mock exams that match the real test
- 7AGMDSS Fundamentals and Sea Areas
- 7BRadio Spectrum, Frequencies, and License Requirements
- 7CDigital Selective Calling (DSC)
- 7DNAVTEX and SafetyNET
- 7EINMARSAT and Narrow-Band Direct-Printing
- 7FDistress, Urgency, and Safety Communications Procedures
- 7GSART, EPIRB, and Survival Craft Equipment
- 7HWatchkeeping, Logkeeping, and Battery/Equipment Testing