1The lesson in plain words
In one sentence…
GMDSS is a chain: alerting, coordination and help continue through information, watchkeeping and decisions.
What is GMDSS?
GMDSS combines ship equipment, shore services and procedures. An alert attracts attention; the whole message continues with explanation, acknowledgement and information.
What are the nine functions?
They are jobs the system must accomplish: alerting, coordinating, on-scene communication, locating and receiving safety information. They are not nine radios or nine buttons.
How do you order traffic?
Danger and assistance required decide it: distress, urgency, safety and routine. A routine call must yield to distress traffic.
Who does what?
Someone on board identifies the problem; a station organizes help; nearby units exchange instructions. The chain divides the tasks and continues with a watch.
2Step by step
GMDSS communication chain
- 1
Identify the problem and gather identity, position, time, facts and people involved.
The chain starts with an identified situation and concrete information.
- 2
Send the alert by an available means that can reach someone able to respond.
The alert attracts attention from a station able to organize help.
- 3
Exchange the information needed to coordinate the response with that station.
Coordination establishes who controls the response and what information is needed.
- 4
Communicate with nearby units and follow their instructions on scene.
On-scene communication lets units exchange instructions.
- 5
Provide data that helps locate the vessel or survivors.
Locating helps rescuers find those needing assistance.
- 6
Keep watch and receive instructions and safety information.
Communication continues while you receive guidance and voyage warnings.
3Key data
- GMDSS functions
- Nine GMDSS functions
- Distress alerting
- Ship-to-shore, shore-to-ship, ship-to-ship
- Traffic priority
- Distress → urgency → safety → routine
- MAYDAY
- Grave and imminent danger
- PAN-PAN
- Very urgent safety message
- SÉCURITÉ
- Safety information
- Ship-to-shore means
- Two separate, independent means
- Channel 16 watch
- When practicable
- MF/HF DSC
- 2187.5 and 8414.5 kHz
- A3 and HF
- HF carriage is not universal
4Key points
- 1.
Alerting → coordination → on-scene → locating → safety.
- 2.
The nine functions are system jobs, not nine radios.
- 3.
Priority: distress → urgency → safety → routine.
- 4.
MAYDAY, PAN-PAN and SÉCURITÉ name different messages.
5Frequent mistakes
Wrong: "The nine functions require nine radios."
Right: They are functions the system must accomplish, not nine buttons or nine mandatory radios.
Wrong: "The alert ends the operator's communication task."
Right: Afterwards, explain, listen for the acknowledgement and continue communicating.
Wrong: "A routine call keeps priority once it has started."
Right: Routine traffic must yield to distress traffic.
6Practice case & exam keys
Situation
In an isolated classroom exercise, the ship's main radio console becomes unavailable. A learner points to a second screen connected to the same radio and says the independent backup is ready.
What should the team establish before accepting that answer?
Show the answer →
Identify the actual alternative distress-alerting means, its service and its support arrangements, rather than counting screens.
Why: Two controls can depend on one radio or service. The team must explain which communication path still works, whether it can reach assistance on this voyage, and how it fits the ship's approved arrangement. This is a functional check, not a universal equipment list.
Exam keys
If you see "nine buttons", remember: the functions are not nine radios.
If you see "A3 = universal HF", reject it: A3 does not make HF carriage universal.
If you read "grave and imminent danger", choose MAYDAY; "very urgent safety message" points to PAN-PAN.
How to read it
Think of a relay: each part receives, adds or directs information until help can act.
Do not confuse a powered device with a completed function: the chain, watch and human decision matter.
7Full lesson & sources
Open the full lesson (diagrams and official references)
GMDSS combines ship equipment, shore services and procedures. SOLAS IV/4 distinguishes nine GMDSS functions from general radiocommunications. Ship-to-shore distress alerting needs two separate, independent means using different services. Distress, urgency, safety and routine traffic have decreasing priority. MAYDAY concerns grave and imminent danger to a vessel or a person requiring immediate assistance; PAN-PAN concerns a very urgent safety message; SÉCURITÉ introduces safety information.
Keep the automatic watches required by the installed equipment and voyage, plus a channel 16 listening watch when practicable. For MF/HF installations, required DSC watch includes 2187.5 and 8414.5 kHz plus at least one suitable additional HF frequency. A3 does not make HF carriage universal.
Think in functions, not boxes on a console
Start by asking what must happen to a message. A person on board identifies a problem; an alert reaches a station able to organize help; the parties exchange enough information to act; and the ship continues to receive instructions and safety information. A powerful transmitter alone cannot complete that chain. Antenna condition, electrical supply, the receiving service and a trained operator all contribute.
The nine SOLAS GMDSS functions cover three directions of distress alerting, search-and-rescue coordination, on-scene communication, locating, reception of maritime safety information, urgency and safety communication, and bridge-to-bridge communication. Learn these as jobs the system must accomplish. They are not nine separate buttons or a requirement to install nine radios.
Distinguish the communication jobs
| Job | What the learner must establish |
|---|---|
| Alerting | Can the available service reach someone able to respond? |
| Coordination | Who is controlling the response and what information is needed? |
| On-scene communication | How will units near the casualty exchange instructions? |
| Locating | What helps rescuers find the vessel or survivors? |
| Safety information | Which warnings affect the ship's intended passage? |
For example, an emergency beacon and a handheld VHF can contribute to different stages of the same incident. The beacon can support alerting and locating; the portable radio can support communication when another unit is within its useful coverage. Do not judge either device by whether it can perform every function.
Select the priority from the situation
Priority reflects the danger and the assistance required, rather than the operator's level of anxiety. A situation can change: an urgent safety problem may develop into grave and imminent danger. Reassess it as facts emerge and tell the station handling the communication when the circumstances change.
Keep the information concrete: identity, position and its age, what has happened, what is needed, and relevant persons involved. State uncertainties as uncertainties. A clear description lets the receiving station assess the situation better than a dramatic but incomplete message.
Build independent capability and an effective watch
For a ship subject to the relevant SOLAS requirement, two separate independent ship-to-shore distress-alerting means must use different radiocommunication services. Two displays connected to the same service do not by themselves demonstrate that requirement. Identify what would remain available after failure of a terminal, its antenna or its normal supply, using the approved ship arrangement.
- 1Identify the voyage and the equipment/service requirements that apply to the ship.
- 2Check the equipment needed for the required automatic watches and appropriate listening watch.
- 3Confirm that identity, position information, power and antennas are ready for the intended use.
- 4Locate the authorized procedures, alternative communication means and radio record.
- 5Explain who will operate the equipment and who must be informed when an incident occurs.
A watch is active readiness: the receiver must be correctly configured, alerts noticed and relevant information passed to the bridge. A device showing a power light does not prove that all these conditions are met.
Official references · 2026-09-09
8Test your knowledge
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