Module 1 — GMDSS fundamentals

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

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.

1. 1Identify the voyage and the equipment/service requirements that apply to the ship.
2. 2Check the equipment needed for the required automatic watches and appropriate listening watch.
3. 3Confirm that identity, position information, power and antennas are ready for the intended use.
4. 4Locate the authorized procedures, alternative communication means and radio record.
5. 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

SOLAS IV/4, IV/12