Module 9 - GMDSS & Safety Equipment
Where VHF Fits GMDSS
What you will learn
Map distress alerting, communication, locating, safety information and survivability to separate system functions.
GMDSS is a system of complementary functions. A VHF DSC set may cover several of them locally, but no single control or device performs every rescue task.
A distress system must first attract attention and identify the casualty. It must then support communication of the situation and assistance required, help rescuers locate people or survival craft, provide maritime safety information before incidents and remain usable when ordinary vessel systems fail.
VHF DSC provides a digital alerting route within suitable coverage; VHF voice provides local distress traffic and coordination. Position input improves the alert, but the crew must know whether it is present and current. A beacon adds an independent alerting and locating path, while a SART supports final on-scene location.
The practical question is not 'Do we have GMDSS equipment?' but 'Which device performs each function on this route, and what happens when its aerial, power, data source or operator is unavailable?' That question reveals hidden single points of failure.
Worked example
A yacht has a fixed VHF/DSC set, a GNSS feed, a registered EPIRB and a handheld VHF for a coastal passage.
- 1Trace the fixed set from aerial through DSC identity and GNSS position to its normal and emergency power.
- 2Check the EPIRB registration, bracket, battery and self-test status as the independent alerting path.
- 3Confirm the handheld is charged, accessible and understood as a short-range fallback rather than a replacement for the masthead installation.
Sense check: The audit is incomplete if the same failed battery, inaccessible locker or untrained person disables every route.
| Function | Possible small-craft element | Pre-departure check |
|---|---|---|
| Alert | VHF DSC or 406 MHz beacon | Identity, registration and test status |
| Communicate | VHF voice | Aerial, channels and trained operator |
| Locate | Beacon homing, radar SART or AIS-SART | Deployment and receiving-system boundary |
| Receive MSI | NAVTEX and appropriate broadcasts | Coverage, selection and current messages |
| Survive failure | Emergency source and independent equipment | Capacity, connection and physical access |
Audit by function
The skipper's inventory lists four radios but says nothing about position data or backup power.
1. Draw the dependencies
Link each set to aerial, identity, position input and power source.
2. Assign each function
Name how the crew alerts, communicates, locates, receives warnings and survives a failure.
3. Exercise the people
Check that more than one person can reach and operate the essential equipment.
Sense check: Several devices can still form one fragile system when they share the same power, aerial or operator.
Common mistake or limitation
- Using the number of devices as a proxy for resilience.
- Assuming a connected position is necessarily current and correctly formatted.
- Expecting an alerting device to provide the full two-way conversation.
Recap
- Alerting, communicating, locating, MSI and survivability are distinct functions.
- VHF DSC and voice cover important local functions but have dependencies.
- Audit equipment, data, power and people together.
Optional quick check
Section 4 of 10
Why is a list of radio devices not yet a GMDSS readiness check?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying GMDSS & Safety Equipment
This public lesson is part of Revision Module 9. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.