Module 9 - GMDSS & Safety Equipment
GMDSS Sea Area A1
What you will learn
Explain what Sea Area A1 promises, what it does not promise, and how to audit a small-craft distress route before departure.
Sea areas describe the shore services available for distress alerting; they are not mileage bands or guarantees that a handheld will work everywhere.
GMDSS Sea Area A1 is an area within the radiotelephone coverage of at least one VHF coast station in which continuous DSC alerting is available. Both parts matter: usable VHF radiotelephone coverage and a coast station maintaining the DSC service. A charted boundary or remembered distance is not a substitute for checking the current service for the route.
VHF is mainly line-of-sight. Aerial height, installation, terrain, vessel movement, power and the coast-station network affect a real link. A fixed set with a sound masthead aerial can reach a station that a low handheld cannot, even when both are in the same named sea area.
Before sailing, identify who could receive the primary alert, how the position reaches the radio, what powers the set after a main-supply failure and what independent method remains. The sea-area label starts that audit; it does not finish it.
| Check | Evidence | Unsafe shortcut |
|---|---|---|
| Service | Current coast-station VHF radiotelephone and continuous DSC coverage | A fixed radius from land |
| Installation | Aerial, set, GNSS input and emergency power checked | The set powered on once |
| Backup | Independent alerting and locating method identified | A mobile phone alone |
Turn a route into a communications plan
A yacht will leave a sheltered harbour, round high ground and spend several hours beyond dependable mobile coverage.
1. Check the service
Use current official information for the coast stations and route rather than a memorised A1 mileage.
2. Check the installation
Confirm aerial condition, position input, radio power and the crew's ability to operate the set.
3. Name the fallback
Identify an independent beacon or other suitable route if the VHF path is lost.
Sense check: If the plan has only one receiver, one power source or one low aerial, the word A1 has concealed rather than controlled the vulnerability.
Common mistake or limitation
- Defining A1 as a fixed distance from the coast.
- Assuming every VHF set and aerial has the coast station's published reach.
- Treating A1 coverage as proof that a distress alert will be received and acted on.
Recap
- A1 requires coast-station VHF radiotelephone coverage and continuous DSC alerting.
- Coverage is service- and installation-dependent, not a universal mileage.
- Plan the receiver, position source, power and independent fallback.
Optional quick check
Section 1 of 10
Which statement accurately describes Sea Area A1?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying GMDSS & Safety Equipment
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